The electrification of railway systems have always presented major challenges to the public electrical power systems. Electric locomotives are usually supplied by a single-phase AC catenary, causing unbalance and the appearance of negative sequence components (NSCs) in the three-phase electrical power grids. In addition, the traction power system of the electric locomotive is usually comprised by uncontrolled rectifiers to convert AC voltage to DC voltage, which produce high levels of current harmonics. Consequently, the operation of electric locomotives causes serious power quality problems to the public electrical power systems. This paper evaluates the use of Shunt Active Power Conditioners (SAPCs) to compensate power quality problems in single-phase 25 kV, 50 Hz railway traction substations, when using the conventional V/V or the Scott traction power transformer between the catenary and the public electrical power systems.