skip to Main Content

The Mystery of the Missing Planet Gear Crack

At ONYX InSight we are detecting and confirming well over 50 failures a year in wind turbine rotating machinery.  It’s our bread and butter.  Most often the cases are very vanilla; we detect an early stage bearing crack with Fleet Monitor, watch it for a few weeks to ensure its trending clearly, then notify the site with recommendation for inspection.   The inspection comes back confirming the damage and we advise the time to repair and risk threshold, whether it be 3 months or 18 months available for planning.  Eventually the repair is conducted in a cost effective manner and the vibration level returns to normal.

Occasionally a failure occurs that takes much more work to confirm and thorough engineering support to minimize the cost – which is always the goal.  One such example is the recent Mystery of the Missing Planet Gear Crack!  In this mystery (eventually solved) the vibration indication was very clear: a planet tooth crack diagnosed (one of the three planets) and trending up.  The turbine was de-rated and inspection ordered.  However …. inspections in the planetary stage in a wind turbine gearbox are challenging.  Typically you are accessing only a limited part of the gears, until you pack up the borescope, remove the rotor lock, and rotate the gearbox a quarter turn, and then get back in there.  It’s time consuming.  Also, you can’t inspect below the oil line unless you drain the box.  In this case, there wasn’t any significant debris being generated, which would limit the effectiveness of a particle counter to confirm the issue.  The question remained , “Do we want to replace the gearbox out without visual indication?”  I’d prefer not to, where possible.

So, inspection after inspection was conducted without an answer.  Eventually after 3 months and 4 inspections, lo and behold, mystery solved! The planet gear is cracked as per the vibration indication.  The site immediately took the turbine offline.  Fortunately, with the damage pre-warned by vibration, the downtime and repair cost were tightly managed.  Running de-rated helped reduce the risk of the damage progressing to a cracked housing, where all the gearbox oil ends up on the yaw deck and down the tower and the price to repair and clean up climbs steeply.  Just like a good mystery novel … we have a happy ending.

And if you really like the technical details, register for our 2018 EU Technical Symposium or US Wind Turbine Technical Symposium.  Events focused for turbine owners, asset/site managers and reliability engineers to get deep into wind farm reliability and maintenance.

Watch out for our upcoming webinar, “The Cost of Major Failures to the Wind Industry – What to Expect in 2018 and How to Reduce Them”, where we talk through practical failure issues and associated cost data.

Back To Top