Siemens SIPROTEC 7SS523 V3.2 Manual page 139

Continuation for (3) and (4) see Figure 5-22, page 120
Continuation for (3) and (4) see Figure 5-22, page 120
Figure 5-24 Low-current mode
Pulse mode
The low-current mode BF I< (XX16/CU) ensures that circuit breaker failure protec-
tion is provided nevertheless. After a set time T-BF I< (XX22/CU) has elapsed, and
if the circuit breaker is closed, a busbar TRIP command for the affected bus zone is
issued.
If the feeder current exceeds this one with the parameter I> BF (XX18/CU) adjusted
limiting value, the low-current mode is blocked. Logic of the current release see Figure
5-21, page 119.
With the operating modes non existent and external, to be set with the param-
eter BF OP MODE (XX15/CU), this function has no influence. For more information on
the operating modes, please refer to the setting notes in Chapter 5.3.6, page 126.
As with other operating modes of the breaker failure protection, the tripping consists
of two stages, i.e. a first stage as "TRIP repetition" on the local breaker and a second
stage for the tripping of the busbar. The parameter T-TRIP repeat (XX25/CU),
which is also used for the current-controlled stages of the breaker failure protection, is
used in the central unit to delay the first stage.
The following figure shows the logic of the low-current operating mode of the breaker
failure protection:
In the operating mode "Pulse mode", the circuit breaker failure protection is initiated
by the opposite end of the line. It operates independently of the CBF function proper
if the binary input ">CBF puls" (FNo. 7614/BU) is allocated accordingly. The "pulse
mode" only operates with the following modes:
• TRIP repetition/Unbalancing
• TRIP repetition/I> query:
Circuit Breaker Failure Protection
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