Rough Balance Busbar Protection and Breaker Failure Protection for the HK Electric's Distribution Network

Abstract

Primary distribution substation busbar forms an electrical node where incoming sources and outgoing circuits come together, feeding in and sending out power directly to customers. If a busbar fails or trips, it will lead to the supply interruption to a large number of customers fed by the outgoing circuits connected to the busbar. The interruption time will be much longer because the supply restoration can only be done at downstream level through multiple switchings. Therefore, a reliable and discriminative busbar protection is crucial to protect this important piece of equipment in the distribution network and to achieve high supply reliability.Proper protection design of a distribution network should also cater for circuit breaker failure when an external fault occurs. When this happens to a circuit breaker connected to a busbar, tripping out of the busbar to clear the fault is inevitable. For this reason, breaker failure protection is normally incorporated into the busbar protection scheme of a primary distribution substation as a total solution.This paper describes the HK Electric's distribution protection system that employs a simple yet effective rough balance differential principle to achieve busbar protection and breaker failure protection with proper fault discrimination. The paper also compares the merits and drawbacks of different busbar and breaker failure protection schemes adopted by us and some other utilities.