An unusual 30-ton capacity crane can pull itself up into a nacelle, and when bolted down, allows lowering a worn gearbox and picking up a new one, all at a lower cost than a conventional crane callout. The design from Denmark’s Liftra, fits in one standard 40-ft. container with a wheel chassis for easy transport. “One is ready for duty now from our Cincinnati office,” says Ryan Huff, Vice President of Liftra’s U.S. operations, “and another will be ready soon.” He says NextEra collaborated in it development and has deployed four such cranes at its wind farms around the U.S.
Only one 40 foot container is needed to transport a Liftra Self-Hoisting Crane when replacing a gearbox or generator.
For the time being, the crane can operate on GE 1.5-MW platforms, Vestas V82 turbines, and Siemens 2.3-MW machines, with the use of interchangeable turbine interfaces. “These crane bases are installed in different configurations depending on turbine model and bolt to the pillow blocks and some around the main-shaft itself,” says Huff.
Getting the crane ready for work goes like this: Workers raise lifting cables to the nacelle using a small light-weight crane mounted up tower. This smaller crane lifts the crane base components in place and are then positioned by a crew of four to five technicians. A winch, down-mounted in the container for the crane system, pulls the Liftra crane up and onto the nacelle where workers pin it into the crane base.
A hoist in the crane pulls the unit up the lines.
The arrangement solves several problems. For instance, costs for a conventional crane vary wildly. “I’ve seen crane costs range from $50,000 to $150,000 per gearbox depending on the location of the wind farm,” says Huff.
A gearbox swap with a conventional crane requires having to first procure it and then assemble it. Once assembled, it’s about a three day operation to remove a gearbox. It is occasionally necessary to first lower the rotor to the ground before removing the gearbox and then reassemble with a replacement unit.
With the Liftra crane, it is a six-day operation. It takes two days to assemble the crane base, two days to install the crane, replace the gearbox, and remove the crane and then another two days to remove the crane base. Although conventional cranes have a slightly shorter working period, we are working to change that with more efficiency in our system,” says Huff.
With the reduced mobilization, eliminated civil improvements, and a higher wind threshold, Huff expects the end user to experience savings of up to 30 to 40% for crane costs.
Once in the nacelle, workers pin the crane in place on the installed crane base.
The Liftra crane also has a smaller footprint, so replacing a gearbox is done using a main-shaft clamp, which allows removing the gearbox without lowering the rotor. The smaller footprint extends as well to civil preparation and reclamation. Most conventional cranes require the installation of a crane pad that Huff says the Liftra design does not require. “And not needing to lower the rotor is a big plus especially at wind turbines surrounded by land-owner crops,” he adds.
The crane’s lifting limit depends on the turbine. The Siemens unit has a weight limit of 24 tons. In GE and Vestas, the cranes have lift capacities of about 19 tons. However, the crane is tested to 30 tons.
When needed, the company would rent a standard tandem-axel tractor to move it. “I’ll send the crane with two operators: one would drive the tractor and the other would drive a flatbed truck & trailer with other base components on it,” says Huff. In addition, the company would need three to four other techs from the wind farm operator to decommission and re-commission the nacelle. “If the customer does not have those resources available, there are 3rd party independent service providers that Huff works with, such as Upwind, Availon, and OMNE Resources.
The Liftra crane can lift 19 tons for a GE turbine and 24 tons from a Siemens. The weights are a function of tower and foundation.
Huff adds that a crane base for the GE 1.6 is in development but the crane won’t change. After that, the company will shift design work to the V80 platform.
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