Analysis of Electric Field and Surface Discharge in Liquid-Solid Insulation System for HVDC Components

High Voltage Direct Current (HVDC) links make it possible to transmit energy for long distances with lower losses. The development of more reliable insulation systems for HVDC components cannot be achieved without understanding the mechanisms of discharge inception and propagation, not only under HVDC constraints, but also under particular conditions such as HVDC superimposed lightning impulse. In this work, the behavior of liquid-solid insulation system under HVDC superimposed lightning impulse is investigated using finite elements based numerical simulation. The simulation combines the quasi-electrostatic model for interface charge accumulation during the DC phase, and the electrohydrodynamic drift-diffusion model for surface discharge propagation during the lightning impulse phase. The results show that the positive charges accumulated on the interface under positive HVDC voltage reduce the electric field intensity in the liquid. As a consequence, it affects the discharge inception and propagation.