Grid Integration of Wind Energy - Siegfried Heier - E-Book

Grid Integration of Wind Energy E-Book

Siegfried Heier

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This popular reference describes the integration ofwind-generated power into electrical power systems and, with theuse of advanced control systems, illustrates how wind farms can bemade to operate like conventional power plants. Fully revised, the third edition provides up-to-date coverage onnew generator developments for wind turbines, recent technicaldevelopments in electrical power conversion systems, control designand essential operating conditions. With expanded coverage ofoffshore technologies, this edition looks at the characteristicsand static and dynamic behaviour of offshore wind farms and theirconnection to the mainland grid. Brand new material includes: * comprehensive treatment of onshore and offshore gridintegration * updated legislative guidelines for the design, construction andinstallation of wind power plants * the fundamental characteristics and theoretical tools ofelectrical and mechanical components and their interactions * new and future types of generators, converters, powerelectronics and controller designs * improved use of grid capacities and grid support for fixed- andvariable-speed controlled wind power plants * options for grid control and power reserve provision in windpower plants and wind farms This resource is an excellent guide for researchers andpractitioners involved in the planning, installation and gridintegration of wind turbines and power plants. It is also highlybeneficial to university students studying wind power technology,renewable energy and power systems, and to practitioners in windengineering, turbine design and manufacture and electrical powerengineering.

