3-phase Motors - 1

Rotating Magnetic Field

3-phase Supply

(3 voltages, 120o apart)

3-phase Motor Stator

(3 Windings, 120o apart)Phase A (Red)

Phase B (Black)Phase C (Blue)

Arrows show Magnetic Fluxwhen phase voltage is POSITIVE

A B C

3-phase Motor Stator

(3 Windings, 120o apart)

Each step is shownhere at 0.5 seconds(6 seconds per cycle)

Green dotted lines show resulting magnet flux

Green arrow shows flux direction

Three-phase sequence produces resulting ROTATINGMAGNETICFLUX

3-phase Motor Stator

(3 Windings, 120o apart)

Each step is shownhere at 0.2 seconds(2.4 seconds per cycle)

3-phase Motor Stator

(3 Windings, 120o apart)

Each step is shownhere at 0.1 seconds(1.2 seconds per cycle)

3-phase Motor Stator

(3 Windings, 120o apart)

This shows continuous1 second per cycle

3-phase Motor Stator

(3 Windings, 120o apart)

The STATOR core is a stack of thin silicon steel LAMINATIONS

3-phase Motor Stator

(3 Windings, 120o apart)

Windings are coils placed in SLOTS around the STATOR

The coils are connected in groups for each of the THREE PHASES

Speed – Frequency - Poles

The SPEED of the rotating magnetic fieldis determined by:

Supply FREQUENCY in Hertz (Hz)

Number of magnetic POLESproduced by the stator windings

Speed – Frequency - PolesThe SPEED of the rotating magnetic field is determined by:

120Synch

fN

P

SynchronousSpeed (rpm)

Frequency(Hz)

Number of Polesper phase

x2 Poles to PAIRSx60 rps to rpm

Production of Torque

Production of Torque

Note that the ROTOR LAGS behind the rotating magnetic field

(Watch the pink dot)