Research on Mechanism and Suppression of Sediment Deposition on Grading Electrodes in Cooling Water Dielectric of HV Converter Valve

The alumina sediment deposited on platinum grading electrodes in the inner cooling system of high voltage converter valve has been proved to be the cause of many operational accidents. To make clear the formation mechanisms of deposited sediment in water dielectric, a simulated setup referring to the inner cooling system was first established. The deposition processes on both anode and cathode electrodes were compared. An electrochemical anti-deposition device, as a measure of the suppression sediment deposition on the grading electrodes, was also designed, based on the similar principle of deposition mechanism on the grading electrodes. The feasibility study of this anti-deposition device was carried out further. In cooing water dielectric, the acidic or basic aluminates, as the source of the alumina sediment, will migrate toward the cathode or anode electrodes under the electric field, and finally deposit on the electrode surface through two stages -of the initial formation and the growth. As for this anti-deposition device, the most important operating parameters are included in the current density and water flow rate near the surface of plate electrodes.