Burton T. (et. al.) Wind energy Handbook
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capacity. It may be seen that the wind-farm output is significantly greater during
the winter months when, of course, the electrical load is highest. In the past, there
has also been considerable study of the extent to which wind generation could be
used to defer the construction of conventional generating plant. This question has
been posed in terms of establishing the ‘capacity credit’ of the wind farm. Capacity
credit is calculated by evaluating the capacity of conventional generation that need
not be constructed while maintaining the same level of generation reliability
(Milligan and Parsons, 1999). If these calculations are carried out carefully using
conventional power syst em reliability techniques it is possible to esta blish long-
0
1000
2000
3000
4000
5000
6000
7000
1990 1998 2005 2015
MW
Consumption
Offshore wind
CHP
Onshore wind
Figure 10.26 Anticipated Growth of Wind Generation in Denmark (after, CIGRE, 1998 and
personal communication)
0
5
10
15
20
25
30
35
40
Jan
Feb
Mar
April
May
Jun
Jul
Aug
Sept
Oct
Nov
Dec
%
Figure 10.27 Monthly Variation in Capacity Factor of a UK Wind Farm
ECONOMIC ASPECTS OF EMBEDDED WIND GENERATION 605
term capacity credits as being approximately equal to the measured capacity factors
of the wind farms providing overall wind energy penetration into the power system
is low. However, it should be emphasized that these are statistically based calcula-
tions and at particular times of peak demand (e.g., on clear cold winter days in
Northern Europe) there may be very little wind generation.
The studies of the 1980s have now been largely superseded by the change to a
market structure for gene ration and supply of electrical energy and developments
in the conventional plan t mix. There is no longer any central control over the
construction of generating plants in the UK and the energy trading system is based
on bilateral agreements with only the final balancing mechanism being under the
control of the network operator. These arrangements are such as to reward predict-
ability and controllability in generating plants and, over time, a market price should
become visible to indicate the extent of the additional costs of wind-energy
generation.
Conventional generators, as well as being a source of electrical energy (kWh), are
also used to provide a range of so-called ancillary services including: (1) system
frequency control, (2) reserve capacity, and (3) black start capability. These services
are essential for the stable operation of the power system and if they are not
provided by conventional thermal, usually steam, plant then alternative sources
need to be found. In a deregulated environment, these servi ces are purchased by
the network operator. For example the National Grid Company in England and
Wales estimates that 100 MW of additional reserve for a year can be obtained for
£10 M (House of Lords, 1999). Using this figure, and assuming that for large
penetrations of wind energy into the UK system it will be necessary to provide 15
percent of the wind output as additional reserve, a cost of 0:17 p=kWh may
immediately be calculated.
Synchronous generators also provide reactive power which is essential to support
the voltage of a power system. It is difficult to transmit reactive power long
distances in a power system and so local reactive sources are required to support
the network voltage. Preliminary work from Denmark (Bruntt, Havsager and
Knudsen, 199 9) indicates that with the large offshore wind farms planned, which
will use induction generators, there is a significant possibility of voltage collapse.
This is now being addressed and possible remedial measures, including reactive
compensators considered.
It is sometimes suggested that large penetrations of wind energy in a power
system will lead to a requirement for energy storage. Although electro-chemical
systems (flow batteries and fuel cells) are now becoming commercially available it
will be very difficult for them to compete with conventional plant, particularly
existing pumped storage, merely to provide generation ancillary services. It is likely
the energy storage systems will have to use their distributed nature and location in
the network to provide additional value, e.g., in terms of overcoming transmission
constraints, as well as taking part in energy trading activities.
As wind power becomes a more significant component of the power system it
will be necessary to integrate its operation more closely with that of the conven-
tional plant. At present renewable generation is operated on a ‘must run’ basis with
reactive power and voltage control being the responsibility of the network operator.
This is entirely appropriate when wind energy is not significant compared with
606 ELECTRICAL SYSTEMS
conventional generation but clearly alternative arrangements will be needed in the
future.
