GE 750 Instruction Manual page 228

750/760
Feeder Management Relay
5–132
A typical autoreclose scheme as implemented in the 760 would respond to faults as
follows:
1. With the breaker closed and protection enabled, a transient fault produces a
current above the pickup of both Instantaneous Overcurrent 1 (lo-set) and Time
Overcurrent 1 elements.
2. The Time Overcurrent element begins to time, and the Instantaneous Overcur-
rent element operates, signaling the breaker to trip and initiate a reclosure.
3. The breaker trips and signals the autoreclose scheme that it is now open. The
Instantaneous Overcurrent 1 and Time Overcurrent 1 elements automatically
reset because the breaker is open.
4. If all requirements of the autoreclose scheme are fulfilled, autoreclose signals
the breaker to close and advances the shot counter. Shot 1 setpoints block the
Instantaneous Overcurrent element from further operation.
5. The breaker closes resulting in an inrush current of the feeder loads.
6. If the fault was transient, the current reduces to the load level before a trip
occurs. The autoreclose scheme eventually resets and the cycle begins again at
Step 1.
7. If the fault is permanent, a current above the pickup of both the Instantaneous
Overcurrent 1 and the Time Overcurrent 1 elements is produced. However, the
Instantaneous Overcurrent 1 element is blocked from operating.
8. While the Time Overcurrent 1 element is timing, any protection devices
between this relay and the fault location are provided an opportunity to isolate
the fault.
9. If no protection downstream from the relay clears the fault, the Time Overcur-
rent 1 element will time-out, signaling the breaker to trip and initiate the
autoreclose scheme again.
10. If the shot counter has not reached its maximum allowed value then the cycle
begins at step 6 using protection setpoints for the current shot.
11. If the shot counter has reached its maximum then the scheme goes to lockout.
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