Benefits of Upgrading the Overhead Line of a DC Railway Line in the Netherlands

Beneﬁts of upgrading the overhead line of a
DC railway line in the Netherlands
a simulation case study
November, 2001
Frederik Groeman, KEMA

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Contents
1 Summary 6
2 Introduction 8
2.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2 Project objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3 Catenary cross-section 10
3.1 Energy (cost) saving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2 CO2 reduction and emission trading . . . . . . . . . . . . . . . . . . . . . . 11
3.3 Increased energy savings by regenerative braking . . . . . . . . . . . . . . . 12
3.4 Traction system performance: higher voltage and more power to the trains 13
3.5 Travel time reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.6 Limitations and drawbacks . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4 Case study 16
4.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.2 The study case track . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.3 The railway traffic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5 Simulation results 18
5.1 Energy losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.2 Traction system performance: supply of higher voltage to the trains . . . . 23
5.3 Travel time reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6 Appraisal of the energy saving 30
6.1 Economical benefits without CO2 emission cost . . . . . . . . . . . . . . . 30
6.2 CO2 reduction and economical benefits including CO2 emission cost . . . . 31
7 Conclusion 34
7.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7.2 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
A Low-voltage power supply systems 37
3

List of Figures
3.1 Description of the catenary wire system . . . . . . . . . . . . . . . . . . . . 11
3.2 Power limitations as a function of voltage (example) . . . . . . . . . . . . . 14
5.1 Momentary energy use and losses in the study case track - 500 mm2
. . . . 19
. . . . 19
. . . 19
5.4 Momentary relative energy losses in the study case track - 500 mm2
. . . . 20
. . . . 20
. . . 20
5.7 Energy balances for the three study cases (100% = power input) . . . . . . 22
5.8 Relative losses for the three study cases (100% = power output at trains) . 23
5.9 Minimum and maximum train voltages as a function of the train – 500 mm2
24
24
24
5.12 Improvement of mean useful train voltage for all 359 trains passing the
study case track in 24 h . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.13 Time-location diagram for the study track on an hour with heavy load (500
mm2
) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.14 Number of trains the travel time of which is reduced by increasing the
overhead wire cross-section – Diﬀerence 500-800 mm2
. . . . . . . . . . . . 29
5.15 Number of trains the travel time of which is reduced by increasing the
. . . . . . . . . . . 29
6.1 Payback period (PBP) in years of an increase of the catenary cross-section
as a function of emission cost . . . . . . . . . . . . . . . . . . . . . . . . . 32
6.2 Internal rate of return (IRR) for upgrading the catenary as a function of
emission cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
7.1 Possible adaptation of voltage limits for a 1500 V DC system in order
to increase energy eﬃciency (measured at the location of a train, during
normal conditions) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
A.1 Schematic representation of a LV railway system) . . . . . . . . . . . . . . 37
4

List of Tables
3.1 Voltage limits for a 1500 V DC system according to EN 50.163 (measured
at the location of a train, during normal conditions) . . . . . . . . . . . . . 13
5.1 Total power supplied and losses at the study case track – 24h . . . . . . . 21
5.2 Comparison of diﬀerent cross-sections with the base case – 24h . . . . . . . 21
5.3 Energy saving with respect to the base case – 24h . . . . . . . . . . . . . . 22
5.4 Minimum voltage along the study case track . . . . . . . . . . . . . . . . . 25
5.5 Time gains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.1 Annual energy saving with respect to the base case . . . . . . . . . . . . . 30
6.2 Annual energy cost saving for the study case track . . . . . . . . . . . . . . 31
6.3 Proﬁtability of overhead wire reinforcement of the study case track – per km 31
6.4 Emission reduction in the study case track . . . . . . . . . . . . . . . . . . 32
6.5 Annual energy cost saving for the study case track . . . . . . . . . . . . . . 32
5

Chapter 1
Summary
In low-voltage railways, transmission losses can be significant. These losses can be reduced
by increasing the conductor cross-section of the overhead line. Large amounts of energy
can be saved, earning back the extra cost of the increased conductor cross-section plus
reinforced gantries.
Increasing the overhead line cross-section also brings other advantages. By reducing the
electrical resistance between a train and the feeding substation, the traction power supply
becomes “stronger”, offering higher power available to trains: trains can accelerate more
quickly, which will give train operators more possibility to comply with the timetables
e.g. in case of a delayed departure. In other words: the performance of the traction power
supply is improved. It is, however, very difficult to estimate the degree of improvement
without carrying out detailed simulations.
The objective of the study described in this report is to quantify and to demonstrate
energy savings and other benefits by means of a detailed simulation case study for a 52,5
km-long heavily loaded Dutch railway line, supplied with 1500 V DC. In this study, the
standard cross-section of 500 mm2
was first increased to 800 mm2
, next to 1000 mm2
.
The study into an upgrade to 800 mm2
per track yielded following results:
• 5% energy saving on the total traction energy consumption, excluding savings from
increased regenerated energy
• If the support gantries of the overhead lines were to be upgraded anyway, the pay-
back period for the extra cost would be at most 9,6 years
• This ’project’ would have an internal rate of return of at least 9,7%
• The mean useful voltage of most trains passing this track would increase by more
than 50 volt, especially those trains that suffer from lower voltages
• 14% of all trains running in the study case track would benefit a net time gain of
10 seconds or more.
If CO2 emission rights were traded at e 33/tonne, the payback period would decrease to
6

