Experimental Study On The Current Carrying Friction And Wear Performance Of A Metro Pantograph-catenary System And Their Wear Prediction Model

Because of its convenience,timeliness and safety,the metro railway has become a main means of transportation for urban residents in China.The metro pantograph-catenary system is the core component of the metro power supply system,so that whether the pantograph-catenary system can work stably and normally determines the safe operation of metro lines.However,during the actual operation of the pantograph-catenary system,abnormal ablation,breakage and shedding of the metal-impregnated carbon strip of the pantograph may occur because of the fluctuation of loads sustained,and the contact wire will also be corrugated,which will result in serious reduction of the current-receiving quality of the pantograph-catenary system and sharp reduction of their service life.Research on the wear performance of the pantograph-catenary system is of great significance to improve the safety of metro operation and reduce the operation and maintenance costs of operating companies.In this thesis,the contact friction pairs consisting of common pantograph materials and copper-silver alloy wire in domestic metro lines were taken the research object,the current-carrying friction and wear characteristics of the pantograph-catenary system under the actual operation conditions of metro lines were experimentally studied by using the ring-on-block current-carrying friction and wear tester under the conditions of electric spark discharge,different sliding speeds,normal loads and currents with a long sliding distance of6000 kilometers.Finally,the prediction model of the contact wire wear rate was established by using MATLAB software.The main conclusions are obtained as follows:(1)Under the condition of electric spark discharge,serious mechanical and electrical wear occur on both contact wires and metal-impregnated carbon strips.Arc discharges is severe,which are results in higher temperature of the metal-impregnated carbon strip and the lowest current-carrying efficiency to 86.57%.An increased capacitive contact between friction pairs results in a greater contact resistance.(2)The macro-morphology of contact wires and the macro-micro-morphology of the metal-impregnated carbon strips were observed.Under the condition of electric spark discharge,the surface material of the metal-impregnated carbon strips spalled extensively because of mechanical action.At the same time,the high temperature,which was produced when the arc discharge was strong,caused thermal stress cracks on the surface of the metal-impregnated carbon strips and caused the original cracks to expand,resulting in a large number of ablation pits.(3)Under current passage through the pantograph-catenary system,the increasing of the normal load can reduce the contact wire wear rate and arc energy.When the sliding speed is increased,the friction coefficient of the friction pair decreases,but the wear rate of the contact wire increases because of the mechanical action of the high speed sliding,and the influence of the sliding speed on the wear rate of the contact wire is weaker than that of the normal load.The current-carrying efficiency decreases first and then increases with increasing speed.(4)Without current passage through the pantograph-catenary system,no oxidation film was formed to protect the friction pair at a low temperature,and severe mechanical wear of the contact wire occurs.As the current increases,the area covered by black oxide film on the contact wire surface becomes larger and larger,which can effectively lubricate the friction pair to a certain extent.The black oxide film reduces the arc damage of the contact wire surface,wear of the friction pair,and friction coefficient.(5)The neural network fitting toolbox in MATLAB software was used to prove that the current,normal load and sliding speed are strongly correlated with the contact wire wear rate.The correlation coefficient is greater than 0.9.A neural network prediction model of the contact wire wear rate is established.A series of prediction results are obtained.Among all predicted contact wire wear rates,more than 75% of these predicted data have the margin of the prediction errors of less than 10%.This suggests the prediction model has a good accuracy.(6)The contact wire wear rate under different loads,contact currents and sliding speeds is predicted by using the prediction model of the contact wire wear rate under some working conditions.It can be seen that the contact wire wear rate is the smallest,about 0.00259 g/km,when the sliding speed is 80 km/h,the current is 320 A,and the normal load is 45 N.