Overvoltages in DC urban light railway systems: Regenerative braking characterization
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Tutor / director / evaluatorBenítez Iglesias, Raúl
CovenanteePolitecnico di Torino
Document typeBachelor thesis
Rights accessRestricted access - author's decision
DC light railway systems are used for public transportation in many cities worldwide. For these DC tram networks, the Traction Electrification System (TES) is normally fed by power substations, which contain the power transformers, AC/DC converters, protective relays and circuit breakers; from these substations several DC feeders (positive cables) are used to energize the Overhead Contact System (OCS). The return current is collected by the rails and by the negative cables. In this kind of infrastructure, overvoltagescanoccurdue to flashes (direct and indirect lightning)as described in standardEN62305 or due to switching operation  or regenerative braking . Thesesecond type of overvoltages are generated during normal operation of the systemand are called “internal overvoltages” .Regardless ofthe type, overvoltages may cause flashover of the line insulation and, travelling along the lines, may enter the supply substations and stress or even damage the insulation of the equipment inside.In the last years, in the tram network of Turin(Italy), internal overvoltageshave damagednetwork installations and vehicle components.According tosome field measurement results carried out in the pastand considering the change in the operation practice of the network andofthe number and type of circulating vehicles, the most dangerous overvoltages seems to be produced by a specific type of tram (model 5044).Unfortunately, the documentation of this particular vehicle is not available.Therefore, a new field measurement campaign was organized to characterizeitsregenerative braking, collecting signals from the control system of the vehicle.The mean purpose of this workis to organize the raw data got by the measurement instruments into a format that can be easily analyzed.Finally, some solutionsto the overvoltage problem are proposed.
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