Thermal ageing effect on the DC cable joints insulations

In this paper the influence of thermal ageing on the space charge accumulated at the interface XLPE/EPR and the electric field in a cylindrical model of a DC power cable joint is presented. The thermal ageing was performed on flat disks of XLPE, EPR and XLPE/EPR at 125 0C for 30, 60 and 90 days and the conductivity σ and electrical permittivity ε_r were measured. With the values of σ and ε_r the charge density accumulated at the XLPE/EPR interface and the electric field were calculated, for unaged and aged samples. The thermal ageing of the XLPE/EPR samples leads to a low drop of the charge density values, charge which causes a reduction of the electric field in XLPE and an enhancement of this in EPR.