Transformers

Current transformer - Wikipedia, the free encyclopediahttp://en.wikipedia.org/wiki/Current_transformer Current transformer From Wikipedia, the free encyclopedia A current transformer (CT) is used for measurement of alternating electric currents. Current transformers, together with voltage transformers (VT) (potential transformers (PT)), are known as instrument transformers. When current in a circuit is too high to apply directly to measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be conveniently connected to measuring and recording instruments. A current transformer isolates the measuring instruments from what may be very high voltage in the monitored circuit. Current transformers are commonly used in metering and protective relays in the electrical power industry. Contents 1 Design 2 Usage 3 Safety precautions 4 Accuracy 4.1 Burden 4.2 Knee-point core-saturation voltage 4.3 Rating factor 4.4 Phase shift 5 Special designs 6 Standards 7 High voltage types 8 See also 9 References 10 External links A CT for operation on a 110 kV grid Design Like any other transformer, a current transformer has a primary winding, a magnetic core and a secondary winding. The alternating current flowing in the primary produces an alternating magnetic field in the core, which then induces an alternating current in the secondary winding circuit. An essential objective of current transformer design is to ensure the primary and secondary circuits are efficiently coupled, so the secondary current is linearly proportional to the primary current. The most common design of CT consists of a length of wire wrapped many times around a silicon steel ring passed 'around' the circuit being measured. The CT's primary circuit therefore consists of a single 'turn' of conductor, with a secondary of many tens or hundreds of turns. The Basic operation of current transformer 1 of 6 2/23/2014 3:01 PM Current transformer - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Current_transformer primary winding may be a permanent part of the current transformer, with a heavy copper bar to carry current through the magnetic core. Window-type current transformers (aka zero sequence current transformers, or ZSCT) are also common, which can have circuit cables run through the middle of an opening in the core to provide a single-turn primary winding. When conductors passing through a CT are not centered in the circular (or oval) opening, slight inaccuracies may occur. Shapes and sizes can vary depending on the end user or switchgear manufacturer. Typical examples of low voltage single ratio metering current transformers are either ring type or plastic molded case. High-voltage current transformers are mounted on porcelain insulators to isolate them from ground. Some CT configurations slip around the bushing of a high-voltage transformer or circuit breaker, which automatically centers the conductor inside the CT window. Current transformers can be mounted on the low voltage or high voltage leads of a power transformer; sometimes a section of bus bar is arranged to be easily removed for exchange of current transformers. SF6 110 kV current transformer TGFM series, Russia Usage Current transformers used in metering equipment for three-phase 400 ampere electricity supply Current transformers are used extensively for measuring current and monitoring the operation of the power grid. Along with voltage leads, revenue-grade CTs drive the electrical utility's watt-hour meter on virtually every building with three-phase service and single-phase services greater than 200 amps. The CT is typically described by its current ratio from primary to secondary. Often, multiple CTs are installed as a "stack" for various uses. For example, protection devices and revenue metering may use separate CTs to provide isolation between metering and protection circuits, and allows current transformers with different characteristics (accuracy, overload performance) to be used for the devices. The primary circuit is largely unaffected by the insertion of the CT. The rated secondary current is commonly standardized at 1 or 5 amperes. For example, a 4000:5 CT secondary winding will supply an output current of 5 amperes when the primary winding current is 4000 amperes. The secondary winding can be single or multi-ratio, with five taps being common for multi-ratio CTs. The load, or burden, of the CT should be a low resistance. If the voltage time integral area is higher than the core's design rating, the core goes into saturation toward the end of each cycle, distorting the waveform and affecting accuracy. Many digital clamp meters utilize a current transformer for measuring AC current Safety precautions Care must be taken that the secondary of a current transformer is not disconnected from its load while current is flowing in the primary, as the transformer secondary will attempt to continue driving current across the effectively infinite impedance up to its core saturation voltage. This may produce a high voltage across the open secondary into the range of several kilovolts, causing arcing, compromising operator and equipment safety, or 2 of 6 2/23/2014 3:01 PM Current transformer - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Current_transformer permanently affect the accuracy of the transformer. Accuracy The accuracy of a CT is directly related to a number of factors including: Burden Burden class/saturation class Rating factor Load External electromagnetic fields Temperature and Physical configuration. The selected tap, for multi-ratio CTs Phase change For the IEC standard, accuracy classes for various types of measurement are set out in IEC 60044-1, Classes 0.1, 0.2s, 0.2, 0.5, 0.5s, 1 and 3. The class designation is an approximate measure of the CT's accuracy. The ratio (primary to secondary current) error of a Class 1 CT is 1% at rated current; the ratio error of a Class 0.5 CT is 0.5% or less. Errors in phase are also important especially in power measuring circuits, and each class has an allowable maximum phase error for a specified load impedance. Current transformers used for protective relaying also have accuracy requirements at overload currents in excess of the normal rating to ensure accurate performance of relays during system faults. A CT with a rating of 2.5L400 specifies with an output from its secondary winding of 20 times its rated secondary current (usually 5 A x 20 = 100 A) and 400 V (IZ drop) its output accuracy will be within 2.5 percent. Burden The secondary load of a current transformer is usually called the "burden" to distinguish it from the load of the circuit whose current is being measured. The burden, in a CT metering circuit is the (largely resistive) impedance presented to its secondary winding. Typical burden ratings for IEC CTs are 1.5 VA, 3 VA, 5 VA, 10 VA, 15 VA, 20 VA, 30 VA, 45 VA and 60 VA. As for ANSI/IEEE burden ratings are B-0.1, B-0.2, B-0.5, B-1.0, B-2.0 and B-4.0. This means a CT with a burden rating of B-0.2 can tolerate up to 0.2 Ω of impedance in the metering circuit before its secondary accuracy falls outside of an accuracy specification. These specification diagrams show accuracy parallelograms on a grid incorporating magnitude and phase angle error scales at the CT's rated burden. Items that contribute to the burden of a current measurement circuit are switch-blocks, meters and intermediate conductors. The most common source of excess burden is the conductor between the meter and the CT. When substation meters are located far from the meter cabinets, the excessive length of wire creates a large resistance. This problem can be reduced by using CTs with 1 ampere secondaries, which will produce less voltage drop between a CT and its metering devices. Knee-point core-saturation voltage The knee-point voltage of a current transformer is the magnitude of the secondary voltage above which the output current ceases to linearly follow the input current within declared accuracy. In testing, if a voltage is applied across the secondary terminals the magnetizing current will increase in proportion to the applied voltage, until the knee point is reached. The knee point is defined as the voltage at which a 10% increase in applied 3 of 6 2/23/2014 3:01 PM Most CTs have rating factors for 35 degrees Celsius and 55 degrees Celsius. The rating factor of a CT is largely dependent upon ambient temperature.wikipedia.2 to 1.5 times rated current. the minimum primary current a CT can accurately measure is "light load.[2] In recent years the introduction of electronic based power and energy meters has allowed the phase error to be calibrated out. Another type (called a Rogowski coil) requires an external integrator in order to provide a voltage output that is proportional to the measured current." or 10% of the nominal current (there are. but constrained within a very small range of the current transformer rating. However. energy meter or power factor meter. but phase shifts as low as a few tenths of a degree for well constructed transformers up to as much as six degrees for simpler designs may be encountered (for the normal power frequencies). the free encyclopedia http://en. One type of specially constructed wideband transformer provides a voltage output that is proportional to the measured current. only displays the magnitude of the current.[2] For the purposes of current measurement. This is made possible by the development of more efficient ferrites and their corresponding hysteresis curves. depending on client requirements. For voltages greater than the knee point. wideband CTs are rated in output volts per ampere of primary current. Recently.Wikipedia. Unlike CTs used for power circuitry.org/wiki/Current_transformer voltage increases the magnetizing current by 50%.Current transformer . It is important to be mindful of ambient temperatures and resultant rating factors when CTs are installed inside padmount transformers or poorly ventilated mechanical rooms. however. the concept of knee point voltage is very pertinent to protection current transformers. although the Canadian and Australian standards are also recognised. this error is generally considered to be negligible at unity power factor but increases in significance as the power factor approaches zero.13 (ANSI). since they are necessarily exposed to fault currents of 20 to 30 times rated current. any phase shift in the measured current can affect the accuracy of the target measurement. typically 1. Phase shift Ideally the secondary current of a current transformer should be perfectly in phase with the primary current. this is impossible to achieve. The knee-point voltage is less applicable for metering current transformers as their accuracy is generally much higher. manufacturers have been moving towards lower nominal primary currents with greater rating factors. CT RATIO Standards Ultimately. there are two main standards to which current transformers are designed. special CTs designed to measure accurately currents as small as 2% of the nominal current). the magnetizing current increases considerably even for small increments in voltage across the secondary terminals. For power and energy measurement. IEC 60044-1 (BSEN 60044-1) & IEEE C57. any phase shift is immaterial as the indicating ammeter. all the measured power is entirely due to the current transformer's phase error.[1] Rating factor Rating factor is a factor by which the nominal full load current of a CT can be multiplied to determine its absolute maximum measurable primary current.[3] Special designs Specially constructed wideband current transformers are also used (usually with an oscilloscope) to measure waveforms of high frequency or pulsed currents within pulsed power systems. 4 of 6 2/23/2014 3:01 PM . Conversely. if the current transformer is used in conjunction with the current circuit of a wattmeter. However. In practice. At true zero power factor. [5] See also Rogowski coil Transformer Instrumentation Transformer types References Guile. Pergamon. insulation life and thermal stability is improved.Current transformer . ^ Anon. 1.itl-uk. The primary of the winding can be evenly distributed around the magnetic core.ccontrolsys. but very often free-standing outdoor current transformers are used. 331. A high-voltage current transformer may contain several cores.com/en/products /measurement-transformers/) Introduction to Protection Current Transformers (http://www. which gives better stability and a higher short-circuit current rating. The General Electric Company Limited of England.com/w/CT_Phase_Angle_Correction 4. ^ http://www. or protection).org/wiki/Current_transformer High voltage types Current transformers are used for protection. live tank current transformers have a substantial part of their enclosure energized at the line voltage and must be mounted on insulators.com/introduction-protectiontransformers. measurement and control in high voltage electrical substations and the electrical grid. ^ http://wiki.pdf) Introduction to Metering / Measurement Current Transformers (http://www.net/pdfs/AN0305-Current_Transformers. the free encyclopedia http://en. 1975 Section 5. In a switchyard. which gives better performance for overloads and transients.customcoils.3 2.answers. Live tank CTs are useful because the primary conductor is short.html) Introduction to Current Transformers (http://www.com/Q/What_is_the_reason_for_using_a_neutral_current_transformer_on_a_transformer External links High Voltage Transformer / Custom Transformers (http://www.com/w/Measurement_Errors_Due_to_CT_Phase_Shift 3.itl-uk. Volume One.com/wordpress/wp-content/uploads/2013/01 /GLEMS%202012%20-%20Inst%20Xformers%20Theory%20and%20Testing. Protective Relays Application Guide Second Edition. ^ Protective Relays Application Guide. each with a secondary winding.Wikipedia. 1975) pages 78-87 5. ISBN 0-08-021729-X. control.[4] A neutral current transformer is used as earth fault protection to measured any fault current flowing through the neutral line from the wye neutral point of a transformer. (1977). p.wikipedia. Since the major insulation of a live-tank current transformer is not exposed to the heat of the primary conductors. Electrical Power Systems.itl-uk.com/instrument-transformer-characteristics.com/products/high-voltagetransformer.ccontrolsys. (The General Electric Company Limited of England.pdf) 5 of 6 2/23/2014 3:01 PM .. Current transformers may be installed inside switchgear or in apparatus bushings. Dead tank current transformers isolate the measured circuit from the enclosure. A.html) Transformer Terminology (http://www. for different purposes (such as metering circuits.elkor.html) Testing Current Transformers (http://powermetrix. ^ a b http://www. Paterson. W. the free encyclopedia http://en. you agree to the Terms of Use and Privacy Policy..php?title=Current_transformer&oldid=593942124" Categories: Transformers (electrical) Electronic test equipment This page was last modified on 4 February 2014 at 20:44. Inc. additional terms may apply.wikipedia. a non-profit organization.Current transformer .wikipedia. Wikipedia® is a registered trademark of the Wikimedia Foundation.Wikipedia. Text is available under the Creative Commons Attribution-ShareAlike License.org/wiki/Current_transformer Retrieved from "http://en. By using this site.org/w/index. 6 of 6 2/23/2014 3:01 PM . . After knee point voltage . electricity4you.blogspot.then it will not saturate in normal case. for metering and 5P class.you have any doubts. So generally manufacture provide knee point voltage maximum compared to other classes).ELECTRICITY 4 YOU: KNEE POINT VOLTAGE TEST. http://electricity4you. Total viewers free download counter | vps servers CONTENTS or knee point test at field PROCEDURE: 1. Q. measure secondary current by using leakage current tester.so generally by designing specially(secondary current only 1amps. Q.What is the knee point voltage? A.com@gmail. 3.. Q. 1 of 2 2/23/2014 3:14 PM . Repeat the steps up 100% of knee point voltage.blogspot.it implies that voltage across secondary winding is small. why we are doing this test? A.you want to communicate with administrator contact with above email...increase the voltage by 10% step by step and measure current as said above... 2.ae/2013/05/knee-point-voltage-test. Why it is important in only PS class? what about metering class and over current and earth fault protection (5P class) ? A.com if you want to share anything.Isolate the CT from all external connections.. Apply 10% of knee point voltage (provided on name plate details) to the secondary circuit by using auto transformer. It is the point at where 50% of secondary current increases in order to increase 10% of voltage in secondary winding. as to minimize ohimic loss in secondary circuit).html ‫تسجيل الدخول‬ ‫إنشاء مدونة إلكترونية‬ «‫المدونة ا لكترونية التالية‬ ‫المزيد‬ 0 WE MAKE U MUCH NEARER TO ELECTRICAL ENGINEERING GENERAL ELECTRICAL KNOWLEDGE TESTING OF EQUIPMENTS COMMISSIONING OF ELECTRICAL EQUIPMENTS ABOUT ME PHOTO GALLERY KNEE POINT VOLTAGE TEST. or LIGHTNING AREESTER. We are just checking the manufacture specification is correct or not..But in PS(the class used only for differential protection purpose) class secondary burden is very high so the voltage across secondary winding is also high which may be divert our CT to saturate position in normal condition also. What is burden? A. BASIC LAWS POWER POTENTIAL DIFFERENCE or VOLTAGE CURRENT INDOOR SUBSTATION OUTDOOR SUBSTATION CIRCUIT BREAKER AUTO RE CLOSE CAPACITIVE VOLTAGE TRANSFORMER SYNCHRONIZATION MOTOR GENERATOR WAVE TRAP HI-POTENTIAL TEST FOR BUS BAR HI-POTENTIAL TEST FOR CABLES WINDING RESISTANCE TEST FOR CT RATIO TEST FOR CT POLARITY TEST FOR CT INSULATION RESISTANCE TEST FOR CT WINDING RESISTANCE TEST FOR POWER TRANSFORMER INSULATION RESISTANCE TEST FOR BUS BAR VECTOR GROUP TEST FOR TRANSFORMER RATIO TEST FOR TRANSFORMER VT or PT RATIO TEST INSULATION RESISTANCE TEST FOR CABLES KNEE POINT VOLTAGE TEST (PS class only) INSULATION RESISTANCE TEST FOR VT or PT POLARITY TEST FOR VT or PT WINDING RESISTANCE TEST FOR VT or PT CURRENT TRANSFORMER POTENTIAL TRANSFORMER POWER TRANSFORMER POWER CABLE BUS BAR INSULATION RESISTANCE TEST FOR TRANSFORMER MAGNETIZATION CURRENT TEST FOR TRANSFORMER MAGNETIC BALANCE TEST FOR TRANSFORMER DIFFERENT TYPES OF CIRCUIT BREAKERS EARTHING WIRE and SURGE ARRESTER SURGE ARRESTER . The load connected to secondary winding (sum of relay impedance meter impedance and control cable resistance and CT secondary winding resistance). 6. current will not increase as starting (proportionally). 4. 5. Q. secondary circuit is small so the voltage drop across burden is small. ..html 2 of 2 2/23/2014 3:14 PM . http://electricity4you.ELECTRICITY 4 YOU: KNEE POINT VOLTAGE TEST..blogspot.ae/2013/05/knee-point-voltage-test. to provide for different requirements of current level as an alternating current source.Wikipedia. A transformer most commonly consists of two windings of wire wound around a common core to effect tight electromagnetic coupling between the windings.org/wiki/Transformer Transformer From Wikipedia. a current flows through the secondary winding drawing power from the primary winding and its power source. the free encyclopedia http://en. The coil that receives the electrical input energy is referred to as the primary winding. but produces a short output pulse as the voltage rises when connected to the DC source. or it may be used for impedance matching between mismatched electrical circuits to effect maximum power transfer between the circuits. while the output coil is called the secondary winding. An alternating electric current flowing through the primary winding (coil) of a transformer generates an electromagnetic field in its surroundings and a varying magnetic flux in the core of the transformer. By electromagnetic induction this magnetic flux generates a varying electromotive force in the secondary winding. A transformer cannot operate with direct current.wikipedia. If a load impedance is connected across the secondary winding.[1][2] Contents 1 Invention 2 Applications 3 Basic principles 4 Basic transformer parameters and construction 5 Construction 6 Classification parameters 7 Types 8 Applications 9 History 10 See also 11 Notes 12 References 13 Bibliography 14 External links 1 of 27 2/24/2014 8:04 PM . The core material is often a laminated iron core. Pole-mounted distribution transformer with center-tapped secondary winding used to provide 'split-phase' power for residential and light commercial service. which in North America is typically rated 120/240 volt.Transformer . Transformers may be used in voltage conversion to transform an AC voltage from one voltage level on the input of the device to another level at the output terminals. resulting in a voltage across the output terminals. the free encyclopedia A transformer is an electrical device that transfers energy between two circuits through electromagnetic induction. transformers can step-up voltage/step-down current from generators to high-voltage transmission lines. Flux is confined within the magnetic core. In terms of voltage conversion. According to Joule's Law.Wikipedia. In the early days of commercial electric power. the future fate of high-voltage alternating current still remained unclear for several reasons: high-voltage sources had a much higher risk of causing severe electrical injuries. power conversion transformers. A broad range of transformer designs are used in electronic and electric power applications. [3] Applications Transformers perform voltage conversion. distribution. many essential appliances could only function at low voltage. The physical principles of the inductive behavior of the transformer are most readily understood and formalized when making some assumptions to construct a simple model which is called the ideal transformer . Thus. and more energy efficient transmission. Ideal transformer The assumptions to characterize the ideal transformer are: The windings of the transformer have no resistance. audio. and utilization of electrical energy. the free encyclopedia http://en. The magnetic field excited in the primary coil gives rise to self-induction as well as mutual induction between coils. Thus. Transformers range in size from thumbnail-sized used in microphones to units weighing hundreds of tons interconnecting the power grid. including miniature. the historical pursuit for a high-voltage low-current electricity transmission system took shape. it is the same flux that links the input and output 2 of 27 2/24/2014 8:04 PM . energy losses are directly proportional to the square of current. The step-up transformer is used to increase the secondary voltage relative to the primary voltage. isolation protection. there is no copper loss in the winding. produces a magnetic field surrounding the wire. which operates at low-voltage high-current. This model differs from real transformers by assuming that the transformer is perfectly constructed and by neglecting that electrical or magnetic losses occur in the materials used to construct the device. and step-down voltage/step-up current to local distribution circuits or industrial customers. the main energy source was direct current (DC). isolation. This self-induction counters the excited field to such a degree that the resulting current through the primary winding is very small when no load draws power from the secondary winding. and hence no voltage drop. cheaper. such as a wire. Therefore. etc. whereas the step-down transformer is used to decrease the secondary voltage relative to the primary voltage. and impedance matching. Although high voltage transmission systems offered many benefits. This law revealed that even a tiny decrease in current or rise in voltage can cause a substantial lowering in energy losses and costs. the introduction of transformers had successfully reduced the safety concerns associated with alternating current and had the ability to lower voltage to a value that was required by most essential appliances. and a changing magnetic field in the vicinity of a wire induces a voltage across the ends of that wire.org/wiki/Transformer Invention The invention of transformers during the late 1800s allowed for longer-distance.Transformer . Basic principles The functioning of a transformer is based on two principles of the laws of electromagnetic induction: An electric current through a conductor. Regarded as one of the most influential electrical innovations of all time.wikipedia. high-frequency. a is the winding turns ratio. the secondary voltage is greater than the primary voltage.wikipedia.[4][5][a][b] VP designates source impressed voltage. If the secondary winding of an ideal transformer has no load. respectively. NP and NS are the number of turns in the primary and secondary windings respectively. with voltage ratio and winding turns ratio both being inversely proportional to the corresponding current ratio. when the number of turns in the primary coil is less than the number of turns in the secondary. i. and. The ideal transformer induces secondary voltage VS as a proportion of the primary voltage VP and respective winding turns as given by the equation . no current flows in the primary winding.e.Transformer .Wikipedia. the secondary voltage is smaller than the primary voltage. lossless and perfectly-coupled transformer having primary and secondary windings with NP and NS turns. where. when the number of turns in the primary coil is greater than the number of turns in the secondary coil. Permeability of the core is infinitely high which implies that net mmf (amp-turns) must be zero (otherwise there would be infinite flux) hence IP NP .org/wiki/Transformer windings. The resulting input and output apparent power are equal as given by the equation . VS designates output voltage. On the other hand.IS NS = 0. Any load impedance ZL connected to the ideal transformer's secondary winding allows energy to flow without loss from primary to secondary circuits. Combining the two equations yields the following ideal transformer identity . The load impedance ZL and secondary voltage VS determine the secondary current IS as follows 3 of 27 2/24/2014 8:04 PM . the value of these ratios being respectively higher and lower than unity for step-down and step-up transformers. Ideal transformer with a source and a load. The circuit diagram (right) shows the conventions used for an ideal. According to this formalism. This formula is a reasonable approximation for the typical commercial transformer. which cause inductive loss. the free encyclopedia http://en. The transformer core does not suffer magnetic hysteresis or eddy currents. Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer. The area is constant.wikipedia.Wikipedia. the flux is the product of the magnetic flux density B and the area A through which it cuts. For an ideal transformer. Ideal transformer and induction law whereas the magnetic field varies with time according to the excitation of the primary. usually iron. Ns is the number of turns in the secondary coil. the free encyclopedia http://en. If ZL = RL where RL is a pure resistance then the power is given by:[9][10] The primary current is given by the following equation:[9][10] Induction law A varying electrical current passing through the primary coil creates a varying magnetic field around the coil which induces a voltage in the secondary winding. the power supplied to the primary and the power dissipated by the load are equal. The apparent impedance ZL' of this secondary circuit load referred to the primary winding circuit is governed by a squared turns ratio multiplication factor relationship derived as follows[7][8] . and dΦ/dt is the derivative[d] of the magnetic flux Φ through one turn of the coil. The voltage induced across the secondary coil may be calculated from Faraday's law of induction.Transformer . being equal to the cross-sectional area of the transformer core. The primary and secondary windings are wrapped around a core of very high magnetic permeability. which states that: where Vs is the instantaneous voltage.[7] the 4 of 27 2/24/2014 8:04 PM . The current through a load connected to the secondary winding and the voltage across it are in the directions indicated in the figure. If the turns of the coil are oriented perpendicularly to the magnetic field lines.[c] so that most of the magnetic flux passes through both the primary and secondary coils.org/wiki/Transformer . which marks the terminals having an in-phase relationship. The changing magnetic field induces an emf across each winding. the free encyclopedia http://en. with polarity dot and X1 markings on LV side terminal Hysteresis losses due to nonlinear application of the voltage applied in the transformer core. acting as it does in opposition to the primary voltage. and on terminal markings. and Eddy current losses due to joule heating in the core that are proportional to the square of the transformer's applied voltage. the real transformer must be viewed as a simple inductor with an impedance Z: 5 of 27 2/24/2014 8:04 PM .Transformer . consist of[18] Instrument transformer. the windings in a real transformer have finite non-zero impedances in the form of: Joule losses due to resistance in the primary and secondary windings[18] Leakage flux that escapes from the core and passes through one winding only resulting in primary and secondary reactive impedance.org/wiki/Transformer instantaneous voltage across the primary winding equals Taking the ratio of the above two equations gives the same voltage ratio and turns ratio relationship shown above.[11] The primary emf. collectively called magnetizing current losses.[12] This is in accordance with Lenz's law. Polarity The relationships of the instantaneous polarity at each of the terminals of the windings of a transformer depend on the direction the windings are wound around the core. nameplates. . If a voltage is applied across the primary terminals of a real transformer while the secondary winding is open without load.wikipedia.Wikipedia. that is. is sometimes termed the counter emf. This relationship is usually denoted by the dot convention in transformer circuit diagrams. the transformer still behaves as described above in the ideal transformer. which states that induction of emf always opposes development of any such change in magnetic field. Identically wound windings produce the same polarity of voltage at the corresponding terminals. Whereas windings in the ideal model have no impedance. As still lossless and perfectly-coupled. [13][14][15][e][f] Real transformer The ideal transformer model neglects the following basic linear aspects in real transformers. Core losses. [21] Air gaps are also used to keep a transformer from saturating. some flux traverses paths that take it outside the windings. the Z impedance and X/R ratio of different capacity transformers tends to vary. the transformers would share power in proportion to their respective volt-ampere ratings (e.[22] Knowledge of leakage inductance is also useful when transformers are operated in parallel. causing the secondary voltage not to be directly proportional to the primary voltage. The combined effect of the leakage flux and the electric field around the windings is what transfers energy from the primary to the secondary.75.75%. the impedance tolerances of commercial transformers are significant.000 kVA unit. It can be shown that if the percent impedance (Z) and associated winding leakage reactance-to-resistance (X/R) ratio of two transformers were hypothetically exactly the same. It is not directly a power loss. but results in inferior voltage regulation.g. especially audio-frequency transformers in circuits that have a DC component flowing in the windings.