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Research on the discharge evolution law of the needle-plate defect in oil-paper insulation at AC voltage

In order to make the changes of relevant physical parameters in the discharge evolution of needle-plate defect in oilpaper insulation, and to establish the mapping relationship between the changes and the fault development process, this paper established a discharge test platform for the development of needle-plate defect in oil-paper insulation, using high frequency current transformer, ultra-high frequency sensor, ultrasonic sensor and Silicon photomultiplier to detect the discharge process simultaneously. The results show that: the discharge process of needle-plate defect in oil-paper insulation can be divided into development stage, stagnation stage and pre-breakdown stage. In the development stage, the statistical parameters such as apparent discharge of high frequency current transformer, pulse repetition rate of ultra-high frequency signal, peak value of ultrasonic signal and intensity of optical signal increase significantly. In the stagnation stage, except the amplitude of high frequency current transformer, other characterization parameters decrease significantly until entering the pre-breakdown stage. The conclusion provides a reference for the protection of transformer.