Page 63 - 360.revista de Alta Velocidad - Nº 5

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

The length of the de-energised catenary is also a fundamental parameter for analysing the
viability of installing this type of systems. Specifically it has been able to conclude that if
this length is lower than established for an interoperable neutral section (402 m), installing
switches will not be viable. The reason lies in considering the circulation in double composition
of a 200 m train. In this case if the distance existing between the train’s first wheel and the
farthest away pantograph from the second composition the train may carry in service (a small
auxiliary distance derived from the coupling of the two trains should also be considered), it is
concluded that this distance is the one that determines the maximum length of the deenergised
section to be used. Therefore, the greater the no-voltage section the simpler it will be to install
a system with these characteristics.

5. AC feeding systems

TPS can be considered to be composed of two main subsystems: electric traction substations
and the railway distribution line (catenary).
The railway distribution line can also be considered composed of the overhead contact line, the
return circuit and other equipment that we could call complementary elements. The overhead
contact line is formed by several conductors (mainly contact wire, catenary wire and droppers)
and their elements of support, cable and insulation (cantilever, tie bar, steady arm, etc.). Its
design is characteristic of each technology company or of each infrastructure manager and is
specially designed to guarantee the transmission of a certain maximum current to each train
(the maximum recommended current in EN 50388 is 680 A for 25 kV 50 Hz) an adequate electrical
contact with the pantograph at a certain maximum speed. The return circuit is composed of
the rails and other components that they group in the set of complementary elements. These
complementary elements depend on each feeding system used.
The configurations of the TPS networks are considered from the point of view of the existing
type of AC power systems and from the point of view of the unilateral or bilateral connection
of the substations. The different types of AC systems of feeding to the High-Speed networks are
the following:
• Simple feeding with rail return.

• Autotransformer (AT system).
• Coaxial.
The fundamental characteristics that determine the use of each one of them is its capacity to
transmit power according to the length of the line and the electromagnetic disturbances that
generate to its surroundings.
5.1 Simple feeding with rail return or additional return conductor

This connection is the configuration adopted when there are sufficient connection points to the
transport line. In this case the distance between collateral substations is usually between 35
and 40 kilometers. If a nominal voltage value is considered in the catenary, this connection is
often referred to as the 1 × kV system. Considering the standard value of electrical voltage
in catenary (25 kV), it is called 1 × 25 kV system. The operating diagram is shown in Figure 9.
Generally the substation transformers are connected to the same electrical phases. In this
way the section of the substation is connected to the same electrical phase, and it is not
necessary to install a neutral zone in the substation. The primary winding of each transformer
is connected to the grid and converts this voltage to that of the train (25 kV). The secondary
winding is therefore connected between the catenary and earth.

International Congress on High-speed Rail: Technologies and Long Term Impacts - Ciudad Real (Spain) - 25th anniversary Madrid-Sevilla corridor 61