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Wind Power Integration Connection and System Operational Aspects 2nd Edition Brendan Fox

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Wind Power Integration Connection and System Operational Aspects 2nd Edition Brendan Fox
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Contents

Preface ix
Preface to Second Edition xi
1 Introduction 1
1.1 Overview 1
1.2 World energy and climate change 2
1.2.1 Renewable energy 2
1.3 Wind energy 5
1.3.1 Background 5
1.3.2 Changes in size and output 6
1.3.3 Energy productivity 7
1.4 Design options 7
1.4.1 Blades 8
1.4.2 Control and the power train 8
1.4.3 Summary of principal design options 9
1.5 Wind farms 10
1.5.1 Offshore wind 11
1.6 Economics 11
1.6.1 Wind turbine prices 11
1.6.2 Electricity-generating costs 11
1.6.3 Carbon dioxide savings 13
1.7 Integration and variability – key issues 14
1.7.1 Wind fluctuations 15
1.7.2 Capacity credits 16
1.7.3 Embedded generation benefits and impacts 17
1.7.4 Storage 17
1.8 Future developments 18
1.8.1 Technology 18
1.8.2 Future price trends 18
1.8.3 Market growth 19
1.8.4 Integration issues 19
2 Power system fundamentals 21
2.1 Introduction 21
2.2 Basic principles 21
2.2.1 Electromagnetism 21
2.2.2 Magnetic circuits 23
2.2.3 Electromagnetic induction 24
2.2.4 Electricity supply 25
2.2.5 The transformer 26
2.3 AC power supply 28
2.3.1 Power in steady-state AC systems 28
2.3.2 Phasors 30
2.3.3 Power in AC systems 33
2.4 Introduction to power systems 34
2.4.1 Three-phase systems 34
2.4.2 Comparison of single- and three-phase systems 35
2.4.3 Three-phase supply 36
2.4.4 Balanced star-connected load 37
2.4.5 Balanced delta-connected load 38
2.4.6 Some useful conventions 39
2.4.7 The complex VA product 39
2.4.8 Equivalent single-phase 41
2.4.9 The per unit system 41
2.5 Power transmission 44
2.5.1 Line parameters 44
2.5.2 Line models 47
2.5.3 Power transmission 48
2.5.4 Voltage regulation 49
3 Wind power technology 53
3.1 Introduction 53
3.2 Historical review of wind power technology 53
3.3 Design choices for large wind turbine generators 55
3.4 Energy extraction and power regulation 56
3.4.1 Energy extraction across the rotor disk 56
3.4.2 Power regulation 59
3.5 Fixed-speed wind turbines 64
3.5.1 Review of the induction (asynchronous) machine 64
3.5.2 Fixed-speed induction generator-based wind turbine 70
3.6 Variable–speed wind turbines 72
3.6.1 Doubly fed induction generator wind turbine 73
3.6.2 Wide-range variable-speed synchronous
generator wind turbine 78
Note: The Betz Limit 86
4 Network integration of wind power 89
4.1 Introduction 89
4.2 Wind farm starting 89
4.3 Network voltage management 91
4.3.1 The voltage level issue 91
vi Wind power integration
4.4 Thermal/active power management 106
4.4.1 Planning approaches/standards 106
4.4.2 Wind farm connection issues 107
4.4.3 Backbone system issues 109
4.4.4 Equipment issues 113
4.5 Network power quality management 115
4.5.1 Dips 116
4.5.2 Harmonics 116
4.5.3 Flicker 117
4.6 Transient system performance 117
4.6.1 Frequency performance and dynamic response 117
4.6.2 Transient response 122
4.7 Fault level issues 127
4.7.1 Equipment capability 127
4.8 Information 129
4.9 Protection 129
4.9.1 System protection 129
4.9.2 Transmission connected wind farms 130
4.9.3 Distribution connected wind farms 133
4.9.4 Wind farm protection 135
5 Operation of power systems 137
5.1 Introduction 137
5.2 Load-frequency control 137
5.2.1 Unit load-frequency control 142
5.2.2 Emergency frequency control 145
5.3 System operation with wind power 150
5.3.1 Overview of system operational challenges of wind power 150
5.3.2 Wind power in Ireland 153
5.3.3 System operation and wind variability 168
5.3.4 System operational modes 179
5.3.5 Capacity credit 186
5.3.6 Ancillary service provision 190
5.3.7 Wind turbine generator inertial response 198
5.3.8 Distributed generation protection 202
5.4 Energy balance 204
5.5 Energy storage/demand-side participation 207
5.5.1 Conventional energy storage 209
5.5.2 Demand-side participation 213
5.5.3 Hydrogen energy storage 215
6 Wind power forecasting 217
6.1 Introduction 217
6.2 Meteorological background 218
Contents vii
6.2.1 Meteorology, weather and climate 218
6.2.2 Atmospheric structure and scales 218
6.3 Numerical weather prediction 219
6.4 Persistence forecasting 222
6.4.1 Error measures 222
6.4.2 Reference models 225
6.5 Advanced wind power forecasting systems 229
6.5.1 Prediktor 234
6.5.2 Statistical models 238
6.5.3 Ensemble forecasting 242
6.6 Conclusions 244
7 Wind power and electricity markets 245
7.1 Introduction 245
7.2 The electrical energy market 247
7.3 Balancing, capacity and ancillary services 249
7.4 Support mechanisms 251
7.5 Costs 252
7.6 Benefits 255
7.7 Investment and risk 256
7.8 Market development 257
8 The future 259
8.1 Introduction 259
8.2 Grid codes and beyond 260
8.3 Co-existence with other forms of low-carbon generation 261
8.4 Demand-side participation 262
8.5 Supply diversity 263
Appendix 1 FACTS technology 265
Appendix 2 Technical criteria for wind farm power stations
connected to the transmission system 271
References 287
Index 297