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608
ELECTRICAL SYSTEMS
Index
50 year return gust 214
A-weighted filter 529
acceleration potential 125, 142, 154
accelerometer 486
access 374
active pitch control 351, 358
active power 439
active stall 475
active stall control 355
actuator disc 42–46, 51–59, 80, 84, 96, 103, 104,
105, 109, 110, 125–126
actuators 471
electric 506
hydraulic 506
added mass 142, 145, 147, 149, 150, 151, 152
added turbulence 36–37
aerodynamic braking system 358, 443, 476, 505
aerodynamic damping 220, 262, 302, 304, 309,
407, 476, 486
aerodynamic design 378
aerodynamic noise 339, 484, 531
aeroelastic instability 286
aerofoil 41, 52, 60, 63, 65, 72, 74, 75, 93–95, 112,
115, 119, 120, 140, 148–152, 154, 156, 160, 161,
164–172
aerofoil data 168–172, 231
empirical 231, 341, 394
air density 209, 379
air pressure measurement 194, 196, 204
air temperature measurement 196, 194, 202, 203,
205
air-gap 366
all-weather access 375
anemometer 192–198, 200, 201, 202, 204, 471
angle of attack 60, 63, 64, 72, 73, 95, 96, 100, 103,
104, 111, 112, 115, 116, 119, 121, 133, 139, 140,
142, 148–152, 153, 160, 164, 165, 168–172
angular momentum 47, 48, 50, 54, 59, 62, 76, 88,
113, 117, 118, 151
annual Energy Calculation 513
annual growth rate 5
annual mean wind speed 336
annulus gear 433, 436
ARMAX model 34
assessment 589
landscape 519, 520
of wind-farm noise 534
assisted stall 181, 475
auto correlation function 242
automatic voltage controller (AVC) 571
average wind speed 185, 200
axial flow induction factor 43, 46, 59, 63, 65, 67,
68, 75, 78, 80, 83, 87, 93, 95, 98, 108, 119, 121,
133, 145
axial induced velocity 48, 56, 97, 132
azimuth 232
azimuthal binning 255
back-scattering 541
background response 221, 302, 322
balance-of-plant 511
ball-screw 352
band-pass filter 488
Batchelor 242
bearing distortion 421
bearing friction 506
bearing life 421, 432
benefit/cost ratio 550
Bernoulli’s equation 44, 105
Bessel functions 83, 151, 152, 153, 154
Betz limit 6, 45
bilinear approximation 508
bilinear or ‘Tustin’ approximation 507
Biot-Savart law 41, 52, 54 ,83, 105, 108, 109, 114
bird strikes 547
birds, impact on 546
blade chord 378
blade element theory 60, 61, 78, 103, 115, 126,
137, 141, 147, 154
blade feathering 351
blade geometry 377
optimum 379
parameter 71, 72, 76, 90
blade pitch set angle 173, 180, 181, 184
blade pitching rate 421
blade resonance 407
blade root 379, 405
fixings 417
blade structural design 377
blade structure 379
blade twist 378, 410
blade twist ( continued)
distribution 74
blade weight 333, 339
blade–tower clearance 218, 373
blade-passing frequency 372, 426, 454, 488
bolt fatigue stresses 461
bolt load increment 462
bolted flange joint 461
bound vorticity 57
boundary layer 13, 18, 59, 63, 66,139, 140, 156,
160, 161, 162, 164, 165, 167, 170
brake, parking 360
brake design
high-speed shaft 447
low-speed shaft 450
torque 447
brake disc temperature rise 445
brake duty 442
brake pads 444
brake, mechanical 360
braking, two level 450
braking loads 427, 431
braking system, aerodynamic 358, 443, 476, 505
broad range variable speed 362, 441
Brush 1
buckling 381, 405, 413, 456, 464
cables 369
callipers 443
Campbell diagram 267
capacitor, power factor correction 559
capacity factor 551
carrier to interference ratio (C/I) 542
cash flow 553
CENELEC 191
centrifugal force 271, 358
centrifugal loads 236, 259
centrifugal relief 236
centrifugal stiffening 259, 267
centrifugal stresses 443, 449
certification 210, 283
