High Voltage Circuit Breakers

GeneralHigh Voltage Circuit Breakers © ABB Power Technology 1_114Q07- 1 - AGENDA  GENERAL    Introduction/ Physics of the electric arc Breaking an alternate current Circuit breaker characteristics  BREAKER TYPES     Breaker technologies Oil circuit breakers Sf6 circuit breakers Vacuum circuit breakers  MAINTENANCE/ DRIVING/ TESTS    Maintenance Driving systems Tests © ABB Power Technology 1_114Q07- 2 - AGENDA  GENERAL    Introduction/ Physics of the electric arc Breaking an alternate current Circuit breaker characteristics  BREAKER TYPES     Breaker technologies Oil circuit breakers Sf6 circuit breakers Vacuum circuit breakers  MAINTENANCE/ DRIVING/ TESTS    Maintenance Driving systems Tests © ABB Power Technology 1_114Q07- 3 - Introduction  The circuit breaker is the last, larger and more important element of the system constituted by the protection equipment. It is responsible of the ultimate clearance of all present disturbances and of the switching manoeuvres involved in normal operation of the system. All this tasks must be performed without the insertion of secondary disturbances by the breaker. In order to fulfil these requirements, the breaker must be highly reliable, both electrically and mechanically.    © ABB Power Technology 1_114Q07- 4 - Introduction  The switching of the configuration of an electrical system operating a circuit breaker is not generally a simple process.  The operation of a breaker in a circuit with a current flow, implies the necessity of extinguishing the electric arc which appears between the contacts. The arc extinction, which must be done under very severe physical and time conditions, may itself provoke transient phenomena accompanied with overvoltages.   © ABB Power Technology 1_114Q07- 5 - According to the standard IEC 265-1:1983, a circuit breaker is a mechanical device of connection, capable of establish, withstand and break the current under the normal operation of the circuit and occasionally, under specific overload in-service conditions, as well as endure specific abnormal circuit currents (e. g. short circuit currents) during a given time (generally fractions of second). Introduction   The main function of circuit breakers is hence to interrupt currents. Its operation consist of:   The physical separation of two points named contacts. The extinction of the arc which inevitably appears, taking the opportunity of the zero pass of the current (AC). When open, to endure the voltage among contacts without restriking. At closing, to withstand the making load or fault currents. When closed, to withstand the permanent flow of load current At opening, to interrupt currents without failure  Finally the circuit breakers must:    © ABB Power Technology 1_114Q07- 6 -   Nevertheless it is not usual that circuit breakers visibly isolate zones for working, hence something else is necessary. Physics of the electric arc  In order to turn gases into electric conductors their temperature should reach a certain limit.  Thus, their molecules and atoms begin to lose electrons and the gases become conductors.  Metals have their own conductive properties due to the existence of free electrons in their inside.  In their surface there is a potential barrier produced by a layer of positive ions in the metal’s inside, which prevents electrons from escaping the surface, unless their kinetic energy is greater than its charge multiplied by the potential barrier.  When the temperature in the metal is raised, energy is transmitted to electrons that may lead them to overcome the potential barrier, thus causing the thermionic emission. Other forms to extract electrons from a metal is to expose it to a strong electric field or to a luminous radiation (photoionic emission)  © ABB Power Technology 1_114Q07- 7 - Discharge phenomena in a gas  When the electric arc appears, the electrons are released due to the thermoelectric emission of the cathode.   The electric field in front of the cathode accelerates the positive ions; this process heats the metal in the cathodic electrode and generates the necessary temperature in the cathode (22000k). This electric field leads to the release of electrons in the cathode.   The electric arcs present the properties of great mobility and easy shifting due to the effect of air currents, magnetic fields, etc. The voltage drop in the arc may be expressed by AYRTON’s formula: Where A and B are linear functions of the arc length B For i o; UA = Ue (extinctionU a voltage)     © ABB Power Technology 1_114Q07- 8 - = A+ I For strong currents: Ua = A Arc temperature  The curve in Fig. shows the temperature of the medium surrounding the arc as a function of the distance to its axis. The temperatures depend on the contacts material. The arcs shows up as an incandescent gas column with an almost straight-line trajectory between the electrodes, which core reaches temperatures between 6,000 and 10,0000 ºC. The surface of contact of the arc with the electrodes appears incandescent. The collision of the molecules with the electrons emitted by the cathode generates the ions of the arc column.   © ABB Power Technology 1_114Q07- 9 - Voltage drop in the arc  The arc can be divided in three zones.  Close to the electrodes, there are two very short zones with high gradients and pronounced voltage drops: UA (anodic) y Ue (cathodic). The third zone presents a smaller voltage drop, U, proportional to the length of the rest of the distance between electrodes. The cathodic drop is lower than the anodic and includes a very small zone. UA and Ue depend on the current intensity (Fig. 1).   © ABB Power Technology 1_114Q07- 10 - Voltage drop in the arc  In the zone of the cathodic drop there are metallic vapours proceeding from the cathode with many positive ions and few electrons.  These electrons have great mobility and they are able to transport from 10% to 20% of the current.  In the arc zone, the shifting of electrons gives place to intense currents.  When the ions go toward the electrodes of opposite sign they accumulate toward the nearby zones causing the voltage drops shown in Fig. 1. These voltage drops are associated to powerful fields that provide the ions enough energy to release new ions.   © ABB Power Technology 1_114Q07- 11 - In the anodic zone, a negative charge generates a voltage drop. Power and energy in the arc  The power absorbed by the arc is equal to multiply the current of the arc Ia by the voltage drop in the column: Pa = I a U a  The energy absorbed by the arc is the integral of the former product, extended to the whole duration of the arc:  This energy is the environment due to conduction, radiation and convection. Part of this heat is absorbed by the dissociation of the flow that surrounds the arc.  transformed W = ∫ o Pand = ∫dissipated to in heat a dt is o I a U a dt T T A high thermal conductivity and an improvement of the refrigeration conditions will reduce the temperature and increase the voltage drop. The rise of the pressure also produces an increase in the voltage drop.  © ABB Power Technology 1_114Q07- 12 - Characteristics of the arc  The relationship among voltage and current in an electric arc is very different from that of metallic conductors. In metallic conductors, the voltage is proportional to the current, and its characteristic is a straight line er. The voltage UA between the electrodes of the arc decreases when the current rises to a limit value and then it rises again when the current decreases. The initial breakdown of the space between electrodes requires a high voltage of ignition for i = o. The growth of current increases tª and the ionisation of the medium that surrounds the arc, consequently raising the conductivity of the column of the arc, which decreases the voltage of the arc.    © ABB Power Technology 1_114Q07- 13 -  Characteristics of the arc  When the current increases, the curve shows a very considerable decline at the beginning and then it decreases more slowly. This is because the arc subsists at a constant current density, which implies a section growth when the current rises and an increase of the air conductivity. If the current of the arc decreases under a given value, the points of the curve do not match, but they are below the curve. This phenomenon is due to the calorific inertia of the arc. The surface of the cathodic stain, the arc diameter, the ionisation current and the tª do not adapt instantly to the new values of current and they give place to a lesser voltage of the arc.    © ABB Power Technology 1_114Q07- 14 -  Characteristics of the arc  The extinction voltage is smaller than the restriking voltage, because when the extinction takes place (following an instant of strong dissipation of heat due to thermal inertia), the column of the arc has thermodynamic and conductive conditions superior to those preceding the restriking.  The restriking occurs after a very short time without arc, of about millionths of second, in which a cooling and an intense deionisation of the arc take place. The arc restriking, with the current in the opposite direction, is produced when the inverse voltage of recovery applied between the electrodes is higher than the restriking voltage. The value of the restriking voltage depends on the separation between electrodes, the pressure of the medium and the concentration of charge carriers, influenced by the refrigeration and thermal conductivity of the medium and the electrodes.  © ABB Power Technology 1_114Q07- 15 -  The arc in alternate current  In an AC circuit the current passes through zero twice in a cycle. If the voltage and current of the arc are registered by an oscillograph, the obtained “voltage-current” curves present forms that depend on the kind of gas, the material of the electrodes, the arc length and the frequency of the current.  The difference of ordinates between the curve of rising current and the curve of decreasing current is due to the thermal capacity of the electrodes and of the gas of the arc and, in particular, of the calorific inertia of the arc (arc hysteresis). © ABB Power Technology 1_114Q07- 16 - The arc in alternate current  RESTRIKING VOLTAGE (Ur)  It is the voltage between electrodes needed to restrike the arc after it extinguishes when the current naturally crosses zero. If the voltage between electrodes is lower than the restriking voltage of the arc, the circuit stays definitely open.  EXTINCTION VOLTAGE (Ue)   It is the peak voltage of the arc when the current reaches zero value. The decreasing shape of the characteristic of the arc and the smaller concentration of charge carriers (resultant from the current decrease) justify the rise of the arc voltage Ua, which peak is the extinction voltage Ue. © ABB Power Technology 1_114Q07- 17 - AGENDA  GENERAL    Introduction/ Physics of the electric arc Breaking an alternate current Circuit breaker characteristics  BREAKER TYPES     Breaker technologies Oil circuit breakers Sf6 circuit breakers Vacuum circuit breakers  MAINTENANCE/ DRIVING/ TESTS    Maintenance Driving systems Tests © ABB Power Technology 1_114Q07- 18 - Breaking an alternate current  If the circuit breaker is capable to open its contacts at the instant when the current crosses zero fast enough so that the voltage between contacts does not reach the restrike voltage, the circuit remains open and, since the electromagnetic energy is null in that instant, no overvoltages are present between contacts.  