Effect of Low Frequency Electrical Aging on Conductive Current Characteristics of Cross-Linked Polyethylene Films

With the construction of offshore wind power projects, cross-linked polyethylene (XLPE) submarine cables are gradually applied to low frequency power transmission. However, the electrical aging characteristics and mechanisms of XLPE at low frequency remain unclear. In order to study the effect of low frequency electrical aging on the electrical conductivity current characteristics of XLPE and its difference from power frequency electrical aging, accelerated electrical aging experiment of XLPE films are conducted under applied AC voltage of 20 Hz and 50 Hz. The electrical conductivity current characteristics of XLPE films are measured at different electric field strengths after 3, 6 and 9 days of electrical aging. The results show that the conductive currents of XLPE increased with the growth of accelerated electrical aging time at both low frequency and power frequency. The conductivity current increases from 6 pA to 147 pA after 9 d of aging at power frequency, and from 6 pA to 307 pA at low frequency. The conductive current increases more at low frequency than at power frequency, the 20 Hz conductivity current is 80%, 63% and 52% higher than the 50 Hz conductivity current at 3 d, 6 d and 9 d aging, respectively. In addition, the electric field remains above the charge injection threshold for a longer period of time in a single cycle at low frequency, so the low frequency voltage enhances the charge carrier mobility and space charge trapping probability in the insulating medium, generating more thermionic and causing more polymer chain breaks, resulting in higher conductivity currents under low frequency aging compared with power frequency.