Investigations on dielectric behaviour of a new ecofriendly dielectric coolant for transformers

Abstract

Electrical transformers are very widely used in the Electrical Power sector at frequencies of 50Hz/60Hz. The liquid dielectric used in power transformers for many decades [1] has been mineral oil. Special applications such as Defence and Airborne equipments use silicone fluid as a dielectric coolant because of its higher operating temperatures of about 150°C– 200°C. Of late, natural vegetable seed oils are also used in power transformers, mainly due to their bio-compatibility, bio-degradability and they are also from a ‘renewable source’. These have resulted in the increased usage of natural esters (vegetable oils) as dielectric fluids in electrical equipments. They have greater advantage of having a high flash point (above 300°C) which is an important property of a dielectric coolant. Therefore, the present work focuses on investigations on the dielectric behavior of a new indigenous vegetable seed oil codenamed as IO-18, particularly for use at high voltage and high frequencies. Though, a few indigenous vegetable oils were considered for initial study, IO-18 was selected for the present extensive investigations as some physical and thermal properties of IO-18 are more advantageous. Extensive investigations were carried out experimentally to study the important dielectric properties namely, breakdown voltage, dielectric dissipation factor and relative permittivity at 50Hz and over a temperature range from room temperature to 90°C in both ‘as received’ condition and treated conditions. Behaviour of the oil under high frequencies and at higher temperatures was also investigated. The results of these investigations have been compared with those of mineral oil and silicone fluid to validate the dielectric behavior of vegetable oil.