Wind turbines for electricity generation - basics

Presently wind turbines are used primarily for electrical power generation. Threephase alternators (AC generators) are used almost exclusively. Even for applications that require DC the lower-cost alternator/rectifier configuration has superceded the DC-generator. When a three-phase generator feeds directly into a grid, that operates at a fixed frequency (e.g. 50 Hz in Europe, 60 Hz in the U.S.A.) the angular velocity of the generator is fixed - or almost fixed. In this situation the power generation capability of the wind turbine will be fully utilized for just one value of wind speed (approximately 8 m/s in Fig. 11-1a). Thanks to the highly developed converter technology of today it is now possible to operate with variable generator speeds even for grid-connected generators (see Fig. 6-18). This yields better utilization of the wind turbine; during gusty winds it also substantially decreases the mechanical stresses in the blades and the shaft between turbine and generator.