Siemens siprotec 7SD5 User Manual page 362

2 Functions
is used to initiate the breaker failure protection. In this case the start signal is main-
tained until the circuit breaker is reported to be open by the auxiliary contact criterion.
Initiation can be blocked via the binary input „>BLOCK BkrFail" (e.g. during test of
the feeder protection relay).
Figure 2-148 Breaker failure protection with common phase initiation
Phase Segregated Phase segregated initiation of the breaker failure protection is necessary if the circuit
Initiation breaker poles can be operated individually, e.g. if single-pole automatic reclosure is
used. This is possible if the device is able to trip single-pole.
If the breaker failure protection is intended to be initiated by further external protection
devices, it is recommended, for security reasons, to connect two binary inputs to the
device. Besides the three trip commands of the external relay to the binary input „>BF
Start L1", „>BF Start L2" and „>BF Start L3" it is recommended to connect
also, for example, the general device pickup to binary input „>BF release". Figure
2-149 shows this connection.
Nevertheless, it is possible to initiate the breaker failure protection in single-channel
mode should a separate release criterion not be available. The binary input „>BF
release" must then not be assigned to any physical input of the device during con-
figuration.
If the external protection device does not provide a general fault detection signal, a
general trip signal can be used instead. Alternatively, the parallel connection of a sep-
arate set of trip contacts can produce such a release signal as shown in Figure 2-150.
The starting condition logic for the delay times is shown in Figure 2-151. In principle,
it is designed similar to that for the common phase initiation, but individually for each
of the three phases. Thus, current flow and initiation conditions are processed for each
phase. In case of single-pole interruption before an automatic reclose cycle, current
disappearance is reliably monitored for the tripped breaker pole only.
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7SD5 Manual
C53000-G1176-C169-1