Application of De-noise Methods Used in Monitoring Leakage Current in Safety Stage of Contamination Insulators

As the leakage current in the safety stage of contamination insulators comprises a large quantity of noises,it is difficult to obtain the valid characteristics of signals.Four wavelet threshold de-noise methods are used respectively to filter the noises from measured leakage current with different signal-to-noise ratios(SNR).Three characteristics,namely,the waveforms,effective value and amplitude value ratio of the triple-harmonic to first-harmonic of pre-and-post de-noised leakage current are acquired,whose de-noise effects are compared and analyzed.The optimal wavelet threshold de-noise method for the leakage current in the safety stage is selected.It is shown by analysis that when SNR is greater than 1.0,the best de-noise method is the self-adaptive threshold method for the waveforms and the effective value of leakage current in the safety stage.However,the approximation effect is basally the same for another characteristic,i.e.amplitude value ratio of triple-harmonic to first-harmonic.As a general result,it is known that the self-adaptive threshold method is the best for extracting the characteristics of the leakage current in the safety stage.