Inrush Inhibit Test Procedure; Inrush Inhibit Test Summary - GE T60 Instruction Manual

8 COMMISSIONING
8.3INRUSH INHIBIT TEST
The Inrush Inhibit Test requires a secondary injection test capable of producing a current with an adjustable second
harmonic component. Use the appropriate commissioning tables at the end of this chapter to record values.
NOTE
This procedure is based upon the example provided in the Differential Characteristic Test Example section. The trans-
former parameters are as follows:
Transformer: Y/y0°, 230/69 kV, CT1 (300:1), CT2 (1000:1)
2nd Harmonic Setting = 20%
1. Connect the relay test set to inject current into the Winding 1 Phase A CT input.
2. Inject currents into the relay as shown in the table below until the biased differential element picks up.
3. Confirm that only the percent differential element has operated.
4. Increase the harmonic content until the element drops out. Record this value as the Inrush Inhibit Level Pickup.
5. Gradually decrease the harmonic content level until the element picks up. Record this value as the Inrush Inhibit
Level Dropout.
6. Switch off the current.
7. Repeat steps 1 through 6 for phases B and C.
8. Repeat steps 1 through 7 for Winding 2 (and Windings 3 and 4 if necessary).
Table 8–1: INRUSH INHIBIT TEST SUMMARY
PHASE
W1 W1 2ND
CURRENT HARMONIC
1 A 0°
A 18.01%
1 A 0°
19.97%
4 A 0°
B 16.72%
4 A 0°
17.60%
2 A 0°
C 15%
2 A 0°
15%
The second harmonic inhibit feature can be verified by setting the
For set to "2-out-of-3":
INRUSH INHIBIT MODE
1. Set the
INRUSH INHIBIT FUNCTION
2. Inject currents into one CT bank (one winding only) until the biased differential operates for all three phases.
3. Apply a second harmonic to Phase A higher than the set threshold and monitor operation of Phases A, B, and C. The
element should stay operated on all three phases.
4. Apply a second harmonic to Phase B with a level less than the set threshold.
5. Increase the second harmonic level in Phase B. When it passes the set threshold, all three phases of differential pro-
tection should drop out.
For set to "Average":
INRUSH INHIBIT MODE
1. Set the
INRUSH INHIBIT FUNCTION
2. Inject currents into one CT bank (one winding only) until the biased differential operates for all three phases.
3. Apply a second harmonic to Phase A with a level greater than the set threshold and monitor the operation of the Per-
cent Differential element. The element should drop out when the injected second harmonic level becomes three times
larger than the set threshold.
GE Multilin
INJECTED
W2 W2 2ND
CURRENT HARMONIC
0 A 0°
0
0 A 0°
0
2 A –180°
15%
2 A –180°
15%
4 A –180°
16.3%
4 A –180°
17.3%
to "Trad. 2nd" and the
INRUSH INHIBIT LEVEL
to "Trad. 2nd" and the
INRUSH INHIBIT LEVEL
T60 Transformer Protection System
8.3 INRUSH INHIBIT TEST

8.3.1 INRUSH INHIBIT TEST PROCEDURE

DISPLAYED
I 2ND
d
HARMONIC
0.997 pu 18% 0.997 pu
0.997 pu 20% 0.997 pu
2 pu 18%
2 pu 20%
2 pu 18%
2 pu 20%
setting as follows:
INRUSH INHIBIT MODE
to "20%".
to "20%".
STATUS
I
r
Operate
Block
4 pu Operate
4 pu Block
4 pu Operate
4 pu Block
8-13
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