Inception and Breakdown Voltages of New Low Pour Point Liquids Under Lightning Impulse

It is important to investigate the pre-breakdown and breakdown behavior of the alternative liquids for effective estimation of the safety margin and other dielectric design aspects of the new insulation systems. In liquid-filled equipment, the focus has been mineral insulating liquids for more than a century. However, the recent research contributes largely to a comparative analysis of the prebreakdown behavior of ester dielectric liquids to mineral oils. It is widely reported that the dielectric performance of mineral oil under lightning impulse as well as AC and DC voltages is better than in ester dielectric liquids. This observation stands valid for tests reported with different electrode configurations in the literature. Furthermore, applying esters for transformers in cold countries has always been a challenge to the transformer owners. Thus, there is a wide scope for research to investigate the behavior of esters as an insulating medium for transformers serving in cold regions. This paper reports the results of a study of the dielectric performance of a new low-pour point synthetic ester and a low-pour point mineral oil under lighting impulse using point-plane electrode configuration. The results of the streamer inception voltage and lightning impulse breakdown voltage for aged and non-aged liquids are presented. The obtained results show that the inception and breakdown voltages of non-aged low pour point synthetic ester are almost similar to mineral oils. However, the inception and breakdown voltages of the investigated aged low pour point synthetic ester are higher than that of the aged mineral oil.