8 –Technical Forums Energy, Environment & Transit
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Utilizing Wayside Energy Storage Substations in Rail
Transit Systems – Some Modelling and Simulation
Results
J.G.Yu, PhD SYSTRA Consulting,Inc
Philadelphia, PA
Martin P. Schroeder American Public Transportation
Association Washington, DC
David Teumim Teumim Technical, LLC
Allentown, PA
Keywords: DC Traction Power Systems, Energy Storage
Devices, Wayside Energy Storage Substations, Computer
Simulation; Energy Savings.
Abstract
The APTA / EPRI Energy Storage Research Consortium [1]
study team, funded by the Transportation Research Board
TCRP program, conducted a study of wayside energy storage
systems coupled with track propulsion networks of actual
system designs. Adding energy storage is aimed at reducing
energy consumption through improved capture of regenerative
braking energy, reduced energy costs through reduction of
peak power demand, improvement of power quality through
low-voltage support, and use of energy storage systems as
supplements to or replacements for conventional electrical
substations under specific conditions. Computer simulations
are performed to assess the benefit of wayside energy storage
systems starting with a look at voltage support.
Introduction
Energy storage devices (ESD) for transit may take different
forms, such as flywheels, batteries, electrochemical capacitors,
or hybrid devices (batteries combined with electrochemical
capacitors, and other variations). Such devices have seen rapid
development in recent years. Their applications have spread
from traditional roles as small scale Uninterruptible Power
Supplies (UPS) to utility scale storage devices.
In DC-traction power systems, wayside energy storage
substations (WESS) using ESD are emerging as a viable
supplement to traditional substations for traction power system
designers. A WESS can be located on its own anywhere along
the track, without the need of medium voltage power supply
sources from the utility. However, it is also recognized that a
WESS can be tied to an AC utility supply using DC/AC
inverters should there be interest in sharing the benefits of
storage between transit systems and utilities, both sharing
similar needs in power quality and peak power reduction. The
systems studied here however, only address a DC connected
WESS. The following discussion will focus on the potential
benefit of ESD-substations to correct voltage support problems
and improve capture ratio of available regenerative braking
energy. Results will also highlight how various general design
parameters affect the performance of energy storage systems.
1 A Typical WESS Design
The main components of a WESS installation and a traditional
rectifier substation are compared in the following figure.
Figure 1: Comparison of the main components between a
rectifier substation and a WESS
The core components of most wayside energy storage
substations consist of a storage medium and a power control
unit, as well as the necessary DC bus and switchgear for
8 –Technical Forums Energy, Environment & Transit
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power distribution to the track, third rail or overhead contact
systems (OCS).
Control of WESS charging and discharging cycles is based on
voltage levels as shown in Figure 2.
Figure 2: Power control diagram for WESS
The main parameters that define a WESS design are:
Energy storage capacity (kWh)
Power rating (kW)
Power conversion efficiency
Maximum current (charging or discharging) (amps)
Control voltage (Vc) and various other voltage levels
for charging and discharging control (volts)
Computer models have been developed that include these
energy storage device parameters [2]
and the associated
constitutive power distribution models of the traction power
systems. Computer simulations predict full-system operating
behaviour, energy storage performance and establish the
degree of sensitivity to various system design parameters.
Additional general system parameters used in simulations
included variables defining electrical performance of circuit
breaker houses and substations, electrical resistances of third
rail and return rail, substation capacity, track alignment data,
vehicle braking and propulsion capabilities, and operational
data such as train headway scheduling, station dwell times,
off-peak operating changes, and various other parameters.
To further identify optimal locations of energy storage devices
within the alignment of candidate conventional propulsion
system designs, simulations without energy storage are
conducted first to establish potential weaknesses within the
system associated with problems of voltage sag or
regenerative braking energy capture. This type of analysis was
conducted for three families of rail systems including light
rail, heavy rail and commuter rail. From these families,
representative system designs were chosen and energy storage
systems sized based on simulation results, energy storage
characteristics, and analysis of data taken from actual
operating transit agencies.
Simulations were performed on three representative systems
organized. For each system, simulation results predicted
performance of the overall system as well as the energy
storage benefit.
