Specialty Lubricants Boost Efficiency And Reliability At Low Temperatures

Enhanced properties can benefit rim/pinion drives on pitch and yaw bearings

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The rapid expansion of wind energy throughout the world has been accompanied by a significant growth in wind power plant size. Rotor diameters of more than 120 meters (nearly 400 feet) and nominal outputs as high as 3 MW have become standard. However, the continuous increase in output and efficiency has not automatically resulted in higher reliability of plants. Rather, it often results in increased maintenance efforts and higher operating costs. Today’s specialty lubricants can help ensure machine efficiency and trouble-free operation, even at low temperatures.

The reliability of modern wind turbines and their components can be enhanced by using lubricants designed to meet specific requirements. New specialty lubricants for gear rim/pinion drives on pitch and yaw bearings can offer good pumpability and metering in central lubrication systems to temperatures as low as -30°C (-22°F), thus contributing to the increased reliability of turbines.

It all depends on which way the wind is blowing
A wind power plant can only be fully effective if it is permanently and perfectly aligned to the direction of the wind. Consequently, changes in wind direction need to be compensated by aligning the yaw system at the proper angle. Electric motors adjust the yaw bearing via gear rim/pinion drives. In addition, to ensure maximum energy yield at varying wind forces, rotor blades are adjusted by means of gear rim/pinion drives.

Often, the prevailing wind direction is constant in many locations which keeps only some of the gear teeth in mesh. For the teeth in mesh, lubricants of extremely high load-carrying capacity offer elevated and reliable protection against wear. Also, the gear teeth which are not in mesh must be protected against corrosion. Another challenge is adhesion. The lubricant on the tooth flanks of open gears might be displaced from the surface, drop off and lead to increased wear.

Lubricant Properties
In order to meet the requirements for lubrication of yaw and pitch bearings, including those noted above, lubricants need the following properties:
• Good adhesion
• Low consumption
• Good wear protection
• Long service life
• Good corrosion protection
• Long-term priming
• Pumpable via central lubrication systems

Lubricants must retain these properties when the weather is cold.

Overall Properties
A special combination of mineral or synthetic base oils and white solid lubricants ensures high load-carrying capacity and reliable wear protection. Good adhesion properties and light color of a specialty lubricant can reduce  consumption, extend maintenance intervals of a wind turbine, and significantly decrease unsightly contamination of a plant. In addition, lower disposal and storage costs ensure further cost savings in plant operation.

A Clean Solution
The black lubricants previously used for yaw and pitch bearings often contained graphite, thus causing contamination inside and outside the wind turbine. Occupational safety for the maintenance staff is at risk due to slippery floors in the plant. In addition, excess grease leaking from the tower and blades can pollute the surrounding area. White, adhesive lubricants without graphite limit these problems.

Lubrication at Low Temperatures
Most open gears of wind power plants are still lubricated by hand. However, maintenance can be reduced to keep downtime to a minimum. For example, central lubrication systems are increasingly being used for the relubrication of open gears. Traditionally, adhesive lubricants are very viscous and difficult to pump at low operating temperatures. The latest developments present open gear lubricants  that can be pumped in automatic lubrication systems at a temperature of -30°C (-22°F).

Adjusting the Nacelle
The sliding layers, e.g., PETP, of a yaw plain bearing can be lubricated with a specialty lubricant in order to prevent stick-slip and wear, thus ensuring a reliable and trouble-free operation. Low friction coefficients minimize the force required to adjust the nacelle. Drive units are protected and energy consumption is reduced during adjustment. The slight difference between static friction and sliding friction values ensure a uniform adjustment movement between start-up and normal operation.

Many Requirements – One Specialty Lubricant
Specialty lubricants offer significant advantages that meet the increasingly demanding requirements of wind power plants, including:
• Reduced lubricant consumption
• Minimized turbine contamination due to light color
• Reduced cleaning costs
• Low disposal costs for used lubricants
• No lubricant drop-off in case of vertical gears
• Trouble-free operation due to wide service temperature range with good pumpability and metering via centralized lubrication systems, down to -30°C (-22°F)
• Increased machine efficiency
• Effective corrosion protection, even after extended periods of standstill
• Suitable for gear rim/pinion drives, as well as yaw plain bearings