Test Universe Advanced Differential Module Application Note Example of Use Transformer ENU

Testing TransformerDifferential Protection Practical Example of Use Testing Transformer Differential Protection Manual Version: Expl_TDiffProt.ENU.1 - Year 2013 © OMICRON electronics. All rights reserved. This manual is a publication of OMICRON electronics GmbH. All rights including translation reserved. The product information, specifications, and technical data embodied in this manual represent the technical status at the time of writing and are subject to change without prior notice. We have done our best to ensure that the information given in this manual is useful, accurate, up-to-date and reliable. However, OMICRON electronics does not assume responsibility for any inaccuracies which may be present. The user is responsible for every application that makes use of an OMICRON product. OMICRON electronics translates this manual from the source language English into a number of other languages. Any translation of this manual is done for local requirements, and in the event of a dispute between the English and a non-English version, the English version of this manual shall govern. 2 Content Preface ......................................................................................................................................................... 4 1 Application Example ............................................................................................................................ 5 2 Theoretical Introduction to Transformer Differential Protection ..................................................... 7 2.1 Protection Principle ........................................................................................................................ 7 2.2 Operating Characteristic ................................................................................................................ 8 2.3 Zero Sequence Elimination ......................................................................................................... 11 2.4 Transformer Inrush ...................................................................................................................... 13 3 Practical Introduction to Transformer Differential Protection Testing ......................................... 15 3.1 Defining the Test Object .............................................................................................................. 16 3.1.1 3.1.2 3.2 Global Hardware Configuration of the CMC Test Set ................................................................. 26 3.2.1 3.2.2 3.2.3 3.3 Example Output Configuration for Differential Protection Relays .................................................... 26 Analog Outputs ............................................................................................................................... 27 Binary Inputs ................................................................................................................................... 27 Local Hardware Configuration for Differential Protection Testing ............................................... 28 3.3.1 3.3.2 3.4 Device Settings ............................................................................................................................... 16 Defining the Differential Protection Parameters .............................................................................. 18 Analog Outputs ............................................................................................................................... 28 Binary Inputs ................................................................................................................................... 28 Defining the Test Configuration ................................................................................................... 29 3.4.1 3.4.2 3.4.3 3.4.4 3.4.5 3.4.6 General Approach ........................................................................................................................... 29 Configuration Test........................................................................................................................... 30 Operating Characteristic Test ......................................................................................................... 33 Trip Times Test ............................................................................................................................... 36 Inrush Blocking Test ....................................................................................................................... 39 Testing Three-Winding Transformer Differential Protection ............................................................ 42 Support....................................................................................................................................................... 