Investigation of the factors affecting the dielectric dissipation factor of synthetic and natural esters

Traditionally, mineral oil has been used as the insulating liquid in transformers due to its high electrical breakdown strength and cooling ability. More recently, natural and synthetic ester based dielectric liquids are increasingly adopted as alternatives, offering much improved fire safety and environmental protection. The dielectric dissipation factor (DDF), via tan delta measurement, has traditionally been used as one of the key metrics for quality evaluation of unused transformer mineral oils. Understanding the chemical differences between esters and mineral oil and which factors affect material properties such as ester DDF is rapidly becoming of greater importance. By monitoring the individual effects of increased ambient temperature and UV exposure on the DDF of synthetic and natural esters, this investigation aims to provide data which can be used to refine interpretation of dielectric dissipation factor for esters. The overall condition of high DDF esters, and the implications this could have for a transformer, are also evaluated to allow conclusions to be drawn on the relevance of a DDF limit in ester standards.