Light Rail
System parameters
The main parameters of the light rail transit (LRT) system
being simulated are listed as follows:
7 Miles of track (double track system)
12 Stations
750V nominal voltage DC traction power system,
7 Traction power substations (TPSS); each equipped with
1.5MW rectifier unit
1 Circuit breaker house (CBH)
2 car trains in operation with regenerative braking
5 Minute headway in peak hours
15 Minute headway in off peak hours and weekends
The following figure shows the motoring and regenerative
braking control diagram for a typical LRT vehicle.
Figure 3: Power control diagram for the LRT vehicle
Train voltage support requirement
Train voltage is a critical performance parameter for the
traction power system. For this particular system, when a
train’s voltage falls below 575V (see Figure 3) corresponding
to a voltage sag condition, the train’s power demand cannot be
fully met by the traction power system, which will have an
adverse impact on the performance of the train. At or below
500V, the train’s traction power motor will be shut down in
order to avoid damage to the equipment.
Under normal conditions (when all substations are in service),
the simulated train voltages are all above 575V, which are
adequate for trains to achieve their on-time performance.
However, when the rectifier in positions A4 or A5 TPSS is out
of service, the minimum train voltage can fall to 504V and
559V respectively. These sags are shown in the following
8 –Technical Forums Energy, Environment & Transit
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figures where it is noted that the data points represent
solutions at time steps in the simulation.
Simulated Train Voltages
(Case 64 - A4 Outage, 5-Minute Headway)
100
200
300
400
500
600
700
800
900
1,000
24.5 25.0 25.5 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 30.0 30.5 31.0 31.5 32.0
Location (miles)
Tra
in V
olt
ag
e (
V)
Train Voltage
Substations
Stations
A1-T
PS
SS
T 0
1
A4-O
UT
ST
07
A6-T
PS
S
A5-T
PS
S
A7-T
PS
S
A2-T
PS
S
A3-T
PS
S
ST
02
ST
03
ST
04
ST
05
ST
06
ST
08
ST
09
ST
12
ST
10
ST
11
A4X
-CB
H
Figure 4: Train voltages under A4-TPSS outage condition
Simulated Train Voltages
(Case 65 - A5 Outage, 5-Minute Headway)
100
200
300
400
500
600
700
800
900
1,000
24.5 25.0 25.5 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 30.0 30.5 31.0 31.5 32.0
Location (miles)
Tra
in V
olt
ag
e (
V)
Train Voltage
Substations
Stations
A1
-TP
SS
ST
01
A4
-TP
SS
ST
07
A6
-TP
SS
A5
-Ou
t
A7
-TP
SS
A2
-TP
SS
A3
-TP
SS
ST
02
ST
03
ST
04
ST
05
ST
06
ST
08
ST
09
ST
12
ST
10
ST
11
A4
X-C
BH
Figure 5: Train voltages under A5-TPSS outage condition
In order to avoid the excessively low voltage conditions when
the rectifier in A4 or A5 TPSS is out of service or has failed,
either a full rectifier substation or a WESS at A4X-CBH
location can be considered as a reinforcement. Addition of
energy storage (WESS) will help support the voltage sag and
provide a potential energy saving benefit by improving capture
of regenerative braking. This simulation and analysis process,
by which we begin with a look at voltage support first and
energy saving second is carried throughout the various mode
analyses.
New WESS option
Returning to the example above, if an appropriately sized
WESS is installed in location A4X, the resulting train voltage
improvements can be shown in Figures 6-7, given that
rectifiers at positions A4 or A5 TPSS are removed.
Simulated Train Voltages
(Case 74b - A4 Outage, 5-Minute Headway)
100
200
300
400
500
600
700
800
900
1,000
24.5 25.0 25.5 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 30.0 30.5 31.0 31.5 32.0
Location (miles)
Tra
in V
olt
ag
e (
V)
Train Voltage
Substations
Stations
A1-T
PS
SS
T 0
1
A4-O
UT
ST
07
A6-T
PS
S
A5-T
PS
S
A7-T
PS
S
A2-T
PS
S
A3-T
PS
S
ST
02
ST
03
ST
04
ST
05
ST
06
ST
08
ST
09
ST
12
ST
10
ST
11
A4X
-ES
D
Figure 6: Train voltages under A4-TPSS outage condition
Simulated Train Voltages
(Case 75b-ESD760V - A5 Outage, 5-Minute Headway)
100
200
300
400
500
600
700
800
900
1,000
24.5 25.0 25.5 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 30.0 30.5 31.0 31.5 32.0
Location (miles)
Tra
in V
olt
ag
e (
V)
Train Voltage
Substations
Stations
A1-T
PS
SS
T 0
1
A4-T
PS
S
ST
07
A6-T
PS
S
A5-O
ut
A7-T
PS
S
A2-T
PS
S
A3-T
PS
S
ST
02
ST
03
ST
04
ST
05
ST
06
ST
08
ST
09
ST
12
ST
10
ST
11
A4X
-ES
D
Figure 7: Train voltages under A5-TPSS outage condition
The above figures indicate that the new WESS installation in
A4X location will be adequate for train voltage support with
either A4 or A5 TPSS rectifier removed. The minimum train
voltages for a system with energy storage are summarized in
Table 1.