www.leonardo-energy.org CHAPTER 1. SUMMARY
6,7 years and the internal rate of return would rise to 14,6%. For higher emission right
cost, the payback period would decrease even further.
Upgrading the track to 1000 mm2
instead of 800 mm2
would lead to even higher energy
saving, but the main improvements are made in the upgrade from 500 to 800 mm2
.
Upgrading to 1000 mm2
still is attractive, but both the payback period and the internal
rate of return are less favourable than upgrading to 800 mm2
. The losses in the return
path become dominant. This raises the question whether it would not be worthwhile to
consider decreasing the return path resistance instead.
Following recommendations are made in this study:
• optimisation of the conductor size regarding energy losses should become a standard
step in the design process of traction power supply systems. Such an optimisation
requires a simulation study as the phenomena occurring are too complicated for
hand-calculations
• standardised minimum voltage levels of EN50163 (the traction power supply voltage
standard), the TSI Energy and the like oﬀer the possibility to design traction power
supply systems with high losses and limited possibilities for regeneration of braking
energy. These voltage levels deserve to be reconsidered from the point of view of
energy saving.
November, 2001 – Page 7 of 38

Chapter 2
Introduction
2.1 Background
Electric railways form a large energy user, covering approximately 50 TWh/year, or 21/2 %
of the total annual electricity consumption in the European Union (source: OECD). The
associated costs are a significant part of railway exploitation, amounting to almost e3
billion annually.
Especially in low-voltage (DC) systems, as used in many parts of Europe, energy losses
between the public electricity network and the trains make a significant contribution to
the total energy costs. Generally speaking, a lower system voltage correlates with higher
losses. The Dutch railway system, for instance, is electrified at 1500 V DC, and the
total energy losses in the railway power supply system are in the order of 10% or over
100 GWh/year. The losses in the overhead wires take a significant share of these losses.
Presently, new railway systems are usually electrified with significantly higher voltages,
for instance 25kV or 15 kV. Thanks to the high voltage, energy losses in such traction
power supply systems are much lower than in low-voltage systems. In countries with an
existing low-voltage system, the costs of upgrading the entire railway system to a high
voltage are high, in the order of e2 million per track kilometre, excluding the costs for
upgrading rolling stock. Considering this cost barrier, it is probable that significant parts
of the railway network will continue to operate at low voltage for several decades.
A straightforward possibility to reduce energy losses without abandoning the existing
power supply system is to increase the conductor cross-section of the overhead line. Large
amounts of energy can be saved, earning back the extra cost of the increased conductor
cross-section.
Increasing the overhead conductor cross-section also brings other advantages. By reducing
the electrical resistance between a train and the feeding substation, the traction power
supply becomes “stronger”, offering higher power available to trains: trains can accel-
erate more quickly, which will give train operators more possibility to comply with the
timetables e.g. in case of a delayed departure. In other words: the performance of the
8

www.leonardo-energy.org CHAPTER 2. INTRODUCTION
traction power supply is improved. It is, however, very difficult to estimate the degree of
improvement without carrying out detailed calculations or measurements.
2.2 Project objectives
The objective of the study described in this report is to quantify and to demonstrate
energy savings and other benefits by means of a detailed simulation case study for a
heavily loaded Dutch railway line, supplied with 1500 V DC.
2.3 Approach
A detailed simulation has been carried out for a railway line with ELBAS-SINANET R
software, with subsequent analysis to determine the effects of increasing the net cross-
section of the overhead line regarding:
• energy saving and CO2 reduction
• energy cost saving
• voltage improvement (performance of the traction power supply)
• driving time improvements.
Railinfrabeheer (the Dutch railway infrastructure administrator) has kindly granted per-
mission to use typical data on the traction power supply system and the railway network.
This report is a sequel to the publication ’Optimal reduction of energy losses in catenary
wires for DC railway systems’1
.

Chapter 3
Effects of increasing the catenary
cross-section
This chapter gives an introduction to the benefits and drawbacks of increasing the catenary
cross-section of low voltage railways.
3.1 Energy (cost) saving
The obvious benefit of increasing the conductor cross-section is energy saving. This energy
saving is realised in two additional ways:
• The power loss of a current I passing through a resistance R equals I2
R. Increasing
the cross-section of the overhead line decreases its resistance (e.g. by ∆R) and thus
the losses (by I2
∆R).
• Trains basically act as a constant power load, as the power is regulated to obtain or
maintain a certain speed. For all types of loads, reducing the resistance of the power
supply implies an increase of the terminal voltage of the load. Constant power loads
will reduce their current, thus reducing the transmission losses. In railway systems,
this implies that reduction of the overhead line resistance does not only reduce the
losses in this overhead line itself (by more than I2
∆R mentioned above) but also
the losses in the return circuit (rails), feeder cables, substations etc.
10

