Turbo alternator

Turbo alternator

• 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.

Turbo alternator