What is Salient Pole Type Rotor?
Salient pole rotors are a type of rotor used in electric machines, such as synchronous generators and motors, that have a large number of protruding poles, or salient poles, mounted on a magnetic wheel. These rotors are generally used in low- to medium-speed machines, with speeds ranging from 125 to 500 RPM.
In synchronous machines, the salient poles are made of steel laminations that are riveted together and fixed to the rotor using a dovetail joint. The rotor winding is placed on the pole-pieces and supported by pole shoes. The ends of the winding are taken out through slip-rings for electrical connection.
In some cases, a damper winding may be provided on the slots of the pole faces, also known as squirrel cage windings. The damper bars are short-circuited at both ends by copper rings. These dampers are used to prevent hunting, which is the oscillation of the rotor, and to provide starting torque in synchronous motors.
One of the main advantages of salient pole rotors is that they can be used to generate a wide range of frequencies by varying the number of poles. This is because the frequency of the generator is proportional to the number of poles, as described by the equation f = Ns*p/120, where Ns is the rotor speed, p is the number of poles, and f is the frequency of the generator. Salient pole rotors typically have between 4 and 60 poles.
However, salient pole rotors have some disadvantages compared to other types of rotors, such as cylindrical rotors. One disadvantage is that the flux distribution in a salient pole rotor is relatively poor, which can result in a lower quality generated emf waveform. Another disadvantage is that salient pole rotors often require damper windings to prevent rotor oscillations during operation. Despite these disadvantages, salient pole rotors are widely used in hydroelectric power plants due to their reliability and low cost.
What is Non-Salient Pole Type Rotor?
Non-salient pole rotors, also known as smooth cylindrical rotors or drum rotors, are a type of rotor used in electric machines that have a smooth, cylindrical shape with a number of slots on the outer periphery for accommodating the rotor winding. These rotors are used in high-speed applications, such as turbo-alternators driven by steam turbines, with speeds ranging from 1500 RPM to 3000 RPM.
One of the main advantages of non-salient pole rotors is that they have a uniform air gap between the stator and rotor, which reduces windage loss and noise compared to salient pole rotors. Non-salient pole rotors are also smaller in diameter but have a longer axial length and are generally more robust in construction. They are typically used in 2-pole or 4-pole machines and do not require damper windings to prevent rotor oscillations.
The flux distribution in a non-salient pole rotor is sinusoidal, which leads to a higher quality generated emf waveform compared to salient pole rotors. Non-salient pole rotors are commonly used in nuclear, gas, and thermal power plants due to their high-speed capabilities and good flux distribution.
Difference Between Salient Pole & Non-Salient Pole Rotor
| Feature | Salient Pole Rotors | Non-Salient Pole Rotors |
|---|---|---|
| Definition | Rotor with projected poles on cylindrical core | Cylindrical rotor with slots for rotor windings |
| Windage loss | High | Low |
| Number of poles | 4-60 | 2 or 4 |
| Flux distribution | Non-uniform | Uniform |
| Speed | 100-600 RPM | 1500-3000 RPM |
| Pole construction | Protruding poles | Smooth, cylindrical surface |
| Suitable prime mover | Water turbine | Steam turbine |
| Construction | Complex | Simple |
| Need for damper windings | Required | Not required |
| Diameter and axial length | Large diameter, small axial length | Small diameter, large axial length |
| Applications | Hydroelectric power plants | Thermal power plants, nuclear power plants, gas power plants, etc. |
| Efficiency | Lower | Higher |
| Power factor | Lower | Higher |
| Noise | Higher | Lower |
| Weight | Higher | Lower |
Key difference Between Salient Pole & Non-Salient Pole Rotor
- Definition: Salient pole rotors consist of projected poles keyed on a cylindrical core, while non-salient pole rotors are cylindrical rotors with slots on their outer periphery to house rotor windings.
- Windage loss: Salient pole rotors have more windage losses due to their uneven air gap, while non-salient pole rotors have fewer windage losses due to their smooth surface.
- Number of poles: Salient pole rotors have more poles, typically ranging from 4 to 60, while non-salient pole rotors have fewer poles, typically 2 or 4.
- Flux distribution: In salient pole rotors, the magnetic flux is not uniform due to the air gap between poles, while in non-salient pole rotors, the flux is uniformly distributed in the air gap.
- Speed: Salient pole rotors are typically used in low- to medium-speed machines, ranging from 100 RPM to 600 RPM, while non-salient pole rotors are typically used in high-speed machines, ranging from 1500 RPM to 3000 RPM.
- Pole construction: Salient pole rotors have protruding poles, while non-salient pole rotors have a smooth, cylindrical surface with no protruding poles.
- Suitable prime mover: Salient pole rotors are typically driven by water turbines, while non-salient pole rotors are typically driven by steam turbines.
- Construction: Salient pole rotors have a more complex construction due to their protruding poles, while non-salient pole rotors have a simpler construction due to their smooth, cylindrical shape.
- Need for damper windings: Salient pole rotors require damper windings to prevent rotor oscillations during operation, while non-salient pole rotors do not require damper windings.
- Diameter and axial length: Salient pole rotors have larger diameters and smaller axial lengths, while non-salient pole rotors have smaller diameters and larger axial lengths.
- Applications: Salient pole rotors are typically used in hydroelectric power plants, while non-salient pole rotors are commonly used in thermal power plants, nuclear power plants, gas power plants, and other high-speed applications.
- Efficiency: Non-salient pole rotors generally have a higher efficiency compared to salient pole rotors due to their smooth surface and uniform flux distribution.
- Power factor: non-salient pole rotors generally have a higher power factor compared to salient pole rotors due to their uniform flux distribution.
- Noise: Non-salient pole rotors generally produce less noise compared to salient pole rotors due to their smooth surface and uniform flux distribution.
- Weight: Non-salient pole rotors generally have a lower weight compared to salient pole rotors due to their smaller diameter and simpler construction.