Modification of dependence of DC insulation resistivity of low density polyethylene (LDPE) on temperature and electric field using inorganic additives

Abstract

One of the reasons which has hampered the use of polyethylene (PE) as an insulating material for HVDC cables is the inherent dependence of its dc insulation resistivity /spl rho//sub /spl nu// on temperature T and electric field E. The objectives of the present work are: (i) to investigate the possibility of modifying the dependence of the insulation resistivity /spl rho//sub /spl nu// of LDPE on temperature and electric field by doping LDPE with an inorganic additive, and (ii) to find a mathematical model representing that dependence. Measurements of de resistivity were made using relatively thick samples (/spl sim/2 mm) of undoped and doped LDPE at different electric fields ranging from 17 kV/mm to 33 kV/mm for temperatures from 50/spl deg/C to 80/spl deg/C. Results indicate that the use of the additive has a significant effect on the rate of decay of the insulation resistivity with temperature in the doped material. Based on these measurements, the dependence /spl rho//sub /spl nu//=f(E,T) was found to conform to the law /spl rho//sub /spl nu//=/spl rho//sub o/e/sup -[/spl alpha/*(E)T+/spl beta/*(E)]/. Nonlinear curve fitting was used to determine the coefficients /spl alpha/*(E) and /spl beta/*(E). It is concluded that use of additives to LDPE can be a promising method for manufacturing insulating materials for HVDC cables.