Distributed Capacitive Sensors for Partial Discharge Detection and Defective Region Identification in Power Transformers

Analyzing of detected partial discharge (PD) signals is a reliable technique to assess the electrical insulation in power transformers. In order to detect and locate the PD sources in power transformers, some distributed simple fine sensors are proposed and used, which are made by a few turns of thin enameled copper wire wrapped around the transformer core. They are distributed sensors, which sense PD voltage signals through capacitive coupling with the transformer windings. Two methods, including broadband and limited-band PD signal analyzing, are considered to identify defective phase and/or region on that phase through the proposed distributed sensors outputs. Transfer functions of these sensors are obtained and it is experimentally shown that although defective phase can be diagnosed, the expected priority to identify defective region is not regarded in broadband analysis, while a suitable limited frequency band can be found to achieve this aim. The idea is implemented on a sample transformer by injecting artificial PD signals to different high-voltage winding sections. The results show that not only PD signals can be detected through the mentioned sensors with high sensitivity, but also defective phase can be diagnosed using broadband analysis. Moreover, defective region can be accurately identified by limited-band analysis.