Research and development of ester filled power transformers
Ester based insulating liquids are manufactured from natural resources such as vegetable oils or synthetically by reacting alcohols with acids. Key advantages of esters over conventional hydrocarbon- based mineral oils are their high flash point and readily biodegradable nature, which enable them to meet the increasing demand on the sustainability of power system infrastructure and make them ideal for the urban environment and other safety-critical applications. For more than forty years, ester liquids have been successfully used in distribution transformers.
In 2014, over 600,000 distribution transformers worldwide were operating with ester liquids and about 25,000 power transformers, most of which were at low to medium voltage levels . The number of ester-filled high voltage power transformers has been increasing in recent years but still remains low. Two of the key milestones in the development are the 420 kV/300 MVA natural ester filled power transformer in Germany, and the 400 kV/240 MVA synthetic ester filled power transformer in the United Kingdom . The requirement of design modifications and lack of experience with long-term operating performance possibly affect the development. However, these challenges will be overcome with more experiences accumulated by manufacturers and end-users.
A tremendous amount of research activities has been conducted by manufacturers, utilities, research institutes, and universities for the development of ester filled high voltage large power transformers. This article introduces some of the research contributions on the application of ester liquids in large power transformers made by the members of the University Transformer Research Alliance (UTRA) over the past two decades.