43 Please use this note only in combination with the related product manual which contains several important safety instructions. The user is responsible for every application that makes use of an OMICRON product. © OMICRON 2013 Page 3 of 43 Preface This paper describes how to test the transformer differential protection function. It contains an application example which will be used throughout the paper. The theoretical background of transformer differential protection will be explained. This paper also covers the definition of the necessary Test Object settings as well as the Hardware Configuration for these tests. Finally the Advanced Differential test modules are used to perform the tests which are needed for this protection function. Supplements: Sample Control Center file Example_AdvDifferential_Transformer.occ (referred to in this document). Requirements: Test Universe 2.41 or later; Advanced Differential and Control Center licenses. Note: © OMICRON 2013 The description of the Differential test module is not a part of this document. Page 4 of 43 1 Application Example 220 kV 400/1 Protection functions (87) Differential Protection (50/51) Definite Time Overcurrent Protection Transformer Differential Relay 600/1 110 kV Figure 1: Feeder connection diagram of the application example © OMICRON 2013 Page 5 of 43 . Side 2 (used for the calculation of the transformation ratio of the transformer) Yyn0 Vector group 400 A / 1 A CT ratio. Pick-up value of the differential protection (Iref is a reference current which can be obtained from the relay manual. 2nd harmonic restraint value (relative to the fundamental frequency differential current) Table 1: Relay parameters for this example Note: © OMICRON 2013 Testing of the Restricted Earth Fault protection function. Second element of the differential protection (there is no stabilization above this value) 20% Idiff Bias current where the first slope ends and the second slope begins. In this case it is the rated current of the transformer) Idiff>>.7 Slope 2 of the differential characteristic 4. Thermal Overload protection function. Page 6 of 43 . Side 1 (used for the calculation of the transformation ratio of the transformer) Rated voltage.5 kV Notes Rated power Rated voltage. Side 1 600 A / 1 A CT ratio.3 Slope 1 of the differential characteristic 0.25 Iref Differential characteristic settings 6. Side 2 CT data 0.Parameter Name Parameter Value Frequency 50 Hz 160 MVA 231 kV Transformer data 115.0 Iref Harmonic restraint settings Idiff>.0 Iref 0. etc. is not part of this document. the generators and the busbars. n I i  I1  I 2   In  0 i 1 During a fault in the protected zone.e. the sum of the currents flowing into a conducting network is zero. i. therefore. Usually differential relays are applied as their main protection against shortcircuit faults within the protected area. as well as the CT ratios and the positions of the CT star-points. Page 7 of 43 . The current differential principle is based on Kirchhoff’s law. I load side 1 I load side 2 Protected Object Side 1 1A 0° 1A -120° 1A 120° Side 2 1A 180° 1A 60° 1A -60° Ph A Protected Object Ph B Ph C Protected Zone Figure 2: Protection principle of the transformer differential protection This principle applies to each phase separately. Note: © OMICRON 2013 The following parts of this document will only focus on transformer differential protection. In this case the sum of the measured currents in at least one phase is not zero.2 2. compensate for their influence.1 Theoretical Introduction to Transformer Differential Protection Protection Principle The most important components in a power transmission and distribution system are the transformers. the relay can detect the fault. the following equation can be calculated for each phase. Therefore. will cause problems with the calculation of the current sums. However. For electromechanical differential relays. Numerical differential relays can calculate these effects and. Therefore. The transformation ratio and the vector group of a transformer. interposing transformers have to be used instead. this is only valid if all CT ratios are the same and if the current is not transformed within the protected object. a current will flow from one phase to another phase or to ground. To compensate for these error currents. Some other effects. the differential protection must be provided with a bias element. Idiff = ISide 1 .ISide 2 Sum Current Transformer Tap changer / Leakage Magnetization Iload Figure 3: Natural error currents of the transformer In Figure 3 it can be seen that the magnitude of the spill current (Sum) depends on the transformer load current. (K1 = 2) *) = only valid for three-winding transformers. etc. e.g. P6x Various conventional (electromechanical) relays *) = only valid for two-winding transformers. SEL5 AEG/ALSTOM/AREVA *). ISide 2   ISide 1  ISide 2  cos SEG/Woodward. also add to this spill current. such as the current transformer accuracy (including CT saturation). (K1 = 2).g. for three-winding transformers see below SIEMENS (K1=1).2. however. e. is the load current. e. e.2 Operating Characteristic If the transformer is equipped with an on-load tap changer (OLTC). Note: The calculation method of the bias current depends on the relay manufacturer (see Table 2). PQ7x.g. series KBCH SEL (k1=2). 