Effect of Pitch and Safety System Design on Dimensioning Loads for Offshore Wind Turbines During Grid Fault

This paper discusses the loads inflicted on large offshore wind turbines from sudden and persistent loss of electrical connection during severe operational conditions. The load case that is discussed is loss of electrical connection during an extreme operating gust. The sudden loss of generator torque leads to an increase in rotor speed and an emergency shutdown situation. The load cases are simulated using the time domain aeroelastic code fast, and compared to the maximum loads the turbine experiences during normal operational conditions. The hydraulic pitch system is modelled in detail, and the effects of changes in the pitch speed are investigated by varying the dimensions of valves and the accumulator. The grid fault does not seem to be dimensioning for structural loads on the tower or the blades, but it would likely be dimensioning for the blade tip deflection towards the tower in the case of a downwind turbine.