Abstract
In order to reduce the changes of contact force between pantograph and catenary, which occur periodically every span, there is a way to lay pre-sag in catenary. However, as β is coming close to 1, where β is ratio train running speed by wave propagation velocity of contact wire, it becomes identified that pre-sag is contributing factor which cause contact force changes. Based on the results of model analysis and simulation, if the project raising operational speed up would be created, which means β is coming close to 1, the author could propose that static height of contact wire keep constant, keeping away from pre-sag.