chord distribution, optimized 338
circulation 52–54, 67, 70, 78–82, 86, 91, 96, 103,
104, 108, 112–117, 148, 150, 151, 152, 163–167
closed-loop 494
closed-loop controller 472
coefficient of performance 343
coherence 249
functions 27
Coleman 104, 107, 108, 111, 112, 113, 126, 133,
137
combined periodic and random
components 253
commercial structure 553
competitive auctions 555
complex terrain 37
compliance 485
component cost 330–331, 334, 342
composites 381
coning 237
connection charges ‘deep’ and ‘shallow’ 601
constant life diagram 387, 391
constant speed operation 25, 78, 177, 178, 189,
196
contact stress 429
control, supervisory 472
control system 471
controller, closed-loop 472
controller gain 493, 494
controller objective 478, 502
cooling 437
Coriolis 18
Coriolis forces 12, 16, 20
Coriolis parameter 19
cost function 502
cost modelling 329, 333
Cp tracking 483
Cp performance curve 173, 174, 177, 183, 185
C
Q
performance curve 65, 176
critical buckling stress 413, 417, 456
critical load case for tower base 300
cross correlation function 241, 248, 276, 297,
306, 317, 323
cross-correlations 26
cross-over frequency 497
cross-spectrum 27
normalized 318
cut-in wind speed 179, 187
cut-out wind speed 188
cycle counting, fatigue 293
cyclic pitch control 492
Damage Equivalent Load 311, 348
damper, tuned mass 412
damping 365, 372
aerodynamic 220, 262, 302, 304, 309, 407, 476,
486
coefficients 408
negative 349, 407, 410
ratio 262–263, 309, 316
structural 221, 262, 309, 407
Danish wind turbine concept 3
data acquisition 196, 197, 204
delay operator 507
Delta 3 angle 349
Delta 3 coupling 271
delta winding 571
design tip speed ratio 71, 77, 90, 92
deterministic and stochastic components,
combination of 288
deterministic loads 228, 280, 294
deterministic rotor loads 304
diameter, optimum machine 332
digital controller 507
direct-drive generators 366, 368
directivity 535
Dirlik 290
discrete controller 507
discrete gust models 215, 253
discretization 507
dispersed generation 568
diurnal 16
diurnal variations 12
doubly-fed induction generators 442
610 INDEX
downslope winds 13
downwind configuration 373
drag coefficient 63, 116, 119, 159–162, 168–171,
219
drag factor 300
Dragt’s correction 200, 201
drive-train 366
compliance 370
dynamics 427
model 364, 427
torsional flexibility 372
DS 472 211, 222, 226, 357
dynamic analysis
codes 282
finite-element method 281
step-by-step 264, 271, 279, 292
dynamic factor 301, 303
dynamic magnification 269
dynamic response 220, 256, 308, 313
dynamic stall 412
E-glass 384
earthing 562
ecological assessment 545
economic aspects 598
economies of scale 329
eddy viscosity 35
efficiency 438, 441
electric actuator 506
electrical distribution networks 570
electrical protection 590
electrical systems 559
Electricity Feed-in-Law 555
electromagnetic interference (EMI) 538
ellipsoidal co-ordinates 127, 142, 143
embedded generation 568
emergency shut-down 431, 443
emergency stop 473
EMI, prediction of 541
EMI problems 540
empirical aerofoil data 231, 341, 394
endurance limit 429
energy
capture 77, 173, 175, 179, 185–189, 192, 199,
202–205, 378
gains 361
recovery period 7
yield 331, 333, 335, 338, 343
Environmental Statement 517
epicyclic arrangement 433
epoxy 389
equilibrium wake 142, 147, 148, 252
equivalent circuit, negative phase sequence 582
equivalent load 403–404
Eurocode 3 458
exceedance level, LA90 530
extreme gust 32
extreme loads 214
extreme values 253
extreme wind speeds 30
FACT database 387
fail-safe component 459
