wind turbine generator system pika t701 acoustic test report · scale. the turbine is located...

Wind Turbine Generator System Pika T701

Acoustic Test Report

Conducted by

High Plains Small Wind Test Center Colby, KS

November 10, 2015

Approval By: _________________________________________________________

Ruth Douglas Miller, Lead Engineer, Date

Review By: ___________________________________________________________

Arlinda Huskey , NWTC, Date

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Table of Contents 1 Background ............................................................................................................................ 4 2 Test Summary ........................................................................................................................ 4 3 Test Turbine Configuration ..................................................................................................... 4 4 Test Site Description .............................................................................................................. 7 5 Test Equipment ..................................................................................................................... 9 5.1 Equipment Descriptions ....................................................................................................... 9 5.2 Instrument Locations ........................................................................................................... 10 6 Results .................................................................................................................................. 10 6.1 Test Conditions ................................................................................................................... 10 6.2 Standardized Wind Speed Calculation ............................................................................... 10 6.3 Apparent Sound Power Level ............................................................................................. 11 6.4 One-Third Octave Analysis ................................................................................................. 12 6.5 Tonality .............................................................................................................................. 15 6.6 Uncertainty ......................................................................................................................... 15 7 Exceptions ........................................................................................................................... 16 7.1 Exceptions to the Standard ............................................................................................... 16 7.2 Exceptions to the Quality Assurance System .................................................................... 16 References .............................................................................................................................. 16 Appendix A. Calibration Sheets ............................................................................................... 17 Appendix B. American Wind Energy Association Standard Acoustic Analysis .......................... 37 Appendix C Uncertainty Assumptions ..................................................................................... 38 Appendix D. Pictures .............................................................................................................. 39

List of Figures Figure 1. Pika T701 wind turbine at High Plains Test Center....................................................... 6 Figure 2. Wiring diagram of turbine and inverter installation …………………………………………………. 6 Figure 3. High Plains SWTC wind rose for May 2014-May 2015 ………………………………………………. 7 Figure 4. Aerial view of the Pika T701 turbine and met tower at the HP test site ...................... 8 Figure 5. Measured and binned sound pressure levels as a function of the standardized wind speed 11 Figure 6. Hub-height sound power levels as a function of the standardized wind speed .......... 12 Figure 7. One-third octave levels (dB) vs frequency ................................................................... 15 Figure 8. Classification of spectral lines for tone Figure 9. Classification of spectral lines for tone Figure A1. Calibration sheet for the primary anemometer, p 1 of 2 ........................................... 17 Figure A2. Calibration sheet for the primary anemometer, p 2 of 2 ........................................... 18 Figure A3. Calibration sheet for the secondary anemometer, p 1 of 1 ....................................... 19 Figure A4. Manufacturer specification sheet for the wind vane, p 1 of 2 ................................... 20 Figure A5. Manufacturer specification sheet for the wind vane, p 2 of 2 ………………………………… 21 Figure A6. Manufacturer specification sheet for the temperature probe, p 1 of 2 ..................... 22 Figure A7. Manufacturer specification sheet for the temperature probe, p 2 of 2...................... 23 Figure A8. Calibration sheet for the pressure transducer ........................................................... 24 Figure A9. Calibration sheet for the power transducer, p 1 of 3................................................. 25 Figure A10. Calibration sheet for the power transducer, p 2 of 3................................................. 26 Figure A11. Calibration sheet for the power transducer, p 3 of 3................................................. 27 Figure A12. Voltage module (temperature & pressure), mfger calibration certificate pg 1 of 1 .. 28 Figure A13. Current module (for power transducer) mfger calibration certificate pg 1 of 1 …….. 29

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Figure A14. NI 9421 digital input module (for both anemometers) mfger data sheet pg 1 of 9 . 30 Figure A15. Calibration sheet for the NoiseLab Sound Measuring System, p 1 of 2 .................... 31 Figure A16. Calibration sheet for the NoiseLab Sound Measuring System, p 1 of 2 .................... 32 Figure A17. Calibration sheet for the NoiseLab Microphone Unit, p 1 of 2 ..………….................... 33 Figure A18. Calibration sheet for the NoiseLab Microphone Unit, p 2 of 2 ..………….................... 34 Figure A19. Calibration sheet for the NoiseLab Acoustical Calibrator p 1 of 2 .………………………… 35 Figure A20. Calibration sheet for the NoiseLab Acoustical Calibrator p 2 of 2 ………………………… 36 Figure D1. Picture of the sound board during the test, 12 March, 2015 …………………………………… 39 Figure D2. The test turbine viewed from the reference microphone position, 12 March 2015 .. 40 Figure D3. Test turbine viewed from the met mast, 12 March, 2015 ………………………………………. 41 Figure D4. Picture of the sound board during the test, 30 March, 2015 …………………………………… 42 Figure D5. The test turbine viewed from the reference microphone position, 30 March 2015 .. 43 Figure D6. Test turbine viewed from the met mast, 30 March, 2015 ………………………………………. 44

