2. Traction chains

Using on-board or distributed energy, the powertrain adapts the driving torque required by the axles. There are two main categories:

• electric traction chain where the axles are driven by an electric motor;

• mechanical or hydrodynamic traction chain.

The first category is by far the most widespread, since it covers both on-board and distributed power sources. The second is reserved for small and medium-powered equipment such as self-propelled railcars.

A century of railway development has been based on the use of DC motors with series excitation collectors, the counterpart being the need to adapt the power supply to medium voltages (600 to 3,000 V). The equipment used to adjust this voltage (starting rheostat) is complex, heavy and of low efficiency...