Construction and working principle with diagram (Three phase Induction Motor)

 





A three-phase induction motor consists of a stator and rotor, and it works on the principle of electromagnetic induction: the stator’s rotating magnetic field induces current in the rotor, producing torque. The diagram below illustrates its construction and working principle clearly.

Construction of a Three-Phase Induction Motor

  • Stator (Stationary Part):

    • Laminated steel core with slots carrying three-phase windings.

    • Connected to a three-phase AC supply.

    • Produces a rotating magnetic field (RMF).

  • Rotor (Rotating Part):

    • Squirrel Cage Rotor: Simple, robust, widely used.

    • Slip-Ring Rotor: Allows external resistance for high starting torque.

    • Mounted on a shaft with bearings and cooling fan.

  • Other Parts:

    • Frame, end covers, shaft, and cooling arrangement.

Working Principle

  • When a three-phase AC supply is applied to the stator windings, a rotating magnetic field (RMF) is produced at synchronous speed:

Ns=120fP

where f = supply frequency, P = number of poles.

  • This RMF cuts the rotor conductors, inducing an EMF (Faraday’s law).

  • The induced EMF produces rotor current, which interacts with the stator’s RMF to produce torque (Lorentz force).

  • The rotor speed is slightly less than synchronous speed, defined by slip:

s=Ns−NrNs

Key Features

  • Self-starting motor.

  • Constant speed operation (slightly less than synchronous).

  • High efficiency and low maintenance.

  • Widely used in industrial drives.




Comments

Post a Comment

Popular posts from this blog

Assignment – Control Systems (Unit 1)

   Assignment – Control Systems (Unit 1) Course: Electrical Engineering Semester: 4 Subject: Control Systems Assignment No.: 01 Maximum Marks: 20 Submission Date: 12/02/2026 Instructions Answer all questions neatly with proper diagrams wherever required. Use standard notation and units. Each question carries equal marks unless specified. Show all steps in derivations and numerical problems. Part A – Short Answer Questions (2 Marks Each) Differentiate between open-loop and closed-loop control systems with suitable examples. Define linear and nonlinear systems. Give one practical example of each. Explain the difference between time-variant and time-invariant systems. Define feedback in control systems. Why is it essential? Differentiate between degenerative (negative) and regenerative (positive) feedback. Part B – Long Answer Questions (Any two) (5 Marks Each) Derive the transfer function of an R-C circuit using Laplace transform. Derive the transfer function of ...
Read more

Assignment – AC Machines (Unit 1)

  Assignment – AC Machines (Unit 1) Course: Electrical Engineering Semester: 4 Subject: AC Machines Assignment No.: 01 Maximum Marks: 20 Submission Date: 27/02/2026 Instructions Answer all questions neatly with proper diagrams wherever required. Use standard notation and units. Each question carries equal marks unless specified. Show all steps in derivations and numerical problems. Part A – Short Answer Questions (2 Marks Each) Explain with neat and clean diagram the Construction and working principle of a three-phase induction motor. Define Slip and slip speed . Explain their significance. Explain Types of three phase induction motors . Draw Equivalent circuit of three phase induction motor and explain its components. Explain Rotor resistance starter – Why is it suitable for slip ring motors? Part B – Long Answer Questions (5 Marks Each) Compare squirrel cage and slip ring induction motors in terms of construction, performance, starting methods, and applications. Explain...
Read more

Assignment 02– Control System & PLC

  Assignment – Control System & PLC  Course: Electrical Engineering Semester: 4 Subject: Control System & PLC **Assignment No.: 02 Maximum Marks: 20 Submission Date: 22/04/2026 Instructions Answer all questions neatly with proper diagrams wherever required. Use standard notation and units. Each question carries equal marks unless specified. Show all steps in derivations and numerical problems. Part A – Short Answer Questions (Any five) (2 Marks Each) Explain the difference between open‑loop and closed‑loop control systems with examples. Define transfer function and explain its importance in system analysis. State the advantages of frequency response analysis over time domain analysis. What is the significance of block diagram reduction in control systems? List the advantages of PLCs compared to conventional relay logic. Explain the role of timers and counters in PLC programming. Write a simple ladder logic program for a lamp controlled by a switch. Part B –...
Read more