ABSTRACT

Insulating liquids are broadly classified as organic, mineral or synthetic. Organic oils started in use late in the nineteenth century, whereas mineral oils were introduced in about 1910 with the development of petroleum refineries. Synthetic liquids with a wide spectrum of properties started to be developed by the petrochemical industry in about 1960. Oil of the naphthenic group has traditionally been favored for impregnating paper to be used in insulating high-voltage (HV) and extra high voltage (EHV) cables, because of its good gas-absorbing properties. The synthetic oils commercially known as askarels are manufactured by chlorinating polychlorobiphenyls (PCBs), aromatic hydrocarbons available as byproducts in some petrochemical industries. The molecules of silicon oils contain silicon and oxygen atoms in addition to their many carbon and hydrogen atoms. Electrical properties include the electrical conductivity of the oil, its permittivity, dissipation factor, and dielectric strength.