Final answer:
The most commonly used rotor in three-phase motors is the Squirrel cage rotor, due to its simplicity, durability, and reduced maintenance requirements compared to other types of rotors like the slip ring or wound rotor.
Step-by-step explanation:
In three-phase motors, the rotor most commonly used is the Squirrel cage rotor. Electric motors, as applications of magnetic force on current-carrying wires, contain loops of wire in a magnetic field. When current flows through these loops, the magnetic field applies a torque, rotating a shaft and converting electrical energy into mechanical work. The squirrel cage rotor is named for its appearance, similar to a hamster or squirrel exercise wheel, consisting of bars of conductive material, such as aluminum or copper, short-circuited by end rings and arranged in a pattern that resembles a cage.
The popularity of the squirrel cage design lies in its simple and rugged construction, relatively low cost, and minimal maintenance requirements. It contrasts with the slip ring or wound rotor designs, which can offer higher starting torque but with increased complexity and maintenance demands.