www.leonardo-energy.org CHAPTER 3. CATENARY CROSS-SECTION
Catenary or overhead wire system details
The key element of the overhead or catenary wire system is the contact or trolley
wire, which transfers the electrical power to the train's pantograph. In order to prevent
a sag of the overhead wire, it is hung to the so-called messenger or catenary wire,
using short wires called droppers. In order to reduce the resistance of the overhead
line, a feeder may be added. In most cases, the overhead line of a Dutch railway
consists a double copper contact wire 2x100 mm2
, a 150 mm2
copper messenger
wire and a copper 150 mm2
feeder wire. The relatively large cross-section of the wire
is related to high currents flowing in the 1500V-overhead line (often 3000 A or
higher).
The contact wire(s) and the messenger wire take part in a complicated mechanical
interaction during train passages and are carefully optimised for mechanical stability
and lifetime. Therefore, the primary choice for reducing the overhead line resistance
is adding or strengthening feeder lines.
Feeder
Dropper
Messenger wire
Double contact
wire
Overhead
line
Figure 3.1: Description of the catenary wire system
The energy saving can be directly associated with the avoidance of CO2 emission in power
plants. This subject is treated in the next section.
The energy saving mentioned above also leads to cost savings, but this relationship is less
straightforward. This is due to the fact that the electricity rate to be paid by the railway
companies is not only determined by the amount of energy (i.e. the kWhs), but also by
the peak load. How the peak load changes if the overhead line cross-section is increased,
is a complicated issue as the changed voltage profile (section 2.4) causes the trains to
drive differently, i.e. to be at a different position at a given point of time, which changes
the summation of the loads of individual trains at a substation. Due to this effect, the
substation peak power may decrease or in some cases even increase.
3.2 CO2 reduction and emission trading
Benefits of energy saving are not only the avoidance of energy cost, but also the avoidance
of CO2 emission and a contribution to the reduction of global warming. The CO2 emission

depends on the average share of fossil fuels in the fuel mix of power plants. In the
Netherlands, the CO2 emission associated to the use of electricity is assumed to be 0,6 kg
CO2 per kWh of electricity used (the average for Europe is 0,4 kg/kWh).
Presently, CO2 emission is free of charge, but emission limits are underway. To allow for
economic optimisation, emission trading schemes are under discussion, and by that time,
CO2 emission rights will have a price. The price will depend on actual market conditions.
The price for CO2 emissions will add to the cost of energy. For this study, a price of e
33 per tonne of CO2 will be considered2
.
The extra cost of energy due to the emission rights is equal to the CO2 emission per kWh
times the price of the emission, i.e. about 20 e/MWh.
3.3 Increased energy savings by regenerative braking
Many trains employ electrodynamical braking in addition to mechanical braking. The
kinetic energy of the train is then converted to electricity by the traction motors. This
electric energy may be dissipated in resistors or fed “back” into the overhead wire. Elec-
trodynamical braking is very attractive compared to mechanical braking, especially on
tracks with long slopes and at trains that are stopping frequently. Its advantages are a
strong extension of the maintenance interval of the mechanical brakes, and energy saving
if the electricity generated is supplied to the overhead line. In the latter case, the term
“regenerative braking” is used. Regenerative braking may lead to large net energy sav-
ings, often more than 10% of the total traction energy consumption in railway systems
and more than 30% in metro systems.
In mountain railways and metro systems, electrodynamical and in many cases even re-
generative braking has been in used since the beginning of 20th
century.
An important prerequisite for regenerative braking is receptivity of the overhead wire for
the power supplied. As, with only scarce exceptions, DC feeding substations are not able
to supply power back to the public electricity network, a regeneratively braking train can
only supply power to the overhead wire if another nearby train can absorb this power3
.
The problem with regenerative braking is that there will always be a voltage drop between
the regenerating and the other train. If the actual voltage level in the traction power
supply system is too high, the regenerating train could push the voltage over the upper
limit, i.e. the maximum allowable system voltage. In order to prevent this, a train will
try to feed just so much power into the overhead wire that the upper voltage limit is not
exceeded. The power that can not be supplied back to the overhead wire is dissipated in
resistors or in mechanical brakes.
Reducing the overhead wire resistance does not only reduce the transmission losses be-
tween a regeneratively braking train and another train, but, more signiﬁcant, it reduces
the voltage drop across the overhead line. The resulting increase of regenerated energy

may lead to energy savings in the same order of magnitude as the energy saving in the
overhead line mentioned in the first section of this chapter, or higher.
3.4 Traction system performance: higher voltage and
more power to the trains
The function of the traction power supply system is to supply the trains with power at an
acceptable voltage quality. The European standard EN 50163 defines limits to minimum
and maximum voltage levels of 1000 and 1800 V for steady state conditions, see the table
below. However, railway infrastructure owners usually design their networks for minimum
voltages above the minimum set in EN 50163, i.e. at more strict requirements, in order
to be able to cope with extreme load conditions.
Permanent Non-permanent
Highest voltage limit 1800 V 1950 V, 5 min.
Lowest voltage limit 1000 V N/A
Table 3.1: Voltage limits for a 1500 V DC system according to EN 50.163 (measured at
the location of a train, during normal conditions)
The voltage should not become too low for the following reasons:
• as mentioned before, a train acts as a constant power load, rather than a resistor-
type of load. If the voltage is low, a train will try to draw more current from the
system. This, however, pulls the voltage down even further due to the ohmic voltage
drop across the resistance of the catenary system. The stability limit of the system
is reached if components (catenary wires, switchgear, rectifiers and transformers)
are becoming overloaded due to excessive currents
• due to the current rating of the equipment and to prevent a breakdown of the
system, each train limits its traction current to a predetermined value. This current
limitation also limits the power available to the train – if e.g. the voltage is reduced
by 10%, the power available to the train also drops by 10%. For very low voltages,
typically below 1200 V, the current limit itself is reduced to increase system stability,
giving even more dramatic power reductions. In many cases this latter reduction
is carried out by the driver, in modern trains such a limitation is automatically
performed. The figure below gives a typical example of the limitations concerned,
with a 4000 A limitation for voltages above 1200 V, linearly decreasing between 1200
and 950 V. The settings of these limitations will probably become standardised in
the future.
These power limitations are most important during acceleration, where trains will
accelerate slower at low voltage conditions. This may lead to delays.

