Interference removal on impulse voltage & current measurements with wavelet analysis

Impulse voltage tests are essential to inspect and test insulation integrity of high voltage apparatus. On the other hand, generated impulse currents are used for different test applications such as investigation of high current effects, electromagnetic interference (EMI) testing, etc. Obtained voltage and current waveforms usually have some sort of interferences originated from the different sources. These interferences have to be removed from the original impulse data in order to evaluate the waveform characteristics precisely. When the interference level is high enough, it might not be possible to distinguish signal parameters from the recorded data. Conventional filtering methods cannot be useful for some interferences such as white noise. In that case, time-frequency filtering methods might be necessary. In this study, the wavelet analysis, which is a powerful time-frequency signal processing tool, is used in order to increase the effectiveness of denoising of impulse current and voltage data. Depending on the signal type that is handled, the major difficulty is to select mother wavelet, decomposition level, thresholding rule and thresholding function, which effects the evaluation of impulse voltage and current characteristics. In this study, the effectiveness of wavelet transform on noisy impulse voltage and current data has been increased by studying the determination of wavelet related above mentioned parameters for common impulse voltage and current waveforms.