On Different Maintenance Strategies for Casted Components of Offshore Wind Turbines

This report, which is a part of the REWIND project, focuses on maintenance expenses for casted components mounted on offshore wind turbines. The maintenance costs for casted components are extracted from a maintenance operation tool, which simulates maintenance operations at wind turbine farms. This maintenance tool uses Crude Monte Carlo Simulations to estimate the expected maintenance costs. Corrective and preventive maintenance strategies with a constant inspection interval or a condition monitoring system are considered. Furthermore, transportation from shore to the wind turbines by boat and helicopter are considered. A case study assuming a wind turbine farm consisting of ten 6 MW wind turbines placed 30 km off the Danish North Sea coast investigates the cost saving potential for casted wind turbine components (low (LSS) and high speed shaft (HSS) and the hub) when optimizing the maintenance and transportation strategy. The case study shows that the maintenance expenses of casted components correspond to roughly 5% of the overall expected maintenance costs when using a corrective maintenance strategy. This amount can be decreased to roughly 2% when using a condition monitoring system and following a preventive maintenance strategy. The maintenance expenses for the hub dominates the maintenance costs of casted components. The maintenance expenses for LSS and HSS are smaller and much less sensitive to the maintenance strategy or the inspection quality.