Windtech: Drive reliability - Step up to multi-megawatt class

Small German wind turbine supplier PowerWind, which has built a strong reputation in the sub-megawatt class, is testing a 2.5MW prototype featuring a fast-speed gear system, permanent-magnet generator and full converter.

The company plans models with 90- and 100-metre rotor sizes.

PowerWind says the new turbine is designed to improve drive-system reliability and lifespan. "As a key drive-system component, gearbox development primarily requires a proper loads set," says Thomas Korzeniewski, the company's head of research and development. "Close communication between a wind turbine supplier and its gearbox supplier during the development process - which usually takes one to two years - is therefore essential."

Korzeniewski has seen poor communication lead to a mismatch between calculated and actual loads. When the development focuses on one main component, other components must be looked at simultaneously, he says. Any change in rotor loads has a direct impact on the gearbox.

Unlike its competitors, PowerWind's machine features a main shaft with two bearings, which Korzeniewski says minimises the effects of rotor bending on the gearbox. The solution creates so-called soft-gearbox support.

The gearbox is attached to the rear of the main shaft and kept in position during operation by hydraulic side supports. These extend gearbox lifespan by offering advanced programmable dampening characteristics under different operating conditions, Korzeniewski explains.

The turbine chassis offers internal components optimised support against load and the rear generator chassis affords maximised horizontal support.

An unusual aspect of the generator chassis - made up of two horizontal and several interconnecting cross-sectional parts - is its vertical orientation, which reduces weight and maximises load-carrying capacity. "This design approach resulted in a rather long generator frame for easy serviceability, with sufficient space inside the nacelle for two redundant power converters," says Korzeniewski. The medium-voltage transformer is located inside the tower foot to meet required voltage levels and other local requirements, he adds.

A clever feature of the turbine is its generator-cooling radiator. After being pre-installed and pre-tested, it can be folded into a horizontal position during road transport, reducing total height. To facilitate gearbox replacement, PowerWind developed a rail system enabling movement of the unit about 60 centimetres horizontally.

Korzeniewski says the two sister models' modular drive system is the most flexible for transport and installation. Nacelles can be transported in their complete form or in sections. Maximum hoisting mass will not exceed 50 tonnes.

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