List of Tables Table 1. Test Results Summary ..................................................................................................... 4 Table 2. Pika T701 Wind Turbine General Data ............................................................................ 5 Table 3. System wiring summary ……………………………………………………………………………………………… 7 Table 4. Sources of Noise Near the Turbine on 12 March, 2015 .................................................. 8 Table 5. Sources of Noise Near the Turbine on 30 March, 2015 .................................................. 8 Table 6. Equipment Used for Acoustic Test .................................................................................. 9 Table 7. Reference Microphone Positions for Turbine and Background Measurements ............. 10 Table 8. Test Parameters Used in Wind Speed Calculations ......................................................... 11 Table 9. Sound Pressure and Power Levels for Standardized Integer Wind Speeds (6 m/s through 11 m/s) .......................................................................................................... 12 Table 10. One-Third Octave Analysis for Wind Speed Bins 6 Through 8 m/s ................................. 12 Table 11. One-Third Octave Analysis for Wind Speed Bins 9 Through 11 m/s ............................... 13 Table 12. Tonality Results (In dBA) Table 13. Type B Uncertainty Components for Sound Power Levels and Tonality ....................... 15 Table B1. AWEA Rated Sound Level ............................................................................................ 31

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1 Background

The Pika Wind T701 1-kW small wind turbine was tested in accordance with AWEA (American Wind Energy Association) Small Wind Turbine Performance and Safety Standard (AWEA Standard 9.1 – 2009)

and IEC (International Electrotechnical Commission) Standard Wind Turbine Generator Systems - Part 11: Acoustic Noise Measurement Techniques, IEC 61400-11, Edition 2.1, 2006-11. This test report refers to these procedures collectively as the Standard.

Testing of the Pika T701 was conducted under contract as part of NREL’s Regional Test Center (RTC) program.

2 Test Summary

The Pika T701 is a three bladed, Horizontal Axis Wind Turbine. It has a 3.0-meter rotor diameter resulting in a rotor swept area of 7.1 m2. The data presented in this report was collected during acoustic tests conducted at High Plains Small Wind Test Center in Colby, KS. Testing was conducted on 12 March 2015 and 30 March 2015.

This test was conducted in accordance with the International Electrotechnical Commission’s (IEC)

standard, Wind Turbine Generator Systems - Part 11: Acoustic Noise Measurement Techniques, IEC

61400-11, Edition 2.1, 2006-11. The additional requirements of AWEA (American Wind Energy

Association) Small Wind Turbine Performance and Safety Standard (AWEA Standard 9.1 – 2009) were

also considered.

Table 1. Test Results Summary

Standardized wind speed at 10 m height, Vs [m/s] 6 7 8 9 10 11

Power output calculated from power curve {W] 270 443 677 954 1237 1483

Measured pitch angle [°] 0.8 0.8 0.8 0.8 0.8 0.8

Estimated rotor speed [rpm: 42.5 x wind speed] N/A N/A N/A N/A N/A N/A

Apparent sound power level [dBA] 79.0 81.0 82.9 84.0 85.1 87.4

Combined uncertainty in sound power level, UC [dBA] 3.6 2.9 2.2 2.4 2.1 1.9

Frequency band of most prevalent tone [Hertz (Hz)] 500 1000 1000 1000 1000 1000

Tonality, ΔLk [dBA] - - - - - -

Tonal audibility, ΔLa,k [dBA] - - - -

NR The difference between total and background noise was less than 3 dB. According to Section 8.2 of the Standard, the wind turbine noise was

less than the background noise.

3 Test Turbine Configuration The data presented in this report was collected during acoustic tests conducted from 12 March 2015 and 30 March 2015 at the High Plains Regional Test Center (HPRTC) in Colby, Kansas. The Pika Energy T701 model specifications are summarized in Table 2. This turbine will be referred to as the Pika T701 for the rest of this report. A photo of the T701 turbine and met tower is included as Figure 1.

