Risk-based operation and maintenance of offshore wind farms

By Mihai Florian, Aalborg University

Since offshore wind is a new and rapidly developing industry, maintenance practices have not yet been developed to minimize effort and expenses. This results in a great deal of waste in the operator’s maintenance budget, rising lifetime cost and lowering power production. Operation and maintenance expenses account for around 30% of levelized cost of energy, and there is potential for considerable reduction.
Risk and reliability centered maintenance is a strategy that has been developed in the aerospace industry, aiming to maintain an acceptable reliability level for a component/system while at the same time reducing the amount of inspections and repairs and making maximum use of a component’s life. The strategy has been proven very efficient in comparison with traditional planning procedures, and has become standard of practice in a wide variety of industries, including offshore based industries like oil and gas.
To minimize lifetime expense, a pre-posterior decision tree is used analyze possible outcomes from various decisions, as illustrated in figure 1. Random outcomes from inspections are calculated using probabilistic model, while various decision rules on repairs are tested using simulation based models to obtain and minimize expected lifetime cost.

Figure 1: Decision tree

Inspection planning and decisions on repairs on a component are made by estimating failure probabilities. The models used for this include information on the health and age of a specific component, general information on failure rates and also observations from various inspection procedures, each inspection leading to a more accurate estimate, as shown in figure 2 in an example for blade maintenance planning. The figure shows how the failure probability estimate changes after having made inspections in year 1, year 2, etc.

Figure 2: Updates on blade failure distribution for turbine blade

Results from an example study on blade maintenance are shown in figure 3, where inspections and repairs were made so that the failure probability does not exceed a certain threshold. The figure shows expected lifetime cost for various thresholds, and identifies the optimal value, minimizing expenses.

Figure 3: Expected lifetime cost for blade maintenance


About Mihai Florian

Mihai Florian is PhD student at Aalborg University with John Dalsgaard Sørensen as supervisor. His work is part of NORCOWE’s WP3 “Offshore deployment and operations”.
A deliverable from WP3 is the formulation of the theoretical framework for a risk-based decision tool for planning of operation and maintenance.
More information about WP3 projects is available in NORCOWE’s annual reports and in presentations from NORCOWE’s Science Meets Industry (SMI) conferences.

International cooperation: This research is coordinated with the research in the EU FP7 projects InnWind, IRPWind and LEANWIND, and the Danish EUDP project “LEX: Torsional Stiffening of Wind Turbine Blades – Mitigating Leading Edge Damages”.




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