Re-building a better gearbox

Broadwind's modular test rig is capable of full-load testing up to 3 MW.

As OEMs build larger wind turbines, they push the bounds of what’s possible for a 20-year service life. Occasionally, the boundaries push back with failures, often of gearboxes. Technicians at Broadwind Services, a division of Broadwind Energy in Abilene, Texas, say they can fix those broken gearboxes and make them better than new in a recently opened a 60,000 ft² facility.

The facility will disassemble, remanufacture, and do full-load testing on large wind turbine gearboxes. “We made upgrades to the overhead cranes, tooling, and equipment for the work cells that will do disassembly and reassembly,” says President of Broadwind Services Paul Seppanen. “An impressive test bench allows full-load testing up to 3 MW. It’s modular so it can handle the full range of gearboxes that are installed in turbines,” he says. Gears that need regrinding and replacement will be shipped to Broadwind’s gearing facility in Chicago.

Broadwind's Seppanan says worn gearboxes can be remanufactured to better than new conditions.

The company says its plan is to put back a better gearbox than it took out. “We can figure out why it failed, and look for the next revision of bearings, for instance, because those manufacturers are constantly innovating as well. Also, wind-gearbox OEMs are making multiple versions of their boxes, sometimes they have a model number that ends in -3 or -4. We can remanufacture an early gearbox version, upgrading it to a later specification, or even beyond the specification of the most recent version of the box. “Proprietary techniques such as superfinishing the gears so they mesh better, improved lubrication equipment, and a range of other enhancements will extend the life of the gearbox,” he says.

Seppanen says root-cause analysis is a core competency at the facility. The company has been inspecting and remanufacturing gearboxes for eight years in the U.S., mostly on the kW scale. “That experience will be put into MW gearboxes,” he adds

Some failures are caused by manufacturing defects, some come from loads and fatigue over the design life, and a small number just fail early. “Many wind turbines have stretched the limits of their gearboxes and in some cases loads they see are beyond what they were designed for. Originally, gearboxes in smaller turbines would run smoothly without substantial failure frequency over their working life.”

Analysis starts in the field often before a gearbox completely fails. Teams will be up-tower with borescopes looking inside the gearbox and using condition or vibration monitoring equipment to diagnose what might be going wrong. That data goes back to the shop for the team that will tear it down. Then working back through a chain of events lets the repair team understand the root cause. We might find damages to a gear or shaft but we know that what really led to that was the bearing that failed early. Experienced engineers will make the analysis. Remanufacturing the gearbox will solve the root-cause problem so when the gearbox goes back to the field it will run longer on its second life.”

Some owners carry a pool of swap boxes. “Part of the company strategy is to also build a pool of spare boxes. When an owner with a turbine down contacts us for one, we’ll sell the spare box to the owner and buy back the damaged “core” in exchange. In the ideal mode, the truck that takes out the remanufactured box hauls back the damaged unit,” he says.