Gearbox failure

Most geared turbines step the rotor's rotational speed up by a factor of roughly a hundred to drive the generator. The gearbox that does this sits at the top of the tower, weighs many tons, and operates under variable, reversing loads. It is the component whose failure most often requires a crane, and a full replacement runs into hundreds of thousands of dollars once the lift, the parts, and the lost production are counted.

Failures rarely begin at the gears. They usually begin at a bearing - commonly on the high-speed shaft or a planet stage - and progress through micropitting, spalling, and debris circulation before the gear teeth themselves are damaged. That progression takes weeks to months, which is precisely why the failure mode is worth detecting early.

The early evidence is in the operating record rather than in the alarm log. Oil and bearing temperatures drift upward for the same load and ambient conditions, vibration signatures gain energy at characteristic frequencies, and the relationship between torque and temperature shifts. None of this crosses a threshold until late, which is the difference between condition monitoring and a fault code.

The economics are what make it the standard example for predictive maintenance. Weeks of warning turn an emergency crane mobilization into a planned lift booked into a maintenance campaign, and offshore, where a crane means a vessel, the difference between the two is larger still.