Environmental Engineering Reference
In-Depth Information
N
j =1 Z I , j
| E R , S |
| E C , D |
Z I , C =
=
(9-6h)
N
j - 1 | E WT , D |
1
N
| E C , D | =
(9-26i)
j
where
Z I, C
= idealized cluster scatter ratio
| E C, D |
= average amplitude of the direct signal incident on the cluster (mV/m)
N
= number of wind turbines in the cluster
Field Measurements of Television Interference
Measurements of television signals in the regions around full-scale operating wind
turbines are used to determine the extent to which the idealized signal scattering just
discussed is modified by local conditions of topography, direct signal strength, transmitter
and wind turbine directions and elevations, and by wind turbine rotor orientation, size,
speed, material, and blade pitch. Background information on field measurement equipment
and observed TVI effects is presented in this section, followed by a comparison of meas-
ured signal scattering data with calculated idealized scatter ratios.
Field Test Equipment
Systematic procedures and equipment for conducting TVI tests in the field are
discussed in several references [ e.g. , Sengupta et al. 1981a and 1983a]. Two types of
measurement systems are described here, for attended and unattended testing.
Attended Testing
A schematic block diagram of a typical experimental arrangement for attended TVI
testing is shown in Figure 9-11, where only those components pertinent to data collection
have been included. With any given TV transmission a portion of the signal is scattered
by the wind turbine. This portion, together with the desired signal from the transmitter, is
picked up by a rotatable antenna , fed to a spectrum analyzer , and recorded on a paper
chart recorder for later evaluation. The combination of the spectrum analyzer and the chart
recorder is used to (a) measure the ambient levels of the video and audio carrier signals ( i.e.
without the wind turbine operating), and (b) to record the total signal received as a function
of time, including any modulation produced by moving wind turbine blades. Two-way
radios provide for communication between the TV test site and the turbine control room.
The general quality of the ambient TV reception and the existence of any wind turbine-
produced video distortion are observed on the screen of the TV receiver. The video
recorder is employed for documentation of interference phenomenon for correlation with
quantitative measurements. It is often convenient to have two TV receivers, with one
displaying the received program while the other feeds the video recorder. The equipment
is usually powered from the 60 Hz utility system. In the absence of such power at the test
site, a portable AC generator is necessary. All of these test instruments can be fitted
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