Variations of the dielectric and mechanical characteristics of the poly (vinyl chloride) film: Electric discharges in air

Abstract

AbstractOne of the principal reasons of the premature failure of the polyvinyl chloride electrical insulation is the action of the discharges in the air voids of the insulation. Therefore, investigation has been carried out of the changes of the dielectrical permittivity ε and the loss factor tan δ of a polyvinyl chloride (PVC) film, plastified by dibutyl phthalate, under the effect of the electrical discharges in the air. Since by the discharges in the presence of oxygen a vigorous formation of ozone takes place the changes of the above mentioned characteristics after the exposure of samples in the ozone have been investigated separately.It has been shown that under the effect of the electrical discharges in the air, the temperature dependences of ε and tan δ have changed essentially. ε is subjected to dispersion over the temperature range from 70 to 100°C; tan δ increases over the whole temperature range, the conductivity losses begin at lower temperatures, and the peak of dipole‐segment losses (DSL), which is strongly pronounced in the initial sample, is no more observed. This is due to the fact that under the effect of ozone and owing to the crosslinking of the polymer chains the peak of DSL is shifted to higher temperatures; as a result, both DSL and the conductivity losses are superimposed.The extension of the sample, leading to an additional orientation of macromolecules, weakens considerably the changes of the dielectrical characteristics due to the discharges.