Client Case Studies

Yaw Ring Replacement

Major component failure occurred due to poor turbine maintenance from previous O&M provider.

The turbine first faulted having power (production issues) which quickly changed into yaw failure. The production issues were due to the yaw failure as the turbine was trying to produce electricity but was not facing into the wind. Unfortunately, there is no way of remotely seeing the direction the wind is coming from, or if the turbines are facing into it.

The turbine was found to be facing out of the wind. The team found the yaw issues were caused by broken yaw teeth.  The team removed the right side worm gearbox from the planet stage and the drive shaft was missing meaning the right side had been doing all the work for an unknown period of time.

Following the first visit we prepared the replacement yaw ring, arranged cranes, the crane pad was tested. We were hindered by strong winds and low-pressure weather fronts.

At the first opportunity the nacelle was lowered into the special frame. The yaw gear ring is part of this and the removal of the nacelle is the only way to change it.

We then began stripping off the claw beams to separate the yaw ring from the nacelle, the nacelle was then lifted from the frame leaving the damaged gear ring on the frame, this was then replaced with the replacement intact ring. The wear parts of the claw beams and some steel were damaged, so they were replaced with refurbished (new spring packs, and PTFE plates and pucks)

During the work we removed the nacelle outer casing, this allowed us to examine the yaw drives. It was found the left hand planet gear was 28:1 ratio, but the right side was 20:1. Also the hardened steel ring had become loose and the actual planet gear had been forced over and was sat at an angle, the left hand retaining bolts had stretched.

The hardened steel ring should not be visible, it sits inside the main chassis and provides an exact friction fit for the base of the planet gear. We carefully cleaned and dressed the ring, and refitted using retaining compound, then re-drilled retaining bolts to ensure it doesn’t come loose again.

The planet gear as already mentioned was 20:1 so incompatible with the left-hand drive. This may well be the reason someone removed the drive shaft between the worm and planet gear. It will have been putting immense stress on the teeth and/or thermal motor overloads.

We had a 28:1 Bonfiglioli planet gear at the workshop, we sent someone to collect this for the following day.

We also had to obtain and replace the 12.9 cap heads holding the planet gear as they had stretched.

The new planet gear was fitted; it was confirmed that now both drives matched. 950rpm motor, to a 40:1 worm gear, to a 28:1 planet gear

The nacelle main frame was refitted back into its GRP cover.

It was then lifted back onto the tower and bolted in place.

The rotor was refitted and bolted in place.

The major reinstatement of all cabling etc began.

At the end of the work the turbine was put into run, it connected to the small generator and was producing, it then switched to the large generator.

Conclusion

Previous O&M installed the right-hand side planet gear but did not understand the relevance of different ratio gearboxes or the consequences. We think rather than the first opinion the O&M forgot to put in the drive shaft, they saw the consequences and removed it to allow the turbine to run without the owners knowing a big mistake had been made. That consequence could have been the loss of the first tooth, persistent yaw errors (motor overloads), but even if the second is the reality tooth damage will have already happened.

Leaving a V47 running on one yaw drive shows a real lack of knowledge of the turbine technology.

We have checked across the site to ensure all the other turbines have drive shafts installed. The next issue to check is whether all the ratios of the worm gearboxes and planet drives match.