Evaluation of quality of mineral insulating oils under storage conditions

Deterioration of electrical properties of mineral insulating oils during storage is one of the problem faced by electrical industry. In this study electrical and physical properties of insulating oils from paraffinic and napthenic crudes were monitored over a period of two years. Instrumental techniques were also used for evaluation of these oils. It has been observed that paraffinic based oils tend to deteriorate faster than naphthenic based oils while stored in drums. The deterioration is more when the oil is stored in drums than when it is stored in glass stoppered bottles. This may be attributed to the catalytic action of the drum material on paraffinic oils. Relatively higher proportions of sulphur and aromatic content found in the paraffinic oils, may be the cause for the faster rate of deterioration. Ionic impurities like sodium and iron found in these oils also contribute to the deterioration of electrical properties. Accelerated ageing studies also indicated similar trend in the oil deterioration.