Application of tuned-mass system on railway catenary to improve dynamic performance

Highlights

• Proposing a method to improve the dynamic performance of railway catenary system.

• Studying the influence of lumped-mass and tuned-mass on the pantograph-catenary interaction.

• Studying the dynamic behaviour of the additional local-DOF-system on the catenary system.

• Suggesting a possible way to implement the tuned-mass system on the existing catenary.

Abstract

Finding a simple and practical method to improve the dynamic behaviour of a specific structure is always desirable in civil and mechanical engineering. The railway catenary system is the overhead power line above the track, interacting together with the train-based pantograph to transfer electric power. Due to vertical stiffness variation and a propagating wave along the catenary, the fluctuation of the contact force becomes significant with operational speed increasing. Therefore, this has become one of the key factors which limits the operational speed and service life of key components. Wire misalignment, structural errors and uneven mass distribution of the catenary can further deteriorate the contact stability. In order to achieve a higher speed on existing lines, the catenary needs large-scale modification implying long out-off-service time. From the designing aspect, all components directly fixed to the catenary, like clamps, steady arms and other fittings, are made as light and small as possible to minimize disturbances. However, in other engineering applications, some well-designed additional mass systems are adopted aiming to improve their dynamic performance. In order to take advantage of these unavoidable masses on the catenary, an investigation on lumped-mass distribution in single-pantograph and multi-pantograph operations is performed with help of a 3D pantograph-catenary finite element (FE) model. The results show that a rightly-tuned mass, here the implementing location and the elasticity of its connection, can positively change the dynamic performance without implementing large-scale modification to the existing system. Through a brief discussion on the mechanism of this positive effect, this paper proposes that applying some artificial tuned-mass system can be a possible method to overcome unfavourable working conditions or even allow speed increase on existing lines.

Introduction

The pantograph-catenary system is widely used to collect and transfer electric current from the stationary infrastructure to the moving trainset. Since the catenary is not continuously supported, the vertical elasticity variation of the catenary causes periodical oscillation when the pantograph slides against the catenary. The oscillation leads to wave propagation forward and backward along the wires of the catenary system. Wire misalignment, structural errors and uneven mass distribution of the catenary make the oscillation heavier and more complicated. If the dynamic response between pantograph and catenary is not sufficiently suppressed, it can lead to poor quality of electric current collection, magnetic interference, short service life of key components, or even excessive movement or structural damage at high speeds [1]. Therefore, the dynamic performance of the pantograph-catenary interaction has become one of the key factors which determines the operational speed.

In order to achieve good dynamic performance and thus high operational speed, there are a lot of investigations ongoing. The common methods to achieve this goal are: increasing the tensile loads on the catenary wires to increase the wave propagation speed, and adopting a low-stiffness-variation catenary designs to minimize the elasticity deviation [1], [2], [3], [4], [5], [6], [7]. With help of these measures, it is possible to achieve operational speeds of 350 km/h and above on newly-built passenger-dedicated lines. However, for a large proportion of the existing railway lines around the world, there is still a huge demand for more reliability and higher operability under increased speed with minimum of modifications. To upgrade the existing catenary systems, other measures, like pre-sag in the mid-span of the catenary, droppers with additional damping, optimized pantograph suspension and actively-control pantograph, have been investigated recently [3], [8], [9], [10], [11], [12]. In addition, the simulation of the pantograph-catenary interaction has been proven to be an efficient method and is widely adopted in the studies on the pantograph-catenary dynamics [13]. Many studies have contributed to improve the numerical models by identifying system damping, including environmental and track perturbations, modeling wind load and comparing simulation with measurement [14], [15], [16], [17], [18], [19], [20], [21].

From the structural aspect, the contact wire of the catenary, which is directly in contact with the pantograph, is suspended to the messenger wire and the supporting structures through droppers to keep the geometry and the vertical elasticity as smooth and uniform as possible. Today, all components fixed to the catenary, e.g. clamps, steady arms and other fittings, have to be made as light and small as possible to minimize disturbances and reflections. These lumped-masses are impossible to be completely removed, but may easily be adjusted on purpose during maintenance to improve the performance. In other engineering applications, some well-designed masses or mass systems are deliberately introduced to beneficially change the dynamic behaviour, such as the masses of stock bridge dampers for overhead power lines, balancing weights used on car wheels and other high-speed rotating bodies, and active and passive tuned-mass systems on large structures, such as buildings and bridges [22], [23], [24]. The additional mass applied neither reduces the overall capacity nor introduces much dynamic disturbance into their systems, but can improve the dynamic behaviour by effectively splitting the resonant peak and reducing the amplitude of mechanical vibration to mitigate excessive oscillations. In order to take advantage of the existing and unavoidable lumped-masses on the railway catenary systems and thus to improve the dynamic performance, it is necessary to carefully investigate the relationship between the lumped masses on the catenary and its resultant dynamic behaviour.

This paper performs a numerical study on additional lumped-mass implementation on a Swedish soft catenary system and its dynamic influence. With help of a 3D pantograph-catenary finite element (FE) model [25], the dynamic performances of different mass arrangements in single-pantograph operation and in multi-pantograph operation are investigated by varying the weight of the catenary clamp and/or introducing additional lumped-masses at different positions on the catenary. To further enhance the dynamic performance, the additional lumped-masses are tuned to the original mass system. This paper takes the following parameters into consideration: the position of the applied mass, the weight of the applied mass and the elasticity of the connection between the mass and the catenary. To address the effect caused by the additional masses, the influencing process of the lumped-mass is shortly described by comparing the results from different mass-applied configurations. Finally, this paper gives some suggestions on the implementation of the tuned-mass system to improve the dynamic behaviour.