fatigue criticality 403, 459
fatigue cycle counting 293
fatigue design 458
of gear teeth 428
of shafts 432
fatigue evaluation
by distortion energy method 424
by maximum shear method 424
fatigue load 212, 309
spectrum 218, 287
fatigue loading 399
fatigue loads, in-plane 212, 309, 404
fatigue properties 385
of wood laminates 391
fatigue spectra combination 311
fatigue strength 384
fatigue stress ranges 310
fatigue stresses 287
fault conditions 212, 473
fault current 591
faults 218
fibre volume fraction 384–385
fictitious grid 589
field testing 190, 192
finance 549
financial close 554
fine pitch 351, 479
finite-element analysis 423, 437, 451
finite-element methods 283
fixed pitch 178, 179, 180, 181
fixed speed operation 360
flapwise bending moment 396, 400
flexural rigidity 414, 416
flicker 484, 581
shadow 527
flow separation 66, 68, 139, 158, 160, 161, 162,
164, 167
forbidden zones 544
forward-scattering 541
foundation, mono-pile 467
piled 466
slab 465
Fourier transform 244
free yaw 477
frequency converter 362, 441, 477
frequency domain 239, 282, 313
frequency response 498
function 314
Fresnel zone 540
friction coefficient 444
friction velocity 19, 21
frozen turbulence hypothesis 242
frozen wake 141, 240, 252, 273
full-span pitch control 354
fuzzy controllers 504
gain margin 497
gain schedule 498
gamma function 185
gear meshing 435
gear ratio 424, 430
INDEX 611
gear ratio (continued)
optimum 433
gear stage 433
gear volume 434
gearbox cost 343
gearbox, integrated 366, 371, 437
Gedser 1
generalized load 257, 268
generalized mass 257
generator mounting 369
generators
direct-drive 366, 368
doubly-fed induction 442
induction 364, 438
synchronous 364
variable slip induction 363, 477, 490
wound rotor induction 483
geographical variation 12
geostrophic drag law 20, 34, 37
geostrophic wind 18, 20
GL rules 210, 357, 387, 389, 403, 465
glass/epoxy 384
glass/polyester 384
Glass Fibre Reinforced Plastic (GFRP) 384
Glauert 51, 56, 66, 67, 84, 85, 86, 99, 101, 102,
103, 106, 107, 112, 113, 117, 133, 137
Goodman diagram 387
Goodman relation 424, 433
Graetz Bridge 441
gravity loading 283, 404
gravity loads 236
Green Certificates 556
grid loss 214, 217, 300, 394, 427, 443, 448
grounding 562
Guidelines for Wind Energy Development 512
Gumbel distribution 31
gust factor 29
gust loading 215
gust models, discrete 215, 253
gust slicing 241, 290, 351, 356, 401, 427
effect 214
gust speed 214
gyroscopic loads 238
H
1
controller 504
harmonic currents 581
harmonics 588
helical gears 436
helical vortex 52, 78, 81
helicoidal vortex sheet 81, 84, 85, 91, 92
high speed shaft 369
high-speed shaft brake design 447
historical development 1
hollow shaft 352
hub ‘dishing’ moment 296
hub ‘dishing’ moment due to stochastic
loading 297
Hutter 1
hydraulic actuator 506
hydraulic cylinder 352, 358
hydrological study 517
impact factor 214, 222
impact on birds 546
impact on the generation system 604
in-plane fatigue loads 404
individual pitch control 492
induced velocity, axial 48, 56, 97, 132
tangential 47, 48, 57
induction factor
axial flow 43, 46, 59, 63, 65, 67, 68, 75, 78, 80,
83, 87, 93, 95, 98, 108, 119, 121, 133, 145
tangential flow 47, 75, 83, 86, 95, 119
induction generators 364, 438
inertia loads 236
infinite life torque 429
inflow angle, or flow angle 52, 57, 69, 72, 77, 78,
80, 85, 87, 90, 121
ingress moisture 389, 438
installations 511
integral length scale 242, 323
integrated gearbox 366, 371, 437
integrator desaturation 480, 508
integrator wind-up 480, 508
