This is a presentation about linear induction motor. here I had explained LIM clearly like effects, construction, working, application and many more. most of people don't know much about this type of motor. I hope this will be usefull to you

1. Linear Induction Motor
Special Electric Machines
Prepared By:
Hanif Pathan
hpathan29@gmail.com
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2. FLOW OF PRESENTATION
 Introduction
 Construction
 Types of LIM
 Principle
 Working
 Various effects in LIM
 Characteristics
 Advantages- Disadvantages
 Application
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3. INTRODUCTION
 “A motor that produces thrust in a straight line by
direct induction rather than with the use of gears
called also Linear induction motor.”
 Linear motors are electric induction motors that
produce motion in a straight line rather than
rotational motion.
 In a traditional electric motor, the rotor (rotating
part) spins inside the stator (static part)
 In a linear motor, the stator is unwrapped and laid
out flat and the "rotor" moves past it in a straight
line.
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4. CONSTRUCTION
•In LIM stator and rotor are called primary and secondary
respectively. If the stator of the poly phase induction motor shown in
the figure is cut along the section and laid on a flat surface, then it
forms the primary of the LIM housing the field system, and
consequently the rotor forms the secondary consisting of flat
aluminum conductors with ferromagnetic core for effective flux
linkage.
•The primary may now be shorter or larger than the secondary.
The shorter component will be the moving part, hence the longer
will stay stationary. A LIM can either be Single-Sided or Double-
Sided.
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5. CONTINUED…
•There is another variant of LIM also being used for increasing
efficiency known as the double sided linear induction motor or DLIM,
as shown in the figure below. Which has a primary winding on either
side of the secondary, for more effective utilization of the induced
flux from both sides.
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6. PRINCIPLE
 In this electric motor design, the force is produced by a linearly
moving magnetic field acting on conductors in the field. Any
conductor, be it a loop, a coil, or simply a piece of plate metal,
that is placed in this field will have eddy currents induced in it
thus creating an opposing magnetic field in accordance
with Lenz's law. The two opposing fields will repel each other,
creating motion as the magnetic field sweeps through the metal.
 LIM is a derived from induction motor that’s why its working
principle is same as induction motor.
 Based on the FARADAY’S LAWS OF INDUCTION,
electromagnetic field i.e., emf is induced at slip frequency on
rotor side. Hence it is named as INDUCTION MOTOR.
 It is a self starting machine, since the rotating magnetic field is
produced when the supply is given to stator side. This approach
is visualized in poly phase induction motor.
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7. WORKING OF LIM
 When the primary of an LIM is excited by a balanced three
phase power supply, a traveling flux is induced in the primary
instead of rotating 3 φ flux, which will travel along the entire
length of the primary.
 Electric current is induced into the aluminum conductors or
the secondary due to the relative motion between the traveling
flux and the conductors.
 This induced current interacts with the traveling flux wave to
produce linear force or thrust F.
 If the secondary is fixed and the primary is free to move, the
force will move the primary in the direction of the force,
resulting in the required rectilinear motion.
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8. CONTINUED…
 When supply is given, the synchronous speed of the field is given by
the equation
Where, fs =supply frequency in Hz, and
p = number of poles,
ns =synchronous speed of the rotation of magnetic field in
revolutions per second.
 The developed field will results in a linear traveling field, the velocity
of which is given by the equation,
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9. CONTINUED…
 where, vs is velocity of the linear traveling field, and t is the
pole pitch. For a slip of s, the speed of the LIM is given by,
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10. VARIOUS EFFECTS IN LIM
1.End effect
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11. CONTINUED…
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2.Edge effect
3.Gap effect

12. CHARACTERISTICS OF LIM
Different forces in LIM
1. Thrust Force
2. Normal Force
3. Lateral Force
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13. 1. Thrust Force
 Thrust Force which is developed is directly proportional to the square
of the applied voltage and this reduces as the slip value is reducing
similar to that of a induction motor with high rotor resistance.
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14. 2. Normal Force
 In DLIM motors, normal force between one stator and reaction plate
is equal and opposite to the normal force generated by second stator
and reaction plate so in maximum DLIM, the net normal force is equal
to zero.
 The force shows the asymmetry of the system.
 In SLIM, there is large net normal force because of fundamental
asymmetry topology.
3. Lateral force
 These forces are acted on perpendicular to the rotor position which in
Y- direction.
 These forces make system unstable because they provide high
frequency(>>60Hz) operation of system.
 Lateral force can be eliminated by using some guided motion of wheel
of LIM.
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15. ADVANTAGES
 Simple in structure
 Direct electromagnetic force (no mechanical elements, no
limitations for speed).
 Economical and cheap maintenance
 Easy expansion for any linear motion of system topology.
 Exact positioning in closed loop systems.
 separate cooling of primary & secondary
 As the platform rides above the track on a cushion of air, there
is no loss of energy to friction.
 As both acceleration and braking are achieved through
electromagnetism, linear motors are much quieter than
ordinary motors.
 No gear Requirement (No need to mechanical rotatory-to-
linear converter) 15

16. DISADVANTAGES
 Power factor and efficiency are less than of rotary motors
because of a ratio of large air gap between inductors and pole
pitch
 Heating Issues
 extra vibrations with distortion
 High in cost
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17. APPLICATION
 Packaging and Material Handling
 Reciprocating compressors and Alternators
 Materials handling
 Presses
 Automatic sliding doors (electric trains, malls)
 Metallic conveyor belts.
 Airport baggage handling
 Accelerators
 People movers
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