7SR11 & 7SR12 Description Of Operation
©2012 Siemens Protection Devices Limited Chapter 1 Page 64 of 76
Section 5: Supervision Functions
5.1 Circuit Breaker Failure (50BF)
The circuit breaker fail function has two time delayed outputs that can be used for combinations of re-tripping or
back-tripping. CB Fail outputs are given after elapse of the 50BF-1 Delay or 50BF-2 Delay settings. The two
timers run concurrently.
The circuit breaker fail protection time delays are initiated either from:
An output Trip Contact of the relay (MENU: OUTPUT CONFIG\TRIP CONFIG\Trip Contacts), or
A binary or virtual input assigned to 50BF Ext Trig (MENU: INPUT CONFIG\INPUT MATRIX\50BF Ext
Trig).
A binary or virtual input assigned to 50BF Mech Trip (MENU: INPUT CONFIG\INPUT MATRIX\ 50BF
Mech Trip).
CB Fail outputs will be issued providing any of the 3 phase currents are above the 50BF Setting or the current in
the fourth CT is above 50BF-I4 for longer than the 50BF-n Delay setting, or for a mechanical protection trip the
circuit breaker is still closed when the 50BF-n Delay setting has expired – indicating that the fault has not been
cleared.
Both 50BF-1 and 50BF-2 can be mapped to any output contact or LED.
An output is also given to indicate the faulted phase, 50BF PhA , 50BF PhB, 50BF PhC and 50BF EF
If the CB Faulty input (MENU: INPUT CONFIG\INPUT MATRIX\CB Faulty) is energised when a CB trip is given
the time delays 50BF-n Delay will be by-passed and the output given immediately.
Operation of the CB Fail elements can be inhibited from:
Inhibit 50BF A binary or virtual input.
Figure 4-5 Logic Diagram: Circuit Breaker Fail Protection (50BF)
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