Types Three-Phase Induction Motor and Equivalent Circuit

ABSTRACT

The three-phase AC induction motor is an electric spinning mechanism designed to operate on a three-phase supply. This three-phase engine is sometimes considered an asynchronous engine. These AC motors are of two types: induction motors for the squirrel cage and wound rotor. The operating principle of this motor is based on making a rotating magnetic field. Over a wide variety of uses, three-phase induction motors account for 85% of the installed power of industrial drive systems

Types Three-Phase Induction Motor

There are two types ) squirrel-cage and wound rotor or Slip Ring Rotor)

squirrel-cage: In this type, metal rods are placed inside the slots, and the coils of the rotor are not isolated from defects of weak torque.

Advantages of Squirrel Cage [3]

Its construction is very simple.
As there are no brushes and slip ring, these
motors requires less maintenance.
High Efficiency
Cheap

wound rotor or Slip Ring Rotor: In this type, the rotor is made of silicon steel strips, and there are slots that fill these slots with a certain number of wire turns.

Advantages of wound rotor
The rotor resistance starter can be used
High Starting Torque
Disadvantage
Less Efficient
Costly
Complicated Construction

Equivalent Circuit IN Three-phase induction motor

The induction engine is similar to the transformer except that its secondary windings are rotatable

by Abbreviation of the rotor equivalent circuit of Figure4 , we obtain the steadystate equivalent circuit for one phase of a wye-connected induction motor, as shown in

The resistor Rr, again locking at the rotor part of the equivalent circuit ,

represents the rotor winding resistance. The power which it uses is the power lost in the rotor winding resistive heating. The additional resistive element to the right end is a slip and rotor resistance function. It arises from the necessity of transforming

the circuit of the rotor not only by the ratio of turns but also by frequency. The power consumed in that element is the machine's evolved power. The power developed is the power converted from electrical to mechanical form, and includes the load power plus mechanical losses such as friction and winding. Subtracting the mechanical losses from the developed power would yield the shaft power, which is the actual power delivered to the load.