0
1000
2000
3000
4000
5000
900 1000 1100 1200 1300 1400 1500
Voltage [V]
Current[A]
0
1200
2400
3600
4800
6000
Power[kW]
Current
Power
Figure 3.2: Power limitations as a function of voltage (example)
Especially at weak points in the network, an increased cross-section increases the voltage
level. With the voltage level, the power available to the trains will increase, too.
3.5 Travel time reduction
Thanks to the increased power available to trains, quicker acceleration will be possible.
This may enable faster timetables. The main benefit may be expected, however, in
conditions when the train traffic is severely delayed. During these conditions, the power
supply system sees its limits (the lower one for voltage, the upper one for current) and
trains experience significant extra delays due to the low voltage. An increased overhead
line cross-section the power supply will not solve the delays, but at least decrease the
proliferation of delays.
3.6 Limitations and drawbacks
Adding extra feeder wires or increasing their cross-section adds to the mechanical loading
of the support structures (gantries plus their foundations). This loading consists of two
components:
• the weight of the wires, including ice loads
• wind load.
Crucial for the economical feasibility of an overhead wire with an increased cross-section
is the question whether the strength of the support structures is sufficient to carry the
extra loads.
If existing support gantries are adequate to carry an increased feeder cross-section, the
extra cost for a feeder wire pays itself back by the energy saving.

If existing support gantries and their foundations need to be replaced by stronger ones, this
cost will not be earned back by energy saving alone. If, however, the support structures
need to be replaced anyway, choosing a stronger support portal and foundation gives
only small additional (differential) costs. Also, if overhead wires need to be replaced
anyway (regular maintenance) and the support structures do not need strengthening,
the differential cost may be favourable. The same applies to electrification of new or
non-electrified existing railway tracks. For this study, the differential cost figures will be
used.

Chapter 4
A case study in the Dutch railway
network
4.1 General
The Dutch railway network is operated by Railinfrabeheer. The entire network (approxi-
mately 4000 single-track km electriﬁed) has been modelled in ELBAS-SINANET software.
A part of this network has been used for the case study. Following cases have been con-
sidered:
• Present catenary conductor cross-section (500 mm2
Cu along the entire track)
• Increased catenary conductor cross-section (800 mm2
Cu along the entire track)
• Strongly increased cross-section (1000 mm2
Cu along the entire track). For this
study case, the entire simulated network was reinforced to 1000 mm2
.
For the 800 and 1000 mm2
simulations, all track data, timetables, train data, . . . have been
taken from a network planning study carried out for Railinfrabeheer by KEMA-ELBAS
in 2000Q1 (which was based on 500 mm2
cross-section of the catenary).
4.2 The study case track
The catenary system has 500 mm2
cross-section per track. For the 800 mm2
and 1000 mm2
variants, the catenary has been upgraded at a 52,5 km long piece of railway of this double-
track railway (105 single-track km). This section of the railway is referred to as “study
case track”.
The study case track is fed by 7 substations, including the substations that are located
at the ends of the study case track. There are 7 passenger railway stations, one freight-
only railway station and two intersections with single-track lines with relatively low traﬃc
density.
16

www.leonardo-energy.org CHAPTER 4. CASE STUDY
4.3 The railway traffic
The traffic at the study case track is very busy, with up to ten trains per hour per track
during rush-hours, and up to 300 trains each day. The daily traffic quantity is up to
12 millions ton-km. The traffic can be characterised as mixed, national passenger trains
being dominant, but international and freight trains, with their relatively large power
demand, also form a considerable load to this railway. The traffic has almost reached the
maximum capacity of the track, which is mainly determined by speed differences between
train types and the required safety distances between trains (block system).
The simulation has been carried out for 24 hours on a busy day, using a timetable for
2001. Trains departed according to the timetable (i.e. the normal situation), but during
the simulation the traffic interaction between trains (e.g. keeping the right distance) and
the interaction between trains and the traction power supply (e.g. power limitations due
to low voltage) were taken into account.
The possibility of some train types to apply regenerative braking, i.e. feeding electrical
energy back to the overhead wire (and other trains) during braking, was not taken into
account (all braking energy converted to heat at the train). The reason for this is, that
the original 500 mm2
study did not consider regenerative braking.

Chapter 5
Simulation results
5.1 Energy losses
For the study case track, the momentary total power delivered to the track is plotted
against time in graphs 5.1 - 5.3 (upper curves). In the same graphs, the momentary total
losses in the track are depicted, too (lower curves).
In the curves, it can be clearly seen that there is no train traffic on this track between 2:00
and 05:30 at night. The sharp variations are due to acceleration manoeuvres of individual
trains: despite the averaging effect by summing the power of the substations, the peaks
are clearly visible. The energy losses calculated are composed of:
• losses in the catenary wires
• losses in the return path (the rails)
• losses in the cabling between the substations and the track.
Not included are following losses:
• The losses in the substation itself for e.g. auxiliary equipment
• losses in the transformers and rectifiers
• losses in the medium-voltage cables between the utility and the (track-side) 1500V
substation.
• Losses in the trains.
In order to give an impression of the energy efficiency of the traction power supply system,
and to show the energy savings clearer, figures 5.4 - 5.6 show the relative losses (i.e. the
losses in the catenary, rails and feeders) as a function of time. These curves are a division
of the losses and the input power depicted in graphs 5.1 - 5.34
.
18

www.leonardo-energy.org CHAPTER 5. SIMULATION RESULTS
Figure 5.1: Momentary energy use and losses in the study case track - 500 mm2

Figure 5.4: Momentary relative energy losses in the study case track - 500 mm2
When comparing the graphs, the energy loss reduction is clearly visible (the graphs have
the same scaling). Also visible is that peak losses up to 25% occur. As this is the average
loss, the peak losses at certain sections of the track are even higher.

