WIND ENERGY SYSTEMS - Cd3wd

More documents

Recommendations

Info

Chapter 6—Asynchronous Generators 6–5 were driving a heat pump or charging batteries as a primary function, then heating domestic hot water with surplus wind power might make economic sense. The basic rule is to not go to any higher form of work than is necessary to do the job. Fixed frequency and fixed voltage systems represent a higher form of work than variable frequency, variable voltage systems, so the actual needs of the load need to be examined to determine just how sophisticated the system really needs to be. If a simpler system will accomplish the task at less cost, it should be used. 2 DC SHUNT GENERATOR WITH BATTERY LOAD Most people immediately think of a simple dc generator and a battery storage system when small wind turbines are mentioned. Many such systems were placed in service in the 1930s or even earlier. They provided power for a radio and a light bulb or two, and occasionally power for some electrical appliances. Some of the machines, especially the Jacobs, seemed almost indestructible. A number of these machines have provided service for over fifty years. These machines nearly all disappeared between 1940 and 1950, partly because centrally generated electricity was cheaper and more reliable, and partly because some Rural Electrical Cooperatives (REC) would not supply electricity to a farm with an operating wind electric system. Today, such small dc systems still have very marginal economics when centrally generated electricity is available. Their primary role would then seem to be to supply limited amounts of power to isolated loads such as weather data stations, fire lookout towers, and summer cottages. They may also provide a backup or emergency system which can be used when centrally generated power is not available due to equipment failure or fuel shortages. A diagram of a simple dc shunt generator connected to a battery is shown in Fig. 2. This circuit has been widely used since copper oxide and selenium rectifiers (diodes) were developed in the 1930s. Silicon diodes with much superior characteristics were developed in the 1950s and are almost exclusively used today. The diode allows current to flow from the generator to the battery, but prevents current flow in the opposite direction. This prevents the battery from being discharged through the generator when the generator voltage is below the battery voltage. The generator consists of a rotor or armature with resistance R a and a field winding with resistance R f on the stator. The armature current I a is brought out of the machine by brushes which press against the commutator, a set of electrical contacts at one end of the armature. The generator terminal voltage V g causes a field current I f to flow in the field winding. This field current flowing in a coil of wire, indicated by an inductor symbol on the left side of Fig. 2, will produce a magnetic flux. The interaction of this flux and the rotating conductors in the armature produces the generated electromotive force (emf) E, whichisgivenby Wind Energy Systems by Dr. Gary L. Johnson November 21, 2001
Chapter 6—Asynchronous Generators 6–6 Figure 2: DC shunt generator in a battery-charging circuit. E = k s ω m Φ p V (1) where Φ p is the magnetic flux per pole, ω m is the mechanical angular velocity of the rotor, and k s is a constant involving the number of poles and number of turns of conductors. We see that the voltage increases with speed for a given flux. This means that at low speeds the generated emf will be less than the battery voltage. This has the advantage that the turbine will not be loaded at low rotational speeds, and hence will be easier to start. The generator rotational speed n can be determined from the angular velocity ω m by n = 60ω m 2π r/min (2) The induced voltage E is in series with the resistance R a of the rotor or armature windings. In this simple model, R a would also include the resistance of the brushes on the commutator bars. by The current flow I f (the excitation current) in the field winding around the poles