what is the difference between the 94 lockout relay and 86
lock out relay. I have noticed that the 94 lockout relay is
activated when the distance realy is activated and 86 is
activated when the 87T differential is activated. but why
can't the same lockouts be used for both the protection
schemes
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Answer Posted / ayman elwardani
86 Lockout relays are used by many utilities in electrical
power transmission substations to trip and hold out of
equipment service within a protected zone on the occurrence
of protection relay operation which requires inspection
and/or repair before the zone may be safely placed back in
service. The original intent of lockout was that on
operation, maintenance or operating personnel would inspect
and repair as required the locked-out zone, and when clear,
would reset the lockout allowing operators to place the
element back in service. However in recent decades, it has
become normal to remotely control substations, resulting in
the absence of on-site personnel to reset a lockout in an
emergency situation
On the other hand, 94 inter-trip relay is used for up or
down stream backup protection to prevent the other side
breaker from supplying the faulty zone. The inter-trip
signal shall be cleared as the fault cleared and associated
relay has been reset.
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