Data Analysis/Procedure

Graph the data for signal strength vs. distance from the wind turbine (Sasarita,

2013, p. 2-30). Use the spreadsheet provided that includes the math to do this.

Look for a reduction in signal strength in the graphs while comparing data from

all of the test frequencies to establish the distance at which the signal level is reduced by

3 dB. This distance will then be used to establish a perimeter around the wind turbine

inside which future testing should not be conducted.

RF field measurements will be made starting at a distance of 767 yards away from

the wind turbine, along Garden Canyon Road (Sasarita, 2013, p. 2-30), and moving

towards the turbine. Measurements made at a greater distance would be invalid due to

shading in the RF path caused by a hill located between the transmit site and Garden

Canyon Road. Table 4 shows the test point distances from the wind turbine. These

distances were first measured using a laser range finer then verified by calculating the

distance using GPS coordinates.

Table 4. Test Point Distances Along Garden Canyon Road (after Sasarita, 2013, p. 2-

28)

Calculated and Measured Distance from Each Test Point to the Wind Turbine

Wind Turbine Latitude 31.505381 31.505381 31.505381 31.505381 31.505381 31.505381 Wind Turbine Longitude -110.317505 -110.317505 -110.317505 -110.317505 -110.317505 -110.317505 Test Point Latitude 31.511407 31.510636 31.510027 31.509349 31.508653 31.507947 Test Point Longitude -110.319702 -110.319067 -110.318749 -110.318668 -110.318633 -110.318568 Calculated Distance 767.37 659.23 579.51 497.36 414.72 330.93

Range Finder 767 659 579 497 415 331

Wind Turbine Latitude 31.505381 31.505381 31.505381 31.505381 Wind Turbine Longitude -110.317505 -110.317505 -110.317505 -110.317505 Test Point Latitude 31.507244 31.506553 31.50619 31.505736 Test Point Longitude -110.31848 -110.318392 -110.318342 -110.318273 Calculated Distance 248.08 169.61 131.18 90.57

Range Finder 248 169 132 90

Wind Turbine Latitude 31.505381 31.505381 31.505381 31.505381 31.505381 31.505381 Wind Turbine Longitude -110.317505 -110.317505 -110.317505 -110.317505 -110.317505 -110.317505 Test Point Latitude 31.505872 31.505827 31.505783 31.50575 31.50571 31.505675 Test Point Longitude -110.31759 -110.317575 -110.317563 -110.317553 -110.317545 -110.317538

Range Finder 60 55 50 45 40 35

Wind Turbine Latitude 31.505381 31.505381 31.505381 31.505381 31.505381 31.505381 Wind Turbine Longitude -110.317505 -110.317505 -110.317505 -110.317505 -110.317505 -110.317505 Test Point Latitude 31.505629 31.505592 31.505552 31.505511 31.505468 31.505428 Test Point Longitude -110.317527 -110.317518 -110.317512 -110.317503 -110.317498 -110.317496

Calculated Distance 30.24 25.69 20.81 15.81 10.60 5.79

Range Finder 30 25 20 15 10 5

Figures 15, 16, and 17 show graphs for frequency groups and the greatest distance

where the signal level deviates by at least 3 dB from the linear trend line per group (p. 2-

32).

Figure 15. Signal Level in dB vs. Distance in Yards for 1.42 MHz to 14.9 MHz,

Showing that the Signal Level Deviates by 3 dB from the Trend Line at

100 Yards (from Sasarita, 2013, p. 2-31)

Figure 16. Signal Level in dB vs. Distance in Yards for 30.0 MHz to 337.5 MHz,

Showing that the Signal Level Deviates by 3 dB from the Trend Line at

420 yards (from Sasarita, 2013, p. 2-31)

Figure 17. Signal Level in dB vs. Distance in Yards for 454.3 MHz to 5,999.0 MHz,

Showing that the Signal Level Deviates by 3 dB from the Trend Line at

380 Yards (from Sasarita, 2013, p. 2-32)

Figures 15–17 establish a minimum test boundary around the wind turbine at 420

yards (Sasarita, 2013, p. 2-32) due to signal strength fluctuations per distance from the

wind turbine. The signal strength for five of the test frequencies either increased or

decreased by several dB from the start of the course at 750 yards toward the wind turbine

at “zero” yards (p. 2-32). There was a hill shading the test route along Garden Canyon

