Environmental Engineering Reference
In-Depth Information
Darrieus VAWT TVI Perception and Tolerance Levels
Most of the above comments also apply to the interference caused by a VAWT like the
Darrieus, but there are differences in detail. In particular, a laboratory study has shown that
the modulation waveform introduced by a Darrieus blade contains broad pulses and narrow
spikes, both repeating at the blade passage frequency [Sengupta and Senior 1979b]. The
pulses produce video distortion with a modulation threshold of perception,
m
P, T
, equal to
the relatively high value of 0.28. The spikes, however, did not produce observable
distortion. During field tests of TV interference around a Darrieus VAWT [Sengupta
et al.
1981b], video distortion levels were observed to be as follows:
m
P, T
» 0.025
m
P, L
» 0.14
m
P, S
»
0.17
From these preliminary results, we can assume that the long-term tolerance for video
distortion caused by a Darrieus VAWT is about the same as for a HAWT,
i.e.
,
m
P,
L
= 0.15.
TVI Effects of Small Wind Turbines
With the growing interest in small-scale wind turbines (rated at about 10 kW or less)
for supplying power to individual residences, there is the possibility that a small wind
turbine could be in the vicinity of a TV receiving antenna. It is of interest to know under
what conditions these two devices are compatible, but at the small distances involved,
interference predictions based on data from large HAWTs are questionable. Laboratory
simulations with scale models of wind turbine rotors are a convenient method for studying
these size effects.
In one study [Sengupta
et al.
1983b], TVI measurements were carried out using 1/8-
scale models of small HAWTs in conjunction with a microwave TV system inside an
anechoic chamber. Two and three-bladed rotors were tested, with metallized and wooden
blades rectangular and trapezoidal in shape. A locally-broadcast TV signal was used as the
RF source of the microwave TV system, after its center frequency was up-converted to 4.0
GHz. Simulated television interference results were then extrapolated to represent TVI
effects of full-scale wind turbines at commercial TV channel frequencies.
Generally, it was found that the two- and three-bladed machines produce similar TVI
effects, the metallized blades providing stronger interference than the wooden blades.
Extrapolation of these results indicates that even at the highest TV frequency, video
distortion produced by small-scale wind turbines with metal blades does not extend beyond
a distance larger than about 2.5 times the rotor diameter. With wood blades the interference
zone is much smaller. At lower TV frequencies the interference distance is correspondingly
smaller. Within this distance, the observed effects are generally small-to-negligible, except
possibly in the forward interference direction.
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