Impulse Pre-stress Effect on AC Partial Discharge Inception Characteristics of Winding Model Sample

The purpose of this study is to elucidate the insulation degradation phenomena of cast resin transformers. We used a winding model sample that simulates the insulation configuration of a cast resin transformer. In this paper, the partial discharge inception voltage (PDIV) under the AC voltage was measured after applying multiple impulse voltages to investigate the effect of impulse voltage on PDIV. As a result, PDIV was significantly decreased by the impulse pre-stress. On the other hand, during repeated measurement of AC-PDIV, it was shown that the decreased PDIV gradually recover to the value before the impulse voltage application. Measured temporary decrease of AC-PDIV is considered to be due to the field enhancement caused by electric charge deposited by the impulse pre-stress without degradation of insulating materials.