Partial Discharge Progress and Breakdown Characteristics of Oil-Impregnated Paper Insulation System for Capacitor Voltage Transformers

Capacitor voltage transformers (CVTs) with aluminum foil/oil-impregnated papers composite insulation system have been operated over 30 years in substations. An insulation diagnosis of CVT is expected to be based on detecting partial discharge (PD). However, PD characteristics from PD inception to breakdown (BD) have not been clarified yet. In an insulation diagnosis of CVT, it is necessary to diagnose a risk level of BD based on PD characteristics. In this article, we investigated the PD characteristics using electrical and optical measurement on the fundamental insulation model of CVT and discussed the PD progress characteristics leading to BD. Experimental results revealed that PD, which was generated from the aluminum foil electrode periphery, progressed from the creeping direction to the penetrating direction of the oil-impregnated papers, and then, BD occurred. When PD penetrated the oil-impregnated paper, PD charge increased, and hydrogen-based gas was generated. This PD progress can be an important factor to establish insulation diagnosis based on PD measurement of CVT.