Study Of Suppressing PD's Narrow Band Noise In The PD Monitoring Frequency Band Using Complex Wavelet Packet Transform

Partial Discharge (PD) in Gas Insulated Switchgear (GIS) is one of the important factors for the fault; therefore the on-line monitoring PD in GIS has been researched at home and abroad in order to guarantee the safe operation of GIS. At the same time, PD pattern recognition is still an advanced problem to be studied, so this paper advance complex wavelets packet transform which is a bran-new technique to suppress narrow band noise, give its constructing methods and specific steps, and then research de-noising the simulative and measured signals in lab with narrow band noise by the complex wavelets packet transform.By using the same filter to construct wavelet packet and by remaining phase spectrum of real wavelet packet filter and changing its amplitude-frequency characteristic, complex wavelets packet is constructed with the same amplitude-frequency characteristics of corresponding real wavelet packet and the same phase spectrum of corresponding complex wavelets, and then give the specific method of constructing complex wavelets packet, evaluate the effect of original PD simulative signals'direct reconstruction after decomposition by using Normalized Correlation Coefficient (NCC) and Variational Trend Parameter (VTP) also and the relative error of the amplitude, verify the capability of restore Non-stationary Oscillating Partial Discharge Signals effectively and the correctness of the complex wavelets packet's construction.Four common simulative signals are disassembled and constructed, the resemble degree analysis on simulative signals with different frequency and strength narrow band noises before and after construction, it is shown that complex wavelets packet transform suppress unsmooth pulse signals more effectively revert signals more powerful.According to the differences between PD signals and the narrow band noise after complex wavelet packet transform, this paper presented the specific combined information of serial WTRIn, which was used to suppress narrow band noise. Through the contrat of suppressing narrow band niose, it was proven that WTRIn had more powerful than simple information and other combined-informations. At last, through the analysis of the impacts of the index n on WTRIn it was shown that WTRI is the-best-denoising-combined-information no matter what frequency and intensity of the narrow band noise.At last, this paper denoised PD admixture simulative and measured signals with different frequency and strength noises by complex wavelets packet transform, overcomed the difficult of more loss using hardware filter and bad effect using wavelets packet transformation when narrow band noise in the monitoring frequency band.