ABB REX 521 Technical Reference Manual, Standard Configurations page 60

REX 521 Protection Relay 1MRS 751802-MUM
Technical Reference Manual, Standard Configurations
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Trip signal
S
1
Q
Lockout
R
Lockout reset
Lockout
(Normally closed)
Close command
Lockout2
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Note that when the lockout function is in use and an auxiliary power failure occurs,
the output relays return to off-state. The same happens in a situation where external
1 1
lockout is used with the output relays PO1, PO2, PO3, SO1 and SO2 and the
auxiliary power failure occurs. When the protection relay has been powered up
again, the output relay states are restored to the state before the power failure and the
output relay used for the lockout function is energized. If the lockout function is used
with the HSPO1 relay, the control of the breaker could be possible when the
auxiliary power of the protection relay is not connected.
To ensure maximum safety when using the lockout function, it is recommended to
use a battery unit as an auxiliary power. Then the fault in the protected object does
not effect the auxiliary supply of the protection relay and the state of the lockout
function is certainly stored in the protection relay's memory.
1
change-over contact
60