ABB REX 521 Technical Reference Manual, Standard Configurations page 159

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Protection Relay
Technical Reference Manual, Standard Configurations
TRIP circuit breaker
CLOSE circuit breaker
Blocking signal to incoming
feeder (START 3I>>)
Circuit-breaker failure
protection
Definite trip alarm
Internal relay fault
Control signal for selecting
the basic angle of Io>-->
(BACTRL)
External reclosure
initialization signal
REX 521
159