SEL Application Guide

Application GuideVolume IV AG2011-11 Single-Phase Testing of the SEL-787, SEL-787-3, and SEL-787-4 REF Elements Jason Young INTRODUCTION This application guide describes how the SEL-787, SEL-787-3, and SEL-787-4 Transformer Protection Relay restricted earth fault (REF) elements operate, enabling users to successfully test the elements. OVERVIEW The SEL-787 has the option of one REF element (REF1), provided the correct card is ordered for Slot E. The SEL-787-3 and SEL-787-4 include either two or three REF elements, depending on the specific part number selected. The relay part numbers that include the REF element are listed in Table 1, where a lowercase x denotes a digit that is irrelevant to this discussion. Table 1 SEL-787, SEL-787-3, and SEL-787-4 Part Numbers With REF Element* Relay Model Part Number REF Elements Available SEL-787-1 7871XxxxxxxAx8xxxxx REF1 SEL-787-E 7871Xxxxxxx7x8xxxxx REF1 SEL-787-3S 7873Sxxxxxx7x8xxxxx REF3A and REF3B SEL-787-3E 7873Exxxxxx7x8xxxxx REF1, REF3A, and REF3B SEL-787-4 7874XxxxxxxAx8xxxxx REF3A and REF3B *Refer to the corresponding model option table (MOT) for a complete list of Slot E and Slot Z options. Note that each input (Winding 1, Winding 2, Winding 3, Winding 4, and IN) can either be 1 A or 5 A nominal. Consult the relay MOT for details on the specific combinations available. Similar to the REF elements in the SEL-387 Current Differential and Overcurrent Relay and the SEL-487E Transformer Protection Relay, the REF elements in the SEL-787, SEL-787-3, and SEL-787-4 function as directional ground overcurrent elements. The ground current in the neutral of the transformer is the operate current, and the residual ground current from selected phase terminals functions as the polarizing quantity. The REF element compares the direction of the operate current and the polarizing current and decides whether the fault is inside or outside the protected zone. The REF directional characteristic is shown in Figure 1. Date Code 20160203 SEL Application Guide 2011-11 respectively) plus the output of the element torque control setting. The assertion of these Relay Word bits enables the directional calculation. |INWPU1| (operating quantity) + – C1 50NREF1 REF1E 50REF1P (setting) 0. as shown in Figure 3. This ensures that the polarizing input is enabled before the operating input is enabled. 50REF1P. 12 IN1 ENABLE 1 IGWPU1 ———————— CRN1 * INOMN1 (polarizing quantity) Re(IGWPU1 • INWPU1*) REFTQ1 CTR2 1 ————— INOMN1 INWPU1 (operating quantity) Figure 3 REF1 Directional Element Logic SEL Application Guide 2011-11 Date Code 20160203 . This is the AND combination of 50NREF1 and 50GREF1 (which correspond to the minimum thresholds for the operating and polarizing quantities. The per-unit operating quantity is compared to the pickup threshold.8 |IGWPU1| (polaring quantity) – + C2 50GREF1 REF1TC (setting) Figure 2 REF1 Element Enable Logic 0 1 S1a 2 IGW1 REF1POL = 1. 12 CTR1 REF1E Σ 0 1 S1b 2 IGW2 REF1POL = 2. while the per-unit polarizing quantity is compared to 80 percent of the same pickup threshold. The logic diagram for these Relay Word bits is shown in Figure 2.2 Operating Current (neutral current transformer [CT]) ϕ Internal Fault Area Polarizing Current (line CTs) Figure 1 REF Directional Element The REF1 directional calculation is enabled by the status of Relay Word bit REF1E. REF1TC. A fault outside of the zone of protection yields φ = 180 degrees.0 cyc REF1R REFTQ1 – THRES1N + C2 REF1RP Figure 4 REF Directional Decision Logic The Relay Word bit REF1BY in Figure 4 accounts for a case in which the line breaker is open.5 cyc 0.5 cyc 0. the polarizing currents are multiplied by their respective CT ratios to give primary amperes and are then divided by the neutral CT ratio and the IN1 current input rating (1 A or 5 A). as shown in Figure 1 and represented by the logic in Figure 4. add security for very small currents and for angle differences approaching ±90 degrees. as shown in Figure 5. Note that the thresholds. These per-unit