Investigating the partial discharge electromagnetic wave propagation in power transformers considering active part characteristics

UHF partial discharge localization in power transformers is getting more interests. One of the great advantages is the immunity of the measurements from external noises due to transformer tank electromagnetic shielding. The time delay of arriving signals to two or more UHF antennas installed in different locations at transformer tank is the key parameter for accurate localization algorithms. Due to presence of active part and transformer tank, unfortunately sometimes there is not a direct path for PD electromagnetic waves to propagate from defect site to antennas positions. Through the propagation path, these waves would be reflected and attenuated striking different materials inside transformer. Some materials like core did not allow the wave to propagate through them. Some parts like windings and dielectric boards impose attenuations to wave energy. Such attenuations in some cases might be so high that energy of the parallel long paths may be stronger than the shortest path and this would result in inaccurate localization. Propagating the wave along such paths are mainly caused by reflecting the waves by transformer tank and other components. In this paper using the CST software, the effects of these issues on PD UHF wave propagation in transformers are studied.