Table 1Minimum Train Voltage and ESD Energy Summary
Case # Scenario A4X Type
Minimum
Train
Voltage (V)
Voltage
Improveme
nt (V)
ESD Energy
(kWh)
64 A4 outage CBH 504 n/a n/a
74b A4 outageESD
(Vc=760V)588 84 3.1
84 A4 outage TPSS 605 101 n/a
65 A5 outage CBH 559 n/a n/a
75b A5 outageESD
(Vc=760V)630 71 3.7
85 A5 outage TPSS 632 73 n/a
Note - ESD power rating at 1500 kW
8 –Technical Forums Energy, Environment & Transit
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WESS parameters
With the installation of the WESS in location A4X, the
system’s receptivity (the ratio of utilized regenerative energy
over the total available regenerative energy) will also be
improved, resulting in a greater potential to recover
regenerative braking energy. As a result, the energy saving
ratio due to regenerative braking (the ratio of energy
consumption with regenerative braking over the energy
consumption without regenerative braking) can be improved.
When all substations are in service and we do not experience a
voltage sag problem, we can take a different look at the effect
of energy storage, principally to save energy. The control
voltages of the WESS may be adjusted to best optimize energy
saving rather than providing voltage support, thus maximizing
the capture of regenerative energy. So, when voltage support is
not needed, an adjustment in the voltage settings of the WESS
can be made for optimal energy saving. Table 2 compares
system-wide energy saving potential resulting from variations
in WESS control voltages. This table also demonstrates the
corresponding energy and power rating requirements for the
WESS. An electricity cost saving analysis utilizing this
strategy is undertaken in the next section.
Table 2 System-wide Energy Summary
Case # A4X TypeReceptivity
(%)
Energy
Savings (%)
ESD Energy
(kWh)
60 CBH 83.6 29.9 n/a
70aESD
(Vc=720V)84.1 30.1 0.20
70bESD
(Vc=760V)84.5 30.2 1.30
70cESD
(Vc=793V)88.0 31.5 2.30
80 TPSS 83.3 29.8 n/a
Note - All TPSS in normal operation
Electricity cost saving analysis
We have shown that a WESS can effectively mitigate
problems associated with low train voltages. To examine the
potential energy and cost saving benefits of energy storage, a
simple electricity cost analysis can be performed using the
options noted above. We start with a comparison of the 15-
minute power averages across all substations in the system
under normal operation with and without a WESS, as shown in
Table 3. The 15-minute averages are used because of the
correlation with utility peak power charging average time
periods, which are in most cases 15-minutes.
Table 3 15-Minute Average Power Values by Substation
With A4X-
TPSS
With A4X-
ESD
With A4X-
TPSS
With A4X-
ESD
A1 403 406 162 165
A2 449 458 178 185
A3 388 408 152 156
A4 382 410 153 159
A4X 208 0 81 0
A5 366 395 137 144
A6 412 425 153 162
A7 361 368 134 138
Sum 2,969 2,870 1,150 1,110
15-Minute Average Power (kW)
5-Minute Headway 15-Minute Headway
Substation
From the table it can be seen that the 15-minute average power
in each substation for 5-minute headways represents the peak
power demand, while 15-minute headways are less as
measured over the same 15 minute period. What this table
shows is the utility supplied power to each substation along
the alignment. Higher power requirements are shown near the
WESS because there is no supply at that point and
neighbouring substations would need to provide the additional
power to charge the WESS, although only marginally. Both
the 5-minute and 15-minute headway conditions are used to
compute the overall energy saving in a 24 hour period. More
specifically, the following 24-hour train operation schedules
are assumed:
5-minutes in peak hours (6-10Am and 4-8PM)
15-minutes in off-peak hours and weekends
No train service between 1AM and 4AM on any day
Using actual published electricity tariffs from a USA utility
company [3]
, the annual cost for each substation is calculated
based on individual traction substation billing arrangements
and the power demands noted in Table 3. These are listed in
Table 4.
