Ester-Based Dielectric Liquids for Grid Resilience and EHV Mobile Transformers

Ester-based dielectric liquids have now been on the market for several decades, providing fire safe and environmentally friendly alternatives to mineral oil which has traditionally been used in transformers and other electrical equipment. Historically, the use of esters was primarily driven by the need for improved fire safety, with the added benefit of lower environmental impact if spills or leaks occurred. The use of a liquid with a high fire point also allowed more compact, lighter designs which can provide higher power output for a given weight. This principle has been used for many years in applications such as rolling stock and wind turbines, where synthetic esters now dominate. At higher voltages, above 100kV, the use of ester-based insulating liquids has increased substantially in the last 20 years. It is now the case that large power transformers used for transmission and generation projects at 400kV plus can be successfully designed, built and filled with esters. This opens the door to innovation in mobile transformers at ever higher voltage levels, where the ability to gain greater power from a smaller footprint is vital. Coupled with high temperature solid insulation, ester liquids offer an excellent solution for large transformers which can be built within road haulage weight limits.

I. Introduction

Worldwide reliance on electricity has never been so high; coupled with factors such as expanding populations and the extension of electrical networks, there is now an increasing need to ensure that outages can be quickly rectified. Providing large power transformers that can be very quickly deployed and put into service is a challenge for utilities since typically it takes many months for such a transformer to be built and commissioned. In order to bridge the gap in the event of a large transformer failure, grid operators are now demanding ever bigger mobile transformers, which can be sent to site in the event of a failure.