Preface

The impetus for the book is the rapid growth of wind power and the implications of
this for future power system planning, operation and control. This would have been
a considerable challenge for the vertically integrated power companies pre-1990. It
has become an even greater challenge in today’s liberalised electricity market
conditions. The aim of the book is to examine the main problems of wind power
integration on a significant scale. The authors then draw on their knowledge and
expertise to help guide the reader through a number of solutions based on current
research and on operational experience of wind power integration to date.
The book’s backdrop was the commitment of the UK government (and European
governments generally) to a target of 10% of electrical energy from renewable energy
sources by 2010, and an ‘aspirational goal’ of 20% by 2020. There has also been a
significant reduction in the cost of wind power plant, and hence energy cost. Where
average wind speeds are 8 m/s or more, as is the case for much of Great Britain and
Ireland, the basic production cost of wind energy is nearly competitive with electricity
from combined cycle gas turbine (CCGT) plant, without the concern about
long-term availability and cost. The downside is that the supply over the system
operational time-scale is difficult to predict. In any case, wind power cannot provide
‘firm capacity’, and therefore suffers commercially in markets such as BETTA
(British electricity trading and transmission arrangements). On the other hand, green
incentives in the form of renewable obligation certificates (ROCs) provide wind
generators with a significant extra income. This is encouraging developers to come
forward in numbers which suggest that the 10% target may be attained. Indeed,
Germany, Spain and Ireland are already experiencing wind energy penetration levels
in the region of 5%, while Denmark reached a level of 20% some years ago.
The book attempts to provide a solid grounding in all significant aspects of
wind power integration for engineers in a variety of disciplines. Thus a mechanical
engineer will learn sufficient electrical power engineering to understand wind farm
voltage regulation and fault ride-through problems; while an electrical engineer
will benefit from the treatment of wind turbine aerodynamics. They will both
wish to understand electricity markets, and in particular how wind energy is likely
to fare.
The introductory chapter charts the remarkable growth of wind energy since
1990. The various technical options for wind power extraction are outlined. This
chapter then goes on to describe the potential problems of large-scale wind integration,
and outlines some possible solutions. The second chapter is essentially an
electrical power engineering primer, which will enable non-electrical engineers to
cope with the concepts presented in Chapters 3 and 4. Chapter 3 deals with wind
turbine generator technology, with particular attention being paid to current variable-
speed designs. Chapter 4 is concerned with wind farm connection, and the
implications for network design – an area lacking an established methodology to
deal with variable generation.
Chapter 5 addresses the key issue of power system operation in the presence of
largely unpredictable wind power with limited scope for control. Energy storage
provides a tempting solution; the treatment here concentrates on realistic, low-cost
options and imaginative use of existing pumped storage plant. The importance
of wind power forecasting is emphasised, and forms the main theme of Chapter 6.
The encouraging progress in the last decade is described. Ensemble forecasting
offers a useful operational tool, not least by providing the system operator with an
indication of forecast reliability. Finally, Chapter 7 summarises the main types of
electricity market, and discusses the prospects for wind power trading. The main
renewable energy support schemes are explained and discussed.
The book arose largely from a number of workshops organised as part of an
EPSRC (Engineering and Physical Sciences Research Council) network on
‘Operation of power systems with significant wind power import’. This was later
known simply as the BLOWING (Bringing Large-scale Operation of Wind Power
into Networks and Grids) network. The book reflects many lively discussions
involving the authors and members of the network, especially Graeme Bathurst,
Richard Brownsword, Edward Clarke, Ruairi Costello, Lewis Dale, Michael Farrell,
Colin Foote, Paul Gardner, Sean Giblin, Nick Goodall, Jim Halliday, Brian Hurley,
Michael Jackson, Daniel Kirschen, Lars Landberg, Derek Lumb, Andy McCrea,
Philip O’Donnell, Thales Papazoglou, Andrew Power and Jennie Weatherill. Janaka
Ekanayake, Gnanasamnbandapillai Ramtharan and Nolan Caliao helped with
Chapter 3. We should also mention Dr Shashi Persaud, whose PhD studies at
Queen’s University in the late 1990s were instrumental in drawing up the network
proposal, and who later helped with its ongoing administration.