Research on the Application Possibility of Power Frequency Current Transformer on Partial Discharge Detection

In transformer partial discharge detection, HFCT at the core, clamp grounding and bushing end screen grounding is often used to monitor high-frequency discharge current. However, this often leads to problems such as low transmission ratio and reducing end screen grounding reliability. Considering that the power frequency current transformer used in the ascending flange is similar in structure to the HFCT used for high frequency sensing, this article explores the possibility of using power frequency current transformers to sense high frequency discharge current. Firstly, starting from the equivalent circuit, the transmission band of the current transformer is theoretically analyzed. Subsequently, based on the true current transformer used in the 500kV transformer, its transmission impedance, linearity and sensing characteristics of discharge pulses under power frequency high current are tested. The results show that the power frequency current transformer has the ability to sense high-frequency current, has good linearity, and has the possibility of application in partial discharge monitoring in actual operation of the transformer.

I. Introduction

Complete insulation of electrical equipment is a prerequisite for normal operation. However, insulation will inevitably deteriorate during long-term operation, causing partial discharge inside the equipment, which may further develop into breakdown and other failures [1]. Therefore, in actual operation, partial discharge is an important part of condition monitoring. Since there is a huge difference between the capacitance of defective part and the other part, the voltage drop across the equipment due to partial discharge is minimal. The high-frequency current generated during the partial discharge process is relatively obvious and can be used as an indication of the occurrence of partial discharge [2].