Analysis Of The Hilbert Spectrum Of Insulator Leakage Current And Abstraction Of The Characteristics

The contamination flashover is the extreme result of the high voltage insulator, and it presents a serious threat to stable and safe operation of power system. To prevent the flashover, it is necessary to study the mechanism of flashover and find the relationship between the leakage current and the flashover process.The Fourier transform is widely used as the traditional tool of analyzing the stationary signals. New analysis method using the Hilbert-Huang Transform, instead of the Fourier transform is used for leakage current because it can't reflex that the frequency spectrum of non-stationary signals varying with times.For the mode mixing phenomena in the Empirical Mode Decomposition (EMD), The Ensemble Empirical Mode Decomposition (EEMD) is used to suppress it. The adjacent data of leakage current are introduced to extend the signal for the purpose of resolving the end problem. As the leakage current in the initial stage of the whole flashover process comprises a large quantity of noises, it is difficult to obtain the valid characteristics of signals.According to the characteristics of the Intrinsic Mode Function (IMF) energy of normalized white noise under EEMD, the EEMD de-noising method based on the characteristics of white noise and EEMD threshold de-noising method are given. The two de-noising method are proved to be effective compared with the wavelet threshold de-noising method. It is also concluded that the two EEMD de-noising method have respective superiorities under the circumstance of different intensity of noise, so it is best to change suitable de-nosing method based on different intensity of noise.The leakage current is also divided into several stages based on the three stages of thought during the whole flashover process, and each stage of leakage current is analyzed in the terms of both time domain waveform and Hilbert spectrum. The intrinsic mode energy ratio, the intrinsic mode energy entropy and the frequency band energy based on Hilbert spectrum during the whole flashover process are analyzed. Related research show that the intrinsic mode energy ratio, the intrinsic mode energy entropy and the frequency band energy based on Hilbert spectrum can be used to predict the development of flashover, and each of them can be an early warning for contamination flashover. Key Words:leakage current;contamination flashover;Hilbert-Huang Transform;Ensemble Empirical Mode Decomposition (EEMD);Hilbert spectrum...