AC induction motors represent a fundamental advancement in electric motor technology, utilizing electromagnetic induction rather than direct current to generate mechanical motion. These motors are essential components in many industrial and commercial applications.
Core Components and Structure
An AC induction motor consists of two main components:
The Stator: The stationary outer component comprising:
Three pairs of electromagnets
Connected to three-phase AC power supply
Electromagnets positioned 120° apart
The Rotor: The rotating inner component featuring:
Conductive bars arranged in a cylindrical pattern
Two conducting end rings connecting the bars
Commonly known as a "squirrel cage" due to its appearance
Operating Principles
Rotating Magnetic Field
The stator creates a rotating magnetic field through:
Three AC currents phase-shifted by 120°
Each electromagnet pair produces an oscillating magnetic field
The combined effect creates a rotating magnetic field
Electromagnetic Induction
The rotor operates based on two fundamental principles:
Faraday's Law of Induction:
The rotating magnetic field induces an EMF in the rotor bars according to:
ϵ=−NdtdΦ
where:
ϵ is the induced EMF
N is the number of conductor turns
dtdΦ is the rate of change of magnetic flux
Lenz's Law:
Induced currents create magnetic fields opposing the change
This opposition creates torque, causing rotor rotation
Speed Characteristics
The rotor speed (nr) always remains less than the synchronous speed (ns) of the rotating magnetic field. This difference is quantified by slip (s):