quantities are used in the torque calculation. comparing the calculation result to positive and negative thresholds. THRES1P – + REF1BY C1 REF1FP Relay Word Bits 1. The result is no decision for approximately 10 degrees on either side of ±90 degrees. Further.3 Typically. Note that in the logic of the SEL-787-3 and SEL-787-4. where φ is the angle between IGWPU1 and INWPU1. This normalization is shown in Figure 3.0 cyc REF1F 1. any time the REF1E Relay Word bit is asserted. The operating current is also divided by the IN1 current input rating so that both IGWPU1 and INWPU1 quantities are in per unit on the same base. The result is that the output of the calculation is negative for an external fault and positive for an internal fault. and SEL-787-4 can be ordered with a combination of 1 A and 5 A current inputs. the SEL-787. Re(IGWPU1 • INWPU1*). THRES1P and THRES1N. the phase and neutral CTs used for REF protection have different ratios. The value Re(IGWPU1 • INWPU1*) equals |IGWPU1| • |INWPU1| • cosφ. SEL-787-3. Therefore. Date Code 20160203 SEL Application Guide 2011-11 . the relay declares an internal fault if φ < ±90 degrees. Therefore. while an internal fault yields φ = 0 degrees. the relay does not have a polarizing quantity to determine the fault location. Winding 1 Winding 2 52-1 52-2 F1 Figure 5 Internal Fault With Low-Voltage Breaker Open In this case. IGW3 and IGW4 are also included in the polarizing quantity summation. 50GREF1 50NREF1 Settings REF1TC a) REF1BY REF52BYP := Y 52A1 52A2 REF1POL := 1. the SEL-787 also provides the option to use the breaker status to indicate an open breaker via the REF52BYP setting.0352 + 2  = M −1  (1) The description and logic diagrams in this section specifically referenced the SEL-787 REF1 element. SEL Application Guide 2011-11 Date Code 20160203 . Figure 7 shows the logic for the time-overcurrent output. However. The default option looks for a lack of polarizing current with the presence of sufficient operating current. the element bypasses the directional calculation and indicates an internal fault. Note that the SEL-787. except as noted. 5. This condition is represented by the assertion of 50NREF1 while 50GREF1 remains deasserted.67   t p TD •  0. When Relay Word bit REF1BY asserts. and SEL-787-4 REF elements can be applied as either instantaneous or time-delayed. 12 50GREF1 50NREF1 b) REF1BY REF1TC (setting) REF1BYP (setting) Figure 6 REF Bypass Logic in the a) SEL-787 and the b) SEL-787-3 and SEL-787-4 The SEL-787-3 and SEL-787-4 contain bypass logic similar to that of the SEL-787.5 Reset 1 Cycle REF1P Figure 7 Time-Overcurrent REF Output The U4 curve (extremely inverse) and TD (time dial) of 0. The operate time for this curve can be calculated using (1). 12 REP1POL := 2. as shown in Figure 6a.4 However. |INWPU1| + 50REF1P – C1 REF1PP REF1F 50REF1P (pickup) U4 Curve TD 0. The REF1F Relay Word bit in Figure 4 can be used for instantaneous operation. allowing the user to define specific bypass criteria. the SEL-787 offers two methods for detecting this condition. As an additional security measure. however. as shown in Figure 6b.5 are hard-coded into the relay. the REF52BYP setting in the SEL-787 has been replaced with a more flexible REF1BYP SELOGIC® control equation setting in the SEL-787-3 and SEL-787-4. the same logic is used in the SEL-787-3 and SEL-787-4. as shown in Figure 4. SEL-787-3. 10. and a bypass logic test. and SEL-787-4: a pickup test. IGW2 IGW1. IGW4 Torque control REF1TC REF1TC REF3ATC REF3BTC Current sensitivity level 50REF1P 50REF1P 50REF3AP 50REF3BP Enable 52A bypass REF52BYP REF1BYP REF3ABYP REF3BBYP Table 3 provides a comparison of the Relay Word bits in the different versions of the SEL-787. Date Code 20160203 SEL Application Guide 2011-11 . IGW2. If the time-delayed output is used for tripping. SEL-787-3. IGW4 IGW1. However. SEL highly recommends upgrading to R209 or later. a directional element test. for instructions on testing the REF3A or REF3B elements. Contact SEL for more details. Table 2 SEL-787 