Change in PD resistance of polymer insulating materials irradiated with γ-ray at high dose rate

In this paper, the change in partial discharge resistance of low density polyethylene and epoxy resin irradiated with γ-ray at high dose rate has been investigated. The samples were irradiated in air up to 100 kGy then up to 1000 kGy by means of a ⁶⁰Co γ-source at a dose rate of 10 kGy/h. By applying an AC voltage of 8 kHz between a pair of needle-plane electrode, partial discharge was generated to degrade the samples. The erosion profile was measured and the maximum value of the erosion depth was employed to evaluate the resistance to partial discharge of the samples. Dielectric spectrum, Fourier transform infrared spectrum, differential scanning calorimetry and gel fraction measurement were performed to analyze the change in the material structure caused by the irradiation. Obtained results show that the change in partial discharge resistance is dependent upon the total dose of irradiation and is varied with the material. It is proposed that the partial discharge resistance is related to the material structure which is altered by the irradiation induced chemical reactions.