ABB RELION 620 Series Technical Manual page 543

1MAC504801-IB E
5.2.5
620 series ANSI
Technical Manual
BLOCK
CB_FAULT_AL
From Timer 3
Enable timer
From Start logic
Timer 2 elapsed
From Timer 2
51P
From level detector 1
CB failure trip mode
"2 out of 4"
51N/G
From level detector 2
CB failure trip mode
"1 out of 3"
CB failure trip mode
"1 out of 4"
CB failure mode "Current"
CB failure mode "Both"
POSCLOSE
CB failure mode "Breaker
status"
CB failure mode "Both"
GUID-30BB8C04-689A-4FA5-85C4-1DF5E3ECE179-ANSI V1 EN
Figure 257: Backup trip logic
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).
50BF 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.
Protection-related functions
AND
OR
AND
AND
AND
OR
AND
OR
OR
Section 5
TRBU
AND
AND
OR
AND
OR
AND
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