These photos show the rotor lift for the first turbine erection at our Lewiston, MN, wind project in November, 2011. This is called “flying the rotor.” Once the three blades are assembled to the rotor hub they become the rotor assembly and are ready to be lifted and attached to the nacelle at the top of the turbine tower. In this case, the rotor assembly weighed approximately 135,000 pounds and needed to be lifted 80 meters above ground. This step is the last large lift of the assembly process and requires two cranes and the entire attention of the construction crew to complete.
Compliance with safety codes requires the winds to be light for such a high and heavy lift. The large crane has straps wrapped around two of the blades near the rotor hub. The smaller crane has a strap wrapped near the end of the third blade and there are additional lines tended by the crew as the lift proceeds to help stabilize the assembly. Radio communication between the crane operators, technicians in the nacelle, and the construction supervisor help coordinate the sequence of movements.
Once the rotor assembly is in a vertical orientation the strap from the smaller crane is released and the large crane makes the final lift to the nacelle. The technicians in the nacelle assist in guiding the final movements for proper positioning. The bolt pattern in the hub is then inserted into the nacelle and technicians torque the nuts for required clamping force. The process of torqueing the joint can take several hours to complete so a stretch of good weather is required. Sometimes crews can work after dark to ensure the step is completed and the assembly is safely attached.