Study On Wetting Characteristics And Mechanism Of Contaminated Composite Insulators

The wetting degree of composite insulators is closely related to external insulation ability and anti-pollution flashover performance.However,the wetting characteristics and mechanism of composite insulators are still unclear.In view of the unique hydrophobicity of composite insulators,this paper systematically studies the pollution wetting test and condensation wetting model of different hydrophobic composite insulators.The main contents are as follows:?1?In this paper,the local electrical conductivity?₂₀,which can be obtained through the phase angle difference between the voltage and current of insulator surface contamination layer,is used to characterize the wetting degree of insulator contaminated layer.Based on the self-made wetting detection device of phase angle difference-electrical conductivity in artificial climate chamber,a wetting test system for contaminated composite insulators was established.?2?A hydrophobicity identification method for composite insulators based on image processing and features selection is proposed.The hydrophobicity images were obtained based on the spray method.Seven geometric features were extracted for the identification of hydrophobicity class?HC?of insulators.By optimizing the features,the features with good correlation with hydrophobic class are obtained as the joint criterion.The accuracy of this method is 98.1%and 95.2%by comparing the recognition results with the spray method and the contact angle method.?3?The influence factors of wetness of composite insulators'contaminated layer were studied.The wetting test of composite insulators was carried out in artificial contamination laboratory.The effects of hydrophobicity on the saturation wetting time of surface contamination,start-up time of local electrical conductivity and the maximum local electrical conductivity,as well as the effects of steam mist velocity,temperature difference,wind speed and insulator material on different hydrophobicity composite insulators were systematically and thoroughly studied.The results show that the hydrophobicity of the surface contaminated layer has a significant effect on the saturation wetting time,start-up time of local electrical conductivity and the maximum local electrical conductivity.The increase of steam mist velocity and temperature difference can obviously accelerate the wetting speed of the contaminated layer,but has little effect on the maximum local electrical conductivity.Wind speed can accelerate the moisture velocity on the upper surface of windward side and increase the maximum local surface conductivity of the polluted layer on the surface of strong hydrophobic insulators.However,the existence of wind speed weakens the moisture velocity on the lower surface of the leeward side.For the three kinds of insulators with the same hydrophobicity class as HC7,the wetting speed from fast to slow is ceramic insulator,glass insulator and composite insulator.And the spray test is designed to prove this phenomenon.?4?The condensation wetting model of the conanminated layer of composite insulators is established.A dynamic model of the contact angle and radius of the water droplets on the surface of the conanminated layer varying with the wetting time is established by using the four thermal resistance model,and the change model of the condensation rate and the number of the water droplets is solved.By comparing the measured cumulative water volume with the theoretical calculated value,it is found that the error of the model is less than 20%.The model further improves the theory of wetness of contaminated layer,and has certain guiding significance for further exploring the mechanism of wetness of contaminated layer on composite insulator surface.