Wavelet transform analysis of arrester voltage in surge motor protection

Studies showed that most motors stator winding failures result from the breakdown of the turn insulation during switching or lightning surges. Failure would be less frequent if motors were properly protected against such surges. Meaningful information is contained in the transient surge signals and should be used in the protection algorithm to increase their speed and accuracy. In this paper, the Electromagnetic Transient Program (EMTP) is used to simulate surge arrester behaviour during switching. The multiscale wavelet transform is then applied to the voltage waveform across the terminals of an induction motor. The instantaneous time-frequency information obtained may be useful for the design of a fast and accurate relay algorithm