ABB RELION REX640 Technical Manual page 1171

1MRS759142 F
CB_FAULT_AL
Enable timer
From Start logic
Timer 2 elapsed
From level detector 1
From level detector 2
POSCLOSE
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.
REX640
Technical Manual
BLOCK
From Timer 3
From Timer 2
2 or 3 ph
I >
1, 2 or 3 ph
I >
0
CB failure mode "Current"
CB failure mode "Both(OR)"
CB failure mode "Both(AND)"
CB failure mode "Breaker
status"
CB failure mode "Both(OR)"
AND
OR
AND
CB failure trip mode
"2 out of 4"
CB failure trip mode
"1 out of 3"
OR
CB failure trip mode
"1 out of 4"
Protection related functions
OR
AND
AND
AND
AND OR
AND
AND
OR
AND OR
AND
OR
TRBU
1171