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Table 2. Summary of T701 published specifications. *: rotor diameter was verified manually by

measuring the radius of the rotor when it was on the ground.

Parameter Value Units

Manufacturer and address Pika Energy Inc 35 Bradley Dr Stop 1 Westbrook, ME 04092

Turbine Serial Number T701-00021

Inverter Serial Number X3001-00044

Production Date 2014

Tower Type Tilting Monopole

Tower Height 16.8 m

Hub Height 16.94 m

Blade make, type, serial number Pika Energy, glass-filled polypropylene, no serial number

Turbine Control System Pika Energy proprietary

Turbine Interface Pika Energy Review (via inverter)

Turbine Type Horizontal axis propeller

Number of Blades 3

Rotor Diameter 3.0* m

Rotor Swept Area 7.1 m2

Blade Pitching Fixed, 0.8° at 75% of blade length

11m/s Reference Power (REbus DC) 1.6 kW

11m/s Reference Power (AC after inverter)

1.45 kW

Cut-in Wind Speed 3.3 m/s

Rated Wind Speed 11 m/s

Rated Rotor Speed 420 RPM

Speed Regulation Type Stall regulation w/ redundant mechanical brake

Yaw Control Passive, upwind with tail

IEC Turbine Design Class II

Turbine DC Output Voltage (nominal) 380 V

Turbine Max Output Current 7 A

Inverter Output Voltage 220/240 VAC

Inverter Output Current Max 13 A

Inverter Output Frequency 60 Hz

6

Figure 1. T701 Turbine installed at High Plains Regional Test Center; view west from data shed, met

tower behind turbine.

A one‐line diagram of the installation wiring for the turbine is shown in Figure 2. The Pika T701 was

connected to the Pika X3001 grid-tie inverter via Pika’s REbus DC Microgrid technology (internal to the

inverter in Figure 2) operating at approximately 380VDC, in accordance with the Pika T701 installation

manual. The Pika X3001 was connected to the electric utility at a nominal voltage of 240VAC and

frequency of 60Hz. The inverter electrical connection to the grid was done in accordance with the Pika

X3001 Installation manual. Wiring between the tower top and the inverter were provided by Pika

Energy and installed as part of the turbine system. Specifications for the installed wires from the tower

base control panel to the grid point of common connection (PCC) are listed in Table 3. The total length

of the wire run was approximately 65 meters.

Figure 2. Wiring diagram of turbine and inverter installation

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Table 3. System wiring summary

Segment Type Approx. length

Turbine to tower base junction box AWG-12 Type UF, 2 conductor +

ground 16.9m

Tower base junction box to inverter AWG-12 Type THHN, 2 conductor +

ground 48m, compliant with AWEA minimum 8 rotor diameters

Inverter to subpanel AWG-12 Type NM-B 2m

4 Test Site Description

The test site is located about 1 mile south and two miles west of the town of Colby, KS. It is essentially

flat with no obstructions: no site calibration is needed as per Annexes A and B of the Standard.

Prevailing winds measured at the test site are from the north in winter, south in summer (see wind rose

in Fig. 3); the average wind speed at 30m is over 7 m/s. Figure 4 shows an aerial view of the site,

perimeter outlined in red. Figure 7 shows a plot of the turbines, obstacles and data shed positions to

scale. The turbine is located 122.3m east and 30m north of the SW corner of the site. Other obstacles

on the property include two 3-m tall power poles at (-21.4, 0) and (-13.4, 0), a 3-m tall data shed at (153,

30), the turbine’s own met tower (110, 30) and a second wind turbine 30m tall, D=12.75m with its

associated met tower, (64, 30) and (32, 30) respectively (measurements in meters east and north of the

SW corner.) A dirt road forms the property’s southern border; the other borders are farm implement

tracks.

Exclusion sectors for the Pika T701 are ≥60 to ≤120 degrees East of true North: exclusion for the wake of

the turbine on its own met tower; and ≥238 to ≤301 degrees East of true North: exclusion for

neighboring turbine and associated met, and two power poles on-site. The data shed does not impose

exclusion sectors.

A summary of the test site conditions is listed in Table 6. Note the turbine-to-met-tower distance is 0.3m

greater than the 2-4D standard requirement; see Fig. 12, p. 16, and Deviations and Exceptions, p. 30.

Figure 3. High Plains SWTC wind rose for May 2014-May 2015.

