Test Example 2 - GE T60 Instruction Manual

CHAPTER 8: COMMISSIONING
4. Read the following differential and restraint current values in the T60 actual values menu.
Phase Differential current (I
0 ∠0°
A
8.631 pu ∠–180°
B
8.631 pu ∠0°
C
5. The actual I /I ratio is now 95.9%. Verify that the element operates correctly.
d r
8.2.2.7 Summary
The tests described the principles of testing the differential element for all regions from the operating characteristic.
For verification of more points, consider adjusting the magnitude of the restraint current I
characteristic and change the other current to vary I
and expected operating values.
A blank result table is provided at the end of this chapter for convenience.

8.2.3 Test example 2

8.2.3.1 D/yg30° transformer with phase A to ground fault on the grounded Wye
Transformer data — D/y30°, 20 MVA, 115/12.47 kv, CT1 (200:1), CT2 (1000:1)
Figure 8-3: Current distribution of a D/yg30° transformer with an LV-side ground fault
Test Phase Injected current
W1 current
Balanced A 0.29 ∠0°
Condition
B 0 ∠0°
C 0.29 ∠–180°
Minimum A 0.137 ∠0°
Pickup
B 0 ∠0°
C 0.137 ∠–180°
Minimum A 0.108 ∠0°
Pickup
B 0 ∠0°
C 0.108 ∠–180°
T60 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
) Phase Restraint current (I
d
0 ∠0°
A
9 pu ∠–180°
B
9 pu ∠0°
C
until the relay operates. Use the Excel tool to compare the actual
d
Displayed current
W2 current Differential
0.926 ∠–180° 0 ∠0°
0 ∠0° 0 ∠0°
0 ∠0° 0 ∠0°
0.521 ∠–180° 0.048 ∠0°
0 ∠0° 0 ∠0°
0 ∠0° 0.048 ∠0°
0.521 ∠–180° 0.102 ∠0°
0 ∠0° 0 ∠0°
0 ∠0° 0.102 ∠0°
DIFFERENTIAL CHARACTERISTIC TEST EXAMPLES
)
r
to the required portion of the
r
Status
Restraint
0.5349 ∠–180° Not Applicable
0 ∠0°
0.5349 ∠0°
0.3 ∠–180° Block
I = 0.048 < Min PKP
d
0 ∠0°
0.3 ∠0°
0.3 ∠–180° Operate
I = 0.102 > Min PKP
d
0 ∠0°
0.3 ∠0°
8
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