The insulator contamination cleaning has a great significance for maintaining the external insulation of power equipment. Aiming at the deficiency of existing contamination cleaning method and the advocate of water saving

the way of hot cleaning the insulator contamination by water vapor is proposed. In this paper

the power system’s security problems which are met when hot water vapor washing the insulator contamination are studied. The flashover voltage of polluted insulator strings in the case of washed by high pressure water vapor or wetted by high temperature water vapor or room temperature water fog is measured. The three different cases simulate the water vapor column washing insulator with no spreading flakes and the spreading flakes of water vapor column wetting the insulator contamination respectively. The average flashover voltage curves of insulator strings in three different cases relate the average voltage to the ESDD. The results show that the average voltage of insulator strings washed by high pressure water vapor is higher than the 35 kV single-phase system highest operation voltage even if the insulator with heavy pollution. The system security can be ensured with overvoltage not appearing. The spreading flakes of water vapor column which decrease the insulator strings flashover voltage should be reduced by choosing proper nozzle and regulating washing distance in field hot cleaning.