Phase analysis of discharge magnitude distributions inside a small void and its applications to diagnosis of deteriorating insulations

A breakdown phenomenon of electrical equipment due to the deterioration of insulation was investigated. The degree of deterioration or breakdown of the insulating system was predicted from the distribution of induced electric charges inside small voids in an insulator-the discharge magnitude distribution. This distribution was measured by a special internal-discharge pulse measurement system, which analyzes it according to the phase area of the applied AC 50-Hz voltage. This technique was used to investigate tree progression in the microvoid of PMMA (polymethyl methacrylate). The density and the growing speed of the trees are analyzed in terms of the discharge magnitude distributions