Page 11 - Wind Energy Handbook

CONTENTS xi

6.5 Number of Blades 340
6.5.1 Overview 340
6.5.2 Ideal relationship between number of blades, rotational speed and
solidity 340
6.5.3 Some performance and cost comparisons 341
6.5.4 Effect of number of blades on loads 345
6.5.5 Noise constraint on rotational speed 346
6.5.6 Visual appearance 346
6.5.7 Single-bladed turbines 346
6.6 Teetering 347
6.6.1 Load relief benefits 347
6.6.2 Limitation of large excursions 349
6.6.3 Pitch–teeter coupling 349
6.6.4 Teeter stability on stall-regulated machines 349
6.7 Power Control 350
6.7.1 Passive stall control 350
6.7.2 Active pitch control 351
6.7.3 Passive pitch control 355
6.7.4 Active stall control 355
6.7.5 Yaw control 356
6.8 Braking Systems 357
6.8.1 Independent braking systems—requirements of standards 357
6.8.2 Aerodynamic brake options 358
6.8.3 Mechanical brake options 360
6.8.4 Parking versus idling 360
6.9 Fixed-speed, Two-speed or Variable-speed Operation 360
6.9.1 Two-speed operation 361
6.9.2 Variable-speed operation 362
6.9.3 Variable-slip operation 363
6.9.4 Other approaches to variable-speed operation 363
6.10 Type of Generator 364
6.10.1 Historical attempts to use synchronous generators 365
6.10.2 Direct-drive generators 366
6.11 Drive-train Mounting Arrangement Options 366
6.11.1 Low-speed shaft mounting 366
6.11.2 High-speed shaft and generator mounting 369
6.12 Drive-train Compliance 370
6.13 Rotor Position with Respect to Tower 373
6.13.1 Upwind configuration 373
6.13.2 Downwind configuration 373
6.14 Tower Stiffness 374
6.15 Personnel Safety and Access Issues 374
References 375

7 Component Design 377
7.1 Blades 377
7.1.1 Introduction 377