REF Element Settings and Operating Current Channels Current Input and Settings Options SEL-787 SEL-787-3 and SEL-787-4 REF1 REF1 REF3A REF3B Operating current input IN IN IAW3 IBW3 Operating current CT ratio CTRN1 CTRN1 CTR3A CTR3B Nominal current INOMN1 INOMN1 INOMW3 INOMW3 Polarizing quantity REF1POL REF1POL REF3APOL REF3BPOL Polarizing quantity options IGW1. Please refer to the following section. Table 3 SEL-787 REF Element Relay Word Bits Relay Word Bit SEL-787 SEL-787-3 and SEL-787-4 REF1 REF1 REF3A REF3B Operating current pickup 50NREF1 50NREF1 50NREF3A 50NREF3B Polarizing current pickup 50GREF1 50GREF1 50GREF3A 50GREF3B Element enable REF1E REF1E REF3AF REF3BF Forward torque output NA REF1FP REF3AFP REF3BFP Internal fault REF1F REF1F REF3AF REF3BF Internal fault time-delayed pickup NA REF1PP REF3APP REF3BPP Internal fault time-delayed timeout REF1P REF1P REF3AP REF3BP Reverse torque output NA REF1RP REF3ARP REF3BRP External fault REF1R REF1R REF3AR REF3BR Bypass NA REF1BY REF3ABY REF3BBY Note that SEL-787 Relays with a firmware version prior to R209 have slightly modified logic. IGW2. This section covers these tests for the REF1 element. a timing test should also be performed. as covered in Service Bulletin 2015. SEL-787-3. REF3A and REF3B Element Testing. and SEL-787-4. IGW3 IGW1. IGW2. REF1 ELEMENT TESTING Three tests are required for the REF elements in the SEL-787.5 Table 2 provides a list of the equivalent settings and current channels used in the different REF elements available in the SEL-787. 1.05 to 3. Note that all current inputs of the test relay are 5 A nominal inputs (i. This is a SELOGIC bypass enable setting with a default value of 1. a A C c B b Winding 2 Winding 1 A a B b C c IN IAW1 IAW2 IBW1 IBW2 ICW1 ICW2 Figure 8 Sample System Three-Line Diagram for REF1 Elements Table 4 Sample System SEL-787 REF1 Settings Setting Description Acceptable Values Assigned Value W1CT Winding 1 CT connection DELTA. **In the SEL-787-3 and SEL-787-4. the equivalent setting is REF1BYP. The three-line diagram of the system is shown in Figure 8. and W2).4* REF52BYP** 52A bypass of REF1 enable Y. and the corresponding settings are listed in Table 4.e. 2. WYE WYE CTR2 Winding 2 phase CT ratio 1 to 10000 500 CTRN1 Neutral (IN) CT ratio 1 to 10000 120 REF1POL Polarizing quantity from winding OFF. The setting is in per unit of the neutral CT ratio and neutral terminal nominal current and is scaled by 80 percent for the polarizing quantity. N Y *Refer to the SEL-787. 50REF1P..6 Sample System In order to explain the necessary tests. that must be tested. SEL-787-3. W1. WYE WYE CTR1 Winding 1 phase CT ratio 1 to 10000 100 W2CT Winding 2 CT connection DELTA.00 0. INOMn = 5. Note that this setting applies to both the operating and polarizing quantities. a sample transformer is used to calculate the test points. where n = N1. or SEL-787-4 Instruction Manual for the recommended pickup setting criteria. 12 2 REF1TC REF1 torque control SELOGIC control equation 1 50REF1P REF1 current sensitivity level (in per unit of nominal) 0. SEL Application Guide 2011-11 Date Code 20160203 . Pickup Test The REF element has a minimum threshold setting. to test the neutral pickup.8 • 50REF1P • CTRN1• = 0. ground current must be injected into Winding 2. Bypass Logic Test To test the REF element bypass logic. Press <Ctrl+X> to abort the target command once the test is finished.10 A.0∠0°A IAW2 = 0.4 • 5= 2. this test can be repeated with IAW1 substituted for IAW2 while keeping IAW2 at 0 A.4 •120 • = 0. ±5 percent plus ±0. rotate the IAW2 angle from 180 degrees to 0 degrees to simulate an external-to-internal fault. 