The first railways were powered by steam engines. Although the first electric railway motor came on the scene halfway through the 19th century, the high infrastructure costs meant that its use was very limited. The first Diesel engines for railway usage were not developed until halfway through the 20th century. The evolution of electric motors for railways and the development of electrification from the middle of the 20th century meant that this kind of motor was suitable for railways. Nowadays, practically all commercial locomotives are powered by electric motors (Faure, 2004; Iwnicki, 2006).
Figure 6 illustrates a flow diagram for the different types of rail engines and motors most widely used throughout their history. The first Diesel locomotives with a mechanical or hydraulic drive immediately gave way to Diesel locomotives with electrical transmission. These locomotives are really hybrids equipped with a Diesel engine that supplies mechanical energy to a generator, which, in turn, supplies the electrical energy to power the electric motors that actually move the drive shafts. Although this may appear to be a contradiction in terms, it actually leads to a better regulation of the motors and greater overall energy efficiency.
Fig. 6. Railway engine and motor types.
The major drawback of electrical traction is the high cost of the infrastructure required to carry the electrical energy to the point of usage. This requires constructing long electrical supply lines called "catenary", (Figure 7). In addition, the locomotives need devices that enable the motor to be connected to the catenary: the most common being "pantographs" or the so-called "floaters". In its favour, electrical traction can be said to be clean, respectful of the environment and efficient, as an optimum regulation of the motors can be achieved. In this work, we will only focus on the functioning and regulation of the most widely used types of electric motors.