Testing the SEL-487E Relay Differential Elements · 6/1/2010 · In the SEL-387, the restraint...

Date Code 20100601 SEL Application Guide 2010-07

Application Guide Volume IV AG2010-07

Testing the SEL-487E Relay Differential Elements

George Alexander, David Costello, Brad Heilman, and Jason Young

INTRODUCTION This application guide describes the differences between the SEL-387 Current Differential and Overcurrent Relay and the SEL-487E Transformer Protection Relay that affect testing. It also describes a method for testing the differential elements using a single-phase current and the in-service relay settings.

RESTRAINT CURRENT CALCULATION In the SEL-387, the restraint quantity, IRT, is the sum of the magnitudes of the compensated winding quantities divided by two.

( )387IRT 0.5 • IAW1C IAW2C= + (1)

where:

IAWnC represents the compensated winding quantities in per unit.

In the SEL-487E and SEL-787 Transformer Protection Relay, the restraint quantity is the sum of the magnitudes of the compensated winding quantities.

( )487EIRT IAW1C IAW2C= + (2)

Thus, for the same applied current, tap settings, and angle compensation settings, the magnitude of the restraint in the SEL-487E is twice that in the SEL-387. To achieve the same effective restraint in the two relays, the percentage restraint slope setting in the SEL-487E is one-half of the same setting in the SEL-387. For example, a restraint slope setting of 50 percent in the SEL-387 is the same as a restraint slope setting of 25 percent in the SEL-487E.

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SEL Application Guide 2010-07 Date Code 20100601

ADAPTIVE RESTRAINT SLOPE CHARACTERISTIC In the SEL-387, SEL-587 Current Differential Relay, and SEL-787, the dual-slope characteristic is implemented as shown in Figure 1. The minimum operate threshold is defined by the setting O87P. When the magnitude of the restraint quantity is greater than IRS0 and less than IRS1, the relay operates based on the Slope 1 setting. When the magnitude of the restraint quantity is greater than the setting IRS1, the operating characteristic changes from Slope 1 to Slope 2.

Figure 1 SEL-387, SEL-587, and SEL-787 Dual-Slope Characteristic

When testing the O87P setting in the SEL-387, the restraint quantity, Irst, must be less than the value IRS0, as shown in Figure 1. IRS0 is not a setting but is defined by the intersection of O87P and the Slope 1 percentage setting, SLP1. To test the Slope 1 restraint setting, the restraint current must be greater than IRS0 and less than IRS1. To test the Slope 2 restraint setting, the restraint current must be greater than IRS1. Note that the Slope 2 characteristic does not pass through the origin.

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The SEL-487E uses either Slope 1 or Slope 2, dynamically switching between the two slopes based on fault-sensing logic. Both slope characteristics pass through the origin, as shown in Figure 2.

Irst (pu)

Iop (pu)

SLP1

O87P • 100SLP1

SLP2

87R Restrained Element Operate Region

Restraint Region

U87P

O87P

IRT1IRT2

IRT1 =O87P • 100SLP2

IRT2 =

Figure 2 SEL-487E Adaptive Slope Characteristic

The logic that switches between Slope 1 and Slope 2 is discussed subsequently, but it is not based solely on the magnitude of the restraint current. The SEL-487E adaptive slope characteristic is shown in Figure 2. The area between SLP1 and SLP2 is an operate region when the relay is using Slope 1 and a restraint region when the relay is using Slope 2.

SEL-487E SLOPE SELECTION LOGIC It is not the intent of this application guide to describe in detail the logic used in the SEL-487E to select Slope 1 or Slope 2. Slope 1 is used for normal operating conditions and most internal faults. Slope 2 is a high-security mode used for most external faults and some internal faults. The SEL-487E has internal and external fault detection logic that is used to select either Slope 1 or Slope 2. The internal fault detection logic is also used to supervise the differential elements.

When the external fault detection logic outputs (CONA, CONB, or CONC) assert, the SEL-487E switches to the high security of Slope 2 for the respective phase differential elements. Whenever these external fault detection outputs are deasserted, the SEL-487E uses Slope 1. The external fault detection logic is based on a comparison of the change in the operate quantity (IOPRAR) and the restraint quantity (IRTRA). If the relay detects a change in the restraint quantity without a corresponding change in the operate quantity, the fault is declared external and the respective CON(φ) asserts.

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When the internal fault detection logic outputs (IFLTA, IFLTB, or IFLTC) assert, the respective phase differential elements are permitted to operate. If the internal fault detection outputs are deasserted, the differential elements are blocked and cannot operate. See Figure 3.

