Effects of low electric current in deionized water dielectric on corrosion of aluminum heat sinks in HV converter valves

The deionized water dielectric is widely used as the cooling medium of the inner cooling system for HV converter valves. Theoretically, the electrolytic current in the cooling water is considered as one of the predominant causes of the corrosion of the aluminum heat sinks. The distribution of the electrolytic current inside the heat sink is revealed by simulating calculation. Corrosion tests with aluminum flake samples in simulated field conditions were conducted. The simulation results show that the electric field distortion around the grading electrode is the leading cause of the electrolytic current through the heat sink. The electrolytic current up to 10.82 μA are mainly collected by the 3.7-mm-wide area near the water inlet/outlet of the heat sink. Corrosion tests indicate that the electrolytic current has aggravated the corrosion of the heat sink in different ways. In the presence of anodic current, pit corrosion is observed due to stray-current corrosion. Whereas when cathodic current conducts through the heat sink, general corrosion occurs as a result of the aggregation of hydroxide ion. Further calculation reveals that over 95 percent of the anodic electrolytic current has contributed to the stray-current corrosion of the heat sink.