3933 US Route 11 Cortland, NY 13045 Telephone: (607) 753-6711 Facsimile: (607) 753-1045 www.intertek.com Intertek Project No. G100413407 Mr. Steve Turek Phone: 952-447-6064 Wind Turbine Industries, Corporation Fax: 952-447-6050 16801 Industrial Cir SE email: steveturek@windturbine.net Prior Lake, MN 55372-3307 Subject: Acoustic noise emission test report for the Wind Turbine Industries Corporation (WTIC) Jacobs 31-20 Wind Energy System tested at the Intertek Small Wind Regional Test Center (RTC). Dear Ms. Huskey, This Test Report represents the results of the evaluation and tests of the above referenced equipment under Intertek Project No. G100413407, as part of the US Department of Energy and National Renewable Energy Laboratory (DOE/NREL) Subcontract Agreement No. AEE 0-40878-02, to the requirements contained in the following standard: AWEA 9.1 Small Wind Turbine Performance and Safety Standard December 2009 This investigation was authorized through signed Intertek Quote no. 500304911, dated May 13 th, 2011. A production sample was installed at the Intertek RTC on October 25 th, 2011. Acoustic noise measurements were taken on two separate days in early November, 2011, and analysis took place in the months of February and March of 2012. This Test Report completes the acoustic testing phase of the Jacobs 31-20 Wind Energy System under Intertek Project No. G100413407. If there are any questions regarding the results contained in this report, or any of the other services offered by Intertek, please do not hesitate to contact the signatories on this report. Please note, this Test Report on its own does not represent authorization for the use of any Intertek certification marks. Completed test reports for duration, power performance, and strength and safety are required to complete the AWEA certification process. Completed by: Joseph M Spossey Reviewed by: Tom Buchal Title: Project Engineer Title: Senior Staff Engineer Signature: Signature Page 1 of 41 This report is for the exclusive use of Intertek s Client and is provided pursuant to the agreement between Intertek and its Client. Intertek s responsibility and liability are limited to the terms and conditions of the agreement. Intertek assumes no liability to any party, other than to the Client in accordance with the agreement, for any loss, expense or damage occasioned by the use of this report. Only the Client is authorized to permit copying or distribution of this report and then only in its entirety. Any use of the Intertek name or one of its marks for the sale or advertisement of the tested material, product or service must first be approved in writing by Intertek. The observations and test results in this report are relevant only the sample tested. This report by itself does not imply that the material, product or service is or has ever been under an Intertek certification program.
Wind Turbine Generator System Acoustic Noise Emissions Test Report for the WTIC Jacobs 31-20 Wind Energy System tested at Intertek Small Wind Regional Test Center Page 2 of 41
1.0 Background This test is conducted as part of the DOE/NREL Subcontract Agreement No. AEE-0-40878-02 for the testing of small wind turbines at regional test centers. The WTIC Jacobs 31-20 Wind Energy System was accepted into this program by Intertek and DOE/NREL. The full scope of type testing and AWEA Certification provided by Intertek for the Jacobs 31-20 horizontal-axis wind turbine is covered by this agreement. This test report is a summary of the results of acoustic noise emission testing, and is one of four tests to be performed on the Jacobs 31-20 turbine; the other three being duration, safety and function, and power performance. Results for these other tests are summarized in their respective Test Reports. The Jacobs 31-20 turbine is installed at Test Station #5 at the Intertek RTC in Otisco, NY. The Jacobs 31-20 is designed for grid-connected power delivery, with a maximum power output of 20 kw. It is designed as a Class II upwind turbine, with speed and power control through side furling and a centrifugal variable pitch governor. The blades of the Jacobs 31-20 drive the low speed shaft of an offset hypoid gearbox with 6.1:1 ratio. The gearbox high-speed shaft drives a brushless three-phase AC synchronous generator with outbound exciter. The