Studies on static charging behaviour of transformer oils

Investigations on paraffinic oils are presented. Charge level measurements on a few paraffinic-based oils and a typical naphthenic-based oil are discussed. Most paraffinic oils were found to have high charge levels, which was attributed to higher ionic contamination and dominant chemical structure. While a charge suppressor reduced the charge levels of high charging oils, it had an adverse effect on other dielectric properties. However, its presence retarded ageing. Paraffinic oils from service transformers showed a significant deterioration in these properties compared to naphthenic oils