Thermal failure analysis of special-shaped crown spring connectors for rail vehicles

Abstract

With the fast development of the rail transit system and the continuous speed increase of rail vehicles in China, the rated current of the power supply system in the trains rises accordingly, so the thermal reliability of the electrical connection system used in the power supply system has become one of the crucial factors whether the train can run normally for a long time. In this paper, aiming at an ablative failure of a special-shaped crown spring connector during the operation of a subway, both the failure mechanism and the solution method are studied. Firstly, the main influencing factors of the failure, both the cable size and the contact resistance degradation of the connector, were screened by fault tree establishment. Then the capacity of the selected cable was evaluated to be insufficient by current carrying test, with 11.6% lower than the safe margin. Further, the contact resistance degradation of the connector caused by vibration and corrosion was about 23%, studied by the experiments and thermal theory. By combining the theoretical model of temperature rise in the contact interface and the finite element simulation, the heat production of the connection system under actual working conditions was estimated to make the insulating materials near the contacts attain to the decomposition temperature, which was verified by the analysis of the failed samples with various service stages. The thermal analysis results was demonstrated to be consistent (less than 5% error) among the finite element simulation, the experiments and an existed thermal design method. Finally, a solution to increase the cable specification from 50 mm2 to 70 mm2 under complicated service conditions is proposed to reduce bulk resistance of the cables and increase the heat dissipation by cable heat conduction, the maximum temperature rise can reduce 18.4% so that the ablation failure of the connectors can be avoided.