Vegetal oils as substitute for mineral oils

Investigations on food quality vegetal oils have shown favorable dielectric characteristics as insulating material for electrical devices. In order to comply with possible applications, characterizations of different seed oils and chemical derivatives have been carried out. Results are compared to unused mineral oils and synthetic organic esters specified values: the electrical properties of vegetable products are close to those of conventional insulating fluids. Particularly, the breakdown strength under AC stress is at least as high as the one of mineral oil. We have prepared samples of blended oils based on refined rapeseed oil and derivatives that satisfy most operation requirements in transformers. The viscosity and pour point can be fitted to appropriate values. The flash and fire points exceed normative requirements by far, and are similar to those of high temperature hydrocarbons or silicones. The thermal properties (specific heat and expansion coefficient) are also good. Nevertheless, regarding typical transformer life times - 30-50 years - ageing may cause problems that could limit the use of biodegradable oils to sealed equipments. Evidence is provided that rapeseed oil and esters based fluids can be used in transformer application with superior environmental, safety and health properties compared to conventional mineral oils ones.