Diagnosis and Analysis of Insulation Damp Defect in a 220kV Current Transformer

As the core equipment of power grid, current transformer undertakes the key functions of power system measurement, control and protection. In this paper, a 220kV oil-immersed current transformer has a metal expander toppling defect, and the test analysis of insulation resistance, DC resistance, dissolved gas in oil, high voltage dielectric loss and partial discharge is carried out. It is initially suspected that the current transformer has insulation damp defect. Through the disassembly analysis of the current transformer, combined with the dielectric loss measurement between capacitance screens, infrared spectrum analysis and other tests and production process troubleshooting, it was determined that the cause of the fault was that the cutting fluid of the primary guide rod was not cleaned up during the manufacturing process of the current transformer, which led to the high water content of the zero screen insulation paper, partial discharge under the action of the operating voltage, and continued to produce hydrogen, methane and other characteristic gases. Ultimately, it caused the current transformer metal expander to overshoot. This diagnostic analysis shows that dissolved gas analysis in oil, high-voltage dielectric loss, capacitance screen dielectric loss, and infrared spectroscopy analysis can effectively diagnose insulation damp defects of current transformers.