7UT5x/7UT6x GEC (K1=1). the magnetization of the transformer. conventional (electromechanical) relays Elin/VATECH. The corresponding solution and further sources for spill currents will be dealt with in the following sections. The differential relay. its transformation ratio varies over the tapping range. ISide 2 max  ISide 1 . This changes the ratio of the currents on side 1 and side 2 and thus produces a spill (out-ofbalance) current in the relay.g. The currents are scaled to the nominal current of the transformer © OMICRON 2013 Page 8 of 43 . This bias element depends on the current flowing through the transformer which. e. must not operate in this case.. under normal conditions. The magnitude of the spill current increases as the load on the transformer increases. Calculation Method Manufacturer Notes ISide 1  ISide 2  AEG/ALSTOM/AREVA *).g. for two-winding transformers see above I Side 1 K1  ISide 2  / K1 min  ISide 1 . DRS GE Multilin SR745 ABB Table 2: Selection of different calculation methods for the bias current (depending on the relay manufacturers). m2 = 4 (072. Idiff ID>> Characteristic Sum Tripping Blocking Current Transformer Tap changer / Leakage ID> Magnetization Ibias Figure 4: Operating characteristic of a transformer differential protection device As shown in Figure 4.147) Ibias Figure 6: Operating Characteristic for the AREVA P633 © OMICRON 2013 Page 9 of 43 .25 (072. the operating characteristic has to cover the spill currents during normal conditions. etc.With this value the construction of an operating characteristic is possible.142) 07 0.) differs widely between manufacturers and relay types. the AREVA P633 is used. Figure 5 and Figure 6 show the parameters and the tripping characteristic of the P633. Figure 5: Relay settings for the differential operating characteristic (AREVA P633) Idiff Idiff>>> = 6 (072.14 IR.144) 0. The design of the operating characteristic (number of line segments.3 ( m1 = 5) 2. slope. For the following example. thus enabling the device to determine between blocking and operating.7 ( 6) m= 2( fixe dv alu e) = m2 4 2.1 07 Idiff> = 0. 25 IRS1 = 4 Ibias Figure 8: Operating characteristic for the SEL-387 © OMICRON 2013 Page 10 of 43 .Figure 7 and Figure 8 show the settings and the operating characteristic of the Schweitzer SEL-387 for comparison. Figure 7: Relay settings for the operating characteristic (SEL-387) Idiff U87P = 6 = P2 SL 1 SLP 70 % % = 30 O87P = 0. the zero-sequence must be eliminated from the currents seen by the relay. Therefore.3 Zero Sequence Elimination External phase-to-phase or three-phase faults cannot cause differential currents.2. with external phase-to-ground faults at a winding with a grounded star-point. during external phase-to-ground faults. The fact that side 2 has a zero sequence current and side 1 does not have one causes a differential current. As the star-point of side 1 is not grounded. may lead to an unwanted operation of the protection relay. This differential current. The following discussion is only valid for numerical relays. Note: The way the elimination is achieved differs between conventional and numerical relays. the current of the faulty phase splits in to the non-faulty phases. This is not the case. however. The zero sequence current of side 2 will be compensated in the delta winding. Zero-sequence current elimination methods for numerical relays Arithmetical Via measurement Side 1 Side 2 Internal correction of the currents by means of mathematical models Disadvantage: like electromechanical relays with YdYinterposing current transformers the sensitivity for phase-to-ground faults is reduced by 1/3 Differential Relay Figure 10: Methods of zero-sequence current elimination (numerical relay) © OMICRON 2013 Page 11 of 43 . I Side 2 I Side 1  2  Inom  I Side 1   1 Inom   1 Inom  IDiff  I Side 1  I Side 2 I Side 2  3  Inom    0   0   2  Inom   3  Inom  1 Inom    1 Inom    0   1 Inom   1 Inom   0  1 Inom  Figure 9: Differential currents due to an external phase-to-earth fault The fault current on the grounded side (side 2) will lead to a current in the faulty phase on the non-grounded side (side 1) as shown in Figure 9. The activation logic of which depends on the manufacturer. Figure 11 shows an example of these settings. 1 Figure 11: Relay settings for the activation of the arithmetical methods of Zero-sequence current elimination (AREVA P633) 1. there is an “error” based on the correction formula which influences the bias currents displayed in the relay. Therefore.Note: This document only focuses on the arithmetical method. the relay will also measure bias currents in the non-faulty phases. The arithmetical method of zero-sequence elimination is activated for side 2 (the 110-kV-side. © OMICRON 2013 Page 12 of 43 . Phase Currents:  2  Inom  I Side 1   1 Inom   1 Inom  I Side 2  3  Inom    0   0  Zero Sequence Elimination for Side 2: I 0 Side 2  I Side 2 1 1 I A  I B  I C    3  Inom  0  0  1 Inom  3 3  I Side 2  I 0 Side 2  3  Inom   1 Inom   2  Inom    0    1 Inom    1 Inom   0   1 Inom   1 Inom  Differential and Bias Currents after Zero Sequence Elimination: IDiff  I Side 1 IBias   I Side 2  2  Inom   2  Inom  0    1 Inom    1 Inom   0   1 Inom   1 Inom  0  I Side 1  I Side 2 2   2  Inom   2  Inom   2  Inom   1      1 Inom    1 Inom     1 Inom  2     1 Inom   1 Inom    1 Inom  Figure 12: Arithmetical zero sequence elimination With the arithmetic zero-sequence current elimination. see Table 1) Figure 12 shows the calculation of the zero sequence elimination with the fault currents from Figure 9. The same effect occurs when using interposing transformers. 