Mar 2013
Electricity Distribution
Switchgear De-rating
Mar 2013
Western Power Distribution
WPD Future Networks Team (01332 827446)
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Innovation Funding Incentive
LV & 11kV Networks
Determine an improved method of de-rating existing oil circuit breakers that have been type tested to BS 116.
When the network X/R ratio is greater than that for which a circuit breaker was type tested, the circuit breaker rating needs to be adjusted to ensure that it can successfully operate under these more onerous conditions.

The CIGRE 304 method of de-rating a circuit breaker under these conditions, assumes that the switchgear was type tested to the IEC 62271 standard, but this is not the case for many existing oil circuit breakers, which were type tested to the BS 116 standard.

This work will address the difference between the two type testing methods to technically justify an improved de-rating method which takes in to account the intricacies of BS 116 type testing.