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The Advantages and Advances of Electric Railways [Viewpoint]

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Abstract

Discusses the advancements made in electric rail transportation and reports on the advantages in offers for the future of mass transportation.
IEEE Electrification Magazine / september 2014
60
VIEWPOINT
side. The losses are small, and, there-
fore, a high efficiency is obtained.
Since World War II, most railway
electrifications have been ac at
industrial frequency, that is, 50 or 60
Hz. These systems are relatively sim-
ple in their structure since power is
transferred through transformers
connecting the three-phase system
to the single-phase system. This
transformation inherently creates an
imbalance of the three-phase grid. To
make the load of the three-phase
system more symmetric, the catena-
ry is sectioned and the different sec-
tions are then fed by different phases
of the three-phase systems.
This sectioning brings several
disadvantages: 1) the load of the
three-phase grid is still nonsymmetric,
2) each transformer has to be dimen-
sioned for the full power since each
section is only fed by one transformer
substation, and 3) the regenerated
power cannot be fed back to vehicles
in adjacent sections. To compensate
for these drawbacks, different mea-
sures have been taken as special
transformers employing different
winding configurations or, more
recently, different kinds of power fac-
tor correction converters.
It is perhaps somewhat surprising,
but none of these disadvantages are
present in a low-frequency system
where the three-phase converters are
symmetric loads to the three-phase
grid and no sectioning is required.
So the question remains, how can
we develop the 50- and 60-Hz system
to overcome these disadvantages?
Why not learn from the system
design of the low-frequency systems?
By replacing the transformers
with static converters, all of these
drawbacks are eliminated. The first
converter-based solutions for 50 Hz
have recently been proposed, merg-
ing the system design at low fre-
quency and industrial frequency.
The key to future railway electrifi-
cation is more power electronics. New
converter concepts developed for
transmission, distribution, and motor
drives are also quickly finding their
way into transportation in general and
electrification of railways in particular.
This development is one of many stra-
tegic areas covered by the IEEE Trans-
portation Electrification initiative.
Biography
Stefan Östlund (stefano@kth.se) is a
professor of electric power engineer-
ing at KTH Royal Institute of Technol-
ogy in Stockholm, Sweden. He has
more than 20 years of experience in
teaching and research on electric
railway traction. His main focus is on
converter systems for rail applica-
tions and new concepts for railway
electrification. He has also done work
on hybrid electric vehicles. He is a
Senior Member of the IEEE.
those supported by other modes
of transport
xtreat the emissions similarly to
other modes of transport (in many
countries, electrical railways must
purchase emission rights)
xestablish a fair regulation of the
remuneration of the energy that
is given back to the public grid.
These actions will lead to a better
usage of the energy, with all of the
environmental advantages it implies.
The remuneration of the regenerated
energy—the third bullet point—would
be particularly critical to stimulate
the investments in dc reversible
substations, which are currently
very infrequent.
Biography
Alberto Garcia Alvarez (albertoga@
renfe.es) received his bachelor in laws
degree from UNED in 1996 and his
Ph.D. degree in economics from UAM
in 2004. He received his Ph.D. degree in
engineering and transport infrastruc-
ture from UPC in 2012. He was an
industrial electromechanical engineer,
ICAI, in 1977 and has worked in rail-
ways since 1981. He is currently the
general director of Renfe Viajeros, the
Spanish train operator specializing in
passenger transport.
The Advantages and Advances (continued from page 64)
Rail Power Supplies (continued from page 4)
TECHNOLOGY LEADERS
viewpoint
IEEE Electrification Magazine / september 2014
64
By Alberto Garcia Alvarez
The Advantages and Advances
of Electric Railways
AILWAYS HAVE BEEN
using electricity for vehicle
propulsion for more than
100 years. Together with pipeline
transportation, it is the only trans-
portation mode that uses a massive
amount of electricity to produce
movement. This entails great advan-
tages, both from an energy and envi-
ronmental point of view:
xxlower consumption of nonrenew-
able energy as an increasingly
important part of the electricity
is generated with nuclear power
and with renewable sources
xxreduced emissions of green-
house gases
xxdelocalization of the local-effect
emissions, which are moved
from the places where transport
activity takes place—in the case
of urban or suburban transport,
typically populated areas—to the
places where power is generated.
These fantastic advantages of
electrical traction are the reasons
why all of the modes of transport are
currently trying to evolve from ther-
mal engines toward electrical motors.
In the last century, the railway has
come a long way in improving its effi-
ciency, with important contributions
such as the evolution of vehicle
motors from dc to ac (synchronous
and asynchronous machines) and,
more recently, to ac permanent mag-
nets synchronous machines; the
adoption of higher voltages in the
electrification, which have reached
up 2 × 25 kV; the connection of trac-
tion substations to 400-kV transmis-
sion networks with very low losses;
and the development and adoption of
modern operation and driving sys-
tems, which allow the global efficien-
cy of traction to improve every day. As
a consequence, the rail industry cur-
rently has strong leadership in power
electronics technologies, and this is
expected to increase in the future.
In addition to the ability to use
electrical power with high efficiency,
the electrified railway has a second
advantage: the trains are permanent-
ly connected to the network through
the catenary. This makes possible the
management and utilization of the
power regenerated when the trains
brake, which eliminates the need for
onboard energy storage and allows
energy to be 1) used by other vehicles
that, at the same moment, are
demanding energy or 2) stored on the
wayside in fixed larger accumulators
(which, compared to onboard sys-
tems, avoids consuming energy for
transporting them), with better effi-
ciency and no limitation in terms of
size and mass. This interconnection
is a competitive advantage of electri-
fied railways compared to other
transport modes, even when the oth-
ers become electrical.
Furthermore, the advances in dis-
tribution electrical smart grids and in
optimization of the railway operation
open up new and promising possibil-
ities for interaction between the elec-
trical railways and the public grid:
the system will be able to decide in
real time whether it is preferable to
return power back to the network or
to store it and whether it is prefera-
ble to stop a train by braking or by
coasting. With these technologies,
the railway will be able to contribute
to the operation of the electrical sys-
tem, responding to the requests of
the electrical system operator (e.g.,
temporarily injecting power into the
grid to balance the demand and gen-
eration if a power plant fails). These
new technologies are expected to
further extend the leadership of elec-
trified railways in terms of energy
efficiency compared to other trans-
port modes.
It is desirable that regulations and
fiscal policies recognize these advantag-
es of the electrical traction with a per-
manent connection to the grid (which
is not the case in many countries now)
to send the appropriate economic sig-
nals to promote global efficiency and to
give value to these advantages. To allow
for a fair competition, it would be nec-
essary, for instance, to
xxequalize the existing taxes sup-
ported by electrical railways and
R
Digital Object Identifier 10.1109/MELE.2014.2339411
Date of publication: 29 September 2014 (continued on page 60)
... Electrified railway has excellent performance compared with other means of transportation [1] . In recent years, China has speeded up the construction of high-speed railway. ...
... Advancement in high-speed railway (HSR) transportation has resulted in more passengers transiting through railway networks [4]. HSR is currently becoming more and more popular, and this mode of public transportation is preferred in several countries due to its speed, safety, energy efficiency and larger passenger handling capacity [5][6][7][8][9]. ...
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