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Figure 4. Aerial view of the Pika T701 and its met tower at the test site. Red circle: Pika met. Green circle: Pika tower. Blue boxes: data shed and transformer pad. Green arrow from turbine to data shed: 30.5m. From met to turbine: 12.3m center-to-center.

Table 4. Sources of Noise Near the Turbine: Data collected 12 March 2015

Designation Bearing from Sound Meas. Board

Distance from Sound Meas. Board

Height Width

[° True] [m] [m] [m]

Prevailing Wind Direction 210 NA NA NA

Met Tower 242 22.6 16.9 0.32

Data Shed 104 27.7 3.6 3.1

Neighboring Turbine 279 64.9 30.48 0.5

Neighboring Met Tower (guyed tower)

282 96.9 30.48 0.2

Table 5. Sources of Noise Near the Turbine: Data collected 30 March 2015

Designation Bearing from Sound Meas. Board

Distance from Sound Meas. Board

Height Width

[° True] [m] [m] [m]

Prevailing Wind Direction 322 NA NA NA

Met Tower 315 21.9 16.9 0.32

Data Shed 52 28.7 3.6 3.1

Neighboring Turbine 295 64.3 30.48 0.5

Neighboring Met Tower (guyed tower)

291 95.7 30.48 0.2

9

5 Test Equipment 5.1 Equipment Descriptions

All test equipment is listed in Table 6 and was calibrated except the temperature sensor (see Exceptions); calibration sheets are included in Appendix A. Table 4 shows the equipment used and calibration due dates. Figure 8 shows placement of the meteorological instruments on the met mast (note that the pressure transducer is located near the base of the met mast). The temperature probe on the met mast employs a radiation shield.

Acoustic data was collected and partly analyzed using NoiseLAB 3.0.16 with a patch upgrade to 3.0.17. Further analysis was conducted using NoiseLAB Batch Processor 3.1.0. The microphone system was calibrated prior and subsequent to each data collection session using a calibrator that conforms to IEC 60942 Class I.

The meteorological Data Acquisition System is comprised of National Instruments modules and LabVIEW programming. The National Instruments cards and chassis were located in the site’s data shed, as was the computer running LabVIEW.

End‐to‐end checks were conducted on all non‐acoustic data channels and results are reported in the turbine commissioning report. The acoustic data collection system was calibrated at the start of each measurement period. All measurement periods were an average of approximately 25 minutes with either the turbine operating or not operating (for background noise measurements). The longest measurement period was approximately 85 minutes with all turbines on the site parked for collection of background data.

Table 6. Equipment Used for Acoustic Test

Channel Instrument Make & Model Mfger Accuracy Calibration

Dates

Primary wind speed

Anemometer NRG 1

st Class

Ser #596700001838 +/-0.06 m/s @

10m/s 3 Dec, 2013

Turbine power output

AC Watt transducer Ohio Semitronics PC5-059EY25

Ser #11110431 +/-0.5% of full

scale 23 Oct, 2013

Wind direction Wind Vane NRG #200P 1% N/A

Turbine Status Internal to Pika Inverter Download from Pika web

server

Reference wind speed

Anemometer NRG #40H: Ser. # 17970000907 1.48% 3 Dec, 2013

Air Pressure Pressure sensor NRG BP20: Ser. #180512465 +/- 0.218 kPa 15 Nov, 2010

Air Temperature Temperature sensor NRG #110S: Ser. #3365 +/- 1.1 °C max

Rain Wetness sensor Novalynx 260-2590

Rotor speed Not available Not available

N/A

Microphone BSWA Tech

Model MPA 211: #451053 1 Jan, 2014

Microphone Unit Bruel & Kjaer Type 4189‐A‐021 1 Jan, 2014

Acoustic Calibrator BSAW CA111: #470128 1 Jan, 2014

DAS NI‐9205 (voltage: WS channel) 3,230 μV 28 Oct., 2013

10

DAS NI‐9203 +/-0.18% slope +/-0.06% offset

28 Oct., 2013

DAS NI‐9421 digital negligible

5.2 Instrument Locations The primary anemometer on the meteorological tower was used to derive the standardized wind speed. This tower was located 12.3 m from the test turbine, at a bearing of 270°E of true north, with the anemometer at a height of 16.9 m. The wind vane was mounted at a height of 11.35 m on the meteorological tower. The turbine tower center was 4.1 rotor diameters from the meteorological tower center, 0.3m greater than the 2-4D standard requirement; see Deviations and Exceptions. Table 7 provides the location of the microphone for the measurement sessions. Table 7. Reference Microphone Positions for Turbine and Background Measurements on 12 March,

