Suitability of natural vegetable seed oil as liquid dielectric coolant in an insulation system

Abstract

The liquid dielectric used along with solid insulation in transformers and other equipments is the mineral oil and is in wide use for several decades particularly for power frequency applications. The active parts of electrical power transformers are normally immersed in mineral oil which acts as an insulating medium between energised parts of electrical equipment [1,2]. Silicone fluid is used as a liquid dielectric for high frequency applications to exploit its higher operating temperatures. In spite of many advantages, poor biodegradability of mineral oil and sensitivity of silicone fluid to corona, results in contamination of soil and water in the event of an accidental spill. In view of this, there have been strong efforts all over the world to find a suitable substitute for mineral oil based transformer oil. Also, replacement for silicone fluid, (mainly used for high voltage / high frequency transformer) has not been explored to a large extent in recent times. Last couple of decades has seen success in the development of natural esters as dielectric coolants for use in transformers. Envirotemp, Biotemp and Rapsol-T are examples which are based on Sunflower oil, Soya bean oil and Rape seed oil. The aim of the present work is to investigate suitability of natural vegetable seed oil as a liquid dielectric coolant for an insulation system, particularly transformers (both power transformers and high frequency and /or high voltage transformers). It is proposed to study and characterize the properties of natural vegetable seed oil to be used in an insulation system. Therefore, an indigenous oil (natural vegetable seed oil) codenamed as IO19 is considered for the study and is investigated for its dielectric behavior. The oil is initially studied for its dielectric properties in “as received” condition and later subjected to various treatments for improving the properties. After treatments, treated fresh sample of IO19 and thermally treated sample of IO19 with and without Nomex are also considered for study. The dielectric behavior of samples of IO19 oil under the influence of temperature and frequency is investigated to check for its suitability in an insulation system. The results are compared with that of silicone fluid.