Simulation and Testing

Both new technology and product developments require intensive simulation and experimental validation. Over the years ZF Wind Power has invested in cutting-edge test infrastructure, simulation models and test algorithms such as DORoTe to prove gearbox robustness.

ZF Wind Power has unique and extensive testing facilities available to:

  • Virtually assess gearbox designs on their dynamic behavior in the wind turbine generator.
  • Provide proven technology on component and subassembly level before prototype gearboxes are manufactured.
  • Perform dedicated tests on bearing arrangements under operational-like conditions.
  • Test gearboxes with overloading and dynamic loading conditions under operation-like loading conditions.
  • Perform accelerated life tests under operational torque-load conditions.

ZF Wind Power testing strength delivers:

  • Insight in the dynamic behavior of the drive train and specifically the gearbox, prior to the manufacturing of the prototype gearboxes.
  • Evaluate performance of prototype gearboxes on a controlled test rig under accelerated testing conditions prior or in parallel with field tests.
  • An increase in reliability of new products.

Production test facilities

ZF Wind Power is able to test and validate all prototypes and serial gearboxes in all its production plants. ZF has a unique global load testing capacity of almost 60 MW (including in the major service locations):

  • 1 x 13200 kW
  • 1 x 6600 kW
  • 2 x 4500 kW
  • 4 x 4100 kW
  • 2 x 4000 kW

13.2 MW dynamic gearbox test rig

ZF Wind Power’s dynamic gearbox test rig is one of the world’s largest test facilities in its kind matching the continuously increasing wind turbine power in the market. By means of this test rig ZF Wind Power is able to test gearboxes under representative wind turbine loading conditions, i.e.wind turbine operational conditions are reproduced by means of a set of dedicated and parameterized load cases programmed into the electrical controller. These test rig features enabling accelerated life testing to identify potential technical risks upfront and, consequently, further improve gearbox reliability.

  • The ‘wind & rotor’ side is composed of an electrical machine (motor 1), an optional speed reducer (3:1 gearbox) and a wind turbine gearbox (gearbox 1).
  • The ‘grid & generator’ side is composed of an electrical machine (motor 2) and an optional speed reducer. The optional speed reducers enable full power testing of wind turbine gearboxes in future so-called hybrid concepts where a low-speed generator is combined with a gearbox with a smaller ratio, e.g. for a nominal generator speed of 500 RPM (in comparison with the usual 1500 RPM).
  • Controller: analogous to the operation of a wind turbine, the ‘wind’ side of the test rig is speed controlled, whereas the ‘generator’ side is torque controlled.
  • Test gearbox 2 is driven at a certain time varying speed - corresponding to variable wind speeds - and loaded with a certain time varying torque by the ‘generator’ – corresponding to the loading from the grid.

The dynamic test rig in a few numbers:

  • Location: production facility Lommel, Belgium
  • Back-to-back gearbox set-up
  • Nominal power: 13.2 MW
  • Peak power: 16.8 MW
  • Nominal speed: 1500 rpm
  • Maximum speed: 2600 rpm
  • Representative loading conditions:
    - start, stop
    - normal operation with variable loading
    - run-pause
    - emergency stops
  • Foundation: 35 x 10 meter
  • Rig: 1,000 tons of steel and over 1,000 m³ of concrete
  • Motor and generator platforms moveable in three directions for accurate aligning of the complete test setup
  • 100% Availability (24/7)
  • Investment: over 10 Million EUR

Dynamic test rig features:

  • Test rig size and capacity matching the continuously increasing wind turbine power in the market.
  • One of the world’s largest test facilities in its kind.
  • Reproducing wind turbine operational conditions in a set of dedicated and parameterized load cases programmed into an electrical controller.
  • Testing gearboxes under representative wind turbine loading conditions.
  • Enabling accelerated life testing to identify potential technical risks upfront and, consequently, further improve gearbox reliability.

  • The ‘wind & rotor’ side is composed of an electrical machine (motor 1), an optional speed reducer (3:1 gearbox) and a wind turbine gearbox (gearbox 1).
  • The ‘grid & generator’ side is composed of an electrical machine (motor 2) and an optional speed reducer. The optional speed reducers enable full power testing of wind turbine gearboxes in future so-called hybrid concepts where a low-speed generator is combined with a gearbox with a smaller ratio, e.g. for a nominal generator speed of 500 RPM (in comparison with the usual 1500 RPM).
  • Controller: analogous to the operation of a wind turbine, the ‘wind’ side of the test rig is speed controlled, whereas the ‘generator’ side is torque controlled.