[20] In some applications increased leakage is desired.[23][24] Equivalent circuit See also: Steinmetz equivalent circuit Referring to the diagram. it is impossible to eliminate all leakage flux because it plays an essential part in the operation of the transformer.000 kVA and 500 kVA units' values being. mercury vapor lamps. However. Nevertheless.Wikipedia. particularly under heavy load.[19] Such flux is termed leakage flux.org/wiki/Transformer .Transformer . Also.[12] Leaky transformers may be used to supply loads that exhibit negative resistance. respectively. and results in leakage inductance in series with the mutually coupled transformer windings. including itself.[12] Leakage flux results in energy being alternately stored in and discharged from the magnetic fields with each cycle of the power supply.wikipedia. the larger unit would carry twice the current). or magnetic bypass shunts may deliberately be introduced in a transformer design to limit the short-circuit current it will supply. such as electric arcs.[25] Winding joule losses and leakage reactances are represented by the following series loop impedances of the model: 6 of 27 2/24/2014 8:04 PM .[19] Transformers are therefore normally Leakage flux of a transformer designed to have very low leakage inductance. and neon signs or for safely handling loads that become periodically short-circuited such as electric arc welders. In practice. Leakage flux Main article: Leakage inductance The ideal transformer model assumes that all flux generated by the primary winding links all the turns of every winding.75 and Z ~ 5%. air gaps. 500 kVA unit in parallel with 1. X/R ~ 3. which can incorporate an ideal transformer. a practical transformer's physical behavior may be represented by an equivalent circuit model. X/R ~ 4. Z ~ 5. corresponding 1. and long magnetic paths. the free encyclopedia http://en. to illustrate. Basic transformer parameters and construction Effect of frequency The time-derivative term in Faraday's Law shows that the flux in the core is the integral with respect to time of the applied voltage. (NP/NS) 2 = a2.[25] Analysis may be simplified by assuming that magnetizing branch impedance is relatively high and relocating the branch to the left of the primary impedances. the relationship between the two being non-linear due to saturation effects.wikipedia. This introduces error but allows combination of primary and referred secondary resistances and reactances by simple summation as two series impedances. Core loss and reactance is represented by the following shunt leg impedances of the model: Core or iron losses: RC Magnetizing reactance: XM. Real transformer equivalent circuit Core losses are caused mostly by hysteresis and eddy current effects in the core and are proportional to the square of the core flux for operation at a given frequency. winding resistance test. magnetizing branch current I0 equals transformer no-load current. and the supply frequency f . Transformer equivalent circuit impedance and transformer ratio parameters can be derived from the following tests: open-circuit test. RC and XM are collectively termed the magnetizing branch of the model. causing a large increase in the magnetizing current and overheating the transformer.org/wiki/Transformer Primary winding: RP.[g] short-circuit test. the flux rises to the point where magnetic saturation of the core occurs.[29] In practice. RS and XS are in practice usually referred to the primary side by multiplying these impedances by the turns ratio squared. core flux lags the induced emf by 90°. All practical 7 of 27 Transformer universal emf equation If the flux in the core is purely sinusoidal. though sometimes termed 'exact' equivalent circuit based on linearity assumptions.[26] The finite permeability core requires a magnetizing current IM to maintain mutual flux in the core.Wikipedia. With open-circuited secondary winding.[26] With sinusoidal supply. the free encyclopedia http://en. number of turns N. retains a number of approximations. core cross- 2/24/2014 8:04 PM . Magnetizing current is in phase with the flux. with the core flux increasing linearly with time. In normal course of circuit equivalence transformation. XS. all impedances of the equivalent circuit shown are by definition linear and such non-linearity effects are not typically reflected in transformer equivalent circuits.[25] The resulting model.[28] Hypothetically an ideal transformer would work with direct-current excitation. the relationship for either winding between its rms voltage Erms of the winding.Transformer . and transformer ratio test. XP Secondary winding: RS. However. The power dissipated by its load would be equal to the power supplied by its primary source. 16. flux (green). frequencies used for some railway electrification systems were much lower (e.[30] Conversely. and converter equipment being supply by. transformers can be physically more compact because a given core is able to transfer more power without reaching saturation and fewer turns are needed to achieve If the flux does not contain even harmonics the same impedance. winding capacitance. including winding resistance. leakage flux. and cooling to establish if safe operation is practical. the transformers used to step-down the high over-head line voltages (e. and those rated for electricity distribution usually perform better than 98%.[32] 8 of 27 2/24/2014 8:04 PM . it is 100% efficient. Large power transformers are vulnerable to insulation failure due to transient voltages with high-frequency components.wikipedia. Larger transformers are generally more efficient than small units. Aircraft and military equipment employ waveshape: 400 Hz power supplies which reduce core and winding weight. As such. Operation of a transformer at other than its design frequency may require assessment of voltages. core losses. such traction transformers have to accommodate different input frequencies and voltage (ranging from as high as 50 Hz down to 16.[29] The emf of a transformer at a given flux density increases with frequency. properties such as core the following equation can be used for loss and conductor skin effect also increase with half-cycle average voltage Eavg of any frequency. sectional area a in m2 and peak magnetic flux density Bpeak in Wb/m2 or T (tesla) is given by the universal emf equation:[18] Power transformer over-excitation condition caused by decreased frequency.g.[31] Energy losses A theoretical (ideal) transformer does not experience energy losses. i. iron core's magnetic characteristics (red) and magnetizing current (blue).[18] By operating at higher frequencies. the free encyclopedia http://en. The power supply to.org/wiki/Transformer transformers must therefore operate with alternating (or pulsed direct) current.e.Transformer . a real transformer is typically 95 to 99% efficient. such transformers' being restricted to be positioned below the passenger compartment.7 Hz and 25 Hz) than normal utility frequencies (50 – 60 Hz) for historical reasons concerned mainly with the limitations of early electric traction motors. For example. However. At a lower frequency. and hysteresis loss. 15 kV) were much heavier for the same power rating than those designed only for the higher frequencies.7 Hz and rated up to 25 kV) while being suitable for multiple AC asynchronous motor and DC converters & motors with varying harmonics mitigation filtering requirements. the magnetizing current will increase. Operation of a transformer at its designed voltage but at a higher frequency than intended will lead to reduced magnetizing current.g. One example of state-of-the-art design is traction transformers used for electric multiple unit and high-speed train service operating across the country border and using different electrical standards. In contrast. such as caused in switching or by lightning.Wikipedia. transformers may need to be equipped with 'volts per hertz' over-excitation relays to protect the transformer from overvoltage at higher than rated frequency. losses. due to several loss mechanisms. [4][37] This transformer hum is especially objectionable in transformers supplied at power frequencies[h] and in high-frequency flyback transformers associated with PAL system CRTs.Wikipedia. hence.org/wiki/Transformer Experimental transformers using superconducting windings achieve efficiencies of 99. it is often useful to express these losses in terms of no-load loss. As frequency increases. all transformers operating at low frequencies use laminated or similar cores. such as the core. However. since energy supplied to its magnetic fields is returned to the supply with the next half-cycle.wikipedia. and. the trade-off is in the additional initial and running cost of the superconducting design.[34] Eddy current losses can be reduced by making the core of a stack of plates electrically insulated from each other. The eddy current loss is a complex function of the square of supply frequency and inverse square of the material thickness. Mechanical vibration and audible noise transmission In addition to magnetostriction. an effect known as magnetostriction.[34] Transformer losses arise from: Winding joule losses Current flowing through winding conductors causes joule heating.6 for iron. Core losses Hysteresis losses Each time the magnetic field is reversed. so that even an idle transformer constitutes a drain on the electrical supply. According to Steinmetz's formula. Designing energy efficient transformers for lower loss requires a larger core.85%. As transformer losses vary with load.[38] There are also radiative losses due to the oscillating magnetic field but these are usually small. the free encyclopedia http://en. half-load loss. while variable winding joule losses dominating increasingly as load increases.[34] [35][36] Eddy current losses Ferromagnetic materials are also good conductors and a core made from such a material also constitutes a single short-circuited turn throughout its entire length. losses to increase. causes it to physically expand and contract slightly with each cycle of the magnetic field. Hysteresis and Eddy current losses are constant at all load levels and dominate overwhelmingly without load. The choice of construction represents a trade-off between initial cost and operating cost. Eddy currents therefore circulate within the core in a plane normal to the flux. increasing initial cost. skin effect and proximity effect causes winding resistance and. the empirical exponent of which varies from about 1. full-load loss. the heat energy due to hysteresis is given by . the frictional energy of which produces an audible noise known as mains hum or transformer hum. f is the frequency. and are responsible for resistive heating of the core material.8 but is often given as 1. or even amorphous steel for the core and thicker wire. η is the hysteresis coefficient and βmax is the maximum flux density. a small amount of energy is lost due to hysteresis within the core. The no-load loss can be significant.Transformer . any leakage flux that intercepts nearby conductive materials such as the transformer's support structure will give rise to eddy currents and be converted to heat. Stray losses Leakage inductance is by itself largely lossless.[33] The increase in efficiency can save considerable energy in a large heavily loaded transformer.4 to 1 . good-quality silicon steel. rather than a solid block. Magnetostriction related transformer hum Magnetic flux in a ferromagnetic material. the alternating magnetic field causes fluctuating forces between the 9 of 27 2/24/2014 8:04 PM . and so on. hysteresis loss is thus given by where. nominally. 10 of 27 2/24/2014 8:04 PM . Shell form design may be more prevalent than core form design for distribution transformer applications due to the relative ease in stacking the core around winding coils. Each lamination is insulated from its neighbors by a thin non-conducting layer of insulation.[40][41][42][43] Shell form design tends to be preferred for extra high voltage and higher MVA applications because.[45] Early transformer developers soon realized that cores constructed from solid iron resulted in prohibitive eddy current losses. thus amplifying audible transformer hum. At higher voltage and power ratings. 230 kV or 75 MVA).[39] Core form and shell form transformers Closed-core transformers are constructed in 'core form' or 'shell form'. shell form transformers tend to be more prevalent.[47] The universal transformer equation indicates a minimum cross-sectional area for the core to avoid saturation. and their designs mitigated this effect with cores consisting of bundles of insulated iron wires.[46] Later designs constructed the core by stacking layers of thin steel laminations.[40] Core form design tends to.[48] but are more laborious and expensive to construct.[49] Thin laminations are generally used on high-frequency transformers.Transformer . shell form = shell type Construction Cores Laminated steel cores Transformers for use at power or audio frequencies typically have cores made of high permeability silicon steel.Wikipedia. Laminated core transformer showing edge of laminations at top of photo The effect of laminations is to confine eddy currents to highly elliptical paths that enclose little flux.[44] The steel has a permeability many times that of free space and the core thus serves to greatly reduce the magnetizing current and confine the flux to a path which closely couples the windings. Thinner laminations reduce losses. than shell form design for high voltage power transformer applications at the lower end of their voltage and power rating ranges (less than or equal to. the free encyclopedia http://en. the transformer is shell form. This energy incites vibration transmission in interconnected metalwork. better short-circuit strength characteristics and higher immunity to transit damage. a principle that has remained in use. as a general rule. though more labor-intensive to manufacture. shell form transformers are characterized as having inherently better kVA-toweight ratio. and so reduce their magnitude. the transformer is core form.[43] Core form = core type. be more economical.wikipedia. and therefore more prevalent.org/wiki/Transformer primary and secondary windings. When windings surround the core. with some of very thin steel laminations able to operate up to 10 kHz. when windings are surrounded by the core. For frequencies extending beyond the VHF band. The cut-core or C-core type is made by winding a steel strip around a rectangular form and then bonding the layers together. is made from a long strip of silicon steel or permalloy wound into a coil. flux (green).[50] Overcurrent protection devices such as fuses must be selected to allow this harmless inrush to pass. iron core's magnetic characteristics (red) and magnetizing current (blue). The closed ring shape eliminates air gaps inherent in the construction of an E-I core. and the core assembled by binding the two C halves together with a steel strap. The higher initial cost of the core material is offset over the life of the transformer by its lower losses at light load. 11 of 27 2/24/2014 8:04 PM . but is very economical to manufacture.wikipedia. but more expensive cores with circular cross-sections are also available. When power is then reapplied.[49] Such a design tends to exhibit more losses.org/wiki/Transformer Laminating the core greatly reduces eddy-current losses One common design of laminated core is made from interleaved stacks of E-shaped steel sheets capped with I-shaped pieces. leading to its name of 'E-I transformer'. the free encyclopedia http://en. The primary and secondary coils are often wound concentrically to cover the entire surface of the core.[51] Distribution transformers can achieve low no-load losses by using cores made with low-loss high-permeability silicon steel or amorphous (non-crystalline) metal alloy. depending on operating frequency. Power transformer inrush current caused by residual flux at switching instant. This minimizes the length of wire needed. These materials combine high magnetic permeability with high bulk electrical resistivity. overhead power transmission lines.[52] Solid cores Powdered iron cores are used in circuits such as switch-mode power supplies that operate above mains frequencies and up to a few tens of kilohertz.[53] A strip construction ensures that the grain boundaries are optimally aligned. forming two C shapes. A steel core's remanence means that it retains a static magnetic field when power is removed. On transformers connected to long. which. or ferrite. Toroidal cores Toroidal transformers are built around a ring-shaped core.Transformer . cores made from non-conductive magnetic ceramic materials called ferrites are common.[49] Some radio-frequency transformers also have movable cores (sometimes called 'slugs') which allow adjustment of the coupling coefficient (and bandwidth) of tuned radio-frequency circuits. induced currents due to geomagnetic disturbances during solar storms can cause saturation of the core and operation of transformer protection devices. It is then cut in two.[21] The cross-section of the ring is usually square or rectangular. the residual field will cause a high inrush current until the effect of the remaining magnetism is reduced.[49] They have the advantage that the flux is always oriented parallel to the metal grains. usually after a few cycles of the applied AC waveform. and also provides screening to minimize the core's magnetic field from generating electromagnetic interference.Wikipedia. reducing reluctance. powdered iron. improving the transformer's efficiency by reducing the core's reluctance. The main disadvantages are higher cost and limited power capacity (see Classification parameters below). Larger power transformers operating at high voltages may be wound with copper rectangular strip conductors insulated by oil-impregnated paper and blocks of pressboard. and are frequently employed in radio-frequency applications. or throughout the whole winding.[12] They have however very high bandwidth. As a consequence.Wikipedia.org/wiki/Transformer Toroidal transformers are more efficient than the cheaper laminated E-I types for a similar power level. but in all cases the individual turns must be electrically insulated from each other to ensure that the current travels throughout every turn.[56] High-frequency transformers operating in the tens to hundreds of kilohertz often have windings made of braided Litz wire to minimize the skin-effect and proximity effect losses. lower exterior magnetic field (about one tenth). an arrangement termed an 'air-core' transformer. The air which comprises the magnetic circuit is essentially lossless. the coils are often wound from enamelled magnet wire. A drawback of toroidal transformer construction is the higher labor cost of winding. in which currents are low and the potential difference between adjacent turns is small. physical size. and weight of inductive components. since even at low power frequencies non-uniform distribution of current would otherwise exist in high-current windings. Air cores A physical core is not an absolute requisite and a functioning transformer can be produced simply by placing the windings near each other.Transformer . and so an air-core transformer eliminates loss due to hysteresis in the core material.[55] For small power and signal transformers. and the strands are arranged so that at certain points in the winding. such as Formvar wire. then inserting a bobbin containing primary and secondary windings. Windings Main article: Windings Electronic symbol for Air Cores The conducting material used for the windings depends upon the application. less mechanical hum (making them superior in audio amplifiers). This is because it is necessary to pass the entire length of a coil winding through the core aperture each time a single turn is added to the coil. typically between a few tens of kilohertz to hundreds of megahertz.[28] Large power transformers use multiplestranded conductors as well. the free encyclopedia http://en. toroidal transformers also tend to exhibit higher inrush current. Because of the lack of a residual gap in the magnetic path. single-bolt mounting. low off-load losses (making them more efficient in standby circuits). and so such designs are unsuitable for use in power distribution. include smaller size (about half).[54] for which a satisfactory coupling coefficient is maintained by carefully overlapping the primary and secondary windings. Small distribution transformers may achieve some of the benefits of a toroidal core by splitting it and forcing it open.[56] Each strand is individually insulated. to reduce losses. resulting in very poor regulation. each portion occupies different relative 12 of 27 2/24/2014 8:04 PM . compared to laminated E-I types. They're also used for resonant transformers such as Tesla coils where they can achieve reasonably low loss in spite of the high leakage inductance. toroidal transformers rated more than a few kVA are uncommon. lower weight (about half).wikipedia. and greater choice of shapes. Other advantages compared to E-I types. Small toroidal core transformer Ferrite toroidal cores are used at higher frequencies.[12] The leakage inductance is inevitably high. Black: Primary winding made of oxygen-free copper. Bottom left: Reduction of leakage inductance would lead to increase of capacitance.[58] Cut view through transformer windings. this life expectancy halving rule holding more narrowly when the increase is between about 7°C to 13 of 27 2/24/2014 8:04 PM . Since most cores are at least moderately conductive they also need insulation. dirt or corrosive ambients.Transformer . The stranded conductor is also more flexible than a solid conductor of similar size.[56] Windings are usually arranged concentrically to minimize flux leakage. such as from water.org/wiki/Transformer Power-frequency transformers may have taps at intermediate points on the winding. bind. Taps may be manually reconnected. vacuum and pressure is used to thoroughly seal. or for automatic voltage regulators for sensitive loads. Automatic on-load tap changers are used in electric power transmission or distribution. Top left: Toroidal transformer. and eliminate entrained air voids in the winding polyester resin insulation coat layer. Coils are split into sections. and those sections interleaved between the sections of the other winding. by multiple dips including typically in terms of final epoxy coat. White: insulator. Modulation transformers in AM transmitters are very similar. on equipment such as arc furnace transformers. a combination of heat. or a manual or automatic switch may be provided for changing taps. VPE windings are similar to VPI windings but provide more protection against environmental effects.Wikipedia. usually on the higher voltage winding side. Right: C-core. The black windings are made of film. Top: Equally low capacitance between all ends of both windings. and reduces eddy current losses in the winding itself.wikipedia. Cooling See also: Arrhenius equation To place the cooling problem in perspective. used for the distribution of audio to public address loudspeakers. The transposition equalizes the current flowing in each strand of the conductor. the accepted rule of thumb is that the life expectancy of insulation in all electric machines including all transformers is halved for about every 7°C to 10°C increase in operating temperature. and cast coil encapsulation processes. have taps to allow adjustment of impedance to each speaker.[57] In the VPI process. for voltage adjustment. A center-tapped transformer is often used in the output stage of an audio power amplifier in a push-pull circuit. the free encyclopedia http://en. The windings of signal transformers minimize leakage inductance and stray capacitance to improve high-frequency response. Audio-frequency transformers. thus increasing resistance to corona. Red: Secondary winding. Dry-type transformer winding insulation systems can be either of standard open-wound 'dip-and-bake' construction or of higher quality designs that include vacuum pressure impregnation (VPI). positions in the complete conductor. but E-core would be similar. Bottom: Lowest capacitance for one end of the secondary winding needed for low-power high-voltage transformers. aiding manufacture. Green spiral: Grain oriented silicon steel. vacuum pressure encapsulation (VPE). model. depending on severity of gas accumulation due to internal arcing.[70] Today. The conservator (reservoir) at top provides liquid-to-atmosphere isolation as coolant level and temperature changes.com/?page=show_article& article=362) which are activated by the first dynamic pressure peak of the shock wave. non-toxic. stable silicone-based oils.[66][67] Building regulations in many jurisdictions require indoor liquid-filled transformers to either use dielectric fluids that are less flammable than oil. As power ratings increase. [64][65] Prolonged operation at elevated temperature degrades insulating properties of winding insulation and dielectric coolant. Cutaway view of liquidimmersed construction transformer. This underlines the need to monitor. and fire-suppression sprinkler systems.[63] An oil-immersed transformer may be equipped with a Buchholz relay.wikipedia. power loading conditions. or fluorinated hydrocarbons may be used where the expense of a fire-resistant liquid offsets additional building cost for a transformer vault. forced-oil cooling. transformer oil testing including dissolved gas analysis provides valuable maintenance information. pumps for forced-liquid cooling. pressurized tanks and 14 of 27 2/24/2014 8:04 PM . that the average age of failure of power transformers is about 10 to 15 years. transformers are often cooled by forced-air cooling. which not only shortens transformer life but can ultimately lead to catastrophic transformer failure. or combinations of these. Many explosions are reported to have been avoided thanks to this technology. or have heat exchangers for water-cooling.[62] Large transformers are filled with transformer oil that both cools and insulates the windings. though concerns over their environmental persistence led to a widespread ban on their use. It is estimated that 50% of power transformers will survive 50 years of use.[63] Transformer oil is a highly refined mineral oil that cools the windings and insulation by circulating within the transformer tank.[68][71] PCBs for new equipment was banned in 1981 and in 2000 for use in existing equipment in United Kingdom[72] Legislation enacted in Canada between 1977 and 1985 essentially bans PCB use in transformers manufactured in or imported into the country after 1980.[68] Air-cooled dry transformers can be more economical where they eliminate the cost of a fire-resistant transformer room.electricenergyonline. and that about 30% of power transformer failures are due to insulation and overloading failures. avoiding transformer explosion before static pressure increases. The tank of liquid filled transformers often has radiators through which the liquid coolant circulates by natural convection or fins. Some large transformers employ electric fans for forced-air cooling. the maximum allowable level of PCB contamination in existing mineral oil transformers being 50 ppm. instead of being liquid-filled. the free encyclopedia http://en.Wikipedia. watercooling. Another protection means consists in fast depressurization systems (http://www. possibly difficult.[50] Oil-immersed transformer installations usually include fire protection measures such as walls.org/wiki/Transformer 8°C in the case of transformer winding cellulose insulation. have their windings enclosed in sealed. is used to either alarm or de-energize the transformer. forecast and manage oil and winding conductor insulation temperature conditions under varying.[59][60][61] Small dry-type and liquid-immersed transformers are often self-cooled by natural convection and radiation heat dissipation.[73] Some transformers. or be installed in fire-resistant rooms. The mineral oil and paper insulation system has been extensively studied and used for more than 100 years.[69] Polychlorinated biphenyls have properties that once favored their use as a dielectric coolant.Transformer . which.[59] With a great body of empirical study as a guide. oil containment. The walls and fins provide required heat dissipation balance. org/wiki/Transformer cooled by nitrogen or sulfur hexafluoride gas. water-cooled. distribution.[i] other . power.[71] Experimental power transformers in the 500-to-1. Duty of a transformer : Continuous. Drying may be done by circulating hot air around the core. Although they all share the 15 of 27 2/24/2014 8:04 PM ..[74][75] Insulation drying Construction of oil-filled transformers requires that the insulation covering the windings be thoroughly dried of residual moisture before the oil is introduced. and it is energy efficient. A lower frequency reduces the effect of inductance. 3-winding. which is normally 50 or 60 Hz. liquid-immersed .forced oil-cooled. Drying is carried out at the factory. audio-frequency.wikipedia. varying.[76] The LFH drying method is also used for service of older transformers. or by vapor-phase drying (VPD) where an evaporated solvent transfers heat by condensation on the coil and core. short-time. n-winding. step-down. Voltage class: From a few volts to hundreds of kilovolts.autotransformer. output voltage and current stabilizer or circuit isolation. [n-1]*6-pulse.Wikipedia. Scott-T. polygon. wye or star. periodic. amplifier output. forced air-cooled. Frequency range: Power-frequency. Constant-potential transformer descriptor : Step-up. Utilization: Pulse. Basic magnetic form: Core form. Circuit application: Such as power supply. The method is called low-frequency heating (LFH) since the current used is at a much lower frequency than that of the power grid. isolation.various possible two-winding combinations of the phase designations delta. and may also be required as a field service.[78] Classification parameters Transformers can be classified in many ways. arc furnace. Types Various specific electrical application designs require a variety of transformer types.. The heating can be controlled very well. zigzag grounding transformer winding. 12-pulse. .000 kVA range have been built with liquid nitrogen or helium cooled superconducting windings.[79][80][81][82] Rectifier phase-shift winding configuration: 2-winding. which eliminates winding losses without affecting core losses. or radio-frequency. Cooling type: Dry and liquid-immersed .[77] Bushings Larger transformers are provided with high-voltage insulated bushings made of polymers or porcelain. A large bushing can be a complex structure since it must provide careful control of the electric field gradient without letting the transformer leak oil. resistance heating by injection of current into the windings is used. and zigzag or interconnected star. .self-cooled. etc. rectifier. . For small transformers. the free encyclopedia http://en. General winding configuration: By EIC vector group . etc. impedance matching. such as the following: Power capacity: From a fraction of a volt-ampere (VA) to over a thousand MVA. intermittent. 