**Meet the author**

Dr Markel Zubiaga Lazkano was born in Elorrio, (Baque country -spain) on June 29, 1983. He received his Bachelor of Science in Electrical Engineering from the Mondragón Goi Eskola Politeknikoa in July 2005, the Master of Science in Electronics Engineering from the University of Mondragon in September 2007 and his PhD degree in 2011. During his PhD, he conducted a collaborative research with Ingeteam technology within the CENIT EOLIA project "Connection and transport of energy for off-shore wind farms" (2007-2010). In the framework of this project, he has published several papers in international conferences (EPE, IECON or SAAEI) and also has collaborated with Intech by writing a chapter in the book "Wind Farm / Book 2".

Throughout his career his research has been focused on electrical engineering aspects of wind power, mainly: control strategy of energy conversion systems, grid integration of wind power and energy transmission.

Nowadays, he is employed as a research scientist at INGETEAM in its RES (Renewable Energy Systems) division since 2011.

Chapter 1

**Preface VII**

**Abstract IX**

**Introduction 1**

**Wind Energy 9**

**References 209**

**Nomenclature 215**

**Offshore Wind Farms 29**

**Power AC Transmission Lines 47**

**Definition of a Base Scenario 95**

**Conclusions and Future Work 205**

**Clarke and Park Transforms 225**

**Resonant Passive Filters 229**

**Evaluation of Harmonic Risk in Offshore Wind Farms 129**

**Analysis of Disturbances in the Power Electric System 159**

**Power Factor Requirements at the Point of Common Coupling 219**

**REE Grid Code Requirements for Voltage Dips 221**

**Comparison and Validation of the Equivalent Feeder 239**

**Considered STATCOM Model to Validate the Proposed Solution 247**

Contents

Chapter 2

Chapter 3

Chapter 4

Chapter 5

Chapter 6

Chapter 7

Chapter 8

Appendix A

Appendix B

Appendix C

Appendix D

Appendix E

Appendix F

Appendix G

### Contents

**Preface XI**

**Abstract XIII**


Preface VII

Denmark was the first country to install a offshore wind farm and since then it is been increasing its offshore wind power capacity. After this first experience in Denmark,

Looking to this other countries, UK starts an ambitious plan of three rounds which currently (2011) is in its second round. In 2000, UK announced the first round of UK offshore wind farm development Round 1. This first round was intended to act as a 'demonstration' to provide developers technological experience. As regards to the current status of this round, it is almost completed: eleven sites are complete and generating power with a total capacity of 962 MW online, one site is fully consented and awaiting construction and other five sites have been withdrawn due to difficulties.

The Round 2 projects were announced in 2003: 15 projects with a combined capacity of up to 7.2 GW. Two of these fifteen sites allocated under Round 2 (Gunfleet 2 and Thanet) are now fully operational bringing the total offshore wind capacity in the UK

In 2007, the Department for Business, Enterprise & Regulatory Reform launched Round 3, this Round opens up the UK waters to up to 33 GW of offshore wind capacity.

Netherlands, installed some wind farms very close to shore in 90s and now it is building large offshore wind farms which are becoming operational since 2007, such as:

Germany also starts a strategic plan to develop offshore wind power, a plan that will lead to build offshore wind farms with a total capacity between 20 to 25 GW by 2030. As a result of this plan two offshore wind farms become operational in 2010. One of them, Alpha ventus (60 MW), is located 100 km into the sea and at 40m water depth.

Spain will begin installing offshore wind capacity according to its offshore development plan in 2012. Spain's Ministry of Industry carried out a study of the coastline to

After this study, experimental offshore wind farm projects have already been built on the sea-bed in sites around Cadiz, Huelva Castellon and in the Ebro Delta with the aim

The biggest distance to shore of an operational offshore wind farm.

identify the best sites for building offshore wind farms in 2008.

to bring the first test station project of 20 MW online by 2012.

Egmond aan Zee (2007) and Prinses Amalia (2008).

other counties start their own plans to develop offshore wind power.

to 1,330 MW.

Preface

### Preface

Denmark was the first country to install a offshore wind farm and since then it is been increasing its offshore wind power capacity. After this first experience in Denmark, other counties start their own plans to develop offshore wind power.

