Breaker Failure Protection - Toshiba GRL100-701B Instruction Manual

2.11 Breaker Failure Protection

When a fault remains uncleared due to a breaker failure, the breaker failure protection (BFP)
clears the fault by backtripping the adjacent breakers.
If the current continues to flow following the output of a trip command, the BFP judges it as a
breaker failure. The existence of the current is detected by an overcurrent element provided for
each phase. For high-speed operation of the BFP, a high-speed reset overcurrent element is used.
In order to prevent the BFP from starting by accident during maintenance work and testing and
thus tripping the adjacent breakers, the BFP has the function of retripping the original breaker.
To confirm that the breaker has failed, a trip command is issued to the original breaker again
before tripping the adjacent breakers to prevent unnecessary tripping of the adjacent breakers in
case of erroneous initiation of the BFP. It is possible to choose not to use retripping at all, or to
use retripping with a backtrip command plus delayed pick-up timer, or retripping with a backtrip
command plus overcurrent detection plus delayed pick-up timer.
Tripping by the BFP is three-phase final tripping and autoreclose is blocked.
An overcurrent element and on-delay timer are provided for each phase and they also operate
correctly on the breaker failure in the event of an evolving fault.
Scheme logic
The BFP is performed on an individual phase basis. Figure 2.11.1 shows the scheme logic for
one phase. The BFP is initiated by a trip signal EXT_CBFIN from the external line protection or
an internal trip signal TRIP. Starting with an external trip signal can be disabled by the scheme
switch [BFEXT]. These trip signals must be present exist as long as the fault persists.
54
A
55
OCBF
B
56
C
TRIP-A0
TRIP-B0
TRIP-C0
EXT_CBFIN-A
1556
&
EXT_CBFIN-B
1557
&
EXT_CBFIN-C
1558
&
[BFEXT]
+
"ON"
1
1588 CBF_BLOCK
The backtrip signal to the adjacent breakers CBF-TRIP is output if the overcurrent element
OCBF operates continuously for the setting time of the delayed pick-up timer TBF2 after the
&
&
&
[BF2]
+
"ON"
&
&
&
≥1
≥1
≥1
[BF1]
"TOC"
"T"
+
Figure 2.11.1 BFP Scheme Logic
 104 
TBF2
t 0
&
≥ 1
t 0
&
t 0
&
50 – 500ms
TBF1
t 0
≥1
&
t 0
≥1
&
t 0
≥1
&
t 0
&
t 0
&
t 0
&
50 – 500ms
6 F 2 S 0 8 5 0
92
CBF-TRIP
88
RETRIP-A
89
RETRIP-B
90
RETRIP-C
91
≥ 1
CBFDET