2015 and 30 March, 2015

Reference Location (H+D/2)

Minimum distance

Maximum distance

Actual Microphone

Location

Allowable Measurement

Tolerance

[m] [m] [m] [m] [m]

18.440 14.752 22.128 14.935 ±0.4

6. Results 6.1 Test Conditions

The analysis was done using the measured wind speed and 10-second averages of the data. The range of standardized wind speeds and wind directions used for the analysis were 4.5 to 12.5 m/s and 195° to 337° east of true north, respectively. The range of temperature and pressure were 16.5°C to 27.3°C and 91.1 kPa to 94.5 kPa, respectively.

6.2 Standardized Wind Speed Calculation Standardized wind speed, Vs, was calculated using Equation 1 below (eq. 7 in the Standard) and the

values in Table 8, where Vz is the measured wind speed.

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Table 8. Test Parameters Used in Wind Speed Calculations

Parameter Symbol Value

Hub height (m) H 16.9

Roughness length (m) z0 0.05

Anemometer height (m) z 16.9

Reference roughness length (m) z0ref 0.05

Reference height (m) zref 10.0

6.3 Apparent Sound Power Level

Sound pressure levels were binned by wind speed. Integer wind speeds values were calculated using

interpolation between bins and extrapolation at the ends. The sound pressure levels were then

background-corrected according to the Standard. Figure 3 shows the scatter plot of the sound pressure

levels of the validated total (operating plus background) and background noise, along with the binned

sound pressure levels. The measured and background corrected apparent sound pressure level at

standardized wind speeds of 6 through 11 m/s are shown in Table 9, along with the calculated sound

power levels. Figure 4 shows the sound power levels graphed against the standardized wind speed.

Figure 5. Measured and binned sound pressure levels as a function of the standardized wind speed

30

35

40

45

50

55

60

4 5 6 7 8 9 10 11 12

Sou

nd

Pre

ssu

re L

eve

l dB

A

Standardized Wind Speed m/s

Measured Sound Pressure Level vs. Wind Speed

Turbine Data

Background Data

Binned BG corrected Total

Binned Total

Binned Background

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Table 9. Sound Pressure and Power Levels for Standardized Integer Wind Speeds (6 -11 m/s)

Wind

Speed

Bin

[m/s]

Total

Sound

Pressure

Level

[dBA)]

Background

Sound Pressure

Level

[dBA]

Background

Corrected

Sound Pressure

Level

[dBA]

Sound

Power

Level

[dBA]

Type A

Uncert.

[dBA]

Type B

Uncert.

[dBA]

Combined

Uncert.

[dBA]

6 47.3 36.5 46.9 79.0 3.5 1.1 3.6

7 49.4 40.0 48.9 81.0 2.7 1.1 2.9

8 51.2 40.6 50.8 82.9 2.0 1.0 2.2

9 52.7 45.0 51.9 84.0 2.1 1.2 2.4

10 54.1 47.3 53.1 85.1 1.6 1.4 2.1

11 56.0 47.7 55.3 87.4 1.4 1.3 1.9

Figure 6. Hub-height sound power levels as a function of the standardized wind speed, with

uncertainty.

6.4 One-Third Octave Analysis One-third octave levels were analyzed at standardized wind speeds of 6, 7, 8, 9, 10, and 11 m/s. The

results are provided in Tables 10 and 11, and Figure 5.

Table 10. One-Third Octave Analysis for Wind Speed Bins 6 Through 8 m/s

Center

Frequency

6 m/s One-Third

Octave Levels

7 m/s One-Third

Octave Levels

8 m/s One-Third

Octave Levels

[Hz] [dBA] [dBA] [dBA]