IRTFKA

Slope(k)

Selection

IRTFA

Restraint Quantity

IASCFC

IATCFC

IAXCFC

IASCFCIATCFC

IAXCFC•••

•••

Operate Quantity

IOPFA

f(IRTFkA)CONA

P87AHBf(IRTFkA)

–

+

–

+

O87P (Setting)

U87P (Setting)

IAMkh2

IAMkh4

E87HBK (Setting)

To Harmonic Calculation

Harmonic Blocking Differential Element

E87HR (Setting)

12

8 Pl

87ABK5

Harmonic Integrity Timer

IRFHRA

AND 2AND 4

Harmonic Restraint

Differential Element

P87AHR

IFLTA

87ABK587XBk2

87UA87UB87UC

AND 1

IFLTA

AND 3

87AHBIf E87HB = Y

87RC87RB 87R

Restraint Differential Element

87U Unrestraint Differential Element

Outputs

P87At Pl*

87RA

Adaptive Security Timer

CONACONBCONC

If E87HR = Y

CON

Pl

12

8 Pl

Pl

87AHR

*Pl = processing intervalt normal mode = 3 Plt high-security mode = 6 Pl

∑

∑

∑

Harmonic Integrity Timer

Figure 3 Filtered A-Phase Differential Element

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Note that the IFLT(φ) output does not assert continuously. The G-Timer in Figure 4 produces an output for 64 processing intervals (2 cycles). After 2 cycles, the IFLT(φ) signal deasserts for 0.5 cycle before asserting for another 2 cycles. 87R(φ) will deassert whenever IFLT(φ) deasserts, because IFLT(φ) supervises the respective phase differential output 87R(φ).

Absolute

IASCALC

IATCALC

IAXCALC

∑

∑

Figure 4 A-Phase Internal and External Fault Detection Logic

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Figure 5 shows a plot of the signals for an internal fault on A-phase. Note that even though 87RA deasserts momentarily, the trip signal, TRPXFMR, is sealed in and does not reset. The 2-cycle window is sufficient time for the relay to detect the fault, issue a trip, and seal in the trip signal.

Figure 5 SEL-487E Event Data for an Internal Fault

TESTING PHILOSOPHY The SEL-487E relay differential may include up to five three-phase current inputs. While it is possible to inject currents into all windings simultaneously, the proposed testing is done in pairs to simplify the calculations and test equipment. Furthermore, only a single-phase current is injected into each of the windings. The procedures detailed in this application guide allow the relays to be tested with the in-service relay settings. The current inputs in the SEL-487E are identified as S, T, U, W, and X. Any two of these windings may be used in the testing. For convenience, we identify the current windings as 1 and 2.

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REQUIRED RELAY SETTINGS The settings shown in Table 1 are required to calculate the test currents for the SEL-487E. Note that if fewer than five windings are used in the differential calculation, the settings associated with the unused currents are not needed.

Table 1 Relay Settings Required for Testing

ECTC TERM = TAPS =

TSCTC = TAPT =

TTCTC = TAPU =

TUCTC = TAPW =

TWCTC = TAPX =

TXCTC = DIOPR =

O87P = DIRTR =

SLP1 = 87QP =

SLP2 = SLPQ1 =

U87P =

UNRESTRAINED PHASE DIFFERENTIAL TEST (U87) Only a single-phase current is injected on one winding input for testing the unrestrained differential element.

Step 1 Select a winding and a phase for testing (S, T, U, W, or X).

Step 2 Calculate the U87 pickup current.

IW1 U87P • TAP1• A= (3)

where:

IW1 is the injected test current at pickup for the selected winding (S, T, W, U, or X).

U87P is the unrestrained differential pickup setting in multiples of TAP.

TAP1 is the tap setting for the winding under test (TAPS, TAPT, TAPW, TAPU, or TAPX).

A is a constant selected from Table 2. TnCTC is the winding compensation setting for the current winding under test.

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Table 2 A and B Constant Values

TnCTC Setting A (Winding 1) B (Winding 2)

0 1 1

1, 3, 5, 7, 9, 11 3 3

6, 12 1.5 1.5

2, 4, 8, 10 3.0 3.0

Step 3 Monitor the Relay Word bit 87UA, 87UB, or 87UC, depending on the phase under test.

Step 4 Start with a 0 A current, and raise the current until 87UA asserts. This value should be within ±5 percent of the calculated value.

Caution: The resulting test current may be above the continuous rating of the relay (three times the nominal rated current). For currents above the continuous rating, the maximum time in seconds that the test current can be applied without damage may be approximated by (4).

max 2test

nom

10000TII

=⎛ ⎞⎜ ⎟⎝ ⎠

(4)

where:

Itest is the current calculated by (3).

Inom is the rated current (1 or 5 A).

RESTRAINED PHASE DIFFERENTIAL PICKUP TEST (O87) Only a single-phase current is injected on one winding input for testing the restrained differential element.


Step 2 Calculate the 87Rn pickup.

IW1 O87P • TAP1• A= (5)

where:

IW1 is the injected test current at pickup for the selected winding (S, T, W, U, or X).

