To: Sean Fairfield/Steven Hitchinson From: Joaquin Moran Algonquin Power Co. General Engineering Services - Chaplin Wind Project
Noise Assessment for Chaplin Wind Project
1. Introduction Algonquin Power Co. (Algonquin) is developing the 177-MW Chaplin Wind Project in the Rural Municipality of Chaplin, Saskatchewan. The project will comprise between 58 and 88 wind turbines installed in rural areas.
As part of the environmental permitting phase of the project, Algonquin has retained Hatch Ltd. (Hatch) to prepare a noise assessment study for the facility. The noise assessment would assume the use of all 88 pads, in order to evaluate the worst-case scenario in terms of noise impact on the receptors.
2. Methodology Since the Province of Saskatchewan does not have any guidelines for sound level modeling for wind turbines, the sound pressure levels at the Points of Reception (POR) used to model the noise receptors were predicted using procedures from the standard ISO 9613-2 (Reference [6]), which is widely used for evaluation of noise impact in environmental assessments recommended in the Ontario Noise Guidelines for Wind Farms document (Reference [1]).
The software package CADNA-A, which implements ISO 9613-2 standard, was used to predict the noise levels at the POR. The acoustical parameters modelled in CADNA-A model correspond to the guidelines provided by the Ontario Ministry of Environment and Climate Change (MOECC) in their Noise Guidelines for Wind Farms publication (Reference [1]). Any obstacle, (ground surface or physical barrier) that did not break the source-POR line of sight was not taken into account as attenuation contribution (no negative path difference), which contributes to a conservative estimate of the sound pressure levels at the receptor locations.
For modelling purposes, the vegetation and other obstacles (such as barns) that block some of the POR from the sources have not been incorporated. Exclusion of these obstacles from the model results in more conservative sound pressure levels predicted at the POR. In reality, these obstacles may help reduce noise impact at the POR.
2.1 Project Location The Project is to be located within the boundaries of the Rural Municipality of Chaplin in the Province of Saskatchewan. Figure A.1 in Appendix A shows the geographical location of the Project along with topographical features.
2.2 Noise Sources A total of 88 Wind Turbine Generators (WTGs) and one substation transformer were evaluated in this study. Table B.1 and Table B.2 in Appendix B present the coordinates of each source included in the model. The sound power levels of the sources are listed in Table B.3.
At this time the finalization of the preferred turbine has not been completed, however, in order to produce a conservative sound emission, a generic sound power level for a typical 2.3 MW WTG at 7 m/s was used for the study. Previous experience with 2.3 MW WTGs shows that noise emissions are the worst at 7 m/s. The point noise sources representing the WTGs were assumed at 80.0 m above ground level as a conservative approximation. The turbine height for the Chaplin Project could be above 80 m, reducing even more the noise impact on receptors.
Hatch has used this methodology in several jurisdictions in North America and this is acceptable to demonstrate a conservative modeled sound profile. Nevertheless, the acoustical model will be updated with the manufacturer’s specified sound power level as soon as the WTG model is selected.
The transformer make and model have not been selected at this point, although it is known that the 34.5-kV/138-kV/175-MVA transformer will be of ONAF (Oil Natural Air Forced) type. A conservative estimate of sound power level was based on the data from the National Electrical Manufacturers Association (NEMA) standard TR 1 – 1993 (2000). This standard provides the maximum sound level values for transformers, and manufacturers routinely meet this specification. The results, based on NEMA, slightly overestimate the impact on the POR since the actual transformer to be procured for the project will be below the NEMA specified sound levels.
The NEMA levels were converted into frequency spectra using empirical correlations for transformer noise from Reference [2]. This calculation is available in Figure B.1 of Appendix B. The point noise source elevation representing the transformer was assumed at 5.0 m above ground level.
Power transformers are considered to be tonal noise sources. A 5-dB penalty was added to the sound power spectrum, as recommended by Publication NPC-104, “Sound Level Adjustments” for tonality.
2.3 Noise Receptors The noise receptors modeled in the study were provided by Algonquin Power, which obtained their locations from high resolution satellite imagery, discussion with landowners, as well as site inspections. All Noise Receptors within the Project study area, which are a minimum 500 m from any proposed wind turbine, in compliance with the Rural Municipality of Chaplin interim development control bylaw, were assessed and included in this noise report.
The noise receptors were represented by points of reception (POR) in the CADNA model placed in the middle of the receptor footprint and elevated at 4.5 m above ground. The minimum distance between WTGs and all potential receptors was kept above 500 m.
The total number of noise receptors located within the Project study area is 39.
It is important to note that over half of the receptors are located on land that is participating in the project (i.e., contains project infrastructure: wind turbines, roads or electrical components).
3. Results For this study, the overall ground attenuation coefficient was assumed to be 0.7 as recommended by Reference [1]. A 40.0 dBA sound pressure value was used as the compliance criterion for the POR used to model the noise receptors, which is in compliance with the Ontario Ministry of Environment guidelines. Table C.1 in Appendix C presents calculated sound pressure levels at the POR along with the distances to the nearest WTG and substation transformer. Figure C.1 displays sound pressure contours calculated at 4.5 m.
4. Summary For the Chaplin Wind Project, the sound pressure levels at the noise receptors have been estimated using the CADNA-A model based on ISO 9613-2 as recommended by the Ontario Noise Guidelines for Wind Farms. The performance limits used for compliance also correspond to those recommended by Ontario guidelines, rural areas with a 40.0-dBA limit. The point noise sources representing the WTGs were assumed at 80.0 m above ground level as a conservative approximation. The turbine height for the Chaplin Project could be above 80 m, reducing even more the noise impact on receptors.
Based on the results obtained in this study, it is concluded that the sound pressure levels at the noise receptors within the Project study area resulting from the operation of the Chaplin Wind Project (based on 88 WTG locations and one substation transformer), will be below 40.0 dBA at all times.
5. References [1]. Noise Guidelines for Wind Farms; Interpretation for Applying MOE NPC Publications to
Wind Power Generation Facilities; Ontario Ministry of the Environment; October 2008.
[2]. Handbook of Noise and Vibration Control; Crocker; 2007; page 1335-1336; Eq. 18 and Table 20.
[3]. NEMA; Standards Publication No. TR 1-1993 (R2000); Transformers, Regulators and Reactors; National Electrical Manufacturers Association.
[4]. ISO 1996-1 Description; Measurement and Assessment of Environmental Noise – Part 1; Basic Quantities and Assessment Procedures.
[5]. NPC-104, “Sound Level Adjustments” Ontario Ministry of the Environment.
[6]. International Organization for Standardization (ISO). Standard 1913-2: Acoustics – Attenuation of sound during propagation outdoors – Part 2: General Method of Calculation.
Table B.3: Sound Power Spectra Used for Modelling the Noise Sources
Spectra ID Description
Octave Spectrum [dBA]
31.5 63 125 250 500 1000 2000 4000 8000 Total
WTG_23_113_7ms Generic sound power levels for a typical 2.3 MW wind turbine generator at 7 m/s. 84.6 92.4 97.6 99.4 100.3 95.9 86.1 68.1 105.0
Tr_34.5kV_138kV_175MVA
Estimated for 34.5-kV/138-kV/175-MVA transformer using sound levels from NEMA TR 1-1993 (R2000) and empirical equations from Handbook of Noise and Vibration Control (Crocker, 2007, page 1335-1336, Eq. 18 and Table 20)
