Volume 2 wind energy 2 10 – electrical parts of wind turbines

Volume 2 wind energy 2 10 – electrical parts of wind turbines Volume 2 wind energy 2 10 – electrical parts of wind turbines Volume 2 wind energy 2 10 – electrical parts of wind turbines Volume 2 wind energy 2 10 – electrical parts of wind turbines Volume 2 wind energy 2 10 – electrical parts of wind turbines Volume 2 wind energy 2 10 – electrical parts of wind turbines Volume 2 wind energy 2 10 – electrical parts of wind turbines

2.10 Electrical Parts of Wind Turbines GS Stavrakakis, Technical University of Crete, Chania, Greece © 2012 Elsevier Ltd All rights reserved 2.10.1 Introduction 2.10.2 Power Control 2.10.2.1 Pitch Control 2.10.2.1.1 Theory and implementation 2.10.2.1.2 Active stall-controlled wind turbines 2.10.2.2 Yaw System 2.10.3 Electricity Production 2.10.3.1 The Generator 2.10.3.2 Wind Turbine Generators 2.10.3.2.1 Asynchronous (induction) generators 2.10.3.2.2 Synchronous generators 2.10.3.3 Power Electronics 2.10.3.3.1 Harmonics 2.10.3.3.2 Ride through 2.10.3.3.3 Fixed-speed systems 2.10.3.3.4 Variable-speed systems 2.10.4 Lightning Protection 2.10.5 Small Wind Turbines 2.10.6 Outlook 2.10.7 Wind Turbine Industry 2.10.7.1 Major Wind Turbine Manufacturers 2.10.7.1.1 Vestas 2.10.7.1.2 Enercon 2.10.7.1.3 Gamesa 2.10.7.1.4 GE Energy 2.10.7.1.5 Siemens 2.10.7.1.6 Suzlon 2.10.7.1.7 Nordex 2.10.7.1.8 Acciona 2.10.7.1.9 REpower 2.10.7.1.10 Goldwind 2.10.7.1.11 WinWind 2.10.7.1.12 Windflow 2.10.7.1.13 Clipper 2.10.7.1.14 Fuhrländer 2.10.7.1.15 Alstom 2.10.7.1.16 AVANTIS 2.10.7.1.17 Sinovel 2.10.7.2 Subproviders 2.10.7.2.1 ABB 2.10.7.2.2 Weier 2.10.7.2.3 VEM 2.10.7.2.4 Phoenix Contact 2.10.7.2.5 Ingeteam 2.10.7.2.6 Maxwell References Further Reading Relevant Websites 270 272 273 273 276 277 279 279 281 281 285 294 295 295 295 297 298 301 303 306 306 306 309 310 313 314 314 317 317 319 322 322 322 322 323 323 324 324 324 324 324 324 325 325 327 328 328 328 Comprehensive Renewable Energy, Volume 269 doi:10.1016/B978-0-08-087872-0.00211-0 270 Electrical Parts of Wind Turbines Glossary Blade The part of a wind generator rotor that catches the wind Horizontal Axis Wind Turbine (HAWT) A ‘normal’ wind turbine design, in which the shaft is parallel to the ground, and the blades are perpendicular to the ground Hub The center of a wind generator rotor, which holds the blades in place and attaches to the shaft Induction motor An AC motor in which the rotating armature has no electrical connections to it (i.e no slip rings), and consists of alternating plates of aluminum and steel Nacelle The protective covering over a generator or motor Permanent magnet A material that retains its magnetic properties after an external magnetic field is removed Pulse Width Modulation (PWM) A regulation method based on Duty Cycle At full power, a pulse-width­ modulated circuit provides electricity 100 percent of the time At half power, the PWM is on half the time and off half the time The speed of this alternation is generally Nomenclature A(γ(t)) turbine rotor swept area (time-varying due to yaw error) B magnetic flux CP power coefficient E electric field intensity E electromotive force fe electrical frequency N number of core windings ns rotor synchronous speed P, Pm mechanical power very fast Used in both solar wind regulators to efficiently provide regulation Rotor (1) The blade and hub assembly of a wind generator (2) The disc part of a vehicle disc brake (3) The armature of a permanent magnet alternator, which spins and contains permanent magnets Slip ring Devices used to transfer electricity to or from rotating parts Used in wound-field alternators, motors, and in some wind generator yaw assemblies Tip Speed Ratio (TSR) The ratio of how much faster than the wind speed, the blade tips are moving Transformer Multiple individual coils of wire wound on a laminate core Transfers power from one circuit to another using magnetic induction Usually used to step voltage up or down Works only with AC current Yaw Rotation parallel to the ground A wind generator yaws to face winds coming from different directions Wind generator A device that captures the force of the wind to provide rotational motion to produce power with an alternator or generator p number of generator pole pairs R turbine rotor radius S slip v(t) hub-height uniform wind speed across the rotor disk γ(t) rotor yaw angle η flux linkage θ(t) blade i pitch angle λ tip speed ratio ρ air density ω(t) rotor angular velocity (mechanical) 2.10.1 Introduction The quest of man for harnessing wind energy goes back into the centuries Windmills have been used for many purposes but it is only lately that the wind power has been effectively exploited to produce electricity (Figure 1) Specifically, during the past 20 years, the wind power industry has evolved into the most important renewable energy sector A wind turbine is a complex machine In order to design efficient and optimally operating wind turbines, knowledge from diverse scientific fields is required: aerodynamics, mechanical engineering, electrical and electronic engineering, materials and industrial engineering, civil engineering, meteorology, and automatic control among others A typical grid-connected wind turbine installation is shown in Figure Though wind turbines can be operated in isolation, this configuration is of diminishing concern Large offshore wind parks, comprising 10 MW wind turbines, seem to be the renewable future As seen in Figure 2, a typical wind turbine is erected on solid, concrete foundation and properly earthed Its output of 690 V is connected through a transformer station to the 20 kV grid line The wind turbine itself consists of the main tower, its three blades, and the nacelle Inside the nacelle and the tower base are housed the various electrical and electronic parts necessary for the efficient and safe conversion of wind power to electrical energy These include the power controls (pitch and yaw), the generator, and the power electronics This is a typical example that is not always followed The transformer station, for example, may be housed in the tower base The ‘electrical system’ of a wind turbine comprises all components for converting mechanical energy into electric power, as well as auxiliary electrical equipment and the control and supervisory system The electrical system thus constitutes the second essential subsystem, following the mechanical one, in a wind turbine (Figure 3) Electrical Parts of Wind Turbines 271 Figure Seventeenth-century flour mill rebuilt by Acciona at the Guerinda wind park, Navarre, Spain From Acciona leaflet, www.acciona-energia.com/ - Clima sensors - Aviation lights - Antennas Rotorblade Nacelle Cooling system Hub - Generator - Brake - Gearbox - Topbox - Hydraulic - Pitch control unit - Axis cabinet - Battery backup - Drives Yaw drive Tower Transformer station Foundation e.g., 20 kV/690 V - Low-voltage distribution panel - Main control cabinet - Inverter technology - Wind park communication Cable route Figure Grid-connected wind turbine The main components of the electrical subsystem are shown in Figure They