Wind turbine Excess Noise evaluation

Transcription

1 Wind turbine Excess Noise evaluation Marko Antila VTT Technical Research Centre of Finland

2 Background Wind turbine construction booming in Finland Now just below 500 MW, target 2.5 GW in 2020 (6 TWh) -> as much as existing capacity needed every year between ! Noise issues have been marginal so far, but now becoming important Finnish Ministry of Environment has just released a wind power noise draft statute for comments 45 db daytime/ 40 db night time L Aeq levels Simple 5 db sanction from excess noise features 10/12/2014 2

3 Wind turbine noise research activities in Finland Due to the booming WT construction lot s of research activities going on in Finland Related to modeling, turbine R&D, but also human perception One of the latest project about human perception was TUMEVA (the noise effects of wind turbine noise) 2-pillar approach: 1. The metrics of the human perception of excess noise (Report: in Finnish) 2. The health effects of the wind turbine noise (Report: in Finnish) This presentation describes the metrics, ideas behind them and their implementation 10/12/2014 3

4 The sound level requirements, sanctions and excess noise Wind turbine broadband and stationary noise Dose-toannoyance ratio Wind turbine noise Wind turbine noise specific features, regular level Wind turbine noise specific features, excess level Regulations Sanctions Final sound pressure level requirements 10/12/2014 4

5 Excess features of wind turbine noise Issue under debate in Finland: When are the specific features at regular level (taken into account in the regulations) and when they represent excess level (leading to sanctions)? Psychoacoustic metrics and related (sliding) sanction proposal for 3 most important excess noise features (rough order of importance): 1. Amplitude modulation 2. Tonal components 3. Impulsive noise Requirement: recorded time-domain signals (not just level information) 10/12/2014 5

6 Excess amplitude modulation and human perception The broadband (aerodynamic) noise is amplitude modulated Modulation frequency always related to the rotating blades ( f m between 0.5 Hz - 2 Hz) Audible (potentially annoying) when modulation is over 20 %, same as 3 db modulation depth There may a sudden turning point in annoyance around 3 db according to the recent studies Individual WT modulation types classified according to the carrier frequency f c 10/12/2014 6

7 Excess amplitude modulation, metrics and human perception Individual WT modulation types classified according to the carrier frequency f c f c between 500 Hz - 1 khz: Swishing amplitude modulation Is generated almost always Propagates initially to all directions, then at 90 degree angle to wind direction, and is attenuated rapidly f c between 200 Hz khz: Thumping/ swooshing amplitude modulation Is generated under specific atmospheric conditions with pitch controller WTs Stable or very stable atmosphere, turbulence Mostly propagated to the wind direction. All source mechanisms or conditions are not known. Also known as excess or enhanced AM (EAM) and other AM (OAM) Also the interaction of several WTs create excess amplitude modulation 10/12/2014 7

8 Methods to evaluate excess AM Listening tests Listening tests for different source types Both recorded and artificial noise used For artificial noise a real time audible model of WT used The am effect obtained directly Calculation methodology Modulation depth is calculated from the signal by dividing it to short sections (modified Hünerbein methodology) Based on the earlier studies and listening tests the annoyance/ sanction is determined 10/12/2014 8

9 Lpt - Lpn [db] Tonal noise Current understanding: tonal noise is rare if the turbine operates properly Defined from recorded signals according to standard IEC (Edition ) If the tonal noise exists the sanction will be used IEC does not define sanction directly However, the standard is based on a methodology development report defining sliding sanction Principle: when tonal noise exceeds masking noise by 4 db, the sliding sanction begins (max 6 db) k = 6 db k = 5 db k = 4 db k = 3 db k = 2 db k = 1 db k = 0 db Masking threshold 4 db -6 31, k 2 k 4 k 8 k 16 k Critical Band Center Frequency [Hz] 10/12/2014 9

10 Impulse noise Impulsiveness defined according to Nordtest-method NT ACOU 112 Strong amplitude modulation (> 5 1 Hz) will also be classified as impulse noise by this method 1. Calculate predicted prominence, P 2. Calculate correction factor K i 3. If K i > 3 db -> impulse noise If impulse noise detected, sanction K i is added before comparison to planned or verified level. 0 K i related to P /12/

11 Conclusions In Finland there will be a lot of WT construction in the next years Noise issues and especially human perception is important, legislation and guidelines are now set In TUMEVA project the excess noise metrics were studied from psychoacoustic point of view Methodology and metrics were assessed and developed to evaluate amplitude modulation, tonal noise and impulse noise Proposal and methodology now exist, will be used in near-future projects Contact: Marko Antila (marko.antila@vtt.fi) 10/12/

12 Some references IEC (2012). IEC : Wind turbines - Part 11 ed. 3.0: Acoustic noise measurement techniques. Switzerland. Nordtest (2002). Nordtest Method NT ACOU 112, Acoustics: prominence of impulsive sounds and for adjustment of LAeq. Espoo, Finland. Nordtest (1993). Nordtest Method NT ACOU 089, Wind turbines - noise: performance. Espoo, Finland. Hünerbein Sv, King A, Piper B and Cand M (2013) Development of an AM Dose-Response Relationship. Work Package B(2) report. In: RenewableUK (ed) Wind Turbine Amplitude Modulation: Research to Improve Understanding as to its Cause and Effect. London, UK: Renewable UK. Larsson C. and Öhlund O. (2014) Amplitude modulation of sound from wind turbines under various meteorological conditions. The Journal of the Acoustical Society of America 135(1): /12/

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