generator is rated for 40-180 VAC operation up to 25 kva. Grid interconnect is provided by a Nexus Nex20 inverter, which fully converts the generator output to single phase 240 VAC for connection to a single/split phase grid. The Nex20 inverter is specifically designed for the Jacobs 31-20 Wind Energy System. The test tower and foundation were designed and approved by ROHN Products LLC. NYS Professional Engineer stamped tower and foundation designs were also provided by ROHN Products LLC. The designs were based off of the Subsurface Investigation and Geotechnical Evaluation detailed in Atlantic Testing Laboratories report number CD3119E-01-05-10 for the Intertek RTC. The electrical network at the testing location is single/split phase 120/240 VAC at 60 Hz. Refer to the wiring diagrams in Appendix A. A summary of the test turbine configuration and manufacturer s declared ratings can be found in Table 1 below. Wiring diagrams of the Jacobs 31-20 as installed at the Intertek RTC can be found in Appendix B. 2.0 Test Objective The purpose of the acoustic test is to characterize the noise emissions of the Jacobs 31-20 turbine. This involves using measurement methods appropriate to the noise emission assessment at locations close to the turbine, in order to avoid errors due to sound propagation, but far enough away to allow for the finite source size. The evaluation herein characterizes the wind turbine noise with respect to a range of wind speeds and directions. Characterizations of the turbines apparent sound power level, 1/3 octave bands, and tonality are made. 3.0 Test Summary This test was conducted in accordance with the first edition of the American Wind Energy Association 9.1 Small Wind Turbine Performance and Safety Standard, dated December 2009. Hereafter, this testing standard and its procedures are referred to as the Standard. Figure 1 is the summary of results from the acoustic noise test conducted on the Jacobs 31-20 turbine. In Figure 1, wind speed is standardized to reference conditions at 10 m above ground level and a roughness length of 0.05 m. The AWEA Rated Sound Level is the level that will not be exceeded 95% of the time, assuming an average wind speed of 5 m/s (11.2 mph), a Rayleigh wind speed distribution, 100% availability, and an observer location 60 m (~200 ft) from the rotor center. The amount of test data analyzed to produce Figure 1 is sufficient to meet the database requirements of the Standards. Table 1 identifies the configuration of the wind turbine system tested for the purpose of this test report. Page 3 of 41
Figure 1 Acoustic noise test results summary Page 4 of 41
Wind Turbine Industries, Corporation Turbine manufacturer and address 16801 Industrial Circle S.E. Prior lake, Minnesota 55372 Model 31-20 Wind Turbine Industries, Corporation Gearbox manufacturer Model: 20kW, Part Number: 60717-900 Serial Number: 03150030 Offset hypoid design Gearbox specifications 6.1:1 gear ratio Winco Inc; Model 20PS4G-27 Generator manufacturer WTIC Part Number: 395358-000 Serial #: W2148 Generator specifications 20 kw, 40-180 VAC, 0-40 Hz, 3-phase, 450-1050 RPM Nexus Inverter manufacturer Model #: NEX20 Serial #: 100 Inverter specifications 20 kw, 240 VAC, 60 Hz, TUV listed - UL 1741 Rotor diameter 9.4 m (31.0 ft.) diameter verified by Intertek Hub height 35.9 m (117.0 ft 8.0 in.) Swept area 70.1 m 2 (755.0 ft 2 ) IEC 61400-2 SWT Class (I, II, III, or IV) II Tower type(s) Lattice Rated electrical power 20.0 kw Cut-in wind speed 4.5 m/s (10.1 mph) Rated wind speed 11.6 m/s (26.0 mph) Survival wind speed 53.6 m/s (120.0 mph) Rotor speed range 175 185 rpm Fixed or variable pitch Variable Number of blades 3 Blade tip pitch angle 1 Advanced Aero Technologies. Inc Blade manufacturer Fiberglass SNs - 310020CGA1849, 310020CGA1854, 310020CGA1852 Proprietary System, Horner Display unit HON:1.13, Oztek Control Control system software Board DSP:1.03 Table 1 Test turbine configuration 4.0 Engineering Judgments or Deviations No judgments, deviations, or exceptions to the AWEA 9.1 Standard were taken for purposes of this test report. Page 5 of 41