will be subsequently analyzed in functional order, that is, the power control/positioning components (pitch and yaw motors) first, followed by the generator, the power electronics and grid connection, and finally, the lightning protection elements From the electrical engineering point of view, wind turbines are nothing more than electricity-generating power plants, like hydroelectric ones or diesel-powered Their electrical systems are similar and must meet the common standards for systems connected to utility grids Therefore, similar safety, supervision, and power quality standards must be met Grid operation requirements are laid out by international and local institutions On the global level, the International Electrotechnical Commission (IEC) has issued a set of general conditions that must be met by the wind farm operators 272 Electrical Parts of Wind Turbines Electrical power Mechanical power Wind power rotor Power conversion and control Gearbox (optional) Power convertor (optional) Generator Power transmission Power transformer Power conversion and control Supply grid Power conversion and Power transmission Figure Subsystems of a wind turbine From Blaabjerg F and and Chen Z (2006) Power Electronics for Modern Wind Turbines San Rafael, CA: Morgan & Claypool 12 10 13 11 14 15 Blades Rotor Pitch Brake Low-speed shaft Gear box Generator Controller Anemometer 10 Wind vane 11 Nacelle 12 High-speed shaft 13 Yaw drive 14 Yaw motor 15 Tower Figure Wind turbine electrical parts Design of wind turbines is aimed at optimum operation, that is, at maximizing conversion of wind energy to electric power, while maintaining fault-free or fault-tolerant working conditions Therefore, a wind turbine’s performance must be judged on three factors: Efficiency of wind power use (through the use of pitch and yaw control and generator selection) Reliability (e.g., lightning protection) Safety (grid connection regulations compliance) Wind turbines have been rapidly evolved in the past years Though a classification of various implementations may seem a little risky, nevertheless it may serve as a useful guide In Figure is shown such a possible picture 2.10.2 Power Control Wind turbines are designed to produce electrical energy as cheaply as possible Wind turbines are therefore generally manufactured so that they yield maximum output at wind speeds around 15 m s−1 (30 knots or 33 mph) It does not pay to design turbines that maximize their output at stronger winds, because such strong winds are rare In case of stronger winds, it is necessary to waste part of Electrical Parts of Wind Turbines 273 Mechanical energy source fixed/variable speed Input Transmission Gearbox Direct drive Heat loss dump load Machine type Multipolar synchronous and novel machines Conventional synchronous machines Induction machines Power conversion Wound rotor (field control) Rotor Permanent magnet Stator Cage rotor M/C Wound rotor or brushless DF Wound Grid connection Large PE converter Output Electrical energy source Fixed frequency or DC Small PE converter Figure Wind turbine classifications Modified from Wallace AK and Oliver JA (1998) Variable-speed generation controlled by passive elements International Conference on Electric Machines Istanbul, Turkey, 2–5 September [1] the excess energy of the wind in order to avoid damaging the wind turbine, while in case of weaker speeds some sort of speed regulation is desirable All wind turbines are therefore designed with some sort of power control There are different ways of doing this safely on modern wind turbines: • Pitch control • Stall control (passive or active) • Yaw control 2.10.2.1 Pitch Control Pitch control refers to altering the pitch angle of the wind turbine’s blades so that the rotor speed, and hence the rotor torque and generated electrical energy are kept at desired levels This is one way to engineer a ‘constant-speed’ wind turbine, and can be implemented either by mechanical (hydraulic) or electrical (motor) mean The latter is mostly employed at present, since, additionally, it is used to control each blade independently (Figure 6) Pitch control is also a safety mechanism since it can limit operating levels to the maximum of the given machine 2.10.2.1.1 Theory and implementation The ability of a wind turbine to extract power from wind is a function of three main factors: Wind power availability Power curve of the machine Ability of the machine to respond to wind perturbations The equation for mechanical power, Pm, produced by a wind turbine is given by, R ; Aịv3 Pm ẳ 0:5ρCp v ½1Š 274 Electrical Parts of Wind Turbines Figure Pitch control where ρ is air density (kg m− 3), θ is blade pitch angle (rad), γ is rotor yaw angle (rad), v is wind velocity (m s−1), ω is rotor angular velocity (rad s−1), R is rotor diameter (m), A(γ) is wind turbine rotor swept area (m2), Cp(ωR/v, θ) is power coefficient, and ωR/v = λ is tip speed ratio (TSR) Looking at eqn [1], it is seen that in an actual turbine, power can be regulated through pitch angle, rotor speed, and yaw angle, and all other parameters being exogenous It is interesting to note, however, that air density affecting power production is not the same in all wind sites since it decreases with increasing altitude Excluding yaw variation, Figure shows a typical power surface 0.5000 0.4000 0.3000 0.2000 0.4000−0.5000 0.1000 0.3000−0.4000 0.0000 Cp 0.2000−0.3000 −0.1000 0.0000−0.1000 0.1000−0.2000 −0.1000−0.0000 −0.2000 −0.3000 −0.4000 −0.2000−0.1000 −0.3000−0.2000 −0.4000−0.3000 −0.5000−0.4000 −5 −2 10 13 16 19 22 25 28 13.0 10.0 TSR 11.5 1.0 2.5 4.0 5.5 7.0 8.5 −0.5000 Pitch Figure Power vs pitch angle/TSR for NREL’s CART machine From Wright AD and Fingersh LJ (2008) Advanced control design for wind turbines part I: Control design, implementation, and initial tests Technical Report NREL/TP-500-42437, March 2008: National Renewable Energy Laboratory, Golden, Colorado, USA Electrical Parts of Wind Turbines 275 plotted for various pitch angles and TSRs [2] Such a surface is usually determined through simulation by using an aerodynamics code such as WT_Perf [3] Power limitation in high winds is typically achieved by using pitch angle control This action, also called ‘pitch-to-feather’, which corresponds to changing the pitch value such that the leading edge of the blade is moved into the wind (increase of θ) The range of blade pitch angles required for power control in this case is about 35° from the pitch reference Therefore, for safe regulation, the pitching system has to act rapidly, with fast pitch change rates of the order of 5° s−1 resulting in high gains within the power control loop 2.10.2.1.1(i) Implementation On a pitch-controlled wind turbine, the turbine’s electronic controller checks the power output of the turbine several times per second When the power output becomes too high, it sends an order to the blade pitch mechanism that immediately pitches (turns) the rotor blades slightly out of the wind Conversely, the blades are turned back into the wind whenever the wind drops again Presently, pitch motors are of very compact design They are mounted on