Raising and lower the wind turbine tower

Raising and lower the wind turbine tower. The 19.5 m. high galvanized steel monopole tower for a wind turbine that uses a worm gear jack screw to raise and lower the wind turbine for servicing, stormy weather etc. The worm gear jack screw with 25 metric tonne capacity, double clevis design, 910 mm stroke, Ratio 32:1. The jack screw must be rated for 25 tonnes, both compression and tension. The tower is 19.5 m. total height, in 4 sections. Wind loading on tower during hoisting process would be an extra force on the screw jack. The 25 tonnes jackscrew unit was powered by an electric motor, Induction Geared, gear reduced, 0.75 kW, 1 Phase, 1:50 reduction ratio, mounted to screw jack by 4 bolt square motor flange. In case of a electric power failure during the raising or lowering of the tower, required that the jack screw system lock the tower in its then current position (ie. tower will not catastrophically go to full vertical, nor crash to ground in an uncontrolled manner).

When raising the tower, the jack screw will be in compression until the tower is almost vertical, then the jackscrew load suddenly switches from compression to tension as the tower tries to "fall" towards fully vertical. During lowering, the jackscrew will be in tension at first, then quickly switch to compression when the tower is about 10 degrees or 20 degrees off vertical. This sudden reversal from tension to compression will add a dynamic loading while the jack screw is close to fully extended. If there is significant backlash (ie. screw thread looseness) in the jackscrew, this sudden dynamic load change would be maximized, and might cause significant whipsaw action on a 19 m. tower with a large mass at the end of the pole. Therefore minimal backlash in the jackscrew would be ideal. Being able to easily (ie. without dis-assembly and rebuilding the entire jackscrew) reduce excessive backlash that develops over time would also be a convenient feature.