IEEE Electrification Magazine - September 2014 - 64
VIEWPOINT
The Advantages and Advances
of Electric Railways
By Alberto Garcia Alvarez
AILWAYS HAVE BEEN
using electricity for vehicle
propulsion for more than
100 years. Together with pipeline
transportation, it is the only transportation mode that uses a massive
amount of electricity to produce
movement. This entails great advantages, both from an energy and environmental point of view:
lower consumption of nonrenewable energy as an increasingly
important part of the electricity
is generated with nuclear power
and with renewable sources
reduced emissions of greenhouse gases
delocalization 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 thermal engines toward electrical motors.
In the last century, the railway has
come a long way in improving its efficiency, with important contributions
such as the evolution of vehicle
motors from dc to ac (synchronous
and asynchronous machines) and,
R
Digital Object Identifier 10.1109/MELE.2014.2339411
Date of publication: 29 September 2014
64
more recently, to ac permanent magnets synchronous machines; the
adoption of higher voltages in the
electrification, which have reached
up 2 × 25 kV; the connection of traction substations to 400-kV transmission networks with very low losses;
and the development and adoption of
modern operation and driving systems, which allow the global efficiency of traction to improve every day. As
a consequence, the rail industry currently 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 permanently 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 systems, avoids consuming energy for
transporting them), with better efficiency and no limitation in terms of
size and mass. This interconnection
is a competitive advantage of electrified railways compared to other
transport modes, even when the others become electrical.
I E E E E l e c t r i f i c ati o n M agaz ine / SEPTEMBER 2014
Furthermore, the advances in distribution electrical smart grids and in
optimization of the railway operation
open up new and promising possibilities for interaction between the electrical 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 preferable 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 system, responding to the requests of
the electrical system operator (e.g.,
temporarily injecting power into the
grid to balance the demand and generation if a power plant fails). These
new technologies are expected to
further extend the leadership of electrified railways in terms of energy
efficiency compared to other transport modes.
It is desirable that regulations and
fiscal policies recognize these advantages of the electrical traction with a permanent connection to the grid (which
is not the case in many countries now)
to send the appropriate economic signals to promote global efficiency and to
give value to these advantages. To allow
for a fair competition, it would be necessary, for instance, to
equalize the existing taxes supported by electrical railways and
(continued on page 60)
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