Siemens SIPROTEC 7SS523 V3.2 Manual page 152

Functions
Delayed
recognition
5.4.2.3 CLOSE Command of the Bus Coupler Circuit Breaker
136
Figure 5-33 Bus coupler with 2 CTs (overlapping measurement)
In this case, bus zone BZB is correctly tripped and bus zone BZA remains in service.
When after a bus fault the circuit breaker reaches its final position and the secondary
CT currents decay, the breaker failure protection may be undercut. To avoid this, the
coupler currents are only processed after the delay time set with the parameter T-CB
open (XX26/CU) has elapsed.
If the bus coupler circuit breaker is open, the current of the coupler bay is set to zero
for the protection of bus zones BZA and BZB (Bild 5-34, page 136).
If the bus coupler circuit breaker is closed onto a short-circuit in bus zone BZB, the
protection trip may be faster than the circuit breaker status processing. This may
cause spurious tripping of the healthy bus zone BZA. To avoid this, a leading contact
for closing the circuit breaker integrates the current of the coupler current transformer
into the protection algorithm.
The circuit breaker position must be detected by the binary input ">CB man.close"
(FNo. 7618/BU).
As soon as an active signal is detected at the binary input, a time delay of 200 ms is
started. After the expiration of this time delay, the auxiliary contact of the circuit break-
er must no longer be in the OPEN position.
The leading recognition of the coupler CT current has to be ensured for all possible
applications of the CLOSE command. Possible applications may include:
• Manual closing control by control-discrepancy switch
• Possibly remote control of the bus coupler circuit breaker by telecontrol or substa-
tion control systems
• Reclosing by an automatic reclosing device
Bild 5-34 Switching onto an earthed busbar
7SS52 V4 Manual
C53000-G1176-C182-1