Looking to this other countries, UK starts an ambitious plan of three rounds which currently (2011) is in its second round. In 2000, UK announced the first round of UK offshore wind farm development Round 1. This first round was intended to act as a 'demonstration' to provide developers technological experience. As regards to the current status of this round, it is almost completed: eleven sites are complete and generating power with a total capacity of 962 MW online, one site is fully consented and awaiting construction and other five sites have been withdrawn due to difficulties.

The Round 2 projects were announced in 2003: 15 projects with a combined capacity of up to 7.2 GW. Two of these fifteen sites allocated under Round 2 (Gunfleet 2 and Thanet) are now fully operational bringing the total offshore wind capacity in the UK to 1,330 MW.

In 2007, the Department for Business, Enterprise & Regulatory Reform launched Round 3, this Round opens up the UK waters to up to 33 GW of offshore wind capacity.

Netherlands, installed some wind farms very close to shore in 90s and now it is building large offshore wind farms which are becoming operational since 2007, such as: Egmond aan Zee (2007) and Prinses Amalia (2008).

Germany also starts a strategic plan to develop offshore wind power, a plan that will lead to build offshore wind farms with a total capacity between 20 to 25 GW by 2030. As a result of this plan two offshore wind farms become operational in 2010. One of them, Alpha ventus (60 MW), is located 100 km into the sea and at 40m water depth. The biggest distance to shore of an operational offshore wind farm.

Spain will begin installing offshore wind capacity according to its offshore development plan in 2012. Spain's Ministry of Industry carried out a study of the coastline to identify the best sites for building offshore wind farms in 2008.

After this study, experimental offshore wind farm projects have already been built on the sea-bed in sites around Cadiz, Huelva Castellon and in the Ebro Delta with the aim to bring the first test station project of 20 MW online by 2012.

#### XII Preface

However, the Spanish Wind Energy Association estimates projects will take around six years from initial proposal to installation, meaning that Spain's first commercial offshore wind farms could be installed by 2015. The association says the industry aims to have 4,000MW of capacity installed in offshore wind farms by 2020.

Looking to these examples, it is possible to see the vital role of the offshore wind technology in the future development of the renewable energy in general and wind power in particular.

Thus, the present book has the aim to contribute to the better knowledge of the several key issues or problematic aspects of the AC offshore wind farms energy transmission and grid integration.

**M. Zubiaga, G. Abad and J. A. Barrena**

University of Mondragon, Spain

**S. Aurtenetxea and A. Cárcar** Ingeteam Corporation, Spain IX

The best places to build a wind farm in land are in use, due to the spectacular growth of the wind power over the last decade. In this scenario offshore wind energy is a promising application of wind power, particularly in countries with high population

On land wind farms have well-adjusted their features and the transmission system to each wind farm size and characteristic. But for offshore wind farms this is an open

This book analyses the offshore wind farm's electric connection infrastructure, thereby contributing to this open discussion. So, a methodology has been developed to select the proper layout for an offshore wind farm for each case. Subsequently a pre-design of the transmission system's support equipment is developed to fulfill the grid code

density, and difficulties in finding suitable sites on land.

discussion.

Abstract

requirements

### Abstract

VIII Preface

in particular.

and grid integration.

However, the Spanish Wind Energy Association estimates projects will take around six years from initial proposal to installation, meaning that Spain's first commercial offshore wind farms could be installed by 2015. The association says the industry aims

Looking to these examples, it is possible to see the vital role of the offshore wind technology in the future development of the renewable energy in general and wind power

Thus, the present book has the aim to contribute to the better knowledge of the several key issues or problematic aspects of the AC offshore wind farms energy transmission

> **M. Zubiaga, G. Abad and J. A. Barrena** University of Mondragon, Spain

> > **S. Aurtenetxea and A. Cárcar** Ingeteam Corporation, Spain

to have 4,000MW of capacity installed in offshore wind farms by 2020.

The best places to build a wind farm in land are in use, due to the spectacular growth of the wind power over the last decade. In this scenario offshore wind energy is a promising application of wind power, particularly in countries with high population density, and difficulties in finding suitable sites on land.