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Table of Contents

Cover

Title Page

Copyright

Preface

Notation

Chapter 1: Wind Energy Power Plants

1.1 Wind Turbine Structures

1.2 A Brief History

1.3 Milestones of Development

1.4 Functional Structures of Wind Turbines

References

Chapter 2: Wind Energy Conversion Systems

2.1 Drive Torque and Rotor Power

2.2 Turbines

2.3 Power Control by Turbine Manipulation

2.4 Mechanical Drive Trains

2.5 System Data of a Wind Power Plant

References

Chapter 3: Generating Electrical Energy from Mechanical Energy

3.1 Constraints and Demands on the Generator

3.2 Energy Converter Systems

3.3 Operational Ranges of Asynchronous and Synchronous Machines

3.4 Static and Dynamic Torque

3.5 Generator Simulation

3.6 Design Aspects

3.7 Machine Data

References

Chapter 4: The Transfer of Electrical Energy to the Supply Grid

4.1 Power Conditioning and Grid Connection

4.2 Grid Protection

4.3 Grid Effects

4.4 Resonance Effects in the Grid During Normal Operation

4.5 Remedial Measures against Grid Effects and Grid Resonances

4.6 Grid Control and Protection

4.7 Grid Connection Rules

4.8 Grid Connection in the Offshore Region

4.9 Integration of the Wind Energy into the Grid and Provision of Energy

References

Chapter 5: Control and Supervision of Wind Turbines

5.1 System Requirements and Operating Modes

5.2 Isolated Operation of Wind Turbines

5.3 Grid Operation of Wind Turbines

5.4 Control Concepts

5.5 Controller Design

5.6 Management System

5.7 Monitoring and Safety Systems

References

Chapter 6: Using Wind Energy

6.1 Wind Conditions and Energy Yields

6.2 Potential and Expansion

6.3 Economic Considerations

6.4 Legal Aspects and the Installation of Turbines

6.5 Ecological Balance

References

Index

End User License Agreement

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Guide

Cover

Table of Contents

Preface

Chapter 1: Wind Energy Power Plants

List of Illustrations

Figure 1.1

Figure 1.2

Figure 1.3

Figure 1.4

Figure 1.5

Figure 1.6

Figure 1.7

Figure 1.8

Figure 1.9

Figure 1.10

Figure 1.11

Figure 1.12

Figure 1.13

Figure 1.14

Figure 1.15

Figure 1.16

Figure 1.17

Figure 1.18

Figure 1.19

Figure 1.20

Figure 1.21

Figure 1.22

Figure 1.23

Figure 1.23

Figure 1.24

Figure 1.26

Figure 1.27

Figure 1.28

Figure 1.29

Figure 1.30

Figure 1.31

Figure 1.32

Figure 1.33

Figure 1.34

Figure 1.35

Figure 1.36

Figure 1.37

Figure 1.38

Figure 2.1

Figure 2.2

Figure 2.3

Figure 2.4

Figure 2.5

Figure 2.6

Figure 2.7

Figure 2.8

Figure 2.9

Figure 2.10

Figure 2.11

Figure 2.12

Figure 2.13

Figure 2.14

Figure 2.15

Figure 2.16

Figure 2.54

Figure 2.17

Figure 2.18

Figure 2.19

Figure 2.20

Figure 2.21

Figure 2.22

Figure 2.23

Figure 2.24

Figure 2.25

Figure 2.26

Figure 2.27

Figure 2.28

Figure 2.29

Figure 2.30

Figure 2.31

Figure 2.32

Figure 2.33

Figure 2.34

Figure 2.35

Figure 2.36

Figure 2.37

Figure 2.38

Figure 2.39

Figure 2.40

Figure 2.41

Figure 2.42

Figure 2.43

Figure 2.44

Figure 2.45

Figure 2.46

Figure 2.47

Figure 2.48

Figure 2.49

Figure 2.50

Figure 2.51

Figure 2.52

Figure 2.53

Figure 2.55

Figure 2.56

Figure 2.57

Figure 2.58

Figure 2.59

Figure 2.60

Figure 2.61

Figure 2.62

Figure 2.63

Figure 2.64

Figure 2.65

Figure 2.66

Figure 2.67

Figure 2.68

Figure 2.69

Figure 2.70

Figure 2.71

Figure 2.73

Figure 2.74

Figure 2.75

Figure 2.76

Figure 2.77

Figure 2.78

Figure 2.79

Figure 2.80

Figure 3.1

Figure 3.2

Figure 3.3

Figure 3.4

Figure 3.5

Figure 3.6

Figure 3.7

Figure 3.8

Figure 3.9

Figure 3.13

Figure 3.10

Figure 3.11

Figure 3.12

Figure 3.14

Figure 3.15

Figure 3.16

Figure 3.17

Figure 3.18

Figure 3.19

Figure 3.20

Figure 3.21

Figure 3.22

Figure 3.23

Figure 3.24

Figure 3.34

Figure 3.25

Figure 3.26

Figure 3.27

Figure 3.28

Figure 3.29

Figure 3.30

Figure 3.31

Figure 3.33

Figure 3.35

Figure 3.36

Figure 3.37

Figure 3.39

Figure 3.40

Figure 3.41

Figure 3.42

Figure 3.43

Figure 3.44

Figure 3.45

Figure 3.46

Figure 3.47

Figure 3.48

Figure 3.49

Figure 3.50

Figure 3.51

Figure 3.52

Figure 3.53

Figure 3.54

Figure 3.55

Figure 3.56

Figure 3.57

Figure 3.58

Figure 3.59

Figure 3.60

Figure 3.61

Figure 3.62

Figure 3.63

Figure 3.64

Figure 3.65

Figure 3.66

Figure 3.67

Figure 3.68

Figure 3.69

Figure 3.70

Figure 3.71

Figure 3.73

Figure 4.1

Figure 4.2

Figure 4.3

Figure 4.4

Figure 4.5

Figure 4.6

Figure 4.7

Figure 4.8

Figure 4.9

Figure 4.10

Figure 4.16

Figure 4.11

Figure 4.12

Figure 4.13

Figure 4.14

Figure 4.15

Figure 4.17

Figure 4.17

Figure 4.18

Figure 4.19

Figure 4.20

Figure 4.22

Figure 4.23

Figure 4.24

Figure 4.25

Figure 4.26

Figure 4.27

Figure 4.28

Figure 4.29

Figure 4.30

Figure 4.31

Figure 4.32

Figure 4.33

Figure 4.34

Figure 4.35

Figure 4.36

Figure 4.37

Figure 4.38

Figure 4.39

Figure 4.40

Figure 4.41

Figure 4.42

Figure 4.43

Figure 4.44

Figure 4.45

Figure 4.46

Figure 4.47

Figure 4.48

Figure 4.49

Figure 4.50

Figure 4.51

Figure 4.52

Figure 4.53

Figure 4.54

Figure 4.55

Figure 4.56

Figure 4.57

Figure 4.58

Figure 4.59

Figure 4.60

Figure 4.61

Figure 4.62

Figure 4.63

Figure 4.64

Figure 4.65

Figure 4.66

Figure 4.67

Figure 4.68

Figure 4.70

Figure 4.71

Figure 4.73

Figure 4.74

Figure 4.75

Figure 4.76

Figure 4.77

Figure 4.78

Figure 4.79

Figure 4.80

Figure 4.81

Figure 4.82

Figure 4.83

Figure 4.84

Figure 4.85

Figure 4.86

Figure 4.87

Figure 4.88

Figure 4.89

Figure 4.91

Figure 4.90

Figure 4.92

Figure 4.93

Figure 4.94

Figure 4.95

Figure 5.1

Figure 5.2

Figure 5.3

Figure 5.4

Figure 5.12

Figure 5.5

Figure 5.6

Figure 5.7

Figure 5.8

Figure 5.9

Figure 5.10

Figure 5.11

Figure 5.13

Figure 5.14

Figure 5.15

Figure 5.16

Figure 5.17

Figure 5.18

Figure 5.19

Figure 5.20

Figure 5.21

Figure 5.22

Figure 5.23

Figure 5.24

Figure 5.26

Figure 5.25

Figure 5.27

Figure 5.28

Figure 5.29

Figure 5.30

Figure 5.31

Figure 5.32

Figure 5.33

Figure 5.34

Figure 5.35

Figure 5.36

Figure 5.37

Figure 5.38

Figure 5.39

Figure 5.40

Figure 5.41

Figure 5.42

Figure 5.43

Figure 5.44

Figure 5.45

Figure 5.46

Figure 5.47

Figure 5.48

Figure 5.49

Figure 5.50

Figure 6.1

Figure 6.2

Figure 6.5

Figure 6.7

Figure 6.8

Figure 6.9

Figure 6.10

Figure 6.11

Figure 6.12

Figure 6.15

Figure 6.13

Figure 6.15

Figure 6.16

Figure 6.17

Figure 6.19

Figure 6.20

Figure 6.18

Figure 6.22

Figure 6.21

Figure 6.23

Figure 6.24

Figure 6.25

Figure 6.26

Figure 6.27

List of Tables

Table 4.1

Table 4.2

Table 4.3

Table 4.4

Table 4.5

Table 4.6

Table 4.7

Table 4.8

Table 4.9

Table 4.10

Table 4.11

Table 5.1

Table 5.2

Table 5.3

Table 5.4

Grid Integration of Wind Energy

Onshore and Offshore Conversion Systems

Third Edition

 

Siegfried Heier

Kassel University, Fraunhofer Institute for Wind Energy and Energy System Technology (IWES) Kassel, Germany

 

Translators: Gunther RothAdliswil, SwitzerlandRachel WaddingtonUK

 

 

 

 

 

Originally published in the German language by Vieweg+Teubner, 65189 Wiesbaden, Germany, as “Siegfried Heier: Windkraftanlagen. 5. Auflage (5th Edition)” © Vieweg+Teubner | Springer Fachmedien Wiesbaden GmbH 2009

Springer Fachmedien is part of Springer Science+Business Media

This edition first published 2014

© 2014, John Wiley & Sons, Ltd

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Library of Congress Cataloging-in-Publication Data

Heier, Siegfried.