6-pulse.Transformer . so the voltage required can be reduced. shell form. [80][82][83] Leakage transformer: Transformer that has loosely coupled windings. using a wye-delta transformer. each with transforming power a capacity of 150 MVA. Autotransformer : Transformer in which part of the winding is common to both primary and secondary circuits.Transformer . current or phase position of high voltage or high power circuits.[83] Polyphase transformer: Any transformer with more than one phase. Audio transformer : Transformer used in audio equipment. Output transformer : Transformer used to match the output of a valve amplifier to its load. Wires have resistance which loses energy through joule heating at a rate corresponding to Transformer at the Limestone square of the Generating Station in Manitoba.[83][84][j] Phase angle regulating transformer : A specialised transformer used to control the flow of real power on three-phase electricity transmission networks. By Canada showing 3 of 5 220kV/66kV transformers.org/wiki/Transformer basic characteristic transformer principles.[80][85] or more commonly. the free encyclopedia http://en.[86] to a higher voltage transformers enable economical transmission of power and distribution.[38] 16 of 27 2/24/2014 8:04 PM . Scott-T transformer: Transformer used for phase transformation from three-phase to two-phase and vice versa. they are customize in construction or electrical properties for certain installation requirements or circuit conditions.[83] Capacitor voltage transformer : Transformer in which capacitor divider is used to reduce high voltage before application to the primary winding.[87] All but a tiny fraction of the world's electrical power has passed through a series of transformers by the time it reaches the consumer. Instrument transformer : Potential or current transformer used to accurately and safely represent voltage.[83] Applications Transformers are used to increase voltage before transmitting electrical energy over long distances through wires.Wikipedia. transformers have shaped the electricity supply industry. Resonant transformer : Transformer that uses resonance to generate a high secondary voltage. An electrical substation in Melbourne. Distribution transformer. Consequently.wikipedia. Australia current. a zigzag grounding winding. power transformer : International standards make a distinction in terms of distribution transformers being used to distribute energy from transmission lines and networks for local consumption and power transformers being used to transfer electric energy between the generator and distribution primary circuits. permitting generation to be located remotely from points of demand. Grounding transformer : Transformer used for grounding three-phase circuits to create a neutral in a three wire system. invented by Rev.Transformer . induction coils relied upon vibrating electrical contacts that regularly interrupted the current in the primary to create the flux changes necessary for induction. thus creating the first toroidal closed-core transformer. the larger the induced secondary emf will be.[89] The relationship between emf and magnetic flux is an equation now known as Faraday's law of induction: . Although Henry's work likely having preceded Faraday's work by a few months. without an interrupter. such as between external cables and internal circuits. Induction coils The first type of transformer to see wide use was the induction coil. the principle of the operation of the transformer.wikipedia. mostly by trial and error. Audio transformers allowed telephone circuits to carry on a two-way conversation over a single pair of wires.[91] However he only applied individual pulses of current to his transformer. the free encyclopedia http://en. Induction coils evolved from scientists' and inventors' efforts to get higher voltages from batteries. A balun transformer converts a signal that is referenced to ground to a signal that has balanced voltages to ground.[90] coils of wire[88] Faraday performed the first experiments on induction between coils of wire.org/wiki/Transformer Transformers are also used extensively in electronic products to step-down the supply voltage to a level suitable for the low voltage circuits they contain. He was one of the first researchers to realize the more turns the secondary winding has in relation to the primary winding. slowly revealed the basic principles of transformers. and it was found AC could power an induction coil directly. was discovered independently and almost simultaneously by Joseph Henry and Michael Faraday in 1831. efforts to build better induction coils. Ireland in 1836. First alternating current transformers By the 1870s. Faraday's experiment with induction between where is the magnitude of the emf in volts and ΦB is the magnetic flux through the circuit in webers. Nicholas Callan of Maynooth College. Between the 1830s and the 1870s. efficient generators producing alternating current (AC) were available. 17 of 27 2/24/2014 8:04 PM .Wikipedia. Signal and audio transformers are used to couple stages of amplifiers and to match devices such as microphones and record players to the input of amplifiers. Since batteries produce direct current (DC) rather than AC. History Discovery of induction Electromagnetic induction. including winding a pair of coils around an iron ring. The transformer also electrically isolates the end user from contact with the supply voltage. Faraday was the first to publish the results of his experiments and thus receive credit for the discovery. and never discovered the relation between the turns ratio and emf in the windings. generators.Wikipedia.[95] Faraday's ring transformer Early series circuit transformer distribution Induction coils with open magnetic circuits are inefficient at transferring power to loads. Until about 1880.org/wiki/Transformer In 1876. Károly Zipernowsky.400 W. 11. as in a) or b). a position in which they have remained dominant ever since. respectively (see images).[96] Closed-core transformers and parallel power distribution In the autumn of 1884.6:19.[95] However. practical transformer designs did not appear until the 1880s. Budapest. Bremerhavn. but within a decade. Their AC systems used arc and incandescent lamps. the free encyclopedia http://en. 120:72 V. The secondary windings could be connected to several 'electric candles' (arc lamps) of his own design.[92] In 1878.wikipedia. Ottó Bláthy and Miksa Déri (ZBD).[95] The two designs were the first application of the two basic transformer constructions in common use to this day. The inherent flaw in this method was that turning off a single lamp (or other electric device) affected the voltage supplied to all others on the same circuit. the Ganz factory.[92] [93] The coils Yablochkov employed functioned essentially as transformers.[40][41][99][100] The Ganz factory had also in the autumn of 1884 made delivery of the world's first five high-efficiency AC transformers. the transformer would be instrumental in the War of Currents.4 A. had determined that open-core devices were impracticable. which can as a class all be termed as either core form or shell form (or alternatively. Italy in 1884.[46] They also exhibited the invention in Turin. 18 of 27 2/24/2014 8:04 PM . Many adjustable transformer designs were introduced to compensate for this problematic characteristic of the series circuit. 1884. by 1883. had installed over fifty systems in Austria-Hungary. the first of these units having been shipped on September 16. then sold the idea to the Westinghouse company in the United States. three engineers associated with the Ganz factory. began manufacturing equipment for electric lighting and. Open-core transformers with a ratio near 1:1 were Germany connected with their primaries in series to allow use of a high voltage for transmission while presenting a low voltage to the lamps. 1900. they described two designs with closed magnetic circuits where copper windings were either a) wound around iron wire ring core or b) surrounded by iron wire core. and in seeing AC distribution systems triumph over their DC counterparts. the paradigm for AC power transmission from a high voltage supply to a low voltage load was a Induction coil. 40 Hz. as they were incapable of reliably regulating voltage. Hungary. where it was adopted for an electric lighting system.[98] In their joint 1885 patent applications for novel transformers (later called ZBD transformers). Russian engineer Pavel Yablochkov invented a lighting system based on a set of induction coils where the primary windings were connected to a source of AC.[95] Efficient.[94] Lucien Gaulard and John Dixon Gibbs first exhibited a device with an open iron core called a 'secondary generator' in London in 1882. the efficiency of their open-core bipolar apparatus remained very low.[101] This first unit had been manufactured to the following specifications: 1.Transformer . series circuit. core type or shell type). and other equipment. including those employing methods of adjusting the core or bypassing the magnetic flux around part of a coil. the Edison Electric Light Company held an option on the US rights for the ZBD transformers. the ZBD engineers designed. They also popularized the word 'transformer' to describe a device for altering the emf of an electric current. the other concerning the ability to have high turns ratio transformers such that the supply network voltage could be much higher (initially 1.[97] This design[113] was first used commercially in the US in 1886[96] but Westinghouse was intent on improving the Stanley design to make it (unlike the ZBD type) easy and cheap to produce. He assigned to William Stanley the task of developing a device for commercial use in United States.[105][108] although the term had already been in use by 1882. and straight iron plates laid in to create a closed magnetic circuit. one-phase.Transformer .Wikipedia. back. businesses and public spaces. [103][104] When employed in parallel connected electric distribution systems. the steampowered Rome-Cerchi power plant.[105][106] Bláthy had suggested the use of closed cores.[111] Although George Westinghouse had bought Gaulard and Gibbs' patents in 1885. shell form. Westinghouse.[112] Stanley's first patented design was for induction coils with single cores of soft iron and adjustable gaps to regulate the emf present in the secondary winding (see image).[102] The ZBD patents included two other major interrelated innovations: one concerning the use of parallel connected.000 V) than the voltage of utilization loads (100 V initially preferred). Stanley and associates soon developed an easier to manufacture core. Prewound copper coils could then be slid into place. the world's first power station that used AC generators to power a parallel connected common electrical network.4 times more efficient than the open-core bipolar devices of Gaulard and Gibbs. with no intentional path through air (see Toroidal cores below). and the Ganz factory supplied electrical equipment for. and Déri had performed the experiments.400 to 2. it was granted in July 1887. shell form.[107] Transformers today are designed on the principles discovered by the three engineers. consisting of a stack of thin 'E‑shaped' iron plates.[101] In both designs.67:1. The new transformers were 3. Westinghouse applied for a patent for the new low-cost design in December 1886. requiring Westinghouse to pursue alternative designs on the same principles. Sketch used by Uppenborn to describe ZBD engineers' 1885 patents and earliest articles.wikipedia. the free encyclopedia http://en. closed-core transformers finally made it technically and economically feasible to provide electric power for lighting in homes. front.[107][114] The ZBD team consisted of Károly Zipernowsky. Ottó Bláthy and Miksa Déri Other early transformers 19 of 27 2/24/2014 8:04 PM . the magnetic flux linking the primary and secondary windings traveled almost entirely within the confines of the iron core. instead of series connected.[95] Core form.org/wiki/Transformer ratio 1. Zipernowsky had suggested the use of parallel shunt connections. Earliest specimens of ZBD-designed high-efficiency constant-potential transformers manufactured at the Ganz factory in 1885.[113] Shell form transformer. utilization loads.[109][110] In 1886. insulated by thin sheets of paper or other insulating material. [37] i. defines polarity as the 'designation of the relative instantaneous directions of the currents entering the primary terminals and leaving the secondary terminals during most of each half cycle'. ^ "The turn ratio of a transformer is the ratio of the number of turns in the high-voltage winding to that in the low-voltage winding". provides a measure of rate of magnetic flux in the core and hence of emf induced in the respective winding. ^ Transformer windings are usually wound around ferromagnetic cores but can also be air-core wound. on primary terminals and X1. or 120 & 360 Hz.Z2. j.. ^ The expression dΦ/dt. Russian-born engineer Mikhail Dolivo-Dobrovolsky developed the first three-phase transformer at the Allgemeine ElektricitätsGesellschaft ('General Electricity Company') in Germany.[116][117] See also Magnetization Inductor Polyphase system Load profile Magnetic core Geomagnetic storm Paraformer Rectiformer Switched-mode power supply Electronic symbol Stanley's 1886 design for adjustable gap open-core induction coils[97] Notes a. ^ A step-down transformer converts a high voltage to a lower voltage while a step-up transformer converts a low voltage to a higher voltage.[115] In 1891. applies to large transformers. The designated terminals H1. namely. (and Y1.. c. b. i. ^ Transformer polarity can also be identified by terminal markings H0. 20 of 27 2/24/2014 8:04 PM . (and Y1.e. dual-tuned resonant transformer for generating very high voltages at high frequency.. Z1 if available) indicate same instantaneous polarities for each winding as in the dot convention.H2. frequencies. ANS Requirements for Instrument Transformers. defined as the derivative of magnetic flux Φ with time t. by the 100 & 300 Hz. n for neutral of the wye winding.X2.H1. Nikola Tesla invented the Tesla coil. y for wye secondary winding. ^ Transformer hum's fundamental noise frequency is two times that of the power frequency as there is an extension and a contraction of core laminations for every cycle of the AC wave and a transformer's audible hum noise level is dominated by the fundamental noise frequency and its first triplen harmonic.Wikipedia.[6] common usage having evolved over time from 'turn ratio' to 'turns ratio'. derived from standards such as IEEE C57.13...org/wiki/Transformer In 1889. Dyn11 denoting D for delta primary winding. is known as the Dyn11 vector group configuration. and 11 for relative phase position on the clock by which the secondary winding leads the primary winding. an isolation transformer having 1:1 turns ratio with output voltage the same as input voltage. by far the most common commercial three-phase transformer. ^ While the above formal definition. Z1.Z3.80.[16] f. the delta-wye transformer. the word 'instantaneous' differentiating from say phasor current.Y2.[17] g.wikipedia. if windings are available) on secondary terminals.[27] h. 30° leading. Each letter prefix designates a different winding and each numeral designates a termination or tap on each winding.Transformer . d. ^ For example. ^ ANSI/IEEE C57. ^ A standardized open-circuit or unloaded transformer test called the Epstein frame can also be used for the characterization of magnetic properties of soft magnetic materials including especially electrical steels. e.X1. an air-cored.12. the free encyclopedia http://en. New York: McGraw-Hill. 300–320. pp.J. (2010). Ula. parlance for small general-purpose transformers to be referred to as 'power' transformers. ^ a b McLaren. 597. 20–21. 2–3.3 'The Ideal Transformer' " (http://books. G. ISBN 0-8493-1889-0. p. 20. E. (2008). 119–122. G. ^ Mack. ^ a b c d Say. P. ISBN 0-7506-1158-8. Analysis of Electric Circuits. A. Retrieved 13 April 2013. Power Transformer Principles and Applications.. William M. pp. Jr.7 'Transformer Testing' in Chapter 3 . ISBN 0-8018-4614-5. Taylor & Francis. §3. and so on. M. pp.5 'Transformers' & §10. "§2. "The World of Physics". ^ Knowlton. (2002). ^ Heathcote. 21.) (1949).). 18.google. 1880–1930 (http://books. [Thomas Nelson and Sons Ltd].au/~aupec/aupec00 /edwards00. McGraw-Hill. 9.pdf). p. ^ a b Winders. Javid.mcgraw-hill.google.com /Polarity%20on%20Transformers. ISBN 0-07-021291-0. Newnes.com/?id=g07Q9M4agp4C& pg=PA122&lpg=PA122& dq=westinghouse+%22universal+system%22). ^ Parker. Egon. 73. D. Retrieved May 19.).org/wiki/Transformer it is not uncommon in colloquial. I. pp. "Slide 13 Impedance Transformation in Lecture 4: Transformers". Jerry C. Lamar University (TSU system member). Shoemaker. (1984). Electrical Machines I: Basics. R. 552 7.com/downloads/products /0071467890/0071467890_ch15. The Lineman's and Cableman's Handbook (11th ed.google. J & P Transformer Book (12th ed. for distribution transformers to be referred to as 'power distribution' transformers. "§18.2 'Definition of Transformer Ratio' in Section 3 . Gleb V. Standard Handbook for Electrical Engineers (8th ed.). ^ "Connections .E. 8. Function. (2005). W.com/?id=fR1rNJhBbmcC& pg=PA72&lpg=PA72& dq=dot+convention+polarity+of+transformer#v=onep age& q=dot%20convention%20polarity%20of%20transfor mer&f=false) (4th ed. Elementary Electric Power and Machines. Saha. ^ Kothari. 3.).com/products /buyersguide/ct_sc. pp. 2007. ^ Tcheslavski. In Whitaker. Fig. pp. Mansour (1959).itee.Circuits with Magnetic Circuits" (http://books. p.google. CRC. ^ "Polarity Markings on Instrument Transformers" (http://www. The Electronics Handbook (2nd ed. James (2001). ^ a b Flanagan.. Alternating Current Machines (5th ed. 14. 12.uq. Networks of Power: Electrification in Western Society. Kay (2001). 16. 2. Baltimore: Johns Hopkins University Press. 17. 6–42. 15. ^ a b c d e Calvert. "Chapter 15 .ca/books/about /Analysis_of_electric_circuits. 1–2. §6-13. James E. [Stanley Thornes (Publishers) Ltd]. "Inside Transformers" (http://www. J. ^ Thomas P.gedigitalenergy. 15–1 to 15–22. K. S. Hughes (1993).edu.. 1998). 485 21 of 27 2/24/2014 8:04 PM .Wikipedia.htm). ELEN 3441 Fundamentals of Power Engineering. University of Denver. Webb. McGraw-Hill. Design. "§3. ^ a b Say.Polarity" (http://www.pdf).html?id=V4FrAAAA MAAJ&redir_esc=y). John J.). (1993). McGraw-Hill. M.du. or even trade. ^ Edwards. "Power Flow in Transformers Via the Poynting Vector" (http://www. Operation.1.5. RWTH Aachen University Institute of Electrical Machines.pdf).cromptonusa. References 1. the free encyclopedia http://en. ^ Brenner.Transformers". p. 4. Nagrath. ISBN 0-470-27451-4. pp.Distribution Transformers" (http://books. ^ Knowlton. 5.Transformer .Transformers (http://books. 6.). ^ a b Jim Breithaupt (2000). 27. pp.. 172. Queensland University of Technology.pdf). pp. 300–320.ca /books?id=FdSQSAC3_EwC&pg=PA1017& lpg=PA1017& dq=transformer+polarity+dot+convention& source=bl&ots=V_ULeEEk6t& sig=SFYhwdztWIVTr1yK6hQc-LOKL44&hl=en& sa=X&ei=37E_Uf-DDsipqgHtpIHwBA& ved=0CEAQ6AEwAw#v=onepage& q=transformer%20polarity%20dot%20convention& f=false). Retrieved 13 April 2013. 68–74.. ISBN 978-0-07-069967-0. Thomas (2006). 19. ISBN 0071467890. ^ Hameyer. Martin (Nov 3. Handbook of Transformer Design & Applications (2nd ed. (Ed. "New Understanding: Physics for Advanced Level (4th Edition)". T. AUPEC 2000 Proceedings.edu/~jcalvert /tech/transfor.1 'Symbols and Polarity of Mutual Inductance' in Chapter 18 .P. Halsted Press. 11. 1017.). pp. 589–590. (1984). ISBN 0-13-257601-5. Tata McGraw-Hill.wikipedia. 13. ^ a b John Avison (1989). (2000). p. 10. p. pp. T. Function.pdf). pp. ^ Kulkarni.1109%2FTPAS. Engineering and Design . Retrieved Mar 27. pp. "Transformers: Basics. 41-42 35. . (2001). ISBN 0-08-030573-3. Operation". Robert M. Retrieved June 21. Electrical Apparatus.. Dept. Frederick E. 585-586 24. Transformer and Inductor Design Handbook.org/researchreport/a016). ^ a b Allan. D.com/literature/drytrans /10transformernoise. pp.Power Transformers" (http://140. 37. IEEE Transactions on Power Apparatus and Systems.blnz.J.shtml). S...). B. Oxford: Pergamon Press.. "Why We Must Be Concerned With Transformers" (http://www. Retrieved May 21. 2012. 45. pp.1109/TPAS.. ^ Riemersma. ^ Haymeyer.pdf). Roach. (2002). 23. Fairmont Press. ^ a b Say. (May 24. "Power Transformer Design" (http://focus. ^ a b Knowlton. J. p. American Council for an EnergyEfficient Economy.pdf).com/news/2008/04/23 /must_concerned_with_transformers_9639. Nadel.federalpacific.316682 (http://dx. 12.org. . RWTH Aachen University Institute of Electrical Machines. Practical Transformer Handbook.1109%2FTPAS. Kay (2001).Hydroelectric Power Plants Electrical Design.1109/TPAS.php?option=com_content& view=article&id=534%3Asteinmetzs-formulafor-magnetic-hysteresis&catid=65%3Amagneticcircuits&Itemid=44). 4. (1981). New York: McGraw-Hill. Switchmode Power Supply Handbook. 15. p.S. ISBN 0-88173-311-3. 39. Introduction to Electrical Machines. Electrical Machines and Their Applications. 562 42. 1. ^ a b c d McLyman. 29–31. (1955). 43. Keith (1999). Aerospaceweb. (http://webstore. ISBN 0-7506-3992-X. p. 1991). p.php?requester=gs&collection=TRD& recid=0043264EA& q=superconducting+transformer&uid=790516502& setcookie=yes). Retrieved 30 January 2013.aerospaceweb. (June 1963).S. 29-31 49. (1999).ieee.1963. Litz. ^ Kubo. 3. ^ Gururaj. 47–49. 34. 44.I.1963.Part 2: Methods of Measurement of the Magnetic Properties .access. 48. 39.ch/webstore/webstore.html).org /xpl/freeabs_all. 30. (1984).67) & 323 (§4.Transformer . ^ Pansini. Murphy. Retrieved 7 February 2013. ^ a b Billings. 38. CRC. 4-1. ^ a b Nailen. 2007. ^ "400 Hz Electrical Systems" (http://www. Lloyd (2001).com/index. 29.8.jsp?isnumber=4072786& arnumber=4072800&count=25&index=12).ieee. ^ Gottlieb.aceee. 46. 142-143 27. R.iec.1049/pe:19910004 (http://dx.com/lit/ml/slup126 /slup126. 40. A. 49 (§2.org /10. "Power Transformers – The Second Century" (http://ieeexplore.wikipedia. H. pp. Sachs. of the Interior.291359 (http://dx. Maintenance. S. 2004). Electrical Transformers and Power Equipment.. Barton. 32.1981. Power Engineering Journal 5 (1): 5–14. ^ Hydroelectric Research and Technical Services Group. pp.doi.291359). Chap. 2009. 26. ^ Knowlton. A. CRC. J. Opportunities for New Appliance and Equipment Efficiency Standards (http://www. ^ a b "Understanding Transformer Noise" (http://www.google. ^ EE-Reviewonline. McGraw-Hill.194.316682).ti. Eckels. doi:10. the free encyclopedia http://en.doi. 39. J. ISBN 0-8247-5393-3.org/wiki/Transformer 22.org/10. ^ Hindmarsh.com. ^ IEC Std 60404-2 Magnetic Materials . p. Richard (May 2005). V. Magnetics Design Handbook. p. Bureau of Reclamation. 31.. p. "Steinmetz's Formula for Magnetic Hysteresis" (http://www. 36–37.76. "Electrical Machines I: Basics. and Diagnostics" (http://permanent. P. Fig. et al. Colonel Wm. 47.279) 36. ISBN 0-07-006719-8. ^ a b EM 1110-2-3006 (1994). (Jan. Electronic and Radio Engineering (4th ed. H. ^ a b c Daniels. pp. U. Boca Raton: CRC Press. U.csa. ISBN 90-5699-703-3.com/partners /viewrecord.jsp?arnumber=61984). 41.com/?id=Lzjs0LNHhVYC).org /10. pp.gov /lps113746/Trnsfrmr. Design. 33.nsf /mysearchajax?Openform&key=60404-2&sorting=& start=1&onglet=1) 28.doi.eereviewonline.1981.129/publications /eng-manuals/em1110-2-3006/c-4. T. doi:10.org/question/electronics /q0219. 23.org /xpl/freeabs_all. Army Corps of Engineers. M. PAS-100 (7): 3398. "Application of Superconducting Technology to Power Transformers" (http://md1. 22 of 27 2/24/2014 8:04 PM .pdf). ^ Terman. Anthony J. S. doi:10.gpo. Irving (1998).. FP. "Chapter 4 . "Natural Frequencies of 3-Phase Transformer Windings" (http://ieeexplore. Newnes. D. 9–14. 10–11.1049%2Fpe%3A19910004). ^ Hindmarsh. Texas Instruments. Transformer Design Principles: With Applications to Core-Form Power Transformers (http://books. ^ a b Dixon. Transformer Engineering: Design and Practice. Khaparde. (2004). ^ a b c Del Vecchio.Wikipedia. ^ Knowlton. pp. ^ a b c Heathcote. IEEE Transactions on Power Apparatus and Systems 82 (66): 318–329. 25. ISBN 0-8247-5653-3. 1016/S0304-8853(00)00126-8 (http://dx. 56.ti.vias. EC&M.2. §2. "Estimation of Insulation Life Based on a Dual Temperature Aging Model" (http://www.prweb. "Analysis of Transformer Failures" (http://www.com. William H. "Permissible Temperatures for Insulation" (http://www.Wikipedia.ie/Archive1 /Files_Misc/REP009THERMIEFinalreport.org/wiki/Transformer 50. Digby. Lee (2004). 2000). p.). "§3. P. ^ "ASTDR ToxFAQs for Polychlorinated Biphenyls" (http://www. Scott H. 2 . H. ^ Prevost.cdc.gepower. Retrieved 29 January 2013. 51.com/lit/ml /slup197/slup197. ^ Hartley. ISBN 0-8247-4875-1. Modern Power Station Practice. p. "PSERC Pub.com/content /basics-large-dry-type-transformers). 36th Annual Conference of the International Association of Engineering Insurers. 68. Eddy Current Losses in Transformer Windings (http://focus. ^ a b c Central Electricity Generating Board (1982). CRC Press. ^ Lee. Reigh. 67.gecompany. ^ a b Willis.edu/documents/publications /reports/2011_reports/Sen_T25_Final_Report_Feb_2011. 1 54. 58.1016%2FS0273-1177%2897%2901096-X). D.). (1997).. (2011). R. The Locomotive. 2-3 23 of 27 2/24/2014 8:04 PM . 403. William H. (~2011). 7 (fig. 3 . 32 63.cindmz. Retrieved Mar 30. The Electric Power Engineering Handbook (Online ed.vias.atsdr.8. ^ a b Sim. Retrieved 11 January 2013.html). 62. "An Analysis of Transformer Failures.pdf). Retrieved May 22.Equipment Types" (http://www. Harlow (ed.pdf).Transformer . Reuben. et al. H. Retrieved 30 January 2013. Shattuck. 65.com/TheLocomotive /AnAnalysisOfTransformerFailuresPart1. In James H. 3 p.wikipedia. Weidmann. Advances in Space Research 22: 17–27.org/kimberlyee /ee_14_11. 60. ^ Pansini. E. L. ^ Boteler. 2001.).pserc. ^ http://www. 2012. ^ Walling. CRC Press. p. p.aspx?id=191). pp. J.1 Power Transformers in Chap. In James H.).htm 70. "Present Status of Amorphous Soft Magnetic Alloys".gov/toxfaqs/tf.uncp. The Scope for Energy Saving in the EU Through the Use of Energy-Efficient Electricity Distribution Transformers (http://www. (2004).7 & §2.6. 64.edu. Thomas A. 57.bplglobal. "Distribution Transformer Thermal Behaviour and Aging in Local-Delivery Distribution Systems" (http://www.seai. 53. Paper 0720. p.aspx). Pergamon Press. H. Bruce (May 2007). Grigsby (Series ed. pp. CRC Press.weidmann-solutions. Grigsby (Series ed. Jim. et al (2001). (1998). 2007. Arizona State University. Institution of Engineering and Technology. ISBN 0-8493-8578-4.K.E.pe/newfacultades /ingenieriasarqui/newelectrica/phocadownload /descargas /E%20BOOK%20Electric%20Power%20Transforme r%20Engineering. doi:10.com /prod_serv/plants_td/en/downloads /cired_dist_transformer.pe/newfacultades /ingenieriasarqui/newelectrica/phocadownload /descargas /E%20BOOK%20Electric%20Power%20Transforme r%20Engineering. Retrieved 11 February 2013..pdf).1016/S0273-1177(97)01096-X (http://dx. pp. 71. doi:10. Retrieved June 10. "The Basics of Large Dry-Type Transformers" (http://ecmweb. ^ a b Tillman. Keith (2007). ^ Kimberly.pdf).doi.1. p. Chap. ^ a b Kulkarni.1016%2FS0304-8853%2800%2900126-8). Ryusuke (June 2. L.com/releases/2013/6 /prweb10836945. "§2.org /10. 52. ^ Hartley. R2–1–to–R2–10. 720–723 59. L.wisc. Pirjola. 19th International Conference on Electricity Distribution. Retrieved 30 January 2013. ^ Hasegawa. ^ Heathcote. Retrieved 12 February 2013. 61. 1. (2004). 6).net /eng/knowledge-center/download. Part 1 – 1988 through 1997" (http://www. Robert F. Jr.org/eltransformers /lee_electronic_transformers_07b_22. Electronic Transformers and Circuits.).1. 55.doi. H.4 Load and Thermal Performance in Chap. §3.org /10. ^ Lane. ^ Sen. 11-02 Transformer Overloading and Assessment of Loss-of-Life for Liquid-Filled Transformers" (http://www. Journal of Magnetism and Magnetic Materials. ^ a b De Keulenaer.pdf).html).pdf). The Electric Power Engineering Handbook (Online ed. the free encyclopedia http://en. et al. H.Ancillary Topics" (http://www. Texas Instrument. "The Effects of Geomagnetic Disturbances On Electrical Systems at the Earth's Surface".).asp?id=140& tid=26). G. L. ^ Dixon. ISBN 0-8493-8578-4.4. "Air-Core Transformers" (http://www. Nevanlinna.1.hsb. 69.H. 2007. L. 215-216: 240–245. Power Distribution Planning Reference Book.pdf). (Nov 2006). (2003). Harlow (ed.uncp.. 66. Power Systems Engineering Research Center.cn /huiyi/Seminar%202006%20New%20Mexico /2006prevostpaperyes.edu. ^ McLyman. Distinguished Members Gallery. 7th Series" (http://archive.1109/PAPCON. Retrieved Feb 23. 9–12. ISBN 0-85296-775-6. §12-341. Randy. p.609815).au/Assets/What-We-Do/Assets /Jemena-Electricity-Network/Planning /Western%20metropolitan%20Melbourne%20transmi ssion%20connection%20and%20subtransmission%2 0capacity.ieee. 2007.0008 (http://dx.gov. McGraw-Hill.afbini.nas. p. Michael (1834). C.ec. 416–417. ^ IEEE PES TC (Fall 2011). N. & Co. doi:10. ^ Chow. (2012). London and New York: Longmans.pdf).pdf). ^ Faraday. Schneider.org/xpl/login. Philosophical Transactions of the Royal Society 124: 77–122. "Experimental Researches on Electricity. McGraw Hill. slide 6.org/details/philtrans08694360). ISBN 0-07-02974-x Check |isbn= value (help). 12-95. 91.pdf). Peacock. pp.609815 (http://dx. 87.com/files /T141+IEEE+Spectrum+XFR. (Jul 1997).ieee. ISBN 9977 and 178-1-907053-20-7 Check |isbn= value (help).1109/6.uk/sots-contaminants. 90.us/assets /consultingengineer/appguidedocs /section6_0307. 10–38 through 10–40. ^ Lawhead.jsp%3F arnumber%3D854186).com.S. 33–40. fig.pdf#page=11). 11. Ian. Tourangeau. 2012.org/wiki/Transformer 72. Retrieved 18 January 2013. Retrieved 27 January 2013. Wayne (Eds. Sudbury.org /10.schneider-electric. ISBN 0-7637-3827-1. ^ Poyser. IEEE PES Transformer Committee. 8–10. Elisa et al (Jan/Feb 2009).superpower-inc. "Three Phase Transformer Winding Configurations and Differential Relay Compensation" (http://basler.wikipedia.org%2Fxpls%2Fabs_all. 66–67 76. p. ^ Mehta. Electricity Today. pp. Donald (Ed. p. BIll.doi. "Section 6 Grounding Systems" (http://static. (2006). ^ Figueroa. ^ a b Beltz.. Horak. E. ^ AEMO et al. pp. pp. Retrieved Nov 30. S. Retrieved Feb 28. 1 88. 2009.jsp?tp=& arnumber=854186&url=http%3A%2F %2Fieeexplore. 75.google. National Academy of Sciences.org/10.854186 (http://dx. 2012. Government of Canada: Environment Canada Department.2000.854186).Transformer . Retrieved Nov 7. Introduction to Electromagnetic Theory: A Modern Perspective (http://books. pp.1834. ^ Ryan. Aversa.1109%2F6. 77. Arthur William (1892). doi:10.pdf). 74. ^ McDonald.Wikipedia. "Application Considerations for High Resistance Ground Retrofits in Pulp and Paper Mills" (http://ieeexplore. ^ AFBI (2011). State of the Seas Report. 83. R. Standard Handbook for Electrical Engineers (11th ed. 549-550 84. 80. Retrieved Aug 6.html). Question and Answer Guide Concerning Polychlorinated Biphenyls (https://www. 78. ^ a b c d e Knowlton. John (2006). H. Hamilton. p. Industrial Power Systems Handbook. "Discussion of Class I & II Terminology" (http://grouper. 171.1098%2Frstl.org/10. 71. ^ Pansini. High Voltage Engineering and Testing. PCBs. Magnetism and Electricity: A Manual for Students in Advanced Classes (http://books.ca /Publications/C7F1F416-C632-4D11BDD4-C823690C2651 /PCBsQuestionandAnswerGuideConcerningPolychlo rinatedBiphenyls. Contaminants" (http://www. 82. the free encyclopedia http://en.1109%2FPAPCON. Hugh M.gc. ^ Knowlton. 248.. (2001).edu/history /members/henry. doi:10. J. 1085 86. §6-7.) (1955). p. Georgia Tech 60th Protective Relay Conference. Walker. ^ "Joseph Henry" (http://www. ISBN 0-662-14595-X.google. "Joint Consultation Paper Western Metropolitan Melbourne Transmission Connection and Subtransmission Capacity" (http://jemena.com/downloads /3phXfmrs.com /books?id=dpnpMhw1zo8C&pg=PA171& dq=isbn%3D0763738271+%22TimeDependent+Magnetic+fields+and+Faraday%27s+La w+of+Induction%22&cd=1#v=onepage& q=&f=false).. p. 349–364. Tai L. Pulp and Paper Industry Technical Conference.1834. fig.2000. ^ a b c Beeman. 