On land wind farms have well-adjusted their features and the transmission system to each wind farm size and characteristic. But for offshore wind farms this is an open discussion.

This book analyses the offshore wind farm's electric connection infrastructure, thereby contributing to this open discussion. So, a methodology has been developed to select the proper layout for an offshore wind farm for each case. Subsequently a pre-design of the transmission system's support equipment is developed to fulfill the grid code requirements

**Chapter 1** 

**Introduction** 

Wind energy is one of the most important energy resources on earth. It is generated by the unequal heat of the planet surface by the sun. In fact, 2 per cent of the energy coming from the sun is converted into wind energy. That is about 50 to 100 times more than the energy

Several scientific analyses have proven wind energy as a huge and well distributed resource throughout the five continents. In this way, the European Environment Agency in one of its technical reports evaluating the European wind potential [1], estimates that this potential will reach 70.000TWh by 2020 and 75.000TWh by 2030, out of which 12.200TWh will be economically competitive potential by 2020. This amount of energy is enough to supply three times the electricity consumption predicted for this year (2020). The same study also evaluates the scenario in 2030 when the economically competitive potential increases to

Today electricity from wind provides a substantial share of total electricity production in only a handful of Member States (see Figure 1.1), but its importance is increasing. One of the reasons for this increment is the reliability of this energy resource, which has been proven from the experience in Denmark. In this country 24% of the total energy production in 2010 was wind-based and the Danish government has planned to increase this percentage to 50%

Following Denmark, the countries with the highest penetration of wind power in electricity

200TWh, seven times the electricity consumption predicted for this year (2030).

consumption are: Portugal (14.8%), Spain (14.4%) and Ireland (10.1%)

converted into biomass by plants.

by 2030.

## **Chapter 1**

### **Introduction**

Wind energy is one of the most important energy resources on earth. It is generated by the unequal heat of the planet surface by the sun. In fact, 2 per cent of the energy coming from the sun is converted into wind energy. That is about 50 to 100 times more than the energy converted into biomass by plants.

Several scientific analyses have proven wind energy as a huge and well distributed resource throughout the five continents. In this way, the European Environment Agency in one of its technical reports evaluating the European wind potential [1], estimates that this potential will reach 70.000TWh by 2020 and 75.000TWh by 2030, out of which 12.200TWh will be economically competitive potential by 2020. This amount of energy is enough to supply three times the electricity consumption predicted for this year (2020). The same study also evaluates the scenario in 2030 when the economically competitive potential increases to 200TWh, seven times the electricity consumption predicted for this year (2030).

Today electricity from wind provides a substantial share of total electricity production in only a handful of Member States (see Figure 1.1), but its importance is increasing. One of the reasons for this increment is the reliability of this energy resource, which has been proven from the experience in Denmark. In this country 24% of the total energy production in 2010 was wind-based and the Danish government has planned to increase this percentage to 50% by 2030.

Following Denmark, the countries with the highest penetration of wind power in electricity consumption are: Portugal (14.8%), Spain (14.4%) and Ireland (10.1%)

Figure 1.2 Net changes in the EU installed capacity 2000-2010 [2].

*140000 MW*

plant investments) by 2030.

*-20000*

*20000*

*40000*

*60000*

*80000*

*100000*

*120000*

*0*

installations, see Figure 1.3.

global leaders.

The considered scenario used by the European Union for the Second Strategic Energy Review [5] suggests that wind will represent more than one third of all electricity production from renewable energy sources by 2020 and almost 40% by 2030, representing an accumulated investment of at least 200-300 billion Euros (or about a quarter of all power

Introduction 3

Due to the fast growth of the onshore wind energy exposed before, in many countries the best places to build a wind farm onshore are already in use, so in the future of this technology, offshore wind power is destined to have an important role. Because, offshore wind energy can be the way to meet the objectives of the new Energy Policy for Europe since it's an indigenous resource for electricity production, as well as clean and renewable. Offshore wind can and must make a substantial contribution to meeting all three key objectives of EU's energy policy: Reducing greenhouse gas emissions, ensuring safety of supply and improving EU competitiveness in a sector in which European businesses are

Nowadays, offshore wind energy is emerging and installation offshore wind farms at sea will become increasingly important. 430 MW of offshore wind power capacity were installed in 2009, the 4% of all the installed wind energy capacity. But, with 1107 MW of new

This trend is not only an issue of the last two years, offshore capacity has been gradually increasing since 2005 and in 2010 it represents around the 10% of all new wind power

installed capacity, 2010 was a record-breaking year for offshore wind power.

```
share %
```
Figure 1.1 Wind share of total electricity consumption in 2010 by country [2].