0. as mentioned above. This is because IG = IA + IB + IC.0 A) ±5 percent plus ±0. Apply current less than the value calculated in (3) (e. ensuring that the condition is either internal or external.8 • 0. and at approximately 80 degrees REF1F should assert. apply 3 A of current to the IN terminal at 0 degrees and 1 A of current to the IAW2 terminal at 180 degrees. the operate current must be above the residual current sensitivity pickup (50REF1P) and the polarizing quantity must be above 80 percent of the same threshold.38∠180°A 5 500 (2) INOMN1 CTR2 (3) Therefore.5∠0° A) to the IN terminal. First. this 20-degree dead band is added to increase the security of the element.g. The calculation for the sample system is (2). and do not apply any current to the phase windings. The calculated minimum currents for the sample system are shown in (2) and (3).10 A. If REF1POL = 12. the same as the pickup test. Winding 2 is the only phase terminal included in the REF element.or C-phases.1∠180° A) to IAW2 and ramp up while monitoring 50GREF1 using the TAR 50GREF1 10000 command. for the sample system.38 A). A simple way to provide ground current to the relay is to inject current only on the A-phase of Winding 2 and nothing on the B. Next. Increase the IN current while monitoring the REF1F Relay Word bit using the TAR REF1F 10000 command. IN= 50REF1P • INOMN1= 0. simulate the situation in Figure 5 by applying operate current and no polarizing current. This element asserts when the IN current exceeds 50REF1P. then this procedure can be altered in two ways. Date Code 20160203 SEL Application Guide 2011-11 . 50NREF1 should assert at the value calculated in (2) (2. Apply current to the IN terminal that is less than that calculated in (2). substituting the sum of the polarizing winding ground currents for IAW2.g.. the residual pickup for Winding 2 must be tested. Second.. Directional Element Test To test the REF directional element.7 For the sample system. Next. Therefore. 1. At approximately 100 degrees REF1R should deassert. Neutral current must be injected independently on the IN input of the relay. ground current can be injected on both polarizing windings simultaneously. Increase the IN current while monitoring the 50NREF1 Relay Word bit using the TAR 50NREF1 10000 command. To test the element. Both Relay Word bits can be monitored using the TAR REF1R 10000 command. apply current less than the value calculated in (2) (e. 50GREF1 should assert at the value calculated in (3) (0. Note that. Apply current to the IN terminal that is greater than the value calculated in (2) and increase the polarizing current above the value calculated in (3).g. Note that the SEL-787-3 and SEL-787-4 include a SELOGIC control equation in place of the REF52BYP setting. This should also have the same effect of blocking the bypass logic and verifying the bottom input into the AND gate in Figure 6b. In this case. This should have the same effect of blocking the bypass logic and verifying the 52A portion of the logic in Figure 6a. The respective calculations for the sample system are shown in (6) and (7). Then use the SER command to verify the operation time. For the sample system. When IAW2 reaches the value calculated in (3) (0. This allows verification that the bypass logic test does not work if polarizing ground current is present.1 A) at 180 degrees and increase the current while monitoring the REF1F Relay Word bit using the TAR REF1F 10000 command. which is the time difference between the assertion of REF1F and REF1P. If REF52BYP = Y. Inject IAW2 less than the value calculated in (3) (e.4 • 5= 8.0352 + 2 = 0. REF1P should be included in the TRXFMR (trip transformer SELOGIC setting) equation instead of REF1F..0∠0°A (4) IN 4x= 4 • 50REF1P • INOMN1= 4 • 0.4 • 5= 4. The relay captures a timestamped record of each assertion and deassertion of all Relay Word bits included in these settings.96 seconds  2 −1    (6)  5. However. Timing Test This test is only required if time-delayed tripping via the REF1P Relay Word bit is desired. close the W2 breaker. Calculate the expected operate time using (1). Add REF1F and REF1P to SER1.0352 + 2 = 0.67  t p4x = 0. Two tests are run for the sample system: one at two multiples of pickup (M = 2) and another at four multiples of pickup (M = 4). To test a time-delayed element. apply 3∠0° A to the IN terminal.8 Note that the logic in Figure 6a should only be enabled when