International Electrotech

Commission Standard IEC 6

and Other Procedure

Acoustic Noise Measurem

Techniques

Arlinda Huskey

National Renewable Energy Laborato

WindPower 2006

June 4-7, 2006

Pittsburgh, Pennsylvania

NREL/PR-500-39978
Disclaimer and Government License

This work has been authored by Midwest Research Institute (MRI) under Contract No. DE-AC36Department of Energy (the “DOE”). The United States Government (the “Government”) retains athe work for publication, acknowledges that the Government retains a non-exclusive, paid-up, irrepublish or reproduce the published form of this work, or allow others to do so, for Government puNeither MRI, the DOE, the Government, nor any other agency thereof, nor any of their employeeor implied, or assumes any liability or responsibility for the accuracy, completeness, or usefulnesproduct, or process disclosed, or represents that its use would not infringe any privately owned ri

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Standards and Other Pro

• IEC 61400-11 Second Edition 

2002 Acoustic Noise Measurement Techniques

– Amendment approved in 2005

• MEASNET, Version 2, January 

2005

• AWEA small wind turbine 

performance and safety standard
IEC 61400-11 2002

• Used by

– Manufacturers to declare acoustic emission – Purchasers to verify declared values– Wind turbine operators to verify declared va– Wind turbine planner or regulator to meet r

permit requirements

• Reporting 

– Sound power level at 6, 7, 8, 9, and 10 m/s– 1/3 octave levels at 6, 7, 8, 9, and 10 m/s– Tonality at 6, 7, 8, 9, and 10 m/s– Uncertainty for all above values
IEC 61400-11 Metho

H

D

H+D/2
2 4 6 8 10 12 14

Measured wind speed @10 m

sound pressure level [dB(A)]

0

102030405060

20 2531.5 40 50 63 80100125160200250315400500630800100012501600200025003150400050006300800010000

1/3rd octave band [Hz]

sound pressure dB(A)

6 m/s7 m/s8 m/s9 m/s10 m/s

5.5 6 6.5 7 

Apparent sound power level [dB(A)]

0

102030405060708090

0 500 1000 1500 

Sound Pressure Level (dB)

Measured sound levels

1/3rd octave levels T

Sound 
IEC 61400-11 Changes from 1s

• Tonality

– Improvement for pitch controlled an

controlled turbines

– Analysis on shorter time periods to 

characterize tones

– Improvement on procedure to identi– Optional audibility criterion added fo

tones

• Sound power levels, 1/3 octave, a

reported for 6, 7, 8, 9, and 10 m/s

– Previously reported for only 8 m/s
IEC 61400-11 Changes from 1s

• Derived wind speed from power a

of rated power

– No previous method but needed for 

reaching rated power before 10 m/s

– A ratio of measured and derived win

before 95% rated power used to despeed from power after 95% rated p

– “Questionable”

• More work and complicated but m

information reported, better repea
Amendment to IEC 614

• Nacelle anemometer method pre

using ratio for wind speed determabove 95% of rated power

• Reporting of rotor speed and pitc

recommended

• In determining the sound pressur

higher order regression will be usoption is linear regression within 
IEC 61400-11 Revision for 3r

• New revision started May 2006• Methods for other wind turbines will be 

(small, low wind speed, offshore)

• Anemometer height (currently 10 mete

height)

• Averaging period (currently 1-minute)• Improvements in 1/3 octave procedure 

purposes

• Improvements in the uncertainty analys• Wind farm verification• Possibly including infrasound, impulsiv

frequency noise
MEASNET

• International MEASuring NETwork of w

institutes

• MEASNET objectives:

– High quality measurements– Uniform interpretation of standards– Interchangeability of results (round robin co

• Expert groups for acoustic noise, powe

power quality, and anemometer calibra

• NREL is MEASNET member approved 

quality and acoustic noise

• Procedures based on IEC with modifica• Faster process of approval than IEC
AWEA Small Wind Turb

Performance and Safety St

• Procedure for evaluating the safety, re

performance, and acoustic characteristwind turbine

• Uses terms very close to the IEC stand

to help the consumer understand bette

• Uses the general methodology of the IE

for quality measurements but has som

better characterize dynamic small wind as overspeed control

• Overall reporting “number” is the Smal

Certification Corporation (SWCC) rated 
Conclusions

• Standards need revision:

– “State–of–the-art” knowledge changes– Wind turbines change 

• The best methods differ based on the t

of wind turbine

• All standards and procedures are to en

and repeatable measurements 

• Terminology can be confusing, make s

understand what number is used