Transient Overvoltages in a Railway System during Braking Mario A. Suárez Electrical Studies H-MV ltda. Medellin, Colombia msuarez@h-mv.com Jorge W. González Electrical Engineering Faculty Universidad Pontificia Bolivariana Medellín, Colombia jorgew.gonzalez@upb.edu.co Israel Celis Customer Mobilization Metro de Medellín Ltda. Medellín, Colombia icelis@metrodemedellin.gov.co Abstract—This paper presents an overvoltage analysis in the dc catenary of The Metro de Medellin railway system. The main objective is to study the sources of damages of motors in the trains. It was achieved a detailed study beginning with the direct measurement of variables and then the construction of a digital model in PSCAD-EMTDC. The simulations indicated a high incidence of braking overvoltages imposed on catenaries and insulations during regeneration. Literature and international standards on traction systems, concerning experiences and standardization of voltages, are analyzed. Keywords-railways; switching overvoltages; braking regeneration; electromagnetic simulation. I. INTRODUCTION The Metro de Medellin is a large capacity railway system that crosses the metropolitan region of Medellin. This system has two lines, A and B. Line A is 23.2 km in length. Line B is 5.6 km in length. The system has rectifying (ac/dc) stations and passenger stations. The Metro de Medellin also offers 3 overhead lines with Metrocable technology. The Metro de Medellin has reported the repeated damages in the traction and compresors motors located in the trains. According to basic measures in the faulted motors, it is suggested that overvoltages could have been the source of damage. In this paper, it is exposed what was done in terms of modeling, simulation and analysis of possible sources of surges on the railway network and that could affect the motors. The modeling of railway systems to study switching overvoltages has been a challenge from the point of view of integrating ac and dc systems, the trains with their controls and the mechanical components. In [1, 2-4] it is mentioned about the lack of models suitable to study switching overvoltages in railway systems. A special topic is the mechanical behavior, nevertheless not much has been done. In [5] a model is developed for the electrical and mechanical torques. Analyses range from the engine and into contact with the rail wheels, involving axles, bogies and mechanical boxes. Nevertheles, the studies do not involve the regenerative braking state and generated overvoltages. Reference [6] studies the switching surges during regenerative braking. However, it is assumed that there are failures in the regenerative braking system in order to create the surges. Reference [2] indicates that there is not much information in the literature regarding switching overvoltages in systems such as trains. In that reference, overvoltage measurements were made and classified for a real train system. In [3] Induced voltages are analyzed in the dc side of a mass system for switching of a capacitor in an ac nearby substation; mitigation mechanisms are proposed. In [4] it is mentioned the lack of standards for application of dc surge arresters, and the lack of literature on these devices. Guidelines for the development of standards are proposed. The reference also indicates a lack of measurement data on surges in dc systems. In [7] it is presented a study to determine resonant voltage level generated within a specific railway system. Reference [8] presented analysis of lightning surges on the lines of electric traction systems using PSCAD-EMTDC. In this paper, in sections II and III, are described basics on dc series motors, and on the control system with special interest on the braking stage. In section IV, the paper analyzes the standards on traction systems in terms of levels and standard voltage ranges. Records of measured variables of interest, with special attention to the voltages are analyzed in section V. In section VI, it is presented a simulation model in PSCAD– EMTDC. The model is accompanied by pictures showing the correlation with the specified operation on the Metro and their relationship to cases reported in the literature. With this model, simulations are achieved to study the influence of certain critical parameters and the overvoltages produced during regenerative braking. Finally, some conclusions and recommendations to avoid surges are presented. II. BASIC CONCEPTS ON THE DC SERIES MOTOR The study of the present work is highly focused on the train motors and on the interactions of the control system. The starting and stopping of motors will be of special interest. This section reviews the basic theory of dc series motor and control system performance. This work was supported by H-MV Ingenieros Ltda. Medellin, Colombia; Metro de Medellin Ltda., Medellin, Colombia and Universidad Pontificia Bolivariana, Medellin, Colombia.