Percent Differential (87) Element Testing
STEADY-STATE PICKUP TEST
5. Repeat the test on all phases related to the restrained-differential
NA NA NA NA NA
2.45 OK WINDING
W1 W2 W3
TEST 0.723 A
2.634A 2.44 2.48 3.16 OK OK
MFG (cycles) % ERROR
2.410 2.490 2.500 3.16 OK OK OK
B PHASE (cy) C PHASE (cy) RESTRAINED DIFFERENTIAL TIMING TESTS (cycles) A PHASE (cy)
6. 3-Phase Restrained-Differential Slope Testing
Differential slope testing is one of the most complex relay tests that can be performed and requires careful planning; a good understanding of the differential relay’s operating fundamentals; and information from the manufacturer regarding the relay’s characteristics.
This section will discuss 3-Phase testing that will require at least six current channels to be performed correctly. Refer to the “1-Phase Restrained-Differential Slope Testing” section of this chapter if your test equipment has less than six-channels.
Six-channel restrained-differential testing is actually very similar to the simple testing discussed in the previous chapter after the phase-angles between windings have been applied correctly.
Six-phase restrained-differential testing is achieved by applying 3-phase balanced currents in each winding, mimicking an ideal-world steady state scenario, and then increasing all three currents in one winding simultaneously until the relay operates. The math is also simplified when you apply balanced three-phase conditions.
We discussed how to interpret the phase-angle-shift settings previously in this chapter which can be summarized by the following figure.
CONNECTION BECkWITH ELECTRIC
M-3310 SEL-387 SEL-587
A
Transformer Connection 01. Yyyy
Transformer Connection 10. DACDACyy
Transformer Connection 04. DABYyy
Transformer Connection 02. YDACyy
Transformer Connection 05. DACYyy
b Transformer Connection 03. YDAByy
W1CTC=12 W2CTC=11
TRCON=YDAB CTCON=YY
Figure 79: Common Phase-Angle Compensation Settings
Let’s figure out the test-settings for balanced full-load conditions for each case. The full load condition for Winding-1 is the Tap1 setting. All three-phases for Winding-1 should start at Tap1. All three-phases for Winding-2 should start at Tap2.
The first case is SEL-387 when both W1CTC and W2CTC=12. Both settings are the same so there is no phase-angle shift for this connection. The Capital “A” (Winding-1) and lower case
“a” (Winding-2) are both at 0º so our A-Phase test conditions will be at 0º. The other two phases will be 120º apart to create a three-phase balanced condition. A-Phase for Winding-2 will start at 180º to be opposite Winding-1 and the other two phases will be 120º apart as shown in the following table.
CONNECTION SEL-387 W1AØ W1BØ W1CØ W2AØ W2BØ W2CØ
A
W1BØ = TAP1@-120º W1CØ = TAP1@120º
W2AØ = TAP2@180º
W2BØ = TAP2@60º
W2CØ = TAP2@-60º
Figure 80: Yy12 or Yy0 3-Phase Differential Restraint Test Connections
The next case is SEL-387 when both W1CTC and W2CTC=0. Both settings are the same so there is no phase-angle shift for this connection. The Capital “A” (Winding-1) and lower case
“a” (Winding-2) are both at 0º so our A-Phase test conditions will be at 0º. The other two phases will be 120º apart to create a three-phase balanced condition. A-Phase for Winding-2 will start at 180º to be opposite Winding-1 and the other two phases will be 120º apart as shown in the following table.
