IEC 61400-4:2012

Wind turbines — Part 4: Design requirements for wind turbine gearboxes

IEC 61400-4:2012(E) is applicable to enclosed speed increasing gearboxes for horizontal axis wind turbine drivetrains with a power rating in excess of 500 kW. This standard applies to wind turbines installed onshore or offshore. It Standard provides guidance on the analysis of the wind turbine loads in relation to the design of the gear and gearbox elements. The gearing elements covered by this standard include such gears as spur, helical or double helical and their combinations in parallel and epicyclic arrangements in the main power path. The standard is based on gearbox designs using rolling element bearings. Also included is guidance on the engineering of shafts, shaft hub interfaces, bearings and the gear case structure in the development of a fully integrated design that meets the rigours of the operating conditions. Lubrication of the transmission is covered along with prototype and production testing. Finally, guidance is provided on the operation and maintenance of the gearbox.

Aérogénérateurs — Partie 4: Exigences de conception des boîtes de vitesses d'aérogénérateurs

General Information

• Status: Published
• Publication Date: 04-Dec-2012
• ICS: 21.200 - Gears
• ICS: 27.180 - Wind turbine energy systems
• Technical Committee: ISO/TC 60 - Gears
• Drafting Committee: ISO/TC 60 - Gears
• Current Stage: 9092 - International Standard to be revised
• Completion Date: 24-Jun-2020

Relations

• Revises: ISO 81400-4:2005/Cor 1:2005 - Wind turbines — Part 4: Design and specification of gearboxes — Technical Corrigendum 1
• Effective Date: 15-Apr-2008
• Revises: ISO 81400-4:2005 - Wind turbines — Part 4: Design and specification of gearboxes
• Effective Date: 15-Apr-2008

Standards Content (Sample)

IEC 61400-4


Edition 1.0 2012-12




INTERNATIONAL



STANDARD









colour

inside









Wind turbines –

Part 4: Design requirements for wind turbine gearboxes






































IEC 61400-4:2012(E)

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IEC 61400-4


Edition 1.0 2012-12




INTERNATIONAL



STANDARD








colour

inside










Wind turbines –

Part 4: Design requirements for wind turbine gearboxes



























INTERNATIONAL

ELECTROTECHNICAL

COMMISSION

PRICE CODE
XG


ICS 27.180 ISBN 978-2-83220-506-8



  Warning! Make sure that you obtained this publication from an authorized distributor.

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– 2 – 61400-4 © IEC:2012(E)
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms, definitions and conventions . 12
3.1 Terms and definitions . 12
3.2 Conventions . 15
4 Symbols, abbreviations and units . 17
4.1 Symbols and units . 17
4.2 Abbreviations . 21
5 Design for reliability . 23
5.1 Design lifetime and reliability . 23
5.2 Design process . 24
5.3 Documentation . 26
5.4 Quality plan . 26
6 Drivetrain operating conditions and loads . 27
6.1 Drivetrain description . 27
6.1.1 General . 27
6.1.2 Interface definition . 27
6.1.3 Specified requirements across interfaces. 28
6.2 Deriving drivetrain loads . 28
6.2.1 Wind turbine load simulation model . 28
6.2.2 Wind turbine load calculations . 29
6.2.3 Reliability of load assumptions . 29
6.3 Results from wind turbine load calculations . 29
6.3.1 General . 29
6.3.2 Time series . 30
6.3.3 Fatigue load . 30
6.3.4 Extreme loads . 31
6.4 Operating conditions . 31
6.4.1 General . 31
6.4.2 Environmental conditions . 31
6.4.3 Operating strategies . 32
6.5 Drivetrain analysis . 32
7 Gearbox design, rating, and manufacturing requirements . 32
7.1 Gearbox cooling . 32
7.2 Gears . 33
7.2.1 Gear reliability considerations. 33
7.2.2 Gear rating . 33
7.2.3 Load factors . 34
7.2.4 Gear materials . 36
7.2.5 Subsurface initiated fatigue . 37
7.2.6 Gear accuracy . 37
7.2.7 Gear manufacturing . 37
7.3 Bearings . 38
7.3.1 General . 38