the breaker is open.0∠0°A (5) Next.38 A) ±5 percent plus ±0. or SER4.67  t p2x = 0. repeat the test with IAW2 = 0 A and the REF1BYP logic evaluating to a logical 0. where M is the multiples of pickup. repeat this test. do not apply current to the IAW2 input.21 seconds  4 −1    (7) ( ( SEL Application Guide 2011-11 ) ) Date Code 20160203 . SER3. The current to be injected in the IN terminal for the two tests is calculated in (4) and (5).5 •  0. Apply the selected test current to the IN terminal for a sufficient time while applying current that is greater than the value calculated in (3) to the polarizing current input (IAW2 in the sample). both greater than the 50REF1P pickup.10 A. 0. use the Sequential Events Recorder (SER) in the relay. calculate the expected operate time for each test using (1).5 •  0. Select two separate test current values. Instead.  5. IN 2x= 2 • 50REF1P • INOMN1= 2 • 0. REF1F will deassert. SER2. If testing the REF1 element in these relays and REF1BYP is not set to 1. 295 08:56:36. =>>ser SEL-787 TRNSFRMR RELAY Date: 09/25/2015 Time: 08:56:43 Time Source: Internal Serial No = 1110310555 CID = 6EB7 # 4 3 2 1 DATE 09/25/2015 09/25/2015 09/25/2015 09/25/2015 FID = SEL-787-R209-V0-Z003001-D20140714 TIME 08:56:35.e. this calculation yields 0. W1. W2. and timing tests for the REF3A and REF3B elements. Sample System The necessary tests are explained using a sample transformer to calculate the test points.9 For each test. simply replace 3A with 3B throughout this section. INOMn = 5. The three-line diagram of the system is shown in Figure 10. directional element. REF3A AND REF3B ELEMENT TESTING This section covers the pickup. and W4). For the sample system. Note that all current inputs of the test relay are 5 A nominal inputs (i. For the sample system.. where n = N1.236 08:56:39.262 08:56:39. bypass logic. W3. respectively. which agrees with expectations. a A C c B b Winding 2 Winding 1 A a B b C c IAW3 IAW1 IAW2 IBW1 IBW2 ICW1 ICW2 Figure 10 Sample System Three-Line Diagram for REF3A Elements Date Code 20160203 SEL Application Guide 2011-11 . and the corresponding settings are listed in Table 5. apply 0. The results from the M = 2 test for the sample system are shown in Figure 9. For testing REF3B elements.5∠0° A to IAW2 and either IN2x or IN4x to the IN terminal for longer than the times calculated in (6) and (7). apply a polarizing current greater than the value calculated in (3) but at 0 degrees to simulate an internal fault.941 seconds.287 ELEMENT REF1F REF1P REF1F REF1P STATE Asserted Asserted Deasserted Deasserted Figure 9 Results for the Sample System M = 2 Test Calculating the difference between the assertion of REF1F and REF1P gives the element operate time. Press <Ctrl+X> to abort the target command once the test is finished. 12 REF3ATC REF3A torque control SELOGIC control equation 1 50REF3AP REF3A current sensitivity level (in per unit of nominal) 0. Pickup Test The REF element has a minimum threshold setting. 1. A simple way to provide ground current to the relay is to inject current only on the A-phase of Winding 2 and nothing on the B.10 Table 5 Sample System SEL-787-3 and SEL-787-4 REF3A Settings Setting Description Acceptable Values Assigned Value W1CT Winding 1 CT connection DELTA.1∠180° A) to IAW2 and ramp up while monitoring 50GREF3A using the TAR 50GREF3A 10000 command. 2.or C-phases. For the sample system. Winding 2 is the only phase terminal included in the REF element. and 124. Apply current that is less than the value calculated in (9) (e.05 to 3. SEL Application Guide 2011-11 Date Code 20160203 . 1. Increase the IAW3 current while monitoring the 50NREF3A Relay Word bit using the TAR 50NREF3A 10000 command. N.00 0. 14.0∠0°A IAW2 = 0. IAW3= 50REF3AP • INOMW3= 0. ground current must be injected into Winding 2.. 