Effect of Impurities on Dissipation Factor of Oil-Impregnated Synthetic Paper

The dielectric loss behavior of lapped dodecylbenzene-impregnated poly (2, 6-diphenyl-1, 4-phenylene oxide) paper insulation has been investigated. It was found that when this composite system is subjected to ac stress, some shoulders are observed in the curve obtained by plotting dissipation factor as a function of measuring stress. After chemical analysis of the impurities involved and after some calculations using Held´s equations, it was found that the shoulder located at 0.1 kV/mm is associated with ionic motion in the liquid layer between paper sheets while the other at 1.2 kV/mm corresponds to ionic motion in the channel enclosed within the paper sheet itself. Furthermore, the dielectric deterioration of a model cable by ac stress application at elevated temperature is thought to result from the increase in ionic motion in the butt gaps. A nitrogen-containing compound is considered to be the source of these ions. These observations suggest that exhaustive removal of ionic impurities is essential for a successful operation of an oil impregnated synthetic polymer paper insulation.