Turbine blades rotate at 10-30 revolutions per minute, but the speed entering the generator is one hundred times higher. One of the answers to that equation is the ring gear. The forged steel ring gear embraces the planetary wheels, allowing them to transform low incoming speed to high outgoing speed.
The rings are 1.3 to 1.8 m in diameter, the most challenging operation in producing them is milling the gears. Any inconsistency in the gear milling operation makes grinding more complicated and time consuming, putting high demands on the tools.