Abstract: Liquid dielectrics are extensively used in electrical apparatus which are operating in distribution and transmission systems. The function of electrical equipment strongly depends on the conditions of liquid dielectric. Liquid dielectrics are used is the most expensive components in power system apparatus like transformers and circuit breakers. A failure of these equipment would cause a heavy loss to the electrical industry and also utilities. Insulation failures are the leading cause of transformer failures and thus the liquid dielectrics plays a major role in the safe operation of transformers. One of the main cause for the failure of transformers is due to the presence of moisture. In this work, the life of insulating medium is estimated by comparing the Breakdown strength and Viscosity of different pure oils with that of the contaminated oils (which contains moisture) and also finding the alternative for mineral oil i.e. vegetable oils which are reliable, cost-effective and environmentally friendly even when they are contaminated.

Keywords: HV(high voltage), BD(breakdown), Breakdown strength.