Proven Design Concepts

The role of the gear unit in the wind turbine

Driven by the turbine rotor and driving the electric generator, the gear unit is an important link in the wind turbine drive train.

  • Transmitting power
  • Increasing speed
  • Reducing torque (torque = rotating force)

Offering the full range

Continuing its pioneering role at the cutting edge of wind power transmission technology, ZF Wind Power has carved out a reputation as a top-tier global supplier of innovative and durable gearboxes, supplying gearboxes to the world leaders in gear-driven wind turbines. With almost 100 years experience in gears and gearboxes in all kinds of industrial and automotive applications and almost 35 years in gearboxes for wind turbines ZF Wind Power has developed – in close cooperation with its customers – cutting-edge designs for wind turbine gearboxes to specifically match the wind turbine structure.

With a long tradition of innovation, ZF Wind Power seeks to differentiate itself in the marketplace by means of quality and reliability in customized solutions for different concepts used by its customers in their markets: Integrated, Conventional, High Speed and Medium Speed. ZF Wind Power offers a range of customized gearboxes that are co-designed, co-developed and custom-built to the precise specifications of the leading wind turbine manufacturers worldwide.

High power-to-weight ratio

ZF Wind Power firmly believes machine optimization is strongly driven by integration with its surrounding application . Therefore significant time, expertise and expenditure on research and development is spent on achieving high power-to-weight ratios. The power-to-weight ratio of a gearbox is important since weight reduction leads to a reduction in the cost of transportation, foundations and installation as well as of the cost of the accompanying tower.

Proven technology

The development of a new product starts from proven and approved technology, which reduces the product validation process to the validation of the specific application of the technology. In addition, new products are conceived based on proven drive train concepts. In this way, ZF Wind Power’s product portfolio is developed in a matrix of torque scale versus drive train concept, where every specific customer concept is covered – from medium to high speed and from conventional to integrated design.

This approach minimizes the time required for conceptual design and guarantees the exclusive use of known and proven concepts, which in turn ensures functionality, quality, and suitability for the ZF Wind Power manufacturing environment.

In each concept, structural elements that interface with other drive train components or with the nacelle carrying structure are designed specifically for the wind turbine. Gearbox internal components and subassemblies are often standardized, however without any compromise on the customer’s design flexibility and the functionality of the drive train.

High speed solutions

With its product range for high speed drive wind turbines ZF Wind Power banks upon proven design concepts in typical configurations of “1 planetary + 2 parallel stages” or “2 planetary + 1 parallel stages”. This ZF product range in combination with the widely used Doubly Fed Induction Generators (DFIG), offer an overall drive train that is both proven in the field as well as cost optimized.

Since bearing technology in wind turbines and especially in the high speed drive train is very challenging due to the dynamic behaviour of the application, ZF Wind Power has invested considerable R&D effort in the design of bearing configurations that withstand typical loading conditions in the wind turbine. To this end, ZF has invested in a dynamic bearing test rig – the most advanced facility in its kind – to perform dedicated tests on bearing arrangements under conditions that mimic the actual operational conditions in the application.

In this way ZF Wind Power pro-actively contributes to the design of robust bearing arrangements for new gearboxes in order to constantly prove and improve performance of wind turbine gearboxes and thereby increase overall operational availability of wind turbines.

Medium speed solutions

ZF is one of the industry leaders when it comes to integrated medium speed drives for wind turbines, with the prototype of our medium speed gearbox already introduced in 2009. With this experience, and following the growing market interest in wind turbines with medium-speed generators, ZF Wind Power is the ideal partner for developing new medium speed drives in the multi-megawatt class. ZF Wind Power firmly believes in the viability of these hybrid solutions, as these systems strike an attractive balance between reliability and complexity.

Advanced gear concepts

ZF Wind Power planetary gear designs include advanced and proven concepts.

the split planet concept for the multi-MW range, which also uses our proven pre-tensioned taper roller bearings in the first planetary stage, enabling a leap in MW scale whilst using planet bearing sizes known from smaller gearbox ranges

the bogie principle which compensates for deformations in the surrounding structures thereby ensuring optimal gear load distribution under all operational conditions. This gearbox design allows our customers to design their nacelle frame structures for strength, leading to minimum weight, instead of for stiffness, which is required for alignment purposes in conventional designs. In the ZF Wind Power rotor side integrated 3MW design an integrated double taper row main bearing transfers rotor loads whilst the gearbox housing stiffens the nacelle frame leading to record low tower top weights. This gearbox design features excellent efficiency through lubrication by means of an external oil tank, instead of an internal oil sump.