Study On The Characteristics Of Electric Contact Between Pantograph And Overhead Contact Line

The electric contact of pantograph and overhead contact line system (OCS) studies the physical and chemical phenomena occurring in the current transmission between OCS and pantograph, which includes the problems and phenomena caused by static contact, sliding contact, open-close contact and etc.The paper describes the thermal conduction process under these three types of contact, which falls into four aspects. The first one is about the static test results of the correlation among temperature rise of the contact wire, contact force and current collection. The second one concentrates on the theories related to the contact resistance, contact temperature, material match, and wear. The third one gives a detail presentation about the causes and effects of arcing. The last one summarizes the requirements of electric contact and the methods to evaluate the contact performance.The contact resistance is the basic parameter of the electric contact of OCS and pantograph, which is subjected to the combination of contact materials of contact wire and pantograph collector strip, contact force, contact type, contact surface and etc.The currents in a stationary vehicle have to be held below the permissible limits. The tests of the correlation among temperature rise, contact force and current collection value between pantograph collector strips and rigid conductor have been made under static contact. The results show that the temperature variation is not sensitive to the contact force when it is between 60～120N. Electric contact performance will not be changed greatly only through changing the contact force.The static current collection value of pantograph, percentage of arcing of OCS and the combination of contact materials of contact wire and pantograph collector strip are the sky parameters to the static contact force.The simulation of thermal conduction process caused by the current of OCS, when train start and short circuit occurs, shows that the normal starting currents will not decrease the operation reliability but short-circuit currents may lead serious damage to the contact wire at the contact point.The wear formed by the sliding contact between strip and contact wire is classified as mechanical, chemical and electrical wear. Mechanical wear can be divided into felt, granule and fatigue wear.In most cases, when the mechanical contact between pantograph and OCS is lost, the current and voltage between strip and the contact wire are higher than those necessary to generate arcing, arcs occurs initially. An arcing ensures that the current flow is upheld and is thus of fundamental importance for energy transmission between moving contacts.There are many causes esponsible for electrical spark and arcing. Arcing formed in different situations have different influences on materials of OCS. A model of arc-melt of OCS and pantograph is developed according to thermal conduction theory. The contact wire is modeled as half-infinity volume, which is under the second boundary condition. The eroding process of contact wire is simulated through solving transient process under static arcing and moving arcing. The result shows that contact wire is eroded to different degree with static and moving arcing. The surface of contact wire is melt in short time under static arcing. Under moving arcing, the erode degree is related to the train speed. The higher the train speed is, the lower the erode degree is.The parameters which are related to contact resistance such as dynamic contact force, percentage of arcing, and contact wire uplift at the support are often measured to evaluate contact performance indirectly. The wear of strip and contact wire is often used to evaluate the operation life of PCS.