This spectacular growth of the wind power share in the electricity consumption is supported in the new installed wind power capacity. In this way, more than 40% of all new electricity generation capacity added to the European grid in 2007 was wind-based [4]. However, this year was not an exception, wind power is been the fastest growing generation technology except for natural gas in the decade (2000-2010), see Figure 1.2.

*share %*

Figure 1.1 Wind share of total electricity consumption in 2010 by country [2].

except for natural gas in the decade (2000-2010), see Figure 1.2.

*Denmark Portugal Spain Ireland Germany EU Netherlands Greece Cyprus Italy Estonia Swedem United Kingdom Austria Lithuania Belgium France Bulgaria Romania Poland Hungary Luxenbourg Latvia Czech Republic Finland*

This spectacular growth of the wind power share in the electricity consumption is supported in the new installed wind power capacity. In this way, more than 40% of all new electricity generation capacity added to the European grid in 2007 was wind-based [4]. However, this year was not an exception, wind power is been the fastest growing generation technology

*0 5 10 15 20 25 30*

Figure 1.2 Net changes in the EU installed capacity 2000-2010 [2].

The considered scenario used by the European Union for the Second Strategic Energy Review [5] suggests that wind will represent more than one third of all electricity production from renewable energy sources by 2020 and almost 40% by 2030, representing an accumulated investment of at least 200-300 billion Euros (or about a quarter of all power plant investments) by 2030.

Due to the fast growth of the onshore wind energy exposed before, in many countries the best places to build a wind farm onshore are already in use, so in the future of this technology, offshore wind power is destined to have an important role. Because, offshore wind energy can be the way to meet the objectives of the new Energy Policy for Europe since it's an indigenous resource for electricity production, as well as clean and renewable.

Offshore wind can and must make a substantial contribution to meeting all three key objectives of EU's energy policy: Reducing greenhouse gas emissions, ensuring safety of supply and improving EU competitiveness in a sector in which European businesses are global leaders.

Nowadays, offshore wind energy is emerging and installation offshore wind farms at sea will become increasingly important. 430 MW of offshore wind power capacity were installed in 2009, the 4% of all the installed wind energy capacity. But, with 1107 MW of new installed capacity, 2010 was a record-breaking year for offshore wind power.

This trend is not only an issue of the last two years, offshore capacity has been gradually increasing since 2005 and in 2010 it represents around the 10% of all new wind power installations, see Figure 1.3. the

Thus, the EU is pushing a stable and favorable framework to promote offshore wind farms and renewable energy in general. To this end, it is implementing plans such as the third internal energy market package of October 2007 [6] or the energy and climate package

Introduction 5

Supported in this favorable framework, Europe has become the world leader in offshore wind power, especially United Kingdom and Denmark. The first offshore wind farm was being installed in Denmark in 1991 and in 2010 the United Kingdom has by far the largest capacity of offshore wind farms with 1.3 GW, around 40% of the world total capacity.

As regards of the rest of the countries of the union, only nine countries have offshore wind

*Cumulative capacity (MW)* 

*Belgium 195 165 Denmark 853.7 207 Finland 26.3 2.3 Germany 92 80 Ireland 25.2 -* 

*Netherlands 246.8 -* 

*Norway 2.3 - Sweden 163.7 - United kingdom 1341.2 652.8* 

*TOTAL 2946.2 1107.1* 

Nevertheless, offshore wind is not only an issue of the mentioned three seas in the European Union. In the south for example, Italy has planned around 4199.6 MW distributed in 11 wind farm projects for the upcoming years. French republic has also planned 3443,5 MW

