State any four salient features of turbo- alternator.
2 Answers
Salient features of turbo alternator: 1) Turbo-alternators are high-speed alternators (3000 rpm). 2) Rotor diameter is kept less to limit the centrifugal force acting on field winding on rotor at high speeds. 3) Rotor axial length (along shaft) is more. 4) Cylindrical rotor construction (non-salient pole) is used. 5) Field poles are less in number either 2 or 4.
Special features of a turbo alternator used in TPS:
Special Futures (Highlights): It is 3-phase generator. A separate excitation is given to alternator by DC generator (Exciter) which is mounted on same shaft. Pilot Exciter is used to excite the main exciter. Generated voltage is 3.3KV, 6.6Kv, 11KV, 17.5KV and 20 KV. Construction of rotor is cylindrical type. Numbers of poles to alternator are two or four. Alternator is smaller in diameter and longer in axial length. It is robust in construction. Generator is high speed machine compare to the water turbine driven generator.( It’s a synchronous speed is 3000 RPM for two poles and 1500 RPM for 4 poles to get 50 Hz frequency.) Cooling is necessary to improve the performance of alternator. Cooling system may be air cooled or hydrogen cooled. Standard rating of turbo alternator is 125, 200, 300 and 500 M watt and Maximum rating of turbo alternator is 500 M watt. Various protections are provided to alternator. Over voltage and under voltage protection. Over frequency under frequency protection. Over load protection. Over temperature protection