For this to happen in 50 Hz networks, the circuit breaker should be able to open in less than ten thousandth of second. u i urd u t ua © ABB Power Technology 1_114Q07- 19 - i Breaking an alternate current  In fast medium-voltage circuit breakers, the current breaks after two or more hundredth of second. Actually, the current breaking always has place through an arc, with the exception of very weak currents or extremely small voltages. The breaker goes from conductive condition to insulating condition with a given puncture voltage or dielectric strength, which grows with time. The conductive condition is provoked by the ionisation of the gas that surrounds the arc. The ionisation is due to the high temperature that the gas reaches and by the electrons released by the cathode. u i Em i u ua urd   urd t © ABB Power Technology 1_114Q07- 20 - Breaking an alternate current  The voltage drop in the arc brings the power required to keep the high temperatures (due to the Joule effect), balancing the heat losses of the arc due to conduction, convection and radiation. As the current decreases when it approaches to zero, the thermal power of the Joule effect is lower than the thermal power given to the environment. This leads to the cooling of the arc and produces a recombination of ions and electrons, which diminish the conductance of the path of the arc. If the curve Up is constantly above the curve Utr , the arc will not restrike and the circuit opening will be definitive. Nevertheless, if the voltage curve Utr crosses the curve Up, at that instant the dielectric puncture of the medium will occur and a new arc suddenly restrikes.   © ABB Power Technology 1_114Q07- 21 - Breaking an alternate current  The final extinction of the arc will be possible in one of the instants when the current crosses zero, providing that the voltage between contacts in those instants is unable to restrike a new arc toward the remainder plasma (between contacts), more or less deionised. The possibility of an arc restrike or its definitive extinction depends on the rate of rise of the TRANSIENT RECOVERY VOLTAGE (TRV), and of the dielectric strength of the zone surrounding the arc at such time. The dielectric strength is a function of tª and the fractional ionisation of the plasma in the instant of the zero crossing of the current. The arc trajectory should acquire briefly a dielectric strength enough to resist the recovery voltage between electrodes. The rate of rise of the transient recovery voltage (TRV) is very important for the value of the breaking capacity of a circuit breaker. In the high voltage circuits, the TRV may reach initial values of around kV/Ts.     © ABB Power Technology 1_114Q07- 22 - Breaking an alternate current  The rate of recovery of the dielectric strength of the arc’s medium is an attribute of the circuit breaker, since it depends on the refrigeration conditions, the deionisation rate of the zone of the arc and the speed of the separation of the contacts. The problem consists in a race between two voltages: the dielectric strength and the transient recovery voltage. If the second does not reach the first, the breaking is definitive and happens when the current crosses zero  © ABB Power Technology 1_114Q07- 23 - Arc extinction process  When a circuit breaker is closed, a pressure among contacts exists and the current density is minimal. © ABB Power Technology 1_114Q07- 24 - Arc extinction process  At the opening maneuver, at the moment of contact parting, the thin layer of fluid (air, oil, SF6, etc) between them is crossed by the current, which implies a very fast rising of the temperature in the contacts originating metallic vapours. The isolating medium surrounding the arc suffers a violent heating which originates its transformation into conductor.  © ABB Power Technology 1_114Q07- 25 - Arc extinction process  The gaseous column strongly ionised turns into plasma Its ionisation and electrical conductivity extremely rise with temperature  © ABB Power Technology 1_114Q07- 26 - Arc extinction process  The renewal of the quenching medium and the zero cross of the current extinguish the arc © ABB Power Technology 1_114Q07- 27 - Arc extinction process. Load current interruption  The simplest case of current interruption is the one corresponding to the normal load current. They are small currents, compared to the high short circuit currents, and its phase angle is close to zero (cosΦ aprox. 0,8). The interruption will take place at the first zero cross of the current. u i u urd   t © ABB Power Technology 1_114Q07- 28 - ua i Arc extinction process. Fault current interruption  The case of close-in faults is characterized by a high current, with a high phase angle close to 90º (load strongly inductive). It can lead to several arc restrikings and the arc extinction does not take place before the 2º or 3º zero cross of the current. u i Em i u ua urd  The arc is established by contact parting. The voltage drop is Ua. At the first zero cross the TRV rises very quickly trying to reach the grid voltage but a restrike occurs because the dielectric strength is not high enough. t urd © ABB Power Technology 1_114Q07- 29 - At this zero cross, the dielectric strength is higher than the TRV and the arc is finally extinguished. Arc extinction process. Other cases  When the short circuit is at the far end of the line, a transient overvoltage may add to the TRV, which can cause restrikings even though the current is not very high. The case of interrupting small inductive currents may also cause some troubles since the arc may extinguish even before the zero cross of the current, hence generating voltage peaks by induction effect, and consequent restrikings.  © ABB Power Technology 1_114Q07- 30 - AGENDA  GENERAL    Introduction/ Physics of the electric arc Breaking an alternate current Circuit breaker characteristics  BREAKER TYPES     Breaker technologies Oil circuit breakers Sf6 circuit breakers Vacuum circuit breakers  MAINTENANCE/ DRIVING/ TESTS    Maintenance Driving systems Tests © ABB Power Technology 1_114Q07- 31 - Circuit Breakers  According to the standard IEC 265-1:1983, a circuit breaker is a mechanical device of connection,  Capable of establish, withstand and break the current under the normal operation of the circuit Occasionally, conditions, under specific overload in-service   Endure specific abnormal circuit currents (e. g. short circuit currents) during a given time (generally fractions of second). © ABB Power Technology 1_114Q07- 32 - Circuit Breakers  The main nominal characteristics of circuit breakers are: Rated voltage Insulation level Rated current Rated frequency Breaking capacity Making capacity Short-time current Sequence of operation Thermal short-time current rating Mechanical short-time current rating           © ABB Power Technology 1_114Q07- 33 - Rated voltage  The rated or nominal voltage of a network (Un) is the standard value of voltage for which the network’s operation and insulation have been designed. The limit values of a network’s voltage (excluding all transitory or abnormal conditions) are the highest and lowest value of voltage that may be present in the network at a given instant or place under normal operation conditions.   Generally, those limit values are around ± 10% from the nominal voltage of the network. Its insulation Other attributes associated to this voltage  The highest voltage for a circuit breaker is the maximum specified for it related to:   © ABB Power Technology 1_114Q07- 34 - Insulation level  The insulation level of a circuit breaker is given by:   Nominal power-frequency withstand voltage Nominal lightning withstand voltage Nominal switching withstand voltage  And eventually by:   These values characterize the device’s insulation regarding its aptitude to withstand overvoltages at power frequency, lightning overvoltages and switching overvoltages of steep wavefront. © ABB Power Technology 1_114Q07- 35 - Insulation level. Lightning wave  Lightning overvoltage waves in overhead lines may have several forms, but those registered by a cathode-ray oscillograph during storms had shown that they might be represented by a non-periodic unidirectional wave of steep front, attenuated afterwards. In order to typify the insulation of a given device, this wave can be standardized as a 1.2/50 waveform;    this is, a waveform which front has a conventional duration T1 = 1.2 µ s, and the conventional duration of the waveform afterwards until it reaches half its amplitude in the tail is of 50 µ s, according to the standard DIN VDE 0432. © ABB Power Technology 1_114Q07- 36 - Insulation level. Switching wave  In high and medium voltage lines, the breaking of the current in a circuit provokes overvoltages, with an unidirectional wave of steep front, attenuated afterwards, that be standardized as a 250/2500 shock wave, this is, a waveform which front has a conventional duration T1 = 250 µ s and T2 = 2500 µ s. These shock voltages are generally triggered by an arrangement in which a given number of capacitors are charged in parallel by a highvoltage direct current source and then discharged in series over a circuit composed by the tested device in parallel with a pure resistance R and a linear inductance L.  © ABB Power Technology 1_114Q07- 37 - Nominal or rated current  It is the current assigned by the manufacturer that the device can endure indefinitely (or for a given time) under normal operation conditions, without suffering any heating higher than that fixed by the standards, and without undergo any modification in its functional features.  LIMITS OF RISE OF TEMPERATURE IN ºC Oil circuit breakers Other circuit breakers Contactors in air 30 35 -Contactors in oil 30 -Oil 30 Voltage coils with insulation type 0* 35 35 Series coils with insulation type are 50 50 The values in the former table 0* for circuit breakers operating outdoors. For circuit breakers Series and voltage coils limits of temperature rise are related to the temperature indoors and 50 50 operating indoors, these with insulation type A Series and voltage coils with insulation type B 70 70 should not the other parts ofºC if the breaker breaker contacts are made of silver or silvery copper. exceed 40 the circuit circuit All 70 70 PART © ABB Power Technology 1_114Q07- 38 - Symmetrical and asymmetrical breaking current  When a sudden short-circuit takes place, the initial current reaches a high value that progressively diminish until it attains the steady state short-circuit value.  Besides, the delay of the relays (which send the opening signal to the breaker after the short-circuit starts) should be taken into account. For this the actual value of the current cleared by the breaker is lower than the initial value of the short-circuit current.    © ABB Power Technology 1_114Q07- 39 - The IEC defines breaking current as follows: The breaking current of a circuit breaker pole is the value of the current in the pole in the instant of contact separation and is expressed by two values:   Symmetrical current Asymmetrical current Symmetrical and asymmetrical breaking current  The symmetrical current is the effective value of the AC component in the pole at the instant of contact separation and its value is given by: x I sim = 2  The asymmetrical current is the RMS value of the total current composed by the AC and DC components in a pole in the instant of contact separation and its value is given by : © ABB Power Technology 1_114Q07- 40 -  x  2 =   + (Y ) I asim  2 2 Symmetrical and asymmetrical breaking current  The extent of the asymmetrical period and its importance of the asymmetry depend, for each phase, on the instantaneous value of the electromotive force (e.m.f.) in the initial moment of the short-circuit and its maximum value when the initial instant corresponds with a zero of the e.m.f. Usually the relationship between the symmetrical and asymmetrical short-circuit currents is expressed by a factor of asymmetry K:   K depends on the relationship between the inductive reactance and the resistance of I asim breaker will the circuit where the circuit = K I sim be mounted. It is generally tabulated in tables.  The breaking capacity of a circuit breaker is calculated as: x K= f   R © ABB Power Technology 1_114Q07- 41 - Pcc SIM = 3 U n I SIM Pcc ASIM = 3 U n I ASIM Pcc ASIM = K Pcc SIM Short circuit making current  This value distinguishes the capacity of a circuit breaker to close its contacts under short-circuit conditions in the system. The making current of a breaker when its contacts close under shortcircuit conditions is the value of the total current (including alternate and direct components) and which are measured from the envelope of the current waveform in its first peak value. The making current of a breaker is that associated to its closing at service voltage. If this value is not present in the nameplate, should be calculated as follows: Making current = 1,8  Isim = 2,55 Isim   © ABB Power Technology 1_114Q07- 42 - Permissible rated short-time current  The permissible rated duration of the short-circuit current is the time during which the closed circuit breaker can endure a current equal to its rated breaking capacity under short-circuit conditions. The rated value of the permissible rated duration of the short-circuit is 1 second, or, if a superior value is needed, 3 seconds. For short-circuits that last more than one second, the relationship between current and duration, unless the manufacturer specifies it otherwise, complies with the following expression: 2 I t = constant   © ABB Power Technology 1_114Q07- 43 - Rated sequence of operation  The rated sequence of operation of a circuit breaker consists in a number of operations established in a certain succession and in given ranges of time. According to the IEC standards, the sequence of operation of a circuit breaker not specified as a recloser can be expressed as follows:   o - t - co - t' - co o - t² - co o= co = opening operation, c = closing operation  Where: closing operation followed by an opening operation t, t', t² time ranges, t y t' expressed in minutes, t² expressed in seconds  For example, a circuit breaker with a double operation sequence o - 0,15seg – co, means than when the fault takes place, the circuit breaker opens, waits 0,15seg, closes and, if the fault continues, it opens again. © ABB Power Technology 1_114Q07- 44 - Breaker Types High Voltage Circuit Breakers © ABB Power Technology 1_114Q07- 45 - AGENDA  GENERAL    Introduction/ Physics of the electric arc Breaking an alternate current Circuit breaker characteristics  BREAKER TYPES     Breaker technologies Oil circuit breakers Sf6 circuit breakers Vacuum circuit breakers  MAINTENANCE/ DRIVING/ TESTS    Maintenance Driving systems Tests © ABB Power Technology 1_114Q07- 46 - Breaker types  The main way to distinguish the different types of breakers is that related with the mediun they use as a dielectric and to break the current. In accordance with that we can distinguish :  Voltage Puncture in OIL, AIR and SF6  Oil breakers Dead tank Low content   © ABB Power Technology 1_114Q07- 47 - Magnetic blast breakers Air blast breakers SF6 breakers Vacuum breakers   Breaker technologies. History. OIL 1900 Contacts in oil without breaking chamber Breaking chamber Oil as dielectric and isolation Dead tank, reaches ratings of 330 kV 63 kA 1930 Low content of oil Porcelain isolator 1973 1979 © ABB Power Technology 1_114Q07- 48 - Low content oil reaches 765 kV y 63 kA At HV becomes not competitive against SF6 Breaker technologies. History. AIR BLAST 1930 Breaking with single and multiple chambers 1955 Very well accepted and introduced into the market 1965 Becomes not so compressors, noise, etc. popular because maintenance, © ABB Power Technology 1_114Q07- 49 - Breaker technologies. History. VACUUM 1920 1963 1973 First development at laboratory Difficulties with manufacturing Still manufacturing difficulties 17 breakers installed at U.S.A 6 Chambers for 138 kV 40 kA 1990 © ABB Power Technology 1_114Q07- 50 - Becomes rather popular at MV Breaker technologies. History. SF6 1950 Beginning of instalation with GIS 1973 Hidro-Quebec complete an instalation with GIS for 765 kV 1984 Beyond 123 kV becomes the most popular technology with auto-puffer breakers 1990 Continues expansion at M.V. y H.V.. New designs with low energy operating mechanisms © ABB Power Technology 1_114Q07- 51 - Selection of the breaking technology  In order to select the appropriate breaking technology, the following aspects should be taken into account:    The highest security for personnel and material The fewer requirements of maintenance The best treatment of switching overvoltages in order to keep them into secure levels (less risk for the material) The best economical conditions, considering cost of acquisition and assembling, as well as maintenance yearly expenses, cost of renewal of damaged material (due to repeated arcs) and cost of indispensable auxiliary systems (like air compression systems in airblast circuit breakers)  © ABB Power Technology 1_114Q07- 52 - Predictable future of each technology  Accordingly to experience it is possible to establish:  The continued monopoly of air breaking for all low voltage applications. The expected decrease (that has already started) of two formerly successful technologies: airblast breaking and oil breaking. The predictable development of vacuum breaking, even when it has been long an uncertainty. The impressive development of SF6 breaking, which dominates nowadays the hole range of medium to high voltage (from 3 kV to 800 kV) The hypothetical birth of static breaking, with a promising but doubtful future.    © ABB Power Technology 1_114Q07- 53 -  Predictable future of each technology Number of breakers by Voltage and thecnology used K.V. 380 220 132 66 45 30 20 15,13,11 TOTAL %TOTAL AÑO 2000 AÑO 1997 AIRE 10 66 43 0 9 6 43 20 197 G.V.A. 0 2 73 143 44 77 2 233 574 P.V.A. 47 260 443 582 900 486 3261 1320 7299 SF6 14 147 451 433 62 33 2920 15 4075 VACÍO 0 0 0 0 20 29 216 9 274 TOTAL 71 475 1010 1158 1035 631 6442 1597 12419 © ABB Power Technology 1_114Q07- 54 - 1,59 2 4,62 5,85 58,77 64,75 32,81 25,79 2,21 1,61 100 100 Magnetic blast circuit breakers  Arc extinction by means of a magnetic field created by the current to interrupt The arc is displaced and elongated by the effect of that magnetic field Only used in LV and MV No flammability hazard    © ABB Power Technology 1_114Q07- 55 - Magnetic blast circuit breakers El principio del soplado magnético consiste en producir, por la acción de un campo magnético excitado por la propia corriente a cortar, un más rápido alargamiento del arco, el cual es canalizado hacia el interior de una cámara de extinción de material aislante, refractario, de gran capacidad calorífica. En base a este principio, es posible lograr la ruptura de muy elevadas corrientes en baja tensión y aún en media tensión, siempre y cuando se cuente con una potencia de refrigeración suficiente en la zona del arco como para impedir el embalamiento térmico post-arco. © ABB Power Technology 1_114Q07- 56 - Interruptores de A..T. Interruptores para el Interior. Magnetic blast circuit breakers Es condición fundamental, en un interruptor de soplado magnético, que el arco se extinga dentro de la cámara de extinción, sin salirse de ella. La misión de esta cámara es laminar el arco y enfriar enérgicamente el plasma de gases ionizados, al paso por cero de la corriente. Conviene destacar que el soplado magnético en los interruptores de corriente alterna, es nulo en el momento de extinguirse el arco (paso por cero de la corriente), no ejerciéndose en estos instantes acción electromagnética alguna sobre los iones y electrones presentes en la columna del mismo, lo cual limita la utilización de este tipo de aparatos para tensiones muy altas. © ABB Power Technology 1_114Q07- 57 - Interruptores de A..T. Interruptores para el Interior. Magnetic blast circuit breakers © ABB Power Technology 1_114Q07- 58 - SECCIÓN DE UN POLO DEL INTERRUPTOR AUTOMATICO Interruptores de A..T. Interruptores para el Interior. Ruptura con solapado Magnético Magnetic blast circuit breakers SECUENCIA DE CORTE DE UN POLO DEL INTERRUPTOR AUTOMATICO © ABB Power Technology 1_114Q07- 59 - Interruptores de A..T. Interruptores para el Interior. Ruptura con solapado Magnético Magnetic blast circuit breakers Ua e i ra =Tensión de arco = F.E.M. del circuito = Corriente = Resistencia del aire La figura ilustra este proceso, en el caso de un circuito de corriente alterna. La técnica utilizada en estos interruptores no pretende cortar bruscamente el arco al paso por cero de la corriente, sino que aprovecha los instantes que preceden y suceden a ese instante para cambiar el régimen de funcionamiento del interruptor, pasando de un arco de pequeña resistencia a un arco de elevada resistencia. La ruptura sobreviene a continuación, al incrementarse esta resistencia hasta el infinito, tal como se tiene en los interruptores de corriente continua. El éxito de esta técnica, inicialmente aplicada a los interruptores de baja tensión y muy especialmente en los interruptores de corriente continua ultrarrápidos hasta 3 kV, llevó a los constructores a extrapolar su utilización a los aparatos de alterna de media tensión, hasta tensiones de 24 kV. Como sea que, para alcanzar una tensión de arco del orden de la tensión de la red, la longitud de aquel debe ser muy importante; y una elevada tensión de arco con corrientes fuertes sería causa de un considerable desarrollo de energía (por defecto Joule), que además de inútil sería perjudicial. Es necesario que en tanto la corriente sea fuerte el arco sea corto, forzando su alargamiento únicamente al ir aproximándose la corriente a cero. Esto se ha conseguido jugando con las secciones de paso ofrecidas al arco, por ejemplo, disponiendo en las pantallas de las cámaras de ruptura rendijas de anchura variable. © ABB Power Technology 1_114Q07- 60 - Interruptores de A..T. Interruptores para el Interior. Ruptura con solapado Magnético Air blast circuit breakers   Arc extinction by high pressure air blast Advantages:  No flammability hazard Compressed air system is needed Noisy operation Expensive maintenance  Disadvantages:     It was competitive at high voltages and high breaking capacities Other characteristics:   Always multiple breaking Dielectric strength rises with pressure It must be re-closed to prevent emptying. © ABB Power Technology 1_114Q07- 61 -   AGENDA  GENERAL    Introduction/ Physics of the electric arc Breaking an alternate current Circuit breaker characteristics  BREAKER TYPES     Breaker technologies Oil circuit breakers Sf6 circuit breakers Vacuum circuit breakers  MAINTENANCE/ DRIVING/ TESTS    Maintenance Driving systems Tests © ABB Power Technology 1_114Q07- 62 - Breaking an alternate current in oil  In the instant of electrodes separation, a considerable resistance named ρ appears between them. Since the current cannot change instantaneously, a voltage takes place between electrodes, forming an arc.  