The totalled energy consumption of the track and losses during the 24-h simulation are
given in the table below:
Total power supplied
to the track
Losses Relative losses
500 mm2
411 MWh 50 MWh 12,1 %
800 mm2
393 MWh 34 MWh 8,7 %
1000 mm2
385 MWh 29 MWh 7,6 %
Table 5.1: Total power supplied and losses at the study case track – 24h
The power supplied to the track is measured at the DC substations (i.e. exclusive of
losses in the substation itself, but including the losses in the power cables between the
substation and the track).
In the table below, the differential figures for power supplied and the losses are shown.
The figures in brackets indicate the relative reduction compared to the 500 mm2 case.
Power supplied to track Losses
800 mm2
-17,9 MWh (-4%) -15,6 MWh (-31%)
1000 mm2
-25,7 MWh (-6%) -20,6 MWh (-41%)
Table 5.2: Comparison of different cross-sections with the base case – 24h
The reduction of total power delivery to the track is higher than the reduction of the
losses in the track thanks to the effect that the voltage at the trains is increased (see
next section), and some trains are able to accelerate quicker. As some train types have
significantly lower conversion efficiencies (between overhead line and wheels) when driving
slowly, this also leads to energy saving (2,8 MWh for the 800 mm2
case).
The higher voltage at the trains also causes the trains to draw less current at a given
power. Some of the power delivered to the study case track is delivered from adjacent
sections, especially if a train is close to the edge of the study case track. Energy saving
at the study case track hence also leads to some energy saving on adjacent tracks.
Energy saving in the track also leads to energy saving in the power system supplying
that track. For energy cost saving, it is adequate to take into account the losses between
the utility supply point and the DC busbar, i.e. losses in the medium-voltage cables, the
traction transformers and the rectifiers. The components mentioned have a relative loss
figure of typically 21/2 %. The losses in these components will decrease by 0,5 MWh in
the 800 mm2
case.
The resulting total energy saving is given in the table below:

Overhead
line case
study
track
Overhead
line other
tracks
Trains Substations
and cabling
Total energy
saving
800 mm2
15,6 MWh 0,9 MWh 2,8 MWh 0,5 MWh 19,7 MWh
1000 mm2
20,6 MWh 1,2 MWh 3,1 MWh 0,6 MWh 25,5 MWh
Table 5.3: Energy saving with respect to the base case – 24h
The total energy saving is significant, although the step from 800 mm2 to 1000 mm2
brings relatively less advantage.
Energy balance and relative losses
The figure below gives the energy balance of the simulated cases for the study case track.
The AC power input of each case is used as a reference (i.e. 100%). With an increasing
cross-section, the shrinking share of the overhead wire losses is clear. Less visible is the
reduction of the other losses, which is approximately one tenth of the energy saving in
the catenary wire.
By definition not shown in the figure is the reduction of the power demand of the train
thanks to the better voltage, which would add approximately one tenth more to the energy
saving.
75%
80%
85%
90%
95%
100%
500 mm2 800 mm2 1000 mm2
MV cables
DC substation
DC feeders
Overhead wire
Return path
Net at train
Figure 5.7: Energy balances for the three study cases (100% = power input)
The figure above shows that more power becomes available to the trains. The reduction
of losses relative to the power used at the trains is shown in the next figure.

0%
2%
4%
6%
8%
10%
12%
14%
16%
500
mm2
800
mm2
1000
mm2
MV cables
DC substation
DC feeders
Overhead wire
Return path
Figure 5.8: Relative losses for the three study cases (100% = power output at trains)
In the figure, it can be seen that the energy losses in the catenary drop below the energy
losses in the return path if the overhead wire cross-section is 1000 mm2
. This raises the
question whether it would be attractive to reduce the resistance of the return path.
5.2 Traction system performance: supply of higher
voltage to the trains
The voltage profiles along the track are shown in figures 5.9 - 5.11. Each graph contains
two pairs of curves, i.e. the minimum and maximum voltage at a given location (x-axis)
having occurred during the 24h simulation. Each pair corresponds to one track of the
double-track railway. The horizontal axis shows the position in km according to the
reference system used, and hence does not start at 0 km.

Figure 5.9: Minimum and maximum train voltages as a function of the train – 500 mm2

The maximum voltages correspond to the unloaded condition where 1800 V is present
along the entire track.
The minimum voltages correspond to the peak load conditions encountered during the 24h
simulation. The higher peaks of these minimum voltage curves correspond to the locations
of substations or switching stations (where the overhead lines of both tracks are cross-
coupled). In the middle between two substations, the minimum voltage is significantly
lower.
The lowest voltages occur at kms 52-56 of the track with a minimum voltage of 1100 V
in the base case. The minimum voltages are shown in the table below.
Case Minimum voltage at 52-56
km
Minimum voltage at other
sections in study case track
(indicative)
500 mm2
1099 V 1200 V
800 mm2
1144 V 1300 V
1000 mm2
1170 V 1350 V
Table 5.4: Minimum voltage along the study case track
As voltages below 1200 V lead to significant power limitations of trains (see chapter 2),
this low voltage may lead to delays between 52-56 km. Increasing the overhead line cross-
section significantly increases the minimum voltage, as shown in the table below. The
main improvement is achieved at the first upgrade from 500 to 800 mm2
.
At the remaining part of the study case track, voltages are higher, although values down
to 1200 V are occurring between all other substations. These voltages may still lead
to some delays in some cases, as the power is somewhat restricted (see figure 3.2). An
upgrade to 800 mm2
leads to a satisfactory voltage profile with minimum voltages of 1300
V or higher, except for one location, where the voltage profile occasionally drops below
1200 V.
Another method to analyse the voltage improvement is by regarding the “mean useful train
voltage” for each train, that is the average voltage that that particular train experienced
during traction (i.e. excluding braking). For those trains that passed the study case track
during the simulation (which were 359 trains), the improvement is shown in the graph
below. Along the horizontal axis are the relevant trains, sorted by the mean useful voltage
in the 500 mm2
case. The first data series (the solid line) shows the mean useful voltages
for these 359 trains in the 500 mm2
case. The scattered series with the rectangles and
the triangles show, per individual train, the mean useful voltage at 800 and 1000 mm2
,
respectively.

