Wind Energy Explained
`Theory, Design and Application
`
`J.F. Manweli, J.G. McGowan and AL. Rogers
`University of Massachusetts, Amherst, USA
`
`JOHN WILEY & SONS, LTD
`i
`
`GE 2018
`Vestas v_ GE
`|PR2018—01015
`
`GE 2018
`Vestas v. GE
`IPR2018-01015
`
`i
`
`

`

`Copyright © 2002 John Wiley & Sons Ltd,
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`Reprinted September 2002
`Reprinted with corrections August 2003
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`British Library Cataloguing in Publication Data
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`A catalogue record for this book is available from the British Library
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`ISBN 0 471 49972 2
`
`Printed from files supplied by the author
`Printed and bound in Great Britain by Antony Rowe Ltd, Chippenham, Wiltshire
`This book is printed on acid—free paper responsibly manufactured from sustainable forestry
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`
`ii
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`

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`Contents
`
`4.2
`
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`General Principles
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`4.3 Wind Turbine Rotor Dynamics
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`4.4
`Detailed and Specialized Dynamic Models
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`References
`
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`Electrical Aspects of Wind Turbines
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`5. 1
`Overview
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`Basic Concepts of Electric Power
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`Power Transformers
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`(cid:9)(cid:1)(cid:10)(cid:14) (cid:2)(cid:34)(cid:21)(cid:31)(cid:32)(cid:32)(cid:1)(cid:2)(cid:23)(cid:32)(cid:23)(cid:21)(cid:41)(cid:39)(cid:31)(cid:21)(cid:19)(cid:32)(cid:48)(cid:23)(cid:38)(cid:42)(cid:31)(cid:37)(cid:33)(cid:23)(cid:34)(cid:41)(cid:48)
`5.6
`Ancillary electrical equipment
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`References
`
`Electrical Machines
`
`Power Converters
`
`5.2
`5.3
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`5 .4
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`5.5
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`.
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`Wind Turbine Design
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`6. 1
`Overview
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`6.2
`Design Procedure
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`6.3 Wind Turbine Topologies
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`6.4
`Materials
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`6.5
`Machine Elements
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`(cid:10)(cid:2)(cid:11)(cid:14) (cid:18)(cid:31)(cid:34)(cid:22)(cid:48)(cid:17)(cid:42)(cid:39)(cid:20)(cid:31)(cid:34)(cid:23)(cid:48)(cid:16)(cid:42)(cid:20)(cid:40)(cid:46)(cid:40)(cid:41)(cid:23)(cid:33)(cid:40)(cid:48)(cid:19)(cid:34)(cid:22)(cid:48)(cid:4)(cid:35)(cid:33)(cid:37)(cid:35)(cid:34)(cid:23)(cid:34)(cid:41)(cid:40)(cid:48)
`6.7 Wind Turbine Subsystems and Components
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`Design Evaluation
`6.8
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`6.9
`Power Curve Prediction
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`
`6.6 Wind Turbine Loads
`
`References
`
`Wind Turbine Control
`
`Introduction
`
`7. 1
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`7.2
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`7.3
`7.4
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`Overview of Wind Turbine Control Systems
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`Typical Grid—connected Turbine Operation
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`Supervisory Control Overview and Implementation
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`7.5
`Dynamic Control Theory and Implementation
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`References
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`Wind Turbine Siting, System Design and Integration
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`8.1
`General Overview”
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`8 .2 Wind Turbine Siting
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`Installation and Operation Issues
`8.3
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`8.4 Wind Farms
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`8.7
`Operation in Severe Climates
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`8.8
`Hybrid Electrical Systems
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`References
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`8.6
`
`Offshore Wind Farms
`
`8.5 Wind Turbines and Wind Farms in Electric Grids
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`(cid:8)(cid:4)(cid:7)(cid:14)
`(cid:8)(cid:4)(cid:13)(cid:14)
`(cid:8)(cid:5)(cid:4)(cid:14)
`(cid:8)(cid:6)(cid:6)(cid:14)
`
`271
`
`283
`3 13
`314
`
`3 17
`
`321
`
`32 1
`
`328
`
`334
`339
`
`346
`367
`
`369
`369
`
`370
`
`377
`381
`
`394
`
`403
`
`409
`410
`422
`
`iii
`
`

