AXIS Explores
Gearboxes
Overview
The gearbox is the heaviest component of a WTG and the most costly to replace.
High wind sites and those with complex terrain can reduce gearbox life significantly, due to the unpredictability of the wind patterns.
Maintenance is critical as many of the moving parts require lubrication and particulates can cause damage if allowed to enter the oil.
Condition monitoring systems are an effective way of highlighting gearbox issues before they become critical.
There are two main types of wind turbines:
Geared
- The original WTG design concept
- Features a gearbox between the low speed shaft and the generator
- More susceptible to damage from excessive wind loads
Direct Drive (DD)
- No gearbox
- More expensive
- Lower maintenance requirements making them more popular offshore
The ratio between geared and DD WTGs is roughly 70:30 by installed capacity1
Key areas where gearboxes typically suffer damage:
Bearings
Axial cracks are the main incidence of damage affecting the medium and high speed bearings.
These appear as White Etch Cracks (WEC) on the inner raceway (the grove that holds the ball bearings).
There is disagreement on the root cause of WEC but ‘torque reversal’ loads from emergency stops are one possibility.
Wind turbines suffer more axial cracks, than comparative equipment with large bearings.
Gearbox teeth
There are two main factors in damage to gearbox teeth:
- Inadequate lubrication
- Contaminants in the lubrication, including sand, dust and metal particles
It can be identified via visual inspection of the teeth or boroscope surveys.
