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National Wind Technology CenterWind Turbine Design According to

IEC 61400-1 (Onshore) and -3 (Offshore) Standards

Overview for NWTCNovember 8, 2005

Sandy ButterfieldNREL

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Outline• Overview of design process• IEC standards organization• Load cases• Determination of design load

– Fatigue– Extreme

• Special cases, e.g. faults• History and origin of design load

cases

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Design and Analysis Phase Test and Verification Phase

ConceptualDesign

Preliminary Design and Analysis

ComponentQualification Tests

Performance andPrototype

Loads Tests

Detailed Design and Analysis

Final Design

Reliability TestsDesign

Refinements

Structural Detailed DesignMech. & Electrical Design

Where does Certification & Standards Fit IntoDesign Process & Product Development Phases?

DESIGN REFINEMENT PRODUCT VALIDATION

Type Certification

Even More Load Case AnalysisControl & Protection System

Maintenance ManualInstallation ManualOperating ManualPersonal SafetyManufacturing Quality Load Verification

Dynamic Behavior

Certification Documentation Type Testing

Certification Loads Test

Power PerformanceDynamic BehaviorNoiseSafety TestPower Quality

Define Certification Requirements

•Standards are seamless(?) woven into design process•Load estimations are continually refined

More Load Case AnalysisControl & Protection System

Preliminary Load Case AnalysisControl & Protection System

Final Loads Document Control & Protection System

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IEC Standards for Wind

• TC88 responsibility

• Working Groups and Maintenance Teams do the work

• WT01 sets certification requirements and Conformity Assessment Board (CAB) has final authority (not TC88)

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WT01 References Technical Standards

DesignEvaluation

TypeTesting

Manufacturing Evaluation

Foundation Design Evaluation(Optional)

Type Characteristic Measurements

(Optional)

Final EvaluationReport

Type Certificate

Boundaries of design evaluation: Project Certificate

•61400-1 ed 3 (Onshore)

•61400-2 ed 2 (Small)

•61400-3 (Offshore)

•61400-4 (Gearboxes)

•61400-12 (Performance)

•61400-13 (loads)

•61400-21 (Power Quality)

•61400-23 (Blades)

•61400-24 (Lightning)

•61400-11 (Noise)

•61400-14 (Sound Power)•ISO 9002

WT01

Offshore Support Structures

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-1 Primary Table of Contents

• 6 External conditions 25– 6.1 General 25– 6.2 Wind turbine classes 25– 6.3 Wind conditions 26– 6.4 Other environmental conditions 35– 6.5 Electrical power network conditions 37

• 7 Structural design 38– 7.1 General 38– 7.2 Design methodology 38– 7.3 Loads 38– 7.4 Design situations and load cases 39– 7.5 Load calculations 46– 7.6 Ultimate limit state analysis 48

• 8 Control and protection system 55• 9 Mechanical systems 57• 10 Electrical system 60• 11 Assessment of structural and electrical compatibility of a wind turbine for

site-specific conditions 62• 12 Assembly, installation and erection 68• 13 Commissioning, operation and maintenance 71

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Annexes• Annex A (Normative) Design parameters for describing wind turbine class S76• Annex B (Informative) Turbulence models 77• Annex C (informative) Assessment of Earthquake Loading 82• Annex D (Informative) Wake and Wind Farm Turbulence 83• Annex E (Informative) Prediction of Wind Distribution for Wind Turbine Sites by Measure-

Correlate-Predict (MCP) Methods 85• Annex F (Informative) Characteristic Wind Turbine Loads for Ultimate Strength Analysis

88• Annex G (Informative) Fatigue Analysis Using Miner’s Rule with Load Extrapolation 91• Annex H (Informative) Bibliography 95

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Clause 6 - Design Classes

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Normal Turbulence Model

0

0,1

0,2

0,3

0,4

0,5

0 5 10 15 20 25 30

Vhub (m/s)

Turb

ule

nc

e in

ten

sit

y

Class A

Class B

Class C

Bonnie’s Version

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Extreme Turbulence Model

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Extreme Coherent Gust w/ Direction Change

