The temperature dependence of space charge accumulation in cross-linked polyethylene

This paper presents the results of laser-induced-pressure-pulse (LIPP) measurements of space charge accumulation in 0.5 mm thick planar XLPE samples with aluminium electrodes, over the temperature range 30–90°C. The applied field strength was 10 kV mm−1. The increase in transit time of the pressure pulse across the sample with increasing temperature indicated that Young's modulus decreased by 50% from 30 to 90°C. It was concluded that electrons injected at the cathode are transported to the anode at temperatures above 40°C, and that electron traps cause an accumulation of negative charge immediately adjacent to both cathode and anode. It appears that a concentration of impurity molecules accumulates close to the cathode, and field-assisted thermal ionisation of these molecules generates an immobile positive space charge adjoining the electronic space charge adjacent to the cathode.