Research On Electric Field Distribution Of Roof Insulator On Emu Under Wetting Contamination And Internal Defects Conditions

High-speed railway has gradually developed into a major carrier of our country, with its strong transport ability, high speed, safety and comfort and other advantages. As a key component of high-speed railway, Electric Motor train Unit (EMU) must be ensured performing safely and reliable to improve the quality of service. Being the main insulation device of EMU, Roof insulator’s fault will cause a railway transportation suspension, which may leading to bad influence on society. Althrough the voltage class is not high, some areas in the high volatage side of roof insulator show high electric field strength which will decrease the insulator reliablity, due to the limited roof space and insulator height. The pantograph supporting insulator made of epoxy is hydrophobic, which will flashover frequently in winter with condensation, fog and haze condition. Flashover is mainly resulted from insulator surface hydrophobicity degradation and pollution, and the prominent factor of material hydrophobicity degradation is corona discharge, which is caused by the high electric field. Under high electric field the bonding interface of the core rod and sheath is prone to electric corrosion, and the electric field through internal gap would be distorted resulted in a discharge, even leading to a insulation breakdown. Through the accurate calculation of the surface and inner electric field of the insulator, not only the foundation of the research into the insulator flashover and inner breakdown can be laid, but also the appropriate optimization of electric field may be proposed to prompt insulator reliablity.According to the quasi-static electric field and the finite element theory a3D FEM (Finite Element Model) of EMU pantograph support insulators was onstructed. The effect of contact wire, pantograph and its bracket, insulator base, and the size of calculation region on the result was studied. Then the electric field of clean and contamination insulator was explored. Combined with the actual operating conditions the influence of over-voltage and harmonics on electric field distribution of insulator was analyzed.Considering the hydrophobicity of epoxy materials, a FEM model of the pantograph support insulator containing water was established. The effect of water droplet, water film and water stream on the surface electric field were revealed. Then the influence of electric field rotation angle and the parameters of water droplet on the the maxmium enhancement factor of the electric field were analyzed through a simplified3D electric field parallel electrodes computational model, and the logic function representation model of the factor was proposed. At last, a grading ring of optimal setting strategies was determined based on comprehensive consideration of both the size and direction of the electric field based on the EMU pantograph support insulator. Aiming at an inner breakdown accident of a busbar supporting insulator, a multi-parameter model for electric field analysis in three dimension was built. Axial electric field distribution inside the busbar supporting insulator was revealed. And the gas and liquid gap were silmulated by different parameter settings of the internal gap, the inner electric field change was calculated. The aberration characteristics of inner electric field through the gap of different size at different location with different conductivity were investigated. Finally, combined with the aberration characteristics inside the composite insulator the cause of the accident was analyzed.