POSCLOSE
Enable timer
From Start logic
CB failure mode ”Current”
CB failure mode ”Breaker
status”
CB failure mode ”Both(OR)”
AND
CB failure trip mode
”1 out of 3"
CB failure trip mode
”1 out of 4"
AND
AND
AND
CB failure trip mode
”2 out of 4"
OR
OR
AND
I >
From level detector 1
TRBU
I
0
>
From level detector 2
AND
OR
OR
OR
OR
CB failure mode ”Both(OR)”
AND
AND
BLOCK
Timer 2 elapsed
From Timer 2
CB_FAULT_AL
From Timer 3
AND
1, 2 or 3 ph
2 or 3 ph
OR
AND
CB failure mode ”Both(AND)”
Figure 664: Backup trip logic
5.2.6
Application
The n-1 criterion is often used in the design of a fault clearance system. This means
that the fault is cleared even if some component in the fault clearance system is
faulty. A circuit breaker is a necessary component in the fault clearance system. For
practical and economical reasons, it is not feasible to duplicate the circuit breaker
for the protected component, but breaker failure protection is used instead.
The breaker failure function issues a backup trip command to up-stream circuit
breakers in case the original circuit breaker fails to trip for the protected
component. The detection of a failure to break the current through the breaker
is made by measuring the current or by detecting the remaining trip signal
(unconditional).
CCBRBRF can also retrip. This means that a second trip signal is sent to the
protected circuit breaker. The retrip function is used to increase the operational
reliability of the breaker. The function can also be used to avoid backup tripping
of several breakers in case mistakes occur during protection relay maintenance and
tests.
1MRS759142 F
Protection related functions
REX640
Technical Manual
1171