Experimental Study On The Effect Of Current On The Friction And Wear Behavior Of Pantograph Strip/Contact Wire With Electric Current

High-speed and faster passenger transportation,heavy-hauland rapid freight transportation is a main development direction of the electrified railway in our country.With the increasing of the running speed,the corresponding traction power is increased largely and the electric current flowing through the pantograph-catenary system is increased to 300～500 A.In operation practice,the wear of the contact strip is found to be so severe that the service life of the pantograph strip is very short.The point contact and high-current characteristics of the pantograph-catenary system have seriously restricted the running speed of electric locomotives.Therefore,it is very significant to study the sliding electrical contact under a high-current.In this paper,The friction and wear behavior and electrical performances of carbon strip/Cu-Ag alloy contact wire under high-current I=200～500 A were tested on a high-speed electric sliding test machine.The effect of the contact force on the friction and wear behavior of the carbon strip under the high-current was also tested.The results can be drawn as follows:(1)With the increase of the electric current,the friction coefficient increases first and then decreases,but the variation of friction coefficient is not distinct,which fluctuates between 0.29 and 0.33.The wear volume of the carbon strip increases sharply with the increase of the electric current,and the main wear mechanisms of the carbon strip include arc ablation and high temperature oxidation.A lot of ablation points,spalling pits and fatigue cracks can been observed on the wear surface.The mass fractions value of Cu and O in the ablation points and spalling pits are very high and reached 33.25%and 22.47%respectively,which are mainly crystal copper and oxide of copper.(2)Under the condition of low-voltage and high-current,the main forms of arc discharge between the carbon strip and Cu-Ag alloy contact wire are short arc discharge and spark discharge.While the current reach to 300 A or more,arc discharge always takes place during the whole experimental test although the contact pair is not separated.In test,the mechanism of arc striking between the carbon strip and contact wire is not due to break down of air gap,but due to melting or carbureting of the micro asperities of the contact surface,which leads to produce gaseous phase arc from metallic phase arc.The current-carrying efficiency of the contact pair decreases with the increase of the current,and the larger the current is,the more seriously the waveform of electric current is distorted.In addition,the temperature rise of the worn surface and the arc discharge energy increase with the increase of the testing current.(3)When the current is equal to 200～500 A,the wear volume of the carbon strip decreases as the contact forces increases,and the effect of electric abrasion is greater than that of mechanical wear.With the increases of the contact force the current-carrying efficiency increases.So we can improve the current-carrying efficiency and service life of the carbon strip by increasing the contact force when the operating speed was increased.When the contact force is equal to 60～80 N,the arc discharge energy increases with the increase of the contact force,and decreases when the contact force is greater than 80 N.The temperature rise of the worn surface decreases with the increase of the contact force,and when the contact force is less than 80 N,the joule heat has a greater effect on the temperature rise of the carbon strip than the arc discharge does.During the test,the short arc discharge is extinguishing easily.So the correlation between the temperature rise of the carbon strip and the arc discharge energy is not significant.The SEM analysis shows that the higher the temperature of the carbon strip,the more thermal cracks the carbon strip has,and the stripping phenomenon is more obvious.