Road just before the start point at 750 yards that may have created standing waves at the

higher frequencies that caused this effect (p. 2-32). The signal levels tended to level out

as the wind turbine was approached until about 300 yards where they either start to

increase or decrease at a high rate. The large signal level swings were greatest at the three

highest frequencies tested where reflections from objects and terrain would have been

greatest. If the wind turbine is causing the RF fields around it to fluctuate according to

distance, these fluctuations should diminish with increasing distance, unlike that shown

in Figure 17 at 2970.02 MHz where the signal peak at 640 yards is the same level as at

340 yards. This peak was also in line with the 5999 MHz peak and the 4500.2 MHz

valley. All three deviations were smaller than the deviations at 160 yards and should have

continued to diminish had the ground been level. In this frequency set, the peak at 335

yards where it increased to 3 dB above the trend line was used as the limit. For the three

figures, the furthest distance from the wind turbine where the signal level deviated from

the trend line by 3 dB was for 337.5 MHz at 420 yards from the wind turbine.

Figures 18, 19, and 20 show the signal level swing from maximum to minimum

caused by blade rotation (Sasarita, 2013, p. 2-33).

Figure 18. Signal Level Swing from Maximum to Minimum Caused by Blade

Rotation for 1.42 MHz to 60 MHz Showing the 3 dB Intersection Point at

445 Yards for 30 MHz (from Sasarita, 2013, p. 2-33).

Figure 19. Signal Level Swing from Maximum to Minimum Caused by Blade

Rotation for 90 MHz to 454.3 MHz Showing the 3 dB Intersection Point at

340 Yards for 90 MHz (from Sasarita, 2013, p. 2-34)

Figure 20. Signal Level Swing from Maximum to Minimum Caused by Blade

Rotation for 725.01 MHz to 5999 MHz Showing the 3 dB Intersection

Point at 185 Yards for 4500.2 MHz (from Sasarita, 2013, p. 2-34)

The 3 dB intersection point at

340 yards.

The 3 dB intersection point at

185 yards.

Ten data points were used from 750 yards to 90 yards, then 12 data points from

60 yards to 5 yards. “More data points were used close to the tower to illustrate the

standing waves created by the tower structure” (Sasarita, 2013, p. 2-32). At 30 MHz and

90 MHz, data was collected at maximum and minimum points instead of at 5 yards

increments (p. 2-32). This was done to again illustrate the standing wave pattern (p. 2-

32).

Data points were collected for 1.42 MHz, a local radio station because their

transmit antenna was located directly in line with the test transmit antenna West of Site

Boston. It illustrates as does data at 2 MHz that the wind turbine structure has little effect

at low frequencies unless very close to the tower.

The 30 MHz graph line in Figure 16 establishes a minimum test boundary around

the wind turbine at 445 yards due to signal strength fluctuations of 3 dB caused by blade

rotation on the wind turbine. The distance of 445 yards due to blade rotation is further

from the wind turbine than that shown in Figure 16 at 337.5 MHz caused by standing

wave patterns around the wind turbine structure. Therefore, the overall perimeter inside

of which there is a disruption to RF signals greater than 3 dB is 445 yards from the wind

turbine. A test boundary of 500 yards would provide for a margin of error of about 10%.

The basic resonance of the wind turbine blades occurs at 2.5 MHz for the blade

structure made up of both blades. Based on this, Table 5 predicts whole number multiples

of this resonant frequency where the lightning protection grounding wires inside the

blade structure acts as a multiple wavelength resonant antenna exhibiting gain and the

ability to broadcast any received RF signal.

Table 5. The Harmonic Multiple of the Wind Turbine Blade Resonance at 2.5 MHz Up

to 225 MHz with the Test Frequencies Highlighted with the Largest Signal

Level Deviations (from Sasarita, 2013, p. 2-37)

Harmonic Multiple Resonant Frequency Harmonic Multiple Resonant Frequency Harmonic Multiple Resonant Frequency Harmonic Multiple Resonant Frequency Harmonic Multiple Resonant Frequency Harmonic Multiple Resonant Frequency 1 2.5 16 40.0 31 77.5 46 115.0 61 152.5 76 190.0 2 5.0 17 42.5 32 80.0 47 117.5 62 155.0 77 192.5 3 7.5 18 45.0 33 82.5 48 120.0 63 157.5 78 195.0 4 10.0 19 47.5 34 85.0 49 122.5 64 160.0 79 197.5