5.0 Test Site Description The RTC has class IV winds, and can accommodate turbines that produce 120V or 240V, 60 Hz power. It is on a hilltop, with previous agricultural land use, near the township of Otisco, NY. It was surveyed, analyzed and developed to be a test site for Intertek s customers. The Jacobs 31-20 is installed and tested at RTC test station #5, which has no prominent obstructions to the east, south, or west as determined by obstacle assessment in accordance with the first edition of IEC 61400-12-1 Wind Turbines Part 12-1: Power performance measurements of electricity producing wind turbines, dated December 2005. The roughness length of the test location is estimated at 0.05 meters for farmland with some vegetation. This value is given in Table 1 of IEC 61400-11. The meteorological equipment tower is due south 23.6 m (77.5 feet) from the turbine, exactly 2.5 times the diameter of the rotor, as recommended in the Standard. All buildings and potential obstacles were identified and defined in the topographical survey, and were considered during obstacle assessment prior to commencement of testing. Figure 2 below shows the layout of the RTC and identifies the test location of the Jacobs 31-20 and its meteorological tower (Met5) in the red box. The elevation data points are given in feet above sea-level, and are plotted in 10 meter intervals. Figure 2 - Intertek RTC topographical survey and WTIC Jacobs 31-20 turbine test location Page 6 of 41
Figure 3 below shows a zoomed view of the turbine and meteorological tower locations. Figure 3 Jacobs 31-20 turbine and Met5 location The Jacobs 31-20 turbine was the only turbine installed at the RTC during the measurement period; therefore no turbines were in operation during the measurement program. The only noise source identified during the measurement period was the interstate that runs north-south in the valley approximately 2.5 miles to the east of the test site. The background noise generated is consistent in all recordings and has no effect on turbine noise data as it is removed in background correction in accordance with the Standard. Page 7 of 41
6.0 Test Equipment The test equipment utilized during the acoustic noise measurement program can be found in Appendix A. The meteorological equipment utilized during this test program is in compliance with the equipment requirements specified within the Standard. Figure 4 displays the arrangement of the meteorological tower with dimensions of instrument locations. The height above ground level to the centerline of the cups of the primary anemometer of 35.87 meters is the same height above ground level as the hub height of the Jacobs 31-20. The reference anemometer and the wind vane are installed at the same height of 33.87 m, and the temperature and pressure sensors are installed at the same height of 21.5 m. Calibration certificates of acoustical equipment used during testing can be found in Appendix D, the calibrations of meteorological equipment are maintained in the Intertek project file and displayed in the Power Performance Test Report. Figure 4 Instrument locations on the meteorological mast Page 8 of 41
7.0 Test Procedure 7.1 General The general method applied during this test program follows the method described in IEC 61400-11, with modifications as described in AWEA 9.1. The main purpose of the test procedure is to provide the apparent A- weighted sound power levels and one-third octave spectra over the typical range of wind speeds that the Jacobs 31-20 is expected to be exposed to. Correction to reference conditions was carried out per the requirements of the Standard. Acoustic noise data was gathered on two separate days in the month of November 2011. On both days, winds were primarily out of the west-southwest, ranging from 240 to 280 with respect to true North. Meteo rological and wind turbine data has been gathered continuously since commissioning of the Jacobs 31-20 on November 1st, 2011. The anemometer for wind speed measurement was located at 35.87 m (117 8 ) above ground level; which is the same height above ground level of the hub height of the turbine. Table 3 below shows the date, time, microphone location, and allowable wind sector for each day acoustic measurements were taken. Date Start End Microphone Allowable Horizontal Distance Time Time Location Sector 03-Nov-11 12:30:00 14:30:00 75 43.9 m (146 feet) 2 40 to 270 11-Nov-11 11:30:00 13:45:00 85 43.9 m (146 feet) 2 50 to 280 Table 3 Acoustic measurement information 7.2 Measurements and procedures 7.2.1 Measurement positions In order to fully characterize the noise emissions of the Jacobs 31-20, the following measurement positions are required. 