IEEE Electrification Magazine - December 2013 - 20

45 kV

230 V
Auxiliary Service Lab

:+ 1
CLM1

Power Line
dc/dccat

:+ 2
CLM2
CLR

700 V

3,500 V

400 V

EV Fast
Chargers

dc/dc1
dc/dc2
UC1

ac/dc
PV Panel

Figure 9. A microgrid concept based on railway power lines. UC: ultracapacitors, EV: electric vehicle, PV: photovoltaic panel, and ES: energy storage.

For safety reasons,
the flywheel was
installed in a
protected pit located
in the high-voltage
equipment area of
the railway
substation.

evolution of speeds over time with
these additional power inputs.
Mechanical losses are the most
important losses in a flywheel, so it is
important to reduce them as much as
possible. to minimize them, two
important measures have been considered: the use of magnetic levitation
to lessen the bearings axial load-a
ring of permanent magnets and an
additional electromagnet for fine regulation have been disposed to do so-
and the reduction of the air pressure
around the flywheel to make smaller
the aerodynamic losses-an inner
pressure of 100 mbar is accomplished.
this results in an average efficiency of 98% when there is
no power exchange. the efficiency during the power
exchange between the flywheel and the load depends
highly on the power level, and it is mainly associated with
the copper losses at the electrical machine, being in the
range of 80-90% in the case of our study. Figures 7 and 8
show the results obtained with the flywheel during the
tests in the railway substation.
Figure 7(a) shows the operating and monitoring environment while the system is working, and Figure 7(b)
shows a sample of the power line voltage and current
injected by the system for storage in a series of tests
regarding absorption and power injection. Figure 8 shows
the results of the dc voltage and the current managed by
the electrical machine in motor mode (storage mode)
and generator mode (recovery mode), and the transition
between stand-by state and consumption state, which is
produced in a few milliseconds. the dc-voltage oscillation is lower than 10%, an acceptable value for the electric system.

I E E E E l e c t r i f i c ati o n M agaz ine / december 2013

as their power lines are highcapacity transportation lines, a more
extended concept of energy management can be considered for railways,
by integrating the train traffic and the
grid stability with renewable energy
generation, electric vehicle recharging,
and energy storage of different types
to increase the reliability of the whole
system. Some projects are currently
being carried out in Spain based on
this idea. Figure 9 shows a schema of
an application example where the
energy management is carried out
from a railway power line, with
mechanical energy storage, storage
with batteries and ultracapacitors, renewable energy generation, electric vehicle charging, and the presence of the grid.
this article presents the technology of flywheels
applied to railway transport, but it does not mean that it is
the most appropriate for this application. Only the combination of different technologies of energy storage and
power supply, advanced control devices, and optimized
strategies of operation will provide the increase in efficiency and reliability that such complex systems require.

biographies
Marcos Lafoz Pastor (marcos.lafoz@ciemat.es) is with centro de investigaciones energéticas, Medioambientales y
tecnológicas in Spain.
Luis García-Tabarés Rodríguez (luis.garcia@ciemat.es) is
with centro de investigaciones energéticas, Medioambientales y tecnológicas in Spain.
Cristina Vázquez Vélez (cristina.vazquez@ciemat.es)
is with centro de investigaciones energéticas, Medioambientales y tecnológicas in Spain.

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