A Comparative Study of Partial Discharge Pulse Time Characteristics of paper Insulation Impregnated with Mineral Oil, Natural Ester and Synthetic Ester Oil

Abstract

Measurement of partial discharge (PD) is one of the common methods for investigation of insulation behaviour in solid, liquid and composite dielectric materials. Power transformer insulations is a composite dielectric material consists of Kraft paper wound on the copper conductor and impregnated in petroleum based mineral oil (MO). Nowadays biodegradable natural ester (NE) and synthetic ester (SE) are used as replacement to mineral oil because of its higher breakdown strength and environmental benefits. PD defects in the transformer Insulation winding impregnated in natural and synthetic ester liquid need to be investigated to determine life expectancy of insulation compared to mineral oil. In this paper Partial discharge measurement are carried out as per guidelines of IEC60270 by modelling transformer insulation as Pigtail specimens and impregnating in MO, NE, SE oils. Generally PD data are represented in Phase resolved partial discharge technique and interpreted as phase-charge-number to determine insulation behaviours. In this paper an alternative PD representation which includes PD pulse time characteristics and its phase position are measured. Analysis is carried out on intra-cluster distribution, the pulse data were arranged to give phase- time- number of distribution. The results obtained are a useful tool for PD diagnosis, from the experimentation it is observed that Intra-cluster pulse distribution time is higher in ester oil compared to mineral oil indicating superior replacement for transformer insulating liquid.