Study on the Mechanism of Partial Discharge Emitting Ultrasonic Wave and Propagation Property Within Power Transformers
|School||Changsha University of Science and Technology|
|Course||High Voltage and Insulation Technology|
|Keywords||transformer partial discharge supersonic wave stratified media transition matrix|
Locating partial discharges (PD) sources inside large transformers is a classical problem in the field of electrical insulation monitoring. Though many PD sources localization methods were presented in the past several decades, but there is no efficient method that can solve PD sources localization in large power transformers until now. The first reason lies in the complex insulating structure and formidable electromagnetic conditions within transformer, which restricted the PD pulse signal extraction severely. The second reason lies in that PD pulse signal is a time variant quantity, its amplitude, phase and frequency are fluctuating, single measurement or limited time measurement could not give the real character of the PD signal completely, so electrical 1ocating methods, which based on the PD pluses propagation characteristic, are difficult to localize PD sources accurately. The last reason lies in that ultrasonic 1ocating method is based on single PD source within transformer at present. But in fact, it always coexisted several PD sources, so ultrasonic 1ocating methods, which based on acoustic emission propagation characteristic,It is difficult to specify the time delay of PD signal accurately.In order to research and realize PD sources localization within power transformer and to improve the accuracy of localization, a new method is presented in this thesis, which is based on array signal processing. The physical process of partial discharge generated ultrasonic waves and the propagation characteristic of ultrasonic are analyzed and tested. Partial discharge will provoke acoustic emission wave, but there are a few papers to discuss the electro acoustics transition process. In this dissertation, the stress process of air.Bubble is analyzed when partial discharge is happening in oil,filled transformer, resorting to the method of electrical.Equivalent circuit for the air.Bubble PD model generated ultrasonic waves. It makes the mechanics of acoustic emission clear.The sound transmission of stratified media is a classical puzzle in the field of applied acoustics, according to the insulating structure within large power transformer, the model of stratified media was established; the problem of transmission of ultrasonic wave through stratified media was analyzed by transition matrix method, the experimental results show that that the proposed method is effective. An ultrasonic wave propagation characteristic testing system was set up;The frequency distribution of ultrasonic wave excited by variant PD model was analyzed. It is convenient for the ultrasonic senor selection.