IEEE Electrification Magazine - September 2013 - 6

of the number of substations.
Because intermediate conductors are
Three-Phase High-Voltage Network
connected to ground -potential, i.e.,
they are set to zero, negative voltages
appear in lower conductors, as illustrated in F
- igure 2(b). The relationship
Traction
Traction
between the voltage of the positive
Substation 1
Substation n
and negative conductors allows us to
call them bivoltage symmetrical systems when they have the same ratio
in both autotransformers; they are
called bivoltage asymmetrical systems otherwise. The autotransformers mentioned earlier reduce the
Subsector 1-Left
Subsector 1-Right Subsector n-Left Subsector n-Right
Sector 1
Sector n
voltage to the allowable range of values for the rolling stock, while the
return current is forced to go through
Figure 1. A general view of a railway electrification system.
the negative -feeders.
monovoltage system shown in Figure 2(a) uses a set of
The traction substations are those parts of the instalconductors at the voltage of the rolling stock and a seclation that carry out the connection of any electrified
ond set of grounded conductors for the return circuit. In
OCL sector to the three-phase network, performing the
the literature, this system is called a monovoltage syssuitable transformation from one voltage to another. The
tem, or 1 # 25 kV, because of the use of 25 kV. In this sysmost common topology in the traction substations is the
tem, all the c
- urrent consumption of a certain train covers
simple bar, which is less expensive but offers reduced
the section between the substation and the train.
operating flexibility. However, in cases where a unique
On the contrary, bivoltage systems are used to transsubstation feeds several OCLs, the use of more complex
port voltage higher than the supplying voltage of the rolltopologies such as rings or double bars is recommended.
ing stock, which is reduced by using autotransformers
In some cases, it is even possible to join the traction and
scattered along the OCL, as shown in Figure 2(b). In certain
transportation substations in a single facility. The topolotechnical publications, this system is called bivoltage, or
gy of the substation can be slightly varied depending on
2 # 25 kV, because of the use of 25 kV and because it
the type of connection of the transformers and to
involves the use of two different levels of voltage in the
maneuver coordinately several substations via remotecatenary, requiring the use of a third set of conductors.
control systems to adapt the topology of electrification to
This system reduces the electric current in most of the
specific necessities. Regarding the connections commonstretch between the traction substation and the rolling
ly used to connect the single-phase loads to the threestock; in fact, only part of the consumption current has to
phase network, different publications remark that the
go over the whole distance. Thus, it is possible to reduce
factors that tip the choice toward one or another form of
electrical losses and voltage drops in the catenary, increasconnection are simplicity, cost, and imbalances in the
ing the length of the sectors with the expected reduction
three-phase network.

High-Voltage Network

Positive-Phase Conductor

Negative-Phase Conductor

(a)
Figure 2. (a) Monovoltage and (b) bivoltage system configurations.

I E E E E l e c t r i f i c atio n Magaz ine / september 2013

High-Voltage Network
(b)

Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2013