Study On AC Flashover Performance And Mechanism Of Composite Insulation In Contamination And Wet Conditions

A composite insulator has advantages of less weight, higher strength, more excellent anti-contaminated characteristic, easier to produce and maintain. Therefore, the composite insulator is widely used by power utilities in many countries. However, as more and more composite insulators are putted into service, kinds of a composite insulator fault were emerged, especially un-certained-reason fault. These problems have been paid highly attention.Aimed at the problems of composites in operation, in the paper the AC flashover characteristic of clean or polluted composite insulators under the contamination and wetting condition, including acid fog, salt fog and icing, is researched by test. Moreover, the AC flashover mechanism of composite insulators under the different polluted-wet precipitation is analyzed.It is elicited by a large of tests that: the polarity effect of the composite insulators' AC flashover characteristic is not obvious. The flashover voltage of polluted composite insulators is decreased with increase of SDD and the fog conductivity in acid fog and salt fog. When SDD is greater than 0.3 mg/cm2, the flashover voltage is decreased slowly with increase of the fog conductivity. And when the fog conductivity is less than 1500 μS/cm, SDD is less than 0.5 mg/cm2, the flashover voltage of 10kV polluted composite insulators is greater than 15kV in acid fog or salt fog. Therefore, it is put forward that polluted composite insulators can not be flashover under normal operation voltage. The AC flashover mechanism of composite insulators is analyzed through the process of the arc produce and development under acid fog, salt fog and icing condition. It is analyzed the effect of acid fog and salt fog on the hydrophobicity on the surface of composite insulators and put forward that the hydrophobicity of composite insulators is decreased because of "salt" reaction in salt fog, while in acid fog the low molecular weight which caused by "special-rupture" reaction can not be vanished. When the fog conductivity is less than 1500 μS/cm, the flashover voltage of clean or polluted composite insulators in salt fog is greater than that in acid fog.The flashover process of icing composite insulators under there kinds of icing states is analyzed. The AC flashover mechanism of icing composite insulators is put forward for the first and it is elicited that the flashover voltage of composite insulators is relation with the icing state. When there is no icicle on the edge of skirts, the process of icingcomposite insulators is the same as the polluted composite insulators and icing can be look as a special kind of contamination. When there are icicles on the skirts but icicles are not bridge the skirts, the icing flashover voltage is relation with the length of icicles. When the shortest distance between the top of icicles and the surface of skirts is longer, the icing flashover voltage is more higher. When the icicles is bridge the skirts, the icing flashover voltage is lowest in all icing states. In this condition, the air gap length between the icicle's top of the downmost skirt and high-voltage electrode determines the flashover voltage. Despite of the icing states, the lowest AC flashover voltage of icing composite insulators is decreased with the increase of icing weight and decreased with the increase of icing water conductivity. Icing weight and icing water conductivity are the two independent parameters which affect on the lowest AC flashover voltage of icing composite insulators. Moreover, the revise methods and formulae of the lowest AC flashover voltage of icing composite insulators have been given. Moreover, It is elicited through the test results that under icing condition the hydrophobicity of composite insulators is decreased, even lost, because of the function of icing and little arc. The effect of circumstance on the AC flashover characteristic and mechanism of clean or polluted composite insulators under the contamination and wetting condition, including acid fog, salt fog and icing, is gre...