Transients in a Wind-mill Driven, Two-speed, Squirrel-cage Induction Generator.

The most widespread generator in wind-mill installations is a doubly fed, slip-ring induction generator. The rotor circuit include a static converter allowing power flow in both directions: from the rotor by negative slip and to the rotor by positive slip. However, in small and medium wind power plants a simple, double-speed, squirrel-cage induction generator may be considered as a suitable alternative replacing a doubly-fed slip-ring induction generator. The higher speed range would be predestined for normal operation, which, however, requires some minimum wind speed. If the wind is weaker, re-switching of the generator to the lower speed range would still secure some power output. Re-switching to other speed is, however, accompanied by heavy transients in currents, torque and power. The aim of the contribution is to present the plots of instantaneous speed, torque current, power and voltage by adjusting the operation to strong, moderate and weak wind. The plots of the torque in the clutch may constitute a base for assessment mechanical stress in the gearbox and wind-mill blades.