4 Transformer Inrush Inrush is a phenomenon which commonly takes place directly after a transformer is energized. if the relay is not stabilized against inrushes. which use frequency analysis or time signal analysis. There are different ways of stabilizing a relay against inrush currents. Harmonic Figure 14: Harmonic blocking scheme © OMICRON 2013 Page 13 of 43 . The three phase currents during an inrush are shown in Figure 13. As they only flow on one side of the transformer. due to saturation of its magnetic core. Figure 13: Transient record of a transformer inrush This inrush current has a unique wave form which is characterized by a high percentage of even harmonics – especially of the second and fourth harmonic. which will lead to an unwanted trip. the relay will interpret them as differential currents.2. The most common methods are described in the following section. the relay will block as shown in Figure 14. Idiff Tripping Blocking ID> Harmonic Blocking Setting I2. > Harmonic Blocking: Whenever the percentage of the second harmonic current exceeds the setting value. This saturation causes high power losses which lead to high currents. During the inrush. the magnitudes of the currents are different in each phase. the blocking is stopped when the differential current exceeds the Idiff>> setting.159) I2. In some phases the harmonic currents may be just enough to block the relay whereas in the remaining phases it may be just insufficient enough. Idiff Idiff>> (072. It shows that. Its harmonic blocking characteristic is displayed in Figure 16. To prevent this unwanted operation the relay can use cross-blocking. These non-blocked phases will cause an unwanted operation.> Harmonic Restraint: The second and fourth harmonic currents will be added to the bias current. in addition to the characteristic in Figure 14. Idiff Tripping Bias Current without Harmonics Bias Current with Harmonics ID> Blocking Ibias Figure 15: Differential protection operating characteristic with harmonic restraint > Wave form analysis: Numerical time domain analysis of the transient current signal is used to recognize wave shapes which are typical for transformer inrushes.143) RushI(2f0)/I(f0) (072. This function blocks the trip in all phases if one phase detects an inrush. The AREVA P633 uses harmonic blocking to prevent unwanted operations during transformer inrush occurrences. Harmonic Figure 16: Inrush blocking characteristic of the AREVA P633 © OMICRON 2013 Page 14 of 43 . Figure 15 shows that the increased bias current will prevent the relay from tripping during inrushes.142) Tripping Blocking Idiff> (072. The Diff Trip Time Characteristic module for testing the trip times of the differential protection. These test modules are: > > > > The Diff Configuration module for testing the configuration of the differential protection which consists of the wiring and the relay parameters such as transformer data. busbars. motors. The Diff Harmonic Restraint module for testing the blocking of the differential trip due to current harmonics. for assets such as transformers. CT data and zero sequence elimination. The Diff Operating Characteristic module for testing the operating characteristic of the differential protection. generators. © OMICRON 2013 Page 15 of 43 .3 Practical Introduction to Transformer Differential Protection Testing The Advanced Differential test modules are designed for testing any kind of three-phase current differential protection functions. These test modules can be found on the Start Page of the OMICRON Test Universe. lines and cables. They can also be inserted into an OCC File (Control Center document). relay type. the Test Object has to be opened by double clicking the Test Object in the OCC file or by clicking the Test Object button in the test module. 3.2). the settings of the relay to be tested must be defined. The CT data is not entered in this RIO function.1 Device Settings General relay settings (for example.1. It will be entered in the RIO function Differential (see chapter 3.1. In order to do that.1 Defining the Test Object Before testing can begin.3. relay ID. substation details) are entered in the RIO function Device. © OMICRON 2013 Page 16 of 43 . These values must be adapted to the respective Hardware Configuration when connecting the outputs in parallel or when using an amplifier.Note: © OMICRON 2013 The parameters V max and I max limit the output of the currents and voltages to prevent damage to the device under test. Page 17 of 43 . The user should consult the manual of the device under test to make sure that its input rating will not be exceeded. the operating characteristic.3.2 Defining the Differential Protection Parameters More specific data concerning the transformer differential relay can be entered in the RIO function Differential. Note: © OMICRON 2013 Once an Advanced Differential test module is inserted. this RIO function is available. general relay settings. the CT data.1. This includes the transformer data. Page 18 of 43 . as well as the harmonic restraint definition. As a transformer differential protection is to be tested. The transformer data has to be entered here. © OMICRON 2013 Page 19 of 43 . This setting has influence on the currents during single-phase faults. they will appear in the respective test modules. 2. The nominal current of each winding is calculated automatically. 3. For each Y winding the star-point grounding can be defined. Note: If the nominal power of the different transformer windings is not equal. Also.Protected Object This first tab contains the definition of the primary equipment which is protected by the relay. 1 2 3 4 1. 4. the nominal voltage and the nominal power have to be defined. For each winding. They can be chosen freely and once they are set. the reference winding of the relay must be entered in the first column. Transformer has to be selected. It can be used to check if the transformer settings have been entered correctly. The names of the transformer windings can be entered here. the vector group of the transformer must be entered. Towards Protected Object Towards Line Relay Relay Relay Relay Figure 17: Definition of the CT star-point direction © OMICRON 2013 Page 20 of 43 . 