REPORT ON THE ACOUSTIC METHOD OF DETECTING PARTIAL DISCHARGE ACTIVITY IN POWER PLANT

Report on the Acoustic Method of Detecting Partial Discharge activity in power plant



Abstract

In recent years, the ultra high frequency (UHF) method is employed to reduce and avoid the noises effects on partial discharge (PD) detection for the power transformer on-site. In order to know the UHF signal radiation from the partial discharge in oil impregnated insulation and its propagation characteristics in a transformer tank, the experiments have been carried out in high voltage laboratory. The current impulse waveforms of PD and its UHF signals are measured through the partial discharge detecting circuit and a coupler respectively. The results show that the electromagnetic wave can be excited from the partial discharge in oil-impregnated insulation with the higher frequency than that in air. The propagation and attenuation characteristics of UHF signals in a metal tank are different from that in opening air. The experimental results also show that the UHF signal can be radiated from the inside of a metal tank through a wire, which makes it possible to measure partial discharge for the power transformer with the coupler fixed at the outside of the tank.

Report on the acoustic method of detecting partial discharge activity in power plant

Introduction

In power system, the failure of major elements can cause disruptions, and result in very expensive losses. To improve the reliability of power system, in recent years, some kinds of condition monitoring devices have been developed 11-21 to detect the partial discharge in transformer on-site, based on the electrical, acoustic or chemical method. For its higher sensitivity to PD activities, the electrical method [3-41 is widely used. The key to on-line PD monitoring of power transformer using electrical methods is to suppress interferences. Despites great efforts have been made; it is still the critical task to suppress the interferences for building an on-line PD monitoring system of the transformer. According to the experience of PD detection in gas insulation substation (GIS)[5-6], The ultra high frequency (UHF) method is proposed to detect the partial discharge in transformer[7-9]. Considering the different partial discharge activities, as well as the different structure configurations between the GIS and the transformer, it is very important to know: 1) Can the UHF signal be excited from the partial discharge origins in transformer? 2) Does the complex inner structure of transformer effect the propagation and attenuation of UHF signals? 3) Can the UHF coulper receive the UHF signals from the outside of the transformer tank? To answer the above questions, the experimental researching works are carried out in this paper.

UHF Couplers

To coulpe the UHF signals excited from the PD origins, the dual-arm broadband Archimedean antenna is employed, shown in Fig. I , with the diameter equal to ?/p and the deepth of back cavity selected to hJ4. The impedance of dual-arm Archimedean antenna is about 164R (Barry, 2000, 141). In order to matching this impedance to the coaxial cable whose impedance is 50?, the printed circuit balun is used, shown ...