Rail Power Supply

Experience and high-performance tools for rail power supply to find and demonstrate optimal solutions

Electrified rail refers primarily to direct current (DC) or alternating current (AC) railway traction systems. DC traction systems form the primary rail system for local transport systems in trams, underground (metro) and suburban rail systems. In the case of AC railways, for historical reasons, there are systems with a range of voltages and frequencies. For the effective design of the rail power supply, a range of feeding and supply concepts are necessary.

Electrified rail refers primarily to d.c. or a.c. railway traction systems. d.c. Traction systems form the primary rail system for local transport systems in trams, underground (metro) and suburban rail systems using nominal voltages from DC 600 V to 1,5 kV. In long-distance services, nominal voltages up to DC 3 kV are common, and there are isolated cases of systems with higher voltages of up to DC 12 kV. With regard to local transport, new tram and metro systems are usually still built with direct current systems. Trolley buses are also classed as electric railways with respect to their traction technology.

In the case of a.c. railways, for historical reasons, there are systems with a range of voltages and frequencies. They primarily run on supply of AC 25 kV/50 Hz or - particularly in Central and Northern Europe - on lower frequency 15 kV/16,7 Hz. In America and Asia, a frequency of 60 Hz is commonly used. In Europe, a.c. railways are intended solely for high-speed traffic and have been selected worldwide as electrical rail systems on high-performance lines - although more recently a.c. has also been used in local transport systems. With regard to modernization and further development of rail traffic the trend has been towards a.c. railway systems.

For the effective design of the rail power supply, a range of feeding and supply concepts have been developed. In general they have several emerging design objectives, including reducing power demand, enhancing security of supply and supply capacity, as well as the use of renewable energy sources. With d.c., possible measures include double-sided feeding between substations, reducing electrical resistance in the contact lines, optimising contact line feeding arrangements, using stationary energy storage devices as well as on rolling stock and increasing nominal contact line voltage. In the case of a.c. railway systems, the focus is increasingly on autotransformer and booster transformer systems, static frequency converters and measures to limit asymmetries in the three-phase supply system, as well as issues around power transmission and distribution. The use of renewable energy sources, such as wind and solar power, along with other measures, is intended to lead to a sustainable reduction in CO2 emissions from railway systems.

Experience and high-performance tools are needed to carry out assignments of this kind and to find and demonstrate optimal solutions. KEMA has these tools at its disposal, with the rail-specific simulation programs SINANET® for d.c. railway systems and WEBANET for a.c. railway systems. The key feature of these tools is the integration of railway traffic simulation on the one hand, and electrical load flow calculations for the rail power supply network on the other. The ELEKTRA program is used for calculations on two-phase railway power networks.