Reclaim Time Setting Guidelines; Autoreclose Shot Counters - GE MiCOM P40 Technical Manual

Chapter 11 - Autoreclose
(a) + (e) - (d) = 50 ms + 280 ms - 85 ms = 245 ms, to allow de-ionising
In practice a few additional cycles would be added to allow for tolerances, so Dead Time 1 could be set to 300 ms
or greater. The overall system dead time is found by adding (d) to the chosen settings then subtracting (a). This
gives 335 ms.
A typical de-ionising time value for single-phase trip on a 220 kV line is 560 ms, so the 1 Pole Dead Time could be
chosen as 600 ms or greater. The overall system dead time is found by adding (d) to the chosen settings then
subtracting (a). This gives 635 ms.
6.3

RECLAIM TIME SETTING GUIDELINES

Several factors influence the choice of the reclaim timer, such as:
Fault incidence/Past experience: Small reclaim times may be required where there is a high incidence of
●
recurrent lightning strikes to prevent unnecessary lockout for transient faults.
Spring charging time: For high speed Autoreclose the reclaim time may be set longer than the spring
●
charging time. A minimum reclaim time of more than 5s may be needed to allow the circuit breaker time to
recover after a trip and close before it can perform another trip-close-trip cycle. This time will depend on the
duty (rating) of the circuit breaker. For delayed Autoreclose this may not be needed as the dead time can be
extended by an extra circuit breaker healthy check / Autoreclose Inhibit Time window time if there is
insufficient energy in the circuit breaker.
Switchgear Maintenance: Excessive operation resulting from short reclaim times can mean shorter
●
maintenance intervals.
When used in conjunction with distance protection, the Reclaim Time setting is generally set greater than the zone
2 delay.
6.4

AUTORECLOSE SHOT COUNTERS

In dual circuit breaker applications, the two circuit breakers are normally arranged to reclose sequentially with one
designated the Leader circuit breaker reclosing after a set dead time. If the Leader circuit breaker remains closed
after the dead time, the second circuit breaker referred to as the Follower recloses after a further delay, the
Follower Time.
The Follower Time is provided to prevent un-necessary operation of the Follower circuit breaker. The Follower Time
should be set sufficiently long as to avoid an un-necessary closure of the Follower circuit breaker where conditions
are such that it would be required to trip again.
After expiry of the dead time, the Leader circuit breaker will attempt Autoreclose. The minimum value of the
Follower time should allow sufficient time for the Autoreclose of the Leader circuit breaker to be considered
successful.
An extreme case may be where instantaneous protection is only provided by distance elements and where
Autoreclose is onto a dead line with a persistent fault at the remote end of the line.
Local end protection (Time delayed Back up protection, like distance Z2 element) may detect this fault after a time
delay (typically > 200 ms). In addition to the delays associated with the back-up protection (typically >200 ms), time
must be allowed for the Leader circuit breaker to re-trip (50 - 100 ms), and a safety margin needs to be added so
that a minimum Follower time could be around 500 ms.
If the Autoreclose of the Leader circuit breaker is successful, the Follower circuit breaker can be allowed to
Autoreclose. Delaying the Autoreclose of the Follower circuit breaker will allow any transients to decay before the
switching. If the transient decay figure is known, it can be used to determine a minimum Follower Time value. The
larger of the two values can then be used as the minimum Follower Time.
342
P446SV
P446SV-TM-EN-1