Effect of gamma radiation on the dielectric characteristics of insulators

Changes in the dielectric characteristics of electric insulators most frequently applied for heavy current and light current cables exposed to the effect of radioactive radiations of high energy have been investigated. During these tests PVC, polyethylene and rubber insulators were aged by intermittent irradiations at increasing doses. After each irradiation cycle the time dependence of the current flowing through the material, the changes in the dielectric loss factor and permittivity as a function of frequency, and the peak value of the recurring voltage were measured, then the complex permittivity and the dispersion factor were determined by calculation. Irradiation was carried out by means of a Co-60 gamma-radiation source. Also the structural causes of the changes in the individual dielectric factors have been analyzed. From the aspect of their resistance to radiation the investigated insulators can be qualified on the basis of their dielectric characteristics measurable without any destruction of the sample, as follows: rubber behaved well, polyethylene was acceptable and PVC had unfavourable properties. Though this order may be altered by taking into account U other parameters, it has been undoubtedly proved that the use of PVC-base insulators in case of radiation hazards were not advisable. (P.J.)