`

`Electrical Aspects of Wind Turbines
`
`.
`
`243
`
`is the reactance of either the capacitor or the inductor and f is the frequency of
`where X'
`the fundamental. For the capacitor and inductor in parallel, resonance implies that:
`
`C227:f =
`
`
`1
`
`L223)“
`
`(2 r”)
`
`(55.5)
`
`where Y” ~= the reciprocal of the reactance (“admittance”) of either the capacitor or the
`inductor.
`
`For this particular filter, the output voltage harmonics will be reduced relative to the
`input by the following scale factor:
`
`f(n)=
`
`
`
`EL
`V1
`
`
`
`
`
`1
`___________.._
`1—[n—(1/n)] 2 XY”
`
`
`
`(5.5.6)
`
`From Equation 5.5.6, f(1) = 1 and flu) approaches 1an for high values of n. For certain
`values of n, the denominator of Equation 5.5.6 goes to zero, indicating a resonant frequency.
`For example, there is a resonant frequency for a value Of 12 >1 at:
`
`
`
`l
`
`1
`
`1
`
`1
`
`nw3[,’XY”+ (xi/”MH
`
`(5.5.7)
`
`Near this resonant frequency, input harmonics are amplified. Thus, this resonant frequency
`should be chosen lower than the lowest occurring input harmonic voltage.
`Further discussion of filters is outside the scepe of this text. It is important to realize,
`however, that sizing of the inductors and capacitors in a filter is related to the harmonics to
`be filtered. Higher—frequency harmonics can be filtered with smaller components. As far as
`filtering is concerned, then, the higher the switching rate in a PWM inverter, for example,
`the better. This is because higher switching rates can reduce the lower—frequency harmonics,
`but increase higher ones. More information on filters is given in Thorborg (1988).
`
`5.6
`
`Ancillary electrical equipment
`
`There is a variety of ancillary electrical equipment associated with a Wind turbine
`installation. It normally includes both high—voltage (generator voltage) and low-voltage
`items. Figure 5.38 illustrates the main high-voltage components for a typical installation.
`Dotted lines indicate items that are often not included. These items are discussed briefly
`
`below.
`
`

`

`244
`
`
`
`Wind Energy Explained
`
`
`
`Slip rings
`
` Contactor
`
`
`
`I-———_———
` Soft start
`
`
`
`
`
`
`
`ClI‘CLllt breaker
`
`
`or fuses
`
`
`Main disconnect
`
`Transformer
`
`Figure 5.38 Wind turbine high~voltage equipment
`
`5. 6. 1
`
`Power cables
`
`Power must be transferred from the generator down the tower to electrical switch gear at the
`base. This is done via power cables. Threewphase generators have four conductors, including
`the ground or neutral. Conductors are normally of copper, and they are sized to minimize
`voltage drop and power losses.
`'
`In most larger wind turbines, the conductors are continuous from the generator down the
`tower to the main contactor. In order that the cables not be wrapped up and damaged as the
`turbine yaws, a substantial amount of slack is left in them so that they ‘droop’ as they hang
`down the tower. The power cables are thus often referred to as droop cables. The slack is
`taken up as the turbine yaws and then released as it yaws back the other way. With ,.
`sufficient slack, the cables seldom or never wrap up tight in most sites. When they do'Wrap
`up too far, however, they must be unwrapped. This may be done manually, after first
`disconnecting them, or by using a yaw drive.
`
`5.6.2
`
`Slip rings
`
`Some turbines, particularly smaller ones, use discontinuous cables. One set of cables is
`connected to the generator. Another set goes down the tower. Slip rings and brushes are
`used to transfer power from one set to the other. In a typical application the slip rings are
`mounted on a cylinder attached to the bottom of the main frame of the turbine. The axis of
`the cylinder lies on the yaw axis, so the cylinder rotates as the turbine yaws. The brushes are
`
`

