Application of Transformer Oil and Biodegradable Ester Mixtures as Insulation for High-Voltage Equipment

Abstract

Synthetic and natural esters as insulating fluids for high voltage equipment have been a focus of much research, especially in the last two decades. This is due to the fact that, unlike mineral oil, ester fluids are biodegradable, non-toxic, safe for the environment and human health, produced from renewable raw materials, and feature high fire resistance. Despite the fact that commercially available ester fluids having excellent insulating properties are offered in the market, both transformer manufacturers and operators are not yet ready for mass-scale transition to the use of biodegradable ester dielectric fluids. In addition, since there is a huge amount of electrical equipment filled with mineral oil, mass-scale replacement of this oil with ester dielectric fluids will be extremely expensive for power companies. A suitable way for making a shift from oil to esters can be partial replacement of mineral oil with ester fluids (for example, topping up during repairs) or complete replacement of mineral oil with biodegradable esters. Whatever of these options is implemented, there will be a mixture of two insulating fluids inside of the equipment. Therefore, specialists intensely study the characteristics and behavior of insulating mixtures based on mineral oil and other dielectric fluid (synthetic ester, natural ester or silicone fluid). The article presents a review of the latest advances in the investigations of mixtures consisting of mineral oil and other dielectric fluids, including the studies of their properties. Problems associated with the operation of equipment in the case of its filling with mixed liquids are discussed.