the outside flange ring of each blade (Enercon E-40, Figure 8) or inside the rotor hub (Lagerway, Figure 9) Meteorological data from anemometers and sensors atop the nacelle measure wind speed and other environmental conditions The power supply, data, and control signals for the pitch system are transferred by a slip ring from the nonrotating part of the nacelle, or stationary-enclosed pivot behind the hub The slip ring is Electrical blade pitch motor Figure Enercon’s pitch control From Enercon, www.enercon.de Figure Blade pitch system inside the rotor hub (Lagerwey LW-72) From Lagerwey, www.lagerweywind.nl 276 Electrical Parts of Wind Turbines Figure 10 Weier 10 kW pitch motor From Weier, http://www.weier-energie.de/ Figure 11 Bosch Rexroth Mobilex GFB pitch motor From Bosch, http://www.boschrexroth.com connected to a central control unit, which includes clamps for distributing power, and control signals for the individual blade drive units Each blade drive unit consists of a switched-mode power supply, a field bus, the motor converter, and an emergency system Pitch motors are manufactured in various sizes to suit wind turbines specifications Output torques range from to 1100 kNm, with corresponding ratios from 60 to over 1600 (Figures 10 and 11) In case of power failure, emergency operation via batteries or capacitor bank is employed ‘Maxwell Techonologies’ has recently introduced a series of ultracapacitor modules that promise a simple, solid state, high-reliability alternative to batteries for energy storage in this type of burst power application Ultracapacitors offer excellent performance, with wide operating temperature range, long life, flexible management, and reduced system size; they are cost-effective as well as highly reliable, particularly when designed with a total systems approach (Figure 12) 2.10.2.1.2 Active stall-controlled wind turbines An increasing number of larger, fixed-speed wind turbines (1 MW and up) are being developed with an ‘active stall’ (also called ‘negative pitch’) power control mechanism Technically, the active stall machines resemble pitch-controlled machines, since they have pitchable blades In order to get a reasonably large torque (turning force) at low wind speeds, the machines will usually be programmed to pitch their blades much like a pitch-controlled machine at low wind speeds (often they use only a few fixed steps depending upon the wind speed) When the machine reaches its rated power, however, an important difference from the pitch-controlled machines is evident: if the generator is about to be overloaded, the machine will pitch its blades in the opposite direction by a few degrees (3–5°) from what a pitch-controlled machine does In other words, it will increase the angle of attack of the rotor blades in order to make the blades go into a ‘deep stall’, thus wasting the excess energy in the wind Only small changes of pitch angle are required to maintain the power output at its rated value, as the range of incidence angles required for power control is much smaller in this case than in the case of pitch control Compared to the pitch-to-feather technique, Electrical Parts of Wind Turbines 277 Figure 12 Ultracapacitor From Maxwell, http://www.maxwell.com/ultracapacitors/products/modules/bmod0094-75v.asp the travel of the pitch mechanism is very much reduced; significantly greater thrust loads are encountered, but the thrust is much more constant, inducing smaller mechanical loads Additionally, in active stall one can control the power output more accurately than with passive stall, so as to avoid overshooting the rated power of the machine at the beginning of a gust of wind Another advantage is that the machine can be run almost exactly at rated power at all high wind speeds A normal passive stall-controlled wind turbine will usually have a drop in the electrical power output for higher wind speeds, as the rotor blades go into deeper stall Typical active stall representatives are the Danish manufacturers Bonus (1 MW and over) and NEG Micon (1.5 and MW) 2.10.2.2 Yaw System The rotor axis of a wind turbine rotor is usually not aligned with the wind, since the wind is continuously changing its direction (Figure 13) The yawed rotor is less efficient than the nonyawed rotor and so it is vital to be able to dynamically align the rotor with the wind (Figure 14) Furthermore, unaligned rotors impose higher loads on the blades, causing additional fatigue damage The output power losses can be approximated by, P ẳ cosị ẵ2 where P is the lost power, γ the yaw error angle, and α a suitable constant (Figure 14) For these reasons, almost all horizontal-axis upwind turbines use forced yawing, that is, a mechanism which uses electric motors and gearboxes to keep the turbine yawed against the wind (Figure 15) Yaw control usually includes several drives and motors to distribute gear loading Active yaw is especially useful in providing maximum adaptability in complex terrains The image in Figure 16 shows the yaw mechanism of a typical 750 kW machine seen from below, looking into the nacelle z y x γ Figure 13 A wind turbine yawed to the wind direction 278 Electrical Parts of Wind Turbines 0.6 0.4 Cp max 0.2 0 20 40 60 Yaw angle (degrees) Figure 14 Maximum power coefficient variation with yaw angle γ Figure 15 Yaw control Figure 16 Yaw mechanism From Windpower, www.windpower.org 80 314 Electrical Parts of Wind Turbines Converter module 3 Converter module Converter module Converter module Generator Gearbox MV transformer Converter module Converter module Figure 77 G128’s modular generator structure From Gamesa brochure, www.gamesacorp.com/en • Wind FREE© Reactive Power Feature provides reactive power even in no wind conditions, which eliminates the need for grid reinforcements in such conditions (VAR-generating equipment) WindRIDE-THRUâ Feature provides low-voltage, zero-voltage, and high-voltage ride-through of grid disturbances, thus guaran­ teeing uninterrupted turbine operation in all conditions, meeting present and future transmission reliability standards WindINERTIAâ Control provides temporary boost in power for underfrequency grid events, similar to conventional synchronous generators with no additional hardware The 1.5 MW machine uses doubly-fed asynchronous generators made by the German firm VEM Sachsenwerk Gmbh (Figure 78) It employs pitch control 2.10.7.1.5 Siemens The German giant Siemens is manufacturing wind turbines as part of their renewable energy sector Their installed machines total more than 6000 worldwide Thanks to its wide know-how, Siemens machines are equipped with in-house technology Siemens produces machines in the 2.5–3.6 MW range, see Table 10 Their generator range comprises squirrel-cage induction generators (either fixed-speed or pole-changing) for their gearbox-based models and a PM generator for their direct-drive MW machine In this model, an outer rotor (the rotor spins on the outside of the stator) is designed (Figure 79) This feature allows the rotor to operate within narrower tolerances, decreasing the dimensions of the nacelle (Figure 80) Improved dual cooling