Electromagnetic Interference from Wind Turbines - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 565

Comparison of Observed and Idealized
Signal Scatter Ratios

For the conditions of a given field test, Equations (9-26) can be used to calculate an
idealized scatter ratio, while the observed scatter ratio is determined for that test using
Equations (9-16). By comparing observed and idealized scatter ratios for a variety of wind
turbines and field conditions, we can estimate the probability that signal interference will
exceed the idealized value by a given amount. This has been done for the 75 field test
cases listed in Table 9-1 [Spera and Sengupta 1994]. Scatter ratios are compared in Figure
9-13 for the backward-scatter zone and Figure 9-14 for the forward-scatter zone.

Table 9-1. TVI Cases Analyzed for Observed vs. Idealized Scatter Ratios
[Spera and Sengupta 1994]

Wind
turbine

No.
of
units

Scatter
zone

No.
of
cases

Wave
lengths
(m)

WT-Receiver
distances
(m)

Data Reference

Mod-1 HAWT
"

1
"

Backward
Forward

16
5

1.6 - 5.0
1.5 - 3.7

1041 - 2745
"

[Sengupta et al. 1981a]
"

Mod-2 HAWT 1 Backward 3 1.6 - 3.4 1603 - 6100 [Sengupta et al. 1983a]

" " Forward 1 0.6 1445 "

" 2 Backward 1 3.4 6254 "

" 2,3 Forward 4 0.5 - 1.4 1354 - 1717 "

17-m VAWT
"

1
"

Backward
Forward

33
12

0.4 - 4.2
"

32 - 133 27 - 31 [Sengupta et al. 1981b]

"

Figure 9-13. Comparison of observed and idealized signal scatter ratios for receivers
in the backward-scatter zone. [Spera and Sengupta 1994]