Electrical Conduction in Medium Viscosity Oil-Paper Films - Part I

The dielectric response of a pipe-type cable insulating oil film has been examined as a function of film thickness in the temperature range from 25 to 85°C at frequencies down to 10-2 Hz. Oil films, having thicknesses of 1-12 mil, were investigated. With films thicker than 6 mil, the dielectric behavior approached that of the oil in bulk form and the long-range charge-carrier migration process was characterized by activation energies lying between 0.72 and 0.85 eV. Reductions in oil-film thickness gave rise to spacecharge effects, which tended to decrease the apparent activation energy; values between 0.57 and 0.63 eV were found to be typical of a 2.5-mil film. The determined activation energies for dc conduction in the respective oil films showed in general a striking agreement with ac values. The involvement of hydrogen ions in the conduction process was suggested.