4. Spin the stator poles
with the rotor blocked
Stator poles
moving CCW
Rotor poles follow
the rotating flux,
but lag behind by
angle δh
5. Spin the stator poles
with the rotor blocked
If the rotor is released, it will accelerate to synchronous speed
6. Hysteresis Power Loss, Ph
max
n
h h rP k f B
where
fr = frequency of flux reversal in the rotor (Hz)
Bmax = maximum value of flux density in the air
gap (T)
Ph = heat-power loss due to hysteresis (W)
kh = constant
8. Mechanical Power Developed (cont)
max
max
5252
120
5252
120
n
h s
h
s
s
s
n
h
h
k f B
T
n
f
n
P
k B
T
P
Independent of frequency
and speed!
9. Hysteresis Motor at Synchronous Speed
No load and
negligible
rotational losses
Induced rotor
magnets remain
locked with the
rotating poles
produced by the
stator
10. Hysteresis Motor at Synchronous Speed
Apply a step
increase in shaft
load.
The rotor slows
down and the
induced rotor
magnets lag the
rotating poles of the
stator by an angle
δmag .
The rotor returns to
synchronous speed
at the new torque
angle.
11. Hysteresis Motor at Synchronous Speed
max
sin( )
@ 90
mag mag
mag mag
T
T occurs
If shaft load causes δmag>90°,
the rotor pulls out if
synchronism, the magnet torque
drops to zero, and the machine
develops hysteresis torque. This
torque is not sufficient to carry
the load.