IEEE Electrification Magazine - September 2014 - 60

VIEWPOINT

The Advantages and Advances
those supported by other modes
of transport
 treat the emissions similarly to
other modes of transport (in many
countries, electrical railways must
purchase emission rights)
 establish 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

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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 infrastructure from UPC in 2012. He was an
industrial electromechanical engineer,
ICAI, in 1977 and has worked in railways since 1981. He is currently the
general director of Renfe Viajeros, the
Spanish train operator specializing in
passenger transport.

TECHNOLOGY LEADERS

Rail Power Supplies
side. The losses are small, and, therefore, 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 simple 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 catenary is sectioned and the different sections 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 dimensioned 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

(continued from page 4)

in adjacent sections. To compensate
for these drawbacks, different measures have been taken as special
transformers employing different
winding configurations or, more
recently, different kinds of power factor 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, merging the system design at low frequency and industrial frequency.

I E E E E l e c t r i f i cati o n M agaz ine / SEPTEMBER 2014

The key to future railway electrification 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 strategic areas covered by the IEEE Transportation Electrification initiative.

Biography
Stefan Östlund (stefano@kth.se) is a
professor of electric power engineering at KTH Royal Institute of Technology 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 applications and new concepts for railway
electrification. He has also done work
on hybrid electric vehicles. He is a
Senior Member of the IEEE.

Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2014