How can the gearbox condition affect the useful life of a wind turbine?

In spite of the apparently simple configuration of a wind turbine there is a great number of factors that have an effect on its useful life and that can lead to failures of its mechanical, structural, electrical or control parts, with varying consequences for its operation.

In industrial processes, the seriousness of a breakdown is estimated in terms of risk, a weighted measure that takes into account the parameters of frequency and impact in order to determine how critical the failure is. In the case of wind turbines the ones that recur most frequently are electrical, but despite the high probability that they might happen, they represent a low risk. That is to say, the solution to the problem is generally simple and does not require a large investment for its repair. On the other hand, structural failures and those that occur in the control systems are a very different matter.

The mechanical part of the wind turbine is where the greatest risk is to be found because, while it is not the most frequent type of failure, it is the one that needs the greatest investment for its repair and causes a longer period of down time of the wind turbine.

The multiplier, the most critical item

Among the items that undergo mechanical wear in wind turbines, the most critical is multiplier, the part that transforms the low number of revolutions per minute transmitted by the hub, where the blades of the wind turbine are fitted and the rotor is supported, to the high number of revolutions per minute that the generator needs to produce energy.

In the multiplier there may be failures caused by wear derived from operation, or as a consequence of the fatigue of the components, or by external contamination (water, air or dust particles) that can lead to the lubrication system causing accelerated wear of the components.

The purpose of the lubricate is, among other functions, to maintain a separation of 10 microns between one body and another. If a dust particle of 30 microns penetrates into this space, it acts like a knife and, as movement is produced between the parts, it generates particles and accelerated wear of the materials.

It can cost as much as 300,000 euros to replace a multiplier

The multiplier is a vital part in a wind turbine and, in view of the critical nature of the breakdowns that can occur in this component, it is the focal point of the preventive maintenance efforts in a wind installation. The operators of installations of between 40 and 50 wind turbines invest around 150m000 euros every year in maintenance and repairing breakdowns of these mechanical components. And the fact is that, ipso the maintenance efforts directed to the multipliers, 35% of all the possible failures that could be recorded are not observable in the periodic checks.

With regard to the different types of failures, a study carried out by Atten2 shows that out of every 10 failures, 9 can be repaired and one requires the replacement of the multiplier, with an estimated cost of between 77,000 and 300,000 euros depending on the power of the wind turbine.

The critical nature of the multiplier is also determined by the seriousness of the faults that it can undergo. Seventy per cent of the breakdowns are classified as serious, with an average cost of 45,000 euros for repair, and 30% are considered as minor breakdowns, which require an investment of €30,000 on average to resolve them. There us also the additional cost of hiring a crane, 15,000 euros more, if it is necessary to bring the mechanism down to ground level for its repair.