Page 53 - 360.revista de Alta Velocidad - Nº 5

Current situation and prospects of electric traction systems used in High-Speed railways

If it is considered that the power P in the wheel of the locomotive is expressed by the following
r
equation:

This power can be related to the electric power P absorbed by the pantograph. To do this, one
TR
must know the overall performance of the locomotive which is usually supplied by the manufac-
turers. In equation (3) the power P is expressed in [kW], F in [kN] and v in [kph].
r j
As an example if it is considered the case of a Renfe S/100 train (8 cars and a total mass of 393
t), equation (1) is expressed as follows:

Considering a speed of 300 kph, a drag resistance of 58 kN is obtained. Taking into account
that for this train has a value on the order of 1,04 and considering a non-slope zone and an
acceleration of 0,25 ms , it obtains a F of 158 kN. Using equation (3) P acquires a value of 13
-2
j
r
MW.
From this example it can be deduced that the power which is necessary to provide from an
electric line for feeding a High-Speed train is very high. If it consider a performance near to 1
(losses in the traction link of the locomotive are negligible), it has that the electrical power
demanded by the pantograph of the train are also 13 MW. Considering the following equation:

Taking into account a pure resistive load, the electrical power demanded by the train in the
pantograph is:

It follows that to transport a given power to the train could be acted on the voltage or current
so that the required value is obtained. Because it is not in the interest of the intensity value
to be high, because the losses that would arise in the transport are proportional to the square
of its value, always tends to increase the value of the voltage and to decrease, as much as
possible, the of the current. Thus, when working with high values of voltage, it is necessary to
always use alternating current.
Considering that, as explained above, the current value is the one that is decreased, a catenary
will be required mechanically lighter because the required conductors will be less heavy because
they do not need a significant geometric section (a characteristic of this type of catenary is in
which only one contact wire is required). The lightness characteristic is essential at High Speed
because the contact between the pantograph and the catenary improves.

For all of the above, High-Speed railways should always use AC systems. Unlike the generation
of electric power in the power plants, where alternating current is always generated in three

International Congress on High-speed Rail: Technologies and Long Term Impacts - Ciudad Real (Spain) - 25th anniversary Madrid-Sevilla corridor 51