There are different rotor constructions, but one type is the salient pole rotor. The word “salient” refers to projecting forward. Salient pole rotors are characterized by their poles being cast from the surface of the core. In addition to salient rotor fields, there are also cylindrical rotor fields. Non-salient (cylindrical) and salient (spherical) rotors have specific parts. This guide is about salient pole rotor in detail.
Salient Pole Rotor
The salient pole rotor is made of steel laminations to minimize the loss of electric current. The reason for this is that the magnetic field around the rotor is changing. Stacking laminations combine poles with the exact dimensions to achieve the required length. Rotors with salient poles do not have a uniform air gap. Under the pole centers, there is a reduced air gap, and between the poles, there is a maximum gap.
There are several poles on salient pole rotors, which are designed for medium and low speeds. Salient pole generators also have a large diameter.
Parts of salient pole rotor
· The Field winding
To wind the field, the former must be incorporated on the former and placed around the pole’s core. Through slip rings, DC is supplied to this device. Field windings generate magnetic fields when direct current flows through them.
· Pole cores and pole shoes
The pole core and shoe are the other parts of the salient pole rotor. A laminated sheet of steel makes up this part. A sinusoidal wave is created around the magnet’s periphery by the pole core, reducing reticence and the pole shoe uniformly distributing the field.
· Winding of the damper
The outermost periphery of the damper is surrounded by copper bars, with both sides of the rings cut out to form the winding.
· The spider
This is the first section of a salient pole rotor! The cast iron allows the magnetic flux to move quickly. The shaft is held, and the pole core and shoe are fixed to the outside wall.
The construction of a salient pole rotor
The salient-pole rotor is used for low- to medium-speed applications, unlike the salient-pole rotor. Usually, these machines are multi-poled and have variable air gap widths. A direct-coupled water turbine and several 12-pole motors are usually used as the prime mover in pumped storage schemes (such as the Dinorwig pumped storage scheme previously described).
Water turbines usually have large rotor diameters and short lengths, with the horizontal axis of rotations to suit their needs. No matter what type of machine you have, the rotor must be wound for the same number of poles as the stator. As a result of the rotor winding carrying DC, a constant flux is generated per pole.
Rotor rotation induces a voltage in stator windings because it induces rotation of the rotor around the stator. In the same way as a conventional induction machine, the 3-phase stator currents generate revolving fields of their own. Due to its rotation at the same speed as the rotor, it is stationary in relation to the rotor field. Because of this magnetic interaction between these two fields, torque is generated in the machine.
Working of salient pole rotor
Stator windings in three-phase input machines produce rotating magnetic flow when supplied with alternating current. As a result of the flux, a magnetic field is generated between the stator and rotor, generating voltage between the rotor bars that generate current energy. Due to the short circuit in the rotor circuit, current flows to the rotor conductors. Starting an engine requires torque generated by rotating flux and steel generating power.
Metal cores cover a wire coil that makes up the alternator rotor. As a result of the stainless steel magnet on the rotor, a specific shape and size are sealed to the driver’s spaces. It is called the current field when the currents travel through the wire coil and create a magnetic field around the core.
Depending on the current strength of a magnetic field, a magnetic field will have different energy levels. To deliver the current lot to the telephone coil, direct current (DC) uses brushes and smoothing rings. A pole produces a magnetic field north and south like a magnet.
By embedding magnets and magnetic fields into the rotor’s construction, the clock’s average direction powered by a rotor-powered engine can be changed from clockwise to counterclockwise.
Features of salient pole rotor
There is a wide diameter and a short axial length on a salient pole rotor. There is a 2/3 coverage of the pole shoes. Diesel engines and hydraulic turbines can also be used with it. Salient pole rotors usually rotate between 100 and 375 revolutions per minute. Due to the slow speed of the water turbine, more pole speeds are needed to achieve the frequency.
It is typical for salient rotors to have between four and sixty pole machines. For speeds below 1000rpm, salient pole rotors are cheaper than non-salient (cylindrical) rotor machines, which are more expensive. Furthermore, there are severe losses of winding. Rotor salient poles do not have consistent flux distributions. An emf waveform generated by a cylindrical machine is not as strong as one caused by an SP waveform.
FAQs (Frequently Asked Questions)
What is the difference between a salient pole and a non-salient pole rotor?
Rotor types of electrical machines are classified according to their construction. It can be classified into two types: a salient pole type or projected pole type rotor (for low speed, with more poles, like Kaplan turbines); and a smooth cylindrical type rotor (for high speed, with two or four bars, like Pelton wheels)
What will happen if we drive salient pole rotors at high speeds?
It is generally found in low- to medium-speed alternators (100-1500 rpm) that salient pole rotors are used. Windage losses are excessive for these rotors if driven at high speeds.
What is the working principle of a salient pole rotor?
Steel laminations are used to minimize the electric current loss in salient pole rotors. As the rotor rotates, the magnetic fields of the rotor change. Laminations are stacked to achieve the required length by stacking poles with the exact dimensions. The air gap in a salient pole rotor is not uniform.
What are the two types of rotors?
Wound rotors and squirrel cage rotors are two types of rotors used in induction motors. Rotor windings are similar to those on stators, and rotor poles are the same as stator poles. An insulated slip ring is mounted on the rotor shaft to connect the windings.
How many poles does an alternator have?
A higher number of poles causes higher magnetic leakage, while a low number of bars causes lower efficiency. Alternators usually have 12 or 16 poles, depending on the trade-off between efficiency and leakage.