Replacement of oil-insulated circuit-breakers/switches by vacuum counterparts

Since 1978, the Hong Kong Electric Company Limited (HEC) has switched to the use of 11 kV vacuum circuit breakers (VCB) in both new projects of primary substations and uprating of existing primary substations. From then on the population of oil circuit breakers (OCB) diminished. By 1989, there were approximately 600 VCBs in the 11 kV system. The in-service OCBs were reduced to some 410 pieces and were supplied by two manufacturers in late 1960s and early 1970s. Both manufacturers were asked to inspect the busbars and housing of the switchboards, and confirm that the residual life was more than fifteen years. The simple and economical way of upgrading is to replace the oil circuit breaker carriages without disturbing the busbars. The author describes the joint efforts devoted by switchgear manufacturers and HEC to design and type test replacement vacuum breakers to achieve cost-effectiveness and minimal supply interruption. Experience of the breaker replacement and the saving in operational costs after employment of vacuum breakers are also presented.<
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