Protection Schemes - GE 750 Instruction Manual

CHAPTER 7: COMMISSIONING
7.4.1 Setpoint
Groups
7.4.2 Phase
Overcurrent
Note
NOTE
750 FEEDER MANAGEMENT RELAY – INSTRUCTION MANUAL
7.4

Protection Schemes

The Active setpoint group is indicated by a continuously illuminated LED, and the Edit
group by an intermittently illuminated LED on the relay faceplate. When changing settings
for testing be careful to check the correct group is adjusted and selected as the active
group.
Verify that settings in a particular setpoint group are being used by the protection
elements when the particular group is selected to be active. There are three alternative
strategies that can be used to provide this verification:
• Test any one protection element that has different settings in different groups
• Test a random selection of protection elements in different groups
• Test all protection elements that are not disabled in every group
Once one of the above strategies is selected, the following procedures are used to test
protection elements.
Phase TOC 1
For these tests, refer to the figures on section 7.1.6 for test connections.
The following procedures, other than the check for Linear Reset Timing, are based on the
"Instantaneous" reset time characteristic. If the "Linear" reset time characteristic is
required, ensure that there is sufficient time between test current injections, or cycle relay
power OFF and ON to discharge the energy measurement accumulator to 0.
The following procedure checks Pickup with one phase for operation:
 Inject current at a level below the pickup level into Phase A.
 Slowly increase the current until the Pickup LED comes on.
Note the pickup value.
 Slowly reduce the current until the Pickup LED goes out.
Note the dropout level, which should be 2% of CT less than pickup
when pickup
 Repeat last 3 steps for Phases B and C.
The following procedure checks indications and operations caused by a Trip function, with
front panel key resetting:
RESET
 Inject current to cause a pickup and wait until the element times to Trip.
 Check that the Trip and Message LEDs are flashing, the Last Trip
message is displayed, and the Output Relay 1 and any others
programmed to operate (as well as their associated LED indicators)
operate.
 Slowly reduce the current until the Pickup LED goes out.
Check that the Trip and Message LEDs are flashing, and that the Output
Relay 1 and any others programmed to operate (as well as their
associated LEDs) reset.
≤
CT or 97 to 98% of pickup when pickup
PROTECTION SCHEMES
>
CT.
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