Investigation of conduction processes of γ-irradiated EPR insulation by conduction current and extended voltage response measurements

The γ-irradiation initiates several degradation mechanisms in insulating polymers, including cross-linking, chain scission, and oxidation, thereby degrading both the mechanical and electrical properties of the materials. Traditionally, the elongation properties are used to qualify the functionality of polymers in radiation environments; however, there is a growing need for non-destructive material testing. One of the substantial advantages of testing electrical properties is that they can be non-destructively measured. Therefore, the conductive properties of γ-irradiated EPR insulation were investigated in this study. The subject of the research, EPR-insulated cable samples, was investigated using current and extended voltage response (EVR) measurements. The samples were irradiated at a dose rate of 0.8 kGy/h. The total absorbed dose was 1.2 MGy. The results showed that the conductive current and the slope of decay voltage increased steadily with absorbed dose. The activation energies of conductivity increased from the initial 0.8 eV to 2 eV after the total dose. From the trap distribution data, the de-trapping rates were calculated for shallow and deep traps. The de-trapping rate showed a strong correlation with conductivity; however, the de-trapping rate was greater for shallow traps, indicating the dominant role of shallow traps in conduction.