As in other areas of the wind industry, hydraulics engineers are looking for ways to improve turbine operating efficiency while reducing maintenance. This leads to a focus on preventative maintenance, rather than just replacing worn parts with new ones from the OEM. Research is also being conducted toward expanding hydraulics in wind transmission drives.

Ken Rohr with Applied Industrial Technologies explains how reducing maintenance costs and improving operating efficiencies are ways operators can improve their return on investment. “We are seeing companies push the envelope to learn how new technologies can help improve operating efficiencies beyond how the system was originally designed,” he says.

According to Rohr, proactively managing oil contamination and preventive maintenance on fluid power systems help keep turbines in peak operating condition. “Old-school maintenance programs of replacing worn parts with new ones at regularly scheduled intervals is being quickly succeeded by preventive maintenance programs that extend part life, and supplement that with replacement-part strategies that offer equal or better parts at a lower cost,” he explains.

Dheeraj Choudhary of Parker Hannifin’s Renewable Energy Division agrees, saying that combining the power density and weight benefits of hydraulics with electronics can make turbines more reliable and precise. “Sealing and connector technologies allow field replacement and repairs without the use of heavy or welding equipment on-site, and they enhance the life of rotational devices such as bearings, the gearbox, and generator,” he says. Choudhary explains that fluid power plays an important role in turbine gearboxes. For instance, new hydraulic systems cool and condition gearbox oil for lubrication and constantly monitor temperature, pressure, vibration, oil particles, and moisture. This helps reduce downtime, gearbox failure, and expensive repairs.

Groups are also doing research to expand the use of hydraulics in wind power. The Center for Compact and Efficient Fluid Power (CCEFP), a National Science Foundation engineering research center, recently launched several projects related to hydraulic applications in wind. One included a grant to study hydrostatic drives for wind transmissions. Brad Bohlmann, sustainability director for CCEFP explains that engineers are investigating using hydrostatic transmissions (HST) in wind applications. “HSTs have been a dominant choice for off-highway propulsion systems for more than 50 years,” he says. “There are literally millions of HSTs currently in use worldwide in very demanding commercial applications where performance, durability, and reliability are critical. Thus, the technology has a long and successful track record, and the proposed turbine drivetrain technology builds on a legacy of success.”

Using a hydrostatic transmission to create a variable-speed wind turbine has many advantages. NREL studies have shown that a variable-speed wind turbine using a continuously-variable mechanical transmission has the potential to extract more energy from wind than a fixed-speed system. The transmission could also eliminate the gearbox and power electronics required for conventional large turbines. It could even potentially obtain variable rotor speed with reliable and efficient permanent-magnet generators, which would eliminate the need for maintenance-prone slip rings. “Replacing the conventional, gearbox-driven drivetrain in a wind turbine with a hydrostatic transmission has the potential to simultaneously improve reliability and increase system efficiency,” Bohlmann says. “The result would be a lower cost of electricity.”

WPE