Study On The Characteristics Of Air Flow Distribution And Sheath Surface Pollution Distribution Of EMU Roof Insulators

The roof insulators of high-speed trains experience multiple meteorological zones in a short period of time,which makes the surface contamination distribution of the roof insulators more complicated,and its insulation performance is facing a severe test.In this thesis,the combination of simulation and experiment is used to analyze the airflow distribution and surface contamination distribution around single、double insulators.Based on this,the pollution flashover test is carried out,and the influence of uneven contamination on the flashover voltage of single and double insulators is discussed.Finally,in order to reduce the pollution of insulator surface and increase the flashover voltage of insulator,an elliptical insulator model was optimized based on the principle of fluid mechanics.The main research contents and conclusions of this thesis are as follows:Fluent was used to simulate the airflow field of single / double insulators with different spacing and different windward angles,and the airflow velocity distribution around the insulator was analyzed.The results show that the greater the forward flow velocity,the greater the velocity and pressure around the insulator,and the higher the negative pressure value,but the trend of airflow velocity is basically the same.When the insulators are in parallel,the influence of the upstream insulator on the downstream insulator is mainly divided into three types: the first is vortex collision interference,which mainly exists when the spacing and the windward angle are small.Due to the vortex of the upstream insulator,it directly collides with the windward surface of the downstream insulator,so that the pressure at the stagnation point of the windward surface of the downstream insulator decreases and the pressure stagnation point moves backward.The other two are wake interference and adjacent interference,mainly due to the increase of the windward angle,the emergence of the gap flow causes the wake of the upstream insulation to be squeezed to one side,making the velocity and pressure inside and outside the downstream insulator asymmetric.The above three kinds of interference will gradually weaken with the increase of spacing and windward angle,and finally show the state of single flow.The Euler two-phase flow is used to carry out the simulation of single / double insulator contamination,and it is verified by artificial wind tunnel test.The results show that the contamination on the surface of the insulator is unevenly distributed under high-speed airflow.The windward sheath edge,the windward cylinder and the leeward side are heavy pollution areas.There is a clear boundary between the leeward side and the crosswind side,which is related to the boundary layer separation.When the double insulators are in series,the leeward surface area of the downstream insulator is relatively small.When the windward angle increases,the leeward surface area gradually increases to be consistent with the upstream insulator.Through the boundary layer separation angle and the circumferential angle corresponding to the lowest point of pressure,a method for calculating the proportion of leeward surface area based on two angles is proposed.Through experimental verification,the relative error is between-8.1 % and 8.7%,indicating that the method has certain reliability.Based on the results of pollution simulation and wind tunnel test,the non-uniform pollution flashover test of insulators is carried out in the artificial climate chamber.The results show that when the pollution of a single insulator is not evenly distributed,the flashover voltage is significantly reduced,and the reduction range is up to 17.57 %.With the increase of the proportion of leeward surface area,the pollution flashover voltage of insulators also increases.When the insulators are connected in parallel,the pollution flashover voltage of the pollution uneven distribution is slightly lower than that of the uniform pollution,and the reduction range is between 1.4 % and 6.9 %.When flashover occurs,the flashover path always appears on the leeward side,and there is a more obvious dry area on the leeward side of the cylinder after flashover,which is obviously different from the annular dry area formed by uniform pollution.In order to reduce the leeward area pollution,an elliptical insulator with variable curvature is optimized and designed,and three parameter combinations are proposed based on the existing insulators.The strength of the insulator rod is briefly checked,and the suitable rod parameter combination is selected.The effectiveness of delaying the boundary layer separation,reducing the area of the contamination area and reducing the contamination is verified by simulation.Through 3D printing technology,the original insulator and optimal elliptical insulator models were made in a 1:2 ratio,and wind tunnel fouling tests and rain flashover tests were conducted to verify that the optimized elliptical insulator model can reduce the pollution on the leeward area of the insulator while still maintaining good electrical performance.The results of this paper can provide reference for the layout of high-voltage equipment on the roof of high-speed trains,as well as reducing the surface pollution of insulators and improving the pollution flashover performance of insulators.