1400
1450
1500
1550
1600
1650
1700
0% 25% 50% 75% 100%
Percentage of trains
Meanusefulvoltage[V]
500 mm2
800 mm2
1000 mm2
Figure 5.12: Improvement of mean useful train voltage for all 359 trains passing the study
case track in 24 h
This graph clearly shows that:
• those trains that suffer from the lowest mean useful voltage benefit the most.
• at 800 mm2
cross-section, the mean useful voltage is increased by 50 volts or more,
at 1000 mm2
by approximately 100 volts or more5
. This applies to more than half
the trains at the study case track.
5.3 Travel time reduction
The graph below shows the train traffic at both tracks of the study case track between
21:00 and 22:00.
The vertical axis shows time, the horizontal axis shows the location and the acronyms
of the stations and the nodes. Feeding substations are not shown in this graph. A line
running from top-left to down-right represents an eastward train, and a line running from
top-right to down-left represents a train in the reverse direction. The slope corresponds
to train speed, a vertical line means standstill. Train numbers are used for identifying
trains within the simulation and do not correspond to the official train numbers used by
the railway company.

40
45
50
55
60
65
70
75
80
85
90
21:00:00
21:10:00
21:20:00
21:30:00
21:40:00
21:50:00
22:00:00
2102
2113
2117
2120
2122
2134
2138
2153
2156
2158
2166
2172
2174
2180
2187
2192
2211
2215
Figure 5.13: Time-location diagram for the study track on an hour with heavy load (500
mm2
)
Low-voltage conditions correspond to locations, where many trains are close together at
a certain point of time, especially if one or more trains are accelerating.
The shaded area corresponds to a time-location area, where time losses due to low voltage
conditions are signiﬁcant6
. Two heavy freight trains (marked 2113 and 2117), two inter-
regional trains (marked 2153 and 2156) and one local train (2174) draw power in their
electrical vicinity.
The travel time for these trains between the stations at 46,5 and 54, as well as the
improvement thanks to the increased overhead wire cross-section is shown in the table
below.

Train nr
Between Travel time [s] Time gained with re-
spect to base case
km km 500
mm2
800
mm2
1000
mm2
800 mm2
1000 mm2
2113
46,5 52 244 244 244 0 0
52 54 87 86 86 1s (1%) 1s (1%)
54 61 292 292 292 0 0
2117
46,5 52 242 238 238 4s (2%) 4s (2%)
52 54 95 87 87 8s (8%) 8s (8%)
54 61 293 291 291 2s (1%) 2s (1%)
2153
46,5 52 209 206 205 3s (1%) 4s (2%)
52 54 52 52 52 0 0
54 61 177 177 177 0 0
2156
46,5 52 194 181 182 13s (7%) 12s (7%
52 54 52 52 52 0 0
54 61 176 176 176 0 0
2174
46,5 52 184 183 184 1s (1%) 0
52 54 100 97 97 3s (3%) 3s (3%)
54 61 228 227 227 1s (0%) 1s (0%)
Table 5.5: Time gains
The table shows that the time gain can be more than 10s, thanks to the better voltage7
.
The time gain values mentioned above take into account, that a train may have to wait
until another train has left the section ahead. This reduces the time gain. It should be
noted, however, that the time gain of a train may be partially or completely offset in the
next railway section, if the train has to wait there for another train. Therefore it is more
realistic to consider the travel time along the entire study case track.
For the total 24-h simulation, many trains would take advantage of an upgrade from 500
mm2
to 800 mm2
. 49 trains (14% of all trains running on the study case track) would
benefit a time gain of 10 s or more along the entire study case track. 95 trains (27%) would
benefit a time gain of 5-9 seconds. More than half the trains would not take advantage
of the increased cross-section, mostly because a time gain in one section of a few seconds
is offset by a time loss in another section. In a few cases (<2%), trains are delayed due
to the changed travelling of other trains.
An upgrade to 1000mm2
brings a slight improvement of the 800 mm2
situation, increasing
the number of trains that win 10s or more to 73 (20% of all trains running on the study
case track).

