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In regard to the construction of a synchronous alternator, hydro alternators have __________.
high speed and smaller diameter
larger diameter and low speed
larger diameter and high speed
low speed and smaller diameter
larger diameter and low speed
Hydro alternators (salient pole generators) are designed for low-speed operation driven by hydraulic turbines, necessitating a large number of poles to maintain the required grid frequency. To accommodate these poles while maintaining structural integrity, a large rotor diameter and a short axial length are employed.
IS 4722
Hydro alternators (salient pole generators) are designed for low-speed operation driven by hydraulic turbines, necessitating a large number of poles to maintain the required grid frequency. To accommodate these poles while maintaining structural integrity, a large rotor diameter and a short axial length are employed.
NsтАЛ=P120fтАЛ тАФ Synchronous speed formula where f is frequency in Hz and P is number of poles
╧ЙsтАЛ=P/22╧АfтАЛ тАФ Angular synchronous speed in rad/s
The relationship between speed NsтАЛ, frequency f, and number of poles P is given by NsтАЛ=P120fтАЛ. Since hydro turbines operate at low speeds (e.g., 50-300 RPM), the number of poles P must be very high. A large rotor diameter is physically required to house a large number of salient poles around the circumference of the rotor.
Hydro alternators utilize salient pole rotors for low-speed operation.
Steam turbine alternators (Turbo-alternators) utilize cylindrical rotors for high-speed operation.
Salient pole rotors have a large diameter and short axial length.
Cylindrical rotors have a small diameter and large axial length.
Optimal for low-head, high-flow hydraulic energy conversion.
Salient poles allow for easier cooling of field windings due to exposed surface area.
Cannot withstand high centrifugal stresses, limiting them to lower speeds.
Higher weight and physical space requirements.
Hydroelectric power plants
Pumped storage power stations
| Feature | Hydro-Alternator | Steam-Alternator |
|---|---|---|
Rotor Construction | Salient Pole (Hydro) | Cylindrical (Turbo) |
Speed | Low Speed | High Speed |
Hydro alternators typically operate between 50 and 500 RPM.
Option A is incorrect as it describes a steam-driven turbo-alternator.
Option C is physically impractical for high-speed applications due to high centrifugal force at the outer periphery.
B is correct тАФ Hydro alternators are characterized by a large rotor diameter and low rotational speed to accommodate the large number of poles required for low-speed hydraulic turbines.
Always remember the trade-off: Low speed necessitates more poles (large diameter), while high speed necessitates fewer poles (small diameter) to handle massive centrifugal forces.
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