Overvoltage Protection of Light Railway Transportation Systems F. Delfino, R. Procopio, Student Member, IEEE, and M. Rossi, Student Member, IEEE Abstract – In this paper the behavior of the power supply system of a typical Light Railway Transportation System (LRTS) subjected to overvoltages of atmospheric origin is analyzed, with the purpose to determine the optimum location of the surge arresters. A complete model of the whole power system has been developed and the transients have been simulated with the electromagnetic code PSCAD-EMTDC. Index Terms—Electromagnetic transient propagation, overvoltage protection, electric traction. I. INTRODUCTION L IGHT railway is a generic term which covers a wide variety of railways and tramways. This modern electric mass-transit system implies economy of construction in one or more ways, such as light weight rails, wooden rails, light bridges, minimal earthworks, sharp curves and steep gradients, narrow track gauge and includes urban and suburban railways, also known as rapid transit, or trolley lines [1-2]. Reliable and effective protection against overvoltages (atmospheric and switching) on contact wires is most important in the smooth and constant running of the trains. To this end, the correct positioning of the surge arresters plays a fundamental role [3-6]. Several configurations for the protection system can be adopted, characterized by different locations and number of the surge arresters: 1. Surge arresters located at the DC busbars of each electrical substation; 2. Surge arresters located at the interface between contact line and feeder cables; 3. Surge arresters located both at the electrical substations and at the interface between contact line and feeder cables. The purpose of the present paper is to simulate the response of the whole system when subjected to an overvoltage wave, in order to determine the "best" configuration in terms both of protection effectiveness and cost economies. Thus, it is not aimed at modeling in an exhaustive way the field-to-line coupling originated by a lightning event [7], which would be so much complicated using a circuital code like PSCAD-EMTDC [8]. As a matter of fact, this would imply the implementation of the Agrawal method [9], which, even in its simplified version, would make the simulation of the system under test be so onerous from a computational point of view. Federico Delfino, Renato Procopio and Mansueto Rossi are with the Department of Electrical Engineering, University of Genoa, via Opera Pia 11a (e-mail: federico.delfino@die.unige.it; rprocopio@epsl.die.unige.it; mansueto@die.unige.it). In other words, the authors’ intention is to set up a simplified tool, which can give some useful information for the system design with the advantage of exhibiting good properties in terms of CPU costs. As will be examined more in details in the following sections, this kind of approach, although simplified, is able to identify among the three possibilities indicated above, the best arresters location. The paper is organized as follows: in section II a brief description of the LRTS is carried out and an equivalent circuital model is defined. In section III the results of the simulations are presented and thoroughly discussed and in section IV some conclusive remarks are drawn. II. SYSTEM MODELING A typical Light Railway Transportation System (LRTS) is powered at 750 V DC nominally with a maximum acceptable deviation of +20% and –33% and distributed by an Overhead Contact System (OCS), supplied by parallel feeder cables. The OCS can include, for each track, a contact wire and two parallel feeder cables. The OCS of one track (500 m long) is connected in parallel to the OCS of the other track at each end of the route, and, in principle, at every tram stop, substation and crossover. The running rails are used to carry the return current and constitute, with the return cables and the Electrical SubStations (ESSs) return negative busbars, the negative return system. Each ESS negative busbar is connected to the rail by means of insulated cables. Each LRTS ESS is fed from the Electricity Supply Board (ESB) MV network with supply voltage 10.5 kV AC and frequency 50 Hz. The ESS absorbs electrical power to energize the OCS at 750 V DC and to supply auxiliary loads at 400/230 V AC. Each traction substation is connected to a MV generally grounded network. Usually, the electric system feeding the LRTS exhibits a modular structure. The borders of each subsystem are represented by the insulated overlaps, whose size is about 30 cm. From the point of view of the overvoltage study, the analysis has been limited only to one subsystem, without any