1 2 1. 2. the CT star-point direction can be chosen according to the wiring of the CTs. With this option.CT In this tab the data for the current transformers is entered. The nominal currents of the CTs are entered here. The relay setting Idiff>> of the P633 corresponds to the harmonic blocking whereas the relay setting Idiff>>> corresponds to the Test Object parameter Idiff>>. Test Max: is the test shot time if the relay does not trip. It should be set higher than the expected relay trip time but shorter than possible trip times of additional protection functions (for example. This method depends on the relay type and Table 2 shows some examples of how to set these parameters. 7. 0. the Zero Sequence Elimination has an influence on the currents during phase-to-ground faults. If the differential current exceeds this value the relay will always trip. 8. 3. The current and time tolerances can be obtained from the relay manual. Therefore. 2. With the settings Reference Winding and Reference Current. 4. 5. The Delay Time defines the pause between two test shots and during this time no currents will be generated. the nominal current which will be used as the reference current can be selected. 4 1 2 5 3 6 7 8 1.3. Since a differential relay typically trips instantaneously this time can be set quite low in this case (for example. As all differential current settings are entered relative to the nominal current. Idiff>> defines the high differential current element. overcurrent protection). The setting Idiff> defines the pick-up of the differential protection function.Protection Device In this tab the basic settings of the protection device are entered.I0. Select the calculation method of the bias current. Select IL . The relay will not trip if the differential current does not exceed this setting. Select No combined characteristic if the relay uses only the phase with the highest current magnitude for the differential and bias current calculation. 6.2 s) to speed up the test. this current has to be defined. this time may be increased to prevent overheating of electromechanical relays. Figure 4 shows the tripping characteristic with these settings as defined in the Test Object and Figure 6 shows the corresponding relay settings of the AREVA P633. The time settings tdiff> and tdiff>> define the trip times of the differential elements. In this example the reference current is the nominal current of the transformer on side 1. © OMICRON 2013 Page 21 of 43 . As described in chapter 2. For the AREVA P633 this option remains cleared as the relay calculates these currents in all three phases simultaneously. if the relay uses numerical zero sequence elimination. 2.125  a a  0. For this it is advantageous to visualize the characteristic and its corner points first (Figure 18). When opening the tab for the first time it will show a default operating characteristic.Characteristic Definition The operating characteristic of the relay can be defined in this tab.39 © OMICRON 2013 Page 22 of 43 .147) Ibias Figure 18: Operating Characteristic for the AREVA P633 with corner points 3. 1. Unknown parameters are replaced by variables like a.25) a: Use P1 in equation II to get the variable a.41  P2 = (4 / 1.7  4  b b  1. The line segments of this characteristic are set by entering their corner points. The necessary steps to enter an operating characteristic are shown below with the example settings of Table 1: 1.25  0.41  0.3  4  0.25  2  Ibias Ibias  0. c etc. Calculate the corner points of the characteristic and the unknown parameters:  P1: Use Idiff> in equation I to get Ibias of P1.144) P3 =0 . The corner points of the characteristic have to be calculated now.3  0. Idiff Idiff>>> = 6 (072.3  Ibias  a Segment 1 from P1 to P2 III : Idiff  0.2125  1.m2 in equation II to get Idiff of P2 Idiff  0.3 m1 = ) .: I : Idiff  2  Ibias Fixed line from (0/0) to P1 II : Idiff  0.125   P1 = (0.7 4 2.25  0.3  0.142) 0.41) b: Use P2 in equation III to get the variable b.2125 P2: Use IR.1 6) m= 2( fixe dv alu e) m2 7 (0 Idiff> = 0. Click Remove All to clear the default line segment. b.125  0.m2 = 4 (072.25 (072.7  Ibias  b Segment 2 from P2 to P3 4. Set up equations for the line segments including fixed lines. 0.125 / 0.41  0.145 ( 072 P2 P1 IR. 0.7  4  1. 56 P3 = (10. P3: Use Idiff>> in equation III to get Ibias of P3.56 / 6) 5. Enter the calculated points as the start and end points of the line segments:  Enter the values of P1 at the Start point: and the values of P2 at the End point: and click Add to define the first line segment.7  Ibias Ibias  10. The slope can be used to check if the settings have been entered correctly: © OMICRON 2013 Page 23 of 43 .39  0. 6  0.7  Ibias  1.39 7. The slope can be used to check if the settings have been entered correctly: Note: It is not necessary to define the horizontal line segments represented by Idiff> and Idiff>>. A Protection Testing Library (PTL) can be found on the OMICRON homepage. © OMICRON 2013 Page 24 of 43 . These values will be added to the resulting operating characteristic automatically. Enter the values of P2 at the Start point: and the values of P3 at the End point: and click Add to define the second line segment. It contains relay specific test files where these calculations are already implemented. © OMICRON 2013 Page 25 of 43 . 