The Corrosion Mechanism of the Aluminum Heat Sink in HVDC Valves is Found

The corrosion of the aluminum heat sinks (AHSs) and the deposition on the surface of the grading electrodes (GEs) in the converter valves seriously threaten the safe and stable operation of the HVDC transmission system. But the corrosion mechanism is not clear so far. The corrosion mechanism of the AHSs is studied and the suppression measures are proposed in this manuscript. Based on a 3-D quasi-static electric field analysis model, the leakage currents in branch pipes (LCBPs) are studied. The conductance matrix can be used to express the contributions of AHSs to the LCBP concerned. The corrosion mechanism of the AHSs stimulated by the electric stress is determined. Concentrated distribution of electric field around the GEs leads to the LCBPs. The LCBPs are the cause of the AHSs corrosion. The effect of four different layout schemes of GEs on the LCBPs is studied at the same conductivity. The efficiency of the optimal layout scheme for suppression of corrosion is up to 98.46% relative to that of the existed layout scheme in actual operating converter valves.