Estimating aging parameter of XLPE and its nanocomposites under AC voltage using step-stress test

Our previous studies showed that the aging parameter, i.e. the n-value, of XLPE was quite different from that of XLPE nanocomposites. In order to investigate the effects of space charge on aging parameter under DC voltage, the n-values of XLPE and its nanocomposites were measured under AC voltage in this report, because few space charge exits in the sample under AC voltage. Step-stress tests were carried out under AC voltage to measure the n-value. The results showed that the aging parameters of XLPE and its nanocomposites under AC voltage were close, i.e. 7.3 and 6.6, respectively. This suggests that space charge accumulation plays an important role in DC aging.

I. Introduction

The influence of space charge on the performance of polymeric insulation, such as cross-linked polyethylene (XLPE), especially under DC fields, has been well recognized [1]–[3]. However, comparing to the condition of AC voltage, the lifetime of XLPE and its nanocomposites under DC voltage has not been well studied. The existence of space charge in DC cable leads to field distortion and accelerated aging [4]–[6]. The local field value may control the carrier generation or field-induced electromechanical deformation [7]–[11]. The local charge densities will change the energy barrier to ageing of those polymer moieties where the charge is trapped and will also determine the recombination rate between positive and negative charge that could control chemical degradation [12]–[13].