Tesla - Wind Turbine Grid ...

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This ENERGIE publication is one of a series highlighting the potential for innovative non-nuclear energy
technologies to become widely applied and contribute superior services to the citizen. European Commissi-
on strategies aim at influencing the scientific and engineering communities, policy makers and key market
actors to create, encourage, acquire and apply cleaner, more efficient and more sustainable energy solutions
for their own benefit and that of our wider society.
Funded under the European Union’s Fifth Framework Programme for Research, technological Development
and Demonstration (RTD), ENERGIE’s range of supports cover research, development, demonstration,
dissemination, replication and market uptake - the full process of converting new ideas into practical solutions
to real needs. Its publications, in print and electronic form, disseminate the results of actions carried out under
this and previous Framework Programmes, including former JOULE-THERMIE actions. Jointly managed by
Directorate-General Energy and Transport & Directorate-General Research, ENERGIE has a total budget of
1042 million W over the period 1999 to 2002.
Delivery is organised principally around two Key Actions, Cleaner Energy Systems, including Renewable
Energies, and Economic and Efficient Energy for a Competitive Europe, within the theme ”Energy, Environ-
ment and Sustainable Development”, supplemented by coordination and cooperative activities of a sectoral
and cross-sectoral nature. With targets guided by the Kyoto Protocol and associated policies, ENERGIE’s
integrated activities are focussed on new solutions which yield direct economic and environmental benefits to
the energy user, and strengthen European competitive advantage by helping to achieve a position of leaders-
hip in the energy technologies of tomorrow. The resulting balanced improvements in energy, environmental
and economic performance will help to ensure a sustainable future for Europe’s citizens.
ENERGIE
with the support of the EUROPEAN COMMISSION
Directorate-General for Energy and Transport
LEGAL NOTICE
Neither the European Commission, nor any person acting on behalf of the Commission,
is responsible for the use which might be made of the information contained in this publication.
© European Communities, 2001
Reproduction is authorised provided the source is acknowledged.
Printed in Germany
Produced by
Deutsches Windenergie-Institut GmbH
Fritz Santjer, Gerhard J. Gerdes · Ebertstraße 96 · D-26382 Wilhelmshaven
Tel.: +49 4421 48080 · Fax: +49 4421 480843
Tech-wise A/S
Peter Christiansen · Kraftværksvej 53 · DK 7000 Fredericia · Denmark
DM Energy
David Milborrow · 23 The Gallops · UK BN7 1LR Lewes · East Sussex · United Kingdom
Wind Turbine Grid Connection
and Interaction
Deutsches Windenergie-Institut GmbH Germany · Tech-wise A/S Denmark · DM Energy United Kingdom
Contents
1
Introduction
......................................
5
2
Overview of Wind Power
Generation and Transmission
........
5
2.1
Components of the System .....................
5
2.2
Supply Network ....................................
6
2.3
Offshore grid connection .......................
6
2.4
Losses ..................................................
9
3
Generator Systems for
Wind Turbines
..................................
9
3.1
Fixed Speed wind turbines .....................
10
3.2
Variable Speed Wind Turbines ...............
10
3.3
Inverter systems .....................................
10
4
Interaction with the Local
Electricity Network
..........................
11
4.1
Short circuit power level ........................
12
4.2
Voltage variations and flicker .................
12
4.3
Harmonics ...........................................
13
4.4
Frequency ............................................
14
4.5
Reactive power .....................................
14
4.6
Protection ...........................................
15
4.7
Network stability .................................
16
4.8
Switching operations and
soft starting .........................................
16
4.9
Costs of Grid Connection ......................
17
4.10 Safety, Standards and Regulations .........
18
4.11 Calculation methods .............................
19
5
Integration into the
National Grid
..................................
22
5.1
Emission Savings ..................................
22
5.2
Energy Credit ......................................
22
5.3
Capacity Credit ...................................
23
6
Case Studies
...................................
24
6.1
Tunø Knob Wind farm, DK ....................
24
6.2
Rejsby Hede Wind Farm, DK ................
24
6.3
Delabole wind farm, UK .......................
26
6.4
Cold Northcott Wind Farm, UK .............
27
6.5
Wybelsumer Polder, D ..........................
27
6.6
Belvedere, D ........................................
28
7
Glossary
..........................................
29
8
References
......................................
29
1 Introduction
wealth of experience upon which to draw. The fact
that Denmark is planning to supply 30 percent of its
electricity needs from wind energy is testimony to
the fact that its potential is considerable.
Wind energy is now firmly established as a mature
technology for electricity generation and over
13,900 MW of capacity is now installed, world-
wide. It is one of the fastest growing electricity-
generating technologies and features in energy
plans across all five continents, both in the
industrialised and the developing world.
2 Overview of Wind
Power Generation and
Transmission
It differs, however, in several respects from the
„conventional“ thermal sources of electricity
generation. Key differences are the small sizes of
individual units, the variable nature of the wind and
the type of electrical generator. Each is considered
in this brochure.
WT convert wind energy into electrical energy,
which is fed into electricity supply systems. The
connection of WT to the supply systems is possible
to the low voltage, medium voltage, high voltage as
well as to the extra high voltage system. While most
of the turbines are nowadays connected to the
medium voltage system of the grid future large
offshore wind farms will be connected to the high
and extra high voltage level.
Small unit sizes: The small unit sizes mean that both
wind farms and individual wind turbines (WT) are
usually connected into low voltage distribution
networks rather than the high voltage transmission
systems and this means that a number of issues
related to power flows and protection systems need
to be addressed. Electrical safety is an important
issue under this heading.
2.1 Components of the System
The three main components for energy conversion in
WT are rotor, gear box and generator. The rotor
converts the fluctuating wind energy into mechani-
cal energy and is thus the driving component in the
conversion system.
Variability: The variable nature of wind is often
perceived as a difficulty, but in fact poses few
problems. The variations in output do not cause any
difficulty in operating electricity systems, as they
are not usually detectable above the normal variati-
ons in supply and demand. With significant amounts
of wind power – roughly 30 % or more of demand -
low cost solutions can be found and some island sys-
tems operate with high proportions of wind energy.
Variability also needs to be taken into account at the
local level, to ensure consumers are not affected by
„flicker“. Appropriate care in electrical design,
however, can eliminate this problem.
The generator and possibly an electronic inverter
absorb the mechanical power while converting it
into electrical energy, fed into a supply grid. The
gear box adapts rotor to generator speed. The gear
box is not necessary for multipole, slow running
generators.
5
The main components for the grid connection of the
WT are the transformer and the substation with the
circuit breaker and the electricity meter inside it.
Because of the high losses in low voltage lines, each
Electrical properties: Early WT followed steam
turbine practice with synchronous generators, but
many modern WT have induction generators. These
draw reactive power from the electricity network,
necessitating careful thought to electrical power
flows. Other machines, however, are capable of
conditioning the electrical output and providing a
controllable power factor. This is an asset, especi-
ally in rural areas, where it may be undesirable to
draw reactive power from the network.
Advances in wind-turbine technology and the
results of nearly two decades of research mean that
the integration of WT and wind farms into elec-
tricity networks generally poses few problems. The
characteristics of the network and of the turbines do
nevertheless need to be evaluated but there is now a
Figure 1.1: Yearly installed capacity of wind energy in
Europe and wold-wide
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