Test gearbox 2 is driven at a certain time varying speed - corresponding to variable wind speeds - and loaded with a certain time varying torque by the ‘generator’ – corresponding to the loading from the grid.

Dynamic bearing test rig

ZF Wind Power’s dynamic bearing test rig is the most advanced facility in its kind. By means of this test rig ZF Wind Power is able to test real size bearings in their actual arrangement as built in the gearbox, under representative wind turbine loading and environmental conditions. In this way bearing behaviour as well as loadability of bearing assemblies can be verified in order to pro-actively contribute to the design of robust bearing arrangements for new gearboxes and continuously improve the reliability of selected bearing arrangements. All tests are based on ZF Wind Power’s “Design Operational Robustness Test”.

Bearing test rig in a few numbers:

  • Investment 2.7 Million EUR
  • Radial force 1500 kN
  • Axial force 400 kN
  • Band width 50 Hz
  • Speed up to 2600 rpm

Robustness test philosophy

ZF Wind Power “Design Operational Robustness Test” (DORoTe) assesses the robustness of a new gearbox design with respect to the operational conditions as specified by the customer.

Our robustness test philosophy translates a set of simulated wind loads (i.e. the typical input design load time series from customers) into a dedicated test program. This test program comprises equivalent load conditions to be applied in a reduced time frame on ZF Wind Power’s 13.2 MW dynamic test rig or dynamic bearing test rig.

Test specification

  • Starting point is an in depth analysis of the rotor torque and rotor speed originating from the simulated wind turbine behaviour. This behaviour is then translated into so-called dynamic load cases, which are applied to the gearbox - using ZF Wind Power’s 13.2 MW dynamic test rig – or on the bearing set-up – using ZF Wind Power’s dynamic bearing test rig.
  • The considered operational time of the wind turbine is reduced to fewer test rig hours by increasing the load within acceptable levels. All loads are applied in a controlled test rig environment. A history of loading conditions is kept and development of possible damage in the gearbox is monitored by means of a condition monitoring system (CMS).
  • For proper evaluation of the DORoTe test the tested gearboxes are submitted to thorough inspection, comparable to evaluation after prototype field validation (full disassembly of the gearbox and inspection of all components).

Added value:

  • DORoTe aims at ‘unveiling the unexpected’ by including low load conditions and transient load cases (e.g. start-stop, emergency stops, …) in the test plan.
  • Typically two years of operational wind conditions can be translated in three months of continuous testing.
  • Early failure mode detection in test rig based prototype validation, before putting up the prototype for field validation.
  • Increasing gearbox reliability and reducing time-to-market.

Simulation philosophy

Increasing the reliability of wind turbine drive trains for wind turbines with ever increasing size requires dedicated simulation models which can provide more insight in the internal gearbox dynamics in the early stages of the design process. These drive train models should contain more than the typical one or two degrees of freedom in standard wind turbine design codes. Therefore ZF Wind Power chose the definitive way forward by developing multibody models of wind turbine gearboxes. These complex numeric gearbox models can then be exchanged with the wind turbine manufacturer in order to investigate the dynamics of the complete drive train even before the real gearbox is validated in the wind turbine.

However, multibody models can only add value to the design process if simulation results prove to be representative and reliable. Therefore ZF Wind Power dedicated an extensive amount of time to (a) thorough verification of these models by means of comparison with hand calculations and existing gear calculation codes and (b) validation based on measurements on real multi-megawatt wind turbine gearboxes in the back-to-back 13.2 MW test rig set-up at ZF Wind Power.

Dynamic simulations add value to the design process through in-depth investigation of the internal gearbox dynamics and possible optimization of various drive train components already in the concept phase:

  • Pro-active avoidance of resonances already in the design phase
  • Efficient product improvement during prototyping phase
  • Pro-active design optimizations based on accurate prediction of specific drive train loads

Shortening of design cycles and thereby speed-up of time to market will be the ultimate goal, without going at the cost of quality and reliability.

In close cooperation with customers ZF’s advanced MBS models of the drive train can be incorporated in detailed wind turbine MBS models, providing better insight in global and local resonances and responses to special wind turbine events. This approach strengthens ZF’s customer relationships, enables shorter development trajectories and helps to deliver strong and high quality products.

Further information

Test benches for wind power gearboxes

More