This arc is constituted by a mixture of metallic particles and volatilised oil, hence forming a blend of gases partially dissociated and ionised and becoming a conductor path of weak resistance when the arc is stable. This resistance gets weaker when the current gets higher, and increases when the arc is enlarged.  © ABB Power Technology 1_114Q07- 63 - Breaking an alternate current in oil  When the electrodes start to separate, as soon as the arc is established, the resistance is very low and does not sensibly modify the condition of current I, which follows its normal variation and until it reaches zero. The arc extinguishes at this instant, but the gaseous path does not disappear and the arc restrikes when the voltage between electrodes reaches the appropriate value. The phenomenon repeats with every change of sign of the current; however, as the arc enlarges, the resistance of the arc grows, the current amplitude diminishes slightly, and the restriking voltage increases noticeably. Finally, the restriking voltage gets to be higher than the voltage between electrodes, hence the arc does not restrike anymore and the circuit is opened.    © ABB Power Technology 1_114Q07- 64 - Arc extinction using oil blast  To extinguish an arc it is required to deionise its path in a very short time (µs). Then, the blast of turbulent gases should be thrown to the ionised files that constitute the arc. Consider two electrodes A and B inside an insulating enclosure cross by a transversal channel. If a given amount of oil is thrown through the channel in the direction of the arrow, the oil will penetrate the arc. At the instant when the current passes through zero, the voltage will stay at its normal value, since an insulating layer had been introduced between electrodes, and this layer would be able to stand that voltage. For the extinction to be ultimate, it is also required that the insulating layer would be capable to endure the recovery voltage Ur for as long as it is present.    This is, the fluid speed must be proportional to the gradient of the recovery voltage. © ABB Power Technology 1_114Q07- 65 - Arc extinction using oil blast  The dielectric strength Ur to be introduced is that of the fluid relative to the shock voltages. For oil, even if it is highly contaminated, it is around 220 kV/cm. In the circuit breakers with transversal blast, the extinction of the arc is aided by the fact that the dielectric strength of oil, under shock voltage, is greater than the dielectric strength of the arc column at the instant of extinction, which is around 7 kV/cm. The speed of the oil is inevitably limited (20 to 40 m/s), however, when the gradient g gets too large, after the voltage rise in a circuit of a given frequency fo, the artifice of multiple channels in parallel is used.   © ABB Power Technology 1_114Q07- 66 - Operation of low oil content CB  When the mobile contact moves away from the fixed contact, the oil provokes a fast cooling of the arc between contacts. The procedure of arc extinction has two stages:  Enlargement and cooling of the arc Self-extinction of the arc.   The extinction of the arc happens in the breaking chamber, in which a blast takes place due to the pressure generated by the arc itself. The breaking chambers present the property that the breaking effect rises as the current to be interrupted increases. The breaking power is limited only by the pressure of the gases product of the arc which must be endured by the breaking chamber.   © ABB Power Technology 1_114Q07- 67 -  This is manufactured with an insulating material, epoxy resin, built up with fibreglass. The insulation from ground is obtained by standoff insulators. Interrupting chambers. Axial blowout  In this kind of chambers, the gases escape through the passage gap of the fixed contact. Since the section of the opening is small, the pressure in the chamber is high even with small currents.  © ABB Power Technology 1_114Q07- 68 - Interrupting chambers. Transverse blowout  In this kind of chambers, the gases escape through side gaps. The heat of the arc vaporises the oil and the gases formed (mainly hydrogen) increase in pressure and force the arc to bow into the vents.  G as e v a c u a t io n © ABB Power Technology 1_114Q07- 69 - Interrupting chambers. Mixed blowout  For high breaking capacities, the blowout of gases towards the arc is perpendicular to the contacts axis; meanwhile for low capacities, the blowout is axial.  Gas The contacts of these circuit breakers can stand, according to the statistics provided by evacuation the manufacturers, the following number of operations without need of replacement.   At rated current 4000 operations. At half of the maximum short-circuit power 8 operations. At full short-circuit power 3 operations.  © ABB Power Technology 1_114Q07- 70 - Oil circuit breakers   The most used since 1900 Advantages:   Lower arc length than in air Better isolation Flammability hazard Oil contamination by arc effect Explosive mixture of gases and air Oldest technology and obsolete Big oil tank where the contact parting off takes place Arc extinction by oil pressure on gasses bubble Improvement with arc extinction chamber  Disadvantages:     Bulk oil/ Dead tank:     © ABB Power Technology 1_114Q07- 71 - Low content oil circuit breakers  Reduced chamber containing the contacts and the oil Oil blast at pressure in the arc Several chambers used as voltage rises Advantages:     Self-regulation (Higher blasting for higher arc intensity) High breaking capacity Fast deionization Low overvoltages Reduced energy dissipation Reduced carbonization Reduced contact wearing    © ABB Power Technology 1_114Q07- 72 -    Breaker Types SF6 High Voltage Circuit Breakers © ABB Power Technology 1_114Q07- 73 - AGENDA  GENERAL    Introduction/ Physics of the electric arc Breaking an alternate current Circuit breaker characteristics  BREAKER TYPES     Breaker technologies Oil circuit breakers Sf6 circuit breakers Vacuum circuit breakers  MAINTENANCE/ DRIVING/ TESTS    Maintenance Driving systems Tests © ABB Power Technology 1_114Q07- 74 - The sf6 as a dielectric gas  Under a few bars of pressure its dielectric strength reaches 5 times that of air. This is due to two reasons:  First, the dimension of its molecule, which effective section of collision with an accelerated electron inside an electric field is higher to that of the nitrogen or oxygen, for example. This means that the electron will endure statistically a greater number of collisions in SF6 than in air. But mainly, the second, which results from the property of the SF6 molecule to capture an electron in an electron-molecule collision, thus forming a negative ion. This property of capturing electrons comes from the extraordinarily electronegative nature of the fluorine atom. When this atom lacks an electron to complete its external layer, it generates an elevated level of attraction towards any electron inside its influence field. This provides this element its well-known chemical reactivity.     This point will be further developed when analysing the deionisation phenomena.. Hence, in the field of current breaking, SF6 is the ideal gas, as it will be analysed below. © ABB Power Technology 1_114Q07- 75 - The SF6 as the breaking gas. Thermal features  In the breaking process of an electric arc, two main qualities are required from the dielectric used as a breaking agent:   the cooling capacity the capacity of deionisation of the arc.  The application of SF6 for this purpose is evident under two features: Thermal and Electronic Given an electric arc formed inside a cylindrical tube containing a gas and crossed by a constant current, it can be demonstrated that the temperature of this arc is maximum in the axis of the tube, and it decreases towards the walls until it reaches the temperature of the tube in the walls.  © ABB Power Technology 1_114Q07- 76 - The SF6 as the breaking gas. Thermal features  When the current increases, it can be observed in most gases the appearance of a thermal threshold and the development in the centre of the tube of a cylindrical zone in which the temperature rapidly rises, called central core. The thermal conductivity of SF6 presents a peak near the thermal threshold that translates in an important heat release.   In SF6 the temperature of the threshold (2.200ºK) is close to the temperature of recombination of the SF6 atoms in molecules. Therefore, there is an important absorption of energy that causes a new descend in temperature, which goes below 2100ºK. At this temperature, the SF6 is basically an insulator and impedes the restrike after the current crosses zero.   © ABB Power Technology 1_114Q07- 77 - The SF6 as the breaking gas. Deionisation  SF6 has another notable feature, related to the strongly electronegative nature of fluorine.  In fact, the atom of fluorine lacks an electron to fulfil its external layer, which creates a high level of attraction over any electron inside its influence field. There is a noticeable decrease in the number of free electrons (responsible of the arc conductivity) below 6,000ºK. Such electrons are captured by the fluorine atoms to form negative ions F-, 185 times slower. Hence, for every captured electron, the current is automatically divided by 185.    Therefore, in the temperature range of 6,000 and 3,000ºK, in which almost all free electrons had been captured, the conductance decreases very faster than in gas without the electronegative properties of fluorine. Summarizing, in SF6, even before the central core has completely disappear while the cooling of the arc, its conductance is almost null, due to the capture of the free electrons by the fluorine atoms, which become electrons traps below 6,000ºK.  © ABB Power Technology 1_114Q07- 78 - Breaking technologies in sf6 . Self-compression  The breaking technology of self-compression in SF6 was first used in high voltage circuit breakers, and then it moved on medium voltage, following its own evolution. The active elements are mounted inside the sealed terminal boxes that constitute the poles.  © ABB Power Technology 1_114Q07- 79 - Breaking technologies in sf6 . Self-compression 1 Lid 2 Gastightness system 3 Driving axle 4 Crankshaft 5 Insulating rod 6 Conical roller bearing 7 Top current tap 8 Casing 9 Bottom 10 Spring 11 Valve 12 Piston 13 Mobile arc contact 14 Mobile main contact 15 Fixed arc contact 16 Insulating nozzle 17 Fixed main contact 18 Molecular sieve 19 Bottom current tap  The current breaking is performed through the contacts of the arc:  The fixed contact is rigidly mounted above the bottom tap. The mobile contact has two parts:    The contact in the centre A contact rod that slides inside a fixed base leaned against the top tap. © ABB Power Technology 1_114Q07- 80 - Breaking technologies in sf6 . Self-compression  A piston is rigidly mounted over the contact rod with the purpose of compress the SF6 during the opening of the contacts. A Teflon nozzle tightly jointed to the piston has the purpose of channelling the SF6 towards the breaking zone. The permanent current crosses the main contacts. The fixed main contact, mounted around the arc contact, is constituted by a ring of silvery fingers that are articulated and assembled over springs. The springs exert a strong centrifugal force, assuring a good contact.     © ABB Power Technology 1_114Q07- 81 - Breaking technologies in sf6 . Self-compression  The mobile main contact has an almost truncated-cone shape, is silvered and firmly linked to the piston. This contact technology has the double purpose to avoid corrosion in the main contacts due to the arc and to keep the device features after a high number of breaks.  © ABB Power Technology 1_114Q07- 82 - Breaking technologies in Sf6. Self-compression  In the first phase of current break, the main contacts separate, while the spring keeps the pressure over the arc contacts, which remain closed. This separation of contacts is simply a sectioning and works without arc forming. At the same time, the relative movement of contacts generates a compression of SF6.   © ABB Power Technology 1_114Q07- 83 - Breaking technologies in Sf6. Self-compression  In the second phase of current break, the separation of the arc contacts takes place and an arc appears between them. The compressed SF6 is released and channelled towards the zone between contacts, sweeping away the arc extremes, rapidly deionisating the zone. When the current crosses zero, the arc extinguishes.   © ABB Power Technology 1_114Q07- 84 - Breaking technologies in Sf6. Self-compression  Once the arc contacts are separated, an electrical arc is established among them with a temperature higher than 10,000ºK, which keeps the current flow.  During this period, it is essential to evacuate the thermal energy of the arc, given by the network. The evacuated energy will be higher as the gas density and its specific heat increase. The heat evacuation during the arc duration is obtained mainly by convection, due to the replacement of a given quantity of hot gas by cold gas. Due to the high temperatures, an important heat exchange by radiation could be expected.   © ABB Power Technology 1_114Q07- 85 - Breaking technologies in Sf6. Self-compression  During the closing manoeuvre, the valve rigidly attached to the piston is opened to allow the gas exchange among the different parts of the pole, aiding the movement of pieces. © ABB Power Technology 1_114Q07- 86 - Breaking technologies in Sf6. Self-compression  The empty tubular contacts ease the fast circulation of hot gases and lead to instability in the arc extremes, which avoid the wearing out of arc contacts. The breaking process by self-compression is especially effective, since it works with the injection of a small quantity of gas between contacts.   In the case of a break of 25 kA at 20 kV, the energy to be evacuated is of around 30,000 Jules, which is the energy provided by the arc to keep it at a temperature from 10,000 to 15,000ºK. 1 g of SF6 will be enough to achieve this.   The break by self-compression in SF6 is used in high voltage in outdoor circuit breakers up to 800 kV and in gas-insulated sealed substations (GIS), where the SF6 is used not only as the break medium but also as the insulator in buses and switches. In medium voltage, the self-compression in SF6 is used in circuit breakers up to 36 kV.  © ABB Power Technology 1_114Q07- 87 - Extinction chambers with a low consumption of driving energy  Recent technological advances allow to obtain extinction chambers of automatic circuit breakers in SF6 which require 40% less mechanical energy to disconnect than the former self-compression chambers based in the pressure generated between a mobile cylinder and a fixed piston. The arc extinction is currently achieved by the following effects:     Self-compression. Arc thermal effect. Effect of assistance to disconnection by expansion gases, patented by GEC ALSTHOM. © ABB Power Technology 1_114Q07- 88 - Extinction chambers with a low consumption of driving energy  Beginning of Disconnection:  The parallel contacts 3 are separated from the mobile contact 4 and the current is commuted to the arc contacts 7. When the contacts 7 separate, the arc takes place and its energy causes the pressure rise of volume Vt closed by contact bar 8 and insulating nozzle 9.  Thermal Effect:  © ABB Power Technology 1_114Q07- 89 -  Effect of Assistance to Disconnection  Extinction chambers with a low consumption of driving energy When the contact bar 8 exits the throat of nozzle 9, the thermal overpressure present in volume Vt is released, which creates a blowout just before the zero crossing of the current, ensuring the arc extinction. At the same time, the rise of pressure originated close to the arc spreads towards piston 10, exerting a driving force over the mobile system, providing the required energy for the manoeuvre in the disconnection springs.  © ABB Power Technology 1_114Q07- 90 - Extinction chambers with a low consumption of driving energy  The arc extinguishes and the molecules of SF6 dissociated by the arc are instantly recombined.  The secondary products of the breaking end up deposited in the molecular sieve 11 without affecting negatively the circuit breaker.  In the particular case of breaking weak currents, such as those present in switching capacitor banks or unloaded lines or transformers, the thermal energy of the arc is too small to generate enough overpressure. To obtain the adequate blowout of the arc, the classical effect of self-compression that takes place in volume Vp is used. Consequently, these chambers have a blowout that depends on the current to be opened, causing:    Maximum blowout in case of short-circuit currents. Reduced blowout in case of small currents; hence, the extinction of such currents generates weak overvoltages. © ABB Power Technology 1_114Q07- 91 - Advantages of the use of Sf6      Lack of maintenance. Electrical and mechanical endurance. Great reliability Reduced size and weight related to its features Adaptable to all kind of installations.    Public and industrial networks Motor switching Capacitors switching and protection  Reduced prices. The SF6 appears as a technology favourably applied to the whole range of electric installations.  © ABB Power Technology 1_114Q07- 92 - Disadvantages of the use of SF6  At pressures higher than 3.5 bars an temperatures lower than –40ºC the gas becomes liquid.  Due to this, in the case of circuit breakers of two pressures, it is required to heat the gas of the extinction chamber to keep the equilibrium at room temperatures lower than 15ºC. In closed places, care should be taken to avoid leaks, since it may provoke suffocation in personnel by lack of oxygen (due to its higher density, the gas is displaced by air). In some places it may be convenient to set up extractors that should operate before the personnel entry.  The gas is odourless, colourless and tasteless.    The secondary products of the arc are toxic, and combined with humidity produce hydrofluoric acid, which attacks porcelain and the cement that seals the nozzles. © ABB Power Technology 1_114Q07- 93 - Effect of the impurities in SF6  This impurities come from the manufacturing technique or the deposits pollution. Test most be performed to detect the different impurities specifying the limits of its content in the gas and the methods to control such impurities (see IEC 376). Nature of impurities       Toxic impurities Impurities that affect the apparatus security Impurities that dilute the product Impurities and odour  Impurities have an unnoticeable effect over the dielectric strength of the sulphur hexafluoride © ABB Power Technology 1_114Q07- 94 - Breakdown in SF6 circuit breakers  The main breakdowns in this type of circuit breakers are the gas leaks, which require special devices to be detected.  In a well-installed apparatus, the gas losses should be less than 2% annual of the total volume of the gas inside the apparatus.  In case of total loss of the gas pressure and due to the high dielectric strength of SF6 the voltage that the contacts can bear when opened is equal to double the phase-to-ground voltage.  Anyways, it is not convenient to operate an SF6 circuit breaker when its pressure has been reduced by a leak and the control circuit should be blocked to avoid an accident. © ABB Power Technology 1_114Q07- 95 - Breaker Types SF6 Dead tank High Voltage Circuit Breakers © ABB Power Technology 1_114Q07- 96 - AGENDA  GENERAL    Physics of the electric arc Breaking an alternate current Circuit breaker characteristics  BREAKER TYPES     Breaker technologies Oil circuit breakers Sf6 circuit breakers Vacuum circuit breakers  MAINTENANCE/ DRIVING/ TESTS    Maintenance Driving systems Tests © ABB Power Technology 1_114Q07- 97 - SF6 Dead tank circuit breakers  The design of this type of circuit breakers, called “deadtank”, consists in three aluminium tanks mounted in a sole support. Inside the tanks are included SF6 breaking chambers. The switching drives can be mechanical (by springs) or hydraulic for higher voltages, and are located inside a control cabin placed in the circuit breaker support  © ABB Power Technology 1_114Q07- 98 - SF6 Dead tank circuit breakers  The SF6 gas has rated conditions of 6 bars at 20ºC and each SF6 chamber has a densimeter associated. The use of SF6 technology in sealed chambers causes that this type of circuit breakers requires low maintenance. The compact and simple design of the dead-tank circuit breaker considerably reduces the support structure and the space required for its location in the installation. Besides, this design allows factory assembling and testing, noticeably diminishing mounting time and complexity. Another feature to consider is the low level of noise at normal operation, which added to the reduced required space, the low needed maintenance and the utilisation of non-toxic materials, convert this type of circuit breakers in an important alternative to diminish visual and environmental impact. The dead tank circuit breakers can be used for rated voltages from 38 kV up to 550 kV.    © ABB Power Technology 1_114Q07- 99 - SF6 Dead tank circuit breakers  The dead-tank circuit breakers utilise, in every breaking chamber, the principle of “autopufferTH”, which consists in a combined system of blowout, called “pufferTH”, and of self-blast (arc overpressure). Besides, they add a zip gearing system of double speed. This design turns the breaking chamber into a compact and relatively small device, which permits the breaking of capacitive currents. There are main contacts and arc contacts, which execute the current break. The main contacts, separated from the arc contacts, open first and do not endure the arc erosion. By means of this system the deadtank circuit breakers present the same maintenance requirements and durability of the conventional circuit breakers.  © ABB Power Technology 1_114Q07- 100 - SF6 Dead tank circuit breakers  When breaking low currents, the circuit breaker utilizes the SF6 blowout system; when breaking high currents, the nozzle design leads to a gas overpressure in the arc zone when the contacts arc begin to separate. This overpressure, added to the gearing system of double speed, makes possible the breaking of current using a small amount of energy and a simple mechanical system. The nozzle design and the zip gearing system of double speed cause that the arc contacts move at double speed, using a small amount of energy. This reduces mechanical stresses, since the speed required to move the connections and the switching mechanism are cut by half, in comparison with a conventional circuit breaker of the same rated voltage.  © ABB Power Technology 1_114Q07- 101 - SF6 Dead tank circuit breakers  Fig. shows a diagram of the breaking chamber in closed position, open position and low and high currents breaking. © ABB Power Technology 1_114Q07- 102 - Breaker Types VACUUM High Voltage Circuit Breakers © ABB Power Technology 1_114Q07- 103 - AGENDA  GENERAL    Introduction/ Physics of the electric arc Breaking an alternate current Circuit breaker characteristics  BREAKER TYPES     Breaker technologies Oil circuit breakers Sf6 circuit breakers Vacuum circuit breakers  MAINTENANCE/ DRIVING/ TESTS    Maintenance Driving systems Tests © ABB Power Technology 1_114Q07- 104 - Vacuum circuit breakers  The vacuum, meaning the air at a vacuum level of around 10-4 to 10-5 Pa (10-6 to 10-7 mmHg) reaches a dielectric strength superior to 199 kV/cm. Such exceptional dielectric strength, in addition to the fact that the arc at vacuum presents a quite low voltage (since the electrons released by the cathode find no obstacles in their path towards the anode) and that the dielectric regeneration of the medium is almost instantaneous (since there are not ionised gas molecules between electrodes), motivated the research of the application of vacuum to circuit breakers.  © ABB Power Technology 1_114Q07- 105 - Vacuum circuit breakers  Even when the technology was presented around 1920, the first vacuum circuit breakers were not in the market until 30 years later. The process of vacuum breaking its quite simple: it is enough to separate the contacts, in a vacuum of 10-4 to 10-5 Pa, to have a vacuum circuit breaker.  © ABB Power Technology 1_114Q07- 106 - 1. 2. 3. 4. 5. 6. 7. Insulating casing Fixed contact Mobile contact Piston rod of mobile contact Insulating guide Metallic membrane Metallic screen Vacuum circuit breakers  Research was first oriented to obtain isolating breaking chambers able to permanently maintain the vacuum, in which inside the contacts would be located.  The contacts should be able to cross the chamber keeping an absolute tightness in the gaskets. © ABB Power Technology 1_114Q07- 107 - Vacuum circuit breakers  Once solved these problems, the research was oriented to the breaking technology, based in the two exceptional properties of vacuum:  Its very elevated dielectric strength. fast deionisation of the space between contacts after the breaking.  The © ABB Power Technology 1_114Q07- 108 - Vacuum circuit breakers  The strike of a high-current arc in vacuum entails an unavoidable vaporisation of the electrodes that rapidly leads to a dynamic pressure between contacts that can be equal to the atmospheric pressure.  Initially this arc is alike to that present in other devices, with the particularity of presenting a conductor column strongly concentrated and originating a unique and incandescent cathodic stain, which boiling surface emits plentiful metallic vapours. © ABB Power Technology 1_114Q07- 109 - Vacuum circuit breakers  When the current decreases, the pressure of these metallic vapours quickly diminishes, due to its fast diffusion towards zones farther from the arc, condensing over metallic screens positioned with that purpose. © ABB Power Technology 1_114Q07- 110 - Vacuum circuit breakers  When the current reaches zero, such as in the case of the vacuum diode, the electrons stop travelling through the space between electrodes; hence, the resistance of this space becomes infinite, facing a inverse voltage, while the anode, now cold, is incapable to emit electrons when acting as a cathode. © ABB Power Technology 1_114Q07- 111 - Vacuum circuit breakers  The automatic vacuum circuit breakers are distinguished by the reduced travel of the mobile contacts from 15 to 25 mm, according to the voltage, and by the rather small switching energy. Originally the technology of vacuum breaking was applied to switches and medium voltage circuit breakers with limited functional features. Recently this technology has been applied to automatic circuit breakers up to 36 kV or 50 kV   © ABB Power Technology 1_114Q07- 112 - Vacuum circuit breakers 1. Fixed contact support 2. Fixed contact terminal 3. Fixed contact 4. Mobile contact 5. Insulating body 6. Mobile contact terminal 7. Mobile contact support 8. Angular connecting rod 9. Insulating arm 10. Contact pressure spring 11. Connection trigger 12. Metallic bellows © ABB Power Technology 1_114Q07- 113 - Maintenance Driving systems Tests High Voltage Circuit Breakers © ABB Power Technology 1_114Q07- 114 - AGENDA  GENERAL    Introduction/ Physics of the electric arc Breaking an alternate current Circuit breaker characteristics  BREAKER TYPES     Breaker technologies Oil circuit breakers Sf6 circuit breakers Vacuum circuit breakers  MAINTENANCE/ DRIVING/ TESTS    Maintenance Driving systems Tests © ABB Power Technology 1_114Q07- 115 - Maintenance of circuit breakers  The manufacturer must provide information related to the maintenance measures to be observed under normal service conditions. It is desirable that the manufacturer indicates the number of switchings (or time) following which it is convenient to perform the maintenance of the different parts of the circuit breaker. Besides, the manufacturer must provide the information related to the circuit breakers inspection after:     A) Short-circuit operation B) Normal service operation  © ABB Power Technology 1_114Q07- 116 - This information must include the number of switchings according to A) and B) following which the circuit breaker should be checked. Maintenance of circuit breakers  Main Circuit     Inspection, adjustment and renovation of contacts. Instructions to measure the transition resistance of the main circuit. Prescriptions of the admissible wear in the contacts. Information about the tolerances of opening and closing times. Samples, tests, drying, filling and/or substitution of the liquid or gas. Recommendations related to quality and absence of pollution. Indication of the required quantity of oil or liquid. Maintenance and adjustment Whenever possible during the inspection the circuit breaker must be operated a few times with the assistance of the drives, to ensure that the drive mechanism operates smoothly and that everything works correctly before the start off of the circuit breaker.  Oil (or any other liquid) and gas for insulation or extinction of the arc    © ABB Power Technology 1_114Q07- 117 - Driving mechanism   Maintenance of circuit breakers  Control circuits, auxiliary circuits, auxiliary equipment  Verification of coils, relays, interlocking gears, adjustable electrical devices, heating and drying devices.  Bearings and similar pieces  Indication in the instructions of the parts to verify. Indication in the instructions of the points to verify Verification of the pneumatic and hydraulic valves. Inspection and substitution of joints. Instructions to inspect the inner of the pressurized containers regarding pollution, periodical inspection and substitution of the air-drying devices and humidity absorption. It is advisable to periodically open the purge valve of the air containers to eliminate condensed water.  Connections   Compressed air and hydraulic systems  © ABB Power Technology 1_114Q07- 118 -  Maintenance of circuit breakers  Resistances and capacitors  Verification of resistances and capacitors. The allowed tolerances must be indicated. Specification of the quantity of oil and grease Instructions regarding the cleaning methods. It is recommended to indicate that the insulating parts should be treated with special care and in case of abnormal conditions, such as saline deposits, cement powder or acid vapours, it might be needed to clean frequently in order to avoid possible flashovers List of spare parts and materials that should be stored (in warehouse). List of special tools required to assembly or inspection (when not provided with the circuit breaker).  Lubrication and greasing   Cleaning    © ABB Power Technology 1_114Q07- 119 - Spare parts and materials   Special tools  Maintenance of circuit breakers. Low oil content  Each delivery of circuit breakers includes detailed instructions regarding their assembly, start off and maintenance. Care should be taken that the circuit breaker, the driving mechanism and the steel structures fit perfectly among them, in order to reduce to minimum the on-site labour. The assembly consist mainly in place in-site the different pieces and fit them together with bolted joints. Manufacturers recommend to perform maintenance in the circuit breaker after 12 to 16 years of service.     Before that it is advisable to check the bolted joints and lubricate the mobile parts every 2 to 4 years. The conditions of the contacts should be checked after switching under loads up to 10 times the short-circuit current. The maintenance of the circuit breaker must be easily performed on-site. The instructions should carry complete information about inspection and maintenance.  © ABB Power Technology 1_114Q07- 120 -   Maintenance of circuit breakers. SF6  For the circuit breaker to require slight maintenance, it is indispensable that its extinction chamber is very simple and has few mobile pieces.  The secondary products of decomposition that do not completely recombine precipitate as metallic fluorides, or deposit in a static filter that also absorbs the residual humidity. This diminish the maintenance costs.  The inspection of circuit breakers must be performed considering the accumulated value of the interrupted currents, the number of switchings executed and the time in operation. The following criteria are valid as guiding values:   An inspection should be performed, at least:  Every ten years After 2,000 switching cycles or After breaking an accumulated short-circuit current of 600 kA. © ABB Power Technology 1_114Q07- 121 -   Maintenance of circuit breakers. SF6  In the inspection a diagnosis measurement is performed with the extinction chamber closed, besides general works such as visual control, check of the high and low voltage joints and verification of all screws in the rack. Thus, it should be checked:    Operation times. Transition resistance of the main breaking space. Absorbed currents of the driving coils. Humidity content and acids concentration in SF6. Gastightness of the SF6 enclosures and the driving system.   © ABB Power Technology 1_114Q07- 122 -  Maintenance of circuit breakers. Extinction chamber  Chamber disassembly  When the resistance between terminals is high it is time to repair the chamber. If there is a spare chamber stored, it can be completely replaced. To disassembly the chamber the gas must be drained through the filling valve or to the atmosphere until the pressure is equal to 1 bar. If the gas is drained to the atmosphere, it is required to use mask and rubber gloves, because the used gas might content harmful decomposition products. It is performed with the pole in open position. The screws that joint the contact to the terminal plate must be removed. It can be entirely replaced or, in case of slight deterioration, it can be cleaned with fine sandpaper. It requires the disassembly of nozzles and arc contacts, and then the dismounting of the crown of the mobile contact. It involves the substitution of the closing/opening valves of compressed air.    Substitution of the fixed contact   © ABB Power Technology 1_114Q07- 123 - Substitution of the mobile contact   Driving maintenance  AGENDA  GENERAL    Introduction/ Physics of the electric arc Breaking an alternate current Circuit breaker characteristics  BREAKER TYPES     Breaker technologies Oil circuit breakers Sf6 circuit breakers Vacuum circuit breakers  MAINTENANCE/ DRIVING/ TESTS    Maintenance Driving systems Tests © ABB Power Technology 1_114Q07- 124 - Driving systems of circuit breakers 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. .Drivingaxle .Openingspring .Dameningdevice p .Draggingspring .Tierod .Gearing .Holdingarm .Striker .Cam .Strikerdamer p .Freetrippingdevice .Closingcoil .Tierod .Freetrippingdevice .Suddentrippingdevice .Closingsprings .Openingcoil .Couplingbar .Mtor o .Draggingspring .Star .Tighteningaxle .Draggingarm . © ABB Power Technology 1_114Q07- 125 - Driving systems of circuit breakers  The main driving systems are the following:    By energy accumulation. By compressed air. By pressurized liquid. © ABB Power Technology 1_114Q07- 126 - Driving systems of CB. Energy accumulation  In this system, the closing drive has a previously accumulated energy, by means of a manually tightened spring or an electrical motor. This device consist in powerful springs that accumulate the energy required for the connection. With this purpose they are tightened manually with a lever or by an electrical motor. This drive always operate with a constant closing force, since during the closing manoeuvre is totally independent from any external source of energy.     Besides, the closing can not start until the springs are totally tightened. Given that the energy is stored in the springs before the closing manoeuvre, the tightening mechanism requires a moderated power, even when the closing force has to be high and the closing, fast. After any closing manoeuvre, the springs are automatically tightened again; hence, the mechanism is always ready to operate immediately, after an opening manoeuvre.  © ABB Power Technology 1_114Q07- 127 - Driving systems of CB. Energy accumulation  The closing manoeuvre is rapidly started by a sudden impulse, moderately strong, sent to the closing coil, and is always completed with any impulse duration.  A voltage drop in the driving conductors or a total lack of driving voltage have no effect over an already-started manoeuvre. The springs of the closing mechanism can also be tightened by a lever.    The driving voltage can be either DC or AC. The driving mechanism can be combined with a simple relay set for the fast automatic reclosing, with a minimal dead time up to only 0.3 seconds. © ABB Power Technology 1_114Q07- 128 - Driving systems of CB. Energy accumulation  The springs store elastic energy and are capable to return it without losses from the moment of storing it until it has to be released.  Consequently, the energy to connect and disconnect is always ready to be used according to the demands of the operation or protections of the electrical system. It is evident that, if a system of energy storage has no losses, it is not required any surveillance system about the storage.   The loading of the energy required for the switchings is obtained by electrical or mechanical means. In case of emergency, the mechanical drives allow to manually storage the springs energy. The energy is transmitted towards the mobile contacts (between which the arc is established and extinguished) by means of secure mechanical transmissions. During the circuit breaker assembly, there is no need to connect pressurized fluids tubes, valves or any other element for the drive service. All that is required are electrical connections.  © ABB Power Technology 1_114Q07- 129 -  Driving systems of CB. Compressed air  The driving system can be manually commanded directly by means of a valve or an electric valve. The connection of the circuit breaker is performed very rapidly using compressed air.  Security valve Manom eter Deposit of air Drain valve  The disconnection springs are tightened during the connection manoeuvre, this means, the compressed air is solely used to connect the circuit breaker. Holding valve Com pressor Pressure relay Motor FOR UNIPOLAR CIRCUIT BREAKER  © ABB Power Technology 1_114Q07- 130 - The driving device is activated by a valve that operates during connection and that can be open manually or by means of an electromagnet, remotely. Driving systems of CB. Compressed air  The electrical command of connection is transmitted to the coil of the driving valve "CON" (4). The outlet for air evacuation (5) in the valve "CON" is closed; the compressed air can directly pass from the pressurized deposit (3) to the driving through a tubular joint. The driving piston (7) moves from position "DES" (O) to position "CON" (C) and the circuit breaker is connected.  © ABB Power Technology 1_114Q07- 131 - 1. 2. 3. 4. 5. 6. 7. 8. 9. SF6 enclosure Driving bar Pressurized deposit " Driving valve "CON Outlets for air evacuation " Driving valveDE S " Driving piston Driving cylinder Auxiliary circuit breaker with position indicator Driving systems of CB. Compressed air  All drives are equipped with two disconnection coils "DES" independent from one another. The disconnection command is electrically transmitted to the coils of the driving valve "DES" (6). Trough the open valve "DES" the compressed air arrives to the driving of the circuit breaker pole. Simultaneously the outlet for air evacuation (5) is closed in the valve "DES" and the driving valve "CON" (4) is retained pneumatically-mechanically using a blocking system. The driving piston (7) moves from position "CON" (C) to position "DES" (O) and the circuit breaker is disconnected. 1. 2. 3. 4. 5. 6. 7. 8. 9. SF6 enclosure Driving bar Pressurized deposit " Driving valve "CON Outlets for air evacuation Driving valve"DES" Driving piston Driving cylinder Auxiliary circuit breaker with position indicator  © ABB Power Technology 1_114Q07- 132 - Driving systems of CB. Pressurized liquid  The pressurized liquid most commonly used is oil. The highly pressurized oil circulates through a closed circuit. The high pressure is provided by pressurized nitrogen. The use of gastight gaskets at high pressure in the connected position allows removing the mechanical holding devices (interlocking triggers). The piston rod of the mobile contact is directly coupled to the receiving device; hence, the intermediate mechanisms disappear, eliminating any mechanical link.   © ABB Power Technology 1_114Q07- 133 - Driving systems of CB. Pressurized liquid  Connection  The coil 14 opens the valve 1 and the pressure of the accumulator 11 passes to piston 10, which closes valve 2 and opens valve 3. When opening valve 3, the pressure goes through piping 7 to valve 5. The high pressure passes to receiving piston 20, which leads the mobile contact to its connected position, compressing the springs M.   © ABB Power Technology 1_114Q07- 134 - Driving systems of CB. Pressurized liquid  Disconnection  When the coil 15 opens the valve 6, the high pressure over piston 10 disappears, the valve 2 is opened and the valve 3 is closed, removing the high pressure in piping 7. The valve 5 is opened, emptying piston 20 to the deposit 22 through the piping 8, by means of the spring M that activates the mobile contact 17 to its disconnected position.  A surveillance pressure relay automatically connects and disconnects the pump-andengine set that keeps the pressure in the accumulators between normal levels. Another pressure relay blocks the operation of the circuit breaker when the pressure descends below the admissible level. The connection interlocking works under a pressure higher than the disconnection interlocking, so any connection manoeuvre can be followed by a immediate © ABB Power Technology 1_114Q07- 135 - Driving systems of CB. Reliability  The following table shows a statistic analysis performed in the Mexican network. It can be clearly observed that the failure level for the circuit breakers with spring-based drives is inferior to the failure level for circuit breakers with other kinds of drives. Type of drive Pneumatic Hydraulic Springs (1) Oil-pneumatic 400 kV Nº interruptions Nº failures 87 50 47 46 26 (29,8%) 24 (48%) 2 (4,25%) 5 (10,8%) 230 kV Nº interruptions 131 191 100 25 Nº failures 31 (23,6%) 16 (8,4%) 0 (0%) 0 (0%)  © ABB Power Technology 1_114Q07- 136 - AGENDA  GENERAL    Introduction/ Physics of the electric arc Breaking an alternate current Circuit breaker characteristics  BREAKER TYPES     Breaker technologies Oil circuit breakers Sf6 circuit breakers Vacuum circuit breakers  MAINTENANCE/ DRIVING/ TESTS    Maintenance Driving systems Tests © ABB Power Technology 1_114Q07- 137 - Tests on high and medium voltage circuit breakers  The type tests comprise:          Mechanical behaviour. Mechanical operation. Heating of any of the parts does not exceed the specified limits. Insulation is according to the specified limits. Capability to establish and break the short-circuit currents. Capability to endure its permissible rated short-time current. Capability to break currents on unloaded cables. Capability to break currents on capacitors banks. Capability to break small inductive currents.  © ABB Power Technology 1_114Q07- 138 - The results of all type tests are recorded in type tests registries that contain all required data to demonstrate its compliance to standards. They also include the data needed to identify the essential characteristics of the tested automatic circuit breaker. Each of the type tests should be performed on a new and clean automatic circuit breaker, and the different type tests can be carried out  Mechanical Tests on circuit breakers  The mechanical tests exclusively comprise the execution of manoeuvres of opening/closing, without voltage or current in the main circuits.  