89.org/groups /transformers/subcommittees/standardsc/F11-Class1Class2Discussion. ^ Heathcote.doi. Donald G. 79. 73.).0008). Mass. 285. M.doi. Robert. "9..1098/rstl. 24 of 27 2/24/2014 8:04 PM . Agri-Food and Biosciences Institute & Northern Ireland Environment Agency. Beatty. Retrieved 14 November 2012. 81.pdf). Retrieved and archived (http://www. (1986).pdf). IEEE Spectrum 34 (7): 43–49.P. 2006.com/et/issue0109/transformer_field_dryout.pdf).webcitation. ^ Fink. 85. Green. Vilcheck. Institution Electrical Engineers. pp.org/6DQTNt5E7) 4 January 2013. "Transforming Transformers [Superconducting windings]" (http://www.: Jones and Bartlett Publishers.com /books?id=JzBAAAAAYAAJ&pg=PA285). Larry. "Low Frequency Heating Field Dry-Out of a 750 MVA 500 kV Auto Transformer" (http://www.electricitytoday. William (2000).ieee. ^ Brown.) (1978). pp. pp. Transformer - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Transformer 92. ^ a b "Stanley Transformer" (http://www.magnet.fsu.edu/education/tutorials /museum/stanleytransformer.html). Los Alamos National Laboratory; University of Florida. Retrieved Jan 9, 2009. 93. ^ De Fonveille, W. (Jan 22, 1880). "Gas and Electricity in Paris" (http://books.google.com /?id=ksa-S7C8dT8C&pg=RA2-PA283). Nature 21 (534): 283. Bibcode:1880Natur..21..282D (http://adsabs.harvard.edu /abs/1880Natur..21..282D). doi:10.1038/021282b0 (http://dx.doi.org/10.1038%2F021282b0). Retrieved Jan 9, 2009. 94. ^ Hughes, Thomas P. (1993). Networks of Power: Electrification in Western Society, 1880-1930 (http://books.google.com/?id=g07Q9M4agp4C& pg=PA96& dq=Networks+of+Power:+Electrification+in+Western +Society,+1880-1930+ganz#v=onepage&q=). Baltimore: The Johns Hopkins University Press. p. 96. ISBN 0-8018-2873-2. Retrieved Sep 9, 2009. 95. ^ a b c d e Uppenborn, F. J. (1889). History of the Transformer (http://www.archive.org/details /historyoftransfo00upperich). London: E. & F. N. Spon. pp. 35–41. 96. ^ a b Coltman, J. W. (Jan. 1988). "The Transformer". Scientific American. pp. 86–95. OSTI 6851152 (http://www.osti.gov/energycitations /product.biblio.jsp?osti_id=6851152). 97. ^ a b Stanley, William, Jr.. "Induction Coil" (http://www.google.com/patents?vid=349611). U.S. Patent 349 311, issued Sept. 21, 1886. Retrieved July 13, 2009. 98. ^ Hughes, p. 95 99. ^ Károly, Simonyi. "The Faraday Law With a Magnetic Ohm's Law" (http://www.termeszetvilaga.hu/kulonsz /k011/46.html). Természet Világa. Retrieved Mar 1, 2012. 100. ^ Lucas, J.R. "Historical Development of the Transformer" (http://www.elect.mrt.ac.lk /Transformer_history_2000.pdf). IEE Sri Lanka Centre. Retrieved Mar 1, 2012. 101. ^ a b Halacsy, A. A.; Von Fuchs, G. H. (April 1961). "Transformer Invented 75 Years Ago" (http://ieeexplore.ieee.org/search /freesearchresult.jsp?newsearch=true& queryText=10.1109%2FAIEEPAS.1961.4500994& x=29&y=16). IEEE Transactions of the American Institute of Electrical Engineers 80 (3): 121–125. doi:10.1109/AIEEPAS.1961.4500994 (http://dx.doi.org /10.1109%2FAIEEPAS.1961.4500994). Retrieved Feb 29, 2012. 102. ^ Jeszenszky, Sándor. "Electrostatics and Electrodynamics at Pest University in the Mid-19th Century" (http://ppp.unipv.it/Collana/Pages/Libri /Saggi /Volta%20and%20the%20History%20of%20Electrici ty/V%26H%20Sect2/V%26H%20175-182.pdf). University of Pavia. Retrieved Mar 3, 2012. 103. ^ "Hungarian Inventors and Their Inventions" (http://www.institutoideal.org /conteudo_eng.php?&sys=biblioteca_eng& arquivo=1&artigo=94&ano=2008). Institute for Developing Alternative Energy in Latin America. Retrieved Mar 3, 2012. 104. ^ "Bláthy, Ottó Titusz" (http://www.omikk.bme.hu /archivum/angol/htm/blathy_o.htm). Budapest University of Technology and Economics, National Technical Information Centre and Library. Retrieved Feb 29, 2012. 105. ^ a b "Bláthy, Ottó Titusz (1860–1939)" (http://www.hpo.hu/English/feltalalok/blathy.html). Hungarian Patent Office. Retrieved Jan 29, 2004. 106. ^ Zipernowsky, K.; Déri, M.; Bláthy, O.T. "Induction Coil" (http://www.freepatentsonline.com /0352105.pdf). U.S. Patent 352 105, issued Nov. 2, 1886. Retrieved July 8, 2009. 107. ^ a b Smil, Vaclav (2005). Creating the Twentieth Century: Technical Innovations of 1867—1914 and Their Lasting Impact (http://books.google.com /?id=w3Mh7qQRM-IC&pg=PA71&lpg=PA71& dq=ZBD+transformer). Oxford: Oxford University Press. p. 71. ISBN 9780198037743. 108. ^ Nagy, Árpád Zoltán (Oct. 11, 1996). "Lecture to Mark the 100th Anniversary of the Discovery of the Electron in 1897 (preliminary text)" (http://www.kfki.hu/~aznagy/lecture/lecture.htm). Budapest. Retrieved July 9, 2009. 109. ^ Oxford English Dictionary (2nd ed.). Oxford University Press. 1989. 110. ^ Hospitalier, Édouard; as translated by Julius Maier (1882). The Modern Applications of Electricity (http://books.google.com /books?id=qt8JAAAAIAAJ). New York: D. Appleton & Co. p. 103. 111. ^ "Ottó Bláthy, Miksa Déri, Károly Zipernowsky" (http://www.iec.ch/cgi-bin /tl_to_htm.pl?section=technology&item=144). IEC Techline. Retrieved Apr 16, 2010. 112. ^ Skrabec, Quentin R. (2007). George Westinghouse: Gentle Genius (http://books.google.com/?id=C3GYdiFM41oC& pg=PA102). Algora Publishing. p. 102. ISBN 978-0-87586-508-9. 25 of 27 2/24/2014 8:04 PM Transformer - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Transformer 113. ^ a b Coltman, J.W.; (Jan–Feb 2002). "The Transformer [Historical Overview]" (http://ieeexplore.ieee.org /xpls/abs_all.jsp?arnumber=974352). Industry Applications Magazine, IEEE 8 (1): 8–15. doi:10.1109/2943.974352 (http://dx.doi.org /10.1109%2F2943.974352). Retrieved Feb 29, 2012. 114. ^ Westinghouse, George, Jr.. "Electrical Converter" (http://www.google.com/patents /about?id=NmRDAAAAEBAJ&dq=366362). U.S. Patent 366 362, issued July 12, 1887. 115. ^ Neidhöfer, Gerhard; in collaboration with VDE "History of Electrical Engineering" Committee (2008). Michael von Dolivo-Dobrowolsky and Three-Phase: The Beginnings of Modern Drive Technology and Power Supply (http://d-nb.info /990964361) (in German) (2 ed.). Berlin: VDE-Verl. ISBN 978-3-8007-3115-2. 116. ^ Uth, Robert (Dec 12, 2000). "Tesla Coil" (http://www.pbs.org/tesla/ins/lab_tescoil.html). Tesla: Master of Lightning. PBS.org. Retrieved May 20, 2008. 117. ^ Tesla, Nikola. "System of Electrical Lighting" (http://patft.uspto.gov/netacgi /nph-Parser?Sect1=PTO1&Sect2=HITOFF& d=PALL& p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm& r=1&f=G&l=50&s1=0454622.PN.& OS=PN/0454622&RS=PN/0454622). U.S. Patent 454 622, issued June 23, 1891. Bibliography Central Electricity Generating Board (1982). Modern Power Station Practice. Pergamon. ISBN 0-08-016436-6. Daniels, A.R. (1985). Introduction to Electrical Machines. Macmillan. ISBN 0-333-19627-9. Flanagan, William M. (1993). Handbook of Transformer Design & Applications (2nd ed.). McGraw-Hill. ISBN 0-07-021291-0. Gottlieb, Irving (1998). Practical Transformer Handbook: for Electronics, Radio and Communications Engineers (http://books.google.com/?id=HFFo2TNIu88C&printsec=frontcover#v=onepage&q&f=false). Elsevier. ISBN 0-7506-3992-X. Hammond, John Winthrop (1941). Men and Volts: The Story of General Electric (http://archive.org /details/menandvoltsstory00hammrich). J.B. Lippincott Company. pp. see esp. 106–107, 178, 238. Harlow, James (2004). Electric Power Transformer Engineering (http://books.google.com /?id=THO9U9f2m9EC&printsec=frontcover#v=onepage&q&f=false). CRC Press. ISBN 0-8493-1704-5. Heathcote, Martin (1998). J & P Transformer Book (http://books.google.com/?id=paPKsOXn5FMC& printsec=frontcover#v=onepage&q&f=false) (12th ed.). Newnes. ISBN 0-7506-1158-8. Hindmarsh, John (1977). Electrical Machines and Their Applications (4th ed.). Exeter: Pergammon. ISBN 0-08-030573-3. Kulkarni, S.V.; Khaparde, S.A. (2004). Transformer Engineering: Design and Practice (http://books.google.com/?id=qy4QT0BlV0MC&printsec=frontcover#v=onepage&q&f=false). CRC Press. ISBN 0-8247-5653-3. McLaren, Peter (1984). Elementary Electric Power and Machines. Ellis Horwood. ISBN 0-470-20057-X. McLyman, Colonel William (2004). Transformer and Inductor Design Handbook (http://books.google.com/?id=s_iMztIS8y4C). CRC. ISBN 0-8247-5393-3. Pansini, Anthony (1999). Electrical Transformers and Power Equipment (http://books.google.com /?id=f77zWwA3oS4C). CRC Press. ISBN 0-88173-311-3. Ryan, H.M. (2004). High Voltage Engineering and Testing (http://books.google.com /?id=Jg1xA65n56oC&pg=PA7&dq=High+Voltage+Engineering+and+Testing#v=onepage& q=High%20Voltage%20Engineering%20and%20Testing&f=false). CRC Press. ISBN 0-85296-775-6. Say, M.G. (1983). Alternating Current Machines (5th ed.). London: Pitman. ISBN 0-273-01969-4. Winders, Jr., John J. (2002). Power Transformer Principles and Applications (http://books.google.com /?id=Sf1ppwGI6uYC&printsec=frontcover#v=onepage&q&f=false). CRC. ISBN 0-8247-0766-4. 26 of 27 2/24/2014 8:04 PM Transformer - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Transformer External links Inside Transformers, composed by J. B. Calvert, from Denver University (http://www.du.edu/~jcalvert /tech/transfor.htm) Substation and Transmission (http://www.dmoz.org/Business/Electronics_and_Electrical /Substation_and_Transmission/) on the Open Directory Project Introduction to Current Transformers (http://www.elkor.net/pdfs/AN0305-Current_Transformers.pdf) Transformer (Interactive Java applet) (http://www.phy.hk/wiki/englishhtm/Transformer.htm), 'Physics is fun' by Chui-king Ng HD video tutorial on transformers (http://www.afrotechmods.com/videos/transformer_tutorial.htm) Three-phase transformer circuits (http://www.allaboutcircuits.com/vol_2/chpt_10/6.html) from All About Circuits Bibliography of Transformer Books (http://www.transformerscommittee.org/info/Bibliographybooks.pdf) by P.M. Balma, from IEEE Transformer Committee Einschalten des Transformators. German Wikipedia article about transformer inrush current at switch on (in German). Retrieved from "http://en.wikipedia.org/w/index.php?title=Transformer&oldid=596900354" Categories: Electrical power conversion Hungarian inventions Russian inventions Transformers (electrical) This page was last modified on 24 February 2014 at 11:30. Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. 27 of 27 2/24/2014 8:04 PM Understanding Current Transformers – Part II Characteristics - Common S... http://blog.protecequip.com/blog/common-sense-testing/understanding-cur... HOME CATEGORIES CONTRIBUTORS CONNECT Understanding Current Transformers – Part II Characteristics Posted by Common Sense Testing on Thursday, October 27, 2011 When looking at the accuracy of a CT a number of factors need to be taken into consideration. These factors will include: • • • • • • • Burden Burden class/saturation class Rating factor Load External electromagnetic fields Temperature and physical conditions, and The selected tap The IEC 60044-1 standard sets out various accuracy classes. The classes are 0.1, 0.2s, 0.2, 0.5, 0.5s, 1 and 3. The class designation is an approximate measure of the CT’s accuracy. For an example; the ratio error of a Class 1 CT is 1% at rated current. The ratio error of Class 0.5 CT is 0.5% or less. Each class also has an allowable maximum phase error for specified load impedance. Current transformers used for protective relays will have accuracy requirements at overload currents in excess of the normal rating to ensure accurate performance of relays during system faults. The load, or burden, in a CT metering circuit is the impedance presented to its secondary winding. This impedance will be largely resistive. Typical burden ratings for IEC CTs are 1.5 VA, 3 VA, 5 VA, 10 VA, 15 VA, 20 VA, 30 VA, 45 VA and 60 VA. ANSI/IEEE burden ratings are B-0.1, B-0.2, B-0.5, B-1.0, B-2.0, and B-4.0. This means a CT with a burden rating of B-0.2 can tolerate up to 0.2 ohms of impedance in the metering circuit before its output current is no longer a fixed ratio of the primary current. Switch-blocks, meters and intermediate conductors will all contribute to the burden of a current measurement circuit. The conductor between the meter and the CT will typically be the source of excess burden. The knee-point of a CT is the magnitude of the secondary voltage after which the output current ceases to follow linearly the input current. Or, in other words, the one-to-one relationship between input and output is no longer within declared accuracy. When testing, a voltage is applied across the secondary terminals and magnetizing current will increase in proportion to the applied voltage up until the knee point. The knee-point is defined as the point at which an increase of applied voltage of 10% results in an increase in magnetizing current of 50%. RECENT ENTRIES • Megger DLRO200-115 Designed for Use in the Workshop, Production Floor, or in the Field • Amprobe DM-III Power Quality Analyzer - Versatile and Essential in Diagnosing Electrical Issues • Fluke 1735 Three Phase Power Logger for Easy Energy Studies • Rent the Doble TDR9100 Circuit Breaker Test System from Protec Today • Assure the Health of Circuit Breakers with the Square D by Schneider S33595 • Dranetz PX5 Integrates Advanced Function-Set for Quality Power Monitoring • Conduct Insulation Tests and Measure Winding Resistance with the Vanguard EZCT-2000B • Megger MIT1025 Designed for Insulation Testing at its Best POPULAR CATEGORIES Figure 1: CT Knee-point The knee-point voltage is less applicable for metering CTs since their accuracy is generally much tighter and constrained within a very small bandwidth of the current transformer rating. Knee-point, however, is very important to protection CTs since they are exposed to currents of 20 to 30 times rated current during faults. Protec Equipment Resources offers a vast inventory of microprocessor-based current transformer test set from Vanguard Instruments. The Vanguard EZCT series of CT test sets are designed specifically for CT testing and will greatly increase productivity and save time during the commissioning and maintenance testing. These sets will perform CT excitation, current-ratio, polarity, and phase angle tests. Depending on model selected, insulation resistance and winding resistance of the CT secondary windings plus secondary burden can be measured. 4 2 0 0 Like 2 • Battery Testing • Breaker Testing • Cable Testing • Earth Testing • Expert Advice • Financial Benefits of Renting • Insulation Testing << Previous Post Comments for Understanding Current Transformers – Part II Characteristics Name: lee Time: Thursday, August 2, 2012 this is great. by much can you overload a metering CT and still operate within its accuracy? Leave a comment Next Post >> • Power Analysis • Protec Webinars • Relay Testing • Resistance Testing 1 of 2 2/23/2014 3:15 PM Understanding Current Transformers – Part II Characteristics - Common S... http://blog.protecequip.com/blog/common-sense-testing/understanding-cur... Name • Testing and Safety • Testing Tips and Tricks • Transformer Testing Email Your comment (No HTML) Type the text from the image below Protec Equipment Resources Inc., 1517 W N Carrier Pkwy, Suite 116, Grand Prairie, Texas 75050 © 2014 Protec Equipment Resources HOME CATEGORIES CONTRIBUTORS CONNECT RENTAL AGREEMENT 2 of 2 2/23/2014 3:15 PM no more bang for the buck. In other words. the secondary coils are saturated. wer Rate Terms Privacy RSS Adeel answered 3 months ago 10 % increase in voltage gives you 50 % increase in excitation current is called knee point voltage.7 degrees? the knee point is where the secondary (back) EMF equals the primary. You might recall that this curve is very much similar to the B-H curve used for the selection of Bmax for the design of mains transformers.com/question/index?qid=20080211061641AA90BJr Answers Home All Categories Science & Mathematics Arts & Humanities Beauty & Style Business & Finance Cars & Transportation Computers & Internet Consumer Electronics Dining Out Education & Reference More International About Follow Watchlist Science & Mathematics > Engineering > Reference Question Next Ask a Question What is Knee Point Voltage of a Current Transformer? What is its significance? deepak_8584 asked 6 years ago Answer last updated 3 months ago Related Questions What is knee point voltage in current transformer? Formula for knee point voltage calculation of current transformer? What is knee point of current and voltage transformers? How to get more Current. To measure this first demagnetise the CT and apply voltage gradually from secondary keeping primary winding open circuited.answers. Knee-voltage is the maximum secondary voltage that the CT will provide to a standard burden without saturating the transformer.com/techpprs Asker's Rating & Comment thankx for information Rate Discover Questions 10 points! Please Help With Transfer Function? Could Someone Help Me With an Engineering Data and Analysis Problem? How to wire a light switch to a speaker? Other Answers (2) drwer2 answered 6 years ago Plot the current vs voltage Oldest How much heat is required to raise the temperature of 789g of liquid ammonia from 25 degrees c to 82. Source: www. The web site quoted below has an excellent write-up on the topic under discussion. Rate 1 of 2 2/23/2014 3:02 PM .selinc. http://in.What is Knee Point Voltage of a Current Transformer? What is its signific. The secondary excitation voltage corresponding to the tangent to the curve gives the knee-voltage of the CT... while doing this above phenomeneo will be obsesrved. Need a low Voltage High Current Transformer? What is the main different between the Voltage transformer and the current transformer? Best Answer eematters answered 6 years ago A plot of secondary excitation voltage (Y-axis) vs secondary excitation current ( X-axis) would show a saturation point at the maximum permeability of the core material.yahoo. com/question/index?qid=20080211061641AA90BJr 2 of 2 2/23/2014 3:02 PM . http://in.answers...yahoo.What is Knee Point Voltage of a Current Transformer? What is its signific. yahoo. In other words. http://in... The web site quoted below has an excellent write-up on the topic under discussion.answers.selinc. Need a low Voltage High Current Transformer? What is the main different between the Voltage transformer and the current transformer? Best Answer eematters answered 6 years ago A plot of secondary excitation voltage (Y-axis) vs secondary excitation current ( X-axis) would show a saturation point at the maximum permeability of the core material. Knee-voltage is the maximum secondary voltage that the CT will provide to a standard burden without saturating the transformer.com/techpprs Asker's Rating & Comment thankx for information Rate Discover Questions 10 points! Please Help With Transfer Function? Could Someone Help Me With an Engineering Data and Analysis Problem? How to wire a light switch to a speaker? Other Answers (2) drwer2 answered 6 years ago Plot the current vs voltage Oldest How much heat is required to raise the temperature of 789g of liquid ammonia from 25 degrees c to 82. wer Rate Terms Privacy RSS Adeel answered 3 months ago 10 % increase in voltage gives you 50 % increase in excitation current is called knee point voltage.What is Knee Point Voltage of a Current Transformer? What is its signific.7 degrees? the knee point is where the secondary (back) EMF equals the primary. The secondary excitation voltage corresponding to the tangent to the curve gives the knee-voltage of the CT. the secondary coils are saturated. You might recall that this curve is very much similar to the B-H curve used for the selection of Bmax for the design of mains transformers. Rate 1 of 2 2/23/2014 3:02 PM . while doing this above phenomeneo will be obsesrved. To measure this first demagnetise the CT and apply voltage gradually from secondary keeping primary winding open circuited. Source: www.com/question/index?qid=20080211061641AA90BJr Answers Home All Categories Science & Mathematics Arts & Humanities Beauty & Style Business & Finance Cars & Transportation Computers & Internet Consumer Electronics Dining Out Education & Reference More International About Follow Watchlist Science & Mathematics > Engineering > Reference Question Next Ask a Question What is Knee Point Voltage of a Current Transformer? What is its significance? deepak_8584 asked 6 years ago Answer last updated 3 months ago Related Questions What is knee point voltage in current transformer? Formula for knee point voltage calculation of current transformer? What is knee point of current and voltage transformers? How to get more Current. no more bang for the buck. com/question/index?qid=20080211061641AA90BJr 2 of 2 2/23/2014 3:02 PM ..answers..yahoo. http://in.What is Knee Point Voltage of a Current Transformer? What is its signific. the free encyclopedia A current transformer (CT) is used for measurement of alternating electric currents. The most common design of CT consists of a length of wire wrapped many times around a silicon steel ring passed 'around' the circuit being measured. the free encyclopedia http://en. Current transformers are commonly used in metering and protective relays in the electrical power industry. Contents 1 Design 2 Usage 3 Safety precautions 4 Accuracy 4. When current in a circuit is too high to apply directly to measuring instruments. a current transformer has a primary winding.4 Phase shift 5 Special designs 6 Standards 7 High voltage types 8 See also 9 References 10 External links A CT for operation on a 110 kV grid Design Like any other transformer. with a secondary of many tens or hundreds of turns. a current transformer produces a reduced current accurately proportional to the current in the circuit. A current transformer isolates the measuring instruments from what may be very high voltage in the monitored circuit. are known as instrument transformers. which can be conveniently connected to measuring and recording instruments. The Basic operation of current transformer 1 of 6 2/23/2014 3:01 PM .Wikipedia. so the secondary current is linearly proportional to the primary current.org/wiki/Current_transformer Current transformer From Wikipedia. The CT's primary circuit therefore consists of a single 'turn' of conductor.3 Rating factor 4.Current transformer .wikipedia.1 Burden 4. The alternating current flowing in the primary produces an alternating magnetic field in the core.2 Knee-point core-saturation voltage 4. a magnetic core and a secondary winding. An essential objective of current transformer design is to ensure the primary and secondary circuits are efficiently coupled. Current transformers. together with voltage transformers (VT) (potential transformers (PT)). which then induces an alternating current in the secondary winding circuit. with a heavy copper bar to carry current through the magnetic core. the core goes into saturation toward the end of each cycle. The secondary winding can be single or multi-ratio. Russia Usage Current transformers used in metering equipment for three-phase 400 ampere electricity supply Current transformers are used extensively for measuring current and monitoring the operation of the power grid. If the voltage time integral area is higher than the core's design rating. Window-type current transformers (aka zero sequence current transformers. which can have circuit cables run through the middle of an opening in the core to provide a single-turn primary winding. or ZSCT) are also common. Along with voltage leads. For example. sometimes a section of bus bar is arranged to be easily removed for exchange of current transformers. or burden. which automatically centers the conductor inside the CT window. overload performance) to be used for the devices. SF6 110 kV current transformer TGFM series. the free encyclopedia http://en.Wikipedia. For example.wikipedia. as the transformer secondary will attempt to continue driving current across the effectively infinite impedance up to its core saturation voltage. Many digital clamp meters utilize a current transformer for measuring AC current Safety precautions Care must be taken that the secondary of a current transformer is not disconnected from its load while current is flowing in the primary. multiple CTs are installed as a "stack" for various uses. Typical examples of low voltage single ratio metering current transformers are either ring type or plastic molded case. a 4000:5 CT secondary winding will supply an output current of 5 amperes when the primary winding current is 4000 amperes. The load. High-voltage current transformers are mounted on porcelain insulators to isolate them from ground. Current transformers can be mounted on the low voltage or high voltage leads of a power transformer. causing arcing. of the CT should be a low resistance. with five taps being common for multi-ratio CTs. Often. When conductors passing through a CT are not centered in the circular (or oval) opening. revenue-grade CTs drive the electrical utility's watt-hour meter on virtually every building with three-phase service and single-phase services greater than 200 amps.Current transformer . or 2 of 6 2/23/2014 3:01 PM . slight inaccuracies may occur. The primary circuit is largely unaffected by the insertion of the CT. The CT is typically described by its current ratio from primary to secondary. Shapes and sizes can vary depending on the end user or switchgear manufacturer. and allows current transformers with different characteristics (accuracy. compromising operator and equipment safety. The rated secondary current is commonly standardized at 1 or 5 amperes. protection devices and revenue metering may use separate CTs to provide isolation between metering and protection circuits. This may produce a high voltage across the open secondary into the range of several kilovolts. distorting the waveform and affecting accuracy. Some CT configurations slip around the bushing of a high-voltage transformer or circuit breaker.org/wiki/Current_transformer primary winding may be a permanent part of the current transformer. Knee-point core-saturation voltage The knee-point voltage of a current transformer is the magnitude of the secondary voltage above which the output current ceases to linearly follow the input current within declared accuracy.5L400 specifies with an output from its secondary winding of 20 times its rated secondary current (usually 5 A x 20 = 100 A) and 400 V (IZ drop) its output accuracy will be within 2. the ratio error of a Class 0. 0. Typical burden ratings for IEC CTs are 1. These specification diagrams show accuracy parallelograms on a grid incorporating magnitude and phase angle error scales at the CT's rated burden. 10 VA. The burden.1.0. B-0.wikipedia.1. Items that contribute to the burden of a current measurement circuit are switch-blocks. and each class has an allowable maximum phase error for a specified load impedance.5s.5 CT is 0. Accuracy The accuracy of a CT is directly related to a number of factors including: Burden Burden class/saturation class Rating factor Load External electromagnetic fields Temperature and Physical configuration.5% or less.Wikipedia. 0.5. 1 and 3. As for ANSI/IEEE burden ratings are B-0. accuracy classes for various types of measurement are set out in IEC 60044-1. The selected tap.0. the excessive length of wire creates a large resistance. 0. 5 VA. Burden The secondary load of a current transformer is usually called the "burden" to distinguish it from the load of the circuit whose current is being measured. until the knee point is reached. The knee point is defined as the voltage at which a 10% increase in applied 3 of 6 2/23/2014 3:01 PM . The ratio (primary to secondary current) error of a Class 1 CT is 1% at rated current.org/wiki/Current_transformer permanently affect the accuracy of the transformer.5. In testing. 0. 30 VA. meters and intermediate conductors. A CT with a rating of 2. Current transformers used for protective relaying also have accuracy requirements at overload currents in excess of the normal rating to ensure accurate performance of relays during system faults. The most common source of excess burden is the conductor between the meter and the CT.0 and B-4. This problem can be reduced by using CTs with 1 ampere secondaries.2.5 VA.5 percent. 20 VA. When substation meters are located far from the meter cabinets. Classes 0.2 Ω of impedance in the metering circuit before its secondary accuracy falls outside of an accuracy specification. 3 VA. B-1. in a CT metering circuit is the (largely resistive) impedance presented to its secondary winding. if a voltage is applied across the secondary terminals the magnetizing current will increase in proportion to the applied voltage.2 can tolerate up to 0. B-2. The class designation is an approximate measure of the CT's accuracy. which will produce less voltage drop between a CT and its metering devices. Errors in phase are also important especially in power measuring circuits. 45 VA and 60 VA.Current transformer . This means a CT with a burden rating of B-0.2s.2. 15 VA. B-0. the free encyclopedia http://en. for multi-ratio CTs Phase change For the IEC standard. " or 10% of the nominal current (there are. In practice. but constrained within a very small range of the current transformer rating. It is important to be mindful of ambient temperatures and resultant rating factors when CTs are installed inside padmount transformers or poorly ventilated mechanical rooms. Phase shift Ideally the secondary current of a current transformer should be perfectly in phase with the primary current. typically 1. the magnetizing current increases considerably even for small increments in voltage across the secondary terminals. Unlike CTs used for power circuitry. For power and energy measurement. if the current transformer is used in conjunction with the current circuit of a wattmeter.13 (ANSI).[1] Rating factor Rating factor is a factor by which the nominal full load current of a CT can be multiplied to determine its absolute maximum measurable primary current.Wikipedia.[2] In recent years the introduction of electronic based power and energy meters has allowed the phase error to be calibrated out. wideband CTs are rated in output volts per ampere of primary current. Another type (called a Rogowski coil) requires an external integrator in order to provide a voltage output that is proportional to the measured current. the minimum primary current a CT can accurately measure is "light load. For voltages greater than the knee point.Current transformer .wikipedia. However. energy meter or power factor meter. Most CTs have rating factors for 35 degrees Celsius and 55 degrees Celsius. 4 of 6 2/23/2014 3:01 PM . however. Conversely. manufacturers have been moving towards lower nominal primary currents with greater rating factors.org/wiki/Current_transformer voltage increases the magnetizing current by 50%. Recently.