Keywords: magnetic force, high speed railway, pantograph, contact wire, traction current, vibration.

In recent years high speed railways are being rapidly developed around the world. Electrical power supplied to high speed trains come from the slide electrical contact between the pantograph and the contact wire. With the increasing operating speed of high speed railways, traction current for high speed trains obviously increases. Meanwhile, magnetic forces arising from the traction current are significantly increased at the same time. Magnetic forces may affect the contact state between the pantograph and contact line. That is a problem of the power supply for the high speed train. In this paper, an equivalent model for the magnetic force between the contact wire and the pantograph has been proposed. The model includes the factors of traction current flow through the contact area, the vibration separated gap between the pantograph and the contact wire, zigzag motion distance and so on. The formula for the magnetic force has been deduced. The relationship between the zigzag motion distance and the magnetic force has been studied. The Influence of the separated distance between the contact wire and the pantograph has also been studied. The magnetic force for the normal operation condition and the short-circuit condition has been analyzed. It is demonstrated that, the relationship between the traction current and magnetic force is linear. The zigzag motion (lateral movement between the pantograph and the contact wire), the distance and the vibration separated gap affect the magnetic force significantly. The magnetic force increases with the increase in the zigzag motion distance. But it is rapidly reduced with the increase in the vibration separated gap. When the vibration separated gap changes from 0.1mm to 3mm, the magnetic force drops to 80%. The magnetic force is a few Newtons when a high speed train operates in a normal situation. But if some short circuiting occurs such as an insulator flashover from a lightning strike, the magnetic force may increase to tens of Newtons. That force would reach up to 20%~30% of the contact force. A finite model for the pantograph and the contact wire has been established to verify the theoretical model. Some experiments have also been carried out.

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