Dielectric behaviour of ester liquid insulation systems under lightning impulse stress

The benefits of both natural and synthetic ester liquids are well known, such as their improved biodegradability, low toxicity, high flash point and ability to absorb moisture. Due to these advantageous properties natural and synthetic ester liquids are being adopted in the power and pulsed power industries as a long term replacement for mineral oils within liquid insulating systems. Significant research efforts have been focused on the electric and dielectric characteristics of natural and synthetic ester liquids within bulk liquid insulating systems [1-3], however review of publications in this field indicate a lack of information on dielectric performance of solid polymer-ester liquid composite insulating systems.
The purpose of this study is to, firstly, evaluate how the chosen ester liquid performs within a bulk liquid insulating system under lightning impulse stress of both positive and negative polarity. The effect relative moisture content of the fluid exerts on the observed breakdown behaviour of the fluid was also evaluate by studying the fluid at two discrete levels of relative humidity, with key parameters such as breakdown voltage and time to breakdown evaluated.