Optimization of Digital Overcurrent Protection Settings in DC Urban Light Railway Systems

DC urban light railway systems are used for public transportation in many towns worldwide. In these systems, short-circuit currents are often similar, both in steady-state magnitude and in rate-of-rise, to normal operation currents. In order to properly set the protection relays, to obtain short-circuit discrimination and to avoid nuisance trippings, it is important to analyze short circuit and normal operation current patterns. It is also important to highlight that normal operation current patterns are not only those related to rolling stock acceleration, but also to zone commutation. This paper presents the results of several measurement campaigns, performed for this purpose, on the tram network of Turin, Italy. The measurements results are then used to propose optimized settings for the installed overcurrent protections.