A New Approach To Desired Contact Force Between Pantograph And Overhead Contact Line System Beased On Sliding Electrical Contact Fundamental Mechanism

In recent years,new materials has been applied to pantograph strips and contact wires,and service condition of contact point between pantograph strips and contact wire has changed a lot,while speed,quantity and reliability requirement of current collection increased significantly.However,contact force is still according to the experience and lack of necessary theoretical support.Considering that structural failure and serious abrasion occurs widely in operating rail lines,here comes the question,if the contact force is reasonable and rational.In view of these,this paper focuses on the relationship between contact force and current,contact area,speed and arcing rate,researches on thermal effect of the current,dynamics and arc phenomenon in the process of sliding electric contact,and proposes a new approach to desired contact force on the purpose to make wear well distributed.Firstly,through reconstruction of the classical electrical contact theory,the paper proposes a kind of virtual contact element,which represents contact force and contact resistance.Based on a limited number of the elements,discrete electrical contact model of pantograph and contact wire has been built,verified by comparing numerical calculation result and measured data from a DC static electrical contact test.Comparing calculation and test results,there are good consistence when contact force is 40?100N.At the same time,this paper explains the reason of uneven temperature distribution and special change in temperature rising curve in test by using the model,and points out that the static electrical contact is essentially a dynamic process,during which a-pots changing continually.Secondly,the paper figures out the characteristic of dynamic contact force,by building up model of pantograph and contact lines.The paper puts forward an optimized method of pantograph modeling,by which multi-mass dynamic model can be established without disassembling pantograph,containing aerodynamic force,position information of each part and inner friction force.Comparing apparent quality to an actual pantograph,the model from given mothod can reflect dynamic response under 13 Hz accurately.Dynamics equations of contact line are established,and its characteristics of the solution are derived,showing that disturbance from pantograph transfer in 2 forms,fluctuation and diffusion.The dynamic coupling model of pantograph and contact line was established by penalty function,and solved by finite mode method,showing that movement of pantograph causes contact force change,and the amplitude of contact force varies with the speed.Thirdly,assuming sliding of pantograph as non-adhesive normal contact,and surface heights following Gaussian distribution,simulation results by the discrete contact model shows that:the ratio of contact force and width of strip can be used as an index of electrical contact,to which the actual contact area is positively proportional,and the contact resistance is negative power relations;the contact state is random that when the contact force is small or changes,the randomness increases.To figure out the sliding process qualitatively,an imaginary surface is created by W-M fractal function and used in simulation.Supposing a-pots change as micro-circuit open and close,cut off current and maintaining voltage as arcing condition,it is inferred that:arc occurred randomly in sliding;arc may occur when contact force greater than 0;when the contact force is small or reducing and the current is large,the probability of arc occurrence increasing.Actual arcing in a metro line consistents with the inference,that arc mainly occurs in the accelerating section where dynamics of pantograph and catenary is in poor condition and the end of accelerating section.According to the sequence of melting spots and bright arc light,it's proposed that arc can be divided into off-line arc,which is air arc occurring when the surface air gap breaks down,and melting arc,which is metal vapor arc occurring when metal vapor is excited.Finally,the paper introduces arc probablility coefficient in contact wire and strip wear calculation,and estimates the wear condition which tallies the site data of trains working condition and contact wire wear measured from testing equipment on a service line.Contact wire is seriously worn in the section where train is accelerating and going through speed range that pantograph and catenary working in poor dynamic performance,and the section where train ends acceleration.It is arcing that makes contact wire wear serious in the testing line,and can be preliminarily predicted in sliding simulation used discrete electrical contact model of pantograph and contact wire based on known current and contact force.It is proposed the method of determining contact force between pantograph and contact wire:the contact resistance and dynamic components of contact force are respectively determined by electrical contact model and dynamic simulation firstly,and then average contact force-velocity curve is determined in contact force-velocity-current(F_c-v-I)space according to limiting conditions of acceptable wear and temperature that related to contact resistance.To the test line,new line and relevant standards,the paper gives some optimization measures and suggestions.