RFL Electronics RFL 9300 - Figure 3-27. Possible Miscoordination of Loss-Of-Load Plus Zone 2 Timer

It has been suggested that 3I
0
operation plus a Zone 2 timer would be a simple way to detect an open conduc-
tor. This would result in a problem coordinating the 3I
0
and the timer with all external ground faults that may not
be cleared before the Zone 2 timer times out. On the other hand, loss-of-load plus a Zone 2 timer is not operated
by external ground faults. The only possible miscoordination occurs for an open-conductor condition on an adja-
cent line where the following conditions are present:
1. There are no other lines connected at the remote bus.
2. There is no SLG fault on either side of the open conductor on the adjacent line. (If there is an SLG fault,
it is assumed that the adjacent line will be cleared before the Zone 2 timer times out.)
The conditions that can result in miscoordination of loss-of-load plus the Zone 2 timer are illustrated in Figure 3-
27. If this condition is a concern, loss-of-load plus Zone 2 timer should be used to alarm, not to trip.
Figure 3-27. Possible miscoordination of loss-of-load plus Zone 2 timer
RFL 9300 RFL Electronics Inc.
August 25, 2000 3 - 30 (973) 334-3100