Application of Acoustic Emission Method for Partial Discharge Research in Selected Elements and Devices of Electric Power Systems

Abstract

The paper presents the systematics of partial discharges (PDs) sources, properties of PDs signals registered by means of electric methods and the possibilities of an acoustic emission (AE) method to create acoustic images describing PDs. The author's AE research methods applied during testing of generator coils bars and oil power transformers as well as obtained acoustic images for registered AE signals and acoustic maps, giving the location of PD sources occurring in the tested objects are presented. The acoustic image includes results of basic and advanced analysis of recorded signals. The basic analysis is carried out in domains of time, frequency and time-frequency. It includes filtration of signals in selected frequency bands, and then determination of frequency characteristics and phase-time characteristics, averaged phase characteristics and average STFT spectrograms for filtered signals. Advanced analysis is conducted in the discrimination threshold domain and includes the determination of amplitude distributions and author's descriptors with the acronyms ADC and ADP. These descriptors classify signals by assigning to each signal a socalled level of signal advancement. Determination of individual elements of the acoustic image is carried out within author's software using the Lab View environment providing recording of signals and analysis of the recorded data. The work presents acoustic images for signal identified real sources of PDs occurring in the tested objects. Acoustic maps for PDs in the tested obj ects are determined from the distributions of ADC descriptors. For examined generator coils bars a family of one-dimensional acoustic maps containing the values of ADC descriptors of signals registered at particular points of the tested obj ect are determined, wherein the parameter in the maps family are values of the voltage applied to the tested obj ect. The work presents families of maps for two selected generators coils bars and the location of PDs sources resulting from these maps. For the tested power oil transformers, acoustic maps are maps of ADC descriptors on the side walls of the tested transformer tank. These maps are obtained by the method of kriging and are the basis for the location of PDs discharges sources in the tested transformer. The work presents such maps for the one selected examined obj ect together with the analysis