IEEE Electrification Magazine - September 2016 - 41

250 kW. When the train does not have an accumulator,
200 kW are burned in the rheostatic system. In the second scenario, part of that power (95 kW) is used for
charging the on-board accumulator, and around
105 kW are also burned. It must be observed that in
both cases the catenary voltage is over the maximum
permanent voltage (890 V), but it does not reach the
maximum nonpermanent voltage (900 V). The power
injected by train 1 in the dc traction system (250 kW) is
approximately the power consumed by train 2 (plus
losses), so no power is demanded from the substations. The voltage level in the substations is very similar to the voltage in train 1. In B, the train 1 is still
braking at lower rate and the train A starts braking,
regenerating 450 kW. In this case, there is no consumption in the network since train 4 is still nonactive,
train 3 is drifting, and 1 and 2 are braking. In such a
situation, there is no power injection in the catenary
and the voltage in all the system is saturated to the
maximum nonpermanent voltage (900 V).
For summarizing the effect of the on-board accumulation, in Figure 13, the energy provided by the two substations is depicted. During the first instants of the
simulation, the accumulation systems are empty in all
trains (worst scenario), so both curves are very similar.
In t = 66 s, the first train brakes, and the accumulator
system is charged; the next power demand in the network is produced also by the first train at t = 95 s, but the
accumulator is already charged, so part of the power is
provided by the on-board device. From that instant, both
curves representing the energy absorbed from the distribution grid start to differ from each other. At the end of
the simulation period (7.5 min), the scenario without onboard accumulation exhibits a substation consumption
of 45.1 kWh, while the second scenario demands from
the distribution network 39.9 kWh. The efficiency of the
system was increased in an 11.53%. It must be remarked
that the peak power of the trains is nearly 700 kW while
the accumulation system peak power is only 95 kW with
a very low-energy capacity (less than 0.6 kWh). The peak
power demand at the substations has been reduced
from 1.336 MW to 1.116 MW. Such an instance corresponds to a situation in which there are two trains in
traction mode and their accumulators are providing a
total power of 170 kW.

Conclusions
The highlights of this article are listed below.
xx
On-board accumulation has proved to be the best
option for the energy recovery in a safe way in light
railway systems from the point of view of flexibility
and investment cost.
xx
Reversible substations and off-board accumulation
could be a good solution to increase the efficiency of
the system, but they cannot be combined with catenary-free segments, and neither the losses in the

traction system nor the performance of the vehicles
are improved.
xx
Depending on the application, the characteristics of
the path, the required traction power, the dc traction
system, and the network operating conditions, the
best combination of batteries/ultracapacitors must be
selected.
xx
The challenge right now is the development of a costeffective accumulation systems with high-energy
density, high-power density, and high cyclability. The
race has been already started.

For Further Reading
J. Swanson and J. Smatlak, "State of the art in light rail alternative power supplies," in Proc. APTA/TRB 2015 Light Rail Conf.,
Minneapolis, MN, Nov. 2015.
V. Gelman, "Energy storage that may be too good to be
true: Comparison between wayside storage and reversible
thyristor controlled rectifiers for heavy rail," IEEE Veh. Technol.
Mag., vol. 8, no. 4, pp. 70-80, Dec. 2013.
D. Cornic, "Efficient recovery of braking energy through a
reversible dc substation," in Proc. Electrical Systems for Aircraft, Railway and Ship Propulsion (ESARS), Bologna, Italy, 2010,
pp. 1-9.

Biographies
Pablo Arboleya (arboleyapablo@uniovi.es) received the
M.Sc. and Ph.D. (with distinction) degrees from the University of Oviedo, Gijon, Spain, in 2001 and 2005, respectively, both in electrical engineering. Currently, he works
as an associate professor in the Department of Electrical Engineering at the University of Oviedo (with tenure
since 2010). He is head of the LEMUR research group
team in charge of developing railway simulators and is
managing editor of the International Journal of Electrical
Power & Energy Systems published by Elsevier. Presently,
his main research interests are focused on the static
and dynamic modeling and operation techniques for
distribution systems and railway traction networks. He
is a Senior Member of the IEEE.
Peru Bidaguren (pbidaguren@cafte.com) received two
M.Sc. degrees from the University of Deusto, Bilbao,
Spain, in 2004 in computer engineering and in 2009 in
industrial engineering (specialized in industrial organization). Currently, he works as a project manager in the
Engineering Department in CAF Turnkey and Engineering (since 2010). He is responsible for power studies
developed by CAF Group.
Urtzi Armendariz (uarmendariz@caftengineering.
com) received an M.Sc. degree in electronic and automation engineering from Mondragon University in 2003. His
professional career has focused on smart electrification
research and development projects, mostly related to
railway and electric mobility domains. Currently, he is
the engineering director of CAF Turnkey and Engineering Company.

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Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2016