Harmonic

Multiple Frequency Resonant Harmonic Multiple Frequency Resonant Harmonic Multiple Frequency Resonant Harmonic Multiple Frequency Resonant Harmonic Multiple Frequency Resonant Harmonic Multiple Frequency Resonant

5 12.5 20 50.0 35 87.5 50 125.0 65 162.5 80 200.0 6 15.0 21 52.5 36 90.0 51 127.5 66 165.0 81 202.5 7 17.5 22 55.0 37 92.5 52 130.0 67 167.5 82 205.0 8 20.0 23 57.5 38 95.0 53 132.5 68 170.0 83 207.5 9 22.5 24 60.0 39 97.5 54 135.0 69 172.5 84 210.0 10 25.0 25 62.5 40 100.0 55 137.5 70 175.0 85 212.5 11 27.5 26 65.0 41 102.5 56 140.0 71 177.5 86 215.0 12 30.0 27 67.5 42 105.0 57 142.5 72 180.0 87 217.5 13 32.5 28 70.0 43 107.5 58 145.0 73 182.5 88 220.0 14 35.0 29 72.5 44 110.0 59 147.5 74 185.0 89 222.5 15 37.5 30 75.0 45 112.5 60 150.0 75 187.5 90 225.0

RF signals from 2.5 MHz up through the Very High Frequency (VHF) (Sasarita,

2013, p. 2-35) band are reradiated by the conductor used for lightning protection (p. 2-

38). As the high end of the VHF band, near 300 MHz is reached, RF signals tend to be

reflected by metal parts and the surface of the blades rather than reradiated by internal

conductors (p. 2-38). This transition is gradual as seen in Figure 21 where re-radiation is

greatest at 30 MHz, and then tends to lose efficiency as the number of wavelengths

increases (p. 2-38). “At 225 MHz, a resonant peak still exists but is small in comparison

to the lower frequencies. The theoretical gain that can be achieved at 16 wavelengths

approaches 10 dB. The radiation pattern tends to narrow, developing a cone directed

beyond the blade tips that is approximately 30 degrees wide. Because of this, signal

fluctuations due to blade spin may be greatest edge on. As the frequency increases into

the ultra high frequency (UHF) band and beyond into the microwave bands, the

reflectivity of the blade surface becomes dominant, causing the widest signal strength

fluctuations facing the blades instead of edge on” (p. 2-38).

Figure 21. Wind Turbine Blades Showing the Resonant Frequency of 2.5 MHz for

the Structure (from Sasarita, 2013, p. 2-36)

“The conductors in the wind turbine blades will reradiate all frequencies above

2.5 MHz” (Sasarita, 2013, p. 2-38) but frequencies that are whole number multiples will

cause resonance, thus greatly increasing the efficiency of the re-radiation (p. 2-38). For

this reason, if testing is conducted in the vicinity of this wind turbine, HF and VHF radios

should avoid using any of the frequencies listed in Table 5 (p. 2-38). “Frequencies half-

way between consecutive harmonics should be used to cause the least amount of

interference” (p. 2-38).

F.

OPERATIONAL SYSTEM TESTS

The premise of this operational system test was to determine any adverse impact

the operational subject wind turbine may cause on a common device used by the Army.

The GPS receiver was selected as the common device and this section documents the

result of that test (Hynes, 2012).

1.

Test Objective

•

Evaluate the influence of the Nordic 1 MW wind turbine on the

performance of a GPS receiver (Hynes, 2012, p. 2).

•

Determine if the wind turbine adversely masks the GPS Satellites or cause

any other interference with a GPS receiver (Hynes, 2012, p. 2).

•

Determine if the use of an EMI reduction device mitigate any negative

impact of the wind turbine on the performance of the GPS receiver

(Hynes, 2012, p. 2).

2.

Test Criteria

No measurable perturbation in the GPS receive signal when operating in the

vicinity of the wind turbine, with turbine blades spinning as well as stationary.

3.

Test Procedures

Two PRO GPS/Serial Logger (PRO Logger, developed by EPG) systems were set

up with one of the antennas deployed with an EMI shield (mounted on passenger side of

HMMWV) and the other without a shield (mounted on driver side of HMMWV) (Hynes,

2012, p. 2). See Figures 22–24.

