Siemens siprotec 7SA522 User Manual page 357

End fault protection
7SA522 Manual
C53000-G1176-C119-2
To realise this intertrip, the desired command — usually the trip command which is in-
tended to trip the adjacent breakers — is assigned to a binary output of the device.
The contact of this output triggers the transmission device.
An end fault is defined here as a short–circuit which has occurred at the end of a line
or protected object, between the circuit breaker and the current transformer set.
This situation is shown in Figure 6-109. The fault is located — as seen from the current
transformers (= measurement location) — on the bus-bar side, thus, it will not be re-
garded by the feeder protection relay as a feeder fault. It can only be detected by either
a reverse stage of the feeder protection or by a bus-bar protection. Nevertheless, a
trip command given to the feeder circuit breaker cannot clear the fault since the oppo-
site end(s) continue(s) to feed the fault. Thus, the fault current does not stop flowing
even though the feeder circuit breaker has properly responded to the trip command.
Feeder
Figure 6-109 End fault between circuit breaker and current transformers
The end fault protection has the task to recognize this situation and to transmit a trip
signal to the remote end(s) of the protected object to clear the fault. For this purpose,
the output command "%) (QG)OW 75,3" is available to trigger a signal transmission
device (e.g. power line carrier, radio wave, or optical fibre) — if applicable, together
with other commands that need to be transfered.
The end fault is recognized when the current continues flowing although the circuit
breaker auxiliary contacts indicate that the breaker is open. In the 7SA522, an addi-
tional criterion is the presence of any breaker failure protection initiate signal. The
scheme functionality is shown in Figure 6-110. If the breaker failure protection is initi-
ated and current flow is recognized (current criteria "L
no circuit breaker pole is closed (auxiliary contact criterion "any pole closed"), then a
timer 7(QG)DXOW is started, after which an intertrip signal is transmitted to the oppo-
site end(s) of the protected object.
Bus-bar
Trip by
protection
I
SC
Functions
∗
>" according Figure 6-99), but
6-209