On Challenges of Using Natural Ester Insulating liquid: Transformer Cold Start

The current study focuses on challenges associated with energizing natural ester liquid-filled power transformer for offshore wind application in cold climate. The study involves additional challenges using natural ester liquids during the storage stage by cooling the transformer down to extreme cold temperatures. The study was applied on a 66 kV KFWF transformer equipped with fiber optic sensors to monitor the temperatures of the winding and the liquid at different locations during the variation of the storage temperature within the cold range. Liquid time constant at different locations were calculated and correlated to the chamber ambient temperature. Induced voltage tests were carried out on the transformer periodically at different cooling temperatures and compared with the reference one before cooling down. Partial discharge (PD) levels variation of value and pattern during warming up in room temperature were thoroughly investigated. The aim of this study is to understand the limits of natural ester liquid under real operation conditions.