Usually, 1,000 switching cycles are carried out, 10% of them are carried out based on opening/closing cycles. The opening is driven by closing the main contacts, being the circuit breaker equipped with its usual switching device.   In these manoeuvres the heating of the electrical components should not exceed those specified by the standards. During this test lubrication is allowed, but mechanical adjustments are not. After the test, all pieces must be in good condition and must not present excessive wear-out. Any permanent deformation that could be present in the mechanical parts must not negatively influence the circuit breaker operation; neither impedes the correct placement of the spare parts.   © ABB Power Technology 1_114Q07- 139 -  Dielectric Tests on circuit breakers  One of the main features of switchgear is the insulation level, defined by the values of nominal power-frequency withstand voltage and nominal lightning withstand voltage and, in switchgear for 300 kV or higher, by the value of nominal switching withstand voltage. The standards set the effective (rms) values and the peak values in kV for the test (nominal) voltages, as a function of the most elevated voltage of the material.  © ABB Power Technology 1_114Q07- 140 - Dielectric Tests on circuit breakers.  The voltage will be applied as following:  Closed position:  Among all parts of the main circuit of each pole and the frame, successively. All parts of the main circuit of the rest of the poles (if any) have to be connected to the frame. Among all parts of the main circuit of all poles connected among themselves and the frame. Between the terminals of each pole successively and the frame, being all parts of the main circuit of the rest of the poles (if any) connected to the frame. Between the terminals of a side connected among themselves and terminals of the opposite side connected among themselves and frame. The tests will be repeated inverting the connections that link terminals with the source and the frame, unless the distribution of terminals of a pole is symmetrical regarding the frame. the the the the  Open position:    © ABB Power Technology 1_114Q07- 141 - Dielectric Tests on circuit breakers. Shock waves   They lie on subjecting the circuit breakers to shock waves of 1.2/50 µs. During each test, five consecutive shock waves are applied.  It is considered that the automatic circuit breaker complies the test if during which neither strikes nor punctures take place. If some puncture or two or more strikes take place, it is considered that the circuit breaker does not comply the test. If only one strike takes place, ten additional shock waves will be applied, and it will be considered that the circuit breaker complies successfully the test solely if during the additional applications neither strikes nor punctures take place.    © ABB Power Technology 1_114Q07- 142 - The circuit breaker must be capable to comply the specified tests with voltages of positive and negative polarity, even when it is enough to carry out the test with one polarity if it is evident that such polarity results in a lower strike voltage. Dielectric Tests on circuit breakers. Shock waves  The test voltages are usually obtained by means of a pulse generator, composed by a given number of capacitors, all equal, that are simultaneously charged in parallel through some resistances, using a source of direct voltage (DC), and are later discharged in series through a circuit that includes the tested device (Marx Principle). The DC voltage is generally obtained from an alternate voltage source, at 50 Hz, by means of metal rectifiers, until a spark is generated in the spark-gaps “e”, all regulated at exactly the same distance, which is related to the voltage to be applied to the device.  © ABB Power Technology 1_114Q07- 143 - Dielectric Tests on circuit breakers. Power freq.  The test voltage will be raised to the given value and will be maintained by one minute. It is considered that the circuit breaker does not comply the test if during which some strike or puncture takes place. In the test, the voltage reached in the test circuit must be stable enough so as not to be affected by the leakage current variations or by partial discharges or pre-discharges. This condition is complied if the total capacitance of the tested device (including the additional capacitances of the circuit) is not higher than 1,000 pF, and the value of the current permanently delivered by the transformer when the device is short-circuited at test voltage is not lower than 1 A (rms value). In the resonant circuit, the stability of the resonance conditions and the constancy of the value of the test voltages depend on the constancy of the circuit impedances and the frequency of the source.    © ABB Power Technology 1_114Q07- 144 - Heating Tests on circuit breakers.  It must be ensured that the device and its main circuits do not become excessively hot when the rated current is circulating through them. The test must be performed over a new device, with clean contacts. Before carrying out the test, the ohmic resistance of the main circuits must be measured. The test must be performed causing the circulation through all poles (with the exception of high voltage switchgear higher to 72.5 kV, in which only one pole is tested) of the rated current at steady state and at power frequency if it is AC, during a time range enough for the heating to be constant (when the variation does not exceed 1ºC by hour).    © ABB Power Technology 1_114Q07- 145 - Heating Tests on circuit breakers.  For other conductors than those of coils, the tª of the different parts will be measured using thermometers or thermocouples located in the available hottest point. For the opening and closing coils that are excited solely during the opening and closing manoeuvres, the heating test consists in feeding these coils at their rated voltage ten successive times with a 2 s interval between the excitation instants, supposing the circuit breaker has an automatic device to open the control circuit at the end of the manoeuvre, or feeding them ten successive times during 1 s being 2 s the interval between excitations. To perform the heating test an adjustable alternate current source is required (exceptionally a DC source) with a capacity equal to the rated current of the tested switchgear. The pertinent measurement devices are also required: voltmeters, ammeters, millivoltmeters, double bridge (Thomson), thermometers, thermocouples, low voltage or very low voltage transformers, etc.   © ABB Power Technology 1_114Q07- 146 - Short circuit Tests on circuit breakers. TRV  The rated transient recovery voltage (TRV) for terminals failure, associated to the rated short-circuit breaking capacity, is the predictable limit voltage of reference of the circuits that the circuit breaker must be able to clear in case of a terminals short-circuit. The waveform of the TRV changes accordingly the configuration of the real circuits. In networks with rated voltages higher than 100 kV and for important short-circuit currents (with respect to the maximum short-circuit current), the TRV presents an initial period during which the rising speed is high and a subsequent period during which such speed is reduced. This waveform is well-enough defined by means of an envelope formed by three straight-line segments determined by four parameters.    © ABB Power Technology 1_114Q07- 147 - Short circuit Tests. Breaking and making cap.  Before accomplishing the tests of breaking capacity and making capacity, it is required to carry out several switchings under no load, during which the accurate operation of the automatic circuit breaker will be verified and the travel speed, closing time and opening time will be registered. The generated overvoltages will not exceed the maximum admissible and external flashover will not take place. If the automatic circuit breaker has an electrical drive, these tests must be performed feeding the closing device at 105% and 85% of the rated voltage of operation of the drive. In case of air-compressed or pressurized oil drives, the tests must be performed at minimum pressure with the shunt triggers fed at 85% the rated voltage of operation and repeated at nominal pressure at 100% the rated voltage of operation and at maximum specified pressure at 110% the rated voltage of operation. In case of energy accumulation drives (springs), the tests must be performed with the shunt triggers fed at 110% and 85% the rated voltage of operation.    © ABB Power Technology 1_114Q07- 148 -  Short circuit Tests. Breaking and making cap.  During the tests of breaking and opening inside the given limits of breaking capacity and making capacity, the circuit breaker must not present exaggerated signs of wear-out neither risk the operator integrity. After every sequence of tests, the mechanical parts and their insulators will be practically in the same conditions that before the tests. After the sequence of the short-circuit test, the automatic circuit breaker will be capable to close and open its steady state rated current at rated voltage, admitting that its possibilities to open and close the shortcircuit current will be considerably reduced after the tests. It is considered that a circuit breaker does not comply the sequence of short-circuit tests if the damages in the main insulation (that is subjected to electrical stresses under normal operation conditions) alter its insulating condition at rated voltage. The fundamental short-circuit tests in the high voltage automatic circuit breakers consist in a series of five basic sequences of short-circuit tests.   © ABB Power Technology 1_114Q07- 149 -  Individual tests in circuit breakers  They have the purpose of evidence the imperfections of the material or the manufacturing that would alter the properties and quality of the tested device. They are acceptance tests performed over a given number of samples to determine by negotiation between the manufacturer and the user. The test site can be the installation site of the apparatus. These tests consist on:        Voltage tests at power-frequency. Voltage tests of the driving and auxiliary circuits. Measurement of the resistance of the main circuit. Tests of mechanical sequence operations. © ABB Power Technology 1_114Q07- 150 - Routine tests in circuit breakers  The routine tests are performed in all circuit breakers. During these tests, the circuit breaker is connected to its driving mechanism without support and switching insulators. The inertia of the switching insulators is compensated mounting special weights with equivalent inertias before the test. The routine tests include the following operations:    Adjustment of the driving mechanism. Measurement of the limit values of the drive voltage and the motor voltage. Voltage test of the drive circuits Verifying the times of opening and closing, the speeds of opening and closing, and the dampening in the final position of the contacts. Pressure tightness tests to each breaking unit. Measurement of the resistance of the main path of current. Voltage test to each breaking unit.    © ABB Power Technology 1_114Q07- 151 -  