Effect of space charge in the aging law of cross-linked polyethylene materials for high voltage DC cables

With the development of high voltage DC (HVDC) transmission, considerably more attention has been paid to aging of the insulation. The inverse power law (IPL), which reflects the service endurance capability of insulation and is used to determine the test voltage for the prequalification and type tests [1], [2], is given as L = t E n, (1) where L and n are material constants, t is the time to failure at field E, and the aging parameter n is a constant.In this article the IPL exponents of XLPE for AC and one nano-filled XLPE and one XLPE for DC cable insulations are compared under AC and DC voltages. In addition, as a temperature gradient normally exists within a cable, the effect of a temperature gradient on the IPL is also investigated, and the space charge distribution for the various cases on the IPL exponent is discussed.