0-4s
57%
5-9s
27%
10-14s
10%
<0s
2%
15-19s
4%
Figure 5.14: Number of trains the travel time of which is reduced by increasing the
0-4s
52%
5-9s
24%
20-24s
1%
10-14s
13%
<0s
3%
15-19s
7%
Figure 5.15: Number of trains the travel time of which is reduced by increasing the

Chapter 6
Appraisal of the energy saving
The energy saving resulting from an increased overhead wire cross-section brings several
benefits, which are assessed in this chapter.
6.1 Economical benefits without CO2 emission cost
The energy savings lead to cost savings. A cost model has been used to estimate the cost
savings due to the energy saving. The annual energy use and energy (cost) saving have
been estimated by extrapolating the 24-h simulation results to one year.
500 mm2
800 mm2
1000 mm2
Annual energy use of
study case track
58,9 GWh/a 56,3 GWh/a 55,2 GWh/a
Annual energy saving
w.r.t. base case
– 2,6 GWh/a (5%) 3,7 GWh/a (6%)
Annual energy cost
saving w.r.t. base case
– 121 ke/a 209 ke/a
Table 6.1: Annual energy saving with respect to the base case
The costs of upgrading the track to 800 or 1000 mm2
depend not only on the material cost
for the copper added (estimated at e 7,5k per single track km for an upgrade to 800 mm2
and e 12,5k for 1000mm2
), but also on the strength of the support gantries. The study
case track is fitted with gantries, that would probably need reinforcement or replacement
if the overhead wires would be upgraded to 800 mm2
or 1000 mm2
. Replacement of these
gantries only for saving energy cost is not an option.
Should the gantries need to be replaced already for another reason, the support gantries
could be designed for one gauge stronger at relatively low extra cost. A rough estimate of
this differential cost is e 3500 per single-track km for a one-step increase of the gantries
30

www.leonardo-energy.org CHAPTER 6. APPRAISAL OF THE ENERGY SAVING
(sufficient for two 800 mm2
overhead lines) and e 7000 per single-track kilometre for a
two-step increase of the gantries (sufficient for two 1000 mm2
overhead lines).
800 mm2
1000 mm2
Investment costs 1,16 Me 2,05 Me
Benefits 121 ke/a 209 ke/a
Payback period 9,6 years 9,8 years
Internal rate of return (20 years) 9,7% 9,3%
Table 6.2: Annual energy cost saving for the study case track
The table makes clear that, if the support gantries are replaced, it is very attractive
to carry out a significant reinforcement of the overhead wire8
. The payback period is
attractive and the internal rate of return is high.
The table below shows the same above quantities, per single-track km, i.e. divided by
105.
800 mm2
1000 mm2
Energy use
(500 mm2
: 561 MWh/km/a)
536 MWh/km/a 526 MWh/km/a
Energy saving 24,4 MWh/km/a 35,0 MWh/km/a
Energy cost saving 1150e/km/a 2000 e/km/a
Investment needed 11.000e/km 19.500e/km
Profitability
Internal rate of return
Payback period
9,7%
9,6 years
9,3%
9,8 years
Table 6.3: Profitability of overhead wire reinforcement of the study case track – per km
In reality, the figures above will be more favorable, as the effect of regeneration of braking
energy has not yet been taken into account.
6.2 CO2 reduction and economical benefits including
CO2 emission cost
If the overhead wires were reinforced, the energy savings would also result into a reduction
of CO2 emissions in fossil-fuelled power plants. For the Netherlands, an average value of
0,6 kg CO2 per kWh is a common figure.
The emission reductions (excluding the emissions due to the extra material use) are shown
in the table below:

800 mm2
1000 mm2
Energy saving 2,6 GWh/a 3,7 GWh/a
Emission reduction 1550 ton/a 2200 ton/a
Same, per single-track km 15 ton/km/a 21 ton/km/a
Table 6.4: Emission reduction in the study case track
If the emission cost would be e 33/tonne, the net energy cost would increase by e
20/MWh. The energy cost saving from table VIII would then be increased as follows:
800 mm2
1000 mm2
COSTS 1,16 Me 2,05 Me
BENEFITS 172 ke/a 260 ke/a
PAYBACK PERIOD 6,7 years 7,9 years
INTERNAL RATE OF RETURN 14,6% 12,3%
Table 6.5: Annual energy cost saving for the study case track
The table shows that, if emission cost apply, it is very attractive to carry out a signiﬁcant
reinforcement of the overhead wire. The payback period is attractive and the internal
rate of return is high. The increase to 800 mm2
yields a higher rate of return and hence
may be more justiﬁed than the increase to 1000 mm2
.
The graphs below show the payback period and the internal rate of return as a function
of the price of CO2 emission.
0
2
4
6
8
10
12
0 25 50 75 100
Emission cost [EUR/tonne]
PBP[years]
800 mm2
1000 mm2
Figure 6.1: Payback period (PBP) in years of an increase of the catenary cross-section as
a function of emission cost

0%
5%
10%
15%
20%
25%
0 25 50 75 100
Emission cost [EUR/tonne]
IRR[%]
800 mm2
1000 mm2
Figure 6.2: Internal rate of return (IRR) for upgrading the catenary as a function of
emission cost

Chapter 7
Conclusion
7.1 Conclusions
A simulation case study has been carried out for a 52,5 km long piece of the Dutch railway
network, reinforcing the overhead line from 500 to 800 or even 1000 mm2
per track. The
case study shows that it is quite attractive to upgrade the cross-section of the overhead
line signiﬁcantly. For the 800 mm2
case, following results were obtained:
• The energy consumption of this track would decrease by 5% or 2,6 GWh/a, corre-
sponding to 1550 ton/a CO2 reduction, excluding savings from increased regenerated
energy
• Energy cost would decrease by e 121.000 annually
• Energy losses in the overhead wires, dominant in the 500 mm2
case, have become
only slightly higher than the losses in the return path
• If the support gantries of the overhead lines were to be upgraded anyway, the ad-
ditional investment cost would be e 1,2 million. The payback period for this extra
cost would be 9,6 years
• This ’project’ would be quite attractive with an internal rate of return at 9,7%
• If CO2 emission rights were traded at e 33/tonne, the annual cost savings would
increase to e 172.000. The payback period would decrease to only 6,7 years and
the internal rate of return would rise to 14,6%. For higher emission right cost, the
payback period would decrease even further
• The worst-case voltage at this track would increase from 1100 to 1150 V
• 14% of all trains using the studied track would beneﬁt a net time gain of 10 seconds
or more
34