0

10

20

30

40

50

-2 0 2 4 6 8 10 12 14Time, t (s)

Win

d sp

eed

V(z

,t)

(m

/s)

15 m/s gust profile

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ECD Direction Change

0

50

100

150

200

0 10 20 30 40

Wind speed, V hub (m/s)

Dire

ctio

n ch

ange

, c

g (

deg)

Figure 6 –Direction change for ECD

0

5

10

15

20

25

30

-2 0 2 4 6 8 10 12

Time, t (s)D

irect

ion

chan

ge (

deg)

Figure 7 - Example of direction change transient

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Power Production

Clause 7 – Design

Clause 7 includes detailed explanations on how to implement each load case.

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2.1 NTM V in < Vhub < Vout Control system fault or loss of electrical network

U N

2.2 NTM V in < Vhub < Vout Protection system or preceding internal electrical fault

U A

2.3 EOG Vhub = Vr2m/s and Vout

External or internal electrical fault including loss of electrical network

U A

2) Power production plus occurrence of fault

2.4 NTM V in < Vhub < Vout Control, protection, or electrical system faults including loss of electrical network

F *

Faults While Operating

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6) Parked (standing still or idling)

6.1 EWM 50 year recur. Period

U N

6.2 EWM 50 year recur. Period.

Loss of electrical networkelectrical network connection

U A

6.3 EWM 1 year recur. Period

Extreme yaw errormisalignment

U N

6.4 NTM Vhub < 0.7 Vref F *

7) Parked and fault conditions

7.1 EWM 1 year recur. periodVhub = Ve1

U A

Non-operating extreme load cases

Must sweep yaw angle

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In Practice Loads Cases are Expanded

Multiple wind speeds, seeds, operating states, etc.

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Synthesizing Simulation Time Series into Design Loads

Multiple time series for one wind speed

Sum all loads into Rainflow (fatigue)

matrix

Scale distribution according to wind

distribution

Sweep wind speed range

Normal Operating (fatigue) Loads

Multiple time series for one wind speed

Extrapolation to 1 & 50 year loads

Fit maximum load statistics to extreme value

model

Sweep wind speed, operating

& fault conditions

Extreme Operating, Faulted & Parked Loads

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Max Design Load Analysis

Loads Summary

Maximum Loads for __________________ (Blade Root, Main Shaft, Tower Head, etc.)

Mx My Mz MT Fx Fy Fz FTExtremeLoad

LoadCase

PartialSafetyFactor units units

Mx max (Matrix lists simultaneous

My max load values for

Mz max all other loads

MT max when the

Fx max Extreme Load is

Fy max maximum)

Fz max

FT

(ListCase

forwhichload

isa

maximum)

(Listsafetyfactor

appliedforthe

LoadCase)

max

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Max/Min Loads Chosen from all Cases

Load Case 1.3b = ECD (11.2 m/s, 15 m/s gust, 64o direction change, causes shut down on yaw error trigger)

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Load Case 2.1c

•Two defining load cases involving emergency shut downs.

•Peak loads could be reduced by nearly 50% if loads were contained through 1.3b and 2.1c events.

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Offshore : 61400-3

• Addresses all marine related design considerations

• Refers to 61400-1 for all turbine issues

• Add waves to the equation

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Two stochastic load sources

•Turbulence spectra

•Broad band

•Wave spectra

•Narrower band

•Approaching system resonances

•Floating system dynamics?

•Foundation design included

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Merging Two Design Paths

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Load Case Table Includes Sea State

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Need Joint Wind/Wave Probability Distributions

WavesTurbulence

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50 year Environmental Contours

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Two Excitation Sources

-Fixed-

-Floating-

•Controls could play a very important role in detecting damaging operating conditions and controlling floating platform stability

•Many more load cases

•Floating dynamics more complicated

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Summary

• Standards are intimately connected to design process

• Load reduction depends on details of load cases (“whack a mole” or “rat killing”)

• Fatigue and extreme loads could be reduced through non-traditional controls

• Floating platforms could present great controls opportunities

• COE?