O87P is the restrained differential pickup setting in per unit of TAP.

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TAP1 is the tap setting for the winding under test (TAPS, TAPT, TAPW, TAPU, or TAPX).

A is a constant selected from Table 2. TnCTC is the winding compensation for the current winding under test.

Step 3 Monitor the Relay Word bit 87RA, 87RB, or 87RC, depending on the phase under test.

Step 4 Start with a 0 A current, and raise the current until 87RA asserts. This value should be within ±5 percent of the calculated value.

SLOPE 1 DIFFERENTIAL TEST The percentage differential element is tested by injecting single-phase currents on two winding inputs. The currents are injected into the windings in pairs. The two currents will either be in phase or 180 degrees out of phase, depending on the compensation settings in the SEL-487E.

Step 1 Select a magnitude of restraint current. The restraint current, IRT, must be greater than IRT1 in Figure 2, so the test is on Slope 1.

100IRT min O87P •SLP1

= (6)

Step 2 Calculate the Winding 1 and Winding 2 currents for the test. Winding 2 is fixed, and the Winding 1 current magnitude is varied to determine the operating point.

SLP1IW2 0.5 • IRTtest • 1 • TAP2 • B100

⎛ ⎞= −⎜ ⎟⎝ ⎠

(7)

where:

IW2 is the Winding 2 test current for the selected winding (S, T, W, U, or X).

IRTtest is the value of IRT chosen in Step 1.

SLP1 is the Slope 1 setting.

TAP2 is the tap setting for Winding 2.

B is a constant determined from Table 2.

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The angle of IW2 will be either 0 degrees or 180 degrees, as determined from Table 3.

Table 3 IW2 Angle

T1CTC – T2CTC IW2 Angle

0, 1, 2, 10, 11, 12 0 degrees

4, 5, 6, 7, 8 180 degrees

3, 9 See Note

In Table 3, T1CTC T2CTC− is the absolute magnitude of the difference between the two winding compensation settings.

Note: If T1CTC T2CTC− is equal to 3 or 9, the test currents on the two windings must be injected into different phases. See Table 4 for details.

Table 4 Test Winding Selection

T1CTC – T2CTC IW1 IW2

−3 or 9 B-phase at 180 degrees A-phase at 0 degrees

3 or −9 B-phase at 0 degrees A-phase at 0 degrees

The magnitude of IW1 at the operating point is as follows:

SLP1IW1op 0.5 • IRTtest • 1 • TAP1• A100

⎛ ⎞= +⎜ ⎟⎝ ⎠

(8)

where:

IW1op is the Winding 1 test current at the operating point.

IRTtest is the value of IRT chosen in Step 1.

SLP1 is the Slope 1 setting.


A is a constant determined from Table 2.

The angle of IW1 is 180 degrees.

Step 3 To start the test, apply the value of IW2 calculated from (7) to Winding 2 and 0.80 • IW1 calculated from (8) to Winding 1.

Step 4 Slowly increase the magnitude of IW1 until the appropriate 87Rn element asserts. The IW1 current should be IW1op ± 5 percent. As shown in Figure 5, the 87Rn element will not remain asserted.

Note: It is possible that due to the relay settings, the initial applied currents may cause the relay to switch to the high-security mode (SLP2). In that case, the currents must be applied for at least

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1 second before raising IW1. Check the status of Relay Word bit CON to see if the high-security mode is selected.

SLOPE 2 DIFFERENTIAL TEST In order to test the SLP2 setting, it is necessary to force the SEL-487E into the high-security mode. The SEL-487E will remain in the high-security mode for a minimum of 3 cycles and a maximum of 60 cycles. Because the relay does not remain in the high-security mode, the test procedure is different than the procedure used for SLP1. This does not allow sufficient time to slowly change the currents as in the test for Slope 1. Because of the transient nature of the high-security mode, we use state simulation for this test. An alternate test procedure that does not require state simulation is presented in Appendix A.

The complete test consists of two parts, and each part consists of two states. The first state of each test causes the SEL-487E to switch to the high-security mode. The second state tests the Slope 2 characteristic. The first test applies a fault above the SLP1 operating zone but below Slope 2. This is a nontrip condition for the time period that the relay is in the Slope 2 high-security mode. Because the high-security mode is transient, the SEL-487E trips after a time delay of approximately 800 milliseconds. The second test shows that the relay trips on the SLP2 characteristic without delay by applying State 2 currents that are above the Slope 2 characteristic.

The relay selects the high-security mode (SLP2) when the change in the restraint current (IRT) is greater than the DIRTR setting and the change in the operate signal (IOP) is less than the DIOPR setting. The default setting for both DIOPR and DIRTR is 1.2 per unit of TAP. Note that the operate and restraint differential signals are calculated using raw instantaneous currents, while the actual differential is calculated using filter 60 Hz signals. This results in a magnitude difference between the signals of √2. The crosshatched region in Figure 6 represents the currents that will result in the high-security mode. This figure assumes there is no current applied to the relay before the test. The area varies based on the actual relay settings (O87P, DIOPR, DIRTR, SLP1, and SLP2).