In the same way, the Iberian Peninsula is no exception to the growth and development of offshore energy. Offshore wind farms with 4466 MW total rated power are planned for the upcoming years, This means that the Iberian Peninsula has planned four times the offshore power in Europe in 2008. Even Croatia (392 MW) and Albania (539 MW) have planned

Furthermore, in the south/center of the European Union, there are two wind farms under construction one in Italy (90 MW, Tricase) and another one in France (105 MW, cote

Table 1.1 Offshore wind cumulative and installed capacity in 2010 by country

and three additional projects in the Mediterranean sea.

offshore wind farms [8].

d'Albatre) located in the English channel.

*Installed capacity 2010 (MW)* 

*652.8* 

farms and most of them located in the North Sea, Irish sea and Baltic sea, Table 1.1.

presented in January 2008 [7].

*Country* 

Furthermore, this energy resource will cover a huge share of the electricity demand, since the exploitable potential by 2020 is likely to be some 30-40 times the installed capacity in 2010 (2.94 GW) , and in the 2030 time horizon it could be up to 150 GW (see Figure 1.4), or some 575 TWh [5].

### *Cumulative capacity (MW)*

Figure 1.4 Estimation for offshore wind power capacity evolution 2000-2030 [3].

Wind energy is now firmly established as a mature technology for electricity generation and an indigenous resource for electricity production with a vast potential that remains largely untapped, especially offshore.

Figure 1.3 Offshore wind power share of total installed wind power capacity [2].

Figure 1.4 Estimation for offshore wind power capacity evolution 2000-2030 [3].

Wind energy is now firmly established as a mature technology for electricity generation and an indigenous resource for electricity production with a vast potential that remains largely

some 575 TWh [5].

untapped, especially offshore.

*0*

*20000*

*40000*

*60000*

*80000*

*100000*

*120000*

*140000*

*160000*

Furthermore, this energy resource will cover a huge share of the electricity demand, since the exploitable potential by 2020 is likely to be some 30-40 times the installed capacity in 2010 (2.94 GW) , and in the 2030 time horizon it could be up to 150 GW (see Figure 1.4), or

*Cumulative capacity (MW)*

Thus, the EU is pushing a stable and favorable framework to promote offshore wind farms and renewable energy in general. To this end, it is implementing plans such as the third internal energy market package of October 2007 [6] or the energy and climate package presented in January 2008 [7].

Supported in this favorable framework, Europe has become the world leader in offshore wind power, especially United Kingdom and Denmark. The first offshore wind farm was being installed in Denmark in 1991 and in 2010 the United Kingdom has by far the largest capacity of offshore wind farms with 1.3 GW, around 40% of the world total capacity.

As regards of the rest of the countries of the union, only nine countries have offshore wind farms and most of them located in the North Sea, Irish sea and Baltic sea, Table 1.1.


Table 1.1 Offshore wind cumulative and installed capacity in 2010 by country

Nevertheless, offshore wind is not only an issue of the mentioned three seas in the European Union. In the south for example, Italy has planned around 4199.6 MW distributed in 11 wind farm projects for the upcoming years. French republic has also planned 3443,5 MW and three additional projects in the Mediterranean sea.

In the same way, the Iberian Peninsula is no exception to the growth and development of offshore energy. Offshore wind farms with 4466 MW total rated power are planned for the upcoming years, This means that the Iberian Peninsula has planned four times the offshore power in Europe in 2008. Even Croatia (392 MW) and Albania (539 MW) have planned offshore wind farms [8].

