This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON COMPONENTS, PACKAGING AND MANUFACTURING TECHNOLOGY 1 Analysis of Electrodynamic Forces in Switching Devices for Railway Applications Alberto Dolara, Member, IEEE, Francesco Grimaccia, Member, IEEE, and Silvio Zuffetti Abstract— Nowadays, the railway transport field imposes strin- gent technological limitations in terms of safety requirements and cost savings, which ask for an accurate design for all the devices installed onboard the trains. Switching devices for railway applications have to be optimized in size, weight, and cost; their accurate design allows to reduce the development costs and time. Moreover, the evaluation of electromagnetic forces acting on the current-carrying parts of switching devices is crucial for their proper operation and sizing, especially referring to movable conductors. This paper provides two methods, namely, an analytical and a numerical one, to evaluate the electrodynamic forces in switching devices with complex-shape circuits. The analytical method is a predesign tool able to evaluate in a fast way the electrodynamic forces on the current-carrying conductors. The numerical tool is a verification model that evaluates the forces generated by currents and flux densities by using a 3-D finite- element method. These methods are here applied to fully analyze a so-called earthing switch for railway application. Numerical results are reported to prove the effectiveness of the proposed methods. Index Terms— Electrical contact, electrodynamic forces, switching devices. I. I NTRODUCTION E UROPEAN railway transport system is recently witnessing a great development in high-speed services for citizens, with many industrial operators across the continent ordering trains with speeds up to 400 km/h. Limitations in size and weight of electric equipment on one hand, and increased safety requirements on the other, ask for a high level of optimization of all the onboard electric devices. Thus, in the field of switching devices for railway applications, it is necessary to properly optimize current-carrying materials, especially the most valuable copper parts. This process has to take into account, at the same time, proper operation in all the operating conditions, proper protection level for people and equipment, and increasingly cost reduction needs. In this context, the knowledge of the electrodynamic force acting on closed electric contacts, carrying high currents, is crucial for the proper operation and sizing of switching devices. This paper aims to fully analyze an earthing switch for high-speed train in order to provide a predesign method Manuscript received January 24, 2017; accepted March 12, 2017. Recommended for publication by Associate Editor J. Shea upon evaluation of reviewers’ comments. A. Dolara and F. Grimaccia are with the Department of Energy, Politecnico di Milan, 20156 Milan, Italy (e-mail: alberto.dolara@polimi.it). S. Zuffetti is with SPII S.p.A., 21047 Saronno, Italy. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TCPMT.2017.2687098 and a verification model able to evaluate the electrody- namic forces acting on closed electric contacts, which carry very high currents for a short time. This has to be done in a fast way and without incurring in very expensive and time-consuming laboratory tests on prototypes. This method can be applied to all switching devices whose current-carrying parts and/or circuits have a rather complex shape. According to [1], an earthing switch is “a mechanical switching device for earthing parts of a circuit, capable of withstanding for a specified time, currents under abnormal conditions such as those of short circuit, but not required to carry currents under normal conditions of the circuit.” Thus, the electrodynamic force acting on closed contacts, when fault current is flowing into its current-carrying parts, must never cause the opening of the contacts. The electrodynamic force acting on closed contact is gen- erally divided into two main components: the force derived from current-carrying conductor loop, usually referred to as Lorentz force, and the force due to current constriction between contacts, usually referred to as Holm force. The latter depends on the electrical behavior of the contact interface. At microscopic scale, real surfaces are rough, containing peaks and valleys, and mechanical contact occurs only in a specific number of areas on the apparent area of contact. Several theories have been developed to model contact phe- nomena. Early electric contact model is ascribed to Holm [2]; it describes the contact mechanism of curved elastic bodies, known as the Hertzian solution, and derives the contact resistance and the repulsion force between contact members. Greenwood and Willamson [3] extended the Holm’s model to a statistical population of asperities. More recent research is based on several methods. Fractal geometry has been applied for the surface description and elastic-plastic deformation on contacting asperities [4], [5]. X-ray [6] and atomic force microscopy scan [7] have been used to produce contact maps and to set up FE model for the calculation of the elasto-plastic deformation due to loading–unloading cycles. Statistical mod- els [8] for elasto-plastic contact between the rough surfaces, taking into account Gaussian distribution for the asperity, have been developed. In [9], a multifield and multiscale theory for the interface between two contact rough surfaces, activated by mechanical load and electric current pulses, is derived. The macroscale level models the contact of two deformable bodies along a common boundary. Mesoscale takes into account for the roughness of the contacting surfaces. In the microscale, only a single asperity is considered. The analysis of a whole 2156-3950 © 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.