- The alternator which coupled directly to the steam turbines are called turbo-alternator .
- The turbine converts heat energy in the steam into mechanical work and the alternator converts mechanical energy into electrical energy .
- The bulk power is generated by three phase turbo alternators at frequency 50 Hz.
- Turbo alternators are cylindrical pole machines having synchronous speeds 3000 rpm (tow pole machines) or 1500 rpm (for four pole machines ).
- Large centrifugal force produced at these speeds, restrict the diameter of the turbo alternators and are
- characterized by small diameters compared to their length.
- The generated voltage is either 6.6kV or kV.
- A separated DC generator is mounted on the same shaft of the turbine and alternator and supplies the exciting current for the field winding of alternator .
- Air cooling is used upto a capacity of 100MW generating units .
- Hydrogen cooling can be used for 500MW generating sets.
Following are the special features of a turbo alternators used in thermal power station :
- The turbo alternator have high rated speed.
- The capacity of turbo alternators is upto 500MW.
- Small turbo-alternators may be air cooled, but for large size units hydrogen cooling is used.
- The turbo alternators have horizontal configuration.
- The rotor of turbo-alternators are of small diameter as compared to its length.