interface protection 596
interference regions 544
internal rate of return (IRR) 550
International Electro-technical Commission
(IEC) 190–199, 204, 205, 209, 215, 357, 392,
397–398, 404, 443
International Energy Agency (IEA) 191, 192,
193, 195, 196, 197
islanding 592, 594
isotropic turbulence 28
Kaimal 22, 404
Kaimal power spectrum 23, 303, 315
Kalman filter 486, 502
Khaya ivorensis 389
Kinner 125, 126, 143, 145, 154
KP1/l performance curve 177, 178, 185, 186
Kutta condition 164
Kutta-Joukowski theorem 41, 54, 70, 80, 163
LaCour 1
laminate 414
specially orthotropic 414
symmetric 413
land and sea breezes 13, 16
landscape assessment 519, 520
Laplace
equation 126
operator 479, 506
transforms 495
variable 494
lattice steel towers 523
lattice towers 464
Legendre polynomial 128, 129, 134, 153
length scales 23
integral 242, 323
life factor 429
lift coefficient 71, 72, 74, 116, 119, 140,141, 167,
169, 170, 219, 239
lift/drag ratio 71, 72, 75, 76, 77, 169, 170
612 INDEX
lifting line theory 99, 100, 109
lightning 563
damage frequency 566
flashes 566
protection 565
limit-state design 212
line-drop compensation (LDC) 572
linear acceleration method 264
linearity 240
assumption 254, 255
linearized model 493
load cases 214–215, 392
load paths 422
load–duration curves 426
local speed ratio 49
Loewy wake-spacing function 154
logarithmic decrement 220, 262, 302, 316
longitudinal stiffness modulus 385
losses 599
low-speed shaft 366
brake design 450
LQG controller 502
machine rating 333
mass flow rate 41, 43, 48, 83, 97, 100, 101, 117
material safety factors 388, 392, 403, 447
mean strain 387
mean stress 404
level 399
MEASNET 191, 193, 196
measure–correlate–predict (MCP) 514
measurement 534, 589
air pressure 194, 196, 204
air temperature 196, 194, 202, 203, 205
mechanical brake 360
mechanical noise 531
meteorogical forecast 34
method of bins 183, 197, 199, 200–207
micrositing 515
Miner’s rule 388
Mod-0 1
Mod-5B 1
modal analysis 223, 256, 262, 276, 281, 283, 313
modal damping coefficient 409, 411
mode shape 224, 258
purification 259
modelling 541
moisture content 389, 392
moisture, ingress 389, 438
momentum theory 46–51, 61–62, 69, 65, 96–103,
116–119, 228
mono-pile foundation 467
Musgrove 2
nacelle bedplate 450
nacelle Loading 298
narrow range variable speed 362, 442
natural frequency 258, 261
near wake region 36
negative damping 349, 407, 410
negative phase sequence equivalent circuit 582
negative pitch control 355
net present value 550
network loss 573
neural networks 504
neutral stratification 18
New Electricity Trading Arrangements
(NETA) 556
Newmark 264
NOABL airflow model 513
noise 361, 435–436, 439, 528
aerodynamic 339, 484, 531
limits 537
mechanical 531
of wind-farm 534
propagation 536
wind-turbine 531
non-dimensional time 145, 146, 151, 152
non-linear gains 500
normal induced velocity 97, 100–102, 105–121,
132
normal shut-down 427
normal turbulence model 395, 397
normalized co-spectrum 318–319
normalized cross spectrum 318
notch filter 484, 499
nuisance tripping 585
number of blades 340
observers 501
on-load tap changers 571
open-access 599
open-loop 494
optimal blade design 68, 75, 77, 87
optimal feedback 502
state 486, 502
optimized chord distribution 338
optimum blade geometry 379
optimum gear ratio 433
optimum machine diameter 332
optimum machine size 330
optimum rated wind speed 335–336
optimum rotational speed 339
optimum tip speed ratio 481
orthogonal mode shapes 259, 261
orthogonality condition 257
out-of-plane bending moment 394, 400