[2] For the purposes of current measurement. there are two main standards to which current transformers are designed. all the measured power is entirely due to the current transformer's phase error.5 times rated current. but phase shifts as low as a few tenths of a degree for well constructed transformers up to as much as six degrees for simpler designs may be encountered (for the normal power frequencies). At true zero power factor. CT RATIO Standards Ultimately. only displays the magnitude of the current. this is impossible to achieve. any phase shift in the measured current can affect the accuracy of the target measurement. IEC 60044-1 (BSEN 60044-1) & IEEE C57. the concept of knee point voltage is very pertinent to protection current transformers.2 to 1. One type of specially constructed wideband transformer provides a voltage output that is proportional to the measured current. although the Canadian and Australian standards are also recognised. this error is generally considered to be negligible at unity power factor but increases in significance as the power factor approaches zero. However. any phase shift is immaterial as the indicating ammeter. The rating factor of a CT is largely dependent upon ambient temperature. special CTs designed to measure accurately currents as small as 2% of the nominal current). depending on client requirements. since they are necessarily exposed to fault currents of 20 to 30 times rated current. The knee-point voltage is less applicable for metering current transformers as their accuracy is generally much higher.[3] Special designs Specially constructed wideband current transformers are also used (usually with an oscilloscope) to measure waveforms of high frequency or pulsed currents within pulsed power systems. This is made possible by the development of more efficient ferrites and their corresponding hysteresis curves. the free encyclopedia http://en. pdf) 5 of 6 2/23/2014 3:01 PM .Current transformer .org/wiki/Current_transformer High voltage types Current transformers are used for protection.com/introduction-protectiontransformers.itl-uk. (1977). (The General Electric Company Limited of England. A high-voltage current transformer may contain several cores. for different purposes (such as metering circuits. Live tank CTs are useful because the primary conductor is short.com/w/Measurement_Errors_Due_to_CT_Phase_Shift 3.itl-uk.com/Q/What_is_the_reason_for_using_a_neutral_current_transformer_on_a_transformer External links High Voltage Transformer / Custom Transformers (http://www.com/wordpress/wp-content/uploads/2013/01 /GLEMS%202012%20-%20Inst%20Xformers%20Theory%20and%20Testing.com/products/high-voltagetransformer. ISBN 0-08-021729-X.ccontrolsys. Pergamon. ^ http://www.Wikipedia.com/instrument-transformer-characteristics.net/pdfs/AN0305-Current_Transformers. which gives better performance for overloads and transients.[4] A neutral current transformer is used as earth fault protection to measured any fault current flowing through the neutral line from the wye neutral point of a transformer. Volume One. 1975 Section 5.wikipedia.3 2. Dead tank current transformers isolate the measured circuit from the enclosure.pdf) Introduction to Metering / Measurement Current Transformers (http://www. In a switchyard.html) Testing Current Transformers (http://powermetrix. or protection).html) Introduction to Current Transformers (http://www. Paterson. insulation life and thermal stability is improved. the free encyclopedia http://en. each with a secondary winding. A.customcoils. control. W. ^ Anon.com/en/products /measurement-transformers/) Introduction to Protection Current Transformers (http://www. Since the major insulation of a live-tank current transformer is not exposed to the heat of the primary conductors. but very often free-standing outdoor current transformers are used. p. 1.itl-uk.ccontrolsys. measurement and control in high voltage electrical substations and the electrical grid. 331. ^ Protective Relays Application Guide. Current transformers may be installed inside switchgear or in apparatus bushings.. live tank current transformers have a substantial part of their enclosure energized at the line voltage and must be mounted on insulators.elkor. Protective Relays Application Guide Second Edition.com/w/CT_Phase_Angle_Correction 4. The primary of the winding can be evenly distributed around the magnetic core. ^ http://wiki.[5] See also Rogowski coil Transformer Instrumentation Transformer types References Guile. Electrical Power Systems.html) Transformer Terminology (http://www. which gives better stability and a higher short-circuit current rating. 1975) pages 78-87 5. ^ a b http://www. The General Electric Company Limited of England.answers. By using this site. additional terms may apply.Wikipedia. you agree to the Terms of Use and Privacy Policy. Wikipedia® is a registered trademark of the Wikimedia Foundation.org/w/index.wikipedia. the free encyclopedia http://en.wikipedia. Inc. a non-profit organization.org/wiki/Current_transformer Retrieved from "http://en..php?title=Current_transformer&oldid=593942124" Categories: Transformers (electrical) Electronic test equipment This page was last modified on 4 February 2014 at 20:44.Current transformer . 6 of 6 2/23/2014 3:01 PM . Text is available under the Creative Commons Attribution-ShareAlike License. .. BASIC LAWS POWER POTENTIAL DIFFERENCE or VOLTAGE CURRENT INDOOR SUBSTATION OUTDOOR SUBSTATION CIRCUIT BREAKER AUTO RE CLOSE CAPACITIVE VOLTAGE TRANSFORMER SYNCHRONIZATION MOTOR GENERATOR WAVE TRAP HI-POTENTIAL TEST FOR BUS BAR HI-POTENTIAL TEST FOR CABLES WINDING RESISTANCE TEST FOR CT RATIO TEST FOR CT POLARITY TEST FOR CT INSULATION RESISTANCE TEST FOR CT WINDING RESISTANCE TEST FOR POWER TRANSFORMER INSULATION RESISTANCE TEST FOR BUS BAR VECTOR GROUP TEST FOR TRANSFORMER RATIO TEST FOR TRANSFORMER VT or PT RATIO TEST INSULATION RESISTANCE TEST FOR CABLES KNEE POINT VOLTAGE TEST (PS class only) INSULATION RESISTANCE TEST FOR VT or PT POLARITY TEST FOR VT or PT WINDING RESISTANCE TEST FOR VT or PT CURRENT TRANSFORMER POTENTIAL TRANSFORMER POWER TRANSFORMER POWER CABLE BUS BAR INSULATION RESISTANCE TEST FOR TRANSFORMER MAGNETIZATION CURRENT TEST FOR TRANSFORMER MAGNETIC BALANCE TEST FOR TRANSFORMER DIFFERENT TYPES OF CIRCUIT BREAKERS EARTHING WIRE and SURGE ARRESTER SURGE ARRESTER .you have any doubts. http://electricity4you. 1 of 2 2/23/2014 3:14 PM . why we are doing this test? A.you want to communicate with administrator contact with above email. current will not increase as starting (proportionally). secondary circuit is small so the voltage drop across burden is small. Q. Q.html ‫تسجيل الدخول‬ ‫إنشاء مدونة إلكترونية‬ «‫المدونة ا لكترونية التالية‬ ‫المزيد‬ 0 WE MAKE U MUCH NEARER TO ELECTRICAL ENGINEERING GENERAL ELECTRICAL KNOWLEDGE TESTING OF EQUIPMENTS COMMISSIONING OF ELECTRICAL EQUIPMENTS ABOUT ME PHOTO GALLERY KNEE POINT VOLTAGE TEST..ae/2013/05/knee-point-voltage-test. 2. What is burden? A.com@gmail. electricity4you. or LIGHTNING AREESTER.. The load connected to secondary winding (sum of relay impedance meter impedance and control cable resistance and CT secondary winding resistance). measure secondary current by using leakage current tester. Why it is important in only PS class? what about metering class and over current and earth fault protection (5P class) ? A. Repeat the steps up 100% of knee point voltage.Isolate the CT from all external connections. Apply 10% of knee point voltage (provided on name plate details) to the secondary circuit by using auto transformer.so generally by designing specially(secondary current only 1amps.But in PS(the class used only for differential protection purpose) class secondary burden is very high so the voltage across secondary winding is also high which may be divert our CT to saturate position in normal condition also.blogspot. Q.increase the voltage by 10% step by step and measure current as said above.ELECTRICITY 4 YOU: KNEE POINT VOLTAGE TEST. It is the point at where 50% of secondary current increases in order to increase 10% of voltage in secondary winding... 3. 6.. for metering and 5P class. as to minimize ohimic loss in secondary circuit). So generally manufacture provide knee point voltage maximum compared to other classes). Total viewers free download counter | vps servers CONTENTS or knee point test at field PROCEDURE: 1. Q.then it will not saturate in normal case. 5. 4.it implies that voltage across secondary winding is small.What is the knee point voltage? A.. After knee point voltage . We are just checking the manufacture specification is correct or not.blogspot.com if you want to share anything. ae/2013/05/knee-point-voltage-test.html 2 of 2 2/23/2014 3:14 PM .. http://electricity4you.ELECTRICITY 4 YOU: KNEE POINT VOLTAGE TEST...blogspot. The knee-point of a CT is the magnitude of the secondary voltage after which the output current ceases to follow linearly the input current. 0. 1 and 3.0. The conductor between the meter and the CT will typically be the source of excess burden.1. August 2. 3 VA. For an example.2. 45 VA and 60 VA. 0. B-2.2 ohms of impedance in the metering circuit before its output current is no longer a fixed ratio of the primary current. and The selected tap The IEC 60044-1 standard sets out various accuracy classes. and phase angle tests. 2012 this is great.protecequip. 5 VA. Or. These sets will perform CT excitation.2s. and B-4. 20 VA. meters and intermediate conductors will all contribute to the burden of a current measurement circuit. the ratio error of a Class 1 CT is 1% at rated current. by much can you overload a metering CT and still operate within its accuracy? Leave a comment Next Post >> • Power Analysis • Protec Webinars • Relay Testing • Resistance Testing 1 of 2 2/23/2014 3:15 PM . 15 VA. or burden.Versatile and Essential in Diagnosing Electrical Issues • Fluke 1735 Three Phase Power Logger for Easy Energy Studies • Rent the Doble TDR9100 Circuit Breaker Test System from Protec Today • Assure the Health of Circuit Breakers with the Square D by Schneider S33595 • Dranetz PX5 Integrates Advanced Function-Set for Quality Power Monitoring • Conduct Insulation Tests and Measure Winding Resistance with the Vanguard EZCT-2000B • Megger MIT1025 Designed for Insulation Testing at its Best POPULAR CATEGORIES Figure 1: CT Knee-point The knee-point voltage is less applicable for metering CTs since their accuracy is generally much tighter and constrained within a very small bandwidth of the current transformer rating.0.com/blog/common-sense-testing/understanding-cur.2.5 CT is 0. 0. Typical burden ratings for IEC CTs are 1. Depending on model selected.5. current-ratio. http://blog. The load. Current transformers used for protective relays will have accuracy requirements at overload currents in excess of the normal rating to ensure accurate performance of relays during system faults. or in the Field • Amprobe DM-III Power Quality Analyzer . however. B-1. the one-to-one relationship between input and output is no longer within declared accuracy. B-0. a voltage is applied across the secondary terminals and magnetizing current will increase in proportion to the applied voltage up until the knee point.. in a CT metering circuit is the impedance presented to its secondary winding. in other words. insulation resistance and winding resistance of the CT secondary windings plus secondary burden can be measured. This impedance will be largely resistive. B-0.5% or less. This means a CT with a burden rating of B-0. The Vanguard EZCT series of CT test sets are designed specifically for CT testing and will greatly increase productivity and save time during the commissioning and maintenance testing. Each class also has an allowable maximum phase error for specified load impedance.. 0. The knee-point is defined as the point at which an increase of applied voltage of 10% results in an increase in magnetizing current of 50%. 4 2 0 0 Like 2 • Battery Testing • Breaker Testing • Cable Testing • Earth Testing • Expert Advice • Financial Benefits of Renting • Insulation Testing << Previous Post Comments for Understanding Current Transformers – Part II Characteristics Name: lee Time: Thursday.5 VA.1. Switch-blocks. When testing... October 27.5. Protec Equipment Resources offers a vast inventory of microprocessor-based current transformer test set from Vanguard Instruments. is very important to protection CTs since they are exposed to currents of 20 to 30 times rated current during faults.0. 30 VA. The class designation is an approximate measure of the CT’s accuracy. HOME CATEGORIES CONTRIBUTORS CONNECT Understanding Current Transformers – Part II Characteristics Posted by Common Sense Testing on Thursday. polarity. The ratio error of Class 0. These factors will include: • • • • • • • Burden Burden class/saturation class Rating factor Load External electromagnetic fields Temperature and physical conditions.Understanding Current Transformers – Part II Characteristics .5s. 2011 When looking at the accuracy of a CT a number of factors need to be taken into consideration. Production Floor.Common S. Knee-point. 10 VA. ANSI/IEEE burden ratings are B-0.2 can tolerate up to 0. The classes are 0. RECENT ENTRIES • Megger DLRO200-115 Designed for Use in the Workshop. Name • Testing and Safety • Testing Tips and Tricks • Transformer Testing Email Your comment (No HTML) Type the text from the image below Protec Equipment Resources Inc.protecequip. Texas 75050 © 2014 Protec Equipment Resources HOME CATEGORIES CONTRIBUTORS CONNECT RENTAL AGREEMENT 2 of 2 2/23/2014 3:15 PM .. Suite 116.. Grand Prairie.Common S.Understanding Current Transformers – Part II Characteristics ... 1517 W N Carrier Pkwy.com/blog/common-sense-testing/understanding-cur. http://blog.. The CT's primary circuit therefore consists of a single 'turn' of conductor.Wikipedia. a magnetic core and a secondary winding. A current transformer isolates the measuring instruments from what may be very high voltage in the monitored circuit. Current transformers are commonly used in metering and protective relays in the electrical power industry. which then induces an alternating current in the secondary winding circuit. the free encyclopedia http://en. together with voltage transformers (VT) (potential transformers (PT)).2 Knee-point core-saturation voltage 4. When current in a circuit is too high to apply directly to measuring instruments. Current transformers. The Basic operation of current transformer 1 of 6 2/23/2014 3:01 PM . which can be conveniently connected to measuring and recording instruments. Contents 1 Design 2 Usage 3 Safety precautions 4 Accuracy 4.wikipedia. with a secondary of many tens or hundreds of turns.3 Rating factor 4. The most common design of CT consists of a length of wire wrapped many times around a silicon steel ring passed 'around' the circuit being measured.Current transformer . so the secondary current is linearly proportional to the primary current. the free encyclopedia A current transformer (CT) is used for measurement of alternating electric currents. An essential objective of current transformer design is to ensure the primary and secondary circuits are efficiently coupled.org/wiki/Current_transformer Current transformer From Wikipedia.1 Burden 4.4 Phase shift 5 Special designs 6 Standards 7 High voltage types 8 See also 9 References 10 External links A CT for operation on a 110 kV grid Design Like any other transformer. a current transformer has a primary winding. a current transformer produces a reduced current accurately proportional to the current in the circuit. are known as instrument transformers. The alternating current flowing in the primary produces an alternating magnetic field in the core. The primary circuit is largely unaffected by the insertion of the CT. Often.Current transformer . protection devices and revenue metering may use separate CTs to provide isolation between metering and protection circuits. causing arcing.wikipedia. For example. For example. sometimes a section of bus bar is arranged to be easily removed for exchange of current transformers. Shapes and sizes can vary depending on the end user or switchgear manufacturer. The load. Some CT configurations slip around the bushing of a high-voltage transformer or circuit breaker. This may produce a high voltage across the open secondary into the range of several kilovolts. If the voltage time integral area is higher than the core's design rating. the free encyclopedia http://en. of the CT should be a low resistance. slight inaccuracies may occur. or 2 of 6 2/23/2014 3:01 PM . multiple CTs are installed as a "stack" for various uses. distorting the waveform and affecting accuracy. with a heavy copper bar to carry current through the magnetic core. which can have circuit cables run through the middle of an opening in the core to provide a single-turn primary winding. as the transformer secondary will attempt to continue driving current across the effectively infinite impedance up to its core saturation voltage. which automatically centers the conductor inside the CT window. a 4000:5 CT secondary winding will supply an output current of 5 amperes when the primary winding current is 4000 amperes.Wikipedia. Typical examples of low voltage single ratio metering current transformers are either ring type or plastic molded case. SF6 110 kV current transformer TGFM series. Many digital clamp meters utilize a current transformer for measuring AC current Safety precautions Care must be taken that the secondary of a current transformer is not disconnected from its load while current is flowing in the primary. Along with voltage leads. and allows current transformers with different characteristics (accuracy. or ZSCT) are also common. When conductors passing through a CT are not centered in the circular (or oval) opening. compromising operator and equipment safety. Window-type current transformers (aka zero sequence current transformers. The rated secondary current is commonly standardized at 1 or 5 amperes. Russia Usage Current transformers used in metering equipment for three-phase 400 ampere electricity supply Current transformers are used extensively for measuring current and monitoring the operation of the power grid. The CT is typically described by its current ratio from primary to secondary. Current transformers can be mounted on the low voltage or high voltage leads of a power transformer. overload performance) to be used for the devices. revenue-grade CTs drive the electrical utility's watt-hour meter on virtually every building with three-phase service and single-phase services greater than 200 amps. or burden. with five taps being common for multi-ratio CTs. High-voltage current transformers are mounted on porcelain insulators to isolate them from ground. The secondary winding can be single or multi-ratio. the core goes into saturation toward the end of each cycle.org/wiki/Current_transformer primary winding may be a permanent part of the current transformer. the free encyclopedia http://en.1. 45 VA and 60 VA. Current transformers used for protective relaying also have accuracy requirements at overload currents in excess of the normal rating to ensure accurate performance of relays during system faults.2 can tolerate up to 0. The burden. if a voltage is applied across the secondary terminals the magnetizing current will increase in proportion to the applied voltage. B-0. When substation meters are located far from the meter cabinets. In testing. meters and intermediate conductors. B-1. As for ANSI/IEEE burden ratings are B-0.5L400 specifies with an output from its secondary winding of 20 times its rated secondary current (usually 5 A x 20 = 100 A) and 400 V (IZ drop) its output accuracy will be within 2.2.5 percent.wikipedia.5 CT is 0.5. 20 VA.5% or less. 30 VA.0. which will produce less voltage drop between a CT and its metering devices.Current transformer . accuracy classes for various types of measurement are set out in IEC 60044-1. 0. Accuracy The accuracy of a CT is directly related to a number of factors including: Burden Burden class/saturation class Rating factor Load External electromagnetic fields Temperature and Physical configuration. and each class has an allowable maximum phase error for a specified load impedance. 5 VA. 0. The class designation is an approximate measure of the CT's accuracy. 0. Classes 0. This means a CT with a burden rating of B-0.1. for multi-ratio CTs Phase change For the IEC standard. the excessive length of wire creates a large resistance. B-0. Items that contribute to the burden of a current measurement circuit are switch-blocks.Wikipedia.2. The knee point is defined as the voltage at which a 10% increase in applied 3 of 6 2/23/2014 3:01 PM . The most common source of excess burden is the conductor between the meter and the CT. B-2.0. The ratio (primary to secondary current) error of a Class 1 CT is 1% at rated current. 10 VA. 3 VA. This problem can be reduced by using CTs with 1 ampere secondaries. Errors in phase are also important especially in power measuring circuits. the ratio error of a Class 0.5 VA.org/wiki/Current_transformer permanently affect the accuracy of the transformer.5s. 0. A CT with a rating of 2. Burden The secondary load of a current transformer is usually called the "burden" to distinguish it from the load of the circuit whose current is being measured. until the knee point is reached.0 and B-4.2 Ω of impedance in the metering circuit before its secondary accuracy falls outside of an accuracy specification. Knee-point core-saturation voltage The knee-point voltage of a current transformer is the magnitude of the secondary voltage above which the output current ceases to linearly follow the input current within declared accuracy. The selected tap. These specification diagrams show accuracy parallelograms on a grid incorporating magnitude and phase angle error scales at the CT's rated burden. in a CT metering circuit is the (largely resistive) impedance presented to its secondary winding. Typical burden ratings for IEC CTs are 1. 1 and 3. 15 VA.2s.5. 13 (ANSI). CT RATIO Standards Ultimately. Conversely. the magnetizing current increases considerably even for small increments in voltage across the secondary terminals. manufacturers have been moving towards lower nominal primary currents with greater rating factors. however. The knee-point voltage is less applicable for metering current transformers as their accuracy is generally much higher. depending on client requirements. all the measured power is entirely due to the current transformer's phase error. this is impossible to achieve. although the Canadian and Australian standards are also recognised. special CTs designed to measure accurately currents as small as 2% of the nominal current). but phase shifts as low as a few tenths of a degree for well constructed transformers up to as much as six degrees for simpler designs may be encountered (for the normal power frequencies).org/wiki/Current_transformer voltage increases the magnetizing current by 50%. typically 1. This is made possible by the development of more efficient ferrites and their corresponding hysteresis curves. One type of specially constructed wideband transformer provides a voltage output that is proportional to the measured current. if the current transformer is used in conjunction with the current circuit of a wattmeter.5 times rated current. It is important to be mindful of ambient temperatures and resultant rating factors when CTs are installed inside padmount transformers or poorly ventilated mechanical rooms. 4 of 6 2/23/2014 3:01 PM .Current transformer . any phase shift in the measured current can affect the accuracy of the target measurement. Another type (called a Rogowski coil) requires an external integrator in order to provide a voltage output that is proportional to the measured current. Phase shift Ideally the secondary current of a current transformer should be perfectly in phase with the primary current. this error is generally considered to be negligible at unity power factor but increases in significance as the power factor approaches zero.wikipedia.2 to 1. IEC 60044-1 (BSEN 60044-1) & IEEE C57. For voltages greater than the knee point.[2] In recent years the introduction of electronic based power and energy meters has allowed the phase error to be calibrated out." or 10% of the nominal current (there are. Unlike CTs used for power circuitry. However. In practice. The rating factor of a CT is largely dependent upon ambient temperature. any phase shift is immaterial as the indicating ammeter. Recently. At true zero power factor. there are two main standards to which current transformers are designed.[1] Rating factor Rating factor is a factor by which the nominal full load current of a CT can be multiplied to determine its absolute maximum measurable primary current. energy meter or power factor meter. Most CTs have rating factors for 35 degrees Celsius and 55 degrees Celsius.[2] For the purposes of current measurement. the free encyclopedia http://en. wideband CTs are rated in output volts per ampere of primary current. the minimum primary current a CT can accurately measure is "light load. but constrained within a very small range of the current transformer rating. For power and energy measurement.Wikipedia. since they are necessarily exposed to fault currents of 20 to 30 times rated current. the concept of knee point voltage is very pertinent to protection current transformers. However. only displays the magnitude of the current.[3] Special designs Specially constructed wideband current transformers are also used (usually with an oscilloscope) to measure waveforms of high frequency or pulsed currents within pulsed power systems. the free encyclopedia http://en.pdf) Introduction to Metering / Measurement Current Transformers (http://www. ^ http://wiki. W.html) Transformer Terminology (http://www.Current transformer .com/en/products /measurement-transformers/) Introduction to Protection Current Transformers (http://www. which gives better performance for overloads and transients. measurement and control in high voltage electrical substations and the electrical grid.com/instrument-transformer-characteristics. Protective Relays Application Guide Second Edition.com/Q/What_is_the_reason_for_using_a_neutral_current_transformer_on_a_transformer External links High Voltage Transformer / Custom Transformers (http://www. (1977). Since the major insulation of a live-tank current transformer is not exposed to the heat of the primary conductors. ISBN 0-08-021729-X. Paterson. p.com/introduction-protectiontransformers. A high-voltage current transformer may contain several cores.com/wordpress/wp-content/uploads/2013/01 /GLEMS%202012%20-%20Inst%20Xformers%20Theory%20and%20Testing. Volume One.answers. (The General Electric Company Limited of England. which gives better stability and a higher short-circuit current rating. 1. ^ a b http://www. control.Wikipedia. or protection).org/wiki/Current_transformer High voltage types Current transformers are used for protection. for different purposes (such as metering circuits.com/w/Measurement_Errors_Due_to_CT_Phase_Shift 3. Live tank CTs are useful because the primary conductor is short.customcoils.. each with a secondary winding. 1975 Section 5. ^ http://www. Current transformers may be installed inside switchgear or in apparatus bushings.itl-uk.ccontrolsys.itl-uk. The General Electric Company Limited of England. insulation life and thermal stability is improved.elkor. Dead tank current transformers isolate the measured circuit from the enclosure.net/pdfs/AN0305-Current_Transformers.ccontrolsys. 331.html) Introduction to Current Transformers (http://www. ^ Protective Relays Application Guide.com/products/high-voltagetransformer. A.html) Testing Current Transformers (http://powermetrix.[5] See also Rogowski coil Transformer Instrumentation Transformer types References Guile. Electrical Power Systems.3 2.pdf) 5 of 6 2/23/2014 3:01 PM . but very often free-standing outdoor current transformers are used. The primary of the winding can be evenly distributed around the magnetic core.itl-uk. 1975) pages 78-87 5.[4] A neutral current transformer is used as earth fault protection to measured any fault current flowing through the neutral line from the wye neutral point of a transformer.com/w/CT_Phase_Angle_Correction 4.wikipedia. live tank current transformers have a substantial part of their enclosure energized at the line voltage and must be mounted on insulators. ^ Anon. Pergamon. In a switchyard. you agree to the Terms of Use and Privacy Policy.org/wiki/Current_transformer Retrieved from "http://en. a non-profit organization. 6 of 6 2/23/2014 3:01 PM .wikipedia. Text is available under the Creative Commons Attribution-ShareAlike License.php?title=Current_transformer&oldid=593942124" Categories: Transformers (electrical) Electronic test equipment This page was last modified on 4 February 2014 at 20:44..wikipedia. By using this site.org/w/index.Current transformer . Wikipedia® is a registered trademark of the Wikimedia Foundation. Inc. additional terms may apply.Wikipedia. the free encyclopedia http://en. .increase the voltage by 10% step by step and measure current as said above. BASIC LAWS POWER POTENTIAL DIFFERENCE or VOLTAGE CURRENT INDOOR SUBSTATION OUTDOOR SUBSTATION CIRCUIT BREAKER AUTO RE CLOSE CAPACITIVE VOLTAGE TRANSFORMER SYNCHRONIZATION MOTOR GENERATOR WAVE TRAP HI-POTENTIAL TEST FOR BUS BAR HI-POTENTIAL TEST FOR CABLES WINDING RESISTANCE TEST FOR CT RATIO TEST FOR CT POLARITY TEST FOR CT INSULATION RESISTANCE TEST FOR CT WINDING RESISTANCE TEST FOR POWER TRANSFORMER INSULATION RESISTANCE TEST FOR BUS BAR VECTOR GROUP TEST FOR TRANSFORMER RATIO TEST FOR TRANSFORMER VT or PT RATIO TEST INSULATION RESISTANCE TEST FOR CABLES KNEE POINT VOLTAGE TEST (PS class only) INSULATION RESISTANCE TEST FOR VT or PT POLARITY TEST FOR VT or PT WINDING RESISTANCE TEST FOR VT or PT CURRENT TRANSFORMER POTENTIAL TRANSFORMER POWER TRANSFORMER POWER CABLE BUS BAR INSULATION RESISTANCE TEST FOR TRANSFORMER MAGNETIZATION CURRENT TEST FOR TRANSFORMER MAGNETIC BALANCE TEST FOR TRANSFORMER DIFFERENT TYPES OF CIRCUIT BREAKERS EARTHING WIRE and SURGE ARRESTER SURGE ARRESTER . So generally manufacture provide knee point voltage maximum compared to other classes)[email protected] want to communicate with administrator contact with above email. Q.then it will not saturate in normal case. electricity4you.html ‫تسجيل الدخول‬ ‫إنشاء مدونة إلكترونية‬ «‫المدونة ا لكترونية التالية‬ ‫المزيد‬ 0 WE MAKE U MUCH NEARER TO ELECTRICAL ENGINEERING GENERAL ELECTRICAL KNOWLEDGE TESTING OF EQUIPMENTS COMMISSIONING OF ELECTRICAL EQUIPMENTS ABOUT ME PHOTO GALLERY KNEE POINT VOLTAGE TEST.Isolate the CT from all external connections.it implies that voltage across secondary winding is small.com if you want to share anything. The load connected to secondary winding (sum of relay impedance meter impedance and control cable resistance and CT secondary winding resistance).. Q.. or LIGHTNING AREESTER. 1 of 2 2/23/2014 3:14 PM . What is burden? A. After knee point voltage . 2. secondary circuit is small so the voltage drop across burden is small. http://electricity4you. Total viewers free download counter | vps servers CONTENTS or knee point test at field PROCEDURE: 1.blogspot.so generally by designing specially(secondary current only 1amps. Why it is important in only PS class? what about metering class and over current and earth fault protection (5P class) ? A. 6.ae/2013/05/knee-point-voltage-test. Q. Q. 3. for metering and 5P class. Apply 10% of knee point voltage (provided on name plate details) to the secondary circuit by using auto transformer. We are just checking the manufacture specification is correct or not.ELECTRICITY 4 YOU: KNEE POINT VOLTAGE TEST... 4..But in PS(the class used only for differential protection purpose) class secondary burden is very high so the voltage across secondary winding is also high which may be divert our CT to saturate position in normal condition also. why we are doing this test? A..you have any doubts.What is the knee point voltage? A. It is the point at where 50% of secondary current increases in order to increase 10% of voltage in secondary winding. as to minimize ohimic loss in secondary circuit).. 