Partial discharge testing is one of the most important testing items in the daily operation of high-voltage transformers. Commonly used partial discharge detection methods include transient ground wave method, ultra-high frequency method, ultrasonic method and pulse current method. Some equipment also needs to use electrochemical method and optical method.

Among them, the detection principle of the pulse current method is determined by the structure of the power transformer. In addition to the inter-turn capacitance, there is a distributed capacitance of hundreds or even thousands of p F between the winding and the iron core, and there are hundreds of p F between the winding and the fuel tank. Distributed capacitance of p F. When a partial discharge occurs in the main insulation circuit such as the winding of the transformer, the high-frequency signal generated by it covers from tens of kilohertz to tens of megahertz, or even to gigahertz. Since hundreds of picofarads are equivalent to high-frequency signals above hundreds of kilohertz, the discharge signal will propagate to all circuits that have a capacitive relationship with the discharge point. One of the circuits must include the core ground circuit. Therefore, installing a broadband current transformer on the core grounding line can effectively receive the discharge signal in the transformer.