1 3 2 4 1. This works in the same way as it was shown with the operating characteristic. the other harmonics can subsequently be adjusted. 4. 3. 2.Harmonic In this tab the harmonic blocking characteristic can be entered. Otherwise a characteristic can be created by entering line segments with start and end points. Enter the tolerances as specified in the relay manual. Select the number of the harmonic that blocks the differential protection. if the harmonic blocking scheme is a straight vertical line from Idiff> to Idiff>> (Test Object parameters). After applying the settings to one harmonic. Enter the harmonic blocking threshold value and click Update. 3. © OMICRON 2013 Page 26 of 43 . therefore.3. It can be opened by double clicking the Hardware Configuration entry in the OCC file. it has to be defined according to the relay’s connections. It is valid for all subsequent test modules and.1 Example Output Configuration for Differential Protection Relays ISide 1 A ISide 1 C ISide 1 B ISide 1 N ISide 2 B ISide 2 N ISide 2 A ISide 2 C Figure 19: Wiring of the analog outputs of the CMC test set.2 Global Hardware Configuration of the CMC Test Set The global Hardware Configuration specifies the general input/output configuration of the CMC test set.2. 3). The binary inputs 1 to 10 can be used. If the relay uses multiple commands to trip the circuit breakers of the transformer. Figure 20: Wiring of the binary inputs of the CMC test set.2. 3.2 Analog Outputs The analog outputs.3 Binary Inputs 3 2 1 2. The binary outputs and analog inputs etc. will not be used for the following tests.3. Trip Side 1 3. For wet contacts adapt the nominal voltages of the binary inputs to the voltage of the circuit breaker trip command or select Potential Free for dry contacts. binary inputs and outputs can all be activated individually in the local Hardware Configuration of the specific test module (see chapter 3. all trip contacts have to be connected to a binary input.2. © OMICRON 2013 Page 27 of 43 . Trip Side 2 1. 3.2 Binary Inputs © OMICRON 2013 Page 28 of 43 .3.3. Therefore.1 Analog Outputs 3. It can be opened by clicking the Hardware Configuration button in the test module. 3. it has to be defined for each test module separately.3 Local Hardware Configuration for Differential Protection Testing The local Hardware Configuration activates the outputs and inputs of the CMC test set for the selected test module. > Trip Times Test: Verifying the trip times of the differential protection elements.1 General Approach When testing the differential protection. CT data and zero sequence elimination. > Operating Characteristic Test: Verifying the position of all operating characteristic line segments.3. the following steps are recommended: > Configuration Test: Testing the wiring and the configuration parameters of the differential protection including transformer data. > Inrush Blocking Test: Verifying the inrush blocking characteristic. These tests can be performed with the advanced differential test modules: > Diff Configuration > Diff Operating Characteristic > Diff Trip Time Characteristic > Diff Harmonic Restraint © OMICRON 2013 Page 29 of 43 .4 Defining the Test Configuration 3.4. The test time should be set long enough to allow the measured currents from the relay to be read.4. 2 3 4 © OMICRON 2013 4. currents flowing through the protected area may lead to an unwanted operation. This setting defines on which side of the transformer the fault and the source should be located for the fault simulation. 1 2. These settings define if the CMC should generate voltages and whether the test should be time synchronized via GPS or IRIG-B. the CT ratios or the CT star-point directions are not set correctly. 1. During these faults the relay must not trip and therefore. In this example neither of these will be necessary. 3. The Trigger Logic has to be defined according to the relay configuration. This way the test will be assessed as failed if any of the trip contacts are triggered. even small differential currents will lead to a trip. The configuration test simulates external faults with fault currents flowing through the protected area. Note: If the relay uses multiple trip contacts. this test confirms that the wiring. Therefore. General General settings of the test are entered in this tab. are correct.3. If the wiring is incorrect or if parameters such as the nominal voltages.2 Configuration Test Differential protection relays are usually set to be very sensitive. Page 30 of 43 . the zero sequence elimination. as well as the above mentioned parameters. they should be linked with OR. The fault type can be defined with this setting. Enter the test current and click Add to set a test point. Note: Only one fault type can be set per test module. if multiple fault types are to be tested. The test current will be relative to the nominal current of the fault side. 3. Add more test modules to the OCC file. © OMICRON 2013 Page 31 of 43 . The current outputs of the CMC are shown in the single line view. 1 2 4 3 1. The new test point appears in the test point list. 4.Test Data In this tab the test points can be entered. 2. © OMICRON 2013 Page 32 of 43 . If these theoretically calculated currents match the currents read out from the relay. It should be kept in mind that the current output will be stopped after the test time is elapsed. 3 Note: 4 Define whether you want to enter the measured phase currents or the calculated differential and bias currents. 