GE 750 User Manual

GE Power Management 750/760 Feeder Management Relay 17-
23
17 COMMISSIONING 17.7 PROTECTION SCHEMES
17
5. Inject the preset current into phase B and note the measured delay time. Check this time against the time
established by the settings. Reset the timer.
6. Preset the injection current level to 7.0 x pickup. Turn the current off, and reset the timer.
7. Inject the preset current into phase C and note the measured delay time. Check this time against the time
established by the settings.
8. Turn current off and disconnect the Stop Trigger.
Linear Reset Timing:
To confirm that the time O/C element is using linear reset timing, if so programmed, inject a current above the
pickup level for approximately half the time required to Trip. Turn the current off, reset the interval timer, and
then re-apply immediately. The time-to-trip should be much less than the trip-time established by the settings.
Voltage Restrained Phase Time Overcurrent:
1. Apply 3-phase nominal voltage to the relay.
2. Inject current below the pickup level into phase A. Slowly increase the current until the PICKUP indicator is
on. Note the pickup value is the pickup current of the Curve in use. Slowly reduce the current until the
PICKUP indicator goes off. Note the dropout level, which should be 2% of CT less than pickup when
pickup
≤
CT or 97 to 98% of pickup when pickup > CT. Reduce the current to zero.
3. Repeat step 2 for current injected into phases B and C.
4. Set all input voltages to 0. Slowly increase phase A current until the PICKUP indicator comes on. Check
that this current is 9-11% of the measured full voltage pickup current. Increase input voltage
V
ab
until the
PICKUP indicator goes out. This should be at 9-11% of the nominal phase-phase voltage. This test estab-
lishes the lower knee of the operating characteristic.
5. Increase voltage
V
ab
to 60% of the nominal phase-phase voltage. (The PICKUP indicator is off.) Increase
phase A current until the PICKUP indicator comes on. This should be at 59-61% of the full voltage mea-
sured pickup current.
6. Increase voltage V
ab
to 130% of nominal. (The PICKUP indicator is off.) Increase phase A current to 90%
of normal pickup, and hold this value. Slowly decrease
V
ab
until the PICKUP indicator just comes on. This
should be at 89-91% of nominal
V
ab
. This establishes the upper knee of the characteristic, and shows the
pickup is not altered above 90% voltage. Reduce current and voltages to 0.
7. Repeat steps 4 through 6 for current injected in phase B and controlling voltage
V
cb
.
8. Repeat steps 4 through 6 for current injected in phase C and controlling voltage
V
ca
.
Trip Timing with Voltage Restraint:
The timing characteristics under voltage restraint can be checked by setting the input voltage to a given level,
establishing a new pickup current, and then following the procedure outlined earlier under Trip Timing.
17.7.4 PHASE TIME OVERCURRENT 2
The procedure to test this element is identical to that for Phase Time O/C 1, with the following exception.
Blocking From Logic Inputs:
1. Inject current to cause a pickup.
2. Assert a logic input to provide a "Block Phase Time 2". The PICKUP indicator should immediately go out.
3. Repeat steps 1 and 2 for logic inputs "Block Phase O/C", "Block All O/C" and “Block 1 TRIP Relay” as
required.

GE 750 Specifications

General

Brand	GE
Model	750
Category	Relays
Language	English