The offshore wind industry is continuously eyeing enhancements in design and manufacturing in order to boost reliability, which in turn can curtail the occurrence and cost of unscheduled maintenance/ activity.

Unscheduled maintenance comes into focus owing to spur-of-the-moment outages and it can result in a precarious situation since downtime is not known until the error is sorted out.

This area continues to gain significance especially in the wake of higher expectations pertaining to operational availability as well as the rising values of offshore wind turbines. On the positive side, information about diverse failure modes, in particular their development and detection, is on the rise. Thus, in many cases condition changes can be spotted in the relatively initial stages, and this knowledge is helpful in gearing up for the required maintenance and to avoid unanticipated outages.

Learning Curve

“The major challenge is to foresee unscheduled failures via analysis of all climatic and operational data especially with regard to major components,” says Ralf Neulinger, Director Operations Renewable Energies, EnBW Erneuerbare und Konventionelle Erzeugung AG. Neulinger says that this process has a learning curve.

“If such level is reached, it will be possible to turn from unscheduled downtime to a much higher rate of scheduled downtime, which allows you to use sufficient logistics and materialson a sufficient price level, and also to reduce loss of revenues during downtime,” adds Neulinger.

Solid Approach

Neulinger says entities need to evaluate a comprehensive strategy. He suggests that it is possible to reduce effects of unscheduled downtime on other components via “intelligent” planning.

“Any O&M strategy has to be updated continuously based on a detailed analysis of any failure that has occurred. Essentially, it is very important to be able to access a turbine on downtime as soon as possible, and using sufficient access equipment (in such cases),” he says.

Stephan Schnitger, Head of Innovation & Optimisation, Energiekontor, too, highlights the significance of a well-rounded strategy. “Each entity should establish preventive maintenance beside its regular maintenance activities. A detailed preventive maintenance strategy reduces operational cost,” he says.

According to him, a successful preventive maintenance strategy should be based on the detailed knowledge of the critical components within a wind farm. For example, an initial analysis of turbines based on type and related vulnerability to breakdown can be a starting point for a technical view. There is also a need to understand the lead time and cost for spare parts. A professional staff organisation will be able to place maintenance and repair work in low wind periods.

Schnitger says the major challenge is to understand the probability of failure and at which point in time.

A successful O&M strategy should be based on developing the “crystal bowl”, which provides such information early enough so that you can make a productive maintenance plan.

Schnitger adds that a growing number of technical analysis methods as well as improvement measures (such as endoscopy, frequency analysis, oil analysis, etc.) require an impartial base for a go/ no-go decision. A matrix of three dimensions provides an impartial view on decisions pro/ con technical measures, such as benefit of measures; cost of measures and follow-up cost of not carried out measures.

Dealing with “high wind times”

Unscheduled or scheduled down time is especially expensive if it occurs during high wind times.

According to specialists, in Europe, winds usually are higher during autumn and winter from September to February. Some recommendations to deal with tough conditions include down time during summer, which is less critical and maintenance activities should be scheduled just before the wind season starts to have the turbines up and running through the entire wind season.

Owners should start as soon as possible to use SCADA data and data from state of the art condition monitoring systems in order to “read” the data correctly. Conducting simple statistical analyses may reveal certain patterns of temperature or vibration levels in bearings , which can indicate unusual behaviour. This can trigger a replacement during the next scheduled event before the part fails.

Another tip is to consider is if the service provider is only incentivised by a time base availability warranty, which means that the owner runs the risk of turbines being down for either scheduled or unscheduled maintenance during high winds. To avoid this, the owner should be involved in the maintenance planning at least by approving the annual maintenance plan and schedule upfront.

Helpful Initiatives

Unscheduled maintenance continues to be a major portion of total operational expenditures, with projects showing major and minor correctives comprising nearly 50% of operating budgets. It is recommended that the combination of effective condition based monitoring products, up-tower repair solutions and lower level component remanufacture will play a pivotal role in reducing these expenditures.

Effective commissioning is a must, but the impact of effective micrositing can be more beneficial, ensuring the correct turbine technology is applied per local site conditions.

Downtimes are more complicated offshore than onshore because of the logistic problems which evolve from the position on the high seas. It isn’t always the most cost efficient way to only concentrate on avoiding downtimes. Entities need to consider how to guarantee efficient and economical performance of turbines. Some of the tools which enable to reduce disruptions to a minimum include technical monitoring, sophisticated sensor systems and professional data evaluation.