Functions
2.22 Circuit Breaker Failure Protection
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
407
Figure 2-196
End fault between circuit breaker and current transformers
The end fault protection has the task to recognize this status and to transmit a trip signal to the remote end of
the line. For this purpose, the command
„BF EndFlt TRIP“
(No. 1495) is available to trigger the intertrip
input of the differential protection — if applicable, together with other commands that need to be transferred.
This can be achieved by external wiring or via CFC.
The end fault is recognized when the current continues flowing although the circuit breaker auxiliary contacts
indicate that the circuit breaker is open. An additional criterion is the presence of any circuit breaker failure pro-
tection initiate signal. Figure 2-197 illustrates the functional principle. If the circuit breaker failure protection is
initiated and current flow is detected (current criteria „L*> current criterion“ according to Figure 2-185), but no
circuit breaker pole is closed (auxiliary contact criterion „ any pole closed“), then the timer
T-EndFault
is start-
ed. At the end of this time an intertrip signal is transmitted to the opposite end(s) of the protected object.
Figure 2-197
Functional scheme of the end fault protection
Pole discrepancy supervision
The pole discrepancy supervision has the task to detect discrepancies in the position of the three circuit breaker
poles. Under steady-state operating conditions, either all three poles of the circuit breaker must be closed, or
all three poles must be open. Discrepancy is permitted only for a short time interval during a 1-pole automatic
reclose cycle.
The scheme functionality is shown in Figure 2-198. The signals which are processed here are the same as
those used for the circuit breaker failure protection. The pole discrepancy condition is established when at least
one pole is closed („
≥
one pole closed“) and at the same time not all three poles are closed („
≥
one pole open“).
Additionally, the current criteria (from Figure 2-185) are processed. Pole discrepancy can only be detected
when current is not flowing through all three poles, i.e. through only one or two poles. When current is flowing
through all three poles, all three poles must be closed even if the circuit breaker auxiliary contacts indicate a
different status.
If pole discrepancy is detected, this is indicated by a fault detection signal. This signal identifies the pole which
was open before the trip command of the pole discrepancy supervision occurred.