Mechanical transmission systems require online health monitoring for several reasons. Gearboxes account for many of the maintenance costs due to repairs, replacements and downtime. Transmission systems feature in many applications including rotor aircraft and wind turbines.

The wind energy industry since its inception has experienced high levels of failure rates. Principal gearbox design defects and structural problems have been notably significant issues of wind turbines and have had to be addressed by the wind turbine manufacturers. Reliability and safety of conventional wind turbines has improved although rates of failures are still disappointingly high.

There still exists a lack of sufficient technology to enable reliable monitoring of the structural and operational conditions of wind turbines and this is currently a significant area of research.

Gearbox monitoring in particular lacks sensor technology to successfully detect tooth damage, high speed and low speed shaft faults. Typically, vibration measurement and spectrum analysis are chosen for gearbox monitoring but, these methods are not able to detect the faults until failure is imminent. More recently acoustic emissions sensors are being developed for early detection of stress and surface defects.

This paper presents a new concept that employs an eddy current sensor fitted to the teeth of an idler gear to detect early micro and macro pitting of the gear tooth surface. A rotating bench test has been carried out to validate the technique where simple eddy current sensors have been fitted to an idler gear. Seeded faults of three different types on an actual gear have been shown to be detectable using this technique. Eddy current sensors are used for their immunity to dust, dirt and oil contamination. Thus this technique is targeted for in-service operation where sensors have not previously been deployed to access the tooth face, flank and root shank.

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