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Rotor of alternator is
Salient
Cylindrical
Either of above
None of above
Either of above
Alternators are categorized based on their rotor construction into Salient Pole rotors and Cylindrical (or Round) rotor types. The choice depends primarily on the prime mover speed and the required mechanical stability at high centrifugal forces.
Alternators are categorized based on their rotor construction into Salient Pole rotors and Cylindrical (or Round) rotor types. The choice depends primarily on the prime mover speed and the required mechanical stability at high centrifugal forces.
NsтАЛ=P120fтАЛ тАФ relationship between synchronous speed, frequency, and number of poles
The salient pole type features projecting poles and is used for low-speed hydro-generators requiring a large number of poles to maintain frequency at low rotational speeds. The cylindrical type, having a smooth, non-projecting rotor with a smaller diameter and longer axial length, is used in high-speed steam or gas turbines (Turbo-alternators) to withstand massive mechanical stresses and centrifugal forces.
Salient pole rotors have a non-uniform air gap.
Cylindrical rotors have a uniform air gap.
Hydro-alternators are typically of the salient pole type.
Turbo-alternators are always of the cylindrical type.
Salient: Better heat dissipation due to large surface area.
Cylindrical: Robust construction capable of handling high centrifugal forces.
Salient: Susceptible to high windage losses at high speeds.
Cylindrical: Requires complex and expensive manufacturing processes.
Salient pole: Hydro-electric power plants.
Cylindrical: Thermal, Nuclear, and Gas power plants.
| Feature | Salient | Cylindrical |
|---|---|---|
Pole Construction | Projecting | Non-projecting |
Operating Speed | Low speed (100-400 RPM) | High speed (1500-3000 RPM) |
The air gap in a salient pole rotor is smaller under the poles and larger in the inter-polar region.
Cylindrical rotors typically use only 2 or 4 poles for 50Hz or 60Hz grid synchronization.
C is correct тАФ Alternators use either salient pole or cylindrical rotor construction depending on the intended speed and application.
Always remember the mnemonic: 'Hydro' is 'High' in poles (Salient) and 'Turbo' is 'Two' poles (Cylindrical) for standard frequencies.