www.leonardo-energy.org CHAPTER 7. CONCLUSION
Upgrading the track to 1000 mm2
instead of 800 mm2
would lead to following results:
• The energy consumption of this track would decrease by 6% or 3,7 GWh/a, corre-
sponding to 2200 ton/a CO2 reduction, excluding savings from increased regenerated
energy
• Energy cost would decrease by e 209.000 annually
• Energy losses in the overhead lines become lower than the losses in the return path
• If the support gantries of the overhead lines were to be upgraded anyway, the ad-
ditional investment cost would be e 2,1 million. The payback period for this extra
cost would again be 9,8 years. This ’project’ would be quite attractive, too, with
an internal rate of return at 9,3%
• The worst-case voltage of this track would increase from 1100 to 1170 V
• 20% of all trains using the studied track would benefit a net time gain of 10 seconds
or more
Generally, the main improvements are seen in the upgrade from 500 to 800 mm2
. Up-
grading to 1000 mm2
still is attractive, but both the payback period and the internal rate
of return are less favourable than upgrading to 800 mm2
. The losses in the return path
become dominant. This raises the question whether it would not be worth to consider
decreasing the return path resistance instead.
7.2 Recommendations
On busy tracks of low-voltage railways, it is very attractive to optimise the catenary cross-
section. It is strongly recommended to add energy optimisation as a design criterion for
DC railway system catenaries.
As it is very difficult to predict the energy savings and other benefits by means of hand
calculations, and in view of the significant possible cost savings, it is recommended to
optimise the catenary cross-section using detailed simulation studies. Key moments are
major overhaul and modification projects comprising the replacement of overhead wires
and/or support structures.
The simulation study also raises another issue. By allowing a large voltage range, the
international standard EN50163 offers the possibility to design traction power supply
systems with high losses and limited possibilities for regeneration of braking energy. It is
recommended to investigate the possibility of shrinking the range of steady-state voltages.
The same recommendation applies to the TSI Energy9
.

www.leonardo-energy.org CHAPTER 7. CONCLUSION
As an illustration only, a possible adaptation of voltage limits from an energy-efficiency
point of view is given in the figure below.
800
1000
1200
1400
1600
1800
2000
EN50163 Reduced
losses
Voltage[V]*
Overvoltages
Non-permanent voltages
Normal steady-state voltage range
Non-permanent voltages
Undervoltages
Figure 7.1: Possible adaptation of voltage limits for a 1500 V DC system in order to
increase energy efficiency (measured at the location of a train, during normal conditions)

Appendix A
Low-voltage power supply systems
In railway systems electrified at 1500 V DC, the traction power is supplied from the public
medium-voltage network. medium-voltage cables bring the power to the railway track.
in substations adjacent to the track, the voltage is transformed to low voltage level by a
transformer and converted to direct current (DC) by a rectifier. The positive terminal of
the rectifier is connected to the catenary, the negative terminal of the rectifier is connected
to the rails. The overhead wire and the rails bring the power to the trains. The figure
below gives a simplified schematic diagram. Substations are spaced 5-20 km.
All substations feed their power in parallel to the track. Hence, the power demand of a
train is dominantly supplied by the nearby substations, but substations farther away also
take their share, albeit a lower one.
Rail
Public electricity network
Transformer
Catenary
Pantograph of the
train
Rectifier
Substation Substation
Figure A.1: Schematic representation of a LV railway system)
37

www.leonardo-energy.org NOTES
Notes
1
Optimal reduction of energy losses in catenary wires for DC railway systems
An ECI-KEMA publication, reference 98430138-TDP 00-12709, July 2000
2
This price may seem high at present (2001), but could become reality in the near future. If the
legislation becomes implemented, the upper limit of the market price will be the penalty for producing
too much emission. The European Parliament has proposed a penalty of about e 50,= per tonne CO2
in 2005, rising to even e 100,= in 2008.
3
Another possibility would be to store the regenerated braking energy in energy buffers like flywheels
or battery systems. This option is not yet very common.
4
Between 2:00 and 05:30 at night, there is no train traffic. The peaks in this period are due to traffic
at other tracks
5
The values displayed in figure 6 are slightly pessimistic for the voltage improvement. The reason is
that figure 6 shows the average voltage along the entire track of the train, which in many cases is longer
than the study case track. Assuming little change in the remainder of the network, in the study case
track itself, the improvement is even higher.
6
The main time gains are indeed achieved at the section with the lowest voltage (kms 52-56). But also
at other locations, significant time gains are achieved: the improvement from 1200 to 1300 V discussed
before does have a favourable effect.
7
The mean useful voltanges for these trains are given below:
Train ID 500 mm2
800 mm2
1000 mm2
2113 1488 V 1534 V 1576 V
2117 1493 V 1523 V 1574 V
2153 1472 V 1529 V 1561 V
2156 1481 V 1538 V 1571 V
Indeed, these trains appear in the lower portion of figure 5.2, 5.2, 5.2
8
Based on 105 km of single track, upgraded at 7.5+3.5=11 ke/km for 800 mm2
and 12.5+7.0=
19.5 ke/km for 1000 mm2
9
EC Directive 96/48 – Interoperability of the trans-European high-speed rail system. Draft Technical
Specification for Interoperability – “Energy” Sub-System

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