Challenge A: A more and more energy efficient railway
Substation with zero auxiliary consumption
G. Vrignaud,
SNCF, Paris, France,
Abstract
Due to the scarcity and the increasing price of energy, the European Union and the national
conference “Grenelle Environnement” organized by the French government have increased
companies awareness to energy cost-saving issues. The SNCF has launched an ambitious
program regarding sustainable development, in order to decrease its energetic cost through
different energy saving actions.
The substation with Zero Auxiliary Consumption « ZAC is fully in line with this energy saving trend:
- Energy moderation,
- Energy efficiency,
- Use for renewable energy.
This project is a first initiative to apply an integration sustainable energy sources within the Fixed
Installations of Electric Traction in France. This feasibility study of the “ZAC” substation dealing with
different technologies of energy production, energy storage and their working domains, allowed
defining the architecture of this autonomous system. The objective of this project is to evaluate the
relevance of substation with a zero auxiliary consumption from a technical but also from an
economical point of view. The sizing validation of the energy production and storage installation has
been realised with a research laboratory.
Introduction
Connected to the secondary of the power transformer or directly to the catenary, the auxiliary’s
consumptions of the electric traction substations are low compared to the traction energy. These
consumptions are estimated at 7 kWh for each substation, constant over the entire year, it
represents about 61.3 MWh. However, applied to the entirety of electric traction substations of the
National Railway Network, an energy saving approach and also the auxiliaries fed by renewable
energies could bring a not negligible economical gain.
The energy saving approach applied to an electric traction substation consists in the energy
moderation and the energy efficiency. The energy moderation aims to stop the absurd and
expensive wasting in all the levels of our society and in our individual behaviours. This can be
obtained with the human factor but also with a management of the priorities. The energy efficiency
gives priority to technical and high-performance solutions, in order to use as the least energy as
possible for a same service provided. The significant part of energy efficiency is linked to the
building energy management.
In this sustainable development context, renewable energies (photovoltaic panels, wind turbines,…)
are more and more used as a complement or in replacement of classical production resources. In
order to guarantee the availability and reliability of the auxiliaries, it is necessary to associate
energy storage systems (batteries, ultra-capacitors, flywheels…). The whole installation will be
controlled by an energy management system.
Challenge A: A more and more energy efficient railway
The application of this energy saving approach to the auxiliaries of an electric traction substation
will allow demonstrating the pertinence of such a system in railway. This feasibility study of the
“ZAC” substation dealing with different technologies of energy production, energy storage and their
working domains, will allow to define the architecture of this autonomous system. The objective of
this project is to evaluate the relevance of substation with a zero auxiliary consumption from a
technical but also from an economical point of view. The sizing validation of the energy production
and storage installation will be realised with a research laboratory. This tries will be completed by
the installation of a prototype on a line post in the draft line electrification Bourges – Saincaize.
Figure 1: Caricatural représentation
Auxiliaries services (identification and load cycle)
A transformer of auxiliaries in a substation ensures the conversion and distribution network usual
voltage with 50Hz frequency. The distribution of auxiliaries is integrated in two control panels: one
alternative and another continuous.
