Estimating the aging parameter of XLPE and its nanocomposites under temperature gradient

The aging parameter n can reflect the aging property of material to some degree and determine the test voltage of the type test and prequalification test of HVDC cables. However, the aging parameter has rarely been studied systematically, especially under temperature gradient. In this paper, step-stress test was carried out to estimate the ageing parameter n of two materials, XLPE and its nanocomposites under temperature gradient. A new method based on the cumulative damage has been used to obtain the ageing parameters, which can fully take the consideration of the voltage procedure and avoid the errors brought by the approximation. Aging parameters of XLPE and its nanocomposite under temperature gradient ΔT =0, 20, 40°C are 13, 15.4, 17.7 and 8.6, 9.4, 10, respectively. The aging parameter n reduces when nano-fillers are introduced into XLPE. As XLPE nonocomposites can depress space charge availably, the larger aging parameter n of XLPE may be explained in terms of space charge effect and thus more severe field distortion at higher DC voltage. It is also suggested that the electrostatic force induced by space charge can contribute to material aging.