[Windkraftanlagen im Netzbetrieb. English]

Grid integration of wind energy / Siegfried Heier ; translated by Rachel Waddington. – Third editon.

pages cm

Translation of: Windkraftanlagen im Netzbetrieb.

Includes bibliographical references and index.

ISBN 978-1-119-96294-6 (hardback)

1. Wind power plants. 2. Wind energy conversion systems. 3. Electric power systems. I. Title.

TK1541.H3513 2014

621.31′2136– dc23

2013041087

A catalogue record for this book is available from the British Library.

ISBN: 978-1-119-96294-6

Preface

In the long run, an ecologically sustainable energy supply can be guaranteed only by the integration of renewable resources. Besides water power, which is already well established, wind energy is by far the most technically advanced of all renewable power sources, and its economic breakthrough the closest. With a few exceptions, wind power will be used mostly for generating electricity.

Just three decades on from the 50 kW class machines of the mid-1980s, the development of wind turbines has led to production converters with outputs in the 3 MW range. Five to ten megawatt turbines are currently being launched in the market. In the development of these machines, successful techniques and innovations originating from small- and medium-sized turbines were carried over to larger ones, and this has led to a considerable improvement in the reliability of wind turbines. The technical availability currently achieves average values of approximately 98%. Furthermore, economic viability has increased enormously. As a result, wind energy has experienced an almost unbelievable upsurge and has already far exceeded the contributions of water power.

The rapid development of wind power has awakened strong public, political and scientific interest, and has triggered widespread discussion over the past few years, much of it concerning the degree to which nature, the environment and the electricity grid can withstand the impact of wind power.

If political requirements regarding the reduction of environmental pollution are to be met, long-term growth in the use of wind power must be the focus. Since obtaining electricity from the wind currently offers the most favourable technical and economic prospects of all the sources of renewable energy, it must be assigned the highest priority. Due to the fact that turbine sizes are still increasing, a high degree of grid penetration must be expected (regionally at any rate), meaning that the connection of wind turbines could come up against its technical limits. This is already the case today in some instances.

The objective of a forward-looking energy supply policy must therefore be to utilize the existing grid as well as possible ones for the supply of wind power. This is made possible by the use of turbines with good grid compatibility in connection with measures for grid reinforcement. In assessing grid effects, control operations and the electrical engineering design of wind turbines play a significant role. The themes developed in this work are therefore particularly concerned with this topic.

This edition of the book has been updated to cover important innovations in this rapidly changing technology in terms of energy converters, generators and controls, grid integration and development. Important additions were made especially in view of offshore use of wind energy. This has resulted in special importance being paid to network connections at sea and on land. The layout of the book has also been updated to achieve a consistent format, and a number of new illustrations have been included. A great deal of new material has also been added to cover changes in legislation.

This book is the result of a 37 years continuous work in research and development, especially as Head of Wind Energy Research and Professor at the University Kassel, in the Electrical Energy Supply Department of the Institut für Elektrische Energietechnik. Close cooperation with the Institut für Solare Energieversorgungstechnik (ISET) e.V. (now Fraunhofer Institut für Windenergiesysteme IWES, Kassel) brought with it a considerable broadening of the horizon of experience. My special thanks go to the founder of the ISET, Professor Dr Werner Kleinkauf. His suggestions and our technical discussions have had a considerable influence on this work.

The help and support of Ms Katherina Messoll, Dr.-Ing. Alejandro Gesino, Dipl.-Ing. Christof Dziendziol. Dipl.-Ing, Adit Ezzahraoui, Dr.-Ing. Gunter Arnold, Dr Boris Valov, Dipl.-Ing. Michael Durstewitz, Dr.-Ing. Martin Hoppe-Kilpper, Dipl.-Ing.Berthold Hahn, Dipl.-Ing. Martin Kraft, Dipl.-Ing. Volker Konig, Dipi.-Ing. Werner Döring, Dipl.-Ing. Bernd Gruss, Dr-Ing. Oliver Haas, Dr.-Ing Rajeh Saiju, Mr Thomas Donbecker, Mr Bernhard Siano, Mr Martin Nagelmilller, Ms Dipl.-Des. Renate Rothkegel, Frau Melanie Schmieder, Ms Anja Clark-Carina and Ms Judith Keuch have contributed greatly to the success of this book.

My grateful thanks also go to ENERCON GmbH for kindly granting permission to use the image of the wind turbine in the design of the front cover.

This book is intended not only for students in technical faculties. The procedural notes and experimental results will also be of great help to engineers both in theory and practice.

My special thanks must go to the publisher, John Wiley & Sons, Ltd and Laura Bell and Peter Mitchell for their readiness to publish this book and for the painstaking preparation involved.

I would like to thank my wife Hannelore for her assistance as adviser for the difficult formulation and for her understanding that was necessary for the creation of this work.

This book is dedicated to my grandchildren Serafin and Mila as well as my daughters Angela, Sandra and Tina.

The issue of the fifth revision marks the third decade of my future-oriented efforts in this sector and documents the headlong development of wind energy utilization. In this scientific and energy segment with its defining technology, successes have been achieved that open up optimistic perspectives for the future of energy supply.