Alternative auxiliary services must ensure the:
- Power supply of battery chargers, heating of cabinets, control panel of outdoor
equipment,
- Power supply of indoor and outdoor lightings of buildings, heating of premises,
protection against fire, portable lightings, radio controlled clock, signalling, telecom and
metering equipment,
Continuous ancillary services must ensure the:
- Power supply of auxiliary circuits of 25kV equipment such as : motor commands
breakers and disconnections, protections, electronic equipment,
- Power supply of driving equipment and control of the facilities such as : power
converters, remote control, PLC, fire detection, intrusion, radio controlled clock,
The charge cycle linked with the consumption of ancillary services is defined under two conditions:
- Standard permanent consumption evaluated at 7kW according to the equipment
characteristics and approved by the feed back campaign of substations recently
implemented,
- Estimated binge according to the maintenance periods in force at SNCF
Challenge A: A more and more energy efficient railway
16
14
Puissance en kW
12
10
8
6
4
2
h
h
h
h
h
h
h
h
23
21
19
17
15
13
11
9
h
7
h
h
5
3
h
h
h
h
h
1
23
21
19
h
h
h
17
15
13
h
9
11
h
h
7
5
h
3
1
h
0
Heure
Cycle de charge représentatif d'une intervention de maintenance préventive
Cycle de charge représentatif d'une intervention de maintenance corrective
Cycle de charge permanent annuel (hors intervention)
Figure 2: Load cycle studied
The energy saving approach
Energy moderation is inseparable from the development of renewable energy. It is an essential
step on the way to energy independence of the reducing consumption of fossil fuels. This approach
perfectly illustrates the procedure to follow to approach an energy virtuous system and not just
financial. It applies to several situations and fields, proposes to open various themes and thus allow
thinking about the best solutions to be implemented by priority.
Tendance = Tendency
Sobriété = Economy
Efficacité = Efficiency
Renouvelables = Renewables
Figure 3: The energy saving approach
Beside human responsibilities and behaviour, the energy economy acts essentially on management
of priorities. It allows identifying within a functional approach, the essential and priority holder
consumers during the operation of the electric power substation. The respect of the standard
“materiel and telecom system requirements for performance IEC 870-4”, is considered as priority
management by supervision system.
Challenge A: A more and more energy efficient railway
Energetic efficiency focus on technical solutions for efficient use less energy possible for the same
service rendered. The current approach linked to the general design of a substation, goes towards
a standardization, which aim consists of apply and install equipment and render the systems
uniform on the railway network. The need of energy efficiency is ideal for the evolution of
standardization procedure through the approach of control of energy. Up to day, changing
technologies specially energy management of building, (heat insulation, lightings, heating) and the
control of electric devices, prove that the new developed systems in industry, take into
consideration these notions and they likely to interfere in the changing of installed equipment.
Two sources of energy improvement have been noticed:
-
la building energy management, by :
 Better heat insulation of building due to the respect of thermal Rule RT2005 (a
study shows energy gain is estimated for about 4000KWH/year).
 Indoor lighting management by setting up of multiplier detector presence with builtin light meter and outdoor lighting by setting up of LED projectors (energy gain is
estimated for about 60% comparing to actual lighting.
 HVAC control in two approaches air heating and geothermal
-
Electrical switch stand by :


Innovation solution allowing to feed the electric command
independently by photovoltaic cell i.e. zero consumption
Full electrical relay
Availability of sources of renewable energy production and storage associated
The aim is to replace the fossil energy by renewable energy. Two solutions might be easily
workable on an isolated site in a substation: Solar energy and wind power.
Concerning storage device, RAGONE diagram has permitted to compare the energetic
performances of each technology. RAGONE diagram is the device commonly admitted; on
logarithmic scale, it places as specific power (in w/kg) according to the specific energy of storage
device (in wh/kg). The outcome of the possible use of three workable solutions is complementary
further to use in electrical substation, batteries, ultra capacitors and flywheel inertia.
Challenge A: A more and more energy efficient railway
Figure 4 : System architecture and storage of energy production with supervision
Model conception
The first design of electric substation with zero auxiliary consumption “CAN” carried out by the
software HOMER ENERGY, shows that the solution generating sources of renewable energy
combined is the most advantageous. The proliferation of solar and wind energy deposits and
substantially reduces the capacity of storage devices with batteries. For their production, these two
sources are balanced and complementary. In fact, the sources of production of photovoltaic energy
are more important during times estivalle while wind generation sources are more important during
winter. Unlike photovoltaic systems or wind energy production, only this combination of two systems
of production of energy consumption leads to a relatively homogeneous, which generates a low
level of availability of energy as well as low in excess energy.
