ABB REX 521 Technical Reference Manual, Standard Configurations page 151

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Protection Relay
Technical Reference Manual, Standard Configurations
TRIP circuit breaker
CLOSE circuit breaker
Uo>> TRIP to the outgoing
feeders
Circuit-breaker failure
protection
Uo>> Start to release blocking
of outgoing feeders
OC blocking signal to
the HV relay (3I>> START)
Internal relay fault
OC blocking signal
from the outgoing feeders
to the 3I>>> stage
Second settings
REX 521
151