Disadvantages of the transmission include costs, energy loss, wear, space requirements, weight and noise emissions.
Geared turbines are often used on steam ships, as the propellers of large ships run at a considerably lower speed (at most a few hundred revolutions per minute) than the driving steam turbines (with a few thousand revolutions per minute). These act here via a reduction gear on the propeller shafts and not directly. This means that high- speed turbines with good efficiency can be combined with slow-running propellers with a low risk of cavitation .
Above all, the gas turbines derived from aircraft turbines for generating electricity are often designed as reduction gear turbines, since jet engines are operated at far higher speeds than 3000 or 3600 / min, which is usual for generating the alternating current frequency of 50 or 60 Hz. The fan of the Pratt & Whitney PW6000 engine with 100 kN thrust rotates at 6350 revolutions per minute.
In the case of smaller, multi-casing steam turbines, at least the high-pressure part is often designed as a geared turbine, since the compact shape of the turbine designed for high speeds allows more effective flow guidance. In this case, the transmission is arranged between the high-pressure and medium / low-pressure parts of the turbo set.
In the case of water turbines that run at a speed far below 3000 / min (for 50 Hz) or 3600 / min (for 60 Hz), the gear ratio in smaller systems is sometimes achieved by a gearbox, but more often by adapting the number of pole pairs in the generator. In the case of wind turbines that rotate even more slowly, however, the version with a gearbox is more common.
One advantage of geared turbines for generating electricity is that the turbine runs at an unchanged speed, i.e. H. can be adapted to generators for a mains frequency of 50 or 60 Hz without changing the flow conditions in the machine . This makes complex adaptation of the blading unnecessary.
When it comes to power generation, geared turbines reach their limits with an output of around 200 MW. Large turbo sets with higher outputs are therefore designed without a gearbox.