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

A vacuum circuit breaker (VCB) has 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 recent exploratory test programs evaluated the interrupting ability of a 15 kV VCB 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. These tests showed that the interrupting performance of the tested VCB was unaffected by the TRV rate of rise to the fastest rates available in the test laboratory. Such a VCB 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