Journal of Thermal Analysis, Vol. 50 (1997) 19-31 Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday THE TEMPERATURE DEPENDENCE OF SPACE CHARGE ACCUMULATION IN CROSS-LINKED POLYETHYLENE K. R. Bambery and R. J. Fleming Department of Physics, Monash University, Clayton, Victoria 3168, Australia Abstract 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~ The applied field strength was 10 kV mm q. 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~ It was concluded that electrons in- j ected at the cathode are transported to the anode at temperatures above 40~ and that electron traps cause an accumulation of negative charge immediately adjacent to both cathode and an- ode. 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. Keywords: LIPP, polyethylene, space charge Introduction The accumulation of space charge in the insulation of electrical power distri- bution cables, during service lifetime, is a major cause of premature cable fail- ure. High electric field stress tests have shown that space charge can increase the electric field strength at the insulator/conductor interface sufficiently to lower the impulse breakdown field strength of the insulator [ 1-5]. Furthermore, high densities of charge, either trapped or in transit, may lead to an increased rate of electrical tree formation, resulting in cable damage and eventually electrical breakdown. Medium voltage XLPE underground power cables are usually designed to operate at temperatures up to 90~ Increased conduction currents, indicative of increased charge mobility in the bulk and/or increased injection levels, are ob- served at elevated temperatures in thin films of low density polyethylene (LDPE) and cross-linked polyethylene (XLPE), two materials widely used as in- 0368-4466/97/$ 5. O0 9 1997 Akad~miai Kiad6, Budapest John Wiley & Sons Limited Chichester