Electromagnetic Interference from Wind Turbines - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 573

Figure 9-20. Theoretical interference zone around a HAWT, expressed in radial coor-
dinates. The modulation index is 0.15, the receiver antenna is beamed at the transmitter, and
the probability of exceedance is set at 1 percent. [Spera and Sengupta 1994]

Darrieus VAWT Interference Zones

Referring again to Equations (9-26), we see that Equations (9-29) can be modified to
define a Darrieus VAWT interference zone by replacing h S with 0.8h M and D with the
blade chord c . Thus, the interference zone around a Darrieus VAWT is much smaller than
that around a HAWT of the same diameter, by a factor approximately equal to 4 c/D.

Interference Zones Around a HAWT Wind Power Station

To estimate the size of the interference zone around a wind power station composed
of many turbines, we first divide the station into M clusters, each containing N turbines.
The turbines within a cluster are assumed to be operating in synchronism and their scatter
ratios are additive, in accordance with Equation (9-26h). Therefore, a reasonable value of
N is ten or less. However, we will assume that the cluster scatter ratios add in a random
or root-sum-square fashion, which leads to the following equations:

M
i -1

F A , W cos 2 ( k f RT )
(z/ D ) 2

h

S NF E
2

| E PS , D |
| E R , D |

(9-3la)

m R =

i

k = 0.5

f or the Backward Zone

(9-3lb)

k = 2.0 f or the Forward Zone

M
i -1

1
M

| E PS , D | =

| E C , D | i

(9-3lc)

where

| E PS, D | = average amplitude of the direct signal incident on the station (mV/m)