Note: This test procedure is valid only if O87P is less than DIOPR.

Irst (pu)

Iop (pu)

SLP1SLP2

87R Restrained ElementU87P

O87P

DIRTR

DIOPR

IRT2 Figure 6 High-Security Mode Region

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Step 1 For ease of testing, select a value of IRT midway between DIRTR and IRT2.

0.5 DIOPRIRTtest1 • DIRTR •100SLP22

⎛ ⎞= +⎜ ⎟⎝ ⎠

(9)

Step 2 Calculate the Winding 1 and Winding 2 currents for State 1. The State 1 currents are the same for Test 1 and Test 2.

IW1 0.555 • IRTtest1• TAP1• A= (10)

where:

IW1 is the Winding 1 test current.

IRTtest1 is the value of IRT chosen in Step 1.



The angle of IW1 is 180 degrees. The magnitude of IW2 is as follows:

IW2 0.445 • IRTtest1• TAP2 • B= (11)

where:





The angle of IW2 is either 0 degrees or 180 degrees, as determined from Table 3. A 10-cycle duration is suggested for State 1.

Step 3 For Test 1, State 2, select a value of IRTtest2 for the State 2 test. IRTtest2 should be greater than the following:

DIOPR 100IRTtest2 •SLP22

> (12)

The winding currents for the test are as follows:

0.95 •SLP2IW1 0.5 • IRTtest2 • 1 • TAP1• A100

⎛ ⎞= +⎜ ⎟⎝ ⎠

(13)

0.95 •SLP2IW2 0.5 • IRTtest2 • 1 • TAP2 • B100

⎛ ⎞= −⎜ ⎟⎝ ⎠

(14)

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The angles are the same as in State 1. The differential will not assert if the test currents are applied for less than 800 milliseconds. A 10-cycle duration is suggested. The relay should not trip even though this current is above the SLP1 characteristic. If the current is applied for longer than 1 second, CON will reset and the relay will trip on SLP1.

Step 4 For Test 2, State 2:


⎛ ⎞= +⎜ ⎟⎝ ⎠

(15)

1.05 • SLP2IW2 0.5 • IRTtest2 • 1 • TAP2 • B100

⎛ ⎞= −⎜ ⎟⎝ ⎠

(16)

The angles are the same as in State 1. The relay should trip immediately because this current is above the SLP2 characteristic.

Monitoring Relay Operation During Slope 2 Tests The SEL-487E includes three separate phase current differential elements, 87RA, 87RB, and 87RC. When a single-phase current is used to test the relay, each of these differentials may see the currents, depending on the relay settings. It is likely that more than one of the differential elements will operate, and they will operate at different levels. Figure 7 shows the response of the SEL-487E to the MET DIF command.

Figure 7 Example Response to MET DIF

In this instance, the 87RA element was being tested; however, the 87RB and 87RC elements operate before 87RA. Figure 8 shows the status of the 87Rn Relay Word bits for the currents of Figure 7.

Figure 8 Example Response to TAR 87RA

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Figure 8 shows that the 87RB and 87RC differential elements may assert when the 87RA element is being tested. Because the 87RB and 87RC elements may assert in SLP2 testing, the SEL-487E may trip even though 87RA has not asserted. Because the test currents are applied for only 800 milliseconds, it is not possible to use the TAR command to monitor the status of the 87RA Relay Word bit. However, it is possible to use the SEL-487E event reports or the Sequential Events Recorder (SER) to check the status of the differential elements and the high-security mode.

Figure 9 is a plot of the SLP2 test in which 87RA does not operate even though the relay did trip because 87RB and 87RC asserted during the test. Further discussion of monitoring the differential elements during testing is included in Appendix B.

Figure 9 shows the operation of CONA, which switches the 87RA element to the high-security mode (SLP2). As a result, the 87RA Relay Word bit does not assert. However, because the switch to the high-security mode is done on a per-differential basis, 87RB and 87RC did not switch to the high-security mode and asserted during the test, causing a trip output.

Figure 9 Example Event Report

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NEGATIVE-SEQUENCE DIFFERENTIAL TEST The negative-sequence differential element is included in the SEL-487E to provide more sensitive protection for internal turn-to-turn faults. The negative-sequence differential logic is shown in Figure 10.