7.2.1.1 Acoustic measurement position Only the required reference microphone location, as defined in Figure 5 below, is used for the acoustic measurement location. The direction of the position is accurate within ±15 relative to the wind direction at the time of measurement. The horizontal distance from the wind turbine tower vertical centerline to the reference microphone position, R 0, was determined using Equation 1 below. In Equation 1, D is the diameter of the turbine and H is the hub height of the turbine. Using the specified tolerance of 20%, this requires the reference microphone location to be within the range of 32.5 m to 48.7 m (106.5 ft to 159.8 ft). Equation 1 Calculating R 0 according to Equation 1 results in a length of 40.6 m (133.17 ft). At 40.6 m the inclination angle φ was greater than 40, and thus outside of the requi red range of 25 to 40. In order to obtain an inc lination angle of 39 a reference microphone distance of 146 feet was needed. This value is within the allowable range mentioned above. To minimize influence due to the edges of the reflecting board on the measurement results, the board was positioned flat on the ground. The edges and gaps under the board were leveled out by means of sand. Page 9 of 41
Figure 5 Standard pattern for microphone measurement positions (plan view) Source: IEC 61400-11: Edition 2.1, November 2006 7.2.1.2 Wind speed and direction measurement position The test anemometer and wind direction transducer are the same instruments mounted on the permanent meteorological mast for power performance testing according to the first edition of IEC 61400-12-1 Wind turbines Part 12-1: Power performance measurements of electricity producing wind turbines, dated December 2005. The location of the instrumentation on the permanent meteorological tower is shown in Section 6 above. The sensors are installed at locations that are compliant with the requirements of the Standards. Wind speed is measured directly by the primary anemometer on the permanent meteorological tower, as it is the primary method for wind speed data collection of the Standard. Figure 6 and equation 2 below were used to determine the acceptability of the permanent meteorological tower location. Given that the anemometer is mounted at the same hub height as the turbine, the angle β as defined in Figure 6 is 90. During the measurement periods identified in Table 3, the anemometer was not in the wake of any portion of any other wind turbine or structure. Page 10 of 41
Figure 6 Allowable region for meteorological mast position as a function of β (plan view) Source: IEC 61400-11: Edition 2.1, November 2006 7.2.2 Acoustic measurement procedures Acoustic measurements at wind speeds up to 15 m/s at hub height were made for the purpose of determining apparent sound power levels, one-third octave band levels, and the AWEA Rated Sound Level. For all acoustic measurements taken during the periods indicated in Table 3 above, the following considerations apply: The complete measurement chain was calibrated at least at one frequency before and after the measurements, or if the microphone was disconnected during repositioning All acoustical signals were recorded and stored for later analysis Periods with intruding intermittent background noise (as from an aircraft) were omitted from the database With the wind turbine stopped, and using the same measurement setup, the background noise was measured immediately before or after each measurement series of wind turbine noise and during similar wind conditions The equivalent continuous A-weighted sound pressure level and one-third octave band spectrum were measured at the microphone locations described in Table 3 above. Each measurement for A-weighted sound pressure level and one-third octave band spectrum was integrated over a period of 10 seconds for both turbine and background noise, as this is the required averaging interval of the Standard. One-third octave bands with center frequencies ranging from 20 Hz to 16 khz were recorded, but values centered on 50 Hz to 10 khz are reported per the Page 11 of 41