Siegfried Heier, Kassel

Notation

Constant factor related to the pivot of the profile

Distance between point of application of lifting force and blade axis ofrotation

Distance along blade axis between the points of application of torque andgravity

Blade deflection and slewing

Far-upstream cross-section of flow

Cross-section of flow at turbine

Broadening downstream cross-section of flow

Long-term flicker factor

Rotor swept area

Short-term flicker factor

Acceleration of the rotor blade centre of gravity

Acceleration of the rotor blade centre of gravity in the rotating coordinatesystem

Coriolis acceleration of rotor blade centre of gravity

Blade bending in direction of deflection

Centripetal acceleration in the rotor head

Centripetal acceleration arising from

Bending acceleration of the rotor blade in the direction of deflection and slew

Blade bending in direction of slew

Centripetal acceleration arising from

Magnification factor for the initial short-circuit alternating current power or the maximum possible short-circuit current

Lift coefficient of blade profile

Capacitor bank capacitance

Torque coefficient of the turbine

Performance coefficient of the turbine

Torsional moment coefficient of blade profile (

/4-related)

Drag coefficient of blade profile

Power factor

Power factor in case of short-circuit

, Theodorsen function

Half-profile depth

Average bearing diameter

Blade element area

Lift force on blade element

Resultant force on blade segment from lift and drag components

Axial force at blade element

Tangential force at blade element

Drag force on blade element

Axial momentum losses by blade streaming

Change of tangential momentum of angular streaming

Moment per unit of width during blade pitch adjustment due toacceleration of air mass and due to air damping

Torsional moment at blade element due to lifting forces

Righting moment in direction of air flow on the blade element

Voltage deviation, voltage drop

Frequency

Grid frequency

Rotor current frequency (the

th harmonic) in asynchronousmachines

Generator frequency

Bearing coefficient dependent upon bearing type and loading

Frequency of the

th subharmonic

Frequency of the

th harmonic

Axial force on bearing

Normal force

Force creating propeller moment

Transverse force component

Actuating force on blade

Centrifugal force

Bearing load direction factor

Transmission ratio between adjustment mechanism and blade pitchadjustment

Total current (rotating pointer)

Total current in phase 1

Total current in phase 2

Total current in phase 3

Total current in longitudinal direction of field coordinates

Total current in transverse direction of field coordinates

Transmission ratio between adjustment motor and blade rotation

Transmission ratio between servomotor and rotor blade adjustment

Transmission ratio between servomotor and blade pitch adjustment inthe case of direct motor drive

Magnetizing current in the stator

Machine-side rotor current (rotating pointer)

Machine-side rotor current in phase 1

Machine-side rotor current in phase 2

Machine-side rotor current in phase 3

Machine-side rotor current in longitudinal direction of field coordinates

Actual value of

Desired value of

Grid-side rotor current (rotating pointer)

Machine-side rotor current in phase 1

Actual value of

Desired value of

No-load current in one machine phase

Stator current

Effective value of fundamental component current

Rotor phase current acting on stator side

Starting current of asynchronous machines

Exciter current

Iron loss current in one machine phase

Electric current or hydraulic flow for blade pitch positioning

Current of reactive power compensation system

Magnetizing current in one machine phase

Effective value of the

th harmonic current

Moment of inertia of blade during rotation around the hub

Moment of inertia of rotor blade when turned about its longitudinalaxis

Moment of inertia of rotor blade taken at the drive motor side

Moment of inertia of generator rotor

Equivalent moment of inertia due to accelerated air mass

Moment of inertia of the drive motor

Moment of inertia of the drive motor acting on the rotor blades

Moment of inertia of all rotating masses

Total moment of inertia of blade pitch adjustment system

Total moment of inertia of the entire blade pitch adjustment systemtaken from the drive side

Total moment of inertia of the entire blade pitch adjustment systemtaken from the blade side

Moment of inertia of transmission elements such as gears, couplings,etc., between drive motor and blade turning mechanism

Rate of change factor of the rotor displacement angle after falling outof step

Characteristic damping

Coefficient of structural and aerodynamic damping

Coefficient of damping for the drive train

Coefficient of friction for bearing friction at rotor blade during bladepitch adjustment

Ratio of the acceleration moments of the drive-train component to theentire rotor system

Total harmonic distortion

Grid-state-dependent and grid short-circuit power-dependent outputvalue of total harmonic distortion

Gradient of relative harmonic content

Elongation factor of relative harmonic content

Torsional stiffness of the drive train

Harmonic distortion of voltage

Factor for the maximum magnification of generator moment

Number of phases of three-phase current windings

Mass of a rotor blade

, dynamic increase in moment

Moment

Torque

Driving torque

Actual value of moment

Driving torque at generator

Motor start-up torque

External torque of blade pitch adjustment drive taking into accountspring and damping characteristics

Driving torque of drive train including losses

Internal torque of blade pitch adjustment drive

Wind turbine driving moment

Torsional moment at rotor blade due to bending

Acceleration moment at the generator

Rotor blade torsional moment during turning about blade longitudinalaxis

Maximum blade torsional moment in extreme situations

Blade torsional moment in normal operation

Acceleration moment in rotor system

Acceleration moment in drive train

Acceleration moment on wind turbine

Coriolis moment in relation to the

axis

Damping moment of the synchronous machine

Desired value of torque

Moment of friction of all blade bearings during blade pitch adjustment

Breakdown torque of asynchronous machine

Pull-out torque of synchronous machine

Dynamic breakdown or pull-out torque

Generator breakdown or pull-out torque

Motor breakdown or pull-out torque

Maximum breakdown or pull-out torque

Maximum moment of synchronous machines due to subtransientshort-circuit currents in the damping winding

