Numerical calculation of current through grading electrodes in inner cooling circuit of HV converter valve

Inorganic sediments deposited on the pin-type grading electrodes in the inner cooling water circuits would affect the normal operation of high voltage (HV) converter valves, which may be caused by the current through the grading electrodes. The distributions of the current through the electrodes in two different converter valves are calculated using the finite element method (FEM) software in this paper. The relationship between the thickness of the sediment on the grading electrodes and the DC current through the electrodes is analyzed. The distributions of current density on the electrodes are compared with the morphology of deposited sediments on the corresponding electrodes. The leakage current through the aluminum radiators from the distributed water circuit is calculated. The results indicate that the sediment deposition is mainly caused by the DC current through the pin-type grading electrode. The sediment thickness has a positive correlation with the magnitude of the DC current. The leakage current through the radiators from distributed water circuit may cause electrochemical corrosion which could generate the source of the sediments.