ERC Researchers Investigate Use of Hydrostatic Transmissions for Wind Power
Researchers affiliated with the Center for Compact and Efficient Fluid Power (CCEFP), an NSF-funded Engineering Research Center (ERC) headquartered at the University of Minnesota, are investigating replacement of the mechanical gearbox of current wind turbines with a hydrostatic transmission (HST) to reduce stress on the gearbox and generator bearings.
Because the power path in an HST is hydraulic, the inherent compliance in the fluid and fluid lines provides a damping effect, which results in large stress reduction in the gearbox and generator during wind gusts. HST use thus offers promise of reducing service needs for these components along with lower costs and improved reliability.
In a conventional utility-scale wind turbine, there is an 80-100X increase between the rotational speed (rpm) of the turbine blades and the speed at which the generator operates. This speed increase is done with a mechanical gearbox, which experiences high stress during wind gusts; this stress is transferred from the gearbox to the generator. As a result, two of the highest service items in a wind turbine are the gearbox and generator bearings. The continuously variable transmission functionality of an HST also allows a constant generator speed independent of the turbine blade rpm. This reduces the need for power electronics substantially, thus lowering cost and further improving reliability