Effect of discharge trace on creeping discharge characteristics in oil/pressboard composite insulation system under impulse voltage application

In order to improve the insulation performance of oil-immersed power transformers, the characteristics of the creeping discharge under impulse voltage have been investigated. In this work, by using streak camera, investigations of the influence of the white discharge trace on the creeping discharge characteristics were implemented. The results showed that the velocity of the discharge developing along the white trace was about a thousand times larger than that of the discharge progressing on the pressboard surface. The results also showed that the length of the discharge progressing on the pressboard surface after the white trace formation was shorter than that before the white trace formation. On the other hand, the discharge time delay became larger. These results are thought to be explained by the residual charge generated by the discharge developing along the white trace.