requirements of the standard. A minimum of 3 measurements within ±0.5 m/s at each integer wind speed were required for both sound pressure and one-third octave analysis. 7.2.3 Non-acoustic measurements Wind speed was measured directly as opposed to derived from the power curve. This is the preferred method for analysis in compliance with the Standard. The wind speed measurement results were adjusted to a height of 10 m and the reference roughness length of 0.05 m as described in section 7.3 below. Direct measurement of wind speed by an anemometer was used for both turbine plus background noise and background noise measurements. Wind speed data was averaged over 10 second periods to align with the averaging of acoustic measurements. Wind direction was measured by a wind direction vane to ensure that measurement locations are kept within 15 of nacelle azimuth positions with respect to upwind, and to measure the position of the anemometer. Wind direction was also averaged over 10 second periods. Air temperature and pressure were measured and recorded according to the requirements of IEC 61400-12-1. For purposes of development of this Test Report, temperature and pressure were also averaged over 10 second periods. 7.3 Data reduction procedures 7.3.1 Wind speed The wind speeds measured at the anemometer on the meteorological mast were corrected to wind speeds at reference conditions, V s, using Equation 3 below: Where: Equation 3 z 0ref is the reference roughness length of 0.05 m; z 0 is the roughness length; H is the rotor center height; z ref is the reference height, 10 m; z is the anemometer height. Equation 3 uses the following principles: The correction for the measured height to the rotor center height uses a logarithmic wind profile with the site roughness length z 0 to account for the actual site conditions. The correction from rotor center height to reference conditions uses a logarithmic wind profile with a reference roughness length z 0ref. This describes the noise characteristic independent of the terrain. The roughness length z 0 was estimated according to Table 1 of IEC 61400-11 Wind turbine generator systems Part 11: Acoustic noise measurement techniques, edition 2.1. A roughness length 0.05 m was used for the Intertek RTC. Page 12 of 41
7.3.2 Correction for background noise All measured sound pressure levels were corrected for the influence of background noise. For average background sound pressure levels that are 6 db or more below the combined level of wind turbine and background noise, the corrected value was obtained using Equation 4 below: Where: L s L s+n L n Equation 4 is the equivalent continuous sound pressure level, in db, of the wind turbine operating alone; is the equivalent continuous sound pressure level, in db, of the wind turbine plus background noise; is the background equivalent continuous sound pressure level, in db. Where the equivalent continuous sound pressure level of the wind turbine plus background noise was less than 6 db but more than 3 db higher than the background level, the correction is by subtraction of 1.3 db and marked with an asterisk, *. These data points are not used for the determination of apparent sound power level. If the difference is less than 3 db, no data points are reported, but it will be reported that the wind turbine noise level was less than the background noise level. 7.3.3 Apparent sound power and one-third octave levels Apparent sound power level is determined by the method of bins, as required by the Standard. The bins are 1 m/s wide, open on the low end, and closed on the high end. For the analysis it was required that there be at least one data point on both sides of the integer wind speed. From the analysis, the equivalent continuous A-weighted sound pressure level at the integer wind speeds, L Aeq,k, was determined. The equivalent continuous A-weighted sound pressure level of the background noise was also determined. The equivalent background level was used to determine the background corrected equivalent continuous sound pressure level of the turbine alone at each integer wind speed and corrected to reference conditions, L Aeq,c,k, as defined as L s in Equation 4 above. Once the bin average background corrected sound pressure levels were determined, Equation 5 below was used to calculate the bin average apparent sound power level, L WA,k, at each integer