Maintenance on wind farms is a complex operation especially when large, heavy components need to be replaced, and this calls for the expertise of a company that has the necessary experience and capability.
Janet Barnes, key account manager at Johnson Crane Hire, says that removing and installing heavy loads at extreme heights brings with it additional particular challenges when these activities are being done in windy conditions.
“Lifting on wind farms require careful planning and attention to detail to ensure that the lifts are conducted safely,” she explains. “Coordination between the wind farm operator and the lifting specialist is essential to ensure that all aspects of the lift are dovetailed to facilitate lifting and replacement of these components safely.”
Due to the height of the wind turbine towers, which range from 80 to 115 metres, it is necessary to provide large capacity cranes that have the lifting capacity, as well as the required reach.
Johnson Crane Hire has the necessary depth within its fleet of cranes to accommodate these challenging lifts. The company recently completed the replacement of the main bearings at the Jeffrey’s Bay Wind Farm, the Noupoort Wind Farm and the Sere Wind Farms.
Barnes explains that the main bearing is housed in the nacelle and weighs approximately 18 t. The wind turbine tower at Jeffrey’s Bay Wind Farm is 80 metres high, while the towers at Noupoort Wind Farm and Sere Wind Farm stand 115 metres tall.
Barnes says that to access the bearing it is necessary to first remove the 60 t rotor and place it on the hard stand. Following this, the main bearing is removed from the nacelle and also placed on the hard stand. The new main bearing is then lifted into position, and the rotor is then replaced.
“This is an intricate operation that requires careful planning as well as close communication between the turbine technician, the lift supervisor and the crane operator to ensure that equipment is handled and placed safely and accurately during the lifts,” Barnes says.
Describing the operation, Barnes explains that the rotor is lowered to a predetermined height where a blade clamp is attached to the lowest (vertical) blade in the star formation. “This is achieved by using a secondary crane to complete this tandem lift or “top and tail operation”. This process is repeated in reverse when the rotor is reattached to the tower,” she says.
Because of the varying heights of the towers and the fact that these lifting contracts ran consecutively it was decided to use a lattice boom mobile crane which offers the capacity to remove and replace the main bearings. This was also considered the most cost effective solution for the customer.
“A major advantage when dealing with Johnson Crane Hire is the level of flexibility applied to complex and challenging lifts,” Barnes says. “Doing these lifts underscores this as it was necessary to commence work in the early hours of the morning when the wind was at its lowest on the site. This was done to ensure optimum levels of safety during the lifting activities.”
While it is unsafe to undertake lifting work in windy conditions, the lifting or removal of the rotor is particularly sensitive to wind force due to the large surface area of the rotor, resulting in extremely low allowable wind speeds, in which these lifts can be performed.
Johnson Crane Hire is continually updating its fleet with new and technologically advanced cranes and equipment to ensure that the company is able to support the market and ever changing needs and requirements.
“An essential element to operating such technologically advanced equipment is to ensure that our operators and support personal are continually trained and sufficiently skilled to operate this equipment. Training and certification is performed both in-house through our accredited training school and facility. This is supported by our equipment suppliers, who provide training and equipment familiarisation, performed both locally and in Europe,” Barnes says.
FROM:CORALYNNE & ASSOCIATES
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JOHNSON CRANE HIRE
TEL: +27 (0)11 455 9242