is given I f = V g R f A (3) The field winding has inductance, but the reactance ωL is zero because only dc is involved. Therefore only the resistances are needed to compute currents or voltages. The flux does not vary linearly with field current because of the saturation of the magnetic circuit. The flux will increase rapidly with increasing I f for small values of I f , but will increase more slowly as I f gets large and the iron of the machine gets more saturated. Also, the flux is not exactly zero when I f is zero, due to the residual magnetism of the poles. The iron tends to act like a permanent magnet after a flux has once been established. This means that the Wind Energy Systems by Dr. Gary L. Johnson November 21, 2001
Page 1 and 2:
WIND ENERGY SYSTEMS Electronic Edit
Page 3 and 4:
ii 4 Wind Turbine Power, Energy, an
Page 5 and 6:
iv 9.9 Wind farm Costs.............
Page 7 and 8:
vi and Chapter 8, so we can give a
Page 9 and 10:
Chapter 1—Introduction 1-1 INTROD
Page 11 and 12:
Chapter 1—Introduction 1-3 same w
Page 13 and 14:
Chapter 1—Introduction 1-5 Thomas
Page 15 and 16:
Chapter 1—Introduction 1-7 Figure
Page 17 and 18:
Chapter 1—Introduction 1-9 power
Page 19 and 20:
Chapter 1—Introduction 1-11 servi
Page 21 and 22:
Chapter 1—Introduction 1-13 incre
Page 23 and 24:
Chapter 1—Introduction 1-15 Figur
Page 25 and 26:
Chapter 1—Introduction 1-17 three
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Chapter 1—Introduction 1-23 [9] R
Page 33 and 34:
Chapter 2—Wind Characteristics 2-
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Chapter 3—Wind Measurements 3-2 g
Page 103 and 104:
Chapter 3—Wind Measurements 3-4 F
Page 105 and 106:
Chapter 3—Wind Measurements 3-6 i
Page 107 and 108:
Chapter 3—Wind Measurements 3-8 F
Page 109 and 110:
Chapter 3—Wind Measurements 3-10
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Chapter 4—Wind Turbine Power 4-1
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
Page 189 and 190:
Page 191 and 192:
Chapter 5—Electrical Network 5-1
Page 193 and 194:
Page 195 and 196:
Page 197 and 198:
Page 199 and 200:
Page 201 and 202:
Page 203 and 204:
Page 205 and 206: Chapter 5—Electrical Network 5-15
Page 253 and 254: Chapter 6—Asynchronous Generators
Page 255: Chapter 6—Asynchronous Generators
Page 297 and 298: Chapter 7—Asynchronous Loads 7-2
Page 307 and 308:
Chapter 7—Asynchronous Loads 7-12
Page 309 and 310:
Page 311 and 312:
Page 313 and 314:
Page 315 and 316:
Page 317 and 318:
Page 319 and 320:
Page 321 and 322:
Page 323 and 324:
Page 325 and 326:
Page 327 and 328:
Page 329 and 330:
Page 331 and 332:
Page 333 and 334:
Page 335 and 336:
Page 337 and 338:
Page 339 and 340:
Page 341 and 342:
Page 343 and 344:
Page 345 and 346:
Page 347 and 348:
Chapter 8—Economics 8-2 are the t
Page 349 and 350:
Chapter 8—Economics 8-4 Table 8.1
Page 351 and 352:
Chapter 8—Economics 8-6 by the di
Page 353 and 354:
Chapter 8—Economics 8-8 understan
Page 355 and 356:
Chapter 8—Economics 8-10 bank at
Page 357 and 358:
Chapter 8—Economics 8-12 i a = 1+
Page 359 and 360:
Chapter 8—Economics 8-14 ( ) 20 1
Page 361 and 362:
Chapter 8—Economics 8-16 and the
Page 363 and 364:
Chapter 8—Economics 8-18 The unit
Page 365 and 366:
Chapter 8—Economics 8-20 L ′ fu
Page 367 and 368:
Chapter 8—Economics 8-22 L ′ vo
Page 369 and 370:
Chapter 8—Economics 8-24 conventi
Page 371 and 372:
Chapter 8—Economics 8-26 7 PROBLE
Page 373 and 374:
Chapter 8—Economics 8-28 [2] Boll
Page 375 and 376:
Chapter 9—Wind Power Plants 9-2 6
Page 377 and 378:
Chapter 9—Wind Power Plants 9-4 w
Page 379 and 380:
Chapter 9—Wind Power Plants 9-6 t
Page 381 and 382:
Chapter 9—Wind Power Plants 9-8 s
Page 383 and 384:
Chapter 9—Wind Power Plants 9-10
Page 385 and 386:
Page 387 and 388:
Page 389 and 390:
Page 391 and 392:
Page 393 and 394:
Page 395 and 396:
Page 397 and 398:
Page 399 and 400:
Page 401 and 402:
Page 403 and 404:
Page 405 and 406:
Page 407 and 408:
Page 409 and 410:
Page 411 and 412:
Page 413 and 414:
Page 415 and 416:
Page 417 and 418:
Page 419:
show all

WIND ENERGY SYSTEMS - Cd3wd

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?