5. Repeat the steps up 100% of knee point voltage. current will not increase as starting (proportionally).blogspot. measure secondary current by using leakage current tester. http://electricity4you..ae/2013/05/knee-point-voltage-test..blogspot.html 2 of 2 2/23/2014 3:14 PM ..ELECTRICITY 4 YOU: KNEE POINT VOLTAGE TEST. Wikipedia. to provide for different requirements of current level as an alternating current source. a current flows through the secondary winding drawing power from the primary winding and its power source.[1][2] Contents 1 Invention 2 Applications 3 Basic principles 4 Basic transformer parameters and construction 5 Construction 6 Classification parameters 7 Types 8 Applications 9 History 10 See also 11 Notes 12 References 13 Bibliography 14 External links 1 of 27 2/24/2014 8:04 PM . Transformers may be used in voltage conversion to transform an AC voltage from one voltage level on the input of the device to another level at the output terminals. A transformer cannot operate with direct current. Pole-mounted distribution transformer with center-tapped secondary winding used to provide 'split-phase' power for residential and light commercial service. but produces a short output pulse as the voltage rises when connected to the DC source. or it may be used for impedance matching between mismatched electrical circuits to effect maximum power transfer between the circuits.wikipedia. The core material is often a laminated iron core. If a load impedance is connected across the secondary winding. which in North America is typically rated 120/240 volt. The coil that receives the electrical input energy is referred to as the primary winding. resulting in a voltage across the output terminals. An alternating electric current flowing through the primary winding (coil) of a transformer generates an electromagnetic field in its surroundings and a varying magnetic flux in the core of the transformer. the free encyclopedia A transformer is an electrical device that transfers energy between two circuits through electromagnetic induction.org/wiki/Transformer Transformer From Wikipedia. By electromagnetic induction this magnetic flux generates a varying electromotive force in the secondary winding.Transformer . A transformer most commonly consists of two windings of wire wound around a common core to effect tight electromagnetic coupling between the windings. the free encyclopedia http://en. while the output coil is called the secondary winding. [3] Applications Transformers perform voltage conversion. the free encyclopedia http://en. the main energy source was direct current (DC). Basic principles The functioning of a transformer is based on two principles of the laws of electromagnetic induction: An electric current through a conductor.Transformer . which operates at low-voltage high-current. power conversion transformers. distribution. whereas the step-down transformer is used to decrease the secondary voltage relative to the primary voltage. The magnetic field excited in the primary coil gives rise to self-induction as well as mutual induction between coils. transformers can step-up voltage/step-down current from generators to high-voltage transmission lines. produces a magnetic field surrounding the wire. Ideal transformer The assumptions to characterize the ideal transformer are: The windings of the transformer have no resistance. high-frequency. and more energy efficient transmission. Although high voltage transmission systems offered many benefits.Wikipedia. In the early days of commercial electric power. Thus. Regarded as one of the most influential electrical innovations of all time. cheaper. Flux is confined within the magnetic core. This law revealed that even a tiny decrease in current or rise in voltage can cause a substantial lowering in energy losses and costs. In terms of voltage conversion. energy losses are directly proportional to the square of current. and utilization of electrical energy. the future fate of high-voltage alternating current still remained unclear for several reasons: high-voltage sources had a much higher risk of causing severe electrical injuries.org/wiki/Transformer Invention The invention of transformers during the late 1800s allowed for longer-distance. and step-down voltage/step-up current to local distribution circuits or industrial customers. This model differs from real transformers by assuming that the transformer is perfectly constructed and by neglecting that electrical or magnetic losses occur in the materials used to construct the device. Therefore. According to Joule's Law. there is no copper loss in the winding. isolation. it is the same flux that links the input and output 2 of 27 2/24/2014 8:04 PM . such as a wire. isolation protection. The physical principles of the inductive behavior of the transformer are most readily understood and formalized when making some assumptions to construct a simple model which is called the ideal transformer . Transformers range in size from thumbnail-sized used in microphones to units weighing hundreds of tons interconnecting the power grid. the introduction of transformers had successfully reduced the safety concerns associated with alternating current and had the ability to lower voltage to a value that was required by most essential appliances. and hence no voltage drop. Thus. The step-up transformer is used to increase the secondary voltage relative to the primary voltage. audio. A broad range of transformer designs are used in electronic and electric power applications. many essential appliances could only function at low voltage. This self-induction counters the excited field to such a degree that the resulting current through the primary winding is very small when no load draws power from the secondary winding. and a changing magnetic field in the vicinity of a wire induces a voltage across the ends of that wire. and impedance matching.wikipedia. the historical pursuit for a high-voltage low-current electricity transmission system took shape. including miniature. etc. the secondary voltage is smaller than the primary voltage. The circuit diagram (right) shows the conventions used for an ideal. On the other hand. the secondary voltage is greater than the primary voltage. The transformer core does not suffer magnetic hysteresis or eddy currents. Combining the two equations yields the following ideal transformer identity . The resulting input and output apparent power are equal as given by the equation . with voltage ratio and winding turns ratio both being inversely proportional to the corresponding current ratio. which cause inductive loss. Permeability of the core is infinitely high which implies that net mmf (amp-turns) must be zero (otherwise there would be infinite flux) hence IP NP . According to this formalism. VS designates output voltage.[4][5][a][b] VP designates source impressed voltage. Any load impedance ZL connected to the ideal transformer's secondary winding allows energy to flow without loss from primary to secondary circuits. where. respectively.e. This formula is a reasonable approximation for the typical commercial transformer. NP and NS are the number of turns in the primary and secondary windings respectively.Wikipedia. no current flows in the primary winding. i.org/wiki/Transformer windings. lossless and perfectly-coupled transformer having primary and secondary windings with NP and NS turns. If the secondary winding of an ideal transformer has no load. when the number of turns in the primary coil is less than the number of turns in the secondary. when the number of turns in the primary coil is greater than the number of turns in the secondary coil. a is the winding turns ratio.wikipedia.IS NS = 0. The load impedance ZL and secondary voltage VS determine the secondary current IS as follows 3 of 27 2/24/2014 8:04 PM .Transformer . and. Ideal transformer with a source and a load. the value of these ratios being respectively higher and lower than unity for step-down and step-up transformers. the free encyclopedia http://en. The ideal transformer induces secondary voltage VS as a proportion of the primary voltage VP and respective winding turns as given by the equation . wikipedia. Ns is the number of turns in the secondary coil. being equal to the cross-sectional area of the transformer core. The area is constant. If the turns of the coil are oriented perpendicularly to the magnetic field lines. The apparent impedance ZL' of this secondary circuit load referred to the primary winding circuit is governed by a squared turns ratio multiplication factor relationship derived as follows[7][8] . usually iron.org/wiki/Transformer . and dΦ/dt is the derivative[d] of the magnetic flux Φ through one turn of the coil. If ZL = RL where RL is a pure resistance then the power is given by:[9][10] The primary current is given by the following equation:[9][10] Induction law A varying electrical current passing through the primary coil creates a varying magnetic field around the coil which induces a voltage in the secondary winding. The current through a load connected to the secondary winding and the voltage across it are in the directions indicated in the figure. the flux is the product of the magnetic flux density B and the area A through which it cuts. The voltage induced across the secondary coil may be calculated from Faraday's law of induction. Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer. Ideal transformer and induction law whereas the magnetic field varies with time according to the excitation of the primary.[7] the 4 of 27 2/24/2014 8:04 PM . For an ideal transformer. the power supplied to the primary and the power dissipated by the load are equal.Wikipedia.Transformer . The primary and secondary windings are wrapped around a core of very high magnetic permeability. which states that: where Vs is the instantaneous voltage. the free encyclopedia http://en.[c] so that most of the magnetic flux passes through both the primary and secondary coils. and on terminal markings. acting as it does in opposition to the primary voltage. is sometimes termed the counter emf. [13][14][15][e][f] Real transformer The ideal transformer model neglects the following basic linear aspects in real transformers. Core losses.Wikipedia. the free encyclopedia http://en. This relationship is usually denoted by the dot convention in transformer circuit diagrams.Transformer . and Eddy current losses due to joule heating in the core that are proportional to the square of the transformer's applied voltage. The changing magnetic field induces an emf across each winding.[11] The primary emf. that is. which marks the terminals having an in-phase relationship.[12] This is in accordance with Lenz's law. collectively called magnetizing current losses. the real transformer must be viewed as a simple inductor with an impedance Z: 5 of 27 2/24/2014 8:04 PM . the windings in a real transformer have finite non-zero impedances in the form of: Joule losses due to resistance in the primary and secondary windings[18] Leakage flux that escapes from the core and passes through one winding only resulting in primary and secondary reactive impedance. with polarity dot and X1 markings on LV side terminal Hysteresis losses due to nonlinear application of the voltage applied in the transformer core. Polarity The relationships of the instantaneous polarity at each of the terminals of the windings of a transformer depend on the direction the windings are wound around the core. Whereas windings in the ideal model have no impedance. Identically wound windings produce the same polarity of voltage at the corresponding terminals. nameplates. the transformer still behaves as described above in the ideal transformer. If a voltage is applied across the primary terminals of a real transformer while the secondary winding is open without load. As still lossless and perfectly-coupled.org/wiki/Transformer instantaneous voltage across the primary winding equals Taking the ratio of the above two equations gives the same voltage ratio and turns ratio relationship shown above. which states that induction of emf always opposes development of any such change in magnetic field.wikipedia. . consist of[18] Instrument transformer. causing the secondary voltage not to be directly proportional to the primary voltage. the free encyclopedia http://en.75.75 and Z ~ 5%.Wikipedia. particularly under heavy load.000 kVA and 500 kVA units' values being. It can be shown that if the percent impedance (Z) and associated winding leakage reactance-to-resistance (X/R) ratio of two transformers were hypothetically exactly the same. which can incorporate an ideal transformer. In practice. respectively.[19] Transformers are therefore normally Leakage flux of a transformer designed to have very low leakage inductance. It is not directly a power loss. and long magnetic paths. Leakage flux Main article: Leakage inductance The ideal transformer model assumes that all flux generated by the primary winding links all the turns of every winding. the larger unit would carry twice the current).Transformer . X/R ~ 3.000 kVA unit.[19] Such flux is termed leakage flux. the impedance tolerances of commercial transformers are significant. air gaps. Z ~ 5. Nevertheless. especially audio-frequency transformers in circuits that have a DC component flowing in the windings.75%. Also.[25] Winding joule losses and leakage reactances are represented by the following series loop impedances of the model: 6 of 27 2/24/2014 8:04 PM . but results in inferior voltage regulation.[22] Knowledge of leakage inductance is also useful when transformers are operated in parallel.wikipedia. some flux traverses paths that take it outside the windings.g.[12] Leaky transformers may be used to supply loads that exhibit negative resistance. or magnetic bypass shunts may deliberately be introduced in a transformer design to limit the short-circuit current it will supply.org/wiki/Transformer . including itself. However. The combined effect of the leakage flux and the electric field around the windings is what transfers energy from the primary to the secondary.[12] Leakage flux results in energy being alternately stored in and discharged from the magnetic fields with each cycle of the power supply. mercury vapor lamps. and results in leakage inductance in series with the mutually coupled transformer windings. 500 kVA unit in parallel with 1. the transformers would share power in proportion to their respective volt-ampere ratings (e. and neon signs or for safely handling loads that become periodically short-circuited such as electric arc welders. the Z impedance and X/R ratio of different capacity transformers tends to vary. such as electric arcs. to illustrate. X/R ~ 4.[23][24] Equivalent circuit See also: Steinmetz equivalent circuit Referring to the diagram. corresponding 1.[21] Air gaps are also used to keep a transformer from saturating.[20] In some applications increased leakage is desired. it is impossible to eliminate all leakage flux because it plays an essential part in the operation of the transformer. a practical transformer's physical behavior may be represented by an equivalent circuit model. [28] Hypothetically an ideal transformer would work with direct-current excitation. core flux lags the induced emf by 90°.Transformer . though sometimes termed 'exact' equivalent circuit based on linearity assumptions. (NP/NS) 2 = a2.org/wiki/Transformer Primary winding: RP. the flux rises to the point where magnetic saturation of the core occurs.[29] In practice. RS and XS are in practice usually referred to the primary side by multiplying these impedances by the turns ratio squared. and the supply frequency f . However.[25] The resulting model. core cross- 2/24/2014 8:04 PM . and transformer ratio test. causing a large increase in the magnetizing current and overheating the transformer. Core loss and reactance is represented by the following shunt leg impedances of the model: Core or iron losses: RC Magnetizing reactance: XM. winding resistance test. RC and XM are collectively termed the magnetizing branch of the model.[26] With sinusoidal supply. Real transformer equivalent circuit Core losses are caused mostly by hysteresis and eddy current effects in the core and are proportional to the square of the core flux for operation at a given frequency. the relationship for either winding between its rms voltage Erms of the winding. the free encyclopedia http://en. retains a number of approximations.Wikipedia. number of turns N. All practical 7 of 27 Transformer universal emf equation If the flux in the core is purely sinusoidal. Transformer equivalent circuit impedance and transformer ratio parameters can be derived from the following tests: open-circuit test. with the core flux increasing linearly with time. XS. With open-circuited secondary winding. This introduces error but allows combination of primary and referred secondary resistances and reactances by simple summation as two series impedances. XP Secondary winding: RS. In normal course of circuit equivalence transformation. Magnetizing current is in phase with the flux. Basic transformer parameters and construction Effect of frequency The time-derivative term in Faraday's Law shows that the flux in the core is the integral with respect to time of the applied voltage. the relationship between the two being non-linear due to saturation effects.wikipedia. all impedances of the equivalent circuit shown are by definition linear and such non-linearity effects are not typically reflected in transformer equivalent circuits. magnetizing branch current I0 equals transformer no-load current.[26] The finite permeability core requires a magnetizing current IM to maintain mutual flux in the core.[25] Analysis may be simplified by assuming that magnetizing branch impedance is relatively high and relocating the branch to the left of the primary impedances.[g] short-circuit test. transformers may need to be equipped with 'volts per hertz' over-excitation relays to protect the transformer from overvoltage at higher than rated frequency.7 Hz and 25 Hz) than normal utility frequencies (50 – 60 Hz) for historical reasons concerned mainly with the limitations of early electric traction motors. The power dissipated by its load would be equal to the power supplied by its primary source.g. the free encyclopedia http://en. and hysteresis loss. due to several loss mechanisms.wikipedia.[31] Energy losses A theoretical (ideal) transformer does not experience energy losses. and converter equipment being supply by. a real transformer is typically 95 to 99% efficient. For example. such transformers' being restricted to be positioned below the passenger compartment.[29] The emf of a transformer at a given flux density increases with frequency.g. and cooling to establish if safe operation is practical. and those rated for electricity distribution usually perform better than 98%. i.Transformer . Aircraft and military equipment employ waveshape: 400 Hz power supplies which reduce core and winding weight. losses. iron core's magnetic characteristics (red) and magnetizing current (blue). In contrast. it is 100% efficient.[30] Conversely. flux (green). Larger transformers are generally more efficient than small units. The power supply to.Wikipedia.[18] By operating at higher frequencies. the transformers used to step-down the high over-head line voltages (e. such as caused in switching or by lightning. such traction transformers have to accommodate different input frequencies and voltage (ranging from as high as 50 Hz down to 16. core losses. Operation of a transformer at its designed voltage but at a higher frequency than intended will lead to reduced magnetizing current. Large power transformers are vulnerable to insulation failure due to transient voltages with high-frequency components. 15 kV) were much heavier for the same power rating than those designed only for the higher frequencies.e. However. 16. As such. Operation of a transformer at other than its design frequency may require assessment of voltages. properties such as core the following equation can be used for loss and conductor skin effect also increase with half-cycle average voltage Eavg of any frequency. the magnetizing current will increase.[32] 8 of 27 2/24/2014 8:04 PM . leakage flux. winding capacitance. frequencies used for some railway electrification systems were much lower (e.7 Hz and rated up to 25 kV) while being suitable for multiple AC asynchronous motor and DC converters & motors with varying harmonics mitigation filtering requirements. sectional area a in m2 and peak magnetic flux density Bpeak in Wb/m2 or T (tesla) is given by the universal emf equation:[18] Power transformer over-excitation condition caused by decreased frequency. At a lower frequency. One example of state-of-the-art design is traction transformers used for electric multiple unit and high-speed train service operating across the country border and using different electrical standards.org/wiki/Transformer transformers must therefore operate with alternating (or pulsed direct) current. including winding resistance. transformers can be physically more compact because a given core is able to transfer more power without reaching saturation and fewer turns are needed to achieve If the flux does not contain even harmonics the same impedance. [34] [35][36] Eddy current losses Ferromagnetic materials are also good conductors and a core made from such a material also constitutes a single short-circuited turn throughout its entire length. the alternating magnetic field causes fluctuating forces between the 9 of 27 2/24/2014 8:04 PM . hence. good-quality silicon steel. The eddy current loss is a complex function of the square of supply frequency and inverse square of the material thickness.Transformer . losses to increase.org/wiki/Transformer Experimental transformers using superconducting windings achieve efficiencies of 99. Core losses Hysteresis losses Each time the magnetic field is reversed.[34] Transformer losses arise from: Winding joule losses Current flowing through winding conductors causes joule heating. the trade-off is in the additional initial and running cost of the superconducting design. Stray losses Leakage inductance is by itself largely lossless. The no-load loss can be significant. and are responsible for resistive heating of the core material. a small amount of energy is lost due to hysteresis within the core. and so on. Designing energy efficient transformers for lower loss requires a larger core. As transformer losses vary with load. Hysteresis and Eddy current losses are constant at all load levels and dominate overwhelmingly without load.6 for iron.[34] Eddy current losses can be reduced by making the core of a stack of plates electrically insulated from each other. it is often useful to express these losses in terms of no-load loss.wikipedia. skin effect and proximity effect causes winding resistance and. the empirical exponent of which varies from about 1. any leakage flux that intercepts nearby conductive materials such as the transformer's support structure will give rise to eddy currents and be converted to heat. causes it to physically expand and contract slightly with each cycle of the magnetic field. the frictional energy of which produces an audible noise known as mains hum or transformer hum. Mechanical vibration and audible noise transmission In addition to magnetostriction. As frequency increases. or even amorphous steel for the core and thicker wire. Magnetostriction related transformer hum Magnetic flux in a ferromagnetic material. However. so that even an idle transformer constitutes a drain on the electrical supply.[4][37] This transformer hum is especially objectionable in transformers supplied at power frequencies[h] and in high-frequency flyback transformers associated with PAL system CRTs.85%. full-load loss. while variable winding joule losses dominating increasingly as load increases. Eddy currents therefore circulate within the core in a plane normal to the flux. all transformers operating at low frequencies use laminated or similar cores. the free encyclopedia http://en. According to Steinmetz's formula.4 to 1 . increasing initial cost.8 but is often given as 1.[38] There are also radiative losses due to the oscillating magnetic field but these are usually small. rather than a solid block. and. since energy supplied to its magnetic fields is returned to the supply with the next half-cycle. The choice of construction represents a trade-off between initial cost and operating cost. hysteresis loss is thus given by where. the heat energy due to hysteresis is given by .[33] The increase in efficiency can save considerable energy in a large heavily loaded transformer. such as the core.Wikipedia. half-load loss. an effect known as magnetostriction. f is the frequency. η is the hysteresis coefficient and βmax is the maximum flux density. the transformer is shell form. as a general rule.[47] The universal transformer equation indicates a minimum cross-sectional area for the core to avoid saturation. a principle that has remained in use.Transformer . shell form transformers are characterized as having inherently better kVA-toweight ratio.[46] Later designs constructed the core by stacking layers of thin steel laminations.[39] Core form and shell form transformers Closed-core transformers are constructed in 'core form' or 'shell form'. when windings are surrounded by the core.[49] Thin laminations are generally used on high-frequency transformers. At higher voltage and power ratings. better short-circuit strength characteristics and higher immunity to transit damage. 230 kV or 75 MVA). though more labor-intensive to manufacture.org/wiki/Transformer primary and secondary windings. Shell form design may be more prevalent than core form design for distribution transformer applications due to the relative ease in stacking the core around winding coils.[40][41][42][43] Shell form design tends to be preferred for extra high voltage and higher MVA applications because. Thinner laminations reduce losses.[43] Core form = core type.[45] Early transformer developers soon realized that cores constructed from solid iron resulted in prohibitive eddy current losses. and therefore more prevalent. with some of very thin steel laminations able to operate up to 10 kHz.[44] The steel has a permeability many times that of free space and the core thus serves to greatly reduce the magnetizing current and confine the flux to a path which closely couples the windings. and their designs mitigated this effect with cores consisting of bundles of insulated iron wires.[40] Core form design tends to. be more economical. thus amplifying audible transformer hum. the free encyclopedia http://en. This energy incites vibration transmission in interconnected metalwork. shell form transformers tend to be more prevalent. When windings surround the core. Each lamination is insulated from its neighbors by a thin non-conducting layer of insulation.[48] but are more laborious and expensive to construct. than shell form design for high voltage power transformer applications at the lower end of their voltage and power rating ranges (less than or equal to. 10 of 27 2/24/2014 8:04 PM .wikipedia.Wikipedia. shell form = shell type Construction Cores Laminated steel cores Transformers for use at power or audio frequencies typically have cores made of high permeability silicon steel. the transformer is core form. and so reduce their magnitude. Laminated core transformer showing edge of laminations at top of photo The effect of laminations is to confine eddy currents to highly elliptical paths that enclose little flux. nominally. the residual field will cause a high inrush current until the effect of the remaining magnetism is reduced. When power is then reapplied. depending on operating frequency. For frequencies extending beyond the VHF band. 11 of 27 2/24/2014 8:04 PM . forming two C shapes.Transformer . which. usually after a few cycles of the applied AC waveform. the free encyclopedia http://en. and also provides screening to minimize the core's magnetic field from generating electromagnetic interference. The higher initial cost of the core material is offset over the life of the transformer by its lower losses at light load. overhead power transmission lines. The primary and secondary coils are often wound concentrically to cover the entire surface of the core. powdered iron. Power transformer inrush current caused by residual flux at switching instant.[53] A strip construction ensures that the grain boundaries are optimally aligned.[50] Overcurrent protection devices such as fuses must be selected to allow this harmless inrush to pass. It is then cut in two.Wikipedia. is made from a long strip of silicon steel or permalloy wound into a coil. This minimizes the length of wire needed.[21] The cross-section of the ring is usually square or rectangular.org/wiki/Transformer Laminating the core greatly reduces eddy-current losses One common design of laminated core is made from interleaved stacks of E-shaped steel sheets capped with I-shaped pieces. These materials combine high magnetic permeability with high bulk electrical resistivity. On transformers connected to long. but is very economical to manufacture.wikipedia. cores made from non-conductive magnetic ceramic materials called ferrites are common. flux (green).[49] They have the advantage that the flux is always oriented parallel to the metal grains.[52] Solid cores Powdered iron cores are used in circuits such as switch-mode power supplies that operate above mains frequencies and up to a few tens of kilohertz. iron core's magnetic characteristics (red) and magnetizing current (blue).[51] Distribution transformers can achieve low no-load losses by using cores made with low-loss high-permeability silicon steel or amorphous (non-crystalline) metal alloy. A steel core's remanence means that it retains a static magnetic field when power is removed. The cut-core or C-core type is made by winding a steel strip around a rectangular form and then bonding the layers together. improving the transformer's efficiency by reducing the core's reluctance. Toroidal cores Toroidal transformers are built around a ring-shaped core. or ferrite.[49] Such a design tends to exhibit more losses. but more expensive cores with circular cross-sections are also available.[49] Some radio-frequency transformers also have movable cores (sometimes called 'slugs') which allow adjustment of the coupling coefficient (and bandwidth) of tuned radio-frequency circuits. and the core assembled by binding the two C halves together with a steel strap. induced currents due to geomagnetic disturbances during solar storms can cause saturation of the core and operation of transformer protection devices. leading to its name of 'E-I transformer'. reducing reluctance. The closed ring shape eliminates air gaps inherent in the construction of an E-I core. [56] Each strand is individually insulated. As a consequence. A drawback of toroidal transformer construction is the higher labor cost of winding. each portion occupies different relative 12 of 27 2/24/2014 8:04 PM . and weight of inductive components. and so such designs are unsuitable for use in power distribution. Windings Main article: Windings Electronic symbol for Air Cores The conducting material used for the windings depends upon the application. typically between a few tens of kilohertz to hundreds of megahertz. the coils are often wound from enamelled magnet wire. less mechanical hum (making them superior in audio amplifiers). The main disadvantages are higher cost and limited power capacity (see Classification parameters below).