Investigations on the suitability of indigenous natural esters as liquid dielectrics

Dielectric liquids used in electrical equipment serve the dual purpose of insulation and cooling. Mineral oil is one such liquid dielectric coolant which is in extensive use in power and distribution transformers. In spite of many advantages, the poor biodegradability of mineral oil 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. Last couple of decades has seen success in the development of natural esters for use in transformers. Envirotemp, Biotemp and Rapsol-T are examples which are based on Sunflower oil, Soya bean oil and Rape seed oil. In the present work, investigations are carried out to study the suitability of few other indigenously available oils codenamed as IO-16, IO-18 and IO-19. In addition, local sunflower, rapeseed and soya bean oils are also being investigated. Till now, oils with and without chemical treatment have been investigated. The parameters studied include Permittivity, Loss factor, Breakdown Voltage, Oxidation Stability and Resistivity. The oils in “as received” condition have shown permittivities in the range of 2.7 to 3.4. Breakdown Voltages were in the range of 35kV to 70kV. Loss Factor (Tanδ) values ranged from 0.01 to 4. Effect of temperature from room temperature of about 25°C upto 100°C has also been studied. The experimental results after chemical treatment have indicated encouraging results with increased permittivities of 3.4 to 3.72, much improved loss factor of 0.002 and Breakdown Voltages of nearly 70kV.