Part I of this paper presents a cylindrical two-layer insulation model and two methods (A and B) for determining the space charge density in the insulation (dual insulation) of dc cable joints. The method A is based on the material parameters (electrical conductivity and permittivity) and the method B - on electroacoustic pulses. The values of the electrical conductivity for different temperatures and electric fields are computed using some experimental results and equations specific to each material. The equations used to compute the electrical conductivity, the electrical field and the superficial space charge densities at the interfaces between the joint's insulation layers are also presented. Finally, the values and the variations of the electrical conductivity with the electric field and temperature are presented and analyzed.

Keywords: Dc cable joints, Cross-linked polyethylene, Ethylene-propylene rubber, Space charge, Electric field, Electrical conductivity.