Sediment deposition model of grading electrode in water cooling circuit of HVDC converter valve

The converter valve is one of the core equipment in high-voltage direct current (HVDC) system, and the cooling system is often used for heat dissipation. However, the cooling system is the weakest component of converter valve, mainly contributed by grading electrode sediment. Here, an electrochemical-diffusion coupling model is built to investigate the sediment deposition behaviour of grading electrode, in which the electrode reaction, electric field, and the fluid flow field are considered. First, the deposition mechanism is investigated in terms of measured results and charged ions motion characteristic. Then, the electrochemical-diffusion coupling model is proposed to study the sediment deposition behaviour on the electrode surface. Results indicate that the maximum sediment thickness and concentration are occurred in the tip section of electrode surface. In addition, the proposed mode is verified by the actual measurement results, which achieved from different connecting way converter valve tower. It is proved that the simulated results has a good coincidence with measured results. Finally, the influence of potential level and temperature on the electrode grading deposition are discussed. Results indicated that the sediments is proportional to the voltage level. In addition, the temperature can promote the deposition rate.