Droppers’ stiffness influence on dynamic interaction between the pantograph and railway catenary

Droppers connecting the contact wire and messenger wire of the railway catenary are characterized by zero or negligible compressive stiffness, hence they become slack under compression that is similar to bars’ buckling. The paper presents a numerical analysis of the influence of droppers slackening phenomenon on the dynamic interaction between the pantograph and catenary. The analysis is based on a simulation method presented by the authors in previous papers, in which the catenary is modelled as a complex cable system. In this paper, the simulation method is modified by introducing the residual compressive stiffness of droppers that is assumed as a given percent of tensile stiffness. Modification leads to geometrically non-linear equations of motion of the pantograph-catenary system. Two different algorithms for solving the problem of non-linearity are proposed, in both of them the Newmark numerical integration method is applied. Results of dynamic response simulations performed for different values of residual compressive stiffness of droppers are presented and compared. It is shown that the contact wire does not cooperate with the messenger wire in a large area around the pantograph when the compressive stiffness of droppers is assumed zero. As a result, the pantograph moving at high speed induces severe vibrations of the catenary. It is also shown that droppers should be designed to have the residual compressive stiffness equal to at least one percent of their tensile stiffness. This is sufficient to ensure an appropriate cooperation between messenger wire and contact wire, which is demonstrated by simulation results fulfilling requirements given in the standard PN-EN 50318: 2002.