Table 4 indicates that the WESS installation will have an
annual electricity cost benefit of $45,000 (based on the current
tariffs) compared against a full rectifier installation in the A4X
location. Additional cost benefits may be possible because a
WESS is typically less expensive than a full rectifier utility
substation.
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Table 4 Summary of Annual Electricity Cost Saving due to
WESS (all figures in US $)
SubstationWith A4X-
TPSS
With A4X-
WESS
Savings with
WESS
A1 $182,342 $184,763 -$2,422
A2 $202,057 $207,687 -$5,630
A3 $173,973 $181,808 -$7,835
A4 $172,945 $183,581 -$10,637
A4X $93,875 $0 $93,875
A5 $161,894 $172,907 -$11,012
A6 $181,397 $189,110 -$7,713
A7 $159,353 $162,810 -$3,456
Sum $1,327,835 $1,282,666 $45,169
Annual Electricity Cost Summary
Metro Rail
System parameters
A similar simulation analysis, again looking at the conditions
of low voltage and regenerative braking energy, is performed
for a heavy rail (subway) system using the simulation
parameters below.
5 Miles Metro System; 4 Stations
700V DC traction power system
4 Traction substations
2 Circuit breaker houses (CBH)
8 Car trains with regenerative braking
2 Minute in peak hours (AM & PM)
5 Minute headway in mid day hours
15 minute headway in off peak and weekend operations
To set up the model, Figures 8-9 show the motoring and
regenerative braking control diagram for a typical metro rail
vehicle and the conditions of low voltage. Simulations will
utilize these characteristics. For this case, sensitivity analyses
are performed to characterize the influence on system design
parameters on overall energy storage performance.
Simulation results indicate that there will be low voltage
occurrences at the east end of the track, as shown in Figure-9.
Figure 8: Power control diagram for the Metro rail vehicle
Simulated Train Voltages
0
100
200
300
400
500
600
700
800
900
1,000
7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5
Location (miles)
Tra
in V
olt
ag
e (
V)
Train Voltage
Substations
Stations
Minimum Voltage
G0
2A
-
PS
SS
top
-
2
G0
4-
TP
SS
G0
5B
-
CB
H
G0
5A
-
TP
SS
G0
2B
-
CB
H
G0
3-
TP
SS
Sto
p-
3
Sto
p-
4
Sto
p-
5
Case 430-2 Min Headway; 750-840V Regen Taper; No ESD
Figure 9: Train voltages with CBH at G05B
The effect of ESD power rating
If an ESD is installed at position G05B at the east end of the
track, the low voltage conditions will be improved. A 3MW
installation is required to achieve 525V or better, as shown in
Figure 10.
Simulated Train Voltages
0
100
200
300
400
500
600
700
800
900
1,000
7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5
Location (miles)
Tra
in V
olt
ag
e (
V)
Train Voltage
Substations
Stations
Minimum Voltage
G0
2A
-
PS
SS
top
-
2
G0
4-
TP
SS
G0
5B
-
3M
W
ES
D
G0
5A
-
TP
SS
G0
2B
-
CB
H
G0
3-
TP
SS
Sto
p-
3
Sto
p-
4
Sto
p-
5Case 431-2 Min Headway; 750-840V Regen Taper; 3MW ESD
Figure 10: Train voltages with 3MW ESD at G05B
A larger installation of 4MW will achieve an even better
result. Simulated load and energy cycles for the ESD are
shown in Figures 11-12.
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Simulated ESD Load Cycle
-4,000
-3,000
-2,000
-1,000
0
1,000
2,000
3,000
4,000
7:40 7:41 7:42 7:43 7:44 7:45
Time
Po
wer
(kW
)
3MW ESD
4MW ESD2 Minute Headway
Figure 11: Simulated ESD load cycles
Simulated ESD Energy Cycle
4
6
8
10
12
14
16
18
20
22
7:40 7:41 7:42 7:43 7:44 7:45
Time
En
erg
y (
kW
h)
3MW ESD
4MW ESD2 Minute Headway
Figure 12: Simulated ESD energy cycles
The effect of headway offset
For peak hour operation (2 minute headway), simulations were
carried out for different offsets between east and west bound
train’s dispatching timing (headway offsets). Such offsets
result in the trains meeting at different locations, which in turn
affect the train voltage and other conditions in the system.