50GREF3A should assert at the value calculated in (9) (0.4 • 5= 2. This is because IG = IA + IB + IC. 4.38∠180°A 5 500 (8) INOMW3 CTR2 (9) To test the neutral pickup. Note that this setting applies to both the operating and polarizing quantities. **Refer to the SEL-787-3 and SEL-787-4 Instruction Manuals for the recommended pickup setting criteria. apply current that is less than the value calculated in (8) (e. 12.5∠0° A) to the IAW3 terminal.g.. 1.8 • 0. REF REF CTR3A Winding 3 A phase CT ratio 1 to 10000 REF3APOL Polarizing quantity from winding OFF. For an SEL-787-4 Relay. the residual pickup for Winding 2 must be tested. acceptable values include OFF.0 A) ±5 percent plus ±0.8 • 50REF3AP • CTR3A • = 0.10 A. To test the element.10 A.4 •120 • = 0. 0. The calculated minimum currents for the sample system are shown in (8) and (9). 50REF3AP. Neutral current must be injected independently on the IAW3 input of the relay.38 A) ±5 percent plus ±0. The setting is in per unit of the neutral CT ratio and neutral terminal nominal current and is scaled by 80 percent for the polarizing quantity. Next. that must be tested. WYE WYE CTR1 Winding 1 phase CT ratio 1 to 10000 100 W2CT Winding 2 CT connection DELTA. 2. WYE WYE CTR2 Winding 2 phase CT ratio 1 to 10000 500 E87W3 Enable Winding 3 in differential element Y.4** REF3ABYP Bypass logic torque control SELOGIC control equation 1 120 2 * *The options shown are for the SEL-787-3S and SEL-787-3E Relay models.g. 50NREF3A should assert at the value calculated in (8) (2. g.11 Directional Element Test To test the REF directional element. and at approximately 80 degrees REF3AF should assert. ensure that the logic in REF3ABYP evaluates to 0.1 A) at 180 degrees and increase the current while monitoring the REF3AF Relay Word bit using the TAR REF3AF 10000 command.38 A) ±5 percent plus ±0. Second. In this case. ground current can be injected on all polarizing windings simultaneously. simulate the situation in Figure 5 by applying operate current and no polarizing current. Instead. REF3AP should be included in the TRXFMR equation instead of REF3AF. Then use the SER command to verify the operation time. This should have the same effect of blocking the bypass logic and verifying the bottom input to the AND gate in Figure 6b. or SER4. When IAW2 reaches the value calculated in (9) (0. ensuring that the condition is either internal or external. Inject IAW2 less than the value calculated in (9) (e. This allows verification that the bypass logic test does not work if polarizing ground current is present. then this procedure can be altered in two ways. Bypass Logic Test To test the REF element bypass logic. If REF3APOL = 12. Apply the selected test current to the IAW3 terminal for a sufficient time while applying current that is greater than the value calculated in (9) to the polarizing current input at 0 degrees. Date Code 20160203 SEL Application Guide 2011-11 . a 20-degree dead band is added to increase the security of the element. apply 3 A of current to the IAW3 terminal at 0 degrees and 1 A of current to the IAW2 terminal at 180 degrees. or 124. as mentioned previously. Note that the logic in Figure 6b should only be enabled when the breaker is open. where M is the multiples of pickup. SER2. then open the Winding 2 breaker to complete this test. substituting the sum of the polarizing winding ground currents for IAW2. Therefore. Next. and do not apply any current to the phase windings.10 A. apply 3∠0° A to the IAW3 terminal. 0. if REF3ABYP = 52A2. However. use the SER in the relay. Calculate the expected operate time using (1). rotate the IAW2 angle from 180 degrees to 0 degrees to simulate an external-to-internal fault. SER3. For the sample system. If REF3ABYP is not set to 1. Add REF3AF and REF3AP to SER1. Select two separate test current values. repeat this test. do not apply current to the IAW2 input. For example. Apply current to the IAW3 terminal that is greater than the value calculated in (8) and increase the polarizing current above the value calculated in (9). the same as the pickup test. To test a time-delayed element. At approximately 100 degrees REF3AR should deassert. the operate current must be above the residual current sensitivity pickup (50REF3AP) and the polarizing quantity must be above 80 percent of the same threshold. for the sample system. the test can be repeated with IAW1 or IAW4 (depending on the setting) instead of IAW2 while keeping IAW2 at 0 A. Note that.. First. The calculation for the sample system is (8). Timing Test A timing test is only required if time-delayed tripping via the REF3AP Relay Word bit is desired. Apply current to the IAW3 terminal that is less than the value calculated in (8). both greater than the 50REF3AP pickup. 