Maximum value of pulsating short-circuit moment of synchronousmachines due to transient currents

Static breakdown or pull-out torque

Static breakdown or pull-out torque at maximum excitation

Static breakdown or pull-out torque with no-load excitation

Coupling torque at generator

Moment with blade pitch adjustment by acceleration of air masses andair damping

Moment with blade pitch adjustment due to acceleration of air masses

Moment with blade pitch adjustment due to air damping

Torsional moment at rotor blade due to lift forces

Maximum moment

Nominal moment

Generator nominal moment

Motor nominal moment

Propeller moment

Reserve moment during acceleration of the blade pitch adjustmentmechanism

Load-dependent moment of friction of a bearing

Load-dependent moment of friction of bearing

Steady-state torque

Pull-up torque

Pull-up torque of a motor (asynchronous machine)

Moment exerted upon blade by actuator

Righting moment in direction of air flow on blade profile

Damping component of drive train moment

Torsional moment at the blade due to teetering of the rotor

Torsionally elastic component of drive-train moment

Load torque

(Electrical) load torque of the generator

Rotational speed

Speed of rotating field or synchronous speed

Number of turbines

Actual value of rotational speed

Rotational speed of blade pitch adjustment drive

Desired value for speed

Generator breakdown-torque speed (asynchronous machine)

Motor breakdown-torque speed (asynchronous machine)

Generator nominal speed (asynchronous machine)

Motor nominal speed (asynchronous machine)

Speed of the harmonic field of ordinal number

Number of pairs of poles in the stator

Number of pairs of poles in the rotor

Average value of power

Power of producer in the grid

Electrical generator power

Total active power in rotor and stator

Power of the load in the grid

Equivalent static bearing loading

Mechanical input power of generator

Nominal power

Moving air mass power

Power for normal positioning procedures

Power for fast positioning procedures

Actual value of total active power

Desired value of total power

Wind turbine power

Maximum wind turbine power

Air gap power of an electrical machine

Standard deviation of power

Compensation reactive power

Total reactive power in rotor and stator

Actual value of total reactive power

Desired value of total reactive power

Radius of a blade element

Radius of the rotor blade centre of mass

Distance between yaw and rotor blade fulcrums

Stator resistance of one machine phase

Rotor resistance of one phase of an asynchronous machine transformedon the stator side

Outer radius of rotor blade

Resistance of the connection elements between higher grid and pointof common coupling

Inner radius of rotor blade

Ohmic resistance of lines and transformers

Resistance between wind turbine and point of common coupling

Slip (of an asynchronous machine)

Breakdown slip (asynchronous machine)

Nominal slip (asynchronous machine)

Slip of the

th harmonic (asynchronous machine)

Grid apparent power

Grid short-circuit power

Initial value of alternating current short-circuit power

Load apparent power

Centre of gravity

Generator rated apparent power

Transformer rated apparent power

Supply apparent power

Time

Time for rotor blade adjustment into a safe operating state

Time for rotor blade adjustment into a safe operating state with pureacceleration processes

Acceleration time of blade positioning drive in the case of fastpositioning procedures

Acceleration time of blade positioning drive system

Acceleration time of direct-driven blades

Acceleration time of

rotor blades adjusted by positioning drivesystem

Blade thickness

Duration of secondary effect of flicker

Delay time

Rotor blade adjustment time at constant speed

Time constant of damping of torque oscillation

Time constant of the exciter circuit

Generator acceleration time constant

, time constant of the rotation speed integrator

Rotor system acceleration time constant

Time constant for the decaying dynamic pull-out torque to itssteady-state value

Wind turbine acceleration time constant

, time constant of integrator for the determination of the angleof torsion (generator side)

Total voltage (rotating pointer) corresponds to stator voltage

Total voltage in quadrature-axis direction of the field coordinates

Magnification factor of the short-circuit power of asynchronousmachines

Magnification factor of the short-circuit power of synchronousmachines

Nominal voltage

Machine-side rotor voltage in phase 1

Machine-side rotor voltage in phase 2

Machine-side rotor voltage in phase 3

Machine-side rotor voltage in direct-axis direction of the fieldcoordinates

Machine-side rotor voltage in quadrature direction of the fieldcoordinates

Stator voltage in phase 1

Stator voltage in phase 2

Stator voltage in phase 3

Stator voltage in quadrature direction of the field coordinates

Chapter 1Wind Energy Power Plants

Rising pollution levels and worrying changes in climate, arising in great part from energy-producing processes, demand the reduction of ever-increasing environmentally damaging emissions. The generation of electricity—particularly by the use of renewable resources—offers considerable scope for the reduction of such emissions. In this context, the immense potentials of solar and wind energy, in addition to the worldwide use of hydropower, are of great importance. Their potential is, however, subject to transient processes of nature. Following intensive development work and introductory steps, the conversion systems needed to exploit these power sources are still in the primary phase of large-scale technical application. For example, in Germany around 8% of electricity is already being provided by wind turbines. However in the German provinces Mecklenburg-Western-Pomerania, Schleswig-Holstein, Brandenburg and Saxony-Anhalt there are about 50% wind power feed in. In Germany more power is supplied by wind energy than by hydroelectric plants.

These environmentally friendly technologies in particular require a suitable development period to establish themselves in a marketplace of high technical standards.

The worldwide potential of wind power means that its contribution to electricity production can be of significant proportions. In many countries, the technical potential and—once established—the economically usable potential of wind power far exceeds electricity consumption. Good prospects and economically attractive expectations for the use of wind power are, however, inextricably linked to the incorporation of this weather-dependent power source into existing power supply structures, or the modification of such structures to take account of changed supply conditions.

