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Chapter 9
Electromagnetic Interference from Wind Turbines

Excerpt

It is well known that any large structure, whether stationary or moving, in the vicinity of a receiver or transmitter of electromagnetic signals may interfere with those signals and degrade the performance of the transmitter∕receiver system. Under certain conditions, the rotor blades of an operating wind turbine may passively reflect a transmitted signal, so that both the transmitted signal and a delayed interference signal (varying periodically at the blade passage frequency) may exist simultaneously in a zone near the turbine. The nature and amount of electromagnetic interference (EMI) in this zone depend on a number of parameters, including location of the wind turbine relative to the transmitter and receiver, type of wind turbine, physical and electrical characteristics of the rotor blades, signal frequency and modulation scheme, receiver antenna characteristics, and the radio wave propagation characteristics in the local atmosphere. When the influence of these parameters on EMI is understood, wind turbines can usually be designed and sited so that any interference with communication signals may not exceed allowable levels.

Figure 9-1 illustrates the field conditions under which a wind turbine may cause EMI. A transmitter, T, sends a direct signal to two receivers, R, and a wind turbine, WT, that may be of either the horizontal- or vertical-axis configuration (HAWT or VAWT). The rotating blades of the turbine produce and transmit a scattered signal. Thus, the receivers may acquire two signals simultaneously, with the scattered signal causing EMI because it is delayed in time or distorted. Signals reflected in a manner analogous to mirror reflection are termed back-scattered. As shown in the figure, about 80 percent of the region around the turbine is the backward-scatter zone. On the other hand, signal scattering that is analogous to shadowing is termed forward scattering, and about 20 percent of the region around a turbine is the forward-scatter or front-scatter zone.

  • Introduction
  • Analysis of Signals with Electromagnetic Interference
  • Idealized Scattering Models of Wind Turbine Rotors
  • Field Measurements of Television Interference
  • Comparison of Observed and Idealized Signal Scatter Ratios
  • Laboratory Simulation of Television Interference
  • Theoretical Prediction of Interference Distances and Zones
  • Radio Interference Effects
  • Potential Interference with Microwave Communication
  • Interference with Navigation Communication Systems
  • References

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