Propagation Characteristic of Partial Discharge Ultra High Frequency Signals Outside Transformer

It is found in field detection that ultra high frequency(UHF) signals can diffract from the joint of transformer.The feasibility of using external UHF sensor for detecting partial discharge activities is discussed,and the external propagation characteristic of UHF electromagnetic wave is investigated via the lab experiment.The wavelet packet analysis of signals shows that the frequency distribution of external signals and the inside signals is quit difference.The relationship between distance of joint and UHF sensor is also researched and the results show that UHF signals may leak outside the transformer through the joints after multiple refraction and reflection in the transformer tank,and the electromagnetic wave expression varies with difference distance.