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1MRS 755310
Feeder Protection Relay
Technical Reference Manual
reclosing can be inhibited via a digital input (CB Close Inhibit). Inhibition of
reclosing is checked only when necessary and can therefore not be used to prevent
initiation or progression of a shot.
For co-ordination of the other protection devices in the network, such as
down-stream fuses, the AR function supports optional blocking of selectable
overcurrent and earth-fault protection stages (refer to section Blocking of protection
stages). By setting a stage with a short operate time to trip and initiate only the first
auto-reclose shot, fast tripping and shot initiation will be achieved. After this, the
stage will be blocked to allow selective delayed tripping of another stage in
accordance with the time-grading plan of the system.
The typical auto-reclose sequence is as follows: the overcurrent or earth-fault
protection detects a network fault, trips the circuit breaker and initiates the first
auto-reclose shot. At the time of shot initiation, the set dead time for shot 1 will start.
When the set dead time elapses, the blocking of selected protection stages will be
activated and the AR function will issue a reclosing command (Close CB
Command) to the circuit breaker, the duration of which is settable. In addition, the
set reclaim time and set cutout time will start when the set dead time elapses. The
blocking of protection stages will be reset on expiration of the cutout time. For the
cutout time, refer to section Fast tripping and initiation of shot 1 using two protection
stages.
If the network fault is cleared, i.e. the auto-reclosure is successful, the set reclaim
time will expire and the AR function will be automatically reset to the quiescent
condition.
However, if the network fault is not cleared, i.e. the auto-reclosure is unsuccessful,
and the protection trips the circuit breaker before expiration of the set reclaim time,
the next shot will be initiated (provided that a further auto-reclosure is allowed). At
the time of shot initiation, the set dead time for shot 2 will start. When the set dead
time elapses, the blocking of selected protection stages (may differ from shot 1) will
be activated and the AR function will issue a reclosing command to the circuit
breaker. In addition, the set reclaim time and set cutout time will start when the set
dead time elapses. The blocking of protection stages will be reset on expiration of
the set cutout time.
If the network fault is cleared, the AR function will be automatically reset after the
reclaim time. However, if the fault is not cleared and the protection trips the circuit
breaker before expiration of the reclaim time, the next shot will be initiated
(provided that a further auto-reclosure is allowed). At the time of shot initiation, the
set dead time for shot 3 will start. When the set dead time elapses, the blocking of
selected protection stages (the same as for shot 2) will be activated and the AR
function will issue a reclosing command to the circuit breaker. In addition, the set
reclaim time and set cutout time will start when the set dead time elapses. The
blocking of protection stages will be reset on expiration of the set cutout time.
If the network fault has still not been cleared, i.e. all selected auto-reclose shots have
been unsuccessful, and the protection trips the circuit breaker before expiration of
the set reclaim time, the AR function will generate a definite trip alarm. The circuit
breaker will now remain open and the AR function will be locked out.
REF 610
29
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