Eskil Bendz

Johan Malmström

ÅF-INFRASTRUKTUR AB

Electromagnetic Interference from Wind Turbines on Onsala Space Observatory

Outline

Introduction

The Saab report Methods to calculate interference levels Main results

The ÅF report Assessment of Saab report Other important considerations

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Introduction

34 Wind Turbines

focus is the 10 encircled

UMTS Radio Base Stations

Purpose:

Estimate and compare interference levels from direct signals and scattered signals [dBW/m2/Hz]

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Space Observatory

18 km

The Saab report

Approach:

Calculate direct signals from UMTS radio base stations

Calculate scattered signals from wind turbines

Compare the two levels of interference at Onsala

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Direct Signals

Method:

Contribution from nearby radio base stations

Free space path loss at 2 GHz Extra attenuation due to terrain

profile (heights and vegetation)

Summarize all signals

Spectral power density: -132 dBW/m2/Hz

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Scattered Signals

Method:

Divide wind turbine into two parts:1. Tower - conical cylinder

2. Blades – elliptical cross section

Material – perfect electric conductor

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Scattered Signals

Method:

Spherical wave

Scattering cross section from each segment

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Scattered Signals

Method:

Calculate contribution from base stations close to the 10 wind turbines

10 towers - spectral power density:-164 dBW/m2/Hz

One blade - spectral power density (maximum):-164 dBW/m2/Hz

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Main results

Both signals above recommended -250 dBW/m2/Hz @ 2 GHz

Direct signal is 32 dB higher than scattered signals (~1500 times)

or Scattered signals increase interference level <0.1%

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The ÅF report

Assessment of the Saab report found no severe errors

Simplifications overestimated the direct signalsE.g. down-tilt reduce direct signals in the Saab report 6-8 dB

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Adjusted signal levels

New values: Direct signal: -142 dBW/m2/Hz (Saab: -132 dBW/m2/Hz) Scattered signals: -159 dBW/m2/Hz (Saab: -164 dBW/m2/Hz)

Direct signal still 17 dB higher than scattered signals (~50 times)

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Other important considerations

Direct emission from radio base stations contributes largely to the interference level

E.g. UMTS, GSM, LTE Direction of antennas Usually three antennas at a site, covering 120

each Suggestions to decrease interference level:

1. Turn off sectors

2. Rearrange antenna directions to obtain a ”zero”

3. Rearrange antenna away from telescopes

4. Increase down-tilt (10 might be obtained)

In accordance with mobile telephone service providers

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Other important considerations

Some other sources that might contribute to the interference level are:

Neighboring radar stations (high power sources) Wireless radio links (narrow beam width) Harmonics or intermodulation products

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