Inrush Inhibit Test - GE T60 Instruction Manual

CHAPTER 8: COMMISSIONING

8.3 Inrush inhibit test

8.3.1 Inrush inhibit test procedure
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.
This procedure is based upon the example provided in the Differential Characteristic Test Example section. The transformer
parameters are as follows.
• Transformer data — 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 following table 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 8-3: Inrush inhibit test summary
Phase Injected
W1 Current W1 2nd
Harmonic
A 1 A ∠0° 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 needs to remain operating 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
protection need to 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
Percent Differential element. The element should drop out when the injected second harmonic level becomes three
times larger than the set threshold.
T60 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
Displayed
W2 Current W2 2nd I
d
Harmonic
0 A ∠0° 0 0.997 pu
0 A ∠0° 0 0.997 pu
2 A ∠–180°
15% 2 pu
2 A ∠–180°
15% 2 pu
4 A ∠–180°
16.3% 2 pu
4 A ∠–180°
17.3% 2 pu
to "Trad. 2nd" and the
INRUSH INHIBIT LEVEL
to "Trad. 2nd" and the
INRUSH INHIBIT LEVEL
2nd I
r
Harmonic
18% 0.997 pu
20% 0.997 pu
18% 4 pu
20% 4 pu
18% 4 pu
20% 4 pu
setting as follows.
INRUSH INHIBIT MODE
to "20%".
to "20%".
INRUSH INHIBIT TEST
Status
Operate
Block
Operate
Block
Operate
Block
8
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