High Frequency Dielectric Properties of Insulation Systems with New Natural Vegetable Seed Oils

Abstract

A transformer comprises of combinations of solid and liquid dielectrics forming an insulation system. Some of the solid insulation used along with insulating oil in power transformers are press boards, treated wood, paper and in high frequency transformers. Nomex, Teflon and Kapton etc. The liquid dielectric enables heat dissipation also. While mineral oil is in wide use for several decades as a liquid dielectric coolant, silicone fluid is used for high voltage/high frequency applications. In spite of many advantages of mineral oil and silicone fluid, they are non-renewable, non-biocompatible and non-biodegradable. Of late, natural esters have been investigated for their suitability as effective alternative liquid dielectric coolant. In the present work, two natural vegetable seed oils, codenamed IO18 & IO19, have been investigated and their dielectric properties studied, for use in an insulation system. The investigations have been divided into different stages. Various dielectric parameters like Breakdown Voltage (BDV), Dissipation Factor (DF) and Relative Permittivity (εr) have been studied initially under ‘as received’ (oil) conditions. Based on the results obtained (for ‘as received’ oils), in the next stage, suitable food grade antioxidants are added in different concentrations and the optimum arrived at with most suitable concentrations of antioxidant for the two oils. BDVs have been determined as a function of temperature (room temperature to 90⁰C) under power frequency voltages. DF and εr have been studied as a function of both temperature and frequency (500Hz-500 kHz). After treatments, selected samples have been subjected to accelerated thermal ageing with and without the presence of Nomex & Teflon. The dielectric properties of the oils are again studied after they are subjected to ageing. The results have been very encouraging.