Mechanical Stresses in Fixed-Speed Wind Turbines Due to Network Disturbances

Electrical faults and other network disturbances generate transients of the generator electromagnetic torque, which result in significant stresses for the wind turbine (WT) mechanical system and may also have a detrimental effect on the fatigue life of important drive train components, such as the gearbox. In this paper the effect of faults and other disturbances, common in rural medium voltage (MV) distribution systems, is analyzed for a typical fixed speed WT, equipped with an induction generator. The resulting torque transients are evaluated and their propagation in the drive train is examined. Important conclusions are drawn with respect to the type of electrical faults to be considered in the design and certification of WTs according to the current IEC 61400-1 Standard. Although the emphasis is placed on the developed torque transients, the methodology presented is also suitable for analyzing electrical stresses in the generator, due to over-currents or over-voltages.