Rainer Lange, Mobil SHC brand advisor at ExxonMobil, explores how lubricants are evolving to optimise wind turbines in some of the most challenging environments on Earth.
Today, wind turbines are installed in increasingly isolated locations, where they are exposed to some of the most extreme weather conditions on the planet.
At sea, offshore wind farms endure 100mph winds and crashing waves. Back on land, installations in mountainous regions and extreme cold climates are now commonplace.
Such places create a very challenging scenario for wind-farm operators – high and variable stress levels in combination with extreme operating conditions.
The role of grease
Lubricants play a fundamental role in the efficient operation and protection of wind turbines. But they, too, suffer at the hands of Mother Nature.
Wind turbines rely on grease to protect pitch, yaw, and main shaft and generator bearings and gears. Many feature a centralised greasing system, which manages the flow and ensures all of these vital components are well lubricated.
With very long grease lines and up to 100kg of grease in a single turbine, optimal lubrication is a critical element of effective and sustained turbine operation.
Cold complications
As temperature decreases, the grease’s resistance to flow increases, affecting central grease systems in two ways:
- Reduced ‘pumpability’: more pressure is required to deliver the grease to lubrication points, which means that system capabilities can be exceeded.
- Reduced ‘slumpability’: less grease flows into the suction side of the pump, so the grease flow in the system can be disrupted.
Take the pitch bearing, for example. In extreme cold conditions, NLGI 1.5, 460 viscosity greases have been found to thicken while travelling to the pitch bearing. This results in excessive power being required to help the grease reach the bearing.
It is therefore essential that the selected lubricant has flow characteristics that guarantee an adequate grease supply to all lubrication points.
Further complications can be experienced in the grease reservoir. Here, the grease travels into the central lubrication system via a pump. The pump is below the reservoir, allowing gravity to help push the grease into the pump. However, a NLGI 1.5, 460 viscosity grease may stick to the sides and be too thick to reach the pump in extreme cold environments, leaving parts of the bearing unprotected.
Ensuring efficient operation
Grease performance can also impact the efficient operation of the turbine and how much power it generates.
When the turbine is not in operation, the grease starts to become thick. A low-temperature environment can aggravate the issue, further increasing the torque needed when generation restarts.
Furthermore, blades must be positioned at the optimal degree to maximise energy generation. However, a thick grease can mean the operating degree is slightly off, which may impact the amount of power generated.
New-generation wind turbine grease
ExxonMobil’s Mobil SHC Grease 102 WT is an example of a lubricant scientifically engineered to operate effectively in extremely cold temperatures. The synthetic grease provides excellent bearing protection and structural stability from -50 to +120°C. In fact, even at -50˚C, Mobil SHC Grease 102 WT offers excellent mobility and pumpability at 600mbar, helping ensure optimum lubrication while also protecting against pressure-related issues.
Protection from within
As wind turbines are installed in ever more challenging environments, wind-farm operators must optimise every element of their operation to help protect their machinery. The right lubricant, such as Mobil SHC Grease 102 WT, can help extend equipment life, reduce maintenance costs and increase uptime – protecting their business from within.