Experimental investigation of iso-paraffinic oil for application in high voltage power transformers

Accelerated industrial growth with the increasing demand of electrification is leading to optimization and often overstressing the available resources in electrical power network. Power transformers are the critical, the most expensive and highly stressed components in power network. Needless to mention, substantial efforts are being made to improve reliability and service life of the transformers. Invariably, insulating oil and oil impregnated paper insulation system is the preferred choice for transformer design. During the service life of the transformer, thermo-electric and chemical stresses as result of the process called ageing results in undesirable changes in physical, chemical and electrical properties of insulating oil. Ageing of the insulation system is a cumulative process and seriously affects reliability and useful life of the transformer. Amongst the available choices of insulating oils, iso-paraffinic oil is gaining popularity on account of being virtually free from sulfur, higher oxidation stability and better thermal conductivity as compared to naphthenic oils. Extensive experimental evaluations have been done to establish the comparisons with available oils. This contribution is discussed on results of long term accelerated ageing for 1000 hours of oxidation stability, open beaker ageing and rotating bomb oxidation stability, corrosive sulfur tests and laboratory ageing results of oils with respect to dissolved gas analysis (DGA), degree of polymerization (DP), and furan. Several diagnostics properties like dissipation factor, electrical resistivity, total acidity, sludge content sulphur and oxidation inhibitor depletion are reported with discussion.