Motors 3 phase Induction Motor

3 Phase Induction Motor Introduction to 3 Induction Motors Dept of E & E, MIT Manipal 3 Phase Induction Motor Introduction to 3 Induction Motors Applications Classification Constructional Features Summary References Edward Hughes, Chapter Nagasarkar & Sukhija, Chapter 8 Nagrath & Kothari, Chapter 12

Introduction Invented by Nikola Tesla, 1888 Dept of E & E, MIT Manipal Introduction Nikola Tesla (1856-1943) Invented by Nikola Tesla, 1888 Converts electrical power into mechanical power Energy transfer by means of electromagnetic induction Widely used for commercial & industrial applications

Applications Industrial & Commercial Applications Pumping Systems Dept of E & E, MIT Manipal Applications Industrial & Commercial Applications Pumping Systems Refrigeration Systems Compressors Fans & Blowers Industrial Drives

Rotating Magnetic Field 3 phase supply is given to a balanced 3 phase winding of stator. 3 alternating magnetic fluxes displaced mutually at 120 deg. Is produced.

Rotating Magnetic Field Considering different instances of time (i) At wt = 0 The instantaneous fluxes are The resultant magnetic flux is 1.5 times peak value and acting at 90 deg. to axis of reference.

Rotating Magnetic Field Similarly (ii) At wt = 60 The instantaneous fluxes are The resultant magnetic flux is 1.5 times peak value and acting at 30 deg. to axis of reference. i.e., rotated by 60 deg w.r.t. previous angle

Rotating Magnetic Field Similarly if various instances are considered upto 360 deg. It is seen that the resultant always has a magnitude of 1.5 times peak value and pointing in a direction at the angle of consideration. For every 360 deg the resultant magnetic field completes one rotation. Inference: When 3 phase currents flows in a balanced 3 phase winding, a rotating magnetic field is created which has constant magnitude, but rotates in synchronism with supply frequency. This speed of rotating magnetic field is SYNCHRONOUS SPEED

Classification Construction Connection Squirrel Cage, Slip Ring Dept of E & E, MIT Manipal Classification Construction Squirrel Cage, Slip Ring Connection Stator : Star, Delta Rotor : Cage, Wound

Dept of E & E, MIT Manipal Construction – Stator Stator frame: Cast Iron, Mechanical Support to stator core Stator core: Stack of cylindrical steel laminations Stator Slots: Inner periphery, Windings Laminations Slots Stator Conductors

Construction – Stator Stator support Outer frame Stator Core Dept of E & E, MIT Manipal Construction – Stator Stator support Outer frame Stator Core Stator Slots Stator insulation Stator windings

Construction – Rotor Types on the basis of rotor construction Dept of E & E, MIT Manipal Construction – Rotor Types on the basis of rotor construction Squirrel Cage Rotor Slip Ring Rotor Cylindrical Laminated core Slots cutout on outer periphery Conductors placed in slots

Construction – Squirrel cage Rotor Dept of E & E, MIT Manipal Construction – Squirrel cage Rotor Rotor bars Skewed arrangement Copper or Aluminum Bars Conductors shorted by end rings Closed rotor circuit End rings

Construction – Slip ring rotor Dept of E & E, MIT Manipal Construction – Slip ring rotor One end of Rotor conductors connected to each other Other ends connected to slip rings External resistance Slip rings in contact with brushes Brushes connected to external resistance Brush Rotor Shaft Slip rings Rotor Conductors

Construction – Squirrel cage Rotor Dept of E & E, MIT Manipal

Construction – Slip Ring Rotor Dept of E & E, MIT Manipal Construction – Slip Ring Rotor Slip rings

Cross Sectional View Terminal Box Stator Cage Rotor Shaft Dept of E & E, MIT Manipal Cross Sectional View Terminal Box Stator Cage Rotor Shaft Ball Bearings Outer Frame Supporting Base

Induction motor setup Dept of E & E, MIT Manipal

Representation Stator Core Stator Slots 3Ø Supply Stator conductors Dept of E & E, MIT Manipal Stator Core 3Ø Supply Stator Slots Stator conductors Rotor Core Shaft Rotor Slots Rotor conductors

Air gap Uniform over stator & rotor periphery Dept of E & E, MIT Manipal Uniform over stator & rotor periphery Must be as small as possible usually of the order 0.5 mm to 1 mm Reduce the leakage flux between stator and rotor Leads to better operating power factor Necessary to facilitate free rotor movement

Lecture 1 Summary Applications, Classifications Dept of E & E, MIT Manipal L1 – 17 Applications, Classifications Main Parts : Stator, Rotor Rotor Squirrel cage : Skewed arrangement, End rings Wound rotor : Slip rings, external resistance Air gap Provided to enable free rotor rotation Rotating magnetic field Rotating nature with resultant of constant magnitude