Furthermore, in the south/center of the European Union, there are two wind farms under construction one in Italy (90 MW, Tricase) and another one in France (105 MW, cote d'Albatre) located in the English channel.

problematic aspects of the energy transmission and grid integration based on this

Introduction 7

In short, the development of an evaluation and simulation methodology to define the most suitable layout depending on the size and location of each wind farm, as for the onshore wind farms. This pre-design has to be suitable to connect to a distribution grid. Therefore, it

To accomplish this goal, this book contributes to the better knowledge of the nature, the causes and the problematic aspects of the electric connection infrastructure. The following

 The influence of the main components of the offshore wind farm in its frequency response is analyzed, to help avoiding harmonic problems in the offshore wind

 Transient over-voltage problems in the electric infrastructure of the offshore wind farms are characterized, more specifically, transient over-voltages caused by

The management of the reactive power through the submarine power cable is

 The passive filters are dimensioned for the considered specific case. Furthermore, the most suitable location for these filters is analyzed (onshore / offshore). The auxiliary equipment to protect the offshore wind farm upon switching actions

The auxiliary equipment to fulfill the grid codes during voltage dips at the PCC are

Then, based on those evaluations of the key issues of the electric connection infrastructure,

Submarine cable modeling options and the accuracy of those models.

several solutions to fulfill the grid codes are proposed and tested via simulation:

representative specific case.

key issues are evaluated.

has to fulfill the grid code requirements.

farm at the pre-design stage.

switching actions and voltage dips at the PCC.

evaluated and dimensioned for a specific case.

and fault clearances are discussed.

dimensioned.

As a result of these efforts, EU companies are leading the development of this technology in the world: Siemens and Vestas are the leading turbine suppliers for offshore wind power and DONG Energy, Vattenfall and E.ON are the leading offshore operators.

This evolution of the wind farms from onshore to offshore have led to some technological challenges, such as the energy transmission system or energy integration in the main grid.

Onshore wind farms have adjusted their characteristics well to the size and features of each wind farm as a result of the huge experience in this field. But for offshore, there are only a few built wind farm examples and the energy transmission is through submarine cables, so the definition of the most suitable layout is still an open discussion.

Offshore wind farms must be provided with reliable and efficient electrical connection and transmission system, in order to fulfill the grid code requirements. Nowadays, there are many and very different alternatives for the offshore wind farms transmission system configurations.

This is because the main difference in the transmission system between onshore wind farms and offshore wind farms is the cable used. Offshore wind farms need submarine cables. That present a high shunt capacitance in comparison to overhead lines [9]. The capacitive charging currents increase the overall current of the cable and thus reduce the power transfer capability of the cable (which is thermally limited).

Due to the spectacular growth of wind energy, many countries have modified their grid codes for wind farms or wind turbines requiring more capabilities. Some countries have specific grid codes referring to wind turbine/farm connections, such as Denmark, Germany or Ireland. The great majority of these countries have their grid code requirements oriented towards three key aspects: Power quality, reactive power control and Low Voltage Ride Through (LVRT).

The new grid code requirements are pushing new propositions in fields like power control, power filters or reactive power compensation, with new control strategies and components for the transmission system in order to integrate energy into the main grid.

These propositions have strong variations depending on the grid codes and the different kind of transmission systems such as: Medium Voltage Alter Current (MVAC) configurations or High Voltage Direct Current (HVDC) configurations.

For onshore wind farms, depending on the size and location features, their characteristics are well adjusted. However, for offshore wind farms the definition of the most suitable layout is still an open discussion.

The objective of this book is to contribute to this open discussion analyzing the key issues of the offshore wind farm's energy transmission and grid integration infrastructure. But, for this purpose, the objective is not the evaluation of all the electric configurations. The aim of the present book is to evaluate a representative case.

The definition of the electric connection infrastructure, starting from three generic characteristics of an offshore wind farm: the rated power of the wind farm, the distance to shore and the average wind speed of the location. In this way, it is possible to identify the

As a result of these efforts, EU companies are leading the development of this technology in the world: Siemens and Vestas are the leading turbine suppliers for offshore wind power

This evolution of the wind farms from onshore to offshore have led to some technological challenges, such as the energy transmission system or energy integration in the main grid.

