As an industry one of our worst nightmares are turbine fires. Foremost the risk to our employees, then the cost and bad publicity. Common causes of wind turbine fires include electrical system failures and lightning strikes. A less discussed source of fires arise from mechanical component failures. Main bearings, brakes and gearboxes have each been associated with the root cause of fires where frictional heat generation was ignition source.
Failed sun pinion retaining plate bolts – the failure of these actual bolts led to a turbine fire. Metallurgical analysis showed the bolts got so hot that the Rockwell C hardness was below the scale (soft like cheese)
Owners and operators typically expect the turbine controller to monitor the turbine mechanical components and shut the turbine in the event of a problem, but in some cases the monitoring system is unable to detect the failure, or there are not the sensors in place to pick up the problem in time.
One example is an internal gearbox bolt failure on the sun shaft retaining plate. This plate is secured with a total of 16 bolts. (Note: the sun shaft is part of the planetary stage of the gearbox).
This is a sun shaft retainer plate that is in good condition. The retainer is held by 16 bolts and keeps the sun shaft in position.
The purpose of the retaining plate is to resist axial loads on the sun shaft and keep it in position. These bolts have failed due to a combination of fatigue and backing out. The next step in the progression of failure is the rotating sun shaft and retaining plate contact the stationary low speed cover. Hammering against it, scoring it and as you can imagine this abuse generates significant heat and debris. The failure of these little bolts has led to a turbine fire.
Failed sun pinion retainer plate. The image shows the 16 sheared bolt ends, sheared pitch tube and other mangled pieces for assembly. The broken retained plate has been removed. In this case the owner was lucky, an encoder fault stopped the turbine. However, in another turbine the frictional heat generation inside the gearbox set the turbine on fire.
Interested in understanding the root cause of failures that have caused turbine fires? Attend the Third Annual Wind Turbine Technical Symposium to get into the details.