system improves energy efficiency Siemens also manufactures a complete line of power converters by the brand name SIMOVERT MASTERDRIVES They cover an output range from 45 to 6800 kW and operate as voltage DC-link converters utilizing fully digital technology They are made for all of the voltages encountered (400, 500, or 690 V) and are quiet tolerant with respect to the specific line conditions The rectifier– regenerative feedback unit, active front end (AFE), ensures clean voltage AFE is a self-commutated, actively controlled line-side converter It filters out harmonics and ensures a sinusoidal current with reduced line stressing Furthermore, the AFE circuit principle permits line voltage fluctuations to be actively compensated Inductive reactive power can be generated and therefore the power factor can be influenced via the line-side converter Power control The blades are mounted on pitch bearings and can be feathered 90° for shutdown purposes Each blade has its own independent fail-safe pitching mechanism allowing fine-tuning to maximize power output On smaller fixed-speed machines, stall control is employed NetConverter® A proprietary grid connection system that is compliant with current grid codes such as ride-through capability for all normal faults Lightning protection Based on the international standard IEC 61400-24 Lightning Protection Level I 2.10.7.1.6 Suzlon Suzlon, an India-born company, was founded in 1995 It presently employs over 14 000 people in 21 countries and operates across the Americas, Asia, Australia, and Europe It has a fully integrated supply chain with manufacturing facilities in three continents, and sophisticated R&D capabilities in Denmark, Germany, India, and The Netherlands It is the market leader in Asia In May 2007, Suzlon acquired a stake in Repower Systems AG, a German-based firm Suzlon is also closely collaborating with Hannsen Transmissions, a Belgian gearbox maker Their wind turbines span a range of 600 kW–2.1 MW (see Table 11) A direct-drive transmission system is used that comprises a three-stage gearbox consisting of one planetary and two helical stages (Figure 81) Suzlon machines employ yaw motors and drives to turn the wind turbine rotor against the wind as well as pitch drives to start and stop the wind turbine generator They use synchronous generators (Figure 82) The small (650 kW) machines use a 4-pole, Table Wind turbine data: GE Energy Turbine type/size Cut-in speed (m s−1) Cut-out speed (m s−1) 1.5 SLE/1.5 MW 3.5 20/25 2.5 XL/2.5 MW 3.5 25 DFIG, doubly fed induction generator Drive train Power control Generator type Grid connection Three-stage planetary/helical Variable speed Independent pitch control 690 V, DFIG Variable speed Independent pitch/active yaw control Permanent magnet Full power conversion Low-voltage ride-through: active crowbar and oversized converter Active and reactive power regulation Low-voltage ride-through: active crowbar and oversized converter Active and reactive power regulation Thunder protection 316 Electrical Parts of Wind Turbines Figure 78 VEM’s double-fed 1.5 MW induction generator From VEM brochure, www.vem-group.com Table 10 Wind turbine data: Siemens Turbine type/size Cut-in speed (m s−1) Cut-out speed (m s−1) SWT­ 82/2.3 3–5 SWT­ 107/3.6 SWT-101/3 Drive train Power control 25 Three-stage planetary/ helical 3.5 25 Three-stage planetary/ helical 3.5 25 Direct drive Variable speed independent pitch control, active yaw Variable speed Independent pitch control, active yaw Variable speed Independent pitch control, active yaw Generator type Grid connection Thunder protection 690 V, induction generator Low-voltage ridethrough 690 V, induction generator Low-voltage ridethrough IEC 61400-24 lightning protection level I IEC 61400-24 lightning protection level I IEC 61400-24 lightning protection level I Permanent magnet Figure 79 Siemens direct-drive permanent magnet generator From Siemens brochure, www.energy.siemens.com/hq/en/power-generation/renewables/ wind-power/ 1500 rpm, squirrel-cage type with 2.5% slip at full load Copper bars are used in the rotor slots and they are circuited at the ends by short circuit rings The larger ones (1.5, 2.1 MW) use a 4-pole, 50 Hz, 1500 rpm slip-ring type with wound rotors The rotor winding is similar to stator windings, being balanced to reduce the vibration levels of the generator Electrical Parts of Wind Turbines 317 Figure 80 Siemens SWT 101 nacelle arrangement From Siemens brochure, www.energy.siemens.com/hq/en/power-generation/renewables/wind­ power/ An interesting feature is implemented in their 250 kW and 1.25 MW machines namely a ‘dual-speed’ squirrel-cage generator The generator’s stator uses special silicon steel laminations to minimize losses, while adequate cooling ducts are provided in the stator stack to maintain temperature within limits Windings are fitted with ‘resistance temperature detectors’ of PT-100 type The effects of wind fluctuations/gusts on power outputs are damped by high slip arrangements in the generators The generators voltage is 690 V In-rush currents during start-up are limited by means of soft starters The wind turbines are provided with various protection schemes to isolate the wind turbines in the event of any faults, including lightning arrestors Furthermore, Suzlon uses a sophisticated control system, incorporating among others: • The Suzlon FlexiSlip that controls the power output of the asynchronous generator over a slip range of up to 16% This reduces mechanical loads in the turbine and consequently lowers component and maintenance costs, and, • IXYS, a system designed for short-time pulse operation to synchronize the generator speed of the wind turbine to the synchronous speed of the grid 2.10.7.1.7 Nordex Nordex is a Danish company launched in 1985 It has set new standards with several innovative products: the first megawatt machine in 1995 and the development and the first wind turbine with a capacity of 2.5 MW in 2000 They have presently installed over 4100 turbines with total capacity of 5.72 GW They produce two lines of wind turbines: 1.5 and 2.5 MW models (see Table 12 and Figure 83) All their machines employ a two-stage planetary plus spur gearbox coupled to doubly-fed asynchronous generators Torque power is split onto the planetary gears to ensure good transmission The power is brought together again in the spur gear Power control is enforced by individual active blade pitch control and active yaw control Pitch control incorporates a number of innovative features such as: • optimized emergency power supply with battery charging management, • automatic lubrication system, and, • ventilated water protection The yaw drive uses four induction motors for smooth operation Nordex uses an intelligent control scheme to ensure low-strain yawing in extreme conditions The use of the doubly-fed generator means only 25–30% of the generated power has to be fed into the grid In their new, third, generation slip-rings are incorporated in the rotor shaft The converter uses isolated gate bipolar transistor (IGBT) technology and is controlled by a microprocessor-based power