Time-distance plots for three different headway offsets on
west bound trains are illustrated in the following figure.
Simulated Trains
7:40
7:41
7:42
7:43
7:44
7:45
7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5
Location (miles)
Tim
e (
hh
:mm
)
WB Offset by 0s
WB Offset by 15s
WB Offset by 30s
Substations
Stations
G0
2A
-
PS
SS
top
-
2
G0
4-
TP
SS
G0
5B
-
TB
D
G0
5A
-
TP
SS
G0
2B
-
CB
H
G0
3-
TP
SS
Sto
p-
3
Sto
p-
4
Sto
p-
5
Time-Distance Plots; 2 Minute Headway
Figure 13: Time-distance plot for peak hour trains under
different headway offsets for WB trains
Minimum train voltages and system receptivity (the ability to
accept regenerative power) under different installations at
different headway offsets are shown in the following figure.
Minimum Train Voltages by Different Installations
(2 Minute Headways; 840V Voltage Limit)
497
604
558
627
655644
593
547
634
617617
562
637
619
520
651
400
450
500
550
600
650
700
0 15 30 45
WB train headway offset (seconds)
Vo
ltag
e (
V)
CBH
3MW Sub
3MW ESD
4MW ESD
Figure 14: Minimum train voltages versus headway offsets
System Receptivity Under Different Installations
(840V Voltage Limit)
67.4
86.9
72.2
66.0
58.1
89.7
76.3
69.5
61.7
72.8
59.1
87.6
61.8
69.7
76.7
90.1
50
55
60
65
70
75
80
85
90
95
0 15 30 45
Headway offset for WB trains
Sy
ete
m R
ece
pti
vit
y (
%)
CBH
3MW Sub
3MW ESD
4MW ESD
Figure 15: System receptivity versus headway offsets
Many factors affect the system receptivity and energy saving
figures, such as track alignment, passenger station locations,
electrical parameters of the traction power system, vehicle
characteristics, train operational characters (acceleration and
braking rates, coasting, offsets in headway dispatches on the
two tracks, timing deviation from regular headways, etc.). The
figures contained in this paper represent nominal conditions.
Variations from these figures can be expected when system
conditions change, but such detailed comparative analyses are
beyond the scope of this investigation. However, the following
sections illustrate the general impact on system performance
given such variations.
The effect of voltage limit
Receptivity variations versus voltage limits are shown in the
following figure.
8 –Technical Forums Energy, Environment & Transit
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System Receptivity Under Voltage Limits
(2 Minute Headway)
69.5
95.74
82.93
77.46
68.62
76.3
61.7
89.7
72.17
79.24
84.38
97.41
55
60
65
70
75
80
85
90
95
100
0 15 30 45
Headway offset for WB trains
Sy
ete
m R
ece
pti
vit
y (
%)
840V Voltage Limit
900V Voltage Limit
970V Voltage Limit
Figure 16: System receptivity versus voltage limits
The effect of headway
Receptivity variations versus headways are shown in the
following figure.
System Receptivity Under Different Installations
(840V Voltage Limit)
68.6
49.7
86.9
68.4
49.5
89.7
77.3
63.5
90.1
77.6
65.1
87.6
45
50
55
60
65
70
75
80
85
90
95
2 5 15
Headway (minutes)
Syete
m R
ece
pti
vit
y (
%)
CBH
3MW Sub
3MW ESD
4MW ESD
Figure 17: System receptivity versus headway
Energy cost savings
The estimated annual cost for the track section and cost
savings [3]
under different options are shown Table 5.
Table 5 Summary of Annual Electricity Cost Savings
(All figures in US $) Substation CBH 3MW Sub 3MW ESD 4MW ESD
Total annual cost $4,874,350 $4,831,516 $4,776,365 $4,760,599
Savings over
3MW Sub Option-$42,833 $0 $55,152 $70,917
Commuter Rail
A 5 mile section of a commuter rail system is simulated to
assess the feasibility of WESS as an alternative to the
traditional rectifier substation for train voltage support. The
noload voltage is at 720V and the nominal voltage 685V.
Regenerative braking is not applied for this system as most
commuter rail vehicles are incapable of braking regeneration.
Train voltage plots under different options at location MP-35
are shown in the following figures.
