World's biggest wind turbine generates new bearing technology

Earthmover and Civil Contractor
October, 2006, Page: 67

DESIGNING A bearing system for a giant wind turbine with an unusual rotor shaft lead to the biggest ever CARB toroidal roller bearing, new bearing assembly techniques and a new method of axial fixation for large bearings.

All wind turbines are large but the Repower 5M wind turbine is huge. Manufactured by Repower Systems AG from Hamburg, the 5M stands 120m above the ground and produces 5MW of electrical power, enough for 7500 houses. With its three-bladed 126m diameter blade span, the 5M is the largest and one of the most efficient wind turbines in the world.

During early design stages and later, the 5M presented a significant technical challenge in several different fields. One of the most crucial was the design, manufacture and installation of a bearing system for the 1.5 metre diameter rotor shaft that supports the 130 tonnes three bladed rotor.

New bearing system

Even though it has to support the heavy rotor, the cast iron rotor shaft is hollow. This is to meet weight, cost and performance requirements and it was just one the factors that had to be considered by SKF when they were given the challenge of designing, manufacturing and installing a bearing system for the shaft.

To eliminate the influence of positional and deflection related errors, the SKF specialists in cooperation with the Repower designers developed a system with the shaft supported by two bearings. In the non-locating position is an SKF CARB toroidal roller bearing. The other bearing, in the locating position, is an SKF axially locating spherical roller bearing. This arrangement offers high load carrying capacity and the lowest possible bearing plus housing weight for a two bearing arrangement.

Simulation, calculation tool

To give Repower a bearing system that would meet all performance requirements, SKF made use an in-house simulation tool: "Beast". It is a dynamic simulation program that can be regarded as a virtual test rig in the computer.

Traditional methods of long and costly experiments on a test rig are replaced by faster, and more detailed computer simulations.

The program was first used in the development of the SKF range of CARB bearings, so naturally it was used again in smaller sized CARB bearings to evaluate how the inclined shaft in the 5M would influence bearing behaviour.

This bearing with its 1.5m inside diameter weighs 2.7t and is the largest of its type ever mande by SKF. So its behaviour on an inclined shaft was an unknown in the early stages of the design process. The finished product represents a milestone in bearing design.