Failure analysis of composite dielectric of power capacitors used in distribution systems

This paper describes the study of the reliability of capacitor units instal led and operated in distribution system during the period 1980 through 1990 . Failures of capacitor units in distribution substations can be very costl y to the supply of reliable power to consumers. To enhance utility reliabil ity, failure analysis, and rates, failure origin and physical damage causes were performed for these capacitor units. Two approaches, statistical and physical, were utilized in this study. 172 the statistical area, failure mo des, reliability levels and failure causes are analyzed. The physical study mainly deals with the mechanism of deterioration of the composite dielectr ic. This paper models capacitor's failure mathematical mode and calculates their failure rate. The results of the study of 2912 capacitor banks including 8736 capacitors installed at 153 distribution substations showed that the failure mode of c apacitor units may be represented by Weibull distribution and each capacito r manufacturer has a different failure rate. Analysis showed that partial d ischarge properties are a critical indicator for capacitor failure mechanis m. Useful conclusions are presented both for power system operators and man ufacturers. The methodology used in this study also applies to other equipment in the d istribution system such as oil switches, transformers, and insulators.