Identification of Defect Type in an Aged 22 kV Cast Resin Transformer from Phase-Resolved PD Patterns

This paper presents identification of defect type in the insulation system of an aged 22 kV cast resin transformer (CRTr) from comparing phase-resolved partial discharge (PRPD) patterns with those in different electrode systems simulating various kinds of defects. Quantitative analysis of the PRPD patterns was performed using a measure of the difference between the two probability distributions, called the Kullback-Leibler (KL) divergence. Comparison of PRPD patterns using KL divergence value (KL-D) suggested the possibility that a defect type in the aged 22 kV CRTr was attributed to inter-layer voids. Furthermore, even for the PRPD pattern of CRTr, which had little apparent change over time, the value of KL-D increased with increasing cumulative application time tc. As a result, it can be said that KL divergence is a useful index in comparing PRPD patterns quantitatively.