## Abstract

Modern wind turbine generator systems (WTGSs) are constructed mainly as systems with a horizontal axis of rotation, a wind wheel consisting of three blades, and high speed (1500/750 rpm) asynchronous generators and gear boxes (with ratio grater than 60); see Fig. 2.1. Asynchronous machines are used because of their advantages, such as simplicity of construction, possibilities of operation at various operational conditions, and low investment and operating costs. Asynchronous generators with squirrel-cage rotors and with wounded (slip-ring) rotors are used. In the second case, power electronic converters or variable resistors are connected to the rotor side of the machine, which makes it possible for the machine to operate at various speeds.^{1}

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## Reference

- 1.Unlike the WTGS with a squirrel-cage rotor asynchronous machine, which operates at constant speed (so-called constant speed system).Google Scholar
- 2.In fact, there is only one manufacturer of such a commercial WTGS.Google Scholar
- 3.Two-speed machine (constant speed system).Google Scholar
- 4.Variable-speed system.Google Scholar
- 5.Also the WTGS standstill can be considered as a state influencing the power system, e.g. by lack of electric energy production.Google Scholar
- 6.Please note that the figures show the WTGS power production measured for various wind conditions for each turbine. Therefore, the curves (e.g. amplitudes of power variations) cannot be directly compared. The curves should be treated here as typical for the given type of wind turbine only.Google Scholar
- 7.Overall costs, effectiveness and reliability of wind turbines are not considered or compared here.Google Scholar
- 8.The wind farm output power variations can be computed as
*-VTIZ1P*, where*zIP*is the ith turbine output power variation and*n*is the number of wind turbines.Google Scholar - 9.An MV voltage equal to 40 kV is given as an example here. Usually an MV voltage equal to 10–30 kV is used.Google Scholar