Contents I. Introduction
Power Quality (PQ) is a multifold problem in modern railway systems, since several elements represent a source of emissions and the propagation occurs through a far from ideal medium, the traction line. The sources of emissions may be identified broadly in: the Electric Sub-Station (ESS), that is characterized by the so-called characteristic harmonics, with a frequency depending on the supply system and its topology, but with amplitude that may be quite variable; the vehicle or train (identified as rolling stock) that emits various components originated from the main traction drive, the front end converter, the auxiliary converters and in principle any electrical system or apparatus of relevant power rating on-board. All these elements are interconnected by an articulated propagation and coupling medium, the traction line, the extends for several km and is surely far from ideal: several aspects, non-idealities and practical issues have been considered in the literature, such as the variable RS position, the multitude of shunt elements connected to the line itself, the rail-to-earth leakage and in general earth's influence, the rail non-linearity.
