Simulation of the electric field in high voltage direct current cables and the influence on the environment

High voltage direct current (HVDC) cable systems are used as long distance electric energy transport solutions, when HV powerlines are not applicable, e.g. in urban or offshore scenarios. The thermal material characteristics of the surrounding environment show an influence on the temperature distribution inside the cable insulation. With a constant applied voltage and due to a nonlinear electric conductivity of the cable insulation space charges accumulate inside the cable insulation. The nonlinear electric conductivity depends on the temperature and on the electric field, resulting in a stationary electric field inside the cable insulation depending on the material characteristics of the surrounding environment. Numerical simulations are used to solve the coupled electro-thermal field problem. Due to neglected insulation losses and different dimensions of the cable and the environment and thus, different spatial resolutions, the temperature and the electric field are computed in weakly coupled simulations. Simulation results show an increasing temperature gradient inside the cable insulation with increasing humidity and thus, with increasing thermal conductivity. With increasing humidity, the electric field increases at the sheath and decreases at the inner conductor of the cable. The change in the electric field contributes to an increased space charge density.