Review of the electrical and thermal behaviour of ester-based dielectric liquids for extra high voltage applications

Ester-based liquids offer the potential for safer and more environmentally friendly power transformers. This can save considerable civil costs in installations, by reducing the requirements for fire protection and simplifying containment. These benefits have been utilised at distribution voltages for almost four decades, in a multitude of applications. In more recent times there has been great interest in using esters for transmission and generation projects, but in order to use these liquids at higher voltages their dielectric and thermal behaviour must be understood. Over ten years of laboratory research and full scale testing have been carried out to evaluate the dielectric and thermal performance of ester-based liquids. This has included studies of fundamental behaviour as well as a wide range of dielectric testing of realistic insulation structures. Work has been carried out by both academic institutions and equipment manufacturers, which has led to a better understanding of the design implications of using these fluids.