Wind turbine gearboxes are subjected to a wide variety of operating conditions, some of which may push the bearings beyond their limits. Damage may be done to the bearings, resulting in a specific premature failure mode known as white etching cracks (WEC), sometimes called brittle, short-life, early, abnormal or white structured flaking (WSF). Measures to make the bearings more robust in these operating conditions are discussed in this article.

The growth of worldwide energy consumption and emerging industrial markets demands an increase of renewable energy shares. The price pressure coming from coal, oil, nuclear and natural gas energy - combined with enormous worldwide production capacities for components of wind turbines - make wind energy a highly competitive market. The testing and validation of gearboxes within the test rig and the turbine environment attract a strong focus to the needs of the industry. The following contribution sums up the typical process requirements and provides examples for successful system and component verifications based on field measurements.

A reader asks: I have heard that new axles no longer need a break-in period. True or false?

It's not a show title that rolls off the tongue, but the Industrial Automation North America and MDA NA @IMTS 2014 show nevertheless may well be one to remember.

Bearings that show wear may not always need to be replaced. Depending on the degree and type of wear, they may be candidates for reconditioning, a process that restores bearings to like-new specifications and performance - at an average 50 to 60 percent of the cost of replacement.

The chemical and physical properties of gear oils may change, depending - more or less - upon their formulation and the environmental conditions under which they are used. This is why - after three years of use in a wind turbine - a gear oil was examined to determine if indeed changes were evident and if the protection of the gears and rolling bearings still met the same requirements as would be expected of fresh oil. Our findings revealed that the existing gear oil - as well as its ability to protect the gears and rolling bearings - had degraded very little compared to fresh oil.

A critical problem for wind turbine gearboxes is failure of rolling element bearings where axial cracks form on the inner rings. This article presents field experience from operating wind turbines that compares the performance of through-hardened and carburized materials. It reveals that through-hardened bearings develop WEA/WECs and fail with axial cracks, whereas carburized bearings do not. The field experience further shows that a carburized bearing with a core having low carbon content, high nickel content, greater compressive residual stresses, and a higher amount of retained austenite provides higher fracture resistance and makes carburized bearings more durable than through-hardened bearings in the wind turbine environment.

In most applications, gearbox reliability is critical to the productivity of the overall plant operation. So it follows that when industry is looking at the best ways to increase efficiency, reduce downtime, and increase profitability, gearbox performance and reliability are key factors. Designing for repair, and writing effective repair procedures, can speed the service time, and provide a quality refurbishment. The best practices listed in this article are proven, effective methods used to install and remove bearings, seals, gears, couplings and shafts within a gearbox.

The complete technical Calendar from the February 2014 issue of Power Transmission Engineering.

Dave Soma, the mechanical supervisor at Leland Olds Station, a coal-fired power plant near Stanton, North Dakota, says he and his maintenance team care deeply about keeping the plant running and providing people electricity, especially in the dead of winter.