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Protection Riddle No.118 - Nuisance tripping
We have 11kv bus for distribution of power. Our breaker no.1 tripped on sensitive earth fault with a fault current of 240amps in CBCT. But with the problem is that our breaker no.2 also tripped along with it withut any fault in it. It happened several times. Current sensed by breaker no.2 was twice of PSM. DMT was assigned to it.

240amps in breaker no. 1 = 48times of PSM with DMT(Definite Minimum time)

Please suggest any solution and reason as to why this tripping happened.
Author : Indrajeet
Sat, September 26th, 2015 - 13:31
We need to know more detail of your concern protection scheme and related single line diagram. However some technical reason such as load side earthing connection and incorrect cable shield earthing connections as illustrated below could be reason of neighbor nuisance tripping of earth fault protection.

Author : Hamid - From: Iran
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