Wind Turbine gearboxes

Although wind turbines are relatively uncomplicated machines, they do work in tough environmental conditions. Therefore, they need extremely reliable and high quality components.
Crucial are the gearboxes which control the propeller pitch on the rotor. S.Me.I produces the RES range of modular planetary gearboxes, as well as custom versions. Nineteen different sizes are available in the range, which is available from UK distributor JBJ Techniques Limited. They cover a range of torque levels from 1000Nm to 500,000Nm. Possible ratios, with up to four stages, go from 3 to over 3000. With a relatively low number of components, the series is built to a modular design, so that a high number of variants can be built to meet the most exacting requirements.

The RES 175 GR is specifically designed for the propeller pitch adjustment on a windmill rotor of more than 500kW and it has been approved by Germanischer Lloyd for this application. Three gearboxes, one for each blade, rotate in unison. Due to the unconventional assembly procedure used for the gearbox, the sealing system plays a crucial role. The oil within the device is pushed outwards by centrifugal force. Therefore to avoid even the slightest leakage, the input shaft is fitted with two seal rings.

The prevailing temperatures, humidity and salinity in which windmills operate all add up to a hostile environment. The gearbox uses two straight roller bearings mounted on the output shaft. The bearings are lifetime-lubricated on a fit-and-forget basis using a grease designed to last over 24 years, the nominal life cycle of the wind turbine.

To aid assembly, the external and internal rings of these high load capacity bearings can be mounted separately. But then, to avoid a complex sealing arrangement, a set of sealing rings is used which consists of a single lip ring placed on the internal side of the gearbox to separate the oil from the grease, plus a ring with a dust cover lip mounted on the external side. The latter is protected by a special O-ring and both fit on a stainless steel wear sleeve.

RES gearboxes are made from case hardened alloy steels (18-5 or 17-6 NiCrMo). Housings are made from a combination of spheroidal graphite cast iron for safety-critical parts and grey cast iron for secondary components.