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Functions
2.22 Circuit Breaker Failure Protection
Figure 2-198
2.22.2
Setting Notes
General
The circuit breaker failure protection and its ancillary functions (end fault protection, pole discrepancy supervi-
sion) can only operate if they were set during configuration of the scope of functions (address 139 BREAKER
FAILURE, setting Enabled or enabled w/ 3I0>).
Circuit breaker failure protection
The circuit breaker failure protection is switched ON or OFF at address 3901 FCT BreakerFail.
The current threshold I> BF (address 3902) should be selected such that the protection will operate with the
smallest expected short-circuit current. A setting of 10 % below the minimum fault current for which circuit
breaker failure protection must operate is recommended. On the other hand, the value should not be set lower
than necessary.
If the circuit breaker failure protection is configured with zero sequence current threshold (address 139 =
enabled w/ 3I0>), the pickup threshold for the zero sequence current 3I0> BF (address 3912) can be set
independently of I> BF.
Normally, the circuit breaker failure protection evaluates the current flow criterion as well as the position of the
circuit breaker auxiliary contact(s). If the auxiliary contact(s) status is not available in the device, this criterion
cannot be processed. In this case, set address 3909 Chk BRK CONTACT to NO.
Two-stage circuit breaker failure protection
With two-stage operation, the trip command is repeated after a time delay T1 to the local feeder circuit breaker,
normally to a different set of trip coils of this circuit breaker. A choice can be made whether this trip repetition
shall be 1-pole or 3-pole if the initial feeder protection trip was 1-pole (provided that 1-pole trip is possible). This
choice is made in address 3903 1p-RETRIP (T1). Set this parameter to YES if the first stage is to trip 1-pole,
otherwise set it to NO.
If the circuit breaker does not respond to this trip repetition, the adjacent circuit breakers are tripped after T2,
i.e. the circuit breakers of the busbar or of the concerned busbar section and, if necessary, also the circuit
breaker at the remote end unless the fault has been cleared.
408
Function diagram of pole discrepancy supervision
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
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