Optimization for Grading Rings of High-Speed Train Roof Post Insulator

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.