20 NR NR NR

25 NR NR NR

31.5 NR NR NR

70

72

74

76

78

80

82

84

86

88

90

4 5 6 7 8 9 10 11 12

sou

nd

po

we

r le

vel d

BA

standardized wind speed m/s

Sound Power Level

13

40 NR NR NR

50 NR NR NR

63 NR 27.4±2.6* NR

80 24.4±2.4* NR NR

100 26.2±2.4 28.8±2.1* 29.1±2.0*

125 28.7±2.4 31.9* 33.3±1.9

160 34.7±2.8 NR 30.1±2.1*

200 35.2±2.7 30.6* 37.2±2.3

250 35.6±2.3 NR 37.4±2.1

315 35.2±2.3 36.5±2.1* 35.3±2.0*

400 35.7±2.1 37.6±2.0 38.3±1.9

500 41.2±2.6 41.5±1.9 39.0±2.0

630 39.8±2.2 40.6±1.9 39.1±1.9

800 39.3±2.0 39.8±1.9 40.7±1.9

1000 40.5±2.0 42.2±1.9 43.8±1.9

1250 39.8±2.0 41.3±1.9 43.0±1.9

1600 38.4±2.1 39.2±1.9 41.1±1.9

2000 37.4±2.1 38.7±1.9 40.7±1.9

2500 37.5±2.1 39.7±1.9 41.5±1.9

3150 33.9±2.2 35.2±1.9 36.8±1.9

4000 30.8±2.1 31.0±2.0* 33.4±2.0

5000 27.4±2.1* 28.9±2.0* 30.6±2.1*

6300 25.7±2.0* NR 28.4±2.0*

8000 NR NR NR

10000 NR NR NR

* The difference between total and background noise was less than 6 dB but greater than 3 dB. A standard background correction of 1.3 dB was

applied according to Section 8.2 of the Standard.



Table 11. One-Third Octave Analysis for Wind Speed Bins 9 Through 11 m/s

Center

Frequency

9 m/s One-Third

Octave Levels

10 m/s One-Third

Octave Levels

11 m/s One-Third

Octave Levels

[Hz] [dBA] [dBA] [dBA]

20 NA 16.5±2.1* 20.1±2.3*

25 NA 20.0±2.2* 24.0±2.3

31.5 NA 22.3±2.1* 25.9±2.3*

40 NA NA 27.9±2.3*

50 NA NA 29.1±2.3*

63 NA NA NA

80 NA NA NA

100 NA NA NA

125 NA NA NA

160 NA NA NA

14

200 NA NA NA

250 NA NA NA

315 NA NA NA

400 32.6±3.2 NA 42.2±2.3*

500 37.2±2.2 NA 41.8±2.1*

630 39.9±2.0 41.7±2.0 44.9±2.1

800 41.9±1.9 43.9±2.0 46.7±2.0

1000 45.1±1.9 46.6±1.9 48.6±2.0

1250 44.4±1.9 46.0±1.9 47.4±1.9

1600 42.4±1.9 43.7±1.9 44.6±1.9

2000 42.0±1.9 43.2±1.9 43.9±1.9

2500 42.3±1.9 43.1±1.9 43.3±1.9

3150 37.3±1.9 37.8±1.9 38.3±2.0

4000 34.1±2.0* 35.1±2.0* 36.3±2.0*

5000 NA NA NA

6300 NA NA NA

8000 NA NA NA

10000 NA NA NA * The difference between total and background noise was less than 6 dB but greater than 3 dB. A standard background correction of 1.3 dB was

applied according to Section 8.2 of the Standard.



Figure 7. Bar graph: 1/3-octave levels (dB) vs frequency

0

10

20

30

40

50

60

20

Hz

25

Hz

31

.5 H

z

40

Hz

50

Hz

63

Hz

80

Hz

10

0 H

z

12

5 H

z

16

0 H

z

20

0 H

z

25

0 H

z

31

5 H

z

40

0 H

z

50

0 H

z

63

0 H

z

80

0 H

z

10

00

Hz

12

50

Hz

16

00

Hz

20

00

Hz

25

00

Hz

31

50

Hz

40

00

Hz

50

00

Hz

63

00

Hz

80

00

Hz

10

00

0 H

z

Sou

nd

Pre

ssu

re L

eve

l (d

BA

)

frequency (Hz)

5 m/s

6 m/s

7 m/s

8 m/s

9 m/s

10 m/s

11 m/s

15

6.5 Tonality

During observation of the turbine in all wind speeds, no prominent tones or changes in sound were

noticed. The turbine does not furl or adjust blade pitch, so no physical changes at higher wind

speed would cause a change in associated noise. While it whirrs more loudly at high wind speed,

the turbine does not make sounds markedly different at any particular wind speed or range of wind

speeds. The tonality analysis resulted in reportable tones for xx m/s, as shown in Table 12.

