Guidelines for Design of Wind Turbines A publication from DNV/Risø Second Edition Guidelines for Design of Wind Turbines 2nd Edition Det Norske Veritas, Copenhagen ([email protected]) and Wind Energy Department, Risø National Laboratory ([email protected]) 2002. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronical, mechanical, photocopying, recording and/or otherwise without the prior written permission of the publishers. This book may not be lent, resold, hired out or otherwise disposed of by way of trade in any form of binding or cover other than that in which it is published, without the prior consent of the publishers. The front-page picture is from Microsoft Clipart Gallery ver. 2.0. Printed by Jydsk Centraltrykkeri, Denmark 2002 ISBN 87-550-2870-5 Guidelines for Design of Wind Turbines − DNV/Risø Preface The guidelines can be used by wind turbine manufacturers, certifying authorities, and wind turbine owners. The guidelines will The guidelines for design of wind turbines also be useful as an introduction and tutorial have been developed with an aim to compile for new technical personnel and as a refer- into one book much of the knowledge about ence for experienced engineers. design and construction of wind turbines that has been gained over the past few years. The guidelines are available as a printed This applies to knowledge achieved from book in a handy format as well as electroni- research projects as well as to knowledge cally in pdf format on a CD-ROM. resulting from practical design experience. In addition, the various rules and methods The development of the guidelines is the required for type approval within the major result of a joint effort between Det Norske markets for the wind turbine industry form a Veritas and Risø National Laboratory. The basis for the guidelines, with emphasis on development has been founded by Danish the international standards for wind turbines Energy Agency, Det Norske Veritas and given by the International Electrotechnical Risø National Laboratory. Commission, IEC. These guidelines for design of wind turbines The objective is to provide guidelines, have been thoroughly reviewed by internal which can be used for design of different and external experts. However, no warranty, types of wind turbines in the future. The expressed or implied, is made by Det Norske guidelines provide recommendations and Veritas and Risø National Laboratory, as to guidance for design together with applica- the accuracy or functionality of the guide- tion-oriented solutions to commonly en- lines, and no responsibility is assumed in countered design problems. connection therewith. Guidelines for Design of Wind Turbines © 2002 Det Norske Veritas and Risø National Laboratory Preface i Guidelines for Design of Wind Turbines − DNV/Risø Contents 1. WIND TURBINE CONCEPTS ......... 1 2.5.1 Transportation, installation and commissioning..................... 28 1.1 INTRODUCTION................................. 1 2.5.2 Normal operation........................ 29 1.2 CONCEPTUAL ASPECTS..................... 1 2.5.3 Service, maintenance and repair. 29 1.2.1 Vertical axis turbines.................... 2 2.6 CODES AND STANDARDS ................ 30 1.2.2 Horizontal axis turbines................ 2 REFERENCES ......................................... 30 1.2.3 Number of rotor blades................. 3 1.2.4 Power control aspects ................... 3 1.3 ECONOMICAL ASPECTS..................... 5 3. EXTERNAL CONDITIONS............ 32 1.4 POWER PRODUCTION ........................ 5 1.4.1 Power curve.................................. 6 3.1 WIND CONDITIONS ......................... 32 1.4.2 Annual energy production ............ 7 3.1.1 10-minute mean wind speed ....... 32 1.5 CONFIGURATIONS AND SIZES ........... 7 3.1.2 Standard deviation of 1.6 FUTURE CONCEPTS ........................... 8 wind speed.................................. 34 REFERENCES ........................................... 9 3.1.3 Turbulence intensity ................... 36 3.1.4 Lateral and vertical turbulence ... 37 3.1.5 Stochastic turbulence models ..... 37 2. SAFETY AND RELIABILITY........ 10 3.1.6 Wind shear.................................. 40 3.1.7 Wind direction............................ 42 2.1 SAFETY PHILOSOPHY...................... 10 3.1.8 Transient wind conditions .......... 43 2.2 SYSTEM SAFETY AND 3.1.9 Extreme winds – gusts................ 43 OPERATIONAL RELIABILITY ............ 11 3.1.10 Site assessment ........................... 46 2.2.1 Control system............................ 12 3.2 OTHER EXTERNAL CONDITIONS...... 48 2.2.2 Protection system........................ 13 3.2.1 Temperatures .............................. 48 2.2.3 Brake system .............................. 