换流阀内水冷系统泄漏电流对散热器腐蚀的影响

换流阀内冷却系统中散热器的腐蚀会导致均压电极结垢并引发漏水和散热失灵等事故,严重威胁高压直流输电系统的安全可靠运行。为了研究水路泄漏电流对铝散热器腐蚀的影响,搭建了由实际散热器组成的模拟阀冷平台,并模拟现场条件进行了运行试验;然后在隔离水箱中进行了铝片试样的电解腐蚀试验,利用失重法和显微观测等手段分析了阴、阳极试样的腐蚀量和腐蚀形貌。结果表明,冷却水路泄漏电流是导致或加剧散热器腐蚀的主导因素,且引起的腐蚀量在散热器腐蚀总量所占比重随着运行时间增加而增加。泄漏电流对同一阀段中不同电位处散热器腐蚀的影响机理存在差异:阀段高电位处散热器只受到阳极泄漏电流的影响,发生具有点蚀形貌特征的杂散电流腐蚀;而低电位处散热器则在阴极泄漏电流作用下,发生具有均匀腐蚀形貌特征的碱性腐蚀。

Influence of Leakage Currents on Corrosion of Heat Sinks in Inner Water Cooling System for Converter Valve

The corrosion of the heat sinks in inner cooling system of the converter valve will lead to the scaling of the equalizing electrodes,water leakage and heat loss failure,which will seriously threaten the safe and reliable operation of the HVDC system.In order to study the effects of leakage currents in cooling water on the corrosion of heat sinks,a simulated valve cooling system with real heat sinks was established in laboratory,and operating experiments were conducted under field conditions.Besides,electrolytic corrosion experiments with aluminum sheets were conducted in separated water cells.The corrosion amount and morphology of negative and anode samples were analyzed by means of weight loss and microscopic observation.Results show that the leakage currents play a leading role in inducing or promoting the corrosion of aluminum heat sinks.And the proportion of the corrosion caused by the leakage current in the total corrosion of the heat sink will increase with the running time.Corrosion of heat sinks within a valve section will be affected by the leakage currents in two different ways:the anodic leakage currents from aluminum to water will induce stray-current corrosion with a pitting morphology in heat sinks at high electric potentials,while the leakage currents in the opposite direction will induce alkaline corrosion characterized with a uniform morphology in heat sinks at low electric potentials.