1. 3-phase Motors - 1
Rotating Magnetic Field

2. 3-phase Motor Stator
o
(3 Windings, 120 apart)
Phase A (Red)
Arrows show Magnetic Flux
when phase voltage is POSITIVE
Phase C (Blue)
A
3-phase Supply
(3 voltages, 120o apart)
Phase B (Black)
B
C

3. 3-phase Motor Stator
o
(3 Windings, 120 apart)
Green arrow shows
flux direction
Three-phase sequence
produces resulting
ROTATING
MAGNETIC
FLUX
Green dotted lines show
resulting magnet flux
Each step is shown
here at 0.5 seconds
(6 seconds per cycle)

4. 3-phase Motor Stator
o
(3 Windings, 120 apart)
Each step is shown
here at 0.2 seconds
(2.4 seconds per cycle)

5. 3-phase Motor Stator
o
(3 Windings, 120 apart)
Each step is shown
here at 0.1 seconds
(1.2 seconds per cycle)

6. 3-phase Motor Stator
o
(3 Windings, 120 apart)
This shows continuous
1 second per cycle

7. 3-phase Motor Stator
o
(3 Windings, 120 apart)
The STATOR core is a
stack of thin silicon steel
LAMINATIONS

8. 3-phase Motor Stator
o
(3 Windings, 120 apart)
Windings are coils placed in
SLOTS around the STATOR
The coils are connected in groups
for each of the THREE PHASES

9. Speed – Frequency - Poles
The SPEED of the rotating magnetic field
is determined by:
Supply FREQUENCY in Hertz (Hz)
Number of magnetic POLES
produced by the stator windings

10. Speed – Frequency - Poles
The SPEED of the rotating magnetic field is determined by:
x2 Poles to PAIRS
x60 rps to rpm
N Synch
Synchronous
Speed (rpm)
Frequency
(Hz)
120 f
=
P Number of Poles
per phase

11. Production of Torque

12. Production of Torque
Note that the ROTOR
LAGS behind the
rotating magnetic field
(Watch the pink dot)