Tests show ability of vacuum circuit breaker to interrupt fast transient recovery voltage rates of rise of transformer secondary faults

A vacuum circuit breaker demonstrated its ability to interrupt short circuits with faster than normal rates of rise of transient recovery voltage (TRV) at levels greater than those produced by most transformer secondary faults. Two exploratory test programs evaluated the interrupting ability of a 15 kV vacuum circuit breaker containing interrupters of the rotating arc type with contacts made from a chromium-copper powder metal mixture. The interrupting conditions covered a wide range of currents from 10% to 130% of the 28 kA rated short circuit current of the tested circuit breaker and a wide range of TRV rates of rise, including: the relatively slow rate of rise, normally used in testing and found in most indoor circuit breaker applications; two faster rates of rise equalling and exceeding those found in a known power plant transformer secondary protection application; and the fastest rates of rise possible in the laboratory which exceed the requirements of most transformer secondary faults. These tests showed that the interrupting performance of the tested vacuum circuit breaker was unaffected by the TRV rate of rise to the fastest rates available in the test lab. Such a vacuum circuit breaker can therefore be used without TRV modifying capacitors to slow down the rate of rise provided by the power system. This ability is particularly important if analysis shows that the expected TRV from a transformer secondary fault has a fast rate of rise beyond the recognized ability of an older circuit breaker to acceptably interrupt.<
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