A 3 phase motor self starts due to a rotating magnetic field in the windings
If a single phase was applied to one winding, it would simply pulse and produce no torque
If we could simply ‘push’ the rotor, it would begin to spin for the same reasons in a 3 phase motor
AC motors convert AC electrical energy to Mechanical energy. AC motors:
the armature of rotor is a magnet (different to DC motors).
the stator is formed by electromagnets (like in DC motors). Effects of AC Supply on Magnetic Poles Consider the rotor to be a permanent magnet.
Current flowing through conductors energize the magnets and develop N and S poles.
The strength of electromagnets depends on current.
First half cycle current flows in one direction.
Second half cycle it flows in opposite direction...
Single Phase Motors
• Similar to a 3 phase induction motor with squirrel cage rotor and main stator windgs.
Main wndgs Centrifugal switch Rotor
Laminated stator slots Wndgs
.Run (main) and Start (Aux) Windings
• The stator has two
One way to solve the single phase problem is to build a 2-phase motor, deriving 2-phase power from single phase. This requires a motor with two windings spaced apart 90o electrical, fed with two phases of current displaced 90o in time. This is called a permanent-split capacitor motor in Figure
Permanent-split capacitor motor
One way to solve the single phase problem is to build a 2-phase motor, deriving 2phase power from single phase. This requires a motor with two windings spaced apart 90o electrical, fed with two