INFLUENCE OF WATER, ELECTRIC FIELD AND IONIZING RADIATION ON ELECTRICAL PROPERITIES OF PVC INSULATIONS

摘要

The effects of water, electric field and high energy radiation exposure (γ-irradiation) on electrical and mechanical properties of poly(vinyl chloride) blended with fillers (plasticizer, lead stabilizer and mica) are presented. The present investigations were carried out on plate samples (disks), a part of them receiving radiation doses of maximum 160 kGy. Because mica plays a role of absorbent for hydrochloric acid formed by PVC degradation, favorable properties are obtained for dose up to 120 kGy. The volume resistivity decreases constantly while tan δ remains unchanged for a large frequency range (10~2-10~5 Hz). The increase in mica content of 14% induces a decrease of resistivity in unirradiated PVC of one order of magnitude. After irradiation at 160 kGy volume resistivity increases by about five times relative to 40 kGy irradiated samples. At 150 kGy tensile strength decreases only with 10%, and elongation at break presents a light modification in the selected dose range. At 40 kGy, when the degradation becomes relevant, the dipoles are not efficiently trapped by mica and the current does not attend a steady state for a long period (more than half an hour). Some considerations concerning the consequences of high energy exposure of poly(vinyl chloride) on electrical behaviour are presented. Water treeing tests (sample exposure to water and electric field) reveal no consistent difference in abosrption currents determined by mica content in PVC blends.