The relationship between surface partial discharge and carbon trace in oil-impregnated paper insulation

In this paper, high voltage, which was raised step by step, was taken on an oil wedge model. Partial discharge (PD) signal was measured by normal IEC 60270 method. And the carbon trace on the pressboard was checked. Using Weibull function, the changes on the type of the PDs, were analyzed. Furthermore, the relationship between the carbon trace and the change of PDs was though about. From the results of the experiments, the PDs changed their type during the high voltage increasing. At the beginning, the PDs were small and produced dim carbon trace. This situation kept on for a long time and the carbon trace gradually extended its range and depth. Then, new type of PDs with very big amplitude appeared just before the breakdown, which we believed produced the breakdown point and due to the breakdown.