Advanced maintenance operations

Abstract

This research aims to develop a maintenance strategy for large offshore DOT wind farms to reduce the costs for O&M. The strategy consists of a logistical solution in the form of a stock keeping scenario and a mechanism to exchange parts of the drive train. Requirements for the maintenance strategy is to be innovative, in order to stand out from conventional wind turbines and to reduce downtime to a maximum of 5%, in order to be competitive with conventional wind turbines.

The research was performed by simulating five stock keeping scenarios and six mechanisms to exchange the complete drive train, or parts of the drive train. Every combination between stock keeping scenario and exchange mechanism was simulated for a 700 MW DOT wind farm located at the proposed wind farm sites of both “Hollandse Kust: Noord-Holland" and “IJmuiden Ver", for 5.0 MW and 7.0 MW turbine configurations.

The simulations were carried out using the O&M Calculator developed by ECN.
The results of the simulations show that the conventional approach to maintaining offshore wind turbines is not the best approach. In terms of a logistical solution, making use of a dedicated maintenance island in the sea or a floating workshop in the form of a service operations vessel (SOV) gives a 2 to 3% higher availability compared to how stock keeping is currently performed.
Nowadays the exchange of components of the drive train is done by expensive and scarce installation vessels. Even though a large intervention like this is not often needed a decrease in downtime of up to 1% can be achieved if DOT wind farms make use of a better exchange mechanism. Best results are achieved for an integral exchange of the complete drive train, hub and blades, in case of component failure.

For a DOT wind farm to reach the industry's goals to reduce downtime to a maximum of 5% the maintenance strategy needs to be changed. The greatest downtime reduction is found in reducing the waiting time for a suitable weather window. Keeping resources closer to the wind farm or improving weather capabilities of your vessel can help in doing so. Conclusively an innovative component exchange, making use of the modular concept of the DOT can ensure a maximum downtime of 5%.