Railway electric traction

Railway electric traction describes the various types of locomotive and multiple units that are used on electrification systems around the world.

[1] Robert Davidson, of Aberdeen, Scotland, created an electric locomotive in 1839 and ran it on the Edinburgh-Glasgow railway at 4 miles per hour.

[1] In 1880, Thomas Edison built a small electrical railway, using a dynamo as the motor and the rails as the current-carrying medium.

They are equipped in most modern rolling stock for lower maintenance cost and easier scalability relative to DC units.

[2] Locomotives and multiple units so equipped can, depending on line configuration and operation rules, pass from one electrification system to another without a stop, coasting for a short distance for the changeover, past the dead section between the different voltages.

Southern England uses some overhead/third rail dual-system locomotives, such as the class 92 for Channel Tunnel, and multiple units, e.g. the Class 319 on Thameslink services, to allow through running between 750 V DC third rail south of London and 25 kV AC overhead north and east of London.