wind speed: Where: Equation 5 L Aeq,c,k is the background corrected A-weighted sound pressure level at the integer wind speeds and under reference conditions; R 1 is the slant distance in meters from the rotor center to the microphone; S 0 is a reference area, S0 = 1 m 2. The 6 db constant in Equation 5 accounts for the approximate pressure doubling that occurs for the sound level measurements on a ground board. The bin average values were used to determine the sound levels at integer wind speeds following linear interpolation. One-third octave band levels of the wind turbine noise are also corrected for the corresponding one-third octave band levels of background noise according to the procedure detailed above. Page 13 of 41
7.3.4 AWEA Rated Sound Level The AWEA Rated Sound Level, L AWEA, is the sound level that will not be exceeded 95% of the time, assuming an average wind speed of 5 m/s (11.2 mph), a Rayleigh wind speed distribution, 100% availability, and an observer location 60 m (200 ft) from the rotor center. Determination of L AWEA is first achieved by interpolation of sound power level to 9.8 m/s; which is the wind speed not to be exceeded 95% of the time with a Rayleigh distribution and an annual average wind speed of 5 m/s. Then using the sound power level at 9.8 m/s, hemispherical propagation is used to determine the sound level at 60 m from rotor center. To solve for L AWEA, Equation 5 above is used. The equation is rearranged to solve for sound pressure (L Aeq,c,k ) and the 6 db constant is removed. The sound power levels at the integer values of 9 and 10 m/s are used to interpolate to 9.8 m/s, because this is the wind speed that will not be exceed 95% of the time assuming an average wind speed of 5 m/s, a Rayleigh wind speed distribution, and 100% availability. The resulting interpolated value at 9.8 m/s is substituted into Equation 5 for the apparent sound power level, L WA,k, and a value of 60 m is used for R 1. Guidance is given in Appendix A of the AWEA 9.1 Standard for obtaining sound levels for different observer locations and background sound levels. 8.0 Test Results 8.1 Database A total of 580 10-second data points were included in the database; 232 of which were turbine noise data points. Table 4 below shows the total number of measurements at each integer wind speed corrected to reference conditions that were included in the database. Turbine + Background Background Only V s Data points V s Data points 2 5 2 2 3 14 3 5 4 16 4 10 5 6 5 7 6 8 6 9 7 20 7 33 8 27 8 59 9 34 9 76 10 43 10 72 11 31 11 49 12 14 12 15 13 10 13 11 Table 4 Analysis database corrected to reference conditions and after removal of periods of intruding intermittent background noise Page 14 of 41
Plots of wind speed, wind direction, temperature, and pressure on days of acoustic measurements are shown in Figures 7, 8, 9, and 10 respectively, below. Figure 7 Measured wind speed on days of acoustic measurement Figure 8 Measured wind direction on days of acoustic measurement Page 15 of 41
Figure 9 Measured air temperature on days of acoustic measurement Figure 10 Measured air pressure on days of acoustic measurement Page 16 of 41
8.2 Apparent sound power level 8.2.1 Uncertainty Type A and B uncertainties are expressed in the form of standard deviations and are combined by the method of combination of variances to form the combined standard uncertainty. The combined standard uncertainty is found as the root sum of the squared components: U A, U B1, U B2, U B3, U B4, U B5, U B6, U B7, U B8, and U B9. Type B, U B, uncertainty is determined by using the typical values provided in Table D.1 in IEC 61400-11, Annex D. The standard typical values were used for U B2 through U B9. The value for U B1 was derived from the calibration data sheet uncertainties. Table 5 below shows the Type B uncertainties used in the determination of results within this Test Report. Item Description Type B Value Type Source U B1 Calibration 0.31 Actual Calibration U B2 Measurement Chain 0.20 Typical IEC 61400-11 U B3 Board 0.30 Typical IEC 61400-11 U B4 Distance 0.10 Typical IEC 61400-11 U B5 Impedance 0.10 Typical IEC 61400-11 U B6 Turbulence 0.40 Typical IEC 61400-11 U B7 Wind Speed Measured 0.90 Typical IEC 61400-11 U B8 Direction 0.30 Typical IEC 61400-11 U B9 Background 0.10 Typical IEC 