Research On Design Problem Of High Current Connector For Rail Transit

High current connectors are widely used in transportation,energy and power,aerospace,etc.In recent years,the rapid development of domestic rail transit technology has not only provided a broader market for high-current connectors,but also put forward higher requirements for the performance of high-current connectors.The expanding demand of rail vehicle input power and in ampacity leads to the deterioration of the thermal effect of high-current connectors in the train power system and the increase of the temperature,thus increasing the risk of power system failure.Once the connector in the power system of the rail vehicle has a thermal failure problem,it will directly cause the loss of the driving force of the train,even the risk of rollover.Therefore,the analysis of thermal failure mechanism,thermal design methods,and targeted improvement measures for high-current connectors for rail vehicles have important practical significance for solving these problems.This subject aimed at the ablation failure problem of a special-shaped crown spring of high-current connector for a certain type of rail vehicle.Based on the connector failure phenomenon and working environment conditions,a fault tree was established to analyze and investigate key influencing factors.Then,using the combination of the finite element thermal simulation and simulation experiments,the effects of cable body resistance,connector contact resistance,and vibration stress on the temperature rise of the connection system were studied,and the thermal failure process and mechanism of the connector were analyzed.Finally,the measures to reduce the temperature rise of the system and to prevent the occurrence of thermal failure were explored from the aspects of heat generation sources and heat dissipation methods,and the improvement measures were verified by finite element simulation.The research results show that one of the main reasons for the thermal failure of the connector is the low specification of the terminated cable and the insufficient current carrying margin of the system(less than 11%of the design standard).Although it does not directly cause thermal failure,it causes the connector and the cable system continues to work in a high temperature environment.The other main reason is that the degradation of the electrical contact performance of the connector causes the temperature of the contact to be 125℃ higher than the allowable safe temperature.The current-carrying temperature rise test of the connector cable system combined with the finite element thermal simulation study and microscopic detection of contact interface proves that the contact performance of the connector is affected by the vibration stress during the operation of the vehicle,the plating layer is damaged,the film resistance is increased.In the case of vibration,the temperature of the connector is increased by 20℃ under low cable specification condition,which causes the maximum temperature of the connector to be close to the softening and decomposition temperature of the insulating material under full-current-carrying conditions,eventually causing a melting fault.Aiming at the root cause of the connector’s melting failure,parallel improvement measures such as increasing the cable specifications and replacing insulating materials with excellent thermal conductivity are adopted.Through the verification of the finite element simulation,it is found that the maximum temperature of the improved connector under working conditions is about 114℃,which is lower than the safe temperature limit of 125℃.The improvement measures are feasible,which can be used for the research of thermal failure and capacity expansion of large current connectors for reference.