Train Voltages - MP32 to MP37
7-8 AM Peak Hours
MP
35-C
BH
Sub-B
34
Sub-B
36
Sub-B
32
0
100
200
300
400
500
600
700
800
32 33 34 35 36 37
Location (milepost)
Vo
ltag
e (
V)
Voltage (v)
Substations
Minimum Voltage
Figure 18: Train voltages under CBH option
Train Voltages - MP32 to MP37
7-8 AM Peak Hours
Su
b-3
5 (
New
)
Sub-3
4
Sub-3
6
Sub-3
2
0
100
200
300
400
500
600
700
800
32 33 34 35 36 37
Location (milepost)
Vo
ltag
e (
V)
Voltage (v)
Substations
Minimum Voltage
Figure 19: Train voltages under substation option
Train Voltages - MP32 to MP37
7-8 AM Peak Hours
ES
D-3
5
Sub-3
4
Sub-3
6
Sub-3
2
0
100
200
300
400
500
600
700
800
32 33 34 35 36 37
Location (milepost)
Vo
lta
ge
(V
)
Voltage (v)
Substations
Minimum Voltage
Figure 20: Train voltages under ESD option (Vc=670V)
The effect of ESD control voltage
Adjusting the control voltage (Vc) of an ESD installation will
achieve different levels of train voltage improvement. On the
other hand, high levels of voltage improvement demand higher
power ratings and larger energy capacities for the device.
Due to the distances between the ESD and the nearby
substations, the charging rate can be limited by the circuit
8 –Technical Forums Energy, Environment & Transit
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resistances. Higher Vc setting can have better improvement of
train voltages. However, this needs to be balanced against the
requirement to maintain sufficient energy rate to keep the
device at desired capacity, so that there is sufficient energy
content for the next discharging cycle.
The following figure shows the load cycle under different
control voltages. The same figure also illustrates the charge
rates limited by the electrical circuits, between 1.6 and 1.8
MW.
Simulated ESD Load Cycle
-2,000
-1,500
-1,000
-500
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
7:40 AM 7:41 AM 7:42 AM 7:43 AM 7:44 AM
Time
Po
wer
(kW
)
Vc=650
Vc=660
Vc=670
Figure 21: ESD load cycle under different control voltages
The maximum charging and discharging rates and minimum
train voltages are compared in Table 6.
Table 6 ESD Rating and Capacity vs. Voltage Improvement ESD Control
VoltageVc=650 Vc=660 Vc=670
Max. MW Output 3.2 3.6 3.8
Max. kWh Usage 31.7 37.5 42.4
Minimum Train
Voltage518 529 536
Summary
This paper presented simulation results for three systems with
potential applications of a WESS as an alternative to
traditional rectifier substations for train voltage support. ESD
power ratings and energy capacities vary with the systems and
the desired levels of voltage improvement, as shown in Figure
22.
ESD Energy Capacity Requirement
3.7
12.5
14.7
31.7
42.4
0
5
10
15
20
25
30
35
40
45
Light Rail 1.5MW
ESD
Metro Rail 3MW
ESD
Metro Rail 4MW
ESD
Commuter Rail 3MW
ESD
Commuter Rail 4MW
ESD
System Types and Power Ratings
En
erg
y (
kW
h)
Figure 22: ESD energy capacity versus system type and power
rating
For two of the systems where regenerative braking is used,
there is added energy saving benefits of an ESD option. It
should be expected that the annual savings will increase in the
future as the electricity tariffs tend to go up in line with
general energy cost increases.
Acknowledgements
The authors thank Mr. Larry Goldstein, Senior Program
Officer for ACRP and TCRP, Transportation Research Board,
for his support with the study. The authors also thank all the
transit agencies, government agencies and vendors of the
APTA/EPRI Energy Storage Research Consortium for their
generous involvement and support of the project. The
simulation results presented in this paper were obtained by
using SYSTRA’s RAILSIM® Load Flow Analyzer.
References
[1] Symposium: TCRP C-75 Wayside Energy for Transit,
APTA/EPRI Energy Storage Research Consortium,
American Public Transportation Association,
Washington, DC, February 10, 2010.
[2] Energy Storage Vendor Advisory Group, APTA/EPRI
Energy Storage Research Consortium, American Public
Transportation Association, 2009.
[3] LADPW Electric Rates - Schedule A-1: Small General
Service (Effective July 1, 2009) (http://www.ladwp.com)