GE 750, Инструкция по эксплуатации

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750/760 Feeder Management Relay GE Power Management
14.8 AUTORECLOSE (760 ONLY) 14 S7 CONTROL
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14.8.7 APPLICATION EXAMPLE
Utility statistics indicate that a large percentage of feeder faults (about 80%) are of a transient nature. Typically,
once the feeder is tripped an autorecloser automatically recloses the feeder breaker after a short time delay. If
the fault was transient, the entire feeder is returned to normal service and customers experience a very short
disturbance. If the fault is permanent and on the load side of another protection point, the reclosure scheme
delays another trip of the breaker until this other device clears the fault so that service is disrupted only for
loads beyond this other protection point.
A common phase protection scheme uses instantaneous elements in conjunction with automatic reclosing.
The design goal is to select settings that will detect faults out to the most distant (in impedance terms) point of
the feeder and provide fast operation. Typically ‘loset’ overcurrent elements are programmed to be blocked
after the first reclosure. This gives downstream devices, such as fuses, time to interrupt a permanent fault,
especially on a feeder tap. Loset elements would then be re-enabled after the scheme is reset. ‘Hiset’ ele-
ments may also be blocked on a subsequent shot with a faster time overcurrent curve selected to allow the
fault to burn off. In this case a permanent fault would then cause a time overcurrent trip.
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 OC 1(loset) and Time OC 1 elements.
2. The Time OC element begins to time, and the Instantaneous OC 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 OC 1 and
Time OC 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 settings block the Instantaneous OC 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 OC 1 and the Time OC 1
elements is produced. However, the Instantaneous OC 1 element is blocked from operating.
8. While the Time OC 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 OC 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 pro-
tection settings for the current shot.
11. If the shot counter has reached its maximum then the scheme goes to lockout.