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Function:
1 Application
This function issues a back-up trip adjacent circuit breakers in case of a
tripping failure of the circuit breaker (CB), and clears the fault as
requested by the object protection.
The breaker-failure function is started by a protection trip command, from
the line and busbar protection through the breaker-related trip relays. The
start can be single-phase or three-phase. Correct fault current clearing or
failure is detected by a current check in each phase. The current level can
be set at 0,1 to 2 times the rated current.
One can either choose to refrain from a retrip of the breaker, use it as an
unconditional retrip, or as a retrip with a current check. A short delay, 0-
150 ms, can be set for the retrip.
The use of retrip limits the impact on the power system if the breaker-fail-
ure protection function (BFP) is started by mistake during testing or other
maintenance work.
A second time step is used for the back-up trip command. It should be
connected to trip the adjacent breakers, to clear the busbar section and
intertrip the opposite side of the object, if so required. The time setting
range is 50-400 ms.
By using separate timers for each phase, correct timing at evolving faults
is ensured.
The timer setting should be selected with a certain margin to allow for
variation in the normal fault clearing time. The properties of the BFP
function allow the use of a small margin.
Fig. 1 Start and trip functions
(X80171-1)
1
V
TTRIP
STARTL1
BUTL1
RTL1
L1
RETRIPL1
1
V
TTRIP
STARTL2
BUTL2
RTL2
RETRIPL2
1
V
TTRIP
STARTL3
BUTL3
RTL3
RETRIPL3
IL1
StartL1
IL2
StartL2
StartL3
IL3
Start3ph
L2
L3
1
V
TTRIP
BACK-UP
TRIP
5
Breaker-failure protection
1MRK 580 171-XEN
Version 1.0-00
October 1996
Optional
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