Environmental Engineering Reference
In-Depth Information
Three potential problem areas were identiied: the possibilities of
acoustic noise
,
electromagnetic interference
with local microwave radio or TV reception, and uncertain
public acceptance of the
aesthetics
of wind turbines on the landscape. Following the initial
Battelle study, specialized research projects concentrating on these potential issues were
undertaken [Balombin 1980, Senior
et al.
1977, Ferber 1977].
Electromagnetic Interference
The irst environmental issue to be actually encountered at the Mod-1 site was the
electromagnetic interference (EMI) problem. Results of the research showed that, while
there would not be a signiicant effect across most frequencies (unless the turbine was close
to, and literally in the path of, a microwave or other antenna), the
upper VHF
and
lower
UHF television bands
were the most vulnerable and could be affected. Analytical tools
began to be developed to predict the possibility of EMI in any given installation. Early
analysis showed that, of the 17 sites under consideration by DOE, the Block Island site
would likely experience TV interference, given the already marginal television reception in
that area. Because it was ideal in all other respects, Block Island was selected for the third
Mod-0A site partially to allow measurement of actual TV interference under complex real-
world situations. A television cable system was irst installed in cooperation with the
nearby town in order to mitigate any effects on the public.
Like Block Island, the area around Boone had TV signals of marginal strength, and
some EMI was encountered there also. EMI measurements around the large-scale Mod-1
turbine with its steel blades, coupled with the Block Island measurements and laboratory
tests at the University of Michigan, led to the development of accurate tools for the
evaluation of future sites. The EMI potential was found to be a predictable function of
blade size and material, rotor speed, and the local transmitter/receiver/turbine geometry (see
Chapter 9).
Acoustic Noise
A second environmental issue at the Mod-1 site was, for a time, an intractable noise
problem. Prior wind turbines were generally relatively quiet, and the Mod-1 itself was not
noticeably noisy close-up. Under certain conditions, however, it emitted low frequency
pressure pulsations. At seemingly random intervals, this would produce unacceptable noise
at various locations a considerable distance from the site, even though at other locations or
times, no noise was detectable. The source was determined to be coupling between the
blade passage and wakes from the heavy tubular legs of the truss tower. Atmospheric
conditions, particularly inversions, combined with the complex mountain terrain could then
focus the noise at some locations distant from the site. Research conducted in the area
eventually led to the development of reined and veriied methods for analyzing and
predicting wind turbine noise (see Chapter 7). The Mod-1 noise problem was eventually
solved by reducing the rotor speed, an operation that required replacing the generator.
Noise generated from blade tips or protrusions (for tip control mechanisms or
aerodynamic brakes) and some gearboxes and hydraulic motors have occasionally led to
some “noisy machines,” regardless of turbine power or rotor size. Careful tip design,
fairings, upwind rotor location, and component selection have led to generally quiet
machines.
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