Study of kinematic viscosity of mixture oils under thermal aging in power transformer

Abstract

This paper presents the experimental results of physicochemical properties studies of mixtures based on mineral oil carried out in the laboratory, under thermal stress at fixed temperature with different intervals for long period. The stability study of thermal aging is an essential tool to estimate the lifetime of insulating oil and therefore for the transformer. The tests results allow to make a comparison between the different mixtures proposed and to select the best. It is shown that the degradation rate of oils represented by kinematic viscosity is changed according to ester rate under thermal stress. We can consider that mixtures are less affected than mineral oil, depending on the ester content in the mixture. Results show the strong correlation between viscosity and dissolved decay product, under thermal stress. The increase in the soluble products in the oils, generated by degradation of oil, affects the physical parameter by increasing the kinematic viscosity. These measures are the main criterion to evaluate the stability of physical parameter of oil in-service.