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7-14 489 Generator Management Relay GE Multilin
7.3 ADDITIONAL FUNCTIONAL TESTS 7 TESTING
7
7.3.8 PHASE DIFFERENTIAL TRIP ACCURACY
These tests will require a dual channel current source. The unit must be capable of injecting prefault cur-
rents and fault currents of a different value. Application of excessive currents (greater than 3 × CT) for
extended periods will cause damage to the relay.
a) MINIMUM PICKUP CHECK
1. Connect the relay test set to inject Channel X current (I
x
) into the G3 terminal and out of H3 terminal (Phase A).
Increase I
x
until the differential element picks up. Record this value as pickup. Switch off the current. The theoretical
pickup can be computed as follows:
(EQ 7.5)
b) SINGLE INFEED FAULT
2. Set the I
x
prefault current equal to 0. Set the fault current equal to CT. Apply the fault. Switch off the current. Record the
operating time.
3. Set the I
x
prefault current equal to 0. Set the fault current equal to 5 × CT. Apply the fault. Switch off the current. Record
the operating time.
c) SLOPE 1 CHECK
4. Connect the relay test set to inject Channel Y current (I
Y
) into the G6 terminal and out of H6 terminal. The angle
between I
x
and I
Y
will be 180°.
5. Set pre-fault current, I
x
and I
Y
equal to zero.
6. Set fault current, I
Y
equal to 1½ CT.
7. At this value the relay should operate according to the following formula:
(EQ 7.6)
8. Set fault current, I
x
equal to 0.95 × I
XOP1
. Apply the fault. The relay should operate. Switch off the current.
9. Set fault current, I
x
equal to 1.05 × I
XOP1
. Apply the fault. The relay should restrain. Switch off the current.
d) SLOPE 2 CHECK
10. Set fault current, I
Y
equal to 2.5 × CT.
11. At this value the relay should operate according to the following formula.
(EQ 7.7)
12. Set fault current, I
x
equal to 0.95 × I
XOP2
. Switch on the test set. The relay should operate. Switch off the current.
13. Set fault current, I
x
equal to 1.05 × I
XOP2
. Switch on the test set. The relay should restrain. Switch off the current.
e) DIRECTIONAL CHECK
14. Set pre-fault current, I
x
and I
Y
equal to 2.5 × CT. At this value the conditions for CT saturation detection are set and the
relay will enable the directional check.
15. Set fault current, I
x
equal to 0.95 × I
XOP2
. Switch on the test set. The relay should restrain. Switch off the current.
16. Repeat Steps 1 through 15 for phases B and C.
NOTE
I
XPU
Pickup setting CT×=
I
XOP1
2 Slope 1 setting–
2 Slope 1 setting+
-------------------------------------------------
3CT×
2
-----------------
×=
I
XOP2
2 Slope 1 setting–
2 Slope 1 setting+
-------------------------------------------------
2.5 CT××=