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9 COMMISSIONING
9.4OVEREXCITATION INHIBIT TEST
The Overexcitation Inhibit Test requires a secondary injection from a source capable of producing an adjustable 5th
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)
5th Harmonic Setting = 10%
1.
Connect the relay test set to inject current into the Winding 1 Phase A CT input.
2.
Inject a current into the relay until the biased Differential element operates.
3.
Confirm that ONLY the differential element has operated.
4.
Increase the 5th harmonic content level until the element drops out. Record this value as the Overexcitation Inhibit
Level Pickup.
5.
Gradually decrease the harmonic content level until the element picks up. Record this value as the Overexcitation
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 9–2: OVEREXCITATION INHIBIT TEST SUMMARY
PHASE
W1
W1 5TH
CURRENT
HARMONIC
1 A ∠0°
A
8%
1 A ∠0°
10%
B
4 A ∠0°
8.5%
4 A ∠0°
9.5%
2 A ∠0°
C
9%
2 A ∠0°
9%
GE Multilin
INJECTED
W2
W2 5TH
CURRENT
HARMONIC
0 A ∠0°
0
0 A ∠0°
0
2 A ∠–180°
9%
2 A ∠–180°
9%
4 A ∠–180°
8.5%
4 A ∠–180°
9.5%
T60 Transformer Protection System
9.4 OVEREXCITATION INHIBIT TEST
9.4.1 OVEREXCITATION INHIBIT TEST PROCEDURE
DISPLAYED
I
5TH
d
HARMONIC
1 pu
8%
1 pu
1 pu
10%
1 pu
2 pu
8%
4 pu
2 pu
10%
4 pu
2 pu
8%
4 pu
2 pu
10%
4 pu
STATUS
I
r
Operate
Block
Operate
Block
Operate
Block
9-13
9
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