312SC

312TC

312XC

( )max 312SC ... 312XC

∑

Figure 10 SEL-487E Negative-Sequence Differential Logic

There are several important differences between the negative-sequence and phase differential elements. First, the negative-sequence differential element uses three times the negative-sequence current from each winding input for its operate and restraint quantities. The compensated negative-sequence quantity from each winding is derived from all three compensated phase currents on the respective winding inputs (3I2kC = IAkC + a2 • IBkC + a • ICkC; where k is the winding S, T, U, V, or W). This adds a degree of complexity to testing the element; however, the negative-sequence element can be tested only with single-phase currents. Second, the restraint quantity, RST87Q, is the maximum magnitude of the compensated negative-sequence currents for each of the windings included in the negative-sequence differential, not the sum, as it is for the phase differential elements. Third, the negative-sequence differential element output (87Q) is based on a single-slope percentage restraint characteristic. It does not have the high-security Slope 2 that is part of the phase differential.

However, as shown in Figure 10, the 87Q output is blocked from operation by the CON Relay Word bit that asserts for external faults detected by the phase differential element. CON is the OR of the individual phase external fault detection logic (CONA, CONB, CONC). As a result, whenever one or more phase differential elements switch to the Slope 2 high-security mode, the negative-sequence differential is blocked. 87Q is also blocked whenever one or more of the phase differential elements detect a harmonic condition, causing the 87QB Relay Word bit to assert. The negative-sequence differential does not include an unrestrained differential element.

Negative-Sequence Differential Pickup Test Only one single-phase current is injected for testing the pickup threshold of the negative-sequence differential element. A single-phase current generates a negative-sequence current quantity (3I2) of the same magnitude.


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Step 2 Calculate the winding current needed to exceed the 87Q minimum pickup current.

IW1 87QP • TAP1= (17)

where:

IW1 is the injected test current on Winding 1 at pickup for the selected winding (S, T, W, U, or X).

87QP is the negative-sequence differential pickup setting in per unit of TAP.

TAP1 is the tap setting for Winding 1 (TAPS, TAPT, TAPW, TAPU, or TAPX).

Step 3 Monitor the Relay Word bit 87Q.

Step 4 Start with a 0 A current, and raise the current until the 87Q Relay Word bit asserts. This value should be within ±5 percent of the calculated value.

SLPQ1 Differential Test The negative-sequence percentage differential element slope is tested with two single-phase currents. The currents are injected into the windings in pairs. The Winding 1 current phase angle is set to 180 degrees, and the Winding 2 current phase angle is determined by the winding compensation settings in the SEL-487E. The Winding 2 current is fixed, and the Winding 1 current is varied to measure the characteristic slope.

Step 1 Select a magnitude of restraint quantity. The restraint quantity, RST87Qtest, must be greater than RST87Qmin, where:

100RST87Qmin 87QP •SLPQ1

= (18)

Step 2 Calculate the Winding 1 and Winding 2 currents for the test. The Winding 2 current is fixed, and the Winding 1 current magnitude is varied to determine the operating point.

IW2 RST87Qtest • TAP2= (19)

where:


RST87Qtest is the value of RST87Q chosen in Step 1.


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The angle of IW2 is determined from Table 5.

Table 5 IW2 Test Angle

T2CTC – T1CTC IW2 Angle (degrees)

0 0

1 or –11 30

–1 or 11 –30

2 or –10 60

–2 or 10 –60

4 or –8 120

–4 or 8 –120

5 or –7 150

–5 or 7 –150

6 180

In Table 5, T2CTC – T1CTC is the difference between the two winding compensation settings. For other TnCTC settings, the angle of IW2 is as follows:

( )IW2angle T2CTC T1CTC • 30= − (20)

The magnitude of IW1 at the operating point is as follows:

SLPQ1IW1op RST87Qtest • 1 • TAP1100

⎛ ⎞= −⎜ ⎟⎝ ⎠

(21)

where:

IW1op is the Winding 1 test current at the operating point on slope SLPQ1.

RST87Qtest is the value of IRT chosen in Step 1.

SLPQ1 is the negative-sequence differential slope setting.


The angle of IW1 is 180 degrees.

Note: Because of the relay settings, it is possible that the initial applied currents may cause the relay to switch to the high-security mode (CON Relay Word bit asserts). In that case, the currents must be applied for at least 1 second before changing the IW1 current. Verify that Relay Word bits CON and 87QB are not asserted.

Step 3 To start the test, apply the value of IW2 calculated from (20) at the angle from Table 5 based on the compensation settings (T2CT and T1CTC) to Winding 2 and 1.1 • IW1op calculated from (21) to Winding 1.

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Step 4 Slowly decrease the magnitude of IW1 until the 87Q element asserts. The IW1 current should be IW1op ± 5 percent.

EXAMPLE TEST CALCULATIONS This section demonstrates the test current calculations for the SEL-487E settings shown in Table 6.

