Grid code modifications require the in service fixed speed wind turbines to ride-trough grid faults. Voltage dips due to electrical grid faults generate transients of the generator electromagnetic torque. These transients result in significant stresses and vibrations affecting the fatigue life of the components. An electro-mechanical model was built to simulate the grid faults that excite the asynchronous generator with poorly damped stator flux oscillations. These oscillations cause transients of the generator electromagnetic torque. This article focuses in estimating the resulting significant stresses transients affecting the fatigue life of drivetrain system due to voltage dips. A rainflow cycle counting method was developed to evaluate the fatigue life of the mechanical system. The methodology analyses the stress history and estimates the mean and amplitudes of the counted cycles, and time of duration to calculate the accumulated damage occurred during the voltage dip event.
Engineering Mechanics, 2012, Vol 19, Issue 2/3, p. 143-154
Voltage dip, Electro-mechanical model, Drivetrain, induction generator, rainflow count, Fatigue