Advances in the field of insulating liquids used in electric power equipment and their perspectives-a review

Petroleum-based oils have been widely used as liquid insulation in electric power industry for over a century because of their ready availability, low viscosity, good aging behavior, and low cost. But, growing environmental concern, material sustainability, and desire for a safe nonflammable insulating liquid in power equipment have driven the researchers and engineers to explore alternative liquids with improved properties, and significance improvements have been achieved in this field. The objective of this review paper is to discuss about some of the developments in the field of liquid insulations, main features, applications, perspectives and engineering problems of several types of insulating liquids such as natural and synthetic organic liquids, cryogenic liquids, and liquefied gases. Properties like fire point, flash point and biodegradability for mineral oil, vegetable oil, silicon oil, and synthetic ester fluids are compared. A few recently installed liquid-filled power equipment with advanced insulating fluids are also mentioned.