electronics module using pulse-width modulation 2.10.7.1.8 Acciona A Spanish company founded in 1989 It is a multifaceted group, with 38% of its assets coming from the energy sector The installed wind capacity was 6300 MW in December 2009 Table 11 Wind turbine data: Suzlon Turbine type/size Cut-in speed (m s−1) Cut-out speed (m s−1) S52/600 kW S64/1.25 MW Drive train Power control Generator type Grid connection 25 One planetary/two helical Induction Suzlon control system: reactive power control, low-voltage ride-through 3.5 25 Double-speed squirrel-cage induction Suzlon control system: reactive power control, low-voltage ride-through S82/1.5 MW 20 25 Slip-rings induction, rotor resistance control via FlexiSlip Slip-rings induction, rotor resistance control via FlexiSlip Suzlon control system: reactive power control, low-voltage ride-through S88/2.1 MW Three-stage: one planetary/two helical Three-stage: one planetary/two helical Three-stage: one planetary/two helical Independent active pitch Yaw control Independent active pitch Yaw control Suzlon FlexiSlip active pitch Yaw control Suzlon FlexiSlip active pitch Yaw control Suzlon control system: reactive power control, low-voltage ride-through Thunder protection Electrical Parts of Wind Turbines 319 Figure 81 Suzlon’s generator From Suzlon brochure, www.suzlon.com Hansen W4 Figure 82 Hansen’s W4 gearbox From Suzlon brochure, www.suzlon.com Table 12 Wind turbine data: Nordex Turbine type/size Cut-in speed (m s−1) Cut-out speed (m s−1) N90/2.5 MW 25 S70/1.5 MW 25 Drive train Three-stage: two-stage planetary and one-stage spur Three-stage: two-stage planetary and one-stage spur Power control Generator type Grid connection Thunder protection Independent active pitch Yaw control Double-fed asynchronous IGBT converter, PWM Aluminum rotor blade tip In accordance with DIN EN 62305 Independent active pitch Yaw control (4 motors) Double-fed asynchronous IGBT converter, PWM In accordance with DIN EN 62305 IGBT, isolated gate bipolar transistor; PWM, pulse-width modulator Acciona manufactures wind turbines and builds wind farms all over the world (Figure 84) Their wind turbine range comprises a 1.5 MW and a MW series (Figure 85 and see Table 13) All their models are built on the same design Power control is effected by individual blade pitch control The active yaw system uses a gear ring integrated into the tower and four to six geared motors integrated into the nacelle Active hydraulic braking is employed The generators are three-phase asynchronous double-fed induction type with wound rotor and excitation by collector rings Generated power is at medium voltage (12 kV) to reduce losses and avoid the need for a transformer Acciona uses Ingeteam’s INGECON-W control system, capable of continuously optimizing its power production in a wide range of wind speeds IGBT pulse-width modulation is used in the power converter 2.10.7.1.9 REpower REpower, founded in 2001, is a powerful German wind turbine manufacturer Their product portfolio comprises several types of turbines with rated outputs ranging between 2.05 and 6.15 MW, with more than 2000 turbines installed worldwide (see Table 14) 320 Electrical Parts of Wind Turbines Figure 83 Nordex S-70’s nacelle (courtesy Nordex) From Nordex brochure, www.nordex-online.com/en Figure 84 Acciona’s Cathedral Rocks wind park in South Australia From Acciona brochure, www.acciona-energia.com/ 10 13 11 14 12 15 Main components Rotor blades Rotor shaft Generator coupling 13 Hydraulic system Hub Gearbox Control system monitoring 11 Generator 14 Yaw bearing Rotor bearing Disk brake Cooling radiator 15 Tower 10 12 Wind measuring system Yaw drive Figure 85 Acciona’s AW 119 MW turbine nacelle From Acciona brochure, www.acciona-energia.com/ Electrical Parts of Wind Turbines Table 13 Wind turbine data: Acciona Cut-in speed (m s−1) Cut-out speed (m s−1) AW 82/1.5 MW AW 119/3 MW Turbine type/size 321 Drive train Power control Generator type Grid connection 20 Three-stage: two planetary, one helical Three-stage: two planetary, one helical 6-Pole doubly fed asynchronous, slip-ring excitation, 12 kV 6-Pole doubly fed asynchronous, slip-ring excitation, 12 kV IGBT converter, PWM INGECON-W 20 Independent active pitch Yaw control (four motors) Independent active pitch Yaw control (six motors) Thunder protection IGBT converter, PWM INGECON-W IGBT, isolated gate bipolar transistor; PWM, pulse-width modulator Table 14 Wind turbine data: REpower Cut-in speed (m s−1) Cut-out speed (m s−1) MM82/ MW 3.5 25 3.4M104/ 3.4 MW 3.5 25 5M/5 MW 3.5 30 Turbine type/size Drive train Power control Generator type Three-stage: two planetary, one spur Three-stage: two planetary, one spur Three-stage: two planetary, one spur Individual blade pitch Yaw control Individual blade pitch Yaw control Individual blade pitch Yaw control 690, 4-pole, doubly fed asynchronous 690 V, 4-pole, doubly fed asynchronous 660 V, 6-pole, doubly fed asynchronous Grid connection Thunder protection IGBT with PWM Fully integrated IGBT with PWM Fully integrated IGBT with PWM Fully integrated IGBT, isolated gate bipolar transistor; PWM, pulse-width modulator REpower’s MW test machine has been installed onshore at the German–Danish frontier in spring 2009 REpower is participating in the ‘Beatrice Demonstrator Project’ to test the performance of its MW turbine on the open sea Two such turbines have been installed near the Beatrice oil field in Moray Firth, 25 km off the Scottish East coast and at a water depth of over 40 m The demonstrator project is part of the European Union-supported ‘DOWNWinD’ project, which is Europe’s largest research and development program in the field of renewable energies All of REpower’s machines are designed on the same principles: The pitch system uses a fail-safe design with separate control and regulation systems for each rotor blade, a virtually maintenance-free electronic system and a high-quality, generously dimensioned blade bearing with permanent track lubrication It is protected by means of an integrated deflector in the spinner while maximum reliability is ensured via redundant blade angle detection, which uses two separate measuring systems The yaw system employs an externally geared, low friction, four-point bearing, driven by oversized, high-quality, gear motors Hydraulic holding brakes with fail-safe function are implemented The drive system consists of a three-stage combined planetary/spur wheel gearbox using elastomer bearings in the torque multiplier for structure-borne sound insulation It achieves low temperature levels due to effective oil cooling system, which uses a three-stage oil filter system The generators are doubly fed asynchronous, optimized for variable speed range and with high overall efficiency They are fully enclosed with air/air heat exchanger for optimized temperature level The converter uses IGBT pulse-width modulation and is water-cooled Lightning protection is according to IEC regulations with internal and external lightning protection External protection includes blade receptors and a lightning rod at the weather mast Reliable protection of bearings