overspeed 213, 358, 443, 448, 473
pad rubbing speed 443
parallel shaft arrangement 433
parking brake 360
partial safety factors 212
partial-span pitch control 354
passive pitch control 355
passive stall control 350
payback period 550
peak aerodynamic torque 448
peak factor 222, 253, 303, 324, 398
performance measurement 190, 191, 193, 207
periodic coefficients 279, 283
periodic loading 264, 267, 289
permitted noise levels 537
persistence forecast 33
INDEX 613
per-unit system 573
phase advance 499
phase margin 497
photomontage 524, 526
PI controller 479, 483, 485, 490
PID controller 479, 484
piled foundation 466
pitch actuation systems 352
pitch actuators 505
pitch angle 60, 65, 70, 72, 77, 118, 148, 179, 180,
181, 185
schedules 356
pitch bearing 419, 506
pitch change rates 351
pitch control 180, 181, 182, 184, 188, 475, 484
active 351, 358
full-span 354
individual 492
negative 355
partial-span 354
passive 355
system 397
pitch rate limits 500
pitch regulation 180, 185, 195, 209
pitch response 398
pitch–teeter coupling 349
pitch-regulated machine 254, 351, 395, 400, 426
pitch-regulation 300
pitching to feather 179, 181, 182, 475
pitching to stall 181
Pitt and Peters 133–138, 145, 154
planet carrier 433
planet gears 433
planning application 517
ply 384, 416
poles 495, 497
poplar 389, 391
power coefficient 6, 44, 45, 46, 49, 50, 55, 64, 65,
68, 69, 77, 79, 80, 81, 92, 98, 102, 106, 176
power curve 341, 351
power factor correction capacitor 559
power flows 573
power fluctuations 426
power measurement 196, 202, 203, 204
power output 6
power quality 484, 580
characteristics 589
power spectra containing periodic
components 291
power spectrum
Kaimal 303, 315
of blade root bending moment 270
of rotor thrust 306
of tip deflection 269
von Karman 23, 242, 251
power swings 351
power system studies 579
power transducer 480
power versus wind speed curve 178–184, 187,
198, 199
pre-pregs 385
pre-warping 508
prediction 534
EMI 541
preloaded flanges 462
preloading 420, 421, 461
pressure drag 63, 66, 101, 139, 157, 161, 166, 168
pressure drop 42, 46, 50, 52, 62, 63, 64, 66, 67,
68, 59, 106, 117, 125, 126, 129, 131, 144
pressure fed lubrication 437
probability distribution of wind speeds 198,200,
205, 206
project appraisal 549
project development 511
project finance 553
properties of composites 384
properties of wood laminates 389
protection, interface 596
prying 461
Pulse Width Modulation 441
Public Utilities Requirements to Purchase Act
(PURPA) 555
quasi-steady aerodynamics 148, 149, 152
quasistatic bending moments 227
quasistatic response 316
R ratio 386
radial velocity 58, 59, 82, 85
rainflow method 293
raptors 546
rate of change of frequency 597
rated power 330, 333, 342
rated wind speed 215, 333, 396, 401, 480
optimum 335–336
Rayleigh distribution 14
reactive power 362, 365, 440
reactive power charges 600
reduced frequency 152
redundancy 561
reservoir method 293
resilient mountings 436
resonance 267
resonant bending moment 228
resonant frequency 488
resonant response 316
resonant root bending moment 320
resonant size reduction factor 301
resonant tip response 220
return on investment 550
return period 214
reverse loading 386, 391
Reynolds number 72, 75, 159–162, 168–170
Reynolds stress 29
Richardson number 24
rock anchors 466
root locus plot 488, 496, 499
root loss factor 87
root vortex 52, 54, 57, 94, 113, 114, 118
rotary transformer 505
rotational sampling 284
rotational speed 338, 341, 343
optimum 339
rotationally sampled
614 INDEX