Technical Session – Track AAcoustic Testing
Presented by:
Joseph SposseyProject Engineer
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Intertek – Renewables
International Small Wind Association of Testers ConferenceIthaca, NY
April 26, 2012
Outline
1. Introduction to the standard
2. Instrumentation
3. Measurements and procedures
4. Data reduction
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5. Sound power level
6. One-third octave
7. Tonality
8. Reporting differences
9. Practical considerations
Introduction to the Standard
Required for:
• AWEA 9.1 Certification
• MCS Certification
Optional:
•
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• IEC Type Certification
Consists of:
• Equipment considerations
• Measurements and procedures
• Data reduction procedures
• Results
Introduction to the standard
• AWEA 9.1
Clause 3.1 – Wind turbine sound levels
shall be measured and reported in
accordance with the latest edition of IEC
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61400-11 ed.2, but incorporating the
additional guidance in this section
• BWEA
• Similar, but with several important deviations
• Covered in Session 2
Introduction to the standard
• AWEA 9.1 Modifications to IEC 61400-11
• 3.1.1 Averaging interval of 10-seconds versus 1-min ute
• 3.1.2 Direct measurement of wind speed (Method 2)
• 3.1.3 Method of bins versus regression analysis
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• 3.1.3 Method of bins versus regression analysis
• 3.1.4 Cover as wide a wind speed range as possible
• 3.1.5 Description of obvious sound changes
• High wind
• Overspeed
• 3.1.6 Tonality analysis not required – prominent ton es to be reported
Introduction to the standard
• Introduction
• Uniform methodology
• Consistency
• Accuracy
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• Use
• Manufacturer
• Purchaser
• Operator
• Planning
• Regulation
IEC 61400-11; Ed 2.1, 2006
Introduction to the standard
• Scope
• Characterization of WT noise emissions
• Close, but not too close!
• Not your average test!
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• Standardization of procedures
• Applicable to all shapes and sizes
• Big versus small
• HAWT versus VAWT
• Tall versus short
IEC 61400-11; Ed 2.1, 2006
Introduction to the standard
• Normative references
• Sound level meters
• Acoustical calibrators
• Methods of measurement
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• Octave band filters
• IEC 61400-12-1
• Definitions
• Symbols and units
IEC 61400-11; Ed 2.1, 2006
Introduction to the standard
• Method
• Measurements
• Setup
• Noise and environmental data
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• Standardization to reference conditions
• Results
• Apparent A-weighted sound power level
• One-third octave
• Tonality
• Directivity (optional)
Instrumentation
• Sound level meter
• Apparent sound power
• Type 1 – IEC 60804
• Size < 13 mm (1/2 inch)
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• One-third octave
• Constant frequency response – 45 Hz to 11.2 kHz
• Class 1 filter – IEC 61260
• Tonality
• Type 1 – IEC 60651
• 20 Hz to 11.2 kHz range
Instrumentation
• Acoustical Calibrator
“The complete sound measurement system, including a ny recording, data logging or
computing systems, shall be calibrated immediately before and after the measurement
session at one or more frequencies using an acousti cal calibrator on the microphone.”
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• Class 1 – IEC 60942
• Data recording/playback systems
“A data recording/playback system is a required par t of the measurement
instrumentation…”
• Type 1 – IEC 60651
• Examples given in Annex B
Instrumentation
Where can I get one of those?
• Microphone, preamplifier, sound level meter, calibr ator, and windscreen
• BSWA Technology
• Bruel & Kjaer
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• PCB Piezotronics
• And many more!
Instrumentation
What does Intertek use?
• BSWA Technology
• Microphone and preamplifier – MPA 201
• Calibrator – CA 111
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• Calibrator – CA 111
• National instruments
• Sound level meter – NI-USB-9233
• NoiseLAB Professional by Delta
• Data recording and playback
• Initial data processing
Instrumentation
• Measurement board and windscreen
• Measurement board
• At least 1 meter diameter
• Plywood or hard chip-board – 12 mm min thick
• Metal – 2.5 mm min thick
• Primary windscreen
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• ½ of an open cell foam sphere
• Diameter ~ 90 mm (3 ½ in)
• Centered around the microphone
• Secondary windscreen
• Wire frame – hemispherical shape
• At least 450 mm in diameter (18 in)
• 13 mm to 25 mm layer of open cell foam
• Porosity of 4 to 8 pores per 10 mm
• Symmetrically placed over the primary windscreen
IEC 61400-11; Ed 2.1, 2006
Instrumentation
• Non-acoustic instruments
• Anemometer
• Power transducer (Method 1)
• Wind direction transmitter
• Temperature sensor
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• Temperature sensor
• Pressure sensor
• Other
• Camera
• Tape measure
• CalibrationsIEC 61400-12-2; Ed 1, 2005
Measurements and procedures
• Acoustic measurement position
• Down wind – required
• Others – optional (Directivity)
• Accurate within ±15°; WRT vane
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• R0 = H + D/2 ; tolerance of 20%
• For VAWTS, R0 = H + D
• Inclination angle; 25 ° < φ > 40°
IEC 61400-11; Ed 2.1, 2006
Measurements and procedures
• Microphone board placement
• Flat on ground
• Level edges and gaps w/soil or sand
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Measurements and procedures
• Examples
• R0
• Inclination angle
• Slant distance, R 1
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1
IEC 61400-11; Ed 2.1, 2006
Measurements and procedures
•Measurement tower location• Sensors mounted in upwind direction• Consider wake of obstacles
• Turbine – extends 10 D• IEC 61400-12-1 Annex A
• Between 10m and hub height• Between 2D and 4D• β angle (direct measurement)
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• β angle (direct measurement)� Calculated in IEC and AWEA±30° to ±90°
� Given in BWEA ±90°
IEC 61400-11; Ed 2.1, 2006
Measurements and procedures
Example – Allowable direction
Given:• Microphone due east (90°)
of turbine• Wind tower due west (270°)
of turbine
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of turbineFind:
• Allowable region for AWEA, BWEA, and IEC
Solution:• Blue hatch area is BWEA
allowable• Black hatch area is
IEC/AWEA allowable
Measurements and procedures
• Acoustic measurement requirements
• Calibrate measurement• Before acoustic measurements• After acoustic measurements• If microphone is disconnected for any reason
• All signals must be recorded and stored for later a nalysis
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• All signals must be recorded and stored for later a nalysis
• Omit periods of intruding intermittent background n oise
• Measure background noise• Immediately before or after turbine noise• During similar conditions
Measurements and procedures
• Acoustic measurement requirements (continued)
• A-weighted sound pressure level measurements
• Measured at reference position, R 0
• Measurement series of at least 30 measurements
•
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• Acoustical and non-acoustical data• Also required for background measurements
• Measurement integrated over 1-minute period (IEC)
• 10-second for AWEA• T (seconds) = 4 x Diameter (meters)
• >3 measurements within ±0.5 m/s at integer wind spe eds
• IEC 61400-11 – 6, 7, 8, 9, 10 m/s (Standardized to 10 m)• AWEA 9.1 and BWEA – Cover as wide a range as possibl e
Measurements and procedures
• Acoustic measurement requirements (continued)
• One-third octave band measurements
• Measured at reference position, R 0
• Determined as energy average of at least 3 spectra
•
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• Corresponding non-acoustical data• Also required for background measurements
• Integrated over 1-minute period (IEC)
• 10-second for AWEA• T (seconds) = 4 x Diameter (meters)
• Centre frequencies from 50 Hz to 10 kHz, inclusive, at a minimum
Measurements and procedures
• Acoustic measurement requirements (continued)
• Narrow band measurements (tonality)
• Measured at reference position, R 0
• Minimum of 2 minutes A-weighted turbine and backgro und noise
•
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• Corresponding non-acoustical data• As close as possible to the integer wind speeds
• Noise clips
• Twelve 10-second energy averaged clips for Turbine noise• Two 60-second energy averaged clips for background noise
Measurements and procedures
• Wind speed measurements
• Method 1 – determination of wind speed from electric output and power
curve
• Nacelle anemometer method
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• Nacelle anemometer method
• κ-Factor method
• Method 2 – determination of wind speed with an anemo meter
• AWEA primary method
• BWEA primary method
Measurements and procedures
• Method 2 – Direct measurement
• Wind speed
• Measured between 10 m and hub height – turbine and b ackground
• Arithmetically averaged over same period as acousti c measurement
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• Corrected to 10 m for AWEA and IEC
• Corrected to hub height for BWEA
• Wind direction
• Ensure that measurements are within 15°of turbine a zimuth
• Arithmetically averaged over same period as acousti c measurement
Measurements and procedures
• Method 2 – Direct measurement
• Other atmospheric conditions
• Air temperature and air pressure
• Required
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• Minimum of recorded every 2 hours
• Rotor speed and pitch angle
• Recommended
• Recommend averaging over similar intervals as acous tics
Data reduction
• Wind speed correction
• Standardized wind speed, V s
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IEC 61400-11; Ed 2.1, 2006
Data reduction
• Wind speed correction
• Roughness length, z 0
• Can be calculated from wind speed measurements at v arious heights
• Typically estimated using Table 1 from IEC 61400 -11
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• Typically estimated using Table 1 from IEC 61400 -11
IEC 61400-11; Ed 2.1, 2006
Data reduction
• Correction for background noise
• All measured sound pressure levels corrected
• For measurements of sound pressure 6 dB greater tha n background
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• For those between 3 dB and 6 dB greater than backgr ound, subtract
1.3 dB “ * “
• For those less than 3 dB – not reportable
IEC 61400-11; Ed 2.1, 2006
Apparent sound power level
• IEC and BWEA – regression analysis
• Turbine and background• 4th order for IEC
• AWEA – method of bins; averaging
• Turbine and background • Interpolate or extrapolate for integer values
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• Interpolate or extrapolate for integer values
• Correct for background; then calculate sound power level
IEC 61400-11; Ed 2.1, 2006
One-Third Octave
• Similar process as apparent sound power level
• Arithmetically average wind speed data
• Energy average one-third octave data
• Correct for background
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• Correct for background
• A-weighting only for IEC and AWEA
• Extrapolate or interpolate for integer values
• > 6 dB separation – use equation 8• 3 < dB > 6 separation – subtract 1.3 dB “ * “• < 3 dB – background noise louder than turbine noise
Tonality
• Covers the same wind speed range as sound power lev el
• Two 1-minute intervals closest to integer wind spee ds used
• Divided into twelve 10-second periods• 12 energy averaged narrowband spectra
• For each 10 -second period, determine:
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• For each 10 -second period, determine:
• Sound pressure level of tone(s)• Sound pressure level of masking noise in critical b and• Tonality
• Overall tonality is energy average of the twelve 10 -second periods
• Covered in more detail in session 2
Reporting differences
• AWEA Rated Sound Level and any tones that were observed
• BWEA
� Noise Label and Immission Map
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� BWEA Reference 60m Sound Level
• IEC
� Apparent sound power level
� One-third octave sound pressure levels
� Values determined in tonality analysis
Practical considerations
How do you test for all three simultaneously?
• Microphone and meteorological tower locations
• Averaging intervals of 10s
• Direct measurement of wind speed
•
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• Database differences easily monitored during testing
• Post processing and reporting
Questions?
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