1.1 Wind Turbine Structures

In the case of hydro, gas or steam, and diesel power stations (among others) the delivery of energy can be regulated and adjusted to match demand by end users (Figure 1.1(a)). In contrast, the conversion system of a wind turbine is subject to external forces (Figure 1.1(b)). The delivery of energy can be affected by changes in wind speed, by machine-dependent factors such as disruption of the airstream around the tower or by load variations on the consumer side in weak grids.

Figure 1.1 Energy delivery and control in electrical supply systems: (a) diesel generators, etc., and (b) wind turbines

The principal components of a modern wind turbine are the tower, the rotor, the nacelle (which accommodates the transmission mechanisms and the generator) and—for horizontal-axis devices—the yaw systems for steering in response to changes in wind direction. Switchgear and protection systems, lines, and maybe also transformers and grids, are required for supplying end users or power storage systems. In response to external influences, a unit for operational control and regulation must adapt the flow of energy in the system to the demands placed upon it. The next two figures show the arrangement of the components in the nacelle and the differences between mechanical–electrical converters in the modern form of wind turbines. Figure 1.2 shows the conventional drive train design in the form of a geared transmission with a high-speed generator. Figure 1.3, by contrast, shows the gearless variant with the generator being driven directly from the turbine. These pictures represent the basis for the functional relationships and considerations of the system.

Figure 1.2 Nacelle of a wind turbine with a gearbox and high-speed 1.5 MW generator (TW 1.5 GE/Tacke). Reproduced by permission of Tacke Windenergie

Figure 1.3 Schematic structure of a gearless wind turbine (Enercon E66, 70 m rotor diameter, 1.8/2 MW nominal output). Reproduced by permission of Enercon

Following a brief glance back into history, developmental stages and different wind turbine designs and systems will be briefly highlighted and the processes of mechanical–electrical power conversion explained. Moreover, particular importance is assigned to the interconnection of wind turbines to form wind farms and their combined effect in grid connection.

1.2 A Brief History

For thousands of years, mankind has been fascinated by the challenge of mastering the wind. The dream of defying Aeolos1 and taming the might of the storm held generations of inventors under its spell. To attain limitless mobility by using the forces of Nature, thereby expanding the horizons of the then known world, was a challenge even in antiquity. Thus, sailing and shipbuilding were constantly pursued and developed despite doldrum, hurricane, tornado and shipwreck. Progress could only be achieved by employing innovative technologies. These, together with an unbridled lust for voyages of discovery, built up in the minds of sovereigns and scholars a mosaic of the world, the contours of which became ever more enclosed as time went by.

With wind-harnessing technology on land and on the sea, potentials could be realized and works undertaken that far outpaced any previously imagined bounds. For example, using only the power of animals and of the human arm, it would never have been possible for the Netherlands to achieve the drainage that it has through wind-powered pumping and land reclamation.

Archaeological discoveries relating to the use of wind energy predate the beginning of the modern era. Their origins lay in the Near and Middle East. Definite indications of windmills and their use, however, date only from the tenth century, in Persia [1.1]. The constructional techniques of the time made use of vertical axes to apply the drag principle of wind energy capture (Figure 1.4). Such mills were mostly found in the Arab countries. Presumably, news of these machines reached Europe as a result of the Crusades. Here, however, horizontal-axis mills with tilted wings or sails (Figure 1.5) made their appearance in the early Middle Ages.

Figure 1.4 Persian windmill (model)

Figure 1.5 Sail windmill

The use of wind energy in Western Europe on a large scale began predominantly in England and Holland in the Middle Ages. Technically mature post mills (Figure 1.6) and Dutch windmills (Figure 1.7) were used mostly for pumping water and for grinding. More than 200 000 (two hundred thousand) of these wooden machines were built throughout North-West Europe, representing by far the greatest proportion of energy capture by technical means in this region. At the beginning of the twentieth century, some 20 000 (twenty thousand) windmills were still in use in Germany.

Figure 1.6 Post mill

Figure 1.7 Dutch windmill

From the nineteenth century onwards, mostly in the USA, the so-called ‘western wheel’ type of turbine became widespread (Figure 1.8). These multibladed fans were built of sheet steel, with around 20 blades, and were used mostly for irrigation. By the end of the 1930s, some 8 million units had been built and installed, representing an enormous economic potential.

Figure 1.8 American wind turbine

1.3 Milestones of Development

The first attempt to use a wind turbine with aerodynamically formed rotor blades to generate electricity was made over half a century ago. Since then, besides the design and construction of large projects in the 1940s by the German engineers Kleinhenz [1.2] and Honnef [1.3], the pilot projects of the American Smith-Putnam (1250 kW nominal output, 53 m rotor diameter, 1941), the Gedser wind turbine in Denmark (200 kW nominal output, 24 m rotor diameter, 1957) and the technically trail-blazing Hütter W34 turbine (100 kW nominal output, 34 m rotor diameter, 1958) are worthy of mention (Figure 1.9).

Figure 1.9 Hütter W 34 turbine

The German constructor Allgaier started the first mass production of wind power plants in the early 1950s. They were designed to supply electricity to farmsteads lying far from the public grid. In coastal areas these turbines drove 10 kW generators; inland they were fitted with 6 kW units. Their aerodynamically formed blades of 10 m diameter could be pitched about the longitudinal axis so as to regulate the power taken from the wind. Even today, some of these turbines (see Figure 1.10) are in operation with full functionality, after more than 50 years of service.

Figure 1.10 Allgaier turbine

After the 1960s, cheaper fossil fuels made wind energy technology economically uninteresting, and it was only in the 1970s that it returned to the spotlight due to rising fuel prices. Some states then developed experimental plants in various output classes.