is achieved by defined lightning conduits coupling for the galvanic insulation of the generator system from the gear system Overvoltage arrester is used in the electric system 322 Electrical Parts of Wind Turbines 2.10.7.1.10 Goldwind China’s Goldwind Science & Technology Co Ltd was established in 1998 Technology was mainly provided under licenses from REpower and Vensys, which they acquired in 2008 Goldwind has been manufacturing turbines in the medium-size range, up to 1.5 MW However, recently the company has been installing, totally self-made, experimental MW machines, while researching on MW models (see Table 15) Goldwind turbines feature independent pitch control Each of the three pitch drives consists of motor gear units with synchronous belt systems Belt drives are insensitive to torque shocks and resistant to moist or dirty environments and completely wear-free The electric drives are robust AC motors controlled by inverters Operation in emergency situations is assured by ultracapacitors, which have significant advantages over lead–acid batteries, such as no maintenance and 20 years lifetime Their direct-drive permanent magnet generator is characterized by an ‘external rotor design’ featuring maximum air gap diameter and low magnet temperatures The generator cooling system is completely passive, while the maximum cooling effect is achieved at high wind speeds when maximum power is produced and consequently maximum heat losses occur Special attendance has been given to safety features of the frequency converter: safe operation is guaranteed by a heavy-duty switch located directly at the generator terminals This switch is able to disconnect the permanent magnet generator under all circumstances Furthermore, no power electronics are located in the nacelle while the passive diode rectifier is in the tower base 2.10.7.1.11 WinWind WinWind is a new company based in Finland, founded in 2002 It currently employs 300 personnel and claims an installed capacity of 150 MW It manufactures two turbine sizes: the MW WWD-1 and the MW WWD-3 Both designs are similar and employ the new Multibrid® concept As described earlier, this is an integrated design using a planetary gear and PM synchronous generator, housed in a common casing As a result, increased reliability is claimed The planetary gear is manufactured by Moventas Wind Oy, while the generator is made by Siemens Both machines use full-power frequency converters employing IGBT bridges on both the generator and the grid side, as well as blade pitch control 2.10.7.1.12 Windflow Windflow is a New Zealand company founded in 2001 Its current workforce numbers 50 people Windflow manufactures a single 500 kW wind turbine, which is however a two-blade design, unlike most manufacturer’s three-blade types (Figure 86) The machine is light, small, inexpensive, and especially suited to strong wind areas (IEC Class 1A) To meet the tough requirements resulting from strong gusts, Windflow uses a patented torque limiting gearbox with a hydraulic system to limit torque fluctuations and allowing the generator shaft to rotate at a constant speed Furthermore, the two-bladed design permits teetering (a see-sawing motion), an important element because it significantly reduces the bending forces on the turbine shaft, gearbox, tower, and foundations The Windflow 500 turbine’s rotor is designed to teeter up to 6° on either side of the normal plane of rotation in response to varying wind forces Pitch-teeter coupling is an important feature of the Windflow 500 design, which, unlike many other two-bladed designs, stabilizes teetering during operation A self-exciting synchronous generator, configured to run in either VAr import or export modes that are fully controllable and not require heavy-duty power electronics 2.10.7.1.13 Clipper Clipper Windpower is a rapidly growing, company engaged in wind energy technology, turbine manufacturing, and wind project development Clipper employs over 750 people and manages over 6500 MW of wind resource development assets The company’s wind turbine model is the 2.5 MW Liberty® (Figure 87) This is a horizontal-axis, three-blade, upwind, pitch-regulated, variable-speed machine It features Clipper’s own Quantum Drive® distributed drive train, a two-stage, helical load-splitting gearbox, four separate MegaFlux® PM synchronous generators, and optimized controls for variable-speed operation with full power conversion Low-voltage ride through is also possible, thus enhancing weak grid situations Table 15 Wind turbine data: Goldwind Turbine type/size Cut-in speed (m s−1) Cut-out speed (m s−1) S48/ 750 kW GW70/ 1.5 MW 25 25 Drive train Power control Generator type Two-stage: planetary, spur Direct drive Stall control, active yaw Ultracapacitor pitch control 690 V, asynchronous Synchronous permanent magnet Grid connection Thunder protection Electrical Parts of Wind Turbines 323 Figure 86 WindFlow’s two-bladed machine From Windflow brochure, www.windflow.co.nz 11 5 10 8 Hub Nacelle Gearbox Main shaft Generators Parking brakes Yaw system Machine base Turbine control unit (TCU) 10 Hydraulic power unit (HPU) 11 On-board jib hoist Figure 87 Liberty nacelle From Clipper brochure, www.clipperwind.com 2.10.7.1.14 Fuhrländer Fuhrländer AG is an independent German company with roots in metal processing and service industries for 40 years They are currently manufacturing turbines in the range 30 kW to 2.5 MW Their top range FL2500 is based on an asynchronous generator with slip-ring motor using an indirect converter Blade pitch is controlled independently Yaw control is effected by four-gear motors 2.10.7.1.15 Alstom Alstom is the world leader in transport and energy infrastructure They have recently acquired Ecotècnia, a firm established in 1981 operating wind farms with more than 2100 MW and 1800 wind turbines primarily in Spain, France, Italy, Portugal, the United Kingdom, and Japan 324 Electrical Parts of Wind Turbines Figure 88 Alstom’s pure torque concept From Alstom brochure, www.power.alstom.com Alstom wind turbines are based on a patented mechanical design concept: the ALSTOM PURE TORQUE™ In this design, the hub is supported directly by a cast frame on two bearings, whereas the gearbox is fully separated from the supporting structure (Figure 88) As a consequence, the deflection loads (red arrows) are transmitted directly to the tower, whereas only torque (green arrows) is transmitted through the shaft to the gearbox Alstom manufactures two lines of wind turbines: the 1.67 MW Eco 80 series and the 3.0 MW Eco 100 series aimed at Class II (8.5 m s−1 average wind speed) and IIa (9 m s−1 average wind speed) sites Both series feature modular nacelles consisting of three modules containing the mechanical components and the control systems, allowing independent verification of their integrity and operational status, resulting in faster and simpler onsite testing Also, variable speed with autonomous pitch control in each blade and active/reactive power control by wound rotor and power electronics is employed 2.10.7.1.16 AVANTIS AVANTIS is a new group of enterprises focusing on