Research On The Influence Of Air Gap Between Layers On The Insulation Performance Of Vehicle Mounted High Voltage Cable Terminals

With the increasing speed and passenger capacity of EMU,the explosion accident of vehicle terminal occurs constantly,which seriously affects the reliability of power supply system in EMU and poses a serious threat to safe operation.In order to avoid the insulation failure of on-board terminal under the influence of large external temperature difference,thus affecting the safe driving of EMU.In this paper,the mechanism of the effect of air gap between the lower layers on the insulation performance of vehicle terminals is studied.In this paper,the characteristics of the heat shrinkable cable terminal,the cold shrinkable cable terminal and the prefabricated cable terminal are compared and analyzed.The structure and function of each composite layer inside the heat shrinkable vehicle terminal that needs to be studied in this paper are explained.The insulation condition of each layer of the vehicle terminal that has insulation fault is dissected and observed layer by layer,and then the reason of the fault is analyzed.At the same time,the insulating material samples of the inner composite layer were extracted,and the relative permittivity,conductivity,Young’s modulus and other material parameters of the samples were measured by Wide-Band dielectric impedance spectrometer and microcomputer controlled electronic universal testing machine.Based on the theory of electromagnetics and thermodynamics,a simulation model of the coupling of electric thermal force multi physical field of the vehicle terminal is established.The internal stress distribution of the terminal under different current carrying and different ambient temperature is explored.The difference of the internal electric field distribution of the terminal under normal and air gap conditions is analyzed.The influence of different air gap sizes on the internal temperature field and electric field of the terminal is studied.The PD test platform of high and low temperature vehicle terminal is built,and the PD characteristics of vehicle terminal under different temperature gradients are explored.The maximum discharge quantity,average discharge quantity,discharge times per second,discharge power and discharge phase interval are obtained.and the failure mechanism of insulation breakdown of vehicle terminal is analyzed.The defect model of double dielectric air gap is made.The influence of different air gap sizes on the partial discharge characteristics is studied by extracting the characteristic parameters such as the maximum discharge quantity,the average discharge quantity and the discharge phase interval.