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Clear Explanation on 3 Phase Induction Motor - in Text, Video

By shaquila | Published on Sep 16,2015


Three phase induction motor is supplied by connecting 380V three-phase AC power, and is named for the existing revolutional slip generated by its rotor and stator rotating in a same direction but at a different rotating speed.

Clear explanation on types:

By working power source

The motor can be divided into DC motor and AC motor. The AC motor could be classified into single-phase motor and three-phase motor.

By the inner structure and working principle

It consists of Permanent magnet synchronous motor, reluctance synchronous motor and magnetic hysteresis synchronous motor.

By Starting and running mode

It could be classified into capacitor starting-type single phase induction motor, capacitor running-type single phase asynchronous motor, the starting and running mode single-phase asynchronous motor, and Phase-separated single-phase induction motor.

By use

It can be divided into drive motor and control motor

By rotor structure

It can be divided into squirrel-cage induction motor and wound-rotor induction motor.

By running speed

It can be divided into high speed motor, low speed motor, constant speed motor, speed control motor.

The low speed motor is divided into geared reduction motor, the electromagnetic deceleration motor, the torque motor and the claw pole synchronous motor.

Clear explanation on its construction:

Stator Core
Stator core, a common part in the motor’s electromagnetic circuit, is composed of many thin metal sheets called lamination.

Stator Windings
The stator windings are connected directly to the power source.

Rotor Construction
About the rotor in a three-phase induction motor, a squirrel cage motor is commonly employed and is the rotating part of the motor’s electromagnetic circuit.

The enclosure is composed of two bearing housings and a frame with a stator mounted inside.And there is a slight air gap to separate the stator and rotor.

Clear explanation Power flow diagram of induction motor:

Stator input electrical power = A

Stator losses = B

Rotor losses = C

Mechanical output = P

A – ( B + C ) = P

Roughly B= 0.03A, C= 0.04A

A – 0.07A = P

0.93A = P, Hence efficiency = (P/A) x 100 = 93%

Explanation on torque characteristics:

For the squirrel cage machine, a fixed rotor is a shortcoming. Think about that the starting torque is directly related to the rotor circuit impedance, as is the percentage slip when running at load and speed. In order to get good starting performance, a high rotor impedance is needed.

To design the rotor bars with unique cross sections for extending the DOL application is the one way to get the rotor eddy currents increased the impedance at starting when the rotor flux in high-frequency.

The above figure suggests squirrel cage motor characteristics. Commonly, the load slip is getting higher with the starting torque’s increasing. It is identified as one of the crucial parameters of squirrel cage design as it is closely connected with the operating efficiency.

The following link address shows the basics of 3 phase induction motor:



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