`

`Electrical Aspects of Wind Turbines
`
`*
`
`245
`
`mounted on the tower in such a way that they contact the slip rings regardless of the
`orientation of the turbine.
`
`Slip rings are not commonly used on larger machines, since they become quite
`expensive as the current carrying capacity increases. In addition, maintenance is required as
`the brushes wear.
`
`5.6.3
`
`Soft start
`
`As indicated in Section 5.4.4, induction generators will draw much more current while
`starting across the line than they would produce when running. Starting in this way has
`numerous disadvantages. High currents can result in early failure of the generator windings,
`and can result
`in voltage drops for loads nearby on the electrical network. Rapid
`acceleration of the entire wind turbine drive train can result in fatigue damage. In isolated
`grids with a limited supply of reactive power,
`it may not be possible to start a large
`induction machine at all.
`
`Due to the high currents that accompany across the line starting of induction machines,
`most wind turbines employ some form of soft start device. These can take a variety of
`forms. In general, they are a type of power electronic converter that, at the very least,
`provides a reduced current to the generator.
`
`5. 6.4
`
`Contactors
`
`The main contactor is a switch that connects the generator cables to the rest of the electrical
`network. When a soft start is employed, the main contactor may be integrated with the soft
`start or it may be a separate item. In the latter case power may be directed through the main
`contactor only after the generator has been brought up to operating speed. At this point the
`soft start would be simultaneously switched out of the circuit.
`
`5.6.5
`
`Circuit breakers or fuses
`
`Somewhere in the circuit between the generator and the electrical grid are circuit breakers
`or fuses. These are intended to open the circuit if the current gets too high, presumably as a
`result of a fault or short circuit. Circuit breakers can be reset after the fault is corrected.
`
`Fuses need to be replaced.
`
`5.6.6 Main disconnect
`
`A main disconnect switch is usually provided between the electrical grid and the entire wind
`turbine electrical system. This switch is normally left closed, but can be Opened if any work
`is being done on the electrical equipment of the turbine. The main disconnect would need to
`be open if any work were to be done on the main contactor and would in any case provide
`an additional measure of safety during any electrical servicing.
`
`

`

`246
`
`Wind Energy Explained
`
`5.6. 7
`
`Power factor correction capacitors
`
`Power factor correction capacitors are frequently employed to improve the power factor of
`
`the generator when viewed from the utility. These are connected as close to the generator as
`is convenient, but typically at the base of the tower or in a nearby control house.
`
`5.6.8
`
`Turbine Electrical Loads
`
`There may a number of electrical loads associated with the operation of wind turbines.
`These could include actuators, hydraulic motors, pitch motors, yaw drives, air compressors,
`control computers, etc. Such loads typically require 120 V or 240 V. Since the generator
`voltage is normally higher than that, a low-voltage supply needs to be provided by the
`utility, or step down transformers need to be obtained. __
`
`References
`
`Bradley, D. A. (1987) Power Electronics, Van Nostrand Reinhold (UK), Wokingarn, England.
`
`Brown, D. R, Hamilton, E. P.
`
`(1984) Electromechanical Engineering Conversion, Macmillan
`
`Publishing, New York.
`
`Edminister, J. A. (1965) Electrical Circuits. Shaum’s Outline Series in Engineering, McGraw Hill
`
`Book Co, New York.
`
`Fuchs, E. F., Erickson, R. W., Pardon, A. A. (1992) Permanent Magnet Machines for Operation with
`
`Large Speed Variations, Proc. of the 1992 American Wind Energy Association Annual Conference,
`
`American Wind Energy Association, Washington DC.
`
`Johnson, Gary L. (1985) Wind Energy Systems, Prentice-Hall, Inc., Englewood Cliffs, NJ.
`
`Manwell, I. F., McGowan, J. G., Adulwahid, U., Rogers, A., McNiff, B. P. (1996) A Graphical
`
`Interface Based Model for Wind Turbine Drive Train Dynamics, Proc. of the 1996 American Wind
`
`Energy Association Annual Conference, American Wind Energy Association, Washington DC.
`
`Nasar, S. A., Unnewehr, L. E. (1979) Electromechanics and Electric Machines, John Wiley, New
`
`York.
`
`Sarina, MS.
`
`(1985) Electric Machines, Steady—State Theory and Dynamic Performance, West
`
`Publishing Company, St. Paul, MN.
`
`Thorborg, K. (1988) Power Electronics, Prentice-Hall, Englewood Cliffs, NJ.
`
`-
`
`Torrey, D. A, Childs, S. E. (1993) Development of a Variable Reluctance Wind Generator, Proc. of
`
`the 1993 American Wind Energy Association Annual Conference, American Wind Energy
`
`Association, Washington DC.
`
`