Table 6 SEL-487E In-Service Settings

ECTC TERM = S, T TAPS = 1.74

TSCTC = 11 TAPT = 6.97

TTCTC = 12 TAPU = NA

TUCTC = NA TAPW = NA

TWCTC = NA TAPX = NA

TXCTC = NA DIOPR = 1.2

O87P = 0.3 DIRTR = 1.2

SLP1 = 12.5 87QP = 0.10

SLP2 = 25 SLPQ1 = 10

U87P = 8

Assume the S windings are IW1 and the T windings are IW2.

Unrestrained Phase Differential Test (U87P) For U87P test on Winding S:

IW1 U87P • TAPS• A= (22)

IW1 8 •1.74 • 3= (23)

IW1 24.11= (24)

Apply IW1 to the S winding. Increase the IW1 single-phase current from zero until Relay Word bit 87U asserts. Repeat the test on other differential-enabled windings, as necessary.

Restrained Phase Differential Pickup Test (O87P) IW1 O87P • TAPS• A= (25)

IW1 0.3•1.74 • 3= (26)

IW1 0.90= (27)

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Slope 1 Differential Test (SLP1)

100IRT min O87P •SLP1

= (28)

100IRT min 0.3 •12.5

= (29)

IRT min 2.4= (30)

Assume IRT equals 4 for the test.

SLP1IW2 0.5 • IRTtest • 1 • TAP2 • B100

⎛ ⎞= −⎜ ⎟⎝ ⎠

(31)

12.5IW2 0.5 • 4 • 1 • 6.97 •1.5100

⎛ ⎞= −⎜ ⎟⎝ ⎠

(32)

IW2 18.29= (33)

Apply IW2 to the T current winding. Because the difference in the TnCTC compensation settings for the windings chosen is 1, the Winding 2 current angle is 0 degrees, per Table 3. The magnitude of IW1 at the operating point is as follows:

SLP1IW1op 0.5 • IRTtest • 1 • TAP1• A100

⎛ ⎞= +⎜ ⎟⎝ ⎠

(34)

12.5IW1op 0.5 • 4 • 1 •1.74 • 3100

⎛ ⎞= +⎜ ⎟⎝ ⎠

(35)

IW1op 6.78= (36)

IW1 is applied to the S winding at 180 degrees. The initial current is as follows:

IW1 0.8 • IW1op= (37)

IW1 5.4= (38)

Increase the IW1 single-phase current from the initial value until the appropriate phase differential Relay Word bit 87RA, 87RB, or 87RC asserts based on the phase under test. Repeat the test for other phases and other winding pairs, as necessary.

Slope 2 Differential Test Determine IRTtest1.


⎛ ⎞= +⎜ ⎟⎝ ⎠

(39)

0.5 1.2IRTtest1 • 1.2 •100252

⎛ ⎞= +⎜ ⎟⎝ ⎠

(40)

IRTtest1 2.12= (41)

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Test 1 Determine the currents for State 1.

IW1 0.555 • IRTtest1• TAP1• A= (42)

IW1 0.555 • 2.12 •1.74 •1.73= (43)

IW1 3.55= (44)

The angle for IW1 is 180 degrees.

IW2 0.445 • IRTtest1• TAP2 • B= (45)

IW2 0.445 • 2.12 • 6.97 •1.5= (46)

IW2 9.87= (47)

The angle for IW1 is 0 degrees, per Table 3. Determine the currents for State 2. The minimum current for IRTtest2 is as follows:

DIOPR 100IRTtest2 •SLP22

> (48)

1.2 100IRTtest2 •252

> (49)

IRTtest2 3.4> (50)

For this test, assume IRTtest2 equals 6. The winding currents for the State 2 test are as follows:


⎛ ⎞= +⎜ ⎟⎝ ⎠

(51)

0.95 • 25IW1 0.5 • 6 • 1 •1.74 •1.73100

⎛ ⎞= +⎜ ⎟⎝ ⎠

(52)

IW1 11.19= (53)

0.95 •SLP2IW2 0.5 • IRTtest2 • 1 • TAP2 • B100

⎛ ⎞= −⎜ ⎟⎝ ⎠

(54)

0.95• 25IW2 0.5 • 6 • 1 • 6.97 •1.5100

⎛ ⎞= −⎜ ⎟⎝ ⎠

(55)

IW2 23.92= (56)

The angles are the same as in State 1.

Table 7 Test 1 Values

State 1 State 2

IW1 3.55 at 180 degrees 11.19 at 180 degrees


Duration 10 cycles 10 cycles

21


Test 2 The State 1 values for Test 2 are the same as those used in Test 1. For this test, assume IRTtest2 equals 6 (the same value as used for Test 1). The winding currents for the State 2 test are as follows:


⎛ ⎞= +⎜ ⎟⎝ ⎠

(57)

1.05 • 25IW1 0.5 • 6 • 1 •1.74 •1.73100

⎛ ⎞= +⎜ ⎟⎝ ⎠

(58)

IW1 11.41= (59)

1.05• SLP2IW2 0.5 • IRTtest2 • 1 • TAP2 • B100

⎛ ⎞= −⎜ ⎟⎝ ⎠

(60)

1.05 • 25IW2 0.5 • 6 • 1 • 6.97 •1.5100

⎛ ⎞= −⎜ ⎟⎝ ⎠

(61)

IW2 23.13= (62)

The angles are the same as in State 1.

