Ageing of biodegradable oils for high voltage insulation systems

In most items of high voltage equipment a mineral or synthetic oil is still used in conjunction with paper as the dielectric medium. However, the environmental impact, lack of natural oil reserves and the difficulties associated with the disposal of used oils, have prompted researchers to direct their focus onto renewable and biodegradable materials. Originally used in capacitors, these oils are now finding usage in some transformer installations particularly in the United States. Of course a degree of processing is required to make these oils into a form suitable for use in high voltage equipment, including the removal of water and solid matter and the addition of antioxidants. At present at least two commercial products are available; namely Biotemp (ABB) and Envirotemp FR3 (Cooper Industries). With increasing pressure towards renewable and biodegradable materials, such oils are likely to find increased use in the future. Therefore it seems prudent to begin investigations of the ageing behaviour of a variety of vegetable based oil systems in the laboratory and assess their potential for application as high voltage insulation oils.