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Detailed Review of Rotor Magnet

Rotor Magnets has many other several names called rotating magnetic core or fly wheel of an alternator. They are basically moving parts in alternators which contain permanent Magnets material which helps them to move around the stators of iron plates in order to generate Alternative current (AC).

Early development:

It can be traced back when 1st rotator machine was established by Anyos Jedlik. Some amendments were done with the passage of time by different scientists

Later in 1935, Francis Watkins produces an electrical "toy". He is considered as the first who understands the concept of interchangeability exists between motors and generators.


Induction and alternators both have stators and rotors. Both designs have two different types in it. Induction motors contains squirrel cage and wound whereas alternators rotors has salient pole and cylinder

  • Squirrel cage rotor:

It is the main rotating part of the indicator, which consists of cylinder with steel laminations, having aluminum or copper in its surface. As the name suggests, they are just similar like cage of the squirrel because the rings and bars are winded in squirrel cage. It generates less heat, and is able to operate in better power capacity.

  • Wound Rotor:

They are also called slip ring rotor, in this type the three phase windings are connected with external slip rings to exterior resistance. The adjustment of the resistance allows the control of torque

  • Salient pole Rotor:

It is large magnet with pole constructed having steel laminations. The direct current is supplied to poles by magnetizing it or by permanent Magnet material. The three phase windings is done to poles in order to induced the voltage

  • Non salient rotor:

It is cylindrical shaped which is made up of solid steel having shafts that are running outside the bars. They are secured by wedges attached to it

Operating principles:

The three phase induction machine the alternating Current which is supplied to stators is able to create rotating flux. The magnetic field is produced by the flux in between the rotors and stators which eventually produced air gap between them. The torque generated is able to start the motor.


1) Necessary induction is provided for torque motor which is proportion to the slip

2) Wound rotor rotate at constant speed with very low starting current speed. When external resistance is reduced the motor speed become high

3) Squirrel cage operated at very low speed and contains large diameter.

4) They have low mechanical strength

Rotor equation:

Rotor equation contain few things like induced voltage, magnetic field, conductor length, synchronous speed and conductor speed


Some preterm magnetic field is applied to rotor in order to form different magnetic paths and after that the rotor is demagnetize. For construction basis rotor and stators are positioned.

Parts of Rotor:

Main parts are rotor core and rotor windings. The winding of the rotor is excited by the supply of direct current (Dc). Further the squirrel cage and phase wound are types of rotor. Rotor is made up of lamination stack which is filled with cast aluminum that act as conductors

Rotor Speed:

It is also known as spinning of rotor. There speed is typically lie between 120-210 m/s range. Mostly the speed is 150 and 190 m/s having smaller rotor diameter.

What is Rotor Voltage: 

The rotor produced voltage circulates the current in the conductors of rotors, which will react to produce force, torque and rotation.

Rotor slip:

Fundamentally the difficult between the synchronous speed and actual speed of rotor is called slip of speed. When the speed of the rotor drops below the stator speed the rotation rate in rotor increased which induced more current and torque. Slip plays as an essential part because it is mandatory to produce torque.

Principle design for rotor:

Magnetic rotors are designed with multiple poles, each of them are alternates in polarity (North Pole and south poles). A shaft is located in Middle in which opposite poles rotates about central point. Mag Spring is capable of supply of most of the rotors. They can stimulate the behavior and calculate the force or torque of each type of magnetic rotor.

Function of rotors in Generators:

In generator the rotor magnets work as armature, which rotates in field, which cuts the line of force and desired output voltage is generated. This voltage is taken from rotor by slip rings and brushes.

Rotor Current:

When the current of the motor is drawn to stationary position in other words the rotor is not spinning the current then become zero at that position

Rotor Shafts:

They are central components of electric motors. It works as carrier shaft for the laminated core of rotor and that's why electrically torque is induced, which has positive connection with transmission.

 Function of rotor magnets in AC Alternator:

In alternator the rotor is generally manufactured by wound copper and electric steel. The rotor spins because of mounted on a shaft that has a bearing at both the ends.  It is connected to something which helps it in rotating, which is normally a diesel engine when the power of the rest of excitation system starts, the rotor then generate magnetic field

Difference between stator and rotors magnets

  • The stators are stationary part where as rotors are rotating part. The winding arrangement of stators is very complex whereas the rotors are easy to understand and use.
  • Supply is given to stators whereas the rotors are self-starters by induction principle


Rotors are small inner parts in alternators which contains permanent Magnets material which moves around the iron plates of stators to generate AC. It requires existing motion to start working of engine or turbine. Actually the rotor works with stators to provide charge. In order to maintain the maintenance the technicians can use inspection cameras that alternators and its two main components are working in good condition.




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