14 3.2.2 Density of air .............................. 49 2.2.4 Failure mode and effects 3.2.3 Humidity..................................... 50 analysis ....................................... 15 3.2.4 Radiation and ultraviolet light .... 50 2.2.5 Fault tree analysis ....................... 16 3.2.5 Ice ............................................... 50 2.3 STRUCTURAL SAFETY..................... 18 3.2.6 Rain, snow and hail .................... 50 2.3.1 Limit states ................................. 18 3.2.7 Atmospheric corrosion 2.3.2 Failure probability and other and abrasion................................ 51 measures of structural reliability. 18 3.2.8 Earthquake.................................. 51 2.3.3 Structural reliability methods ..... 19 3.2.9 Lightning .................................... 53 2.3.4 Code format, characteristic REFERENCES ......................................... 53 values, and partial safety factors. 19 2.3.5 Code calibration.......................... 20 2.3.6 Example – axially loaded 4. LOADS............................................... 55 steel tower................................... 22 2.3.7 Example – fatigue of FRP 4.1 LOAD CASES................................... 55 blade root in bending .................. 24 4.1.1 Design situations ........................ 55 2.3.8 Tests and calculations for 4.1.2 Wind events................................ 55 verification.................................. 26 4.1.3 Design load cases ....................... 55 2.3.9 Inspection and 4.2 LOAD TYPES ................................... 58 inspection intervals ..................... 26 4.2.1 Inertia and gravity loads ............. 58 2.4 MECHANICAL SAFETY .................... 27 4.2.2 Aerodynamic loads..................... 59 2.5 LABOUR SAFETY ............................ 28 4.2.3 Functional loads.......................... 60 ii Contents Guidelines for Design of Wind Turbines − DNV/Risø 4.2.4 Other loads.................................. 60 5.2.5 Materials................................... 118 4.3 AEROELASTIC LOAD 5.2.6 Standards .................................. 119 CALCULATIONS .............................. 60 REFERENCES ....................................... 119 4.3.1 Model elements........................... 61 4.3.2 Aeroelastic models for load prediction.................................... 70 6. NACELLE ....................................... 120 4.3.3 Aerodynamic data assessment .... 70 6.1 MAIN SHAFT................................. 120 4.3.4 Special considerations ................ 72 6.1.1 Determination of design loads.. 120 4.4 LOAD ANALYSIS AND SYNTHESIS ... 76 6.1.2 Strength analysis....................... 120 4.4.1 Fatigue loads............................... 76 6.1.3 Fatigue strength ........................ 121 4.4.2 Ultimate loads............................. 82 6.1.4 Ultimate strength ...................... 125 4.5 SIMPLIFIED LOAD CALCULATIONS .. 86 6.1.5 Main shaft-gear connection ...... 126 4.5.1 Parametrised empirical models... 86 6.1.6 Materials................................... 126 4.5.2 The simple load basis ................. 86 6.1.7 Standards .................................. 127 4.5.3 Quasi-static method .................... 87 6.2 MAIN BEARING ............................ 127 4.5.4 Peak factor approach for 6.2.1 Determination of design loads.. 129 extreme loads.............................. 88 6.2.2 Selection of bearing types......... 130 4.5.5 Parametrised load spectra ........... 89 6.2.3 Operational and 4.6 SITE-SPECIFIC DESIGN LOADS ......... 92 environmental conditions.......... 130 4.7 LOADS FROM OTHER SOURCES 6.2.4 Seals, lubrication THAN WIND..................................... 93 and temperatures....................... 130 4.7.1 Wave loads ................................. 93 6.2.5 Rating life calculations ............. 132 4.7.2 Current loads .............................. 99 6.2.6 Connection to main shaft.......... 133 4.7.3 Ice loads...................................... 99 6.2.7 Bearing housing........................ 133 4.7.4 Earthquake loads......................... 99 6.2.8 Connection to machine frame... 133 4.8 LOAD COMBINATION ...................... 99 6.2.9 Standards .................................. 133 REFERENCES ....................................... 101 6.3 MAIN GEAR .................................. 133 6.3.1 Gear types................................. 134 6.3.2 Loads and capacity ................... 137 5. ROTOR............................................ 104 6.3.3 Codes and standards ................. 141 5.1 BLADES........................................ 104 6.3.4 Lubrication ............................... 141 5.1.1 Blade geometry......................... 104 6.3.5 Materials