Circuit Breaker Failure Protection; Function Description - Siemens SIPROTEC 7SD610 Manual

Functions

2.13 Circuit Breaker Failure Protection

2.13 Circuit Breaker Failure Protection
The circuit breaker failure protection provides rapid back-up fault clearance in the event that the circuit breaker
fails to respond to a trip command from a protection function of the local circuit breaker.
2.13.1

Function Description

General
Whenever e.g. a short-circuit protection relay of a feeder issues a trip command to the circuit breaker, this is
repeated to the circuit breaker failure protection (Figure 2-64). A timer T–BF in the circuit breaker failure pro-
tection is started. The timer runs as long as a trip command is present and current continues to flow through
the circuit breaker poles.
Figure 2-64
Normally, the circuit breaker will open and interrupt the fault current. The current monitoring stage quickly resets
(typical 10 ms) and stops the timer T–BF.
If the trip command is not carried out (circuit breaker failure case), current continues to flow and the timer runs
to its set limit. The circuit breaker failure protection then issues a command to trip the backup circuit breakers
and interrupt the fault current.
The reset time of the feeder protection is not relevant because the circuit breaker failure protection itself rec-
ognizes the interruption of the current.
For protection functions where the tripping criterion is not dependent on current (e.g. Buchholz protection),
current flow is not a reliable criterion for proper operation of the circuit breaker. In such cases, the circuit breaker
position can be derived from the auxiliary contacts of the circuit breaker. Therefore, instead of monitoring the
current, the position of the auxiliary contacts is monitored (see Figure 2-65). For this purpose, the outputs from
the auxiliary contacts must be fed to binary inputs on the relay (refer also to Section 2.16.1).
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Simplified function diagram of circuit breaker failure protection with current flow monitoring
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011