CONNECTION SEL-387 W1AØ W1BØ W1CØ W2AØ W2BØ W2CØ
A
W1BØ = TAP1@-120º W1CØ = TAP1@120º
W2AØ = TAP2@180º
W2BØ = TAP2@60º
W2CØ = TAP2@-60º
Figure 81: Dd0 3-Phase Differential Restraint Test Connections
The next case is SEL-387 with W1CTC=0 and W2CTC =1. The Capital “A” (Winding-1) is at 0º so our A-Phase test conditions will be at 0º. The other two phases will be 120º apart to create a three-phase balanced condition. The lower case “a” is at -30º so there is a phase shift between windings. Remember that we apply Winding-2 current 180º out-of-phase so the A-Phase for Winding-2 will start at 150º
(
−30° +180°)
to be opposite Winding-1. The other two phases will be 120º apart as shown in the following table.CONNECTION SEL-387 W1AØ W1BØ W1CØ W2AØ W2BØ W2CØ
A
W1BØ = TAP1@-120º
W1CØ = TAP1@120º
W2AØ = TAP2@150º W2BØ = TAP2@30º
W2CØ = TAP2@-90º
Figure 82: Dy1 3-Phase Differential Restraint Test Connections
The next case is SEL-387 with W1CTC=12 and W2CTC =1. The Capital “A” (Winding-1) is at 0º so our A-Phase test conditions will be at 0º. The other two phases will be 120º apart to create a three-phase balanced condition. The lower case “a” is at -30º so there is a phase shift between windings. Remember that we apply Winding-2 current 180º out-of-phase so the A-Phase for Winding-2 will start at 150º
(
−30° +180°)
to be opposite Winding-1. The other two phases will be 120º apart as shown in the following table.CONNECTION SEL-387 W1AØ W1BØ W1CØ W2AØ W2BØ W2CØ
A
180 0
W1BØ = TAP1@-120º
W1CØ = TAP1@120º
W2AØ = TAP2@150º W2BØ = TAP2@30º
W2CØ = TAP2@-90º
Figure 83: Yd1 3-Phase Differential Restraint Test Connections
The next case is SEL-387 with W1CTC=0 and W2CTC =11 The Capital “A” (Winding-1) is at 0º so our A-Phase test conditions will be at 0º. The other two phases will be 120º apart to create a three-phase balanced condition. The lower case “a” is at 30º so there is a phase shift between windings. Remember that we apply Winding-2 current 180º out-of-phase so the A-Phase for Winding-2 will start at 210º (-150º)
(
30° +180°)
to be opposite Winding-1. The other two phases will be 120º apart as shown in the following table.CONNECTION SEL-387 W1AØ W1BØ W1CØ W2AØ W2BØ W2CØ
A
W1BØ = TAP1@-120º W1CØ = TAP1@120º
W2AØ = TAP2@-150º
W2BØ = TAP2@90º
W2CØ = TAP2@-30º
Figure 84: Dy11 3-Phase Differential Restraint Test Connections
The Relay Testing Handbook
The next case is SEL-387 with W1CTC=12 and W2CTC =11 The Capital “A” (Winding-1) is at 0º so our A-Phase test conditions will be at 0º. The other two phases will be 120º apart to create a three-phase balanced condition. The lower case “a” is at 30º so there is a phase shift between windings. Remember that we apply Winding-2 current 180º out-of-phase so the A-Phase for Winding-2 will start at 210º (-150º)
(
30° +180°)
to be opposite Winding-1. The other two phases will be 120º apart as shown in the following table.CONNECTION SEL-387 W1AØ W1BØ W1CØ W2AØ W2BØ W2CØ
B
W1BØ = TAP1@-120º W1CØ = TAP1@120º
W2AØ = TAP2@-150º
W2BØ = TAP2@90º
W2CØ = TAP2@-30º
Figure 85: Yd11 3-Phase Differential Restraint Test Connections
A) Test-Set Connections
The connection diagram for the SEL-387 is as follows:
Figure 86: Schweitzer Electric SEL-387 Transformer Protective Relay Connections
Follow the AØ primary buss through the Phase A CTs then follow the CT secondary to terminal Z01(IAW1). This is where we will connect the first current from our test-set.
Connect the neutral of the test-set current channel to Z02 by following the other side of the CT to its relay terminal. Keep following the primary buss through the transformer to the Phase A' CT and then follow the secondary to terminal Z08. This is the neutral of the CTs so we will connect the test-set’s second current-channel-neutral-terminal to Z08.
Follow the other side of the CT to terminal Z07 (IAW2) which is where we will connect the second channel current from the test-set. Follow the other phases to determine the following connections when testing B or C phases.
The test-set connections for a 3-Phase Restrained-Differential Slope test are displayed in the next figure.
SEL-387 RELAY RELAY TEST SET
Magnitude Phase Angle W1AØ Test Amps 0°
Element
Output Timer
Input
Frequency Test Hz
W1BØ Test Amps -120° (240°) Test Hz
W1CØ Test Amps 120° Test Hz
W2AØ Test Amps W2AØ Test° Test Hz
W2BØ Test Amps W2BØ Test° Test Hz
W2CØ Test° Test Hz W2CØ Test Amps
C1 Amps
Alternate Timer Connection (PS = Phase Shift) IAW1 Z01
Figure 87: 3-Phase Restrained-Differential Slope Test-Set Connections