Analysis and Treatment of Partial Discharge Exceeding the Standard in a 750 kV Transformer Delivery Test

In the factory long-term induction withstand voltage band partial discharge measurement test, a 750 kV power transformer has a phenomenon of serious excessive partial discharge in the medium voltage winding at a voltage of 1.5 U_m\sqrt3 . In order to accurately determine the cause of excessive partial discharge and deal with it, the methods of external judgment, group positioning and disintegration inspection are used to finally determine that the partial discharge point is located between the transformer excitation coil and the voltage regulating coil. According to the results of the cause analysis, a treatment plan was adopted to replace all the insulating parts between the excitation coil and the voltage regulating coil, and to conduct a comprehensive inspection of the body and assembly process components. After the treatment, the re-test of the transformer factory test and the special hand-over test on site were successfully passed. The analysis of the causes of overshoot and the effect of the treatment plan have been verified, providing reference for the subsequent analysis and treatment of such phenomena.