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Breaker Failure Testing

 
PREPARATION
Before testing, check the settings of your relay and the connections from your test set. 

STEP 1: Fault


The relay senses the fault after about one cycle and triggers the output contact to trip.

 

 

 

 

 

 

 

 

 

 

 

STEP 2: Trip Contact



The trip contact receives the command to trip but does not trip. The relay closes the contact to signal a breaker trip. This usually takes about 1ms.

STEP 3: Maximum Circuit Breaker Clearing Time



During this time, the circuit breaker will either clear the fault or not. If it does not, the relay should be running a timer for Breaker Failure Time Delay. If the breaker closes properly, it will usually take between 2-3 cycles to clear the fault depending on the type of breaker.

STEP 4: Verify Fault Clearance



After the breaker clears the fault it will take the relay about 1 cycle to recognize that the fault is cleared on its 52a contact.

STEP 5: Security Margin



This is the wait time needed to confirm that the breaker has tripped. If the breaker is still open after the security margin, you are in breaker failure. The relay should send out a Direct Transfer Trip (DTT) or another relay’s timer should run out and send a trip to its respective breaker.

 

 

 

 

 

 

 

 

 

 

 

STEP 6: Distributed Breaker Failure Trip



During this step, the relay will either send out a trip to the next breaker upstream, or the timer in the breaker upstream will run out and send out a trip on its own. If the relays are set up for a distributed breaker failure trip, the remote relay receiving the DTT signal will trip as soon as it sees the signal, assuming that the local relay is still seeing the fault. 

 

 

 

 

 

 

 

 

 

 

 

 

STEP 7: Maximum Circuit Breaker Clearing Time

During this time, the circuit breaker will either clear the fault or not. If it does not, the relay should be running a timer for Breaker Failure Time Delay. If the breaker closes properly, it will usually take between 2-3 cycles to clear the fault depending on the type of breaker.

After this step, the fault is cleared.

 

Megger test sets related to this application note:
SMRT36
SMRT410
MPRT8445

 

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