Study and characterization of PD in impregnated polypropylene capacitors

Measurements of partial discharge (PD) in models of impregnated polypropylene capacitors with and without specific defects have been conducted. Two different regimes of discharges (in the liquid and in gas bubbles) are illustrated. The effect of temperature on the decrease of the insulation property is underlined. Four specific defects have been artificially introduced in the test cell (poor impregnation, bad contact, fold in the polypropylene (PP) film, cavity). The relevance of parameters such as skewness and kurtosis to characterize PD distributions is discussed. New parameters based upon the mean position of the PD in the voltage phase are proposed for a better recognition of the defects inducing PD.