Turbines of the Year 2020: Drivetrains

Understanding of full systems and modularity helps push gearbox design

ZF Shift 7k… Modular design and record-breaking torque density
ZF Shift 7k… Modular design and record-breaking torque density

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MEDAL WINNER

GOLD ZF Shift 7k modular gearbox

ZF Wind Power recently crossed the 200Nm/kg torque density barrier with its new Shift 7k high-speed gearbox platform, a little over two years after the Shift 6k set the previous torque density record of 175Nm/kg.

The "over 200Nm/kg" torque density value applies to the Shift 7k at platform level, with higher densities achievable by dedicated designs, according to a ZF expert

A key enabling factor of this successful launch is an in-depth understanding of how an entire system works. Even load-sharing between all planetary gear planets is crucial.

Inspired by the automotive industry, the Shift platform is fully modular with a high degree of scalability, offering maximum design flexibility and faster development of new products. All Shift platforms, from 3k to 7k, are made of standardised building blocks.

The 7k version has three planetary stages with seven, six and four planets in descending order and, remarkably, journal bearings only in the first stage. The fourth stage is a parallel gear. Four-stage gearboxes have more components than three-stage equivalents but these are smaller in size.
To meet global requirements, the maximum nacelle width is 4.2 metres. This translates to a maximum 2.1m first-stage ring gear outer diameter for the 7k platform.

Input torque levels of 7,000- 8000kNm allow intermediate turbine enhancements. The corresponding turbine specifications are 6.5MW-7MW, with matching 180m-plus rotors. The 7k gearbox has a mass of about 40 tonnes.

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