High frequency spectrum analysis of transient overvoltage across VCB switched large induction motors

Transient overvoltage Due to Switching Operation of large induction motors by vacuum circuit breaker can result in severe stator failures. The protection of the motor with MOA surge arresters only, is not guaranteed. A full motor protection will be provided by using C-R surge suppressors to eliminate multiple re-ignitions. The optimum selection of the C and R values depend on the frequency and values of the vervoltages. In this paper, Fast Fourier Transform (FFT) was used to analyze the transient over voltages generated during switching of vacuum circuit breaker (VCB). A waste water treatment plant pumping station driven by induction motors was used as a case study. The case study was simulated by using Alternative Transients Program (ATP) to mimic a typical system behavior in actual operation. The results of the analysis showed the frequencies of the transient components of the switching over voltage. Such information could be used for selection of proper filters that could be used to eliminate such components and provide additional protection required.