Onshore wind farms have adjusted their characteristics well to the size and features of each wind farm as a result of the huge experience in this field. But for offshore, there are only a few built wind farm examples and the energy transmission is through submarine cables, so

Offshore wind farms must be provided with reliable and efficient electrical connection and transmission system, in order to fulfill the grid code requirements. Nowadays, there are many and very different alternatives for the offshore wind farms transmission system

This is because the main difference in the transmission system between onshore wind farms and offshore wind farms is the cable used. Offshore wind farms need submarine cables. That present a high shunt capacitance in comparison to overhead lines [9]. The capacitive charging currents increase the overall current of the cable and thus reduce the power

Due to the spectacular growth of wind energy, many countries have modified their grid codes for wind farms or wind turbines requiring more capabilities. Some countries have specific grid codes referring to wind turbine/farm connections, such as Denmark, Germany or Ireland. The great majority of these countries have their grid code requirements oriented towards three key aspects: Power quality, reactive power control and Low Voltage Ride

The new grid code requirements are pushing new propositions in fields like power control, power filters or reactive power compensation, with new control strategies and components

These propositions have strong variations depending on the grid codes and the different kind of transmission systems such as: Medium Voltage Alter Current (MVAC)

For onshore wind farms, depending on the size and location features, their characteristics are well adjusted. However, for offshore wind farms the definition of the most suitable

The objective of this book is to contribute to this open discussion analyzing the key issues of the offshore wind farm's energy transmission and grid integration infrastructure. But, for this purpose, the objective is not the evaluation of all the electric configurations. The aim of

The definition of the electric connection infrastructure, starting from three generic characteristics of an offshore wind farm: the rated power of the wind farm, the distance to shore and the average wind speed of the location. In this way, it is possible to identify the

for the transmission system in order to integrate energy into the main grid.

configurations or High Voltage Direct Current (HVDC) configurations.

and DONG Energy, Vattenfall and E.ON are the leading offshore operators.

the definition of the most suitable layout is still an open discussion.

transfer capability of the cable (which is thermally limited).

configurations.

Through (LVRT).

layout is still an open discussion.

the present book is to evaluate a representative case.

problematic aspects of the energy transmission and grid integration based on this representative specific case.

In short, the development of an evaluation and simulation methodology to define the most suitable layout depending on the size and location of each wind farm, as for the onshore wind farms. This pre-design has to be suitable to connect to a distribution grid. Therefore, it has to fulfill the grid code requirements.

To accomplish this goal, this book contributes to the better knowledge of the nature, the causes and the problematic aspects of the electric connection infrastructure. The following key issues are evaluated.


Then, based on those evaluations of the key issues of the electric connection infrastructure, several solutions to fulfill the grid codes are proposed and tested via simulation:


**Chapter 2** 

**Wind Energy** 

The aim of this chapter is to introduce the reader to the wind energy. In this way, as the primary source of wind energy, how the wind is created and its characteristics are

Due to its nature, the wind is an un-programmable energy source. However, it is possible to estimate the wind speed and direction for a specific location using wind patterns. Therefore, in the present chapter, how to describe the wind behavior for a specific location, the kinetic

To convert the wind energy into a useful energy has to be harvested. The uptake of wind energy in all the wind machines is achieved through the action of wind on the blades, is in these blades where the kinetic energy contained in the wind is converted into mechanic energy. Thus, the different ways to harvest this energy are evaluated, such as: different kind

Once, the wind and the fundamentals of the wind machines are familiar, the advantages /

The unequal heat of the Earth surface by the sun is the main reason in the generation of the

The sun's radiation heats different parts of the earth at different rates; this causes the unequal heat of the atmosphere. Hot air rises, reducing the atmospheric pressure at the earth's surface, and cooler air is drawn in to replace it, causing wind. But not all air mass displacement can be denominate as wind, only horizontal air movements. When air mass

The wind in a specific location is determinate by global and local factors. Global winds are caused by global factors and upon this large scale wind systems are always superimposed

The geostrophic wind is found at altitudes above 1000 m from ground level and it's not very

The regions around equator, at 0° latitude are heated more by the sun than the regions in the poles. So, the wind rises from the equator and moves north and south in the higher layers of the atmosphere. At the Poles, due to the cooling of the air, the air mass sinks down, and

energy contained in the wind and its probability to occur is described.

disadvantages between offshore and onshore energy are discussed.

wind. So, wind energy is a converted form of solar energy.

has vertical displacement is called as "convection air current"

evaluated.

**2.1 The wind** 

local winds.

Global or geostrophic winds

returns to the equator.

much influenced by the surface of the earth.

rises

of blades, generators, turbines…
