50BF - Breaker Failure Protection

Summary

The detection of a failure to break the current through the breaker is made by measuring the current, circuit breaker (CB) State and by detecting a trip signal from a primary protection scheme. In case of original breaker trip failure, 50BF protection failure protection first sends a re-trip signal to the original breaker. If the original breaker does not trip for the protected component, 50BF protection issues a back-up trip command to adjacent circuit breaker.

Icons and diagrams

Model overview

The breaker failure function issues a back-up trip command to adjacent circuit breakers in case the original circuit breaker fails to trip for the protected component. The detection of a failure to break the current through the breaker is made by measuring the current, CB State and by detecting a trip signal from a primary protection scheme. 50BF can also re-trip. This means that a second trip signal is sent to the protected circuit breaker. The function can also be used to avoid back-up tripping of several breakers in case mistakes occur during relay maintenance and tests. The re-trip and backup trip timer is initiated with an input Breaker Failure Initiate which is connected with the trip signal of the primary protection scheme of the breaker. The input reset can reset both Re-Trip and BF-Trip output.

Parameters

The below figure shows the control panel of the 50BF relay model.

The following parameters are tunable:

Parameter tab of 50BF Relay

Name	Unit	Description	Sample values
Pick up current	pu or A	Breaker failure current pickup threshold. The units should be the same as that for the input signal.	5.0
Re-trip time	sec	Breaker Failure Re-trip Time Pickup	1.0
Breaker failure trip time	sec	Breaker Failure Trip Time Pickup	2.0

Input and output signals
The module has 4 inputs and 3 outputs:

50BF Relay I/O

Name	Type (unit)	Description
Iabc	pu or A	A 3-dimension per-unit/actual value of true RMS for three-phase currents, in the order of Ia, Ib and Ic.
CB_status	-	A 3-dimension status of Circuit breaker, in the order of State_A, State_B and State_C.
BFI	-	Breaker Failure Initiate
Reset	-	The reset signal for the relay. The relay will be reset when this signal becomes 1.
Re-Trip	-	Re-Trip
BF-Trip	-	Circuit Breaker failure trip
m	-	Phase A, B and C failure detection