Table 8 Test 2 Values

State 1 State 2



Duration 10 cycles 10 cycles

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Figure 11 is a plot of the event file from Test 1. It is important to note that the SEL-487E did trip during State 1. However, the trip was the result of the 87RB and 87RC differential elements. The test was for the 87A differential element; the 87RA differential element did not operate during either State 1 or State 2. As previously mentioned, when performing single-phase current testing, it is important to monitor the proper Relay Word bits. This test demonstrates that the SEL-487E is secure for a fault just below the Slope 2 characteristic when it is in the high-security mode.

Figure 11 Test 1 Event Plot

Figure 12 is a plot of the event file from Test 2. In this test, the 87RA differential element operated as expected during State 2. This test demonstrates that the SEL-487E operates for a fault above the Slope 2 characteristic when it is in the high-security mode.

Figure 12 Test 2 Event Plot

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Negative-Sequence Differential Pickup Test (87QP) Increase the IW1 single-phase current from zero until Relay Word bit 87Q asserts. At this point, IW1/TAP1 should be within ±5 percent of relay setting 87QP. Repeat the test for all differential-enabled winding inputs.

IW1 87QP • TAP= n (63)

IW1 0.1•1.74= (64)

IW1 0.174= (65)

Restrained Negative-Sequence Slope Test (SLPQ1) The minimum restraint quantity is as follows:

100RST87Qmin 87QP •SLPQ1

= (66)

100RST87Qmin 0.1•10

= (67)

RST87Qmin 1= (68)

Assume RST87Qtest = 2.

IW2 RST87Qtest • TAP2= (69)

IW2 2 • 6.97= (70)

IW2 13.94= (71)

TTCTC = 12 and TSCTC = 11, so T2CTC – T2CTC = 1. The angle of IW2 is 30 degrees.

SLPQ1IW1op RST87Qtest • 1 • TAP1100

⎛ ⎞= −⎜ ⎟⎝ ⎠

(72)

10IW1op 2 • 1 •1.74100

⎛ ⎞= −⎜ ⎟⎝ ⎠

(73)

IW1op 3.13= (74)

The angle of IW1 is 180 degrees. The initial current is as follows:

IW1initial 1.1• 3.13= (75)

IW1initial 3.45= (76)

Decrease current IW1 until Relay Word bit 87Q asserts. Repeat the test on other phases and other differential-enabled winding pairs, as necessary.

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CONCLUSION This application guide presents the differences between the SEL-387 and SEL-487E differential relay elements and their operation. It also presents techniques and examples for testing the SEL-487E differential relay elements using single-phase currents. In general, the minimum pickup, unrestrained differential, and Slope 1 differential elements in the SEL-387 and SEL-487E use very similar techniques. The Slope 2 differential tests are significantly different, because the Slope 2 characteristics in the two relays operate in a completely different manner. The negative-sequence differential element tests are unique to the SEL-487E.

To help with the calculation of test quantities used in testing the SEL-487E, an Excel spreadsheet is available for download with this application guide at http://www.selinc.com.

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APPENDIX A: ALTERNATE SLOPE 2 TEST This test procedure does not require state simulation. Because state simulation is not used, the range of values that can be used for IRT is limited. Two tests are performed. The first test has an operate signal above Slope 1 and below Slope 2. The relay asserts the CON Relay Word bit and enters the high-security mode. If the current is applied for less than 800 milliseconds, the relay will not trip. If the current is applied longer than 1 second, the CON Relay Word bit deasserts and the relay trips on Slope 1. The second test applies an operate current above Slope 2. The relay trips on Slope 2 without time delay.

The value of IRT must be between the following:

DIRTRIRT min2

= (77)

DIOPR •100IRT max2 •SLP2

= (78)

Step 1 For ease of testing, select a value of IRT midway between DIRTR and IRT2.


⎛ ⎞= +⎜ ⎟⎝ ⎠

(79)

Step 2 Select a value of IOP that is midway between Slope 1 and Slope 2.

SLP1 SLP2IOPtest1 IRTtest •200+

= (80)

Step 3 Calculate the Winding 1 and Winding 2 currents for Test 1.

IOPtest1 IRTtest1IW1 • TAP1• A2+

= (81)

where:






IOPtest1 IRTtest1IW2 • TAP2 • B2−

= (82)

where:


26





The angle of IW2 is either 0 degrees or 180 degrees, as determined from Table 3.

Step 4 Apply the currents to the relay. The CON Relay Word bit asserts for 1 second. After 1 second, CON deasserts, and the relay trips on Slope 1.