Figure 6. Classification of spectral lines for the 3,849 Hz tone (typical in the 10 m/s bin)

Figure 7. Classification of spectral lines for the 3,921 Hz tone (typical in the 11 m/s bin)

6.6 Uncertainty

The type A uncertainties for sound power levels, one-third octave levels, and tonality were calculated using the methods prescribed in the Standard. The type B uncertainty components are shown in Table 13.

Table 13. Type B Uncertainty Components for Sound Power Levels and Tonality

Var Description

Type B

Uncertainty for

Sound Power

Level (SPL)

dBA

Type B

Uncertainty for

1/3 Octave

Levels (TOB)

dBA

Type B

Uncertainty

for Tonality

dBA

Comment

UB1 Calibration 0.25 0.25 0.25 Assumption; some instruments out

of cal so used high value

UB2 Instrument 0.2 0.2 0.2 Assumption, used typical value

UB3 Board 1.7 1.7 1.7 The board was placed well and

used the typical value

UB4 Distance 0.1 0.1 0.1 Assumption, used typical value

UB5 Impedance 0.2 0.2 0.2 Assumption, used typical value

UB6 Turbulence 0.6 0.6 0.6 Assumption, used typical value

UB7 Wind speed,

measured

Varies with

wind speed

Varies with wind

speed

Varies with

wind speed

Calculated per IEC 61400-12-1 Ed.

1.0, 205-12, and converted to dBA

for SPL and TOB.

Typical value for tonality

UB8 Direction 0.3 0.3 0.3 Assumption, used typical value

UB9 Background Varies with

wind speed

Varies with wind

speed and one-

third octave center

frequency bin

Varies by

tone

Difference between measured bin

center SPL and background-

corrected bin center SPL

16

7 Exceptions

7.1 Exceptions to the Standard

The analysis prescribed in the standard was altered for the small wind turbine by using 10-second averages instead of 1-minute averages to better characterize the dynamic nature of this turbine. In addition, binning by wind speed was used instead of regression analysis, and the integer values were calculated by interpolating between bins and extrapolating at the ends.

7.2 Exceptions to the Quality Assurance System The primary anemometer and data acquisition modules were used past the calibration due dates. The instruments and modules were post-test calibrated. The anemometer and modules were found to be within tolerances.

References International Electrotechnical Commission (IEC). (2006). Wind Turbine Generator Systems – Part 11 Acoustic Noise Measurement Techniques, IEC 61400-11, Ed 2.1, 2006-11, Geneva, Switzerland.

17

Appendix A - Calibration Data Sheets for Pika T701 Test Instruments

Primary Anemometer – Pre-Test Calibration

Figure A1. Primary anemometer manufacturer calibration sheet pg 1 of 2.

18

Figure A2. Primary anemometer manufacturer calibration sheet pg 2 of 2.

19

Secondary Anemometer

Figure A3. Secondary anemometer 3rd-party calibration sheet pg 1 of 1.

20

Wind Direction Vane

Figure A4. Wind direction vane manufacturer specification sheet pg 1 of 2.

21

Figure A5. Wind direction vane manufacturer specification sheet pg 2 of 2.

22

Temperature Probe

Figure A6. Temperature probe manufacturer specification sheet pg 1 of 2.

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Figure A7. Temperature probe manufacturer specification sheet pg 2 of 2.

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Pressure Transducer

Figure A8. Pressure transducer manufacturer calibration sheet pg 1 of 1.

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Power Transducer

Figure A9. Power transducer manufacturer calibration sheet pg 1 of 3.

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DAS Boards

Figure A12. Voltage module (for temperature & pressure), manufacturer calibration certificate pg 1 of 1.

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Figure A13. Current module (for power transducer) manufacturer calibration certificate pg 1 of 1.

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Figure A14. NI 9421 digital input module (for both anemometers) manufacturer data sheet pg 1 of

9. Remaining pages available on request.

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Figure A15. Calibration certificate for NoiseLab Sound Measuring System p 1 of 2.

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Figure A16. Calibration certificate for NoiseLab Sound Measuring System p 2 of 2.

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Figure A17. Calibration certificate for NoiseLab Microphone Unit p 1 of 2.

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Figure A18. Calibration certificate for NoiseLab Microphone Unit p 2 of 2.

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Figure A19. Calibration certificate for NoiseLab Acoustical Calibrator p 1 of 2.

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Figure A20. Calibration certificate for NoiseLab Acoustical Calibrator p 2 of 2.