61400-11 Table 5 Type B Uncertainties Type A uncertainty, U A, is evaluated by using statistical methods to a series of repeated determinations. U A, the parameter describing the type A uncertainty is the standard error of the estimated L Aeq,c,k at each integer wind speed. Table 6 below shows the continuous A-weighted sound pressure levels and the type A uncertainties at integer wind speeds. Data marked with as asterisk (*) in Table 6 below represent equivalent continuous sound pressure levels of wind turbine plus background noise that were less than 6 db but more than 3 db higher than the background sound level. Wind Speed L Aeq,c,k Type A Uncertainty m/s db(a) db(a) 3 *37.20 1.29 4 *40.24 2.53 5 48.65 2.54 6 51.05 9.27 7 59.79 5.17 8 61.02 6.32 9 61.61 4.99 10 62.28 3.96 11 62.34 2.67 12 62.10 3.25 13 62.41 4.29 Table 6 Continuous A-weighted sound pressure levels and type A uncertainties at integer wind speeds Page 17 of 41
Table 7 below shows the apparent sound power levels and combined uncertainty at integer wind speeds. 8.2.2 Apparent sound power level results Wind Speed L WA Combined Uncertainty m/s db(a) db(a) 5 88.78 2.79 6 91.18 9.34 7 99.92 5.29 8 101.15 6.42 9 101.74 5.12 10 102.41 4.12 11 102.47 2.90 12 102.23 3.45 13 102.54 4.44 Table 7 Apparent sound power levels at integer wind speeds The apparent sound power level at integer wind speeds was derived following the procedure outlined in section 7.3.3 of this Test Report. Using the method of bins the apparent sound power level was determined at integer wind speeds. Figure 10 below shows the measured data pairs of sound pressure levels recorded at various standardized wind speeds. Figure 10 10-second averaged A-weighted sound pressure levels as a function of standardized wind speed Page 18 of 41
Figure 11 below shows the combined uncertainty and apparent sound power levels at integer wind speeds. The uncertainty is shown using error bars in the y-direction. Figure 11 Combined uncertainty and apparent sound power levels at integer wind speeds The large scatter of data in Figure 10 and the large uncertainties of apparent sound power levels are a direct relationship to the overall performance of the turbine. Over a large range of wind speeds the turbine yaws frequently and thus introduces a large amount of variability in rotational speed. This directly affects the output power of the turbine, and is also directly related to the noise levels that were observed by both the microphone and Intertek personnel. Page 19 of 41
8.3 One-third octave band spectra 8.3.1 Uncertainty For the one-third octave band a similar approach as described in section 8.2.1 above is followed, but with the modifications as described in IEC 61400-11, Annex D. For category A uncertainty the U A for each band is the standard error on the averaged band level, computed as the standard deviation divided by, where N is the number of measured spectra. For category B uncertainty the U B3 value is considered to be much larger than for apparent sound power levels, and is estimated in IEC 61400-11, Annex D as a typical value of 1.7 db. The other category B values remain the same, as described in Table 5 in section 8.2.1 of this Test Report. The combined uncertainty, U c, is again the root sum square of the category A and category B values. 8.3.2 One-third octave results The A-weighted third octave spectra at integer wind speeds were derived following the procedure outlined in section 7.3.3 of this Test Report. Figure 12 through 15 below show the background corrected third octave spectra over the range of 3 m/s to 13 m/s. For areas in Figures 12 through 15 where no data is shown, this represents turbine continuous sound pressure levels that were less than the background continuous sound pressure levels. Figure 12 Third octave spectra at 3 m/s, 4 m/s, and 5 m/s integer wind speeds Page 20 of 41
Figure 13 - Third octave spectra at 6 m/s, 7 m/s, and 8 m/s integer wind speeds Figure 14 - Third octave spectra at 9 m/s, 10 m/s, and 11 m/s integer wind speeds Page 21 of 41
Figure 15 - Third octave spectra at 12 m/s and 13 m/s integer wind speeds Page 22 of 41
