Page 60 - 360.revista de Alta Velocidad - Nº 5

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

Figure 7. Mechanical layout of a neutral section of catenary. (Source: Adif).
Logically, on passing from catenary 1 to catenary 3, the pantograph will connect to voltage V1.
The same will happen with the V2 voltage on passing on the sectioning of catenary 2. The rest
of the time, the voltage of catenary 3 will vary depending on the difference of the electrical
phases of the voltages of the ends and on the impedance of the de-energised section.
It can be seen that if the time rates of the voltages of the collateral voltage transformers
are consecutive (60⁰ phase difference), the electric voltage between the ends of the neutral
section is roughly the nominal voltage of the secondary of the transformers. If the rates are
not consecutive (phase difference of 120⁰), the voltage between ends will be roughly √3 times
the nominal voltage of the secondary.
A neutral section may be announced with enough time for the train to be able to carry out the
opening operation of the traction switch . As seen above, the opening requirement is due to the
1
pantograph energizing the de-energised catenary for a few seconds using the end sectionings, an
action that may involve the electrical bypassing of both routes if the train has two pantographs
that connect catenaries 1 and 2 via catenary 3 when passing over the sectionings. Furthermore,
in short neutral sections, it has been seen that a very high speeds the arc extinction might
not have occurred when the pantograph is already in the second sectioning. In any event, the
greater the length of the de-energised section, the fewer problems will occur although the loss
of speed the train suffers will generally be higher.
The need for installing neutral sections in high-speed lines may entail the following problems:

• Breakdowns on the catenary if a train enters with the traction switch closed. In the event
of circulating under ATP this type of incidents will not occur.
• Trains that stop in the section de-energised (for different reasons) and which cannot start
up again on their own. Normally a train stopping affects the regularity of the rest of the
trains circulating behind it, as some minutes are required for energising the de-energised
section and being able to start to run again.
• Generation of fatigue in the train’s traction equipment due to continuous openings and
closings of the circuit.

It should be pointed out here that the train’s lost speed when passing through the neutral

1 Automatic process if circulating under ATP.

58 360.revista de alta velocidad