Overexcitation Inhibit Test; Frequency Element Tests; Overexcitation Inhibit Test Procedure - GE T60 Instruction Manual

OVEREXCITATION INHIBIT TEST

8.4 Overexcitation inhibit test

8.4.1 Overexcitation inhibit test procedure

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.
This procedure is based upon the example provided in the Differential Characteristic Test Example section. The transformer
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 8-4: Overexcitation inhibit test summary
Phase Injected
W1 Current
1 A ∠0°
A
1 A ∠0°
B 4 A ∠0°
4 A ∠0°
C 2 A ∠0°
2 A ∠0°

8.5 Frequency element tests

8
8.5.1 Testing underfrequency and overfrequency elements
Underfrequency and overfrequency protection requires techniques with subtle testing implications. Whereas most
protection is designed to detect changes from normal to fault conditions that occur virtually instantaneously, power
system inertia requires frequency protection to pick up while the frequency is changing slowly. Frequency measurement is
inherently sensitive to noise, making high precision in combination with high speed challenging for both relays and test
equipment.
Injection to a particular T60 frequency element must be to its configured source and to the channels that the source uses
for frequency measurement. For frequency measurement, a source uses the first quantity configured in the following
order:
1. Phase voltages
2. Auxiliary voltage
8-14
W1 5th W2 Current W2 5th
Harmonic Harmonic
0 A ∠0°
8% 0
0 A ∠0°
10% 0
8.5% 2 A ∠–180° 9%
9.5% 2 A ∠–180° 9%
9% 4 A ∠–180° 8.5%
9% 4 A ∠–180° 9.5%
Displayed
I 5th I
d r
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
T60 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 8: COMMISSIONING
Status
Operate
Block
Operate
Block
Operate
Block