Date post: | 28-Mar-2015 |
Category: |
Documents |
Upload: | leonardo-catlett |
View: | 219 times |
Download: | 2 times |
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
2
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]
3
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
4
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
5
Scattered Signals
Method:
Divide wind turbine into two parts:1. Tower - conical cylinder
2. Blades – elliptical cross section
Material – perfect electric conductor
6
Scattered Signals
Method:
Spherical wave
Scattering cross section from each segment
7
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
8
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%
9
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
10
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)
11
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
12
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
13