The Windmills Project

Team:Irene Fiori – U. of PisaLara Giordano – INFN NapoliEmanuele Marchetti – U. of Firenze, dept. of earth sciencesFederico Paoletti – INFN PisaGillian Mayer – AEI Hannover

G Mayer – ILIAS WG1 meeting – Perugia – September 19th, 2005

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Motivation:• Measurements of seismic effects of a wind power plant

on GEO 600 • Prediction for the planned wind power plant at VIRGO

In this talk:

1. Determination of the characteristic frequencies

2. GEO microseism

3. Windspeed and seismic wave field analysis

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Specifications:

height diameter

Nordex N90 100 m 90 m

Nordex S77 85 m 77 m

Enron Wind 1.5s 85 m 70.5 m

Enron Wind 1.5 85 m 65 m

All power plants have in common:• 3 blades• canonical steel tower• concrete foundations

They differ in height and diameterof the rotor:

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Map of the site:

RIF has been taken directly on the foundations of T4

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GEO 600

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1. Characteristic frequencies

Timeseries at an N90:

• N90 was off• clear oscillation at 1.9 Hz• another persisting frequency at 0.29 Hz

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1. Characteristic frequencies

1. structural resonance

2. structural resonance

Nordex N90 0.29 Hz 1.9 Hz

Nordex S77 0.37 Hz 2.5 Hz

Enron Wind 1.5s 0.29 Hz 2.2 Hz

Enron Wind 1.5 0.29 Hz 2.3 Hz

• Department of steelworks determined shapes of structural resonances*

Low High frequency

*) P. Schaumann, M. Seidel: Einschwingverhalten von Windenergieanlagen – Berechnungenund Messungen, Hannover, 2000

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1. Characteristic frequencies

Spectra of wind power plants:

• Nordex S77 running• not only resonance peaks, but also peaks which are related to the blade pass frequency (period T 5 s)

• Enron Wind 1.5 off• two main peaks, corresponding to two resonance frequencies

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1. Characteristic frequencies

0.37 Hz 1. struct. resonance

approx. 2.5 Hz 2. struct. resonance

0.17 Hz blade pass frequency

0.51 Hz 3rd harmonic

1.0 Hz 6th harmonic

1.5 Hz 9th harmonic

approx. 2.0 Hz 12th harmonic

approx. 2.5 Hz 15th harmonic

frequency correspondence

A closer look at the spectrumshows which frequenciesappear:

• higher harmonics seem to be present, but are difficult to distinguish• peak around 18 Hz is very likely the generator

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2. GEO microseism

Large coherence of STS-2at low frequencies:

Microseism

• signals are coherent in frequency range of windmills 1st structural res. peak (0.3 Hz) • produced by the windmills? • different sources like the North Sea?

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2. GEO microseism

• TCC - TFE: + 0.7 s signal reaches TFE first• TCC - TFN: + 0.2 s signal reaches TFN first• TFE - TFN: - 0.5 s signal reaches TFE first

Correlograms for microseism:

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2. GEO microseism

Result:

• velocity: 650 m/s (depends on day)• angle: 43° NE

Problem:

• There‘s no obvious source where these waves could come from• expected sources: North Sea/Baltic Sea, Hannover

Possible explanation:

The measured signal could be a superposition of several (at least two) signals of different sources

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Map of the site:

GEO 600

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3. Field measurements

Aquisition times:

After the second day we left the stations outside even during nighttime. For station A02 and A03 we lack GPStiming.

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3. Field measurements

Windspeed analysis:• seismometer output (RIF) scales with windspeed• allows rough correction of data taken at different wind conditions

• medium and high wind spectra look the same• low wind: 0.3 Hz peak persists

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3. Field measurements

Detailed view of RMS in frequency bands:

• Every frequency is affected by wind except from the highest band another hint that the peak at 18 Hz has an internal source• lowest frequency band (red) shows the effect of the adjustment of the rotor• at least a windspeed of 1 m/s is needed to make the wind power plant run

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3. Field measurements

Coherence:

• extremly bad coherence for all stations except from D1 (25 m from RIF) no chance to make correlograms• possible explanation: directly on the basement (RIF) large amplification of the signal once the signal reached the ground heavily damped, peaks get broad, coherence is lost.

also interference from other windmills

D1 - RIF, all three components other stations, only vertical component

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3. Field measurements

High resolution view of low frequency coherence between D1 and central STS-2:

A dip at 0.29 Hz can clearly be seen. The correlogram shows, that the signal first reaches the STS-2, than D1. low frequency part is microseism as discussed above

Low frequencies

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3. Field measurements

Higher frequencies• new measurement because of bad coherence: E1 near T3, E2 200 m east of E1• much better coherence now, even at a distance of 200 m• some high frequency peaks survive

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3. Field measurements

Comparison: medium wind and no wind conditions, vertical component

• night-time: low antropic noise • light green/blue: spectra at no wind, wind power plants weren‘t running• dark green/blue: spectra with medium wind, very likely that all wind power plants were running• no significant difference in A1 spectra (near GEO)

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Conclusions:

• all windmills have got two structural resonances, persist also when the windmills are not running

• when running, one can see the blade pass frequency, the 3rd harmonic and higher harmonics of the 3rd

• low frequency noise produced by the windmills is quickly damped and dominated by the local microseism

• although the last picture shows that it‘s very unlikely that higher frequencies reach GEO, this cannot yet be excluded. However, if there is an effect it is certainly small.