This section submitted by Ashley Crowther, Global VP – InSight, Romax Technology
Modern gearboxes provide greater reliability to the wind-energy industry thanks to improvements in their design and operation. These include better bearing selection, design process, manufacturing quality, transportation, lubrication systems, and end-of-line testing. Reliability issues will never completely go away, but staying on top of issues can help reduce maintenance costs at aging wind farms.
Currently the most common failure modes are parallel-stage bearing axial cracking, planet-bearing fatigue (wear out) and gear-tooth cracks or liberation. Most often failures are the result of micropitting, heat treat type or quality, harsh loading and poor lubrication. The root cause is often not due to just one source. Many parallel stage issues can be repaired uptower, but planet stage repairs typically take place downtower.
Knowing the condition of your assets is the first place to start. Knowledge that the failure is impending can also reduce downtime. Regular temperature and oil analysis can help inform you as to the condition of the gearbox. Temperatures will rise when bearings are significantly damaged, improperly set or if the cooler is not functioning well. However, temperature may not alert you to bearing cracks. Determine the filter condition by checking how much debris is being generated – is it full of metal? Take a picture of the swarf magnet as well. This low-cost activity allows a short list for borescope inspections.
A routine maintenance schedule tends to reduce reliability issues. If a large wind farm is having two to four issues per year with main bearings and gearboxes, scheduling repairs concurrently saves on bringing a crane out.
Good maintenance practices can help extend gearbox life. For example, a supply of dry, clean lubricant increases bearing life significantly. Ensure filters are changed regularly and an oil sampling and analysis program is in place. Offline filters, typically 3 micron, can be retrofit if necessary. These have a lower flow rate, running in a kidney loop and effectively reduce wear from debris. Other options are available to ensure dryer oil. It’s also important to flush and change oil in accordance with quality requirements and watch out for water in it. Breathers, sealing, oil and climate conditions all influencing gearbox life.
Some damage is hard to find using these basic approaches, such as parallel-stage bearing cracks and planet-bearing damage. Other approaches may be more expensive but worthwhile. For example, permanent vibration monitoring costs a bit more and is a large capital cost retrofit, but can effectively identify damage well ahead of a failure. Take time to do educate yourself to find the best approaches for your project.