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61400-4 © IEC:2012(E) – 3 –
7.3.2 Bearing reliability considerations . 38
7.3.3 Bearing steel quality requirements . 39
7.3.4 General design considerations . 39
7.3.5 Bearing interface requirements . 42
7.3.6 Bearing design issues. 43
7.3.7 Bearing lubrication . 46
7.3.8 Rating calculations . 47
7.4 Shafts, keys, housing joints, splines and fasteners . 50
7.4.1 Shafts . 50
7.4.2 Shaft-hub connections . 50
7.4.3 Flexible splines . 51
7.4.4 Shaft seals . 51
7.4.5 Fasteners . 51
7.4.6 Circlips (snap rings) . 52
7.5 Structural elements . 52
7.5.1 Introduction . 52
7.5.2 Reliability considerations . 53
7.5.3 Deflection analysis . 53
7.5.4 Strength verification. 53
7.5.5 Static strength assessment . 54
7.5.6 Fatigue strength assessment . 58
7.5.7 Material tests . 62
7.5.8 Documentation . 63
7.6 Lubrication . 63
7.6.1 General considerations . 63
7.6.2 Type of lubricant . 64
7.6.3 Lubricant characteristics . 65
7.6.4 Method of lubrication . 66
7.6.5 Oil quantity . 67
7.6.6 Operating temperatures . 68
7.6.7 Temperature control . 68
7.6.8 Lubricant condition monitoring . 69
7.6.9 Lubricant cleanliness . 69
7.6.10 Lubricant filter . 70
7.6.11 Ports . 71
7.6.12 Oil level indicator . 71
7.6.13 Magnetic plugs . 71
7.6.14 Breather . 72
7.6.15 Flow sensor . 72
7.6.16 Serviceability . 72
8 Design verification . 72
8.1 General . 72
8.2 Test planning . 72
8.2.1 Identifying test criteria . 72
8.2.2 New designs or substantive changes . 73
8.2.3 Overall test plan . 73
8.2.4 Specific test plans . 73
8.3 Workshop prototype testing . 74
8.3.1 General . 74

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– 4 – 61400-4 © IEC:2012(E)
8.3.2 Component testing . 74
8.3.3 Workshop testing of a prototype gearbox . 74
8.3.4 Lubrication system testing . 75
8.4 Field test . 75
8.4.1 General . 75
8.4.2 Validation of loads . 75
8.4.3 Type test of gearbox in wind turbine . 76
8.5 Production testing . 77
8.5.1 Acceptance testing . 77
8.5.2 Sound emission testing . 77
8.5.3 Vibration testing . 77
8.5.4 Lubrication system considerations . 77
8.5.5 System temperatures . 77
8.6 Robustness test . 77
8.7 Field lubricant temperature and cleanliness . 77
8.8 Bearing specific validation . 78
8.8.1 Design reviews . 78
8.8.2 Prototype verification/validation . 78
8.9 Test documentation . 79
9 Operation, service and maintenance requirements . 79
9.1 Service and maintenance requirements . 79
9.2 Inspection requirements . 79
9.3 Commissioning and run-in . 79
9.4 Transport, handling and storage . 80
9.5 Repair . 80
9.6 Installation and exchange . 80
9.7 Condition monitoring . 80
9.8 Lubrication . 80
9.8.1 Oil type requirements . 80
9.8.2 Lubrication system. 80
9.8.3 Oil test and analysis . 81
9.9 Operations and maintenance documentation . 81
Annex A (informative) Examples of drivetrain interfaces and loads specifications . 82
Annex B (informative) Gearbox design and manufacturing considerations . 93
Annex C (informative) Bearing design considerations . 96
Annex D (informative) Considerations for gearbox structural elements . 122
Annex E (informative) Recommendations for lubricant performance in wind turbine
gearboxes . 125
Annex F (informative) Design verification documentation . 140
Annex G (informative) Bearing calculation documentation . 143
Bibliography . 151

Figure 1 – Shaft designation in 3-stage parallel shaft gearboxes . 15
Figure 2 – Shaft designation in 3-stage gearboxes with one planet stage . 16
Figure 3 – Shaft designation in 3-stage gearboxes with two planet stages . 17
Figure 4 – Design process flow chart . 25
Figure 5 – Examples of bearing selection criteria . 39

