Pitch bearings are one of the subassemblies with high failure rates and largest contributors to overall downtime. The average life of a pitch bearing varies by manufacturer, turbine, and site operating conditions. Given the current design constraints, as the diameter of wind turbine rotors increase, and projects are placed in more turbulent sites, failure rates are expected to rise.
It is a challenging application, the bearings are installed packed with grease and we hope they will rotate back and forwards for 20 odd years without needing to be replaced. In the case where the rotor needs to be lifted down for repair often has the owner wondering, replace just one or replace all three?
Due to slow rotational speeds, pitch bearings operate in boundary lubrication, which can result in more rapid accumulation of surface damages compared to bearings that operate with sufficient film thickness. Extensive root cause analysis work has identified common causes of failures, including ellipse truncation, cage wear and surface fatigue cracks originating at stress concentrations, and quality issues from poor induction hardening. The root cause is not the same in every case.
The pitch bearings can sometimes be inspected by borescope and there are some solutions to extend life.
Figure: Extensive Root Cause Analysis Investigation for one Common Turbine Firmly Pointed at Ellipse Truncation as the Root Cause
The nuts and bolts of a number of serial failures in common wind turbine platforms will be key on the agenda at The Second Annual Romax InSight Wind Turbine Technical Symposium taking place this September in Breckenridge, Colorado. Other topics we will discuss include pitch bearings, main bearings and cutting edge diagnostics. Reliability engineers at Romax InSight and top turbine owners in the USA will be expanding on those topics. A good deal of sharing and discourse helps attendees with understanding issues and how to improve turbine operations.