In wind power stations both fluid (lubricating oils) and consistent (lubricating greases) lubricants are used. The main task of the lubricant is to ensure reliable operation of the machine elements. Important lubrication points in wind turbines are in the main gear drive, the yaw system gear, the main and generator bearing, the pitch adjustment unit and the nacelle slewing ring. Lubricants must satisfy a number of performance requirements that are unique to this industry. The turbines are located all over the world, on mountain tops, along coastlines, in deserts, etc. So, in addition to the longevity issues, lubricants must be able to withstand a variety of environmental conditions, including temperature extremes and moisture, in addition to being able to resist corrosion and oxidation. All these characteristics should be maintained over an extended period of time. Changes to the design of wind turbines create additional demands on lubricants that are used in the wind power industry. As interest in the industry grows, engineers are working to improve the efficiency and the output of wind turbines. Gearbox designs contain more equipment designed to produce more work, and more work means the generation of more heat in the gearbox. As a result, lubricants must function at higher operating loads while helping to reduce temperatures in the gearbox.
In addition, plant operators require prolonged oil service life and grease relubrication intervals. While the engine oil of a car is changed after 15,000 to 30,000 km, which corresponds to an oil service life of 300 to 600 hours at an average speed of 50 km/h, the gear oil in a wind turbine is changed after as many as 25,000 to 50,000 service hours. Commodity lubricants as defined by various standards cannot meet the expectations of today’s wind industry. Even in today’s widely used turbines with a power output of 2 to 3MW, conventional lubricants are tried to their limits. Turbines designed to generate 5MW pose conditions that are simply too much for the lubricants as described in various international standards, and there are already 9MW units that are being tested!
Still, the role of lubricants is widely underestimated in the wind energy sector, although it has a decisive influence on the performance, efficiency, maintenance requirements and service life of the equipment. An additional aspect to consider in wind power stations is that maintenance and repair jobs often have to be carried out under adverse conditions. This problem will be aggravated in the high-capacity offshore wind parks that are going to be built (e.g. when unplanned maintenance becomes necessary during unfavorable weather.) If conditions are too harsh, a defective component may even mean that the turbine is forced to remain idle for some time—downtimes of several months are quite conceivable. High-grade lubricants can help prevent such failures and extend maintenance intervals. If just a single inspection is rendered unnecessary, this will compensate for the total lubricant costs arising during the whole service life of a plant.