1. The necessary formulae can be obtained from the relay manual. During the test the differential current must be zero in each phase. Now the measured currents can be read from the relay and entered here. 1 2. This activates the input fields for the measured currents. the differential and bias currents that should be measured by the relay must be calculated. If a trip occurs during the test time. it is recommended that at least one phase-toground fault is placed at the grounded side of the transformer. 2 3. To test the numerical zero sequence elimination. the test can be assessed as passed. 4. For most of the digital differential relays the option Idiff and Ibias is the easiest way to assess the relay behavior. the test will automatically be assessed as failed. In order to assess the test. Start the test by clicking the Start/continue test button on the toolbar. The test can be assessed with this option. The test current and the status of the test are displayed here.Test This tab is used to assess and document the test. Select this option if the test should be time synchronized via GPS or IRIG-B. This way a test shot will only be assessed as tripped if all of the trip contacts are triggered. 4 If this option remains unselected. 1 2. In this example it is not necessary to select the voltage output.3 Operating Characteristic Test This test confirms the operating characteristic of the differential relay. Test shots are placed in the operating characteristic diagram and if they are above the operating characteristic. If. If they are below the characteristic the relay must not trip. 3 5. General General settings of the test are entered in this tab. a search test will only search within the specified tolerances. This setting activates a voltage output during the test. 4.3. they should be linked with AND.4. this option is selected. In this case the test will always be assessed as passed. 1. the Trigger Logic has to be defined according to the relay configuration. the search test will also search outside of the tolerance band. however. 5 © OMICRON 2013 Page 33 of 43 . the relay must trip. Note: If the relay uses multiple trip contacts. A pre-fault current can be applied before each test shot. For the operating characteristic test. 2 3. In order to confirm that the operating characteristic is within the specified tolerances.Shot Test With the shot test. This can be done by clicking the operating characteristic diagram and then clicking Add to set the previously clicked test shot. test shots can be placed above and below the operating characteristic outside the tolerance band. the test shots can be set by entering the currents Idiff and Ibias manually. it is recommended that test shot pairs are placed close to the boundary of the tolerance band. © OMICRON 2013 Page 34 of 43 . To test the operating characteristic. test shots can be placed in the operating characteristic diagram. Alternatively. vertical search lines can be added by clicking the operating characteristic diagram and then clicking Add or by manually entering the current Ibias of the search line. When testing the operating characteristic it is recommended that each line segment is tested at two different positions (if possible). This ensures that the characteristic settings are assessed properly. These test positions should not be too close to each other and also not too close to the corner points of the operating characteristic. The test module will automatically place test shots along this line to search for the exact position of the operating characteristic. Remove all test shots before adding search lines or vice versa. With the search test. If multiple fault types are to be tested. more test modules can be added to the OCC file.Search Test With the search test. Note: It is not possible to do a shot test and a search test in the same test module. © OMICRON 2013 Page 35 of 43 . the exact position of the operating characteristic can be found. Only one fault type can be set per test module. it can be quickly confirmed whether the operating characteristic is within the specified tolerance band. whereas with the shot test. Therefore.4. 2 © OMICRON 2013 Page 36 of 43 . In this example it is not necessary to select this function. This setting activates a voltage output during the test. In this example it is not necessary to select the voltage output. The new tolerances can be entered below as Diff Current Factors and Diff Time Factors. Select Use evaluation factors to overwrite the test object tolerances. 1 2. test shots with different differential currents are applied to measure the corresponding trip times.3. Factors 1.4 Trip Times Test This test confirms the trip times of the differential protection function. they should be linked with AND. All the test shots in this test module will be placed on this line. 3. 2. The resulting test line is also shown in the operating characteristic diagram. This setting defines the slope of the test line. Therefore. For the trip times test. This way a test shot will only be assessed as tripped if all of the trip contacts are triggered. For the majority of differential relays this setting can remain at the default value.General 1 2 2 3 1. Note: If the relay uses multiple trip contacts. © OMICRON 2013 Page 37 of 43 . it is advantageous to have not more than one intersection with the operating characteristic. A pre-fault current can be applied before each test shot. the Trigger Logic has to be defined according to the relay configuration. Test 2 1 In the test tab the test shots are defined. either click on the trip time test plane (1) or enter the differential current manually (2) and then click Add. This ensures that the trip times corresponding to each differential current element are tested. more test modules can be added to the OCC file. To place a new test shot. Note: Only one fault type can be set per test module. it is recommended that one test shot is placed above Idiff> and one above Idiff>> (Test Object parameters). © OMICRON 2013 Page 38 of 43 . In order to test the trip time settings of the relay. If multiple fault types are to be tested. 