renewable energies, with a strong emphasis on wind power The group comprises companies from the United States, Brazil, Europe, and Asia with headquarters in Beihai, China AVANTIS manufactures two turbine models: the 2.5 MW AV928 (Figure 89) and the 2.3 MV AV1010 aimed at Class IIa sites Both feature direct-drive PM generators Independent pitch control and with full IGBT rectifier/inverter are standard 2.10.7.1.17 Sinovel Sinovel Wind Group Co is a high-tech Chinese enterprise engaged in independently developing, designing, manufacturing, and marketing large-scale onshore/offshore wind turbines adapted to different wind zones and environment In 2009, the installed capacity of Sinovel was 3510 MW, making her a serious contender in the wind turbine market Sinovel manufactures two basic types of wind turbines: the MW SL3000 and the 1.5 MW SL1500 Both series employ advanced power-generating technologies such as variable-speed control, pitch-regulated system, and DFIG, while maintaining low-voltage ride-through capability and adaptability to all grid codes and requirements Various configurations for different wind regimes are also available 2.10.7.2 2.10.7.2.1 Subproviders ABB ABB Lightning Protection Group, a branch of ABB, provides a range of lightning arresters against overvoltages, dedicated to wind turbine installations These include both Class I and Class II arresters (see Section 2.10.4 for definitions) for every part of the wind turbine installation (Figure 90) 2.10.7.2.2 Weier Weier was founded 60 years ago and has been developing, designing, and producing electric machines such as motors, generators, and rotating inverters Their ‘Clean Energy’ product range includes generators for wind power plants, natural gas block-type thermal power plants, hydroelectric power plants, and clean energy-saving motors Conventional designed generators range from 0.125 kW up to 1.5 MW for large and small wind power plants (Figure 91) A comprehensive range of synchronous PM generators for small wind power plants is also manufactured Electrical power output levels of 0.5–10 kW are available They feature internal rotors for input speeds ranging from to 1250 rpm and laminated stators Furthermore, Weier is manufacturing a full range of pitch motors for use in variable-speed wind turbines At present, Weier is developing large generators of 1–3 MW, and up to MW in the near future In addition, output and security management systems, as well as grid connections to the integrated network, are researched 2.10.7.2.3 VEM VEM is the second-largest manufacturer of electrical machinery in Germany producing rotating electrical machines for the following sectors: mechanical engineering, plant construction, the chemical, oil, and gas industries, energy and environmental engineering, wind power plant construction, transport engineering, steelworks and rolling mills, and ship-building Electrical Parts of Wind Turbines 325 Figure 89 Avanti’s AV928 wind turbine From Avantis brochure, www.avantis-energy.com Figure 90 ABB’s overvoltage protection arresters From ABB brochure, www.abb.com/motors&drives The VEM series of wind power generators spans the whole spectrum: asynchronous squirrel-cage, double-fed asynchronous, and synchronous electrically or permanently excited Furthermore low-speed synchronous machines for gearless or single-stage gear solutions are available on request Output range covers 1–6 MW and voltage 690 V–12 kV (Figure 92) The cooling system is air­ to-water or air-to-air The rotor design of double-fed generators generally comprises medium-voltage coils, while the main slip and earthing slip rings are generally made of stainless steel, enabling VEM wind power generators to operate without problems in coastal areas or offshore Redundant earthing systems, combined with specially developed bearing insulation, also ensure safe control of the converter operation 2.10.7.2.4 Phoenix Contact Phoenix Contact is a leading German developer and manufacturer of industrial electrical and electronic technology It offers a diverse product range including components and system solutions for industrial and device connection, automation, electronic interface, and surge protection (Figure 93) 2.10.7.2.5 Ingeteam Ingeteam is a Spanish company, founded in 1974 It specializes in technology directed at the industry and energy sectors Ingeteam’s core business is based on power and control electronics, generator, motor and electric machine technology, and applications engineering 326 Electrical Parts of Wind Turbines Figure 91 Weier’s MW generator From Weier brochure, www.weier-energie.de Figure 92 VEM’s 5.4 MW wind turbine generator From VEM brochure, www.vem-group.com Figure 93 Flashtrab arrester combination for four-conductor networks in a TN-C system Specifically for the wind energy sector they manufacture converters, generators (in collaboration with Indar Electric), control electronics, pitch controllers, as well as solutions to remote control and maintenance of wind parks Their standard range of power converters are PWM-controlled and principally based on IGBT power semiconductors, with a very low inductance DC bus They are equipped with latest generation digital signal processing microprocessors, 32 bit parallel multiprocessing and include Advanced Vector Control algorithms on the PWM capable of applying rotor control (DFM) or stator Electrical Parts of Wind Turbines 327 000 kW Figure 94 Ingeteam’s MW power converter From Ingeteam Energy, S.A., www.ingeteam.com control (full converter) to the generator (Figure 94) Thus, total real and reactive power control is achieved They include generator and grid-side disconnection switches Ingeteam has recently developed Ingecon® CleanPower concept, a new topology for variable speed control The topology, named as xDFM, uses an additional generator acting as an exciter while the power converter is not directly connected to the grid In this way, better power quality, grid fault tolerance, and other benefits are claimed Indar Electric’s generators have output powers ranging from 850 kW to MW and voltages from 690 V to 15 kV They are doubly-fed asynchronous or PM synchronous as well as xDFM 2.10.7.2.6 Maxwell Maxwell Technologies is a fast growing company specializing in the manufacture of ultracapacitors for a wide range of industrial applications Ultracapacitors, also known as electric double-layer capacitors, or supercapacitors, are alternative energy storage devices that store energy by electrostatically (physically) separating positive and negative charges This is in contrast to batteries that store energy via orbital electron exchange (chemically) The lack of chemical reaction permits ultracapacitors to be charged and discharged up to 000 000 times (compared to 100 or 1000 s of charge/discharge cycles in batteries) – and at a faster rate than batteries In particular, their new BMOD0094 P075 power module is directed for the safe operation and grid power quality for the most powerful wind turbine pitch drive and backup power generation systems Based on compact, robust construction and top-grade components, it is designed