Salt Migration Phenomena During Phase Transition in Cooling Water and Its Impact on Leakage Current

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 110kV full-size insulator test,melting path is changed due to contamination,and leakage current is higher than 20mA in sample(ESDD= 0.1mg/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.