Supplying energy to railway trains- Distribution of electricity

Energy is the basis of all means of transport:

• animals and humans for caravans or the transport of heavy loads using wheeled vehicles;

• the wind pushing the sails of ships at sea ;

• steam driving the pistons of a locomotive engine;

• combustion of a fossil liquid in the cylinders of a motor vehicle or boat engine;

• the combustion of gas powering an aircraft turboshaft engine.

In all cases except wind power, land, air and sea vehicles carry their own energy source to ensure autonomy.

Since the development of industrial electricity, railroads have had a special feature: the track is equipped with a power line, so that electrical energy is "captured", rather than carried, by the rail vehicle. This has two key consequences:

• autonomy is infinite (as long as the line is electrified);

• the transformation of electrical energy into mechanical energy generates no emissions other than very little heat due to losses. This is why, from the end of the 19th century, urban transport was the first to use this energy to replace the highly polluting horse, steam or internal combustion engine.

There are two distinct parts to train power supply. The first is the supply of the necessary power to the rail network in the right form and at the right level: these are the substations, which act as interface power stations with the general network.

The second part, developed in this article, analyzes the functions and their constraints, to ensure the distribution of electrical power in line. Electrical, mechanical and aerodynamic constraints are all important.

These technologies need to be adapted to the different types of train operation. For example, from the outset, metro networks, most of which were built in tunnels, favored power supply by conductors fixed to the ground (commonly known as the "3rd rail"), in keeping with the limited dimensions of such infrastructures. Similarly, the recent redevelopment of tramway networks has led to innovations that respect the urban environment, thanks in particular to ground power supply.

As is the case for all transport infrastructure, the guarantee of proper operation under the most severe conditions in terms of operating density and economic performance depends on rigorous maintenance, the main aspects of which we will analyze below.

Electric rail traction has benefited from advances and developments in electrical engineering and electronics right...