Biodegradable Insulating Liquids used in Paper Oil Insulating System

Biodegradable ester-based electro insulating fluids have been tested for many dielectric properties and have been proposed and already used in electric devices as the substituent for mineral oil. Some properties are advantageous as high flash and fire point (> 250°), low impact of the water content on dielectric properties (H₂O saturation hundreds ppm), positive impact on cellulose aging compared to mineral oil, readily biodegradability (OECD 301), etc. However, some properties are contradictory as high viscosity, relatively low oxidation stability, high pour point (eg. -17 - - 23°C rapeseed oil), etc. When employing such as fluid in the e.g. power transformer one needs to face also to the problems with material compatibility. Interactions of some materials in the transformer, such as structural elements, seals, inner part of bushings, separating plane, internal corrosion protection, etc. can interact with the organic ester to produce undesirable chemical reactions that can negatively affect the electrical and other properties of this liquids and oil leaks, failures etc. The paper describes the compatibility problems of such rapeseed based insulating liquid with other materials used in the transformer.