Electrical machines are devices that convert electrical energy into mechanical energy or vice versa. The rotor is a critical component of electrical machines, and its construction varies based on the type of machine. Here are the different types of electrical machine rotor constructions commonly used:
Squirrel-cage rotor:
This type of rotor is predominantly used in induction motors, which are widely used in various industrial applications and household appliances.
The rotor consists of a laminated cylindrical core made of steel.
Copper or aluminum bars are placed in parallel slots on the surface of the core, forming a "squirrel-cage" shape.
The ends of these bars are short-circuited by metal rings at both ends of the rotor, which allows the rotor currents to flow through the bars.
When the stator windings induce a magnetic field, it causes the rotor to rotate due to the interaction between the magnetic fields.
Wound rotor:
This type of rotor is commonly used in wound-rotor induction motors and some synchronous motors.
The rotor consists of a laminated steel core similar to the squirrel-cage rotor.
Instead of short-circuited bars, the wound rotor has insulated coils of wire placed in its slots.
The free ends of these coils are brought out through slip rings, which provide electrical connections to the external circuit.
The external circuit can then control the rotor's electrical characteristics, such as resistance and reactance, allowing for a better control of the motor's performance.
Salient pole rotor:
Salient pole rotors are used in synchronous machines, such as synchronous generators and synchronous motors.
The rotor consists of large projecting poles with concentrated windings.
These poles are usually excited by a direct current to create a magnetic field that synchronizes with the rotating magnetic field of the stator.
The salient pole design allows for easy manufacturing and maintenance, and it is suitable for applications requiring low-speed operation.
Cylindrical rotor:
Cylindrical rotors are used in some synchronous machines and doubly-fed induction generators.
The rotor consists of a solid or laminated cylindrical core made of steel.
The rotor windings are distributed uniformly across the surface of the core, providing a more balanced and smooth magnetic field distribution.
This type of rotor design offers advantages in terms of mechanical strength and high-speed operation.
These are the primary types of electrical machine rotor constructions commonly encountered in various applications. Each design has its advantages and is selected based on the specific requirements of the application and the desired performance characteristics.