AC partial discharge characteristics and accumulation charge after lightning impulse in cast resin transformer

Summary

Cast resin transformer (voltage transformer: VT) composed of solid insulation might cause insulation performance degradation by defects such as void existing in the insulation system. In a factory, AC PD test is usually conducted after applying a number of applications of standard lightning impulse voltage to practical VT. Lightning impulse voltage test is made in the power equipment to guarantee surge insulation performance. However, it is reported that withstand lightning impulse voltage test may give influence on AC partial discharge characteristics, especially partial discharge inception voltage (PDIV). This effect is considered to arise from the charge accumulated in the void by the impulse voltage pre-stress. This paper deals with the influence of lightning impulse application on subsequent AC partial discharge characteristics with accumulated charge by the pre-stress considered. An attempt is made to measure impulse partial discharge, and estimate the accumulated charge. Investigation is also made on the impulse pre-stress effect on the subsequent AC PD characteristics for a model specimen simulating insulation system of a cast resin transformer. An attempt is also made to estimate the accumulated surface charge density after the impulse voltage application. Moreover, we measure impulse PD current and then estimate the charge of impulse PD so as to examine the correlation between the impulse PD charge and the accumulated charge estimated from the reduction of the first AC PDIV.

Additional informations

Authors

M. KOZAKO, M. HIKITA, T. UMEMURA, K. IIDA, Y. NAKAMURA, T. NAKAMAE, T. MAEDA, M. HIGASHIYAMA

Keywords

Partial Discharge, Lightning Impulse, Pre-stress, Cast Resin Transformer