for reliability and safety under harsh temperature, humidity, and vibration conditions In addition, their smaller, cylindrical BOOSTCAP® range provides extended power availability, allowing critical information and functions to remain available during dips, sags, and outages in the main power source (Figure 95) Furthermore, they can relieve batteries of burst power functions, thereby reducing costs and maximizing space and energy efficiency Figure 95 BoostCap ultracapacitor From Maxwell brochure, www.maxwell.com/ultracapacitors/index.asp 328 Electrical Parts of Wind Turbines References [1] Wallace AK and Oliver JA (1998) Variable-speed generation controlled by passive elements International Conference on Electric Machines Istanbul, Turkey, 2–5 September [2] Wright AD and Fingersh LJ (2008) Advanced control design for wind turbines part I: Control design, implementation, and initial tests Technical Report NREL/TP-500-42437 National Renewable Energy Laboratory (NREL), Golden, Colorado, USA [3] Buhl ML, Jr WT_Perf user’s guide NREL codes http://nwtc/designcodes/simulators/wtperf/WT_Perf.pdf [4] Wenxin Z and Karl AS (2007) Individual blade pitch for active yaw control of a horizontal-axis wind turbine 45th AIAA Aerospace Sciences Meeting and Exhibit Reno, Nevada, 8–11 January [5] Fitzgerald AE, Kingsley C, Jr., and Umans SD (2003) Electric Machinery New York, NY: McGraw-Hill [6] Lundberg S (2003) Configuration Study of Large Wind Parks Licentiate Thesis, Chalmers University of Technology [7] Boeing Engineering and Construction Company (1979) Mod-2 wind turbine system concept and preliminary design report vol II, Detailed report NASA CR-159609 NASA Lewis Research Center, Cleveland, Ohio [8] Kundur P (1994) Power System Stability and Control New York, NY: McGraw Hill Inc [9] Voith Turbo www.voithturbo.com/wind-technology_product.htm [10] Müller H, Pöller M, Basteck A, et al (2006) Grid compatibility of variable speed wind turbines with directly coupled synchronous generator and hydro-dynamically controlled gearbox Sixth International Workshop on Large Scale Integration of Wind Power and Transmission Networks for Offshore Wind Farms Delft, NL: Offshore Wind Farms, 26–28 October [11] Hanselmann D (2003) Brushless Permanent Magnet Motor Design Rhode Island, USA: The Writer’s Collective [12] Siegfriedsen S and Bohemeke G (1998) Multibrid technology: A significant step to multi-megawatt wind turbines Wind Energy 1: 89–100 [13] Multibrid www.multibrid.com [14] Tsili M and Papathanassiou S (2009) A review of grid code technical requirements for wind farms IET Renewable Power Generation 3: 308–332 [15] Petru T (2003) Modeling of Wind Turbines for Power System Studies PhD Thesis, Chalmers University of Technology [16] Chen Z and Spooner E (1998) Grid interface options for variable-speed, permanent magnet generators IEE Proceedings Electric Power Applications 145: 273–283 [17] Chen Z, Arnalte S, and McCormick M (2000) A fuzzy logic controlled power electronic system for variable speed wind energy conversion systems 8th IEE International Conference on PEVD’2000 London, UK, September 2000, pp 114–119 [18] Papathanassiou S, Vokas G, and Papadopoulos M (1995) Use of power electronic converters in wind turbines and photovoltaic generators Proceedings ISIE ’95 Athens, July 1995 [19] Lampola P (2000) Directly Driven, Low-Speed Permanent-Magnet Generators for Wind Power Applications Espoo, Finland: Helsinki University of Technology, Laboratory of Electromechanics [20] Warneke O (1984) Use of a double-fed induction machine in the Growian large wind energy converter Siemens Power Engineering VI, pp 56–59 [21] International Conference on Lightning Protection: Topic XI, ICLP 2006, 18–22 September 2006, Kanazawa, Japan [22] IEC 61400-24: Wind-turbine generator system – Part 24: Lightning protection International Electrotechnical Commission, Geneva, Switzerland [23] IEC 61024-1-1:1993-09: Protection of structures against lightning – Part 1: General principles – Section 1: Guide A: Selection of protection levels for lightning-protection systems International Electrotechnical Commission, Geneva, Switzerland [24] Yoh Y (2006) A new lightning protection system for wind turbines using two ring-shaped electrodes IEEJ Transactions on Electrical and Electronic Engineering 1: 314–319 [25] Sakki R (2009) Technology trends of wind power generators Nordic Conference IAS Technical Seminar on Wind Power Technologies Stockholm, Sweden, 13–15 September [26] IEC 61400-21 (2000) Wind turbine generator systems – Part 21: Measurement and assessment of power quality characteristics of grid connected wind turbines IEC Draft 88/124/ CDV Further Reading [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] Burton T, Sharpe D, Jenkins N and Bossanyi E (2001) Wind Energy Handbook Chichester, UK: Wiley Elliott DL, Holladay CG, Barchet WR, et al (1987) Wind Energy Resource Atlas of the United States Golden, CO: Solar Energy Research Institute Hansen M (2008) Aerodynamics of Wind Turbines, Rotors, Loads and Structure London, UK: James & James Ltd Hau E (2006) Wind Turbines Berlin, Germany: Springer Nelson V (2009) Wind Energy: Renewable Energy and the Environment Boca Raton, FL: Taylor and Francis Patel MR (1999) Wind and Solar Power Systems Boca Raton, FL: CRC Press Stiebler M (2008) Wind Energy Systems for Electric Power Generation Berlin, Germany: Springer Troen I and Petersen E (1991) European Wind Atlas Risoe, Denmark: Risoe National Laboratory White FM (1999) Fluid Dynamics New York, NY: McGraw-Hill Wind Energy Department of Risoe National Laboratory and Det Norske Veritas (2001) Guidelines for Design of Wind Turbines Copenhagen, Denmark: Wind Energy Department of Risoe National Laboratory and Det Norske Veritas [11] Bertin JJ (2002) Aerodynamics for Engineers, 4th edn New Jersey, NJ: Prentice Hall [12] Bianchi FD, De Battista H and Mantz Ricardo J (2007) Wind Turbine Control Systems London, UK: Springer Relevant Websites www.awea.org – American Wind Energy Association www.canwea.ca – Canadian Wind Energy Association www.ciemat.es/portal.do – Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT) www.windpower.org/ – Danish Wind Energy Association www.nrel.gov/wind – DOE National Renewable Energy Laboratory www.ewea.org – European Wind Energy Association http://www.iec.ch/ – International Electrotechnical Committee (IEC) http://www.bwea.com/ – Renewable UK www.allsmallwindturbines.com – Small wind turbines www.thewindpower.net – The WindPower ... 0.0000 Cp 0 .20 00−0.3000 −0 .100 0 0.0000−0 .100 0 0 .100 0−0 .20 00 −0 .100 0−0.0000 −0 .20 00 −0.3000 −0.4000 −0 .20 00−0 .100 0 −0.3000−0 .20 00 −0.4000−0.3000 −0.5000−0.4000 −5 2 10 13 16 19 22 25 28 13.0 10. 0 TSR... Stator winding assembly of a wind turbine Electrical Parts of Wind Turbines 28 1 Figure 20 DC motor armature 2. 10. 3 .2 Wind Turbine Generators In principle, any type of generator can be used in a wind. .. design turbines that maximize their output at stronger winds, because such strong winds are rare In case of stronger winds, it is necessary to waste part of Electrical Parts of Wind Turbines 27 3