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Developing process of partial discharge in oil-paper insulation under needle-plate defects

Understanding the developing progress of partial discharge in oil-paper insulation is essential for the maintenance and operation of transformers. Therefore, we performed partial discharge tests on typical defects in oil-paper insulation under AC voltage and statistically analyzed the partial discharge signals. The progress is divided into three stages according to the PRPD spectrogram. With the raising of voltage, negative streamer discharges that possess a higher apparent discharge magnitude begin to happen in bubbles, which will cause irreversible damage to paper, leading to the breakdown of oil-paper insulation.