[12] The leakage inductance is inevitably high. Small distribution transformers may achieve some of the benefits of a toroidal core by splitting it and forcing it open. and are frequently employed in radio-frequency applications. The air which comprises the magnetic circuit is essentially lossless. Larger power transformers operating at high voltages may be wound with copper rectangular strip conductors insulated by oil-impregnated paper and blocks of pressboard. include smaller size (about half).[12] They have however very high bandwidth. lower exterior magnetic field (about one tenth).[55] For small power and signal transformers. They're also used for resonant transformers such as Tesla coils where they can achieve reasonably low loss in spite of the high leakage inductance. low off-load losses (making them more efficient in standby circuits). and greater choice of shapes. such as Formvar wire. but in all cases the individual turns must be electrically insulated from each other to ensure that the current travels throughout every turn. in which currents are low and the potential difference between adjacent turns is small. Air cores A physical core is not an absolute requisite and a functioning transformer can be produced simply by placing the windings near each other.[28] Large power transformers use multiplestranded conductors as well. then inserting a bobbin containing primary and secondary windings.wikipedia. resulting in very poor regulation.[54] for which a satisfactory coupling coefficient is maintained by carefully overlapping the primary and secondary windings. This is because it is necessary to pass the entire length of a coil winding through the core aperture each time a single turn is added to the coil.[56] High-frequency transformers operating in the tens to hundreds of kilohertz often have windings made of braided Litz wire to minimize the skin-effect and proximity effect losses. to reduce losses. and so an air-core transformer eliminates loss due to hysteresis in the core material. single-bolt mounting. Small toroidal core transformer Ferrite toroidal cores are used at higher frequencies. physical size. compared to laminated E-I types. Other advantages compared to E-I types. or throughout the whole winding.org/wiki/Transformer Toroidal transformers are more efficient than the cheaper laminated E-I types for a similar power level. the free encyclopedia http://en.Wikipedia. since even at low power frequencies non-uniform distribution of current would otherwise exist in high-current windings. Because of the lack of a residual gap in the magnetic path. and the strands are arranged so that at certain points in the winding.Transformer . an arrangement termed an 'air-core' transformer. toroidal transformers also tend to exhibit higher inrush current. lower weight (about half). toroidal transformers rated more than a few kVA are uncommon. Right: C-core. The windings of signal transformers minimize leakage inductance and stray capacitance to improve high-frequency response. and cast coil encapsulation processes. Cooling See also: Arrhenius equation To place the cooling problem in perspective. but E-core would be similar. Top: Equally low capacitance between all ends of both windings. for voltage adjustment. VPE windings are similar to VPI windings but provide more protection against environmental effects. thus increasing resistance to corona. vacuum pressure encapsulation (VPE). Top left: Toroidal transformer. Red: Secondary winding. vacuum and pressure is used to thoroughly seal. Bottom left: Reduction of leakage inductance would lead to increase of capacitance. White: insulator.Transformer . Modulation transformers in AM transmitters are very similar. the accepted rule of thumb is that the life expectancy of insulation in all electric machines including all transformers is halved for about every 7°C to 10°C increase in operating temperature.wikipedia. a combination of heat. dirt or corrosive ambients.[56] Windings are usually arranged concentrically to minimize flux leakage. on equipment such as arc furnace transformers. or for automatic voltage regulators for sensitive loads. Taps may be manually reconnected. The stranded conductor is also more flexible than a solid conductor of similar size. or a manual or automatic switch may be provided for changing taps. have taps to allow adjustment of impedance to each speaker. Bottom: Lowest capacitance for one end of the secondary winding needed for low-power high-voltage transformers. A center-tapped transformer is often used in the output stage of an audio power amplifier in a push-pull circuit.Wikipedia. and eliminate entrained air voids in the winding polyester resin insulation coat layer. the free encyclopedia http://en. by multiple dips including typically in terms of final epoxy coat. The black windings are made of film. usually on the higher voltage winding side.org/wiki/Transformer Power-frequency transformers may have taps at intermediate points on the winding. Black: Primary winding made of oxygen-free copper. Automatic on-load tap changers are used in electric power transmission or distribution. used for the distribution of audio to public address loudspeakers. bind. Dry-type transformer winding insulation systems can be either of standard open-wound 'dip-and-bake' construction or of higher quality designs that include vacuum pressure impregnation (VPI).[57] In the VPI process. positions in the complete conductor.[58] Cut view through transformer windings. aiding manufacture. this life expectancy halving rule holding more narrowly when the increase is between about 7°C to 13 of 27 2/24/2014 8:04 PM . and reduces eddy current losses in the winding itself. Coils are split into sections. Audio-frequency transformers. The transposition equalizes the current flowing in each strand of the conductor. and those sections interleaved between the sections of the other winding. such as from water. Since most cores are at least moderately conductive they also need insulation. Green spiral: Grain oriented silicon steel. or be installed in fire-resistant rooms.[50] Oil-immersed transformer installations usually include fire protection measures such as walls.[59] With a great body of empirical study as a guide. have their windings enclosed in sealed.Transformer .[69] Polychlorinated biphenyls have properties that once favored their use as a dielectric coolant.[59][60][61] Small dry-type and liquid-immersed transformers are often self-cooled by natural convection and radiation heat dissipation.electricenergyonline.Wikipedia.[70] Today.[63] An oil-immersed transformer may be equipped with a Buchholz relay. The conservator (reservoir) at top provides liquid-to-atmosphere isolation as coolant level and temperature changes.[63] Transformer oil is a highly refined mineral oil that cools the windings and insulation by circulating within the transformer tank. non-toxic. Another protection means consists in fast depressurization systems (http://www. Some large transformers employ electric fans for forced-air cooling.[73] Some transformers. the maximum allowable level of PCB contamination in existing mineral oil transformers being 50 ppm. is used to either alarm or de-energize the transformer. transformers are often cooled by forced-air cooling.[68][71] PCBs for new equipment was banned in 1981 and in 2000 for use in existing equipment in United Kingdom[72] Legislation enacted in Canada between 1977 and 1985 essentially bans PCB use in transformers manufactured in or imported into the country after 1980. transformer oil testing including dissolved gas analysis provides valuable maintenance information. the free encyclopedia http://en. [64][65] Prolonged operation at elevated temperature degrades insulating properties of winding insulation and dielectric coolant.[66][67] Building regulations in many jurisdictions require indoor liquid-filled transformers to either use dielectric fluids that are less flammable than oil. pumps for forced-liquid cooling. forecast and manage oil and winding conductor insulation temperature conditions under varying. though concerns over their environmental persistence led to a widespread ban on their use.org/wiki/Transformer 8°C in the case of transformer winding cellulose insulation.wikipedia. model. which. watercooling.com/?page=show_article& article=362) which are activated by the first dynamic pressure peak of the shock wave. which not only shortens transformer life but can ultimately lead to catastrophic transformer failure.[68] Air-cooled dry transformers can be more economical where they eliminate the cost of a fire-resistant transformer room. It is estimated that 50% of power transformers will survive 50 years of use. oil containment. The walls and fins provide required heat dissipation balance. Cutaway view of liquidimmersed construction transformer. that the average age of failure of power transformers is about 10 to 15 years. pressurized tanks and 14 of 27 2/24/2014 8:04 PM . avoiding transformer explosion before static pressure increases. As power ratings increase. The mineral oil and paper insulation system has been extensively studied and used for more than 100 years. stable silicone-based oils. depending on severity of gas accumulation due to internal arcing. The tank of liquid filled transformers often has radiators through which the liquid coolant circulates by natural convection or fins. or fluorinated hydrocarbons may be used where the expense of a fire-resistant liquid offsets additional building cost for a transformer vault. and fire-suppression sprinkler systems. or combinations of these. This underlines the need to monitor. and that about 30% of power transformer failures are due to insulation and overloading failures. power loading conditions. Many explosions are reported to have been avoided thanks to this technology.[62] Large transformers are filled with transformer oil that both cools and insulates the windings. instead of being liquid-filled. or have heat exchangers for water-cooling. possibly difficult. forced-oil cooling. . step-down. 6-pulse. forced air-cooled. isolation.various possible two-winding combinations of the phase designations delta. Frequency range: Power-frequency.self-cooled.forced oil-cooled. wye or star. amplifier output. which eliminates winding losses without affecting core losses. [n-1]*6-pulse. zigzag grounding transformer winding. polygon.Transformer . short-time. water-cooled.autotransformer.[74][75] Insulation drying Construction of oil-filled transformers requires that the insulation covering the windings be thoroughly dried of residual moisture before the oil is introduced.000 kVA range have been built with liquid nitrogen or helium cooled superconducting windings. The method is called low-frequency heating (LFH) since the current used is at a much lower frequency than that of the power grid.[78] Classification parameters Transformers can be classified in many ways. Constant-potential transformer descriptor : Step-up. resistance heating by injection of current into the windings is used. Basic magnetic form: Core form. Although they all share the 15 of 27 2/24/2014 8:04 PM . liquid-immersed . the free encyclopedia http://en. 3-winding. such as the following: Power capacity: From a fraction of a volt-ampere (VA) to over a thousand MVA. or radio-frequency. etc. so the voltage required can be reduced.[i] other . Utilization: Pulse. A lower frequency reduces the effect of inductance. Types Various specific electrical application designs require a variety of transformer types. Voltage class: From a few volts to hundreds of kilovolts. and may also be required as a field service. which is normally 50 or 60 Hz. . For small transformers. periodic. General winding configuration: By EIC vector group . intermittent.. Scott-T. Drying may be done by circulating hot air around the core. Cooling type: Dry and liquid-immersed .Wikipedia. audio-frequency.wikipedia. shell form. distribution. Circuit application: Such as power supply. Drying is carried out at the factory. Duty of a transformer : Continuous. 12-pulse. arc furnace. and it is energy efficient.[79][80][81][82] Rectifier phase-shift winding configuration: 2-winding. n-winding. varying. and zigzag or interconnected star. .[77] Bushings Larger transformers are provided with high-voltage insulated bushings made of polymers or porcelain.. output voltage and current stabilizer or circuit isolation. etc. power.[71] Experimental power transformers in the 500-to-1. impedance matching.org/wiki/Transformer cooled by nitrogen or sulfur hexafluoride gas. The heating can be controlled very well. rectifier. or by vapor-phase drying (VPD) where an evaporated solvent transfers heat by condensation on the coil and core.[76] The LFH drying method is also used for service of older transformers. A large bushing can be a complex structure since it must provide careful control of the electric field gradient without letting the transformer leak oil. [86] to a higher voltage transformers enable economical transmission of power and distribution. a zigzag grounding winding. they are customize in construction or electrical properties for certain installation requirements or circuit conditions. transformers have shaped the electricity supply industry. the free encyclopedia http://en.[83] Polyphase transformer: Any transformer with more than one phase.wikipedia. Autotransformer : Transformer in which part of the winding is common to both primary and secondary circuits. Grounding transformer : Transformer used for grounding three-phase circuits to create a neutral in a three wire system. Resonant transformer : Transformer that uses resonance to generate a high secondary voltage.[38] 16 of 27 2/24/2014 8:04 PM . Audio transformer : Transformer used in audio equipment.Wikipedia.[80][85] or more commonly. using a wye-delta transformer.Transformer .[83] Applications Transformers are used to increase voltage before transmitting electrical energy over long distances through wires. [80][82][83] Leakage transformer: Transformer that has loosely coupled windings.[83] Capacitor voltage transformer : Transformer in which capacitor divider is used to reduce high voltage before application to the primary winding. By Canada showing 3 of 5 220kV/66kV transformers. Wires have resistance which loses energy through joule heating at a rate corresponding to Transformer at the Limestone square of the Generating Station in Manitoba. current or phase position of high voltage or high power circuits. Instrument transformer : Potential or current transformer used to accurately and safely represent voltage. An electrical substation in Melbourne.[87] All but a tiny fraction of the world's electrical power has passed through a series of transformers by the time it reaches the consumer.org/wiki/Transformer basic characteristic transformer principles. power transformer : International standards make a distinction in terms of distribution transformers being used to distribute energy from transmission lines and networks for local consumption and power transformers being used to transfer electric energy between the generator and distribution primary circuits.[83][84][j] Phase angle regulating transformer : A specialised transformer used to control the flow of real power on three-phase electricity transmission networks. Consequently. permitting generation to be located remotely from points of demand. Output transformer : Transformer used to match the output of a valve amplifier to its load. Distribution transformer. Australia current. Scott-T transformer: Transformer used for phase transformation from three-phase to two-phase and vice versa. each with transforming power a capacity of 150 MVA. Ireland in 1836. First alternating current transformers By the 1870s. Although Henry's work likely having preceded Faraday's work by a few months. History Discovery of induction Electromagnetic induction. Induction coils The first type of transformer to see wide use was the induction coil. Since batteries produce direct current (DC) rather than AC. including winding a pair of coils around an iron ring. Faraday was the first to publish the results of his experiments and thus receive credit for the discovery. mostly by trial and error.[89] The relationship between emf and magnetic flux is an equation now known as Faraday's law of induction: .wikipedia. 17 of 27 2/24/2014 8:04 PM . Audio transformers allowed telephone circuits to carry on a two-way conversation over a single pair of wires. Between the 1830s and the 1870s. Induction coils evolved from scientists' and inventors' efforts to get higher voltages from batteries. thus creating the first toroidal closed-core transformer. A balun transformer converts a signal that is referenced to ground to a signal that has balanced voltages to ground. efficient generators producing alternating current (AC) were available. the larger the induced secondary emf will be.[91] However he only applied individual pulses of current to his transformer. such as between external cables and internal circuits. the free encyclopedia http://en.[90] coils of wire[88] Faraday performed the first experiments on induction between coils of wire.Wikipedia. the principle of the operation of the transformer. slowly revealed the basic principles of transformers. without an interrupter. invented by Rev. efforts to build better induction coils. The transformer also electrically isolates the end user from contact with the supply voltage. and it was found AC could power an induction coil directly. induction coils relied upon vibrating electrical contacts that regularly interrupted the current in the primary to create the flux changes necessary for induction.org/wiki/Transformer Transformers are also used extensively in electronic products to step-down the supply voltage to a level suitable for the low voltage circuits they contain. Nicholas Callan of Maynooth College. was discovered independently and almost simultaneously by Joseph Henry and Michael Faraday in 1831.Transformer . He was one of the first researchers to realize the more turns the secondary winding has in relation to the primary winding. and never discovered the relation between the turns ratio and emf in the windings. Faraday's experiment with induction between where is the magnitude of the emf in volts and ΦB is the magnetic flux through the circuit in webers. Signal and audio transformers are used to couple stages of amplifiers and to match devices such as microphones and record players to the input of amplifiers. had determined that open-core devices were impracticable.[46] They also exhibited the invention in Turin. but within a decade.[92] In 1878. a position in which they have remained dominant ever since. 11. Ottó Bláthy and Miksa Déri (ZBD). the free encyclopedia http://en.4 A. and other equipment. the Ganz factory. 18 of 27 2/24/2014 8:04 PM .[95] Faraday's ring transformer Early series circuit transformer distribution Induction coils with open magnetic circuits are inefficient at transferring power to loads. 1884.org/wiki/Transformer In 1876. The secondary windings could be connected to several 'electric candles' (arc lamps) of his own design. they described two designs with closed magnetic circuits where copper windings were either a) wound around iron wire ring core or b) surrounded by iron wire core. the efficiency of their open-core bipolar apparatus remained very low.[98] In their joint 1885 patent applications for novel transformers (later called ZBD transformers).[40][41][99][100] The Ganz factory had also in the autumn of 1884 made delivery of the world's first five high-efficiency AC transformers. the paradigm for AC power transmission from a high voltage supply to a low voltage load was a Induction coil.[92] [93] The coils Yablochkov employed functioned essentially as transformers. Russian engineer Pavel Yablochkov invented a lighting system based on a set of induction coils where the primary windings were connected to a source of AC.[95] However. 120:72 V. 1900. the first of these units having been shipped on September 16. Until about 1880.6:19.[101] This first unit had been manufactured to the following specifications: 1. three engineers associated with the Ganz factory. which can as a class all be termed as either core form or shell form (or alternatively. Károly Zipernowsky. as in a) or b).Wikipedia. Budapest. series circuit. and in seeing AC distribution systems triumph over their DC counterparts.[95] The two designs were the first application of the two basic transformer constructions in common use to this day. respectively (see images). where it was adopted for an electric lighting system. as they were incapable of reliably regulating voltage.[95] Efficient.400 W. Italy in 1884. Bremerhavn. Open-core transformers with a ratio near 1:1 were Germany connected with their primaries in series to allow use of a high voltage for transmission while presenting a low voltage to the lamps. had installed over fifty systems in Austria-Hungary.[96] Closed-core transformers and parallel power distribution In the autumn of 1884. then sold the idea to the Westinghouse company in the United States. The inherent flaw in this method was that turning off a single lamp (or other electric device) affected the voltage supplied to all others on the same circuit. Their AC systems used arc and incandescent lamps. Hungary. practical transformer designs did not appear until the 1880s. core type or shell type). generators. by 1883. Many adjustable transformer designs were introduced to compensate for this problematic characteristic of the series circuit.Transformer . 40 Hz.wikipedia. began manufacturing equipment for electric lighting and. including those employing methods of adjusting the core or bypassing the magnetic flux around part of a coil. the transformer would be instrumental in the War of Currents.[94] Lucien Gaulard and John Dixon Gibbs first exhibited a device with an open iron core called a 'secondary generator' in London in 1882. 4 times more efficient than the open-core bipolar devices of Gaulard and Gibbs.67:1.[109][110] In 1886. front.[101] In both designs. the magnetic flux linking the primary and secondary windings traveled almost entirely within the confines of the iron core. it was granted in July 1887.[105][108] although the term had already been in use by 1882. the free encyclopedia http://en. and straight iron plates laid in to create a closed magnetic circuit. back. closed-core transformers finally made it technically and economically feasible to provide electric power for lighting in homes.[111] Although George Westinghouse had bought Gaulard and Gibbs' patents in 1885. and Déri had performed the experiments. businesses and public spaces. consisting of a stack of thin 'E‑shaped' iron plates. requiring Westinghouse to pursue alternative designs on the same principles. utilization loads. The new transformers were 3.000 V) than the voltage of utilization loads (100 V initially preferred).[107][114] The ZBD team consisted of Károly Zipernowsky. Westinghouse.[102] The ZBD patents included two other major interrelated innovations: one concerning the use of parallel connected. Ottó Bláthy and Miksa Déri Other early transformers 19 of 27 2/24/2014 8:04 PM . one-phase.[97] This design[113] was first used commercially in the US in 1886[96] but Westinghouse was intent on improving the Stanley design to make it (unlike the ZBD type) easy and cheap to produce. with no intentional path through air (see Toroidal cores below).[107] Transformers today are designed on the principles discovered by the three engineers.wikipedia. instead of series connected. [103][104] When employed in parallel connected electric distribution systems. the steampowered Rome-Cerchi power plant.400 to 2.[112] Stanley's first patented design was for induction coils with single cores of soft iron and adjustable gaps to regulate the emf present in the secondary winding (see image). shell form.[113] Shell form transformer. the Edison Electric Light Company held an option on the US rights for the ZBD transformers. the other concerning the ability to have high turns ratio transformers such that the supply network voltage could be much higher (initially 1. Sketch used by Uppenborn to describe ZBD engineers' 1885 patents and earliest articles. the ZBD engineers designed. insulated by thin sheets of paper or other insulating material. Stanley and associates soon developed an easier to manufacture core. Earliest specimens of ZBD-designed high-efficiency constant-potential transformers manufactured at the Ganz factory in 1885.Transformer . and the Ganz factory supplied electrical equipment for. Westinghouse applied for a patent for the new low-cost design in December 1886. shell form. He assigned to William Stanley the task of developing a device for commercial use in United States. They also popularized the word 'transformer' to describe a device for altering the emf of an electric current.[105][106] Bláthy had suggested the use of closed cores.org/wiki/Transformer ratio 1.Wikipedia.[95] Core form. the world's first power station that used AC generators to power a parallel connected common electrical network. Prewound copper coils could then be slid into place. Zipernowsky had suggested the use of parallel shunt connections. The designated terminals H1.Wikipedia. ^ The expression dΦ/dt.[17] g. the word 'instantaneous' differentiating from say phasor current. c. namely.80. frequencies. (and Y1. by the 100 & 300 Hz. Z1 if available) indicate same instantaneous polarities for each winding as in the dot convention. Z1.Y2. the free encyclopedia http://en. ^ A standardized open-circuit or unloaded transformer test called the Epstein frame can also be used for the characterization of magnetic properties of soft magnetic materials including especially electrical steels. n for neutral of the wye winding. Nikola Tesla invented the Tesla coil.Z3.[16] f.[37] i. ^ A step-down transformer converts a high voltage to a lower voltage while a step-up transformer converts a low voltage to a higher voltage. Dyn11 denoting D for delta primary winding.X1. j. d. the delta-wye transformer.X2. an air-cored. e. on primary terminals and X1. (and Y1. ANS Requirements for Instrument Transformers.12. b. defines polarity as the 'designation of the relative instantaneous directions of the currents entering the primary terminals and leaving the secondary terminals during most of each half cycle'.H1. ^ Transformer windings are usually wound around ferromagnetic cores but can also be air-core wound. Russian-born engineer Mikhail Dolivo-Dobrovolsky developed the first three-phase transformer at the Allgemeine ElektricitätsGesellschaft ('General Electricity Company') in Germany. ^ Transformer hum's fundamental noise frequency is two times that of the power frequency as there is an extension and a contraction of core laminations for every cycle of the AC wave and a transformer's audible hum noise level is dominated by the fundamental noise frequency and its first triplen harmonic.Transformer . ^ For example.13. dual-tuned resonant transformer for generating very high voltages at high frequency.[115] In 1891. 20 of 27 2/24/2014 8:04 PM . ^ Transformer polarity can also be identified by terminal markings H0.[27] h. derived from standards such as IEEE C57. ^ "The turn ratio of a transformer is the ratio of the number of turns in the high-voltage winding to that in the low-voltage winding".. ^ While the above formal definition. and 11 for relative phase position on the clock by which the secondary winding leads the primary winding. is known as the Dyn11 vector group configuration. provides a measure of rate of magnetic flux in the core and hence of emf induced in the respective winding.[116][117] See also Magnetization Inductor Polyphase system Load profile Magnetic core Geomagnetic storm Paraformer Rectiformer Switched-mode power supply Electronic symbol Stanley's 1886 design for adjustable gap open-core induction coils[97] Notes a.wikipedia.Z2.. or 120 & 360 Hz. defined as the derivative of magnetic flux Φ with time t. 30° leading.. i. applies to large transformers. by far the most common commercial three-phase transformer..org/wiki/Transformer In 1889.H2. y for wye secondary winding. if windings are available) on secondary terminals. an isolation transformer having 1:1 turns ratio with output voltage the same as input voltage.. ^ ANSI/IEEE C57.[6] common usage having evolved over time from 'turn ratio' to 'turns ratio'. Each letter prefix designates a different winding and each numeral designates a termination or tap on each winding.e. wikipedia.com/?id=fR1rNJhBbmcC& pg=PA72&lpg=PA72& dq=dot+convention+polarity+of+transformer#v=onep age& q=dot%20convention%20polarity%20of%20transfor mer&f=false) (4th ed.1.). K. (1984). ISBN 0-7506-1158-8. §6-13.com/downloads/products /0071467890/0071467890_ch15. Martin (Nov 3. (2002). ^ Tcheslavski. Egon. "Chapter 15 .org/wiki/Transformer it is not uncommon in colloquial.ca/books/about /Analysis_of_electric_circuits. Networks of Power: Electrification in Western Society. ^ Brenner.google. 11. University of Denver.. ^ Edwards. pp. Kay (2001). "New Understanding: Physics for Advanced Level (4th Edition)".. Power Transformer Principles and Applications. [Thomas Nelson and Sons Ltd]. pp. 1017. ^ a b c d Say.Transformers (http://books. 9.edu. pp. ISBN 0071467890.).Transformers". Ula.3 'The Ideal Transformer' " (http://books.google. 20–21. Jr. (Ed.Polarity" (http://www. In Whitaker.. 300–320. 2007.pdf). 20. "Slide 13 Impedance Transformation in Lecture 4: Transformers". 6–42.) (1949). References 1.htm). Alternating Current Machines (5th ed. CRC. ^ "Connections . ISBN 0-07-021291-0. New York: McGraw-Hill. and so on. The Lineman's and Cableman's Handbook (11th ed. 14. A.pdf). M. "The World of Physics". Javid. 18.). 589–590. 15.. "§2. (2005).7 'Transformer Testing' in Chapter 3 . 5. §3.google. 1–2. ELEN 3441 Fundamentals of Power Engineering. 119–122. 6. T. Lamar University (TSU system member). p.E. "§3. Taylor & Francis. D. (2000). ^ Heathcote.5 'Transformers' & §10. The Electronics Handbook (2nd ed.ca /books?id=FdSQSAC3_EwC&pg=PA1017& lpg=PA1017& dq=transformer+polarity+dot+convention& source=bl&ots=V_ULeEEk6t& sig=SFYhwdztWIVTr1yK6hQc-LOKL44&hl=en& sa=X&ei=37E_Uf-DDsipqgHtpIHwBA& ved=0CEAQ6AEwAw#v=onepage& q=transformer%20polarity%20dot%20convention& f=false).au/~aupec/aupec00 /edwards00. [Stanley Thornes (Publishers) Ltd].uq.cromptonusa. James E. 13. Saha. R. (1984). pp. 172.du. 2–3. ISBN 0-8493-1889-0.5. G. (2008). Standard Handbook for Electrical Engineers (8th ed. RWTH Aachen University Institute of Electrical Machines. Tata McGraw-Hill. S. 17. ^ Hameyer.com/?id=g07Q9M4agp4C& pg=PA122&lpg=PA122& dq=westinghouse+%22universal+system%22). 8. 3.J. Queensland University of Technology. ISBN 978-0-07-069967-0. parlance for small general-purpose transformers to be referred to as 'power' transformers.1 'Symbols and Polarity of Mutual Inductance' in Chapter 18 . ISBN 0-470-27451-4.Transformer . ^ Knowlton. J. 1880–1930 (http://books. 73. pp. pp.Wikipedia.). E. 4. 300–320. ^ a b Flanagan. ISBN 0-8018-4614-5.P. ^ a b c d e Calvert. Gleb V.html?id=V4FrAAAA MAAJ&redir_esc=y).pdf). McGraw-Hill. Newnes.).google. William M. McGraw-Hill. p. "Inside Transformers" (http://www. 21. ^ a b Winders. 12. G. 10. "§18. I. 2. P. AUPEC 2000 Proceedings.). pp. Thomas (2006). Webb. ^ "Polarity Markings on Instrument Transformers" (http://www. 485 21 of 27 2/24/2014 8:04 PM . John J. M. ISBN 0-13-257601-5. ^ Parker. Retrieved 13 April 2013. Design. 