Step 5 For Test 2, an IOP midway between Slope 2 and DIOPR is selected. It is assumed that DIOPR is at the default setting of 1.2.

1.2IRTtest2IOPtest2

2

+= (83)

Step 6 Calculate the Winding 1 and Winding 2 currents for Test 2.

IOPtest2 IRTtest1IW1 • TAP1• A2+

= (84)

where:






IOPtest2 IRTtest1IW2 • TAP2 • B2−

= (85)

where:





The angle of IW2 is either 0 degrees or 180 degrees, as determined from Table 3.

Step 7 Apply the currents to the relay. The CON Relay Word bit asserts momentarily. The relay trips on Slope 2 without the 1-second time delay.

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APPENDIX B: MONITORING RELAY OPERATION DURING TESTING

Monitoring Relay Word Bits During Testing As shown in the event reports of Figure 5, Figure 9, Figure 11, and Figure 12, the differential Relay Word bits 87RA, 87RB, and 87RC do not assert continuously when the relay is in the trip state. If an output contact is required to connect to an automated test set, it is desirable to have a contact that is continuously asserted. As noted previously, the trip output cannot be used because it may assert if one of the other phase differentials asserts.

It is possible to use the programmable SELOGIC® control equations to make the phase differentials continuous for testing purposes. Figure 13 shows the settings required use timer PCT11 to provide a 2-cycle dropout. This extended dropout keeps the PCT11 output up continuously during the test. Instead of monitoring Relay Word bit 87RA directly, use the Relay Word bit PCT11Q to indicate assertion of the differential element.

PCT11PU := 0.000000

PCT11DO := 2.000000

PCT11IN := 87RA

Figure 13 Protection Logic

Similar logic may be used for Relay Word bits 87RB and 87RC.

SER Point Considerations It is also possible to use the SER in the SEL-487E to monitor the operation of the various elements during testing. A sample SER file is shown in Figure 14. Note that there are multiple entries, because 87RA is not continuously asserted. If the test currents are applied to the relay for a prolonged time, the SER data from the start of the test sequence may be overwritten by later events. This can be avoided by using the logic described in (13) or by using the SER chatter criteria settings, as shown in Figure 15. Figure 16 shows the same test record as Figure 14, but the use of the chatter criteria settings reduced the number of differential operations recorded during the test.

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# DATE TIME ELEMENT STATE

35 10/23/2009 07:45:48.4019 CONA ASSERTED

34 10/23/2009 07:45:48.4039 50SP1 Asserted

33 10/23/2009 07:45:48.4039 50TP1 Asserted

32 10/23/2009 07:45:48.4309 DIFF TRIP ASSERTED

31 10/23/2009 07:45:48.5749 CONA DEASSERTED

30 10/23/2009 07:45:48.5874 87RA_TRIP Asserted

29 10/23/2009 07:45:48.6084 87RA_TRIP Deasserted

28 10/23/2009 07:45:48.6184 87RA_TRIP Asserted


26 10/23/2009 07:45:48.6559 87RA_TRIP Asserted

25 10/23/2009 07:45:48.6604 87Q ASSERTED


23 10/23/2009 07:45:48.6934 87RA_TRIP Asserted


21 10/23/2009 07:45:48.7309 87RA_TRIP Asserted


19 10/23/2009 07:45:48.7684 87RA_TRIP Asserted


17 10/23/2009 07:45:48.8104 87RA_TRIP Asserted


15 10/23/2009 07:45:48.8519 87RA_TRIP Asserted


13 10/23/2009 07:45:48.8934 87RA_TRIP Asserted


11 10/23/2009 07:45:48.9309 87RA_TRIP Asserted


9 10/23/2009 07:45:48.9684 87RA_TRIP Asserted


7 10/23/2009 07:45:49.0104 87RA_TRIP Asserted


5 10/23/2009 07:45:49.0519 87RA_TRIP Asserted


3 10/23/2009 07:45:49.0684 87Q DEASSERTED

2 10/23/2009 07:45:49.0874 50SP1 Deasserted

1 10/23/2009 07:45:49.0874 50TP1 Deasserted

Figure 14 Sample SER Report

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Figure 15 SER Chatter Criteria

Figure 16 SER After Chatter Criteria

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FACTORY ASSISTANCE We appreciate your interest in SEL products and services. If you have questions or comments, please contact us at:

Schweitzer Engineering Laboratories, Inc. 2350 NE Hopkins Court Pullman, WA 99163-5603 USA Telephone: +1.509.332.1890 Fax: +1.509.332.7990 www.selinc.com • [email protected]

© 2010 by Schweitzer Engineering Laboratories, Inc. All rights reserved.

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Testing the SEL-487E Relay Differential Elements · 6/1/2010 · In the SEL-387, the restraint...

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