Siemens SIPROTEC 7SD610 Manual page 192

Functions
2.13 Circuit Breaker Failure Protection
Figure 2-81
Circuit breaker not operational
These delays are not necessary if the control circuit of the local circuit breaker is faulted (e.g. control voltage
failure or air pressure failure) since it is apparent that the circuit breaker is not capable of clearning the fault. If
the relay is informed about this disturbance (via the binary input „>CB faulty"), the adjacent circuit breakers
(busbar and remote end if applicable) are tripped after the time T3-BkrDefective (address 3907) which is
usually set to 0.
Address 3908 Trip BkrDefect. determines to which output the trip command is routed in the event that the
circuit breaker is not operational when a feeder protection trip occurs. Select that output which is used to trip
the adjacent circuit breakers (bus-bar trip).
End fault protection
The end fault protection can be switched separately ON or OFF in address 3921 End Flt. stage. An end
fault is a short-circuit between the circuit breaker and the current transformer set of the feeder. The end fault
protection presumes that the device is informed about the circuit breaker position via circuit breaker auxiliary
contacts connected to binary inputs.
If, during an end fault, the circuit breaker is tripped by a reverse stage of the feeder protection or by the busbar
protection (the fault is a busbar fault as determined from the location of the current transformers), the fault
current will continue to flow, because the fault is fed from the remote end of the feeder circuit.
The time T-EndFault (address 3922) is started when, during the time of pickup condition of the feeder pro-
tection, the circuit breaker auxiliary contacts indicate open poles and, at the same time, current flow is still de-
tected (address 3902). The trip command of the end fault protection is intended for the transmission of an in-
tertrip signal to the remote end circuit breaker.
Thus, the delay time must be set so that it can bridge out short transient apparent end fault conditions which
may occur during switching of the circuit breaker.
Pole discrepancy supervision
In address 3931 PoleDiscrepancy (pole discrepancy protection), the pole discrepancy supervision can be
switched separately ON or OFF. It is only useful if the circuit breaker poles can be operated individually. It avoids
that only one or two poles of the local circuit breaker are open continuously. It has to be provided that either the
auxiliary contacts of each pole or the series connection of the NO auxiliary contacts and the series connection
of the NC auxiliary contacts are connected to the device's binary inputs. If these conditions are not fulfilled,
switch address 3931 OFF.
192
Time sequence example for normal clearance of a fault, and with circuit breaker failure, using
single-stage breaker failure protection
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011