The work done under the pre design validation of previous guides into three main parts:
The first studies the development of a model in MATLAB/SIMULINK, in order to observe the system
behaviour in terms of power out put fluctuations intrinsic to generators of renewable wind and
photovoltaic types as wells as based on different combinations of storage systems in place.
The second part validates the previous results experimentally on a test bench locates in the school
HEI in Lille.
At last, the third part, occupies the validation of the first design of the system in order to assess the
needs of production and storage of sub station further to the specific constraints of sunshine and
wind.
Challenge A: A more and more energy efficient railway
The simulation results show the interest of a combination of storage systems with batteries and ultra
capacitors. In fact, the battery will provide or store the power fluctuations in order to obtain the
output of the power converter P charge of 7Kw.
Profiles of real power from renewable generators are very volatile. The battery will undergo very
large changes in its terminals. Yet, it is not expected to produce as many rounds in such a short
time. We must, therefore, put in place in the supervision of the filtering equation powers to smooth
these variations in order not to reduce the lifetime of this storage system.
Figure 5 : Model concept of MATLAB / SIMULINK system
The figure here below shows the management of the slow component from the battery and the
management of the fast component by ultra capacitors.
Curve of power sent to
the battery
Curve of power sent to
the ultra capacitor
Figure 6 : Monitoring and filtering of all battery ultra capacitors
Challenge A: A more and more energy efficient railway
The many experiments conducted have proved the optimal design of a final source of combined
photovoltaic and wind. The power of the annual consumption of 62.1MWh/year of auxiliary services
of the electric traction substation needs to be implemented:
 A solar power 23KW ( area 116sq.m. according to the technologies)
 Wind power of 25kW at a high level of 20meters
In spite of first design approach and validation of laboratory tests, many questions still remain about
the implementation of energy storage devices. In fact, defining the time of the unavailability of
energy production facility and the weather very random does not ensure the objective full autonomy
of the installation by design optimized storage devices. But laboratory tests have provided certainly
on the choice of the association of battery components and ultra capacitors but eh distribution of
absorbed power between the two storage components to be installed is not validated.
These questions and uncertainties pushed to think of applications and of a more interesting
management from a technical and economic point of view.
Economic balance
The cost of energy expended by SNCF company linked to the consumption of auxiliary services of a
traction substation is estimated at 3000€ in 2010. The trend of changes in the cost of energy
following the introduction of the NOME expected to increase 35% in 2020.
The estimated cost for the installation of energy production previously dimensioned:
 For the photovoltaic about 850€/sq.m installed on the ground (converters included , all
fees included in the design of the installation commissioning and on-site staff training)
about 98k€.
 For a three-bladed wind about 100k€ for 20kw power (price including wind turbine tower
control wiring and engineering costs of installation and commissioning).
Even if the interest environment is established under the CAN substation is clearly not very
profitable in a purely economical aspect.
Prototype
The different approaches discussed above lead to a reflection judicious use of a process of energy
control. Why the company SNCF will try a system based on renewable energy line item in the draft
line electrification 2x25kV Bourges – Saincaize. Integrated monitoring software will benefit from a
return to experience and validate the optimal approach to adopt.
These first results will validate the methodologies and resultants presented above. The entire
equipment of the facility is sized to allow a constant supply of daily 5kWh. Storage devices with
batteries are designed to ensure the system power for three days.
Batteries
mission
Challenge A: A more and more energy efficient railway
Figure 7 : Architecture of prototype
Conclusion
The results of this first initiative highlighted several conclusions:
The different studied solutions to the need for energy, efficiency are easy to implement, require no
major extra cost vis a vis the current cost equipment installed. SNCF integrate progressively theses
solutions in the technical specification and design of electric traction substations.
The design showed that the integration of systems for producing energy is an interesting approach
in environmental says, and in the aim to reduce energetic costs. We can also say that it is not
relevant to the auxiliary power of an electric traction substation with a full autonomy in a process
called purely economic.
The return of experience on the implementation of a prototype on a line item will define a threshold
characteristic specifying interest.