Why hot flush...
Wide variations in speed and load, changing wind direction, climatic extremes and limited space inside nacelles conspire to reduce wind turbine availability and increase maintenance costs. The primary culprit is the gearbox, followed by blades and generators.
Recent estimates show wind farm energy output averages 10 percent below projections and that half the shortfall is due to gearbox unavailability. Operation and maintenance (O&M) costs start escalating in the fourth year of operation, with gearboxes being the single largest issue. While wind turbines have design lives of 20 to 30 years, gearbox warranties are often as short as two years.
The most problematic of all gearbox issues is bearing failures, a challenge expected to increase as turbines get larger. Gearbox reliability problems are being addressed with advanced designs, better materials and with another important strategy: oil contamination control.
Next-generation contamination control technologies, already proven in industrial plants and mobile equipment, can essentially reduce particle and water contamination problems the two most common and damaging oil contaminants to zero.
Particle Oil Contamination...
With rigorous particle contamination control, bearing life can increase 2.6 to 3.7 times, resulting in greater gearbox reliability, uptime and energy production, extended warranty periods and a higher return on investment. Surprisingly, particles invisible to the unaided eye, about 1 µm in size, can knock out a 20-ton gearbox. How can this happen? In spite of their size, the dynamic clearances between moving parts in gearboxes are also on the order of 1 µm, separated by a thin film of lubricant.
Particles the size of or slightly larger than the oil film thickness enter the contact zone and damage surfaces. In sliding contacts like gear teeth, hard particles plow through and abrasively wear away surfaces while increasing frictional energy losses and heating. In rolling contacts, particles dent surfaces, leading to roughening and surface-initiated fatigue spalling. Hard ductile steel particles, typical of gear wear debris, are the most damaging, but large quantities of any hard particle seriously degrade bearing life. Particle contamination also reduces the service life of gear lubricants. The surfaces of fresh metallic wear particles and freshly worn components are catalytic, accelerating oil degradation by oxidation. Oxidation products include acids, oil thickeners that lead to cold start problems and gummy substances that coat and insulate heat exchange surfaces and foul flow controls and passages. One classic study found fresh metal surfaces accelerate oil oxidation by six to eight times, as measured by build-up of oil acidity. While copper (found in tubing and bronze bushings) is troublesome, it's likely that the large amount of steel wear debris in gearboxes is the major offender in wind turbines.
Hard ductile particles, typical of gear tooth wear, produce the greatest bearing life decrement. More fragile particles tend to shatter in contact zones, producing less damage per particle.
"Oil coolers have been compared to a 30 micron or finer filter"
Wind Turbine Failure