Railway electrification systems and configurations

Several different type of railway traction electric power system configurations have been used in the USA and all over the World. The choice of the system depends on the train service requirements, such as commuter rail, freight rail, light rail, train loads and the electric utility power supply. The railway electrification load is one of the most difficult kinds of load to be fed by an electric utility and presents a challenge both for the railway company and the utility. For the utility, it requires over sized substation facilities and may result in power quality deterioration for its other customers. These utility challenges have been met using different methods for the different railway electrification system configurations. Some countries have used low frequency (15-20 Hz) railway electrification systems to maximize the efficiency and reduce costs, while the others have maintained the 50/60 Hz frequency and have developed high voltage innovative designs to meet these challenges. The low frequency railway electrification system option has been used in European countries and US for almost a century and has provided satisfactory operation. With the modern day power electronics technology available for frequency conversion and the high power quality demanded by the utility power customers, the low frequency systems could be an increasingly viable option to provide an affordable and desirable railway electrification systems.