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Appendix B. American Wind Energy Association Standard Acoustic Analysis The American Wind Energy Association (AWEA) standard requires that the wind turbine sound levels be measured and reported in accordance with the IEC 61400-11 standard, and includes the following modifications:

• Using a 10-second averaging period

• Using the measured wind speed

• Using the method of bins

• Covering a wide wind speed range as possible

• Describing any obvious changes in sound at high wind speeds

• Reporting the AWEA Rated Sound Level. The data were collected at one-second intervals and averaged by the data acquisition systems (NoiseLab for acoustic measurements and the Labview VI for all other measurements) to 10-second intervals. To ensure that the acoustic data were collected downwind from the turbine, the wind direction was filtered to assure that the measurement board was within 15 degrees of the downwind position. The data were also filtered by the provided status to determine the total (operating plus background), background, and interrupted/excluded data. The data were binned by the standardized wind speed into 1m/s wind speed bins centered on the integer wind speed. The bin centers were calculated by interpolation (and extrapolation at the ends). The AWEA Rated Sound Level is defined as: the sound level that will not be exceeded 95% of the time (assuming an average wind speed of 5 m/s); a Rayleigh wind speed distribution; 100% availability; and an observer location that is 60 m from the rotor center. This requirement defines the AWEA wind speed to be 9.8 m/s at hub height. The total and background noise for 9.8 m/s were obtained by interpolation between the 9 and 10 m/s binned values. The two values are used to obtain the background corrected sound pressure level. Next, the sound power level is calculated at the hub by adding a correction for hub height. The AWEA Rated Sound Level is then calculated by subtracting the 60-m distance correction:

𝐿𝐴𝑊𝐸𝐴 = 𝐿9.8𝑚 + 10 ∗ log (4 ∗ 𝜋 ∗ 22.592) − 10 ∗ log (4 ∗ 𝜋 ∗ 602) where L9.8m is the background-corrected sound pressure level at the microphone at 9.8 m/s hub-height wind speed, 22.59m is the slant distance in meters from the hub to the ground, and the reference cross-sectional area of the sound pressure is 1m2. Hub height being 16.94m and microphone distance 14.94m, the slant distance 22.59m = √(16.922+14.942). Table B1. AWEA Rated Sound Level

AWEA Rated Sound Level

dBA

Combined

Uncertainty

dBA

38.3 2.2

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Appendix C. Uncertainty Calculations

Type B uncertainty values are described in Section 6; UB7a, the wind speed uncertainty, is further

described below. Type A uncertainty was calculated thus: the deviation of sound pressure level of each

measurement point from the average sound pressure level within its 1-m/s wind speed bin was squared,

and these numbers were summed within each wind speed bin. The square root of the sum divided by

the number of data points less two is equal to the type A error:

𝑈𝐴 = √(∑(𝑆𝑃𝐿𝑎𝑣𝑔 − 𝑆𝑃𝐿𝑚𝑒𝑎𝑠)2/(𝑁 − 2) . The same formula was used for 1/3-octave

uncertainty.

The wind speed uncertainty was calculated using the same formula used for this uncertainty in the

power performance report. The values below are: n= wind speed bin; 0.0693 + 0.00693U = operational

characteristic error. Calibration and mounting effects are each 0.01; terrain effect is 0.02, and error

from the digital data acquisition system is assumed negligible. All these errors are squared and summed;

the square root of the result is multiplied by the sensitivity factor which is the difference in sound

pressure levels between adjacent wind speed bins divided by the difference in wind speeds.

𝑈𝐵7𝑎

= √0.06932 + 2 × 0.0693 × 0.006932 × 𝑈(𝑛) + (0.01482 + 0.006932 + 0.012 + 0.022) × 𝑈(𝑛)2

× |𝑆𝑃𝐿(𝑛) − 𝑆𝑃𝐿(𝑛 − 1)

𝑈(𝑛) − 𝑈(𝑛 − 1)|

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Appendix D. Pictures

Figure D1. Picture of the sound board during the test 12 March, 2015

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Figure D2. The test turbine as viewed from the reference microphone position 12 March 2015

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Figure D3. The test turbine as viewed from the meteorological mast 12 March 2015

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Figure D4. Picture of the sound board during the test 30 March, 2015

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Figure D5. The test turbine as viewed from the reference microphone position 30 March 2015; met

mast to left.

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Figure D6. The test turbine as viewed from the meteorological mast 30 March 2015

wind turbine generator system pika t701 acoustic test report · scale. the turbine is located...

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