抄録
Polyvinyl chloride (PVC) is the most popular insulating material for electrical wiring instruments. The exothermic reaction at over 150°C may cause deterioration of insulating properties in the PVC. Therefore, it is important to clarify heat degradation in the PVC, not only to investigate ignition of electrical wiring instruments but also to use electric products safely. It is known that ultraviolet ray (UV) irradiation causes PVC chemical deterioration and the conductivity increases.
Generally it has been considered that the electrical breakdown property, electrical conduction and insulating performance are affected by the space charge accumulation in the insulation material. A high temperature pulsed electroacoustic (PEA) system up to 250°C has been developed, and the PEA system can measure the space charge distribution and conduction current in the high temperature, simultaneously. In this paper, the space charge distribution and conduction current have been measured up to electrical breakdown in the non-UV-irradiated sample (normal PVC), 353nm and 253nm UV-irradiated PVC sample in the range from room temperature to 200°C under DC electric field. In the short wavelength UV irradiated (253nm-300hour) PVC sample, the deterioration of breakdown strength at 90 to 150°C, and the negative packet-like charges are observed at 60 to 100°C, the positive charge accumulated in front of both the anode and the cathode over 90°C, and electric field is higher near the cathode side because the amount of positive charge of cathode side is larger.