Optimal Maintenance Policy for Wind Turbine Gearbox with Minimum Requirement For Full Capacity Operation

This study investigates a commonly used maintenance strategy for wind turbine gearboxes in a wind farm located in southern Morocco. The gearbox condition is monitored through temperature sensors, and when a critical temperature threshold is reached, the turbine’s production rate is deliberately reduced to facilitate cooling. After a predefined cooling period, the turbine resumes its normal production rate. As these overheating-cooling cycles become more frequent over time, operators must decide when to replace the gearbox. The replacement involves either installing a new identical unit or refurbishing the existing one, with the timing of this decision relying solely on the judgment of the maintenance crew. In collaboration with this wind farm, we develop an analytical model and a solution procedure to optimize the gearbox renewal period. The model balances the costs associated with production losses during cooling phases and the financial and operational impacts of gearbox renewal. A critical constraint considered in the model is the minimum Full Capacity Operating Rate (FCOR) that must be maintained throughout the renewal cycle. The optimization model determines the ideal renewal period, T*, that minimizes the total cost per unit of time while ensuring compliance with the required FCOR. The model is extensively tested using various problem instances. An example is presented, and a sensitivity analysis is conducted to evaluate the influence of gearbox reliability and production loss costs on the optimal maintenance strategy. The results underscore the importance of model- and data-driven decision-making in optimizing maintenance operations and highlight the significant impact of reliability variations on maintenance planning.