Stray-current corrosion of aluminum heat sinks in different inner water cooling systems for HV converter valves

The corrosion of aluminum heat sinks has been proved to be the leading cause of many operation problems in the inner cooling system of HV converter valves. The distribution of the electrolytic current through the full-aluminum heat sink or the heat sink embedded with annular electrodes is revealed by the simulating calculation. Two experimental setups of simulated cooling systems were established. Corrosion tests with aluminum flake samples and stainless steel flake samples were carried out in the simulated field conditions. The simulating calculation results reveal that the 3.7-mm-wide area near the inlet/outlet of the full-aluminum heat sink or the inner surface of the stainless steel electrode collects the majority of the electrolytic current. Corrosion tests prove the occurrence of stray-current corrosion in the full-aluminum heat sinks at high electric potentials. Further calculation indicates that 95 percent of the anodic current has contributed to the stray-current corrosion. Yet in the heat sink embedded with stainless steel electrodes, the electrolytic current has not led to stray-current corrosion whether in the aluminum substrate or in the electrodes.