GE T60

8-8 T60 Transformer Protection System GE Multilin
8.2 DIFFERENTIAL CHARACTERISTIC TEST EXAMPLES 8 COMMISSIONING
8
f) SLOPE 2 TEST
Inject currents in such a manner that the magnitude of I
r
is larger than the restraint current at Breakpoint 2; that is,
(EQ 8.11)
1. Change the current magnitudes as follows:
2. The following differential and restraint current should be read from the T60 actual values menu:
Since and lower than the required 95%, the Percent Differential element will not operate.
3. Adjust the I
1
current as shown below (thereby increasing I
d
) and verify that the relay operates.
4. The following differential and restraint current should appear in the T60 actual values menu:
5. The actual ratio is now 95.9%. Verify that the element operates correctly.
g) SUMMARY
The above tests describe the principles of testing the differential element for all regions from the operating characteristic.
For verification of more points, one should consider adjusting the magnitude of the restraint current I
r
to the desired portion
of the characteristic and change the other current to vary I
d
until the relay operates. Use the Excel tool to compare the
actual and expected operating values.
A blank result table is provided at the end of this chapter for convenience.
WINDING 1 WINDING 2
PHASE SINGLE CURRENT (I
1
) PHASE SINGLE CURRENT (I
2
)
A0 A 0° A 0 A 0°
B 0.5 A 0° B 9 A –180°
C 0.5 A –180° C 9 A 0°
PHASE DIFFERENTIAL CURRENT (I
d
) PHASE RESTRAINT CURRENT (I
r
)
A0 0° A 0 0°
B 8.078 pu –180° B 9 pu –180°
C 8.078 pu 0° C 9 pu 0°
WINDING 1 WINDING 2
PHASE SINGLE CURRENT (I
1
) PHASE SINGLE CURRENT (I
2
)
A0 A 0° A 0 A 0°
B 0.2 A 0° B 9 A –180°
C 0.2 A –180° C 9 A 0°
PHASE DIFFERENTIAL CURRENT (I
d
) PHASE RESTRAINT CURRENT (I
r
)
A0 0° A 0 0°
B 8.631 pu –180° B 9 pu –180°
C 8.631 pu 0° C 9 pu 0°
I
r
I
r
Break 2 8 pu=
I
d
I
r
 89.8%=
I
d
I
r
