In order to exercise control on the maximal intensity of electric field for the pantograph post insulators and fittings surface on high-speed trains, the finite element software COMSOL was applied to analyze the electric field distribution of post insulators in the presence and absence of the grading ring. According to the simulation results, the depth and degree of grading ring are the significant influencing factors in the distribution of electric field along the insulator surface and the surrounding air area. Based on these simulation results, the solid model was processed and the lightning impulse flashover voltage test was carried out. As indicated by the test results, the permissible lightning impulse voltage of 50% negative polarity exhibited a linear relationship with the depth value, while 50% of the permissible lightning impulse voltage generated with the addition of grading ring cover that was 70mm in depth satisfied the requirement of 170kV as specified in OV4 standard. Based on the results of simulation analysis and test, the parameters of the grading ring that can be applied in engineering works were identified in this paper, thus providing a reference for the adoption of the scheme to reduce the abnormal flashover frequency induced by the local high intensity electric field.INDEX TERMS high-speed train, roof composite insulator, grading ring, lightning impulse voltage, electric field distribution

To study the icing flashover characteristics displayed by insulators on the roof of a high-speed train at a low-speed or static state, an environment with a low temperature and high humidity is established in the artificial climate chamber to carry out the icing flashover test of composite insulator under a static state. The results of the study indicate the presence of ice ridges bridging the sheath at the edge of the sheath when the ambient wind speed is less than 2m/s. The arc appears firstly at the end of the ice ridge, and it is likely that the arc at the adjacent tip converges in the air and then further extends to the edge of the next sheath. The arc melts the ice ridges at the end and enables it to stick to the tip of the ice ridge in the form of water droplets, and therefore the existence of droplets results in the distortion of the electric field near them. Moreover, the elongation of droplets and the bridging of ice edges accelerate the process of flashover. The research results can offer a reference to the structural optimization design of anti-icing insulators for high-speed trains in the future.

The plastic deformation characteristic of cone hole open-die cold extrusion was analyzed based on the concepts of hydrodynamics, the stream function of instantaneous velocity field was built. According to the determination of the equation of stream function, the kinematically admissible continuity unstable velocity field and the shape and position of its relevant velocity discontinuity were built. The factors of velocity field were analyzed. The theoretical model of extrusion power was obtained by the upper bounding theory. The factors of the angle of the cone hole generatrix were analyzed by programming and calculating.

No abstract

Abstract. Based on the characteristic distortion and the influence factors of cone parts by cold extrusion, cold extrusion process of a center hole conical part is simulated by Abaqus software, then the shape of the hole generatrix after cold extrusion is obtained by this method. According to simulation, the relation between the initial parameters of a center hole conical part with the hole generatrix after cold extrusion is built, and it provides a theoretical basis for the application of cold extrusion process of cone parts.