text: There is usually a high-pressure turbine at one end, followed by an intermediate-pressure turbine, and finally one, two, or three low-pressure turbines, and the shaft that connects to the generator. As steam moves through the system and loses pressure and thermal energy, it expands in volume, requiring increasing diameter and longer blades at each succeeding stage to extract the remaining energy. The entire rotating mass may be over 200 metric tons and  long. It is so heavy that it must be kept turning slowly even when shut down (at 3 rpm) so that the shaft will not bow even slightly and become unbalanced. This is so important that it is one of only six functions of blackout emergency power batteries on site. (The other five being emergency lighting, communication, station alarms, generator hydrogen seal system, and turbogenerator lube oil.)
  For a typical late 20th-century power station, superheated steam from the boiler is delivered through  diameter piping at  and  to the high-pressure turbine, where it falls in pressure to  and to  in temperature through the stage. It exits via  diameter cold reheat lines and passes back into the boiler, where the steam is reheated in special reheat pendant tubes back to . The hot reheat steam is conducted to the intermediate pressure turbine, where it falls in both temperature and pressure and exits directly to the long-bladed low-pressure turbines and finally exits to the condenser.