2 2. only fundamental frequency currents without harmonics will be generated.3. © OMICRON 2013 Page 39 of 43 . the Trigger Logic has to be defined according to the relay configuration. 1 Select this option to apply a post-fault after each test shot. the test will be assessed as passed.5 Inrush Blocking Test This test confirms the operation of the inrush blocking function. Note: If the relay trips during the post-fault. This setting activates a voltage output during the test. This way a test shot will only be assessed as blocked if none of the trip contacts are triggered. General 1. they should be linked with OR. During the post-fault period. For the inrush blocking test. In this example it is not necessary to select this function. The test module generates differential currents which contain harmonics which allows the inrush blocking characteristic to be tested. Note: If the relay uses multiple trip contacts.4. 3 3. The fault type can be defined with this setting. If different phases are to be tested.Shot Test 2 1 4 3 The shot test applies test shots to the harmonic restraint test plane. 1. this will be the second harmonic. 2. This option is used to define the number of the harmonic that should be tested. This plane shows the harmonic blocking characteristic with the differential current and the percentage of the harmonic current. © OMICRON 2013 Page 40 of 43 . more test modules can be added to the OCC file. To set a new test shot click the test plane and then click Add. 4. For the inrush blocking in this example. The differential current and the harmonic percentage can also be entered manually and then Add is clicked to define the test shot. 3. Note: Only one test phase can be set per test module. 3. If different phases are to be tested. If. it is recommended that the characteristic is tested outside the tolerance band just above Idiff> and just below Idiff>> (or at any other parameter that limits the harmonic blocking). it is selected. Remove all test shots before adding search lines or vice versa. 1. © OMICRON 2013 Page 41 of 43 . the search test will also search outside the tolerance band. This option is used to define the number of the harmonic that should be tested. The test phase can be defined with this setting. For the inrush blocking in this example. a search test will only search within the specified tolerances.Search Test 2 1 4 3 5 The search applies test shots along horizontal search lines to determine the harmonic blocking characteristic. Note: Only one test phase can be set per test module. Or by entering the differential current of the search line manually and then clicking Add. 5. In this case the test will always be assessed as passed. If this option remains unselected. Note: It is not possible to do a shot test and a search test in the same test module. however. more test modules can be added to the OCC file. Apply search lines by clicking on the characteristic and then clicking Add. this will be the second harmonic. When testing the operating characteristic. 2. 4. the global Hardware Configuration and the local Hardware Configurations of each test module have to be adapted.6 Testing Three-Winding Transformer Differential Protection A test for three-winding transformer differential protection devices uses the same basic steps as the test for two-winding transformer differential protection devices.at. However. it is sufficient to perform the trip times test and the inrush blocking test once. Additionally.3.4. © OMICRON 2013 Page 42 of 43 . the stability test and the operating characteristic test must cover each winding of the transformer. Note: For most three-winding transformer differential relays. Side 1 to Side 2: > Stability Test > Operating Characteristic Test > Trip Times Test > Inrush Blocking Test Side 1 to Side 3: > Stability Test > Operating Characteristic Test Note: To test from Side 1 to Side 3 the relay has to be rewired. Feedback regarding this application is welcome by email at TU-feedback@omicron. OMICRON Academy – Learn More www. Browse through the knowledge library and find application notes.omicronusa.omicronusa.omicron. conference papers.com/support Offering our customers outstanding support is one of our top priorities.at/support www.com/customer The customer area on our website is an international knowledge exchange platform.at/customer www.omicronusa. articles about daily working experiences. you can find our Service Center or Sales Partner closest to you at www. If you need any support. you can reach well-educated technicians for all of your questions. 6833 Klaus. Austria. +43 59495 © OMICRON 2014 Page 43 of 43 . Oberes Ried 1.Support When you are working with our products we want to provide you with the greatest possible benefits.omicronusa. Customer Area – Stay Informed www. Additionally. At our technical support hotline. 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