IEEE Electrification Magazine - September 2016 - 38

S4
L3

S5
L4

S 10

L9
T4

Figure 10. A case study.

The SC is in charge of energizing the charging rail or
bar. It also provides the protection elements, and it contains several switching elements in series and parallel for
security and availability reasons. It can be mounted in
surface or underground installation. Again, even when
the visual impact of the underground installation is nearly zero, it is more expensive and contains more auxiliary
equipment like water pumps for avoid flooding or air
conditioning systems. The switching equipment in the
detail of Figure 8 corresponds to an underground installation. In the case of Figure 9, the switching equipment is
surface mounted.
The SIP is installed on board and in the infrastructure
side, being responsible of the safe energization of the bar in
presence of a train. It has several redundant detection elements, and it is communicates with the SC and the SIM
that centralizes all the information. The SIM communicates with the network operator.
In a hybrid path with wired and catenary-free zones, a
typical operation is as follows. When a train arrives to a
catenary-free section, the track elements warn the unit
about its arrival to the catenary-free area, and the train
lowers the pantograph to enter it. When the train is near
to the charging point, the SIP together with the SIM place
the train at the charging point and lower the contact shoe
or raise the pantograph for the overhead charging system.
Then, the SIM activates the SC, the accumulator is
charged, the train raises the contact shoe or lowers the
pantograph, and it leaves the charging station.

Case Study
For analyzing the behavior of the on-board accumulator
and the savings produced by the system, two different
scenarios will be presented. Both of them are systems
with catenary. In the first scenario, all trains are
equipped with regenerative braking but without onboard accumulation system. In the second scenario, the
trains are equipped with a small accumulator too. This

accumulator has been sized to increase the efficiency at
a reduced cost; it does not need to provide all the traction power. The system is a 15-km common linear configuration with ten stops, two of them connected to the
ac network through rectifier substations as shown in
Figure 10. Both substations are nonreversible diodebased substations. The short circuit power of the 13.8-kV
distribution network where the substations are connected is 500 MVA. The rated power of each substation
is 1.62 MVA, and the power transformer ratio is
13.8 kV/560 V with a short circuit voltage of 5.5%. The dc
rated voltage is 750 V. The trains are similar to the ones
described in previous sections, but in this case, the
OESS is smaller. The maximum charging and discharging power is 95 kW, and it only has one module of ultracapacitors with a total capacity of 585 Wh. The
maximum permanent voltage has been set to 900 V, and
the maximum permanent voltage is 890 V, the minimum voltage is 550 V. The feeding system impedance is
39 mΩ/km and the rail impedance is 6.2 mΩ/km. The
line lengths are in Table 4.
There are four trains in the system, trains 1 and 3
depart from stop 1 with the destination stop 10 at t1 =
0 min and t3 = 1 min, respectively. On the other side, trains
2 and 4 depart from stop 10 with the destination stop 1 at
t2 = 1.8 min and t4 = 3.4 min, respectively. Obviously, the
whole system is a dual track railway. The simulated time
interval is 7.5 min.
The data presented in Figures 11-13 were obtained
through simulations. Two different software packages
were used for performing such simulations. The first
one (ITINER) is the proprietary CAF software for the
electromechanical simulation of the trains. From this
software, the power demanded by the traction equipment of a single train is obtained at each instant and
position for a given train and a given path. The interaction of the traction equipment with its on-board accumulation system as well as the interaction among all

TABLE 4. A case study of line lengths.
Length (m)

2,100

2,108

2,400

1,812

1,820

1,720

2,750

1,760

570

I E E E E l e c t r i f i c ati o n M agaz ine / SEPTEMBER 2016

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