REACTOR SWITCHING TESTS OF A VACUUM CIRCUIT BREAKER, FARGO SUBSTATION MISSOURI RIVER BASIN PROJECT,

A 13.8-kv vacuum-type circuit breaker at Fargo Substation performed well on reactor switching tests, usually clearing at the first current zero after contact part (for the first contact to clear). Average arcing time for the 3 phases was 0.35 cycles. This new-type breaker shows no tendency to restriking but a slight tendency to current chopping with breaker operating at 84% of continuous current rating. Moderate overvoltage transients were recorded during closing operations. The tests demonstrate a very regular pattern of clearing by the 3 interrupters during point-on-cycle switching. This breaker can be expected to provide reasonably maintenance-free reactor switching service and reasonable life within its range of applicability. Since it has low interrupting capabilities (12,000 amp, symmetrical) its use would be limited normally to locations with fault currents at or below this amount. At stations with higher interrupting current capabilities, the advantages of a vacuum breaker can be used for reactor switching service if it is applied between the reactor and the reactor neutral or by protecting the circuit with fuses of adequate interrupting capabilities. Since these tests do not provide information on interrupter life or frequency of contact adjustment, the breaker should be left in service for further study. (Author)