Figure 22. HMMWV Showing GPS Antennas Mounted on Each Side (after Hynes,

2012, p. 2)

EMI Shielded GPS Antenna

Unshielded GPS Antenna

Two PRO Orientation Sensors (developed by EPG) were set up in the back of the

HMMWV, and two model GPS-018x-M16 GPS receivers inside the HMMWV cab. The

orientation sensors record the orientation (heading, pitch, and roll) of the respective GPS

receiver. The GPS receiver records its position as the HMMWV moves.

Figure 23. Orientation Sensors Mounted on Bench in Back of HMMWV (from

Hynes, 2012, p. 3)

Figure 24. PRO Loggers (from Hynes, 2012, p. 3)

Drive the HMMWV around the wind turbine and record the GPS receiver signals

and the Orientation Sensor measurements.

4.

Data Required

GPS receive signals and Orientation Sensor measurements correlated with the

position of the wind turbine, with turbine blades spinning as well as stationary.

5.

Data Analysis/Procedure

The recorded signals and measurements were uploaded into the MPGPA Data

Analyzer to display the GPS signals received. The position of the GPS receiver was then

plotted on Google Earth. The Orientation Sensor measurements were plotted in Excel to

display heading, pitch, and roll with respect to GPS time (UTC).

The number of satellites tracked by the PRO Logger varied between 6 and 11

during the entire test. The number of satellites tracked dropped to six when the turbine

started and stopped as well as when the blades were stationary. Below the turbine, facing

West, the number of satellites tracked was between 8 and 10. Measurements at this

location were only taken with the turbine blades stationary.

The PRO Logger data plotted on Google Earth followed the route driven. Several

plots were made (Figures 25–38) to illustrate that accurate GPS signals were received

over the entire route travelled. Several Orientation Sensor plots were made and they were

all similar to that shown in Figure 39.

a.

MPGPA-DA Plots for GPS with Antenna Unshielded

Figure 25. MPGPA-DA Plot Showing GPS Performance (No EMI Shield, Turbine

Blades Stationary) (from Hynes, 2012, p. 10)

Figure 26. Below Wind Turbine Facing West (No EMI Shield, Turbine Blades

Stationary) (from Hynes, 2012, p. 12)

Figure 27. Notch Occurred While Moving GPS Over Survey Point, Not While

Driving by Wind Turbine (No EMI Shield, Wind Turbine Starting and

Stopping) (from Hynes, 2012, p. 24)

Figure 28. GPS Performance While Driving by Wind Turbine (No EMI Shield, Wind

Turbine Starting and Stopping) (from Hynes, 2012, p. 26)

Figure 29. MPGPA-DA Plot Showing GPS Performance (No EMI Shield, Turbine

Blades Spinning Continuously) (from Hynes, 2012, p. 38)

Figure 30. MPGPA-DA Plot Showing GPS Performance (No EMI Shield, Turbine

Blades Spinning Continuously While Driving By) (from Hynes, 2012, p.

b.

MPGPA-DA Plots for GPS with Antenna Shielded

Figure 31. GPS Antenna with EMI Shield and Blades Stationary (from Hynes, 2012,

p. 17)

Figure 32. GPS Antenna with EMI Shield (Below Wind Turbine Facing West, Blades

Stationary) (from Hynes, 2012, p. 19)

Figure 33. Turbine Starting Up, Then Shutting Down (GPS Antenna with EMI

Shield) (from Hynes, 2012, p. 31)

Figure 34. Turbine Starting Up, Then Shutting Down While Driving By (GPS

Antenna with EMI Shield) (from Hynes, 2012, p. 33)

Figure 35. MPGPA-DA Plot Showing GPS Performance (GPS Antenna with EMI

Shield, Turbine Blades Spinning Continuously While Driving the Entire

Route) (from Hynes, 2012, p. 45)

Figure 36. MPGPA-DA Plot Showing GPS Performance (GPS Antenna with EMI

Shield, Turbine Blades Spinning Continuously While Driving By) (from

Figure 37. PRO Logger GPS Data for Entire Route Driven Plotted on Google Earth

(from Hynes, 2012, p. 15)

Figure 38. PRO Logger GPS Data for Route Near Turbine Plotted on Google Earth

(from Hynes, 2012, p. 22)

Figure 39. Orientation Sensor Plot (from Hynes, 2012, p. 21)

In document The electromagnetic impact of wind turbines (Page 58-78)