In particular in the USA, Sweden and the Federal Republic of Germany, turbines with outputs in the megawatt class have attracted most attention. Here, with the exception of the American MOD-2 (Figure 1.11) with five units and the Swedish–American WTS-4 (Figure 1.12) with five or two units, large converters such as the German GROWIAN (Figure 1.13), the Swedish WTS-75 AEOLUS model, the Danish Tvind turbine and the US MOD-5B variants in Hawaii were all one-offs. Despite many and varied teething troubles with the pilot installations, it was clear even then that technical solutions could be expected in the foreseeable future that would permit the reliable operation of large-scale wind turbines. Second-generation megawatt-class systems such as the WKA 60 (Figure 1.14) and the Aeolus II (Figure 1.15) have confirmed this expectation.

Figure 1.11 MOD 2 in the Goodnoe Hills (USA): 2.5 MW nominal output, 91 m rotor diameter, 61 m hub height

Figure 1.12 WTS-4 turbine in Medicine Bow, USA.: 4 MW nominal output, 78 m rotor diameter, 80 m tower height

Figure 1.13 GROWIAN by Brunsbüttel/Dithmarschen, 3 MW capacity, 100 m rotor diameter, 100 m hub height

Figure 1.14 WKA 60 in Kaiser-Wilhelm-Koog: 1.2 MW nominal output, 60 m rotor diameter, 50 m tower height

Figure 1.15 AEOLUS II near Wilhelmshaven: 3 MW nominal output, 80 m rotor diameter, 88 m tower height

Mainly in the US state of California, but also in Denmark, Holland and the Federal Republic of Germany, considerable efforts were being made, independently of the development of large turbines, to use wind power to supply energy to the grid on a large scale. In the 1980s, wind turbines with total capacity of around 1500 MW were installed in California alone. In the initial phases, turbines of the 50 kW categories were used (Figure 1.16). Scaling-up the systems that were successful through the 100, 150 and 250 kW classes (Figures 1.17 and 1.18) and the 500/600 kW order of magnitude (Figures 1.19 and 1.20) has led to wind farms with turbines in the megawatt range (Figure 1.21).

Figure 1.16 Wind farm in California with turbines in the 50/100 kW class

Figure 1.17 Wind farm in California with turbines in the 250 kW class

Figure 1.18 Wind farm in North Friesland with turbines of the 250 kW class

Figure 1.19 Wind farm in Wyoming with turbines in the 600 kW class

Figure 1.20 Wind farm on Fehmarn Island with turbines of the 500 kW class

Figure 1.21 Wind farm with 1.5 MW turbines

This development has made the mass production of wind turbines possible. A considerable improvement of performance can thus be achieved. Progressively increasing turbine size (see Figures 1.22 to 1.23) using designs of widely differing types and costs has led to the development of machines in the 500 kW and megawatt classes that are remarkable for their high availability and good return-on-investment potential.

Figure 1.22 Size progression of stall-regulated turbines of the same design (fixed-speed, fixed-pitch machines) from NEG Micon / Nordtank. Reproduced by kind permission of NEG Micon

Figure 1.23 Size progression of Bonus turbines: (a,b) fixed-speed, stall-controlled turbines; (c,d) active (combi-)stall turbines with a slight blade pitch adjustment

Figure 1.24 Size progression of Nordex turbines: (a,b,c) fixed-speed, fixed-pitch machines; (d) a large-scale, variable-speed, variable-pitch unit

Figure 1.25 Size progression of Vestas turbines: (a) small, fixed-speed, fixed-pitch machine; (b,c,d) larger variable-pitch units; (d,e) machines with speed elasticity; or double-fed asynchronous generators; (f) machines with permanent excited synchronous generators.

The individual manufacturers have chosen very different routes to market success in relation to this trend. NEG Micon has retained the classic Danish stall-regulated turbines with an asynchronous generator rigidly coupled to the grid in the power classes up to 1.5 MW (Figure 1.22). Bonus (Figure 1.23), Nordex (Figure 1.24) and Vestas (Figure 1.25) as well as GE/Tacke (Figure 1.26) have altered their turbine configuration in the different size classes, particularly with regard to the turbine regulation (stall or pitch) and generator systems (fixed-speed or variable-speed with a thyristor/ IGBT frequency converter). Currently 3 to 5 MW systems from all well-known manufacturers are being operated as prototypes or are available on the market.

Figure 1.26 Size progression of turbines from GE / Tacke: first (a,b) and second (c,d,e,f) generation machines, from fixed-speed, fixed-pitch turbines (a to d) to large-scale, pitch-controlled, variable-speed turbines (e,f)

One new development has been the trend towards gearless wind turbines. Several attempts have been made to introduce and establish in the market small, high-speed, horizontal-axis turbines with direct-drive generators. Up until now these attempts have met with limited success. Microturbines (Figure 1.27) with a permanent-magnet synchronous generator driven directly from the turbine are usually used as battery chargers. The success of such systems is rooted in their attractive design and low price as well as in the modern worldwide sales concept and the simple installation of the plants.

Figure 1.27 Small system-compatible turbine from aerosmart. Reproduced by permission of Aerodyn Energiesystems GmbH

To some degree, companies that have entered into the production of wind generators at a later stage have been able to draw upon existing developments and techniques, thus allowing their first efforts to overtakethe systems of established manufacturers. DeWind started its development (Figure 1.28) with a pitch-regulated 600 kW turbine and a variable-speed generator system (double-fed asynchronous machine), which could not have been produced at an economical cost a few years previously and which is currently favoured by most manufacturers. Then 1 and 2 MW systems of the same design followed.

