| During the running of Electric Multiple Units(EMU),the composite insulators on the roof of EMU suffer from the effect of high-speed airflow,and the dirty particles in the air collide and deposit on the surface of the insulators forming a pollution layer,and it can cause local electric arc or abnormal flashover of insulator in areas with high leakage current density when the pollution layer is damp.Therefore,it is very important to analyze the contamination accumulation characteristics,flashover characteristics and optimize the electrode structure of the composite insulators to ensure the EMU running on time.Investigating the spatial distribution characteristics of sand particles along the Lanzhou-Xinjiang high-speed railway,the insulator A with the largest value of umbrella outstretched is selected as the object in the four insulators A,B,C and D,to carried out insulators contamination test in the closed high-speed wind tunnel,FLUENT software is used to simulate and analyze the airflow field around the insulator,and explain the results of the contamination test.The results show that the contamination density on the surface of the insulator is uneven,the contamination density on the Leeward side is much higher than that on the crosswind and windward side,and the contamination density on the upper surface is much higher than that on the lower surface.The contamination density on the insulator surface tends to saturation when the pollution time reaches 24 h.The contamination density on Leeward side is higher than that on windward side and crosswind side because of vortex phenomenon and negative pressure area on Leeward side of insulator which is favorable for the adsorption and deposition of dirty particles.The flashover voltage of insulators is obtained by means of continuous voltage boosting method in this paper,and the influence of equivalent salt density on flashover characteristics of insulators is compared and analyzed.The test results show that the pollution flashover voltage of the same type of composite insulator decreases with the increase of the equivalent salt density,and the flashover voltage of composite insulators D is the highest at the same contamination density.After several flashover tests,the insulation sheath on the side of high-voltage metal of insulator D was punctured,and the puncture-hole was approximately circular.It is concluded that there is an air gap between the metal and the sheath which distorts the electric field lead to the insulation sheath was punctured.There is a local tip at the junction of insulator and pantograph frame,which will lead to the local electric field concentration.In order to improve the distribution of electric field on the high-voltage side,three types of equalizing shielding devices are designed in this article,it is found that the electric field at the top of the insulator decreases with the increase of the cover depth,but the change of the shield radius has little effect on the distribution of electricfield near the insulator.At the same time,the shielding device will affect the airflow field near the top of the insulator,so that the velocity distribution,the position and the size of the vortex phenomenon will change.The different sizes of shielding devices are made based on the analysis of the electric field and the characteristics of the airflow field,and the flashover voltage and lightning impulse voltage are obtained when the shielding devices are added.the results show that the parameters of shielding device are limited by the withstand voltage in TB/T 3077-2017.Considering the electric field distribution,airflow field characteristics and experimental verification,the type and parameters of the equalizing shield device are recommended.The research content can provide certain reference for the following test appraise and engineering application. |
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