14. REF3AF will deassert. The relay captures a time-stamped record of each assertion and deassertion of all Relay Word bits included in these settings. This element asserts when the IAW3 current exceeds 50REF3AP. which is the time difference between the assertion of REF3AF and REF3AP. Both Relay Word bits can be monitored using the TAR REF3AR 10000 command. Increase the IAW3 current while monitoring the REF3AF Relay Word bit using the TAR REF3AF 10000 command. respectively. One option is to use the system unbalance when load is first applied to the transformer to verify the neutral CT polarity. provided sufficient unbalance current is flowing. and if it is correct. Available: http://www. IAW32x= 2 • 50REF3AP • INOMW3= 2 • 0. and SEL-787-4 REF elements with single-phase. Costello. please refer to [1]. SEL-787-3.67  t p2x = 0.selinc. Spokane. SEL Application Guide 2011-11 Date Code 20160203 . This works. Haas.5 •  0.0352 + 2 = 0. “Analysis of an Autotransformer Restricted Earth Fault Application. An additional test is described with calculations for testing the time-overcurrent output of the REF element.12 Two tests are run for the sample system: one at two multiples of pickup (M = 2) and another at four multiples of pickup (M = 4). CONCLUSION This application guide demonstrates a simple method of testing the SEL-787. REFERENCE [1] N. The current to be injected in the IAW3 terminal for the two tests is calculated in (10) and (11). Post-fault event analysis can confirm neutral CT polarity. For more information on REF applications.96 seconds  2 −1    (12)  5. D. The respective calculations for the sample system are shown in (12) and (13). Separate tests must be performed to validate the pickup.4 • 5= 4. directional element. and D.0∠0°A (11) Next. Alternatively. steady-state current injection. the REF element can be enabled to trip at that time.0352 + 2 =  4 −1    (13) ( ( ) ) For each test.4 • 5= 8.0∠0°A (10) IAW34x= 4 • 50REF3AP • INOMW3= 4 • 0.com. October 2007. apply a polarizing current that is greater than the value calculated in (9) but at 0 degrees to simulate an internal fault.5 •  0. Fischer.21 seconds = 0. A common problem in REF applications is incorrect polarity of the neutral CT. apply 0. calculate the expected operate time for each test using (1). and bypass portions of the element logic. set the REF element but do not allow it to trip until the relay system is exposed to its first external fault. For the sample system.5∠0° A to IAW2 and either IAW32x or IAW34x to the IAW3 terminal for longer than the time calculated in (12) and (13).  5. WA.” proceedings of the 34th Annual Western Protective Relay Conference. Be sure to complete a primary injection test or other means of verifying proper CT polarity.67  t p4x 0. com Date Code 20160203 SEL Application Guide 2011-11 . If you have questions or comments.7990 www. Inc. please contact us at: Schweitzer Engineering Laboratories.com • [email protected] FACTORY ASSISTANCE We appreciate your interest in SEL products and services.selinc.332.509.332. 2350 NE Hopkins Court Pullman. WA 99163-5603 USA Telephone: +1.509.1890 Fax: +1. SEL Application Guide 2011-11 *AG2011-11* Date Code 20160203 .S. SEL products appearing in this document may be covered by U. 2016 by Schweitzer Engineering Laboratories. No SEL trademarks may be used without written permission. All rights reserved. and Foreign patents. Inc. All brand or product names appearing in this document are the trademark or registered trademark of their respective holders.14 © 2011.