Analysis of Partial Discharge Signals Using Stockwell Transform

Abstract

Partial Discharge (PD) is characterized by current pulses that appear in high voltage (HV) electrical equipments obtained from ionization process when damaged insulation is submitted to high values of electric. That means ageing and deterioration is mainly occurs due to the presence of partial discharge in an insulator used in the high voltage power equipments. The process of deterioration develop until the insulation system is unable to withstand which causes sudden failure of live assets often release high amount of energy leading to explosion. So occurrence of PD leads to major problem for both economic and safety implication and its monitoring is most important activity by transmission companies. PD monitoring is a useful method of assessing the aging degree of the insulation, manufacturing defects or chemical/mechanical damage. Many sources of noise (e.g. DSI, random noise gaussian noise and power frequency noise) directly affect the PD estimation. In order to get original PD signal noise has to be removed. So for the extraction of original PD one from noisy, Wavelet transform is used. It can simultaneously give information about occurrence of PD pulse, time and pulse spectrum, and also de-noise PD pulse. Different type wavelets are used for observation and analysis of PD signals in high voltage apparatus in order to get actual PD pulse. Wavelet denoising technique comprises different denoising performance indices for the comparative analysis of the noisy PD signal. But wavelet fails to explain about frequency and phase information of the de-noised signal. So getting the final denoising result Stockwell transform is used for time frequency analysis of the denoised PD signal. The S-transform has an advantage in that it provides multi resolution analysis while retaining the absolute phase of each frequency component of the signal. But it suffers from poor energy concentration in the time frequency domain In present days we are using modified stockwell transform for detection of partial discharge signals. In modified S-transform gaussian window of variable length is used that scales the signal with the frequency to improve energy concentration.