Space charge dynamics in lapped dielectric

The lapped dielectric which has superior electrical, mechanical and chemical properties has been used for HVDC cable insulation for many years. Space charge dynamics in such insulation have been studied in this paper. Three kinds of laboratory made samples with polypropylene and Kraft paper laminated have been investigated by the pulsed electroacoustic (PEA) technique under 5kV/mm up to 50kV/mm at room temperature. No charge injection was observed in polypropylene sample when stressed from 5kV/mm to10 kV/mm. The results of polypropylene lapped Kraft paper (PPLP) sample show that charge peaks at the two electrodes drop very quickly after applying voltage. At the same time, a large amount of charges accumulate at the interface area with the same polarity as the closed electrode. The other lapped sample with Kraft paper between two polypropylene layers was also studied at 5kV/mm. The opposite charge polarity peaks were found from the interfaces, suggesting that the ionization in Kraft paper may have a major influence on the electrical performance of the lapped dielectric.