中文摘要：

2008年中国南方地区遭受历史罕见的覆冰灾害，绝缘子在低温高湿环境下的覆冰闪络成为电力系统中的频发事故。基于低温下高锰酸钾溶液的冷凝实验可知，冰水相变过程中盐分会发生迁移，过冷却水的凝结由底层向表层逐步发展。洁净绝缘子盐分迁移实验表明，融冰水电导率接近于覆冰水电导率的1．5-2．5倍，冷凝速度愈慢，盐分迁移现象愈明显；表面污秽主要影响底层冰融冰水的电导率，而对表层冰的影响较小。由110kV全尺寸玻璃绝缘子覆冰闪络实验可知，污秽的存在会造成融冰路径的变化，底层冰由于具有较高的含盐量而首先融化，与洁净绝缘子相比，染污0．1mg／cm。的试品泄漏电流在20mA以上的维持时间提高了2．86倍。结果表明：冰水相变前盐分的迁移会改变冰层中的盐分分布状态，引起融冰过程中泄漏电流的升高，这是造成覆冰闪络电压降低的重要原因。

英文摘要：

Ice accumulation on insulators always happens in south China in the early spring. In the year 2008, Southern cities suffered from serious icing disaster, leading to great economic loss. Ice flashover is one of the most common accidents in the power grid. According to the potassium permanganate .solution freezing process, which only occurs before cooling water is totally frozen, the salt migration phenomena can be verified. Cooling droplet is freezing from the bottom surface to the top. Salt migration experiments of clean insulators show that melting water conductivity is 1.5-2.5 times higher than the original one, and ESDD （equivalent salt deposit density） has a greater impact on the bottom ice layer than on the top layer. Finally according to the ll0kV full-size insulator test, melting path is changed due to contamination, and leakage current is higher than 20mA in sample （ESDD= 0. lmg/cm2） lasting for 200 seconds, which is 2.86 times longer than the clean one. Conclusions can be drawn that salt distribution in solid ice layer is changed by salt migration during phase transition, leading to leakage current increase, and it is a critical reason for the reduction of ice flashover.