Investigation on the propagation characteristics of PD-induced electromagnetic waves in an actual 110 kV power transformer and its simulation results

Partial discharge (PD) detection using the ultra-high frequency (UHF) method is a well-known advanced insulation diagnosis method in power transformers. Investigation on propagation characteristics of electromagnetic (EM) waves in the power transformer is required for significant improvement of detecting PD signal by UHF method. In this paper, a 110/35/10kV three-phase oil-filled transformer with complete internal structure was utilized to investigate the propagation characteristics of EM waves. The amplitude, cumulative energy and frequency band energy of EM waves in different positions were analyzed. As a comparison, a simulation model whose size is same as the experimental transformer, built by CST Microwave Studio was also performed. The results show that the amplitude and cumulative energy of EM waves have similar change law, that is, they decrease non-linearly and the attenuation rate slows down with increasing distance from the PD source. During the propagation of EM waves, the higher frequency bands suffer greater attenuation leading to the less energy ratio. Compared with experimental results, numerical simulation brings about adequately accurate values and shows the similar trend with experiment. The results serve as the essential guides to improve the sensitivity of UHF detection and efficiency of online monitoring by UHF detection, and as a notable concern to optimize the band width for high-frequency detection.