(1) Description of Operation 7SR224
Page 52 of 66 ©2009 Siemens Protection Devices Limited
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 circuit breaker fail protection time delays are initiated either from:
An output Trip Contact of the relay (MENU: OUTPUT CONFIG\BINARY OUTPUT
CONFIG\Trip Contacts), or
A binary input configured 50BF Ext Trip (MENU: INPUT CONFIG\BINARY INPUT
MATRIX\50BF Ext Trip).
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.
If the 50BF CB Faulty input (MENU: INPUT CONFIG\INPUT MATRIX\50BF 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 5.1-1 Logic Diagram: Circuit Breaker Fail Protection (50BF)
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