Gearboxes

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.

GEARBOXES - OVERVIEW

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

1. https://www.prnewswire.com/news-releases/wind-gearbox-and-direct-drive-update-2017---global-market-size-competitive-landscape-and-key-country-analysis-to-2021-300514654.html#:~:text=The%20share%20of%20global%20wind,to%20reach%2032.2%25%20in%202021.

GEARBOXES - TYPES OF DAMAGE

Two key areas of 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.