7SR242 Duobias Description Of Operation
©2010 Siemens Protection Devices Limited Chapter 1 Page 44 of 52
Section 5: Supervision Functions
5.1 Circuit Breaker Failure (50BF)
Two CB Fail elements are provided – one element per winding.
Each 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-n-1 Delay or 50BF-n-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\BINARY OUTPUT CONFIG\CBn Trip
Contacts), or
A binary or virtual input assigned to 50BF-n Ext Trip (MENU: INPUT CONFIG\INPUT MATRIX\50BF Ext
Trip).
A binary or virtual input assigned to 50BF-n Mech Trip (MENU: INPUT CONFIG\INPUT MATRIX\ 50BF-
n Mech Trip).
CB Fail outputs will be issued providing any of the 3 phase currents are above the 50BF-n Setting or the current
in the fourth CT is above 50BF-n-I4 for longer than the 50BF-n-n Delay setting, or for a mechanical protection trip
the circuit breaker is still closed when the 50BF-n-n Delay setting has expired – indicating that the fault has not
been cleared.
Both 50BF-n-1 and 50BF-n-2 can be mapped to any output contact or LED.
If the 50BF-n CB Faulty input (MENU: INPUT CONFIG\INPUT MATRIX\CB Faulty) is energised when a CB trip
is given the time delays 50BF-n-n Delay will be by-passed and the output given immediately.
Operation of the CB Fail elements can be inhibited from:
Inhibit 50BF-n A binary or virtual input.
Figure 5-1 Logic Diagram: Circuit Breaker Fail Protection (50BF)
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