Auto-reclosing

Auto-reclosing

Auto-reclosing is employed on 132kV, 33kV, 11kV and 6.6kV networks. Delayed auto-reclosing at 132kV is detailed in CP338 - 132kV Protection.

The policy for application on the 33kV, 11kV and 6.6kV networks is detailed in EPD321 - policy for automatic reclosing of 33/11/6.6kV overhead lines.

Auto-reclosing is:

  • utilised at 33kV but only in the form of a single shot reclose initiated from the main protection, and inhibited by a permanent intertrip-receive or busbar protection operation
  • employed extensively at 11kV and 6.6kV to ensure that as far as possible supplies are maintained for non-damage faults on overhead line networks.

Modern reclosers are utilised in conjunction with existing reclosers, sectionalisers and auto-sectionalising links.

The maximum number of trips is four with the preferred mode of operation to utilise two instantaneous protection trips followed by two Inverse Definite Minimum Time (IDMT) trips.

The number of instantaneous trips can be varied but the last trip will always be IDMT. There will be a standard dead time of 5s between each reclosure and a reclaim time of 15s.

Sensitive earth fault protection is also used and a single auto-reclose shot is allowed following a trip.

Modern reclosers and protection also employ sequence co-ordination to minimise the number of trips seen on the network, and this is to be employed wherever possible.

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