Influence of FGM layer on the distribution of the electric field in DC cable joints insulations

This paper presents the results of a study regarding the influence of a Field Grading Material (FGM) on the electric field and temperature distributions in the insulations of a power cable joint model. The computation was performed at steady state for a cable joint insulation consisting of Ethylene Propylene Rubber (EPR) installed for a cable with Cross-linked Polyethylene (XLPE) insulation. The presence of the FGM layer leads to important modifications of the electric field values, especially near the corners of the cable joint inner semiconductive layer. The results also show that the maximum electric field and temperature values, as well as the surface charge density values present at the interface between the insulations are lowered by using a FGM layer. This leads to reduced electric stresses and charge injection. The reduction of the surface charge density values also reduces the values of the residual electric field and leads to a slowdown of insulation ageing.