Tables 8 and 9 below represent the correction to all measured sound pressure levels for the influence of background noise on the turbine. The data marked with an asterisk, *, indicates corrected data when the continuous sound pressure level of the wind turbine plus the background noise is less than 6 db but more than 3 db higher than the background level. Where data is missing, the turbine continuous sound pressure levels were less than the background continuous sound pressure levels. Table 8 Background corrected one-third octave spectra and combined uncertainty at integer wind speeds between 3 m/s and 7 m/s Page 23 of 41
Table 9 Background corrected one-third octave spectra and combined uncertainty at integer wind speeds between 8 m/s and 13 m/s Page 24 of 41
8.4 AWEA Rated Sound Power Level The AWEA Rated Sound Power Level was derived following the procedure outlined in section 7.3.4 of this Test Report. The AWEA Rated Sound Power Level of the Jacobs 31-20 is 55.81 dba. This value is the sound level that is likely to not be exceeded at an average wind speed of 5 m/s (11.2 mph) observed by a person standing 60 m (200 ft) from the rotor center. 8.5 Tonality A tonality analysis is not required for testing in compliance with the requirements of AWEA 9.1, however characterizations of changes in sound and prominent tones that were observed during the testing period are to be reported. During the measurement period, several unique noise characteristics of the Jacobs 31-20 turbine were observed. At lower wind speeds the sheet metal tail vibrates as turbulent wind passes through the rotor and the vibration of the tail can be heard. As wind speed increases the gearbox produces a whining or humming noise that is present throughout operation. The tonal characteristics of the gearbox are easily identifiable, and the intensity appears to increase as the wind speed increases. On days when turbulent wind conditions are present the gearbox hum appears to be more prominent due to the frequent variations in rotational speed and turbine azimuth. The tonal characteristics of the Jacobs 31-20 are believed to be largely related to mechanical components, and remained consistent from commissioning of the turbine through the date on this Test Report. Page 25 of 41
Appendix The following sections can be found within this Appendix: A Test equipment B Wiring diagrams C Photographs of the test site D Calibration certificates for acoustical equipment Page 26 of 41
A Test equipment A.1 Equipment list Description Manufacturer/Model Serial # / Asset # Primary anemometer Reference anemometer Wind vane Barometric pressure sensor Temperature/RH sensor Power transducer Current transducer Microphone / Preamplifier Sound Level Meter Acoustical Calibrator Adolf Thies GmbH 4.3351.00.140 Adolf Thies GmbH 4.3351.00.141 Adolf Thies GmbH 4.3150.00.141 Vaisala PTB330 Adolf Thies GmbH 1.1005.54.241 Ohio Semitronics DMT-1040EY44 Ohio Semitronics 13480 BSWA Technology MPA201 National Instruments NI USB 9233 BSWA Technology CA111 Calibration date Calibration due date 05110086 21-Sep-2011 21-Sep-2012 05110087 21-Sep-2011 21-Sep-2012 04100018 08-Aug-2011 08-Aug-2012 F1420001 12-Aug-2011 12-Aug-2012 85764 12-Aug-2011 12-Aug-2012 A333* 24-Oct-2011 24-Oct-2012 A333* 24-Oct-2011 24-Oct-2012 461272** 13-Sep-2011 13-Sep-2012 151A3AF** 14-Sep-2011 14-Sep-2012 470103** 13-Sep-2011 13-Sep-2012 *Intertek calibration database Asset #; PT and CT calibrated as a system **BSWA equipment, NI module, and acoustic laptop calibrated both as a system and individually. A.2 Software Description Manufacturer Model Comments Acoustic recording and processing Delta NoiseLab Professional Verified software Analysis tool Microsoft Excel 2003 Verified software Page 27 of 41
B Wiring diagrams B.1 Typical wiring diagram for Jacobs 31-20 Page 28 of 41
B.2 Block diagram of Jacobs 31-20 setup at Intertek RTC Page 29 of 41
C Photographs of the test site C.1 November 3 rd, 2011 measurement location Page 30 of 41
C.2 November 11 th, 2011 measurement location Page 31 of 41
C.3 View from turbine tower to permanent meteorological tower Page 32 of 41
C.4 View from permanent meteorological tower to turbine tower Page 33 of 41
C.5 Microphone board and microphone with wind screen; November 3 rd, 2011 Page 34 of 41
D Calibration certificates for acoustical equipment D.1 Microphone and preamplifier Page 35 of 41
Page 36 of 41
Page 37 of 41
D.2 Sound level meter Page 38 of 41
Page 39 of 41
D.3 Acoustical calibrator Page 40 of 41
Page 41 of 41