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61400-4 © IEC:2012(E) – 5 –
Figure 6 – Blind bearing assembly . 45
Figure 7 – Definition of section factor n of a notched component . 56
pl,σ
Figure 8 – Idealized elastic plastic stress-strain curve . 57
Figure 9 – Synthetic S/N curve (adapted from Haibach, 2006) . 60
Figure A.1 – Modular drivetrain . 82
Figure A.2 – Modular drivetrain with 3-point suspension . 83
Figure A.3 – Integrated drivetrain . 83
Figure A.4 – Reference system for modular drivetrain . 85
Figure A.5 – Rear view of drivetrain . 86
Figure A.6 – Reference system for modular drivetrain with 3-point suspension . 87
Figure A.7 – Reference system for integrated drivetrain . 88
Figure A.8 – Example of rainflow counting per DLC . 90
Figure A.9 – Example of load revolution distribution (LRD) . 91
Figure C.1 – Load bin reduction by lumping neighbouring load bins . 97
Figure C.2 – Consumed life index (CLI) . 99
Figure C.3 – Time share distribution . 99
Figure C.4 – Effects of clearance and preload on pressure distribution in radial roller
bearings (from Brandlein et al, 1999) . 102
Figure C.5 – Nomenclature for bearing curvature . 103
Figure C.6 – Stress distribution over the elliptical contact area . 105
Figure C.7 – Examples of locating and non-locating bearing arrangements . 114
Figure C.8 – Examples of locating bearing arrangements . 114
Figure C.9 – Examples of accommodation of axial displacements . 114
Figure C.10 – Examples of cross-locating bearing arrangements . 115
Figure C.11 – Examples of bearing arrangements with paired mounting . 115
Figure D.1 – Locations of failure for local (A) and global (B) failure . 123
Figure D.2 – Local and global failure for two different notch radii . 123
Figure D.3 – Haigh-diagram for evaluation of mean stress influence (Haibach, 2006) . 124
Figure E.1 – Viscosity requirements versus pitch line velocity . 126
Figure E.2 – Test apparatus for filterability evaluation . 134
Figure E.3 – Example for circuit design of combined filtration and cooling system . 138

Table 1 – Symbols used in the document . 18
Table 2 – Abbreviations . 21
Table 3 – Mesh load factor K for planetary stages . 35
γ
Table 4 – Required gear accuracy . 37
Table 5 – Temperature gradients for calculation of operating clearance . 44
Table 6 – Bearing lubricant temperature for calculation of viscosity ratio, κ . 46
Table 7 – Guide values for maximum contact stress at Miner’s sum dynamic
equivalent bearing load . 49
Table 8 – Minimum safety factors for the different methods . 50
Table 9 – Partial safety factors for materials . 55
Table 10 – Partial safety factors γ for synthetic S/N-curves of cast iron materials . 61
m
Table 11 – Recommended cleanliness levels . 70

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Table A.1 – Drivetrain elements and local coordinate systems . 84
Table A.2 – Drivetrain element interface dimensions . 85
Table A.3 – Interface requirements for modular drivetrain . 86
Table A.4 – Interface requirements for modular drivetrain with 3-point suspension . 87
Table A.5 – Interface requirements for integrated drivetrain . 88
Table A.6 – Engineering data and required design load descriptions . 89
Table A.7 – Rainflow matrix example . 89
Table A.8 – Example of load duration distribution (LDD) . 91
Table A.9 – Extreme load matrix example . 92
Table B.1 – Recommended gear tooth surface roughness. 94
Table C.1 – Guide values for basic rating life L for preliminary bearing selection . 96
h10
Table C.2 – Static load factors for radial bearings . 101
Table C.3 – Bearing types for combined loads with axial loads in double directions . 110
Table C.4 – Bearing types for combined loads with axial loads in single direction . 111
Table C.5 – Bearing types for pure radial load . 112
Table C.6 – Bearing types for axial load . 113
Table C.7 – Bearing selection: Legend . 116
Table C.8 – Bearing selection: Low speed shaft (LSS) / planet carrier . 117
Table C.9 – Bearing selection: Low speed intermediate shaft (LSIS) . 118
Table C.10 – Bearing selection: High speed intermediate shaft (HSIS) . 119
Table C.11 – Bearing selection: High speed shaft (HSS) . 120
Table C.12 – Bearing selection: Planet bearing . 121
Table D.1 – Typical material properties . 122
Table E.1 – Viscosity grade at operating temperature for oils with VI = 90 . 127
Table E.2 – Viscosity grade at operating temperature for oils with VI = 120 . 128
Table E.3 – Viscosity grade at operating temperature for oils with VI = 160 . 129
Table E.4 – Viscosity grade at operating temperature for oils with VI = 240 . 130
Table E.5 – Standardized test methods for evaluating WT lubricants (fresh oil) . 132
Table E.6 – Non-standardized test methods for lubricant performance (fresh oil) . 133
Table E.7– Guidelines for lubricant parameter limits . 136
Table F.1 – Design validation and verification documentation . 140

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61400-4 © IEC:2012(E) – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

WIND TURBINES –

Part 4: Design requirements for wind turbine gearboxes

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