27. 19. ^ Kothari. 1998). ^ a b Jim Breithaupt (2000). Halsted Press. p.itee. p. Retrieved May 19. Nagrath. for distribution transformers to be referred to as 'power distribution' transformers.edu/~jcalvert /tech/transfor. 16. Fig. 597. Baltimore: Johns Hopkins University Press. Elementary Electric Power and Machines. W. pp. ^ Knowlton.2 'Definition of Transformer Ratio' in Section 3 .gedigitalenergy. 15–1 to 15–22. the free encyclopedia http://en. Retrieved 13 April 2013. Function. James (2001). ^ Mack.com /Polarity%20on%20Transformers. ^ a b John Avison (1989). J & P Transformer Book (12th ed. Hughes (1993).). (2010). (1993).pdf). pp. ^ Thomas P. Shoemaker. Mansour (1959). ^ a b Say. p. 552 7. or even trade. Jerry C. ^ a b McLaren.mcgraw-hill. "Power Flow in Transformers Via the Poynting Vector" (http://www. Operation. Electrical Machines I: Basics. McGraw-Hill. Analysis of Electric Circuits.Circuits with Magnetic Circuits" (http://books. Handbook of Transformer Design & Applications (2nd ed. pp. 68–74.com/products /buyersguide/ct_sc.Distribution Transformers" (http://books.. J. doi:10. 25. pp.S..com/news/2008/04/23 /must_concerned_with_transformers_9639. IEEE Transactions on Power Apparatus and Systems. ISBN 0-08-030573-3. V. ISBN 0-8247-5653-3. p. S. U. p. Barton.jsp?isnumber=4072786& arnumber=4072800&count=25&index=12). 562 42. 47–49. CRC.1963. pp. Magnetics Design Handbook. the free encyclopedia http://en. CRC. Function. S.doi. Electronic and Radio Engineering (4th ed. pp. (Jan. Electrical Apparatus. 44. Fig. ^ IEC Std 60404-2 Magnetic Materials . McGraw-Hill. P.1049/pe:19910004 (http://dx.1963. 3. pp. ^ a b Knowlton.1049%2Fpe%3A19910004). 38. Aerospaceweb.). ^ Hindmarsh. p. 45.. "Power Transformer Design" (http://focus.. 49 (§2. Maintenance. 2012. 47. Engineering and Design .org/wiki/Transformer 22. "Why We Must Be Concerned With Transformers" (http://www.194. ^ Kulkarni. .ieee. "Chapter 4 . pp.iec. of the Interior. 46.pdf). (2004). ISBN 0-88173-311-3.Hydroelectric Power Plants Electrical Design.67) & 323 (§4. doi:10. Introduction to Electrical Machines. Roach. ISBN 0-7506-3992-X. Transformer and Inductor Design Handbook. pp. ^ a b Billings. Nadel. Opportunities for New Appliance and Equipment Efficiency Standards (http://www. 31.291359). ^ a b Allan. 39. A. 32. p.com/literature/drytrans /10transformernoise. ^ Knowlton. ^ a b Nailen. 585-586 24.org /10. 9–14. et al.8. Texas Instruments. "Transformers: Basics. 23. Kay (2001).1109/TPAS. D. ^ a b c d McLyman.com/index. Boca Raton: CRC Press. Bureau of Reclamation.google. "Steinmetz's Formula for Magnetic Hysteresis" (http://www. Richard (May 2005).ieee. 10–11. ^ a b c Heathcote.csa. 26.html).I. (May 24.. 23. Chap. S. Transformer Engineering: Design and Practice.J. 48.pdf). (1999). Anthony J. ^ Kubo. J. "Electrical Machines I: Basics. ^ Hindmarsh. Eckels. ^ Haymeyer. 142-143 27. 1991). Operation". H.org/researchreport/a016). Transformer Design Principles: With Applications to Core-Form Power Transformers (http://books. 22 of 27 2/24/2014 8:04 PM .pdf). ISBN 90-5699-703-3. (June 1963).316682).1109%2FTPAS.ti. Retrieved 7 February 2013. 29.1981.org /xpl/freeabs_all.access.1981. 30. Sachs. ^ a b c Del Vecchio. ISBN 0-07-006719-8. U.. A.nsf /mysearchajax?Openform&key=60404-2&sorting=& start=1&onglet=1) 28. 2009. 43. (1955). Lloyd (2001). (http://webstore. pp. 37. 4. Colonel Wm. 33.jsp?arnumber=61984).gpo. 41-42 35. p. "Natural Frequencies of 3-Phase Transformer Windings" (http://ieeexplore. Electrical Machines and Their Applications. Retrieved June 21.doi. Keith (1999). J. 36–37. 39. Murphy. Electrical Transformers and Power Equipment. ^ Gururaj. 15.pdf). Retrieved May 21. doi:10. pp.Wikipedia. R.shtml). Retrieved Mar 27. New York: McGraw-Hill.. Khaparde. D. Robert M. ^ a b c Daniels.ch/webstore/webstore. ^ a b Say. Army Corps of Engineers. T.com/lit/ml/slup126 /slup126. Irving (1998). Fairmont Press. 29–31.Part 2: Methods of Measurement of the Magnetic Properties . 40. American Council for an EnergyEfficient Economy. ^ EE-Reviewonline. 41.316682 (http://dx.1109%2FTPAS. 29-31 49. pp. Power Engineering Journal 5 (1): 5–14. 1.org /10. Design. ^ a b EM 1110-2-3006 (1994).291359 (http://dx. Newnes. and Diagnostics" (http://permanent.com/?id=Lzjs0LNHhVYC). ^ a b Dixon.com. ^ Terman.php?requester=gs&collection=TRD& recid=0043264EA& q=superconducting+transformer&uid=790516502& setcookie=yes). "Power Transformers – The Second Century" (http://ieeexplore.org/question/electronics /q0219. (1981). p.com/partners /viewrecord. 34. 39.gov /lps113746/Trnsfrmr. pp. . M.org/10. Retrieved 30 January 2013. (2002). ^ "400 Hz Electrical Systems" (http://www..Transformer .blnz.1109/TPAS.org /xpl/freeabs_all. (2001). ^ Pansini.org. (1984).php?option=com_content& view=article&id=534%3Asteinmetzs-formulafor-magnetic-hysteresis&catid=65%3Amagneticcircuits&Itemid=44). Switchmode Power Supply Handbook.eereviewonline.wikipedia. ^ Hydroelectric Research and Technical Services Group. FP. ^ a b "Understanding Transformer Noise" (http://www. ISBN 0-8247-5393-3.279) 36. 2007. PAS-100 (7): 3398. RWTH Aachen University Institute of Electrical Machines. ^ Knowlton. Dept. "Application of Superconducting Technology to Power Transformers" (http://md1.. B. Practical Transformer Handbook. 4-1. 12.S. Litz.aerospaceweb. p.76.federalpacific. H. ^ Riemersma.doi. T.Power Transformers" (http://140.aceee. Frederick E. p. IEEE Transactions on Power Apparatus and Systems 82 (66): 318–329. Oxford: Pergamon Press.129/publications /eng-manuals/em1110-2-3006/c-4. 2004). ^ Gottlieb. ti. 67. 2 . 6). H. 61. 1 54.pdf).cindmz.pdf). Chap. EC&M. 215-216: 240–245.wikipedia. Pergamon Press. 71.8. Retrieved 30 January 2013. Electronic Transformers and Circuits.hsb. ^ Hasegawa. Retrieved Mar 30. p. ^ a b Willis. et al (2001). Pirjola. Jim.1.gepower. William H. "Permissible Temperatures for Insulation" (http://www. Jr. 2007.uncp.com/releases/2013/6 /prweb10836945. "Analysis of Transformer Failures" (http://www.).atsdr.1016%2FS0304-8853%2800%2900126-8). Harlow (ed.E. (~2011). 58. G. p. et al. ^ Walling.aspx?id=191).com/lit/ml /slup197/slup197. "§3. 65.doi. "Air-Core Transformers" (http://www.pdf).vias.pe/newfacultades /ingenieriasarqui/newelectrica/phocadownload /descargas /E%20BOOK%20Electric%20Power%20Transforme r%20Engineering. ^ Hartley.Transformer . Shattuck.bplglobal. p. The Electric Power Engineering Handbook (Online ed. Nevanlinna. Retrieved 11 February 2013.cn /huiyi/Seminar%202006%20New%20Mexico /2006prevostpaperyes. the free encyclopedia http://en.pdf). L.cdc.htm 70. CRC Press.. ^ McLyman. CRC Press. §2. pp. Grigsby (Series ed. The Locomotive. 7 (fig. ^ Sen. L.7 & §2. doi:10. ^ Lane. H. pp. H. 62. The Scope for Energy Saving in the EU Through the Use of Energy-Efficient Electricity Distribution Transformers (http://www. §3. doi:10.1 Power Transformers in Chap. Weidmann. The Electric Power Engineering Handbook (Online ed.K. ISBN 0-8493-8578-4.H. H. CRC Press. "The Effects of Geomagnetic Disturbances On Electrical Systems at the Earth's Surface". L. Bruce (May 2007).1. 403. 51. p. p.). Lee (2004). Journal of Magnetism and Magnetic Materials. ^ a b De Keulenaer.pdf)..4 Load and Thermal Performance in Chap. "§2. 66.seai. L. "Distribution Transformer Thermal Behaviour and Aging in Local-Delivery Distribution Systems" (http://www. p. (1998). ^ a b Sim. 36th Annual Conference of the International Association of Engineering Insurers. Retrieved May 22. 3 . "PSERC Pub. Retrieved 30 January 2013. Eddy Current Losses in Transformer Windings (http://focus.Ancillary Topics" (http://www. ^ Heathcote. Robert F. (2004).org/eltransformers /lee_electronic_transformers_07b_22. Power Distribution Planning Reference Book. ^ Dixon. 3 p. 2001. Modern Power Station Practice. Grigsby (Series ed. 64.). Retrieved 12 February 2013.1016/S0304-8853(00)00126-8 (http://dx. 69. E. ^ a b c Central Electricity Generating Board (1982). pp. 57. 1. (1997).pe/newfacultades /ingenieriasarqui/newelectrica/phocadownload /descargas /E%20BOOK%20Electric%20Power%20Transforme r%20Engineering. ^ Lee.edu. Ryusuke (June 2.).4.6.com. 2000). 60. 55. ^ Pansini. Power Systems Engineering Research Center.2. Advances in Space Research 22: 17–27..org/wiki/Transformer 50. Retrieved June 10. Arizona State University. (Nov 2006). "Present Status of Amorphous Soft Magnetic Alloys". "An Analysis of Transformer Failures.1. et al.ie/Archive1 /Files_Misc/REP009THERMIEFinalreport.html). Scott H. P. ^ "ASTDR ToxFAQs for Polychlorinated Biphenyls" (http://www.weidmann-solutions. 720–723 59.1016/S0273-1177(97)01096-X (http://dx.org/kimberlyee /ee_14_11.edu. Reuben.uncp. In James H. R2–1–to–R2–10.wisc. Retrieved 29 January 2013. Texas Instrument. Keith (2007).net /eng/knowledge-center/download. ^ Prevost.1016%2FS0273-1177%2897%2901096-X). ^ a b Kulkarni. Retrieved 11 January 2013. Harlow (ed.pdf).doi. Digby.aspx). Institution of Engineering and Technology. D. 2007. 52.pdf).edu/documents/publications /reports/2011_reports/Sen_T25_Final_Report_Feb_2011.org /10. (2011).asp?id=140& tid=26).). 11-02 Transformer Overloading and Assessment of Loss-of-Life for Liquid-Filled Transformers" (http://www.Equipment Types" (http://www. In James H. William H.pserc.gov/toxfaqs/tf. J.com/TheLocomotive /AnAnalysisOfTransformerFailuresPart1. R. 2-3 23 of 27 2/24/2014 8:04 PM . 19th International Conference on Electricity Distribution. Reigh. Thomas A. ^ Kimberly. ^ Boteler.com/content /basics-large-dry-type-transformers). Part 1 – 1988 through 1997" (http://www. "The Basics of Large Dry-Type Transformers" (http://ecmweb.html). ISBN 0-8247-4875-1. 53. (2004). 32 63.Wikipedia.prweb. ^ http://www.org /10. 2012. ISBN 0-8493-8578-4. L.gecompany. (2003).). "Estimation of Insulation Life Based on a Dual Temperature Aging Model" (http://www. ^ a b Tillman. 68.vias. Paper 0720.com /prod_serv/plants_td/en/downloads /cired_dist_transformer. 56. ^ Hartley. H. 8–10. Schneider.1834. Retrieved 18 January 2013.. ^ Mehta. ISBN 0-07-02974-x Check |isbn= value (help). "Section 6 Grounding Systems" (http://static.ec. 79. doi:10. 75. p. 90.html). the free encyclopedia http://en. R.1109%2FPAPCON.com.google. ^ AEMO et al.org/details/philtrans08694360). 1 88. "Discussion of Class I & II Terminology" (http://grouper. Wayne (Eds.pdf). Mass.0008).1109%2F6. ^ a b Beltz. Elisa et al (Jan/Feb 2009). (2012).jsp%3F arnumber%3D854186).nas.wikipedia. ^ AFBI (2011). 78. McGraw Hill.org/10. ^ Fink. ISBN 0-85296-775-6. 2012. 80.afbini. p. J.1109/PAPCON. "Joint Consultation Paper Western Metropolitan Melbourne Transmission Connection and Subtransmission Capacity" (http://jemena.609815 (http://dx.us/assets /consultingengineer/appguidedocs /section6_0307.P. "Transforming Transformers [Superconducting windings]" (http://www. ^ a b c Beeman. 85. pp. London and New York: Longmans. Pulp and Paper Industry Technical Conference. Ian. ^ Poyser. fig. Hugh M. Institution Electrical Engineers. Agri-Food and Biosciences Institute & Northern Ireland Environment Agency. Standard Handbook for Electrical Engineers (11th ed. 87. "Three Phase Transformer Winding Configurations and Differential Relay Compensation" (http://basler. 77.. ^ Heathcote.. "Experimental Researches on Electricity. §6-7. Aversa. p. 89. ^ "Joseph Henry" (http://www. 349–364.com /books?id=dpnpMhw1zo8C&pg=PA171& dq=isbn%3D0763738271+%22TimeDependent+Magnetic+fields+and+Faraday%27s+La w+of+Induction%22&cd=1#v=onepage& q=&f=false).2000. Sudbury. 7th Series" (http://archive. 82.doi. ^ a b c d e Knowlton. Beatty.pdf). Retrieved Nov 30. William (2000).1834..uk/sots-contaminants. Government of Canada: Environment Canada Department. 33–40.pdf). 81.pdf).google. N. p. pp. Introduction to Electromagnetic Theory: A Modern Perspective (http://books. §12-341. 24 of 27 2/24/2014 8:04 PM .gc.org/xpl/login. 2009.).com/et/issue0109/transformer_field_dryout.609815).doi.org /10. 71.org/10. Randy. Retrieved 14 November 2012. ^ Figueroa. "Low Frequency Heating Field Dry-Out of a 750 MVA 500 kV Auto Transformer" (http://www. Retrieved Feb 23. (1986). pp.pdf). John (2006). 11. 66–67 76. ^ Chow. ^ Pansini. Philosophical Transactions of the Royal Society 124: 77–122.superpower-inc.2000. 416–417. pp. Retrieved Nov 7. p. 83. Retrieved 27 January 2013. Donald (Ed.org%2Fxpls%2Fabs_all. 73.Transformer . Magnetism and Electricity: A Manual for Students in Advanced Classes (http://books. ^ Ryan. doi:10. Tourangeau. PCBs. IEEE PES Transformer Committee. National Academy of Sciences. (2006).org/groups /transformers/subcommittees/standardsc/F11-Class1Class2Discussion. Peacock. Hamilton.pdf#page=11). 285. (Jul 1997). Retrieved and archived (http://www. & Co.) (1978). ^ Faraday. Larry.webcitation.org/6DQTNt5E7) 4 January 2013.S.org/wiki/Transformer 72. ^ IEEE PES TC (Fall 2011). ^ McDonald.ieee. Industrial Power Systems Handbook. 91. p.ca /Publications/C7F1F416-C632-4D11BDD4-C823690C2651 /PCBsQuestionandAnswerGuideConcerningPolychlo rinatedBiphenyls. 2012.edu/history /members/henry. IEEE Spectrum 34 (7): 43–49. Retrieved Feb 28. State of the Seas Report. McGraw-Hill.com /books?id=JzBAAAAAYAAJ&pg=PA285). 248.doi. 1085 86. Arthur William (1892). Contaminants" (http://www.pdf).com/downloads /3phXfmrs. S. ^ Knowlton.Wikipedia. Michael (1834).au/Assets/What-We-Do/Assets /Jemena-Electricity-Network/Planning /Western%20metropolitan%20Melbourne%20transmi ssion%20connection%20and%20subtransmission%2 0capacity. 12-95.gov. 2007. Question and Answer Guide Concerning Polychlorinated Biphenyls (https://www.ieee. 74. 549-550 84.pdf). slide 6. Donald G. Tai L. 171. Robert. 9–12. p. ISBN 9977 and 178-1-907053-20-7 Check |isbn= value (help). E. High Voltage Engineering and Testing.electricitytoday. ISBN 0-662-14595-X.0008 (http://dx. pp. Distinguished Members Gallery.1098%2Frstl.) (1955).schneider-electric. Vilcheck. 2006. ^ Lawhead. pp. BIll. M.1109/6. H.com/files /T141+IEEE+Spectrum+XFR.854186 (http://dx. Retrieved Aug 6. pp. 10–38 through 10–40. C.854186).jsp?tp=& arnumber=854186&url=http%3A%2F %2Fieeexplore. Horak.ieee. pp. "9. ^ Brown. Walker. fig. (2001). Green. Electricity Today. ISBN 0-7637-3827-1. Georgia Tech 60th Protective Relay Conference.: Jones and Bartlett Publishers. doi:10. "Application Considerations for High Resistance Ground Retrofits in Pulp and Paper Mills" (http://ieeexplore.1098/rstl. Árpád Zoltán (Oct. Retrieved Feb 29. Déri.osti. 110.. 100.. IEC Techline. Oxford University Press. Quentin R.4500994 (http://dx. Retrieved Sep 9. 106. Networks of Power: Electrification in Western Society. Creating the Twentieth Century: Technical Innovations of 1867—1914 and Their Lasting Impact (http://books. 105.institutoideal.gov/energycitations /product. 2009. Retrieved Jan 9. ^ a b "Stanley Transformer" (http://www.282D (http://adsabs.pl?section=technology&item=144).1961. (1889).pdf). ^ Oxford English Dictionary (2nd ed. Institute for Developing Alternative Energy in Latin America.S.jsp?osti_id=6851152). Nature 21 (534): 283.edu/education/tutorials /museum/stanleytransformer.1109%2FAIEEPAS.google.com /0352105. "The Faraday Law With a Magnetic Ohm's Law" (http://www.bme. 2010. H. ^ a b "Bláthy.ch/cgi-bin /tl_to_htm. Retrieved Feb 29. O. ^ Hughes. issued Sept. "The Transformer". Retrieved Mar 1. U.org /conteudo_eng. (April 1961). doi:10. M.hu /archivum/angol/htm/blathy_o. Édouard. University of Florida.org/details /historyoftransfo00upperich).Transformer . K.google.org/wiki/Transformer 92. 107. University of Pavia. Károly Zipernowsky" (http://www. "Gas and Electricity in Paris" (http://books. 103. London: E. pp.harvard. Retrieved Jan 9. Baltimore: The Johns Hopkins University Press.com /books?id=qt8JAAAAIAAJ).hu/English/feltalalok/blathy. ^ "Bláthy.pdf). ISBN 0-8018-2873-2.freepatentsonline.ac. "Induction Coil" (http://www. the free encyclopedia http://en.. 11. U. 1996).org /10.hpo. as translated by Julius Maier (1882).hu/kulonsz /k011/46. 104.1961.google.doi. 108.jsp?newsearch=true& queryText=10.1109%2FAIEEPAS.google.lk /Transformer_history_2000. "Transformer Invented 75 Years Ago" (http://ieeexplore.21. W. 102. (2007). National Technical Information Centre and Library. ISBN 9780198037743. "Historical Development of the Transformer" (http://www. Ottó Titusz" (http://www. ^ a b Coltman. N. 2004.google. issued Nov. ^ Nagy. p.elect. ^ a b Halacsy.. A. ^ Lucas.. Patent 349 311. 21.1038%2F021282b0). 1886.html).com/?id=g07Q9M4agp4C& pg=PA96& dq=Networks+of+Power:+Electrification+in+Western +Society. Retrieved Jan 29. (1993). 2009.Wikipedia. Budapest. Bláthy.biblio. Scientific American. p. 97.1961. Sándor. 1880). ^ a b Smil. F.R. p.unipv. 96. J.org/search /freesearchresult. 1988). ^ "Hungarian Inventors and Their Inventions" (http://www.com/patents?vid=349611). 1989. A. 2012. p.1038/021282b0 (http://dx.termeszetvilaga.org/10. Retrieved July 9.iec.omikk. Los Alamos National Laboratory. (Jan. (Jan 22. New York: D. George Westinghouse: Gentle Genius (http://books.htm). Retrieved Mar 3. J. Thomas P. ^ Zipernowsky.com/?id=C3GYdiFM41oC& pg=PA102). 71. ^ "Ottó Bláthy.edu /abs/1880Natur. Hungarian Patent Office. IEEE Transactions of the American Institute of Electrical Engineers 80 (3): 121–125. W. G. 2009. The Modern Applications of Electricity (http://books. 2009. 109. ^ Skrabec. Természet Világa. ^ Jeszenszky. ^ Károly. p.it/Collana/Pages/Libri /Saggi /Volta%20and%20the%20History%20of%20Electrici ty/V%26H%20Sect2/V%26H%20175-182. Retrieved Mar 1. 95 99.google. "Electrostatics and Electrodynamics at Pest University in the Mid-19th Century" (http://ppp. Jr. Algora Publishing. Spon.282D). ^ a b c d e Uppenborn. 2012.com /?id=ksa-S7C8dT8C&pg=RA2-PA283). 35–41. 1880-1930 (http://books.com /?id=w3Mh7qQRM-IC&pg=PA71&lpg=PA71& dq=ZBD+transformer).mrt.T.. 86–95. "Induction Coil" (http://www.ieee.magnet. pp.php?&sys=biblioteca_eng& arquivo=1&artigo=94&ano=2008). Von Fuchs.1109/AIEEPAS. Oxford: Oxford University Press.kfki. J. ^ De Fonveille.pdf).). 2012. 2009. 95. Bibcode:1880Natur.html). 111. "Lecture to Mark the 100th Anniversary of the Discovery of the Electron in 1897 (preliminary text)" (http://www. History of the Transformer (http://www.+1880-1930+ganz#v=onepage&q=). 2012.wikipedia.html). Appleton & Co. Patent 352 105. 98.. Ottó Titusz (1860–1939)" (http://www. 103. 2009.. 102. IEE Sri Lanka Centre. ^ Hughes.doi. OSTI 6851152 (http://www. Budapest University of Technology and Economics. 94. Retrieved Mar 3. 1886. Simonyi.htm). 25 of 27 2/24/2014 8:04 PM . William. & F. 96. ^ Hospitalier.hu/~aznagy/lecture/lecture. 101. 2. Retrieved Apr 16.21.archive. Miksa Déri. 2012. 2012. Retrieved July 13. Retrieved July 8.4500994& x=29&y=16). 112. ^ a b Stanley.S.fsu.4500994). doi:10. Vaclav (2005). ISBN 978-0-87586-508-9. 93. html). Transformer and Inductor Design Handbook (http://books. Bibliography Central Electricity Generating Board (1982).. ^ Uth.google.). Tesla: Master of Lightning.org /10. McGraw-Hill. Colonel William (2004). ISBN 0-08-016436-6.org /details/menandvoltsstory00hammrich).com /?id=Sf1ppwGI6uYC&printsec=frontcover#v=onepage&q&f=false). 117.com /?id=Jg1xA65n56oC&pg=PA7&dq=High+Voltage+Engineering+and+Testing#v=onepage& q=High%20Voltage%20Engineering%20and%20Testing&f=false). Modern Power Station Practice. ISBN 0-08-030573-3. "System of Electrical Lighting" (http://patft. ^ Neidhöfer. Gottlieb. in collaboration with VDE "History of Electrical Engineering" Committee (2008). ISBN 0-333-19627-9. Lippincott Company.com/?id=s_iMztIS8y4C). ISBN 0-8247-5393-3.G.Wikipedia.R.google.. Harlow. (2004). Transformer Engineering: Design and Practice (http://books.uspto.).. issued July 12.com /?id=f77zWwA3oS4C).S. (1993). Nikola. A. Exeter: Pergammon.PN. CRC.974352 (http://dx. ISBN 0-7506-1158-8. (2004). 238. 1891.google. Patent 454 622.Transformer .com/?id=qy4QT0BlV0MC&printsec=frontcover#v=onepage&q&f=false).. CRC Press. Michael von Dolivo-Dobrowolsky and Three-Phase: The Beginnings of Modern Drive Technology and Power Supply (http://d-nb.wikipedia.S. McLaren.974352).htm& r=1&f=G&l=50&s1=0454622. U. Handbook of Transformer Design & Applications (2nd ed. 178. Say. J.doi.1109%2F2943. Men and Volts: The Story of General Electric (http://archive. (1985). 2012. George. ISBN 0-8247-0766-4.com/patents /about?id=NmRDAAAAEBAJ&dq=366362). Power Transformer Principles and Applications (http://books. Electrical Machines and Their Applications (4th ed.org/tesla/ins/lab_tescoil.). Pansini. ISBN 0-07-021291-0. "Tesla Coil" (http://www.com/?id=HFFo2TNIu88C&printsec=frontcover#v=onepage&q&f=false).google.org/wiki/Transformer 113. ^ a b Coltman. Irving (1998). Electric Power Transformer Engineering (http://books.1109/2943.pbs. M. Winders. Jr. S.B. CRC Press. U. Ryan. James (2004). ISBN 0-470-20057-X. William M. CRC Press.). CRC. (1983). IEEE 8 (1): 8–15. (2002).). "The Transformer [Historical Overview]" (http://ieeexplore. Alternating Current Machines (5th ed. Patent 366 362.org /xpls/abs_all. 2000). Hammond.org. John (1977). Anthony (1999).com/?id=paPKsOXn5FMC& printsec=frontcover#v=onepage&q&f=false) (12th ed. Hindmarsh. Heathcote.google. John J.A. Newnes. 26 of 27 2/24/2014 8:04 PM . 114. Peter (1984). "Electrical Converter" (http://www.info /990964361) (in German) (2 ed. see esp. 106–107. John Winthrop (1941). Robert (Dec 12. ^ Westinghouse.google. Industry Applications Magazine. Retrieved May 20. Pergamon. the free encyclopedia http://en. Ellis Horwood. Elementary Electric Power and Machines. Martin (1998). ISBN 0-273-01969-4.V. CRC Press. PBS. ISBN 978-3-8007-3115-2. Introduction to Electrical Machines. pp. S.com /?id=THO9U9f2m9EC&printsec=frontcover#v=onepage&q&f=false). ^ Tesla. Jr. Practical Transformer Handbook: for Electronics. ISBN 0-8247-5653-3. Berlin: VDE-Verl. McLyman.google. High Voltage Engineering and Testing (http://books.M. Daniels. London: Pitman.gov/netacgi /nph-Parser?Sect1=PTO1&Sect2=HITOFF& d=PALL& p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum. 116. Flanagan. issued June 23. Radio and Communications Engineers (http://books. ISBN 0-8493-1704-5. (Jan–Feb 2002). J & P Transformer Book (http://books.google. 2008. Elsevier.google. 115. Gerhard. Electrical Transformers and Power Equipment (http://books.& OS=PN/0454622&RS=PN/0454622).jsp?arnumber=974352).W. Retrieved Feb 29.ieee. H. Kulkarni. ISBN 0-88173-311-3. ISBN 0-85296-775-6. J. Khaparde. doi:10. Macmillan. ISBN 0-7506-3992-X. 1887. additional terms may apply.pdf) Transformer (Interactive Java applet) (http://www.org/Business/Electronics_and_Electrical /Substation_and_Transmission/) on the Open Directory Project Introduction to Current Transformers (http://www.pdf) by P.wikipedia.afrotechmods.edu/~jcalvert /tech/transfor.com/vol_2/chpt_10/6. B. composed by J.htm) Three-phase transformer circuits (http://www.org/info/Bibliographybooks. By using this site.elkor. Inc. the free encyclopedia http://en.M.phy. Calvert. Balma.org/wiki/Transformer External links Inside Transformers. 'Physics is fun' by Chui-king Ng HD video tutorial on transformers (http://www. 27 of 27 2/24/2014 8:04 PM .. from IEEE Transformer Committee Einschalten des Transformators.hk/wiki/englishhtm/Transformer. a non-profit organization.net/pdfs/AN0305-Current_Transformers. Retrieved from "http://en. from Denver University (http://www.du. you agree to the Terms of Use and Privacy Policy.com/videos/transformer_tutorial.dmoz.org/w/index.Transformer . Wikipedia® is a registered trademark of the Wikimedia Foundation.allaboutcircuits.wikipedia.htm). Text is available under the Creative Commons Attribution-ShareAlike License.php?title=Transformer&oldid=596900354" Categories: Electrical power conversion Hungarian inventions Russian inventions Transformers (electrical) This page was last modified on 24 February 2014 at 11:30.html) from All About Circuits Bibliography of Transformer Books (http://www.transformerscommittee.htm) Substation and Transmission (http://www. German Wikipedia article about transformer inrush current at switch on (in German).Wikipedia. Protec Equipment Resources offers a vast inventory of microprocessor-based current transformer test set from Vanguard Instruments. a voltage is applied across the secondary terminals and magnetizing current will increase in proportion to the applied voltage up until the knee point.2 ohms of impedance in the metering circuit before its output current is no longer a fixed ratio of the primary current. http://blog. 4 2 0 0 Like 2 • Battery Testing • Breaker Testing • Cable Testing • Earth Testing • Expert Advice • Financial Benefits of Renting • Insulation Testing << Previous Post Comments for Understanding Current Transformers – Part II Characteristics Name: lee Time: Thursday. 0. 20 VA. polarity.0. is very important to protection CTs since they are exposed to currents of 20 to 30 times rated current during faults.1. insulation resistance and winding resistance of the CT secondary windings plus secondary burden can be measured. These sets will perform CT excitation. B-2. The knee-point is defined as the point at which an increase of applied voltage of 10% results in an increase in magnetizing current of 50%. in other words. The conductor between the meter and the CT will typically be the source of excess burden. August 2. The Vanguard EZCT series of CT test sets are designed specifically for CT testing and will greatly increase productivity and save time during the commissioning and maintenance testing. Each class also has an allowable maximum phase error for specified load impedance. current-ratio. 15 VA. however. 10 VA.2 can tolerate up to 0. Production Floor.5% or less. by much can you overload a metering CT and still operate within its accuracy? Leave a comment Next Post >> • Power Analysis • Protec Webinars • Relay Testing • Resistance Testing 1 of 2 2/23/2014 3:15 PM . and The selected tap The IEC 60044-1 standard sets out various accuracy classes.Versatile and Essential in Diagnosing Electrical Issues • Fluke 1735 Three Phase Power Logger for Easy Energy Studies • Rent the Doble TDR9100 Circuit Breaker Test System from Protec Today • Assure the Health of Circuit Breakers with the Square D by Schneider S33595 • Dranetz PX5 Integrates Advanced Function-Set for Quality Power Monitoring • Conduct Insulation Tests and Measure Winding Resistance with the Vanguard EZCT-2000B • Megger MIT1025 Designed for Insulation Testing at its Best POPULAR CATEGORIES Figure 1: CT Knee-point The knee-point voltage is less applicable for metering CTs since their accuracy is generally much tighter and constrained within a very small bandwidth of the current transformer rating.Understanding Current Transformers – Part II Characteristics .. in a CT metering circuit is the impedance presented to its secondary winding. the one-to-one relationship between input and output is no longer within declared accuracy. October 27. and B-4. When testing. 0. The classes are 0. meters and intermediate conductors will all contribute to the burden of a current measurement circuit.5s. Current transformers used for protective relays will have accuracy requirements at overload currents in excess of the normal rating to ensure accurate performance of relays during system faults. B-0. or in the Field • Amprobe DM-III Power Quality Analyzer .1. Switch-blocks. Typical burden ratings for IEC CTs are 1. This impedance will be largely resistive.2s. ANSI/IEEE burden ratings are B-0.0. B-1.2.. 1 and 3. The load. Depending on model selected. HOME CATEGORIES CONTRIBUTORS CONNECT Understanding Current Transformers – Part II Characteristics Posted by Common Sense Testing on Thursday. For an example.com/blog/common-sense-testing/understanding-cur.. 2012 this is great. the ratio error of a Class 1 CT is 1% at rated current.2.5 VA. or burden.. 3 VA.5. 30 VA. 0.protecequip. The class designation is an approximate measure of the CT’s accuracy. RECENT ENTRIES • Megger DLRO200-115 Designed for Use in the Workshop. Knee-point. 2011 When looking at the accuracy of a CT a number of factors need to be taken into consideration. and phase angle tests.5 CT is 0.0. These factors will include: • • • • • • • Burden Burden class/saturation class Rating factor Load External electromagnetic fields Temperature and physical conditions.Common S. This means a CT with a burden rating of B-0. 0. B-0. 45 VA and 60 VA. The knee-point of a CT is the magnitude of the secondary voltage after which the output current ceases to follow linearly the input current. 5 VA. Or.5. The ratio error of Class 0. . Name • Testing and Safety • Testing Tips and Tricks • Transformer Testing Email Your comment (No HTML) Type the text from the image below Protec Equipment Resources Inc..protecequip. Suite 116. Texas 75050 © 2014 Protec Equipment Resources HOME CATEGORIES CONTRIBUTORS CONNECT RENTAL AGREEMENT 2 of 2 2/23/2014 3:15 PM .com/blog/common-sense-testing/understanding-cur. http://blog. Grand Prairie.. 1517 W N Carrier Pkwy...Understanding Current Transformers – Part II Characteristics .Common S. answers.7 degrees? the knee point is where the secondary (back) EMF equals the primary. wer Rate Terms Privacy RSS Adeel answered 3 months ago 10 % increase in voltage gives you 50 % increase in excitation current is called knee point voltage. Need a low Voltage High Current Transformer? What is the main different between the Voltage transformer and the current transformer? Best Answer eematters answered 6 years ago A plot of secondary excitation voltage (Y-axis) vs secondary excitation current ( X-axis) would show a saturation point at the maximum permeability of the core material. The web site quoted below has an excellent write-up on the topic under discussion.. In other words..yahoo. You might recall that this curve is very much similar to the B-H curve used for the selection of Bmax for the design of mains transformers. Rate 1 of 2 2/23/2014 3:02 PM . Knee-voltage is the maximum secondary voltage that the CT will provide to a standard burden without saturating the transformer.com/question/index?qid=20080211061641AA90BJr Answers Home All Categories Science & Mathematics Arts & Humanities Beauty & Style Business & Finance Cars & Transportation Computers & Internet Consumer Electronics Dining Out Education & Reference More International About Follow Watchlist Science & Mathematics > Engineering > Reference Question Next Ask a Question What is Knee Point Voltage of a Current Transformer? What is its significance? deepak_8584 asked 6 years ago Answer last updated 3 months ago Related Questions What is knee point voltage in current transformer? Formula for knee point voltage calculation of current transformer? What is knee point of current and voltage transformers? How to get more Current. the secondary coils are saturated. The secondary excitation voltage corresponding to the tangent to the curve gives the knee-voltage of the CT.What is Knee Point Voltage of a Current Transformer? What is its signific. no more bang for the buck. while doing this above phenomeneo will be obsesrved. http://in. To measure this first demagnetise the CT and apply voltage gradually from secondary keeping primary winding open circuited.selinc. Source: www.com/techpprs Asker's Rating & Comment thankx for information Rate Discover Questions 10 points! Please Help With Transfer Function? Could Someone Help Me With an Engineering Data and Analysis Problem? How to wire a light switch to a speaker? Other Answers (2) drwer2 answered 6 years ago Plot the current vs voltage Oldest How much heat is required to raise the temperature of 789g of liquid ammonia from 25 degrees c to 82. yahoo..answers.com/question/index?qid=20080211061641AA90BJr 2 of 2 2/23/2014 3:02 PM . http://in..What is Knee Point Voltage of a Current Transformer? What is its signific.