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How do you exchange an 11,000kg gearbox at a height of 70m?

Friday, 20 November 2020 17:02

Late September 2020, Certion took care of the exchange of the gearbox of a Vestas V66-1.75MW wind turbine in Flevoland. This operation involved the lifting of an 11,000kg gearbox - equalling the weight of seven mid-size cars - to a height of 70m. How do you get such a plan off the ground?

 Days 1 & 2 - preparation
Preparations for the hoisting operations are started on Monday and Tuesday: blocking the rotor (the total assembly of the three blades, including the centre), dismounting the shrink coupling between the gearbox and the main shaft to which the rotor is connected, disassembling the coupling towards the generator, unscrewing multiple bolts and disconnecting cables plus the removal of conduits.

Day 3 - hoisting day according to the positioning&hoisting plan
Wednesday is hoisting day. The crane arrives early in the morning and is built up at the appropriate site according to a pre-determined positioningplan.

0.1mm precision operation
At the moment when the crane is ready, the preparations in the wind turbine have already been finalized for 'D-Day'. The gearbox with shrink coupling can now be suspended in the hook of the crane, after having been removed from the machine housing with utmost precision. The gearbox is slid onto the main shaft with a fit that allows a maximum play of +/- 0.1mm. Operating at this height and handling such a weight is a true challenge, which requires experienced technicians, a skilled crane operator, clear communication, favourable weather conditions plus ultimate concentration.

Hooking on, hoisting and sliding
Following its descent, the old gearbox is placed on a special - extra robust - pallet. Thereafter, the replacement gearbox plus shrink coupling is suspended in the hook of the crane (hooked on), after which the assembly is lifted. The next challenge then is to slide the new gearbox on the main shaft, taking account of the play allowed as a maximum.

Hoisting job finished, packing up...
Once the new gearbox has been properly fitted in the machine housing, the roof can be re-positioned. The crane has now finished its job and can be 'packed up' again for its next operation. All in all, these hoisting operations take a day, after which final assembly and mounting can be started.

Days 4 & 5 - final assembly and mounting
Thursday and Friday are needed for multiple operations: final assembly, mounting and aligning, so that the wind turbine can produce sustainable energy in a safe manner. If all goes well, the turbine can be started for a first test on Friday afternoon. If there are no issues, the turbine's operation will be continued and we will be back on Saturday for a final check.

Neat and tidy working for safety's sake
The dimensions of the machine housing (or nacelle) of this type of wind turbine are impressive: 10m long, 3.3m wide and 4m high. All the same, it is crammed with components, cables, conduits, control boxes and - obviously - the gear box. Even the high-voltage transformer has its own separate room within the machine housing. The material crowdedness necessitates a neat and structured approach to the operation, so that the required working space is cleared, and safety enhanced.

This job has been completed safely and satisfactorily; let's move on to the next challenge!

How do you exchange an 11,000kg gearbox at a height of 70m?