Figure 1.28 DeWind 4 (600 kW, 46/48 m rotor diameter). Reproduced by permission of DeWind

The development of wind power systems has largely been carried out by medium-sized companies. Smaller manufacturers, however, face financial limits in the development of MW systems. The 1.5 MW turbine MD 70/MD 77 (Figure 1.29), again with the double-fed asynchronous generator design, which was developed by pro pro for the manufacturers BWU, Fuhrländer, Jacobs Energie (now REpower Systems) and Südwind / Nordex is opening up new developmental and market opportunities for smaller companies in the field of large-scale plants.

Figure 1.29 Joint development of the 1.5 MW MD 70/MD 77 turbine (70/77 m rotor diameter)

Vertical-axis rotors, so-called Darrieus turbines, are enchantingly simple in structure. In their basic form they have up until now mostly been built with gearing and generators at base level (Figure 1.30). Variants in the form of so-called H-Darrieus gearless turbines in the 300 kW class were first designed with rotating towers and large multiple generators at ground level (Figure 1.31(a)). Further development led to machines with fixed tripods and annular generators in the head (Figure 1.31(b)). These variants have not, however, been successful in establishing themselves widely in the wind power market.

Figure 1.30 Fixed-speed 300 kW Darrieus unit with gearing and a conventional generator

Figure 1.31 Variable-speed 300 kW gearless H-Darrieus unit

The Enercon E 40 horizontal-axis turbine was the first system in the 500 kW class with a direct-drive generator to establish itself in the market with great success in a very short time. Figure 1.32 shows the schematic construction of the nacelle. The generator, specially developed for this model, connects directly to the turbine and needs no independent bearings. In this way, wear on mechanical components running at high speed is reduced to a minimum. Operational run times of 180 000 hours have been quoted for many years.

Figure 1.32 Schematic layout of the Enercon E 40 gearless turbine. Reproduced by kind permission of Enercon

The gearless E 30, E 40, E 58, E 66 and E 112/E 126 models from Enercon were produced as a development of the stall-regulated geared models E15/E16 and E17/E18, by way of the E 32/E 33 variable-pitch turbines (Figure 1.33). In parallel, but with a slight delay, the conversion from thyristors to pulse inverters was accomplished. This configuration thus unites the advantages of variable speeds (and the associated reduction in drive-train loading) with those of a grid supply having substantially lower harmonic feedback.

Figure 1.33 Enercon turbines from variable-speed geared models with thyristor inverters (a,b,c) to gearless configurations with pulse inverters (d,e,f,g,h); (a,b) with fixed and (c,d,e,f,g,h) with variable pitch. Reproduced by kind permission of Enercon

In comparison to the gearless designs with electrically excited synchronous generators, as shown in Figure 1.33(d) to (h), permanent-magnet machines permit the arrangement of higher numbers of poles around the rotor or stator. By using high-quality permanently magnetic materials, relatively favourable construction sizes can thus be achieved(Figure 1.34) and very high efficiencies attained, particularly in the partial load range. Such a plant configuration of the 600 kW class (Figure 1.34(a)) has been able to achieve excellent returns over several years of fault-free operation. A 2 MW unit with such a generator design (Figure 1.34(b)) was designed with a medium-voltage generator of 4 kV system voltage.

Figure 1.34 Gearless wind turbines with permanent-magnet synchronous generator (46 m rotor diameter, 600 kW nominal output)

A further possibility, which has been considered for large, slow-running turbines in particular, is the combination of a low-speed generator and a turbine-side gearbox, as shown in Figure 1.35. The single-stage gearbox turns the generator shaft at around eight times the turbine speed of approximately 100 revolutions per minute. Thus, even for units in the 5 MW range, generators in compact and technically favourable construction sizes of approximately 3 m diameter can be used.

Figure 1.35 Nacelle of the large-scale Multibrid N 5000 (5 MW, 116 m rotor diameter) with single-stage gearing, integral hub and low-speed synchronous generator. Reproduced by permission of Multibrid Entwicklungsgesellschaft GmbH

Further large-scale turbines in the 5MW class with a rotor diameter of over 125m are REpower 5 M and 6 M and Siemens SWT 6-154 (Fig. 1.36). A double-fed asynchronous generator with medium-voltage isolation in the low-voltage range (950 V stator-side or 690 V rotor-side) is used in the Repower system. The Siemens turbine has a direct drive permanent excited synchronous generator.

Figure 1.36 Offshore turbines: (a) Repower offshore and onshore turbine 5M/6M, 5 MW/6 MW nominal output power, 126,5 m rotor diameter. Source: Repower; (b) Siemens offshore turbine SWT 6-154, 6 MW nominal output power, 154 m rotor diameter. Source: Siemens

In the following we consider various real operational situations, the essential differences between the systems involved and the resulting effects on supply to the grid, taking as a basis the functional structure of wind power machines and their influences.

1.4 Functional Structures of Wind Turbines

For the following consideration, which is mainly concerned with the mechanical interaction of electrical components and with interventions to modify output, we will draw upon the nacelle layout shown in Figure 1.2. With the correct design, the influences of the tower and of steering in response to changes in wind direction can be handled separately (Section 2.2.1) or treated as changes in wind velocity. The block diagram shown in Figure 1.37 (see page 28), which illustrates the links between the most important components and the associated energy conversion stages, may serve as the basis for later detailed observations. This diagram also gives an idea of how operation can be influenced by control and supervisory processes. Furthermore, the central position occupied by the generator is made particularly clear.

Figure 1.37 Functional chain and conversion stages of a wind energy converter