Page 56 - 360.revista de Alta Velocidad - Nº 5

Martínez Acevedo, José Conrado. Berrios Villalba, Antonio. Peregrín García, Eugenio.

3.1 Disturbances in the transmission line

These disturbances are mainly the following (Figure 2):
1. Imbalances of currents and voltages at different points in the network, due to the character
of the single-phase load.
2. Harmonic currents and voltages that produce the phenomenon of harmonic distortion. They
are usually originated by the electronic equipment of the locomotive and even by the elec-
tric arcs produced in the interaction between the pantograph and the catenary. Harmonic
distortion affects the characteristics of the mains voltage, deteriorating the quality of the
service.
3. Voltage fluctuations in the network. It has its origin in the variations of the regime of the
load, that is to say, in the randomness of the circulations of the trains and in the variability
of the power demanded by each one of them. Voltage fluctuations cause variations in the
supply voltage to users near the common connection point.
4. Voltage sag. They are caused by defects in the traction circuit causing harmful effects that
may become unacceptable by users connected in the environment of the common connec-
tion point.

Figure 2. Disturbances. (Source: Author).

3.2 Imbalances of currents and voltages

Of all the disturbances produced on the transmission line, the imbalances of line currents and
voltages are the most important (Figure 3). If the same electrical phase of the network were
always used, the three-phase system would be decompensated. Therefore, in the electrical
supply of High-Speed lines, the phases are always alternated or rotated.

54 360.revista de alta velocidad