Hysteresis motor is a type of synchronous type motor with uniform air gap. It can work from both single phase or 3-phase supply.

1. HYSTERESIS MOTOR
-- NAUSHEEN ( CUJ/I/2014/IEE/032 )
-- DIVYA KRITIKA (CUJ/I/2014/IEE/040)

2. INTRODUCTION:
 HYSTERESIS MOTOR:
 Synchronous motor with uniform air
gap
 Without d.c. excitation
 Operate from single phase or 3-
phase supply
 Torque produced due to hysteresis
and eddy current induced in rotor

3. CONSTRUCTIONS:
 STATOR CONSTRUCTION:
 Similar to induction motor
 Connected either to single phase or 3- phase supply
 Single phase – stator winding is of permanent split capacitor
type

4. Smooth cylinder
 ROTOR CONSTRUCTION
 Core : aluminium or other
nonmagnetic material
 Outer layer : thin rings to form
laminated rotor
 Smooth cylinder , no windings

5. HYSTERESIS LOOP ( B-H LOOP)
 Relationship between the induced
magnetic flux density (B) and the
magnetizing force (H).
 A ferromagnetic material that has
never been previously magnetized or
has been thoroughly demagnetized will
follow the dashed line as H is increased.
 Point ‘a’ – all the magnetic domains are
aligned. Materials has reached to the
point of magnetic saturation
 H is reduced to zero, the curve will
move from point "a" to point "b."Some
of the magnetic domains remain aligned
but some have lost their alignment.

6.  magnetizing force is reversed, the curve moves to point "c", where the flux has
been reduced to zero. This is called the point of coercivity on the curve
 magnetizing force is increased in the negative direction, the material will again
become magnetically saturated but in the opposite direction (point "d")
 Reducing H to zero brings the curve to point "e." It will have a level of residual
magnetism equal to that achieved in the other direction. Increasing H back in the
positive direction will return B to zero
 the curve did not return to the origin of the graph because some force is required
to remove the residual magnetism. The curve will take a different path from point
"f" back to the saturation point where it with complete the loop

7. OPERATION :
Rotor poles
“induced” by Stator
Flux
Stator Flux
establishes these
magnetic poles
Rotor poles follow
the rotating flux,
but lag behind by
angle δh
 3- Phase or single
phase supply is applied
to the stator, a
rotating magnetic
field is produced
 Rotating magnetic
field induces poles
within it
 Induced rotor flux
lags behind rotating
stator flux

8.  Angle between stator and rotor
magnetic field is responsible for
production of torque
 Angle depends upon shape of
hysteresis loop , independendent on
frequency
 Additional torque due to eddy current

9.  Ideal material would have
rectangular hysteresis loop ( loop
1)
 Ordinary steels are not suitable
as they resemble to loop 3
 Cobalt vanadium type materials
are used as they have loop a/c to
2 which approximates to loop 1

11. It is clear that the torque is proportional to the slip. Therefore, as the speed
of the rotor increases the value of Ʈe decreases. As the speed of the motor
reaches synchronous speed, the slip becomes zero and torque also become zero.
As the electromagnet torque is developed by the motor is because of the
hysteresis loss and remains constant at all rotor speed until the breakdown
torque. At the synchronous speed, the eddy current torque is zero and only
torque due to hysteresis loss is present.

12. TORQUE – SPEED CHARACTERISTICS
 ideal torque speed curve is shown
by curve 1
For practical hysteresis motor –
curve 2
Deviation for ideal characteristic
is due to presence of harmonics
Torque is constant at high speed
including synchronous speed

13. ADVANTAGES OF HYSTERESIS MOTOR:
 Smooth , viberation free operation
 Low noise
 Steady state speed is directly controlled by electrical input
frequency
 Positive starting ( non- zero torque at rest)
 Constant torque

14. DISADVANTAGES OF HYSTERESIS
MOTOR:
 Low efficiency
 Low power
 Hunting phenomenon

15. APPLICATIONS :
Hysteresis motors are particularly well suited for driving
 Electric clocks
 Timing devices
 Tape – decks
 Other precision audio equipment

16. REFERENCE :
 www.google.co.in
 www.wikipidea.org
 www.slideshare.com
 www.worldbook.com
 www.youtube.com
 www.circuitglobe.com
 Electric Machines ( 2nd edition ) by Ashfaq Husain

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