Reliability is one of the most important features of the wind turbine gearbox, especially in offshore wind turbines (OWTs). This paper describes a general way to perform gear contact fatigue reliability analysis for wind turbines considering inspection and repair. A simplified predictive surface pitting model for estimating gear fatigue lives is applied to establish the ‘so-called’ limit stated functions. The National Renewable Energy Laboratory (NREL)’s 750kW land-based wind turbine is used to perform time domain simulations considering different wind speeds that the turbine will experience, whose occurrence frequencies are described by a generalized gamma distribution. The time series of the torques in the main shaft are obtained from the global dynamic response analysis of the wind turbine. The time series of the gear contact forces are obtained from the dynamic analysis of the gearbox through multi-body simulation. The 2-parameter Weibull distribution is used to fit the long-term probability distribution of the gear tooth contact pressures. The reliability analysis is based on fracture mechanics (FM) analysis of crack growth. Finally the sensitivity of the reliability index and failure probability on initial crack size, critical crack size, detectable crack size, crack size after repair, material property and environmental loads is estimated considering the effect of inspection.

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