Partial Discharge Features of Insulation for Power Electronic Transformers Under Time-Temperature Ageing

Under the combination of temperature and high frequency electrical stress, partial discharge (PD) intensity will increase at the insulation system of power electronic transformer (PET), which leads to premature insulation failure, and finally threatens the reliability of PET. In order to obtain PD features under high frequency square wave voltage combined with high temperature, and different aging time of insulation system in PET. A combined electric-thermal experiment platform is established to simulate the discharge characteristics of typical insulation dielectric films (polyimide, PI) under temperature from 80∼155 °C and ageing time from 0∼50 h respectively. The variation trend of discharge repetition rate, average discharge amplitude and the shape of phase resolved partial discharge (PRPD) spectrum are considered, and then the discharge mechanism is analyzed. The experimental results show that the rise of temperature contribute to the augmentation of discharge repetition rate and the average discharge amplitude, with an increase in amplitude from 0.3 V to 0.6 V, and the phase of the discharge signal widens. As the ageing time goes up, the discharge repetition rate and the average discharge amplitude increase too, but the change is most obvious in the early aging period, leaping from 0.2 V to 0.32 V. It is of practical value to reveal the mechanism of high frequency electro-thermal stress and improve the operation reliability of power electronic transformer.