AC MOTOR TYPES
The important information in this chapter is summarized below.
AC Motor Types Summary
In a split-phase motor, a starting winding is utilized. This winding has a higher
resistance and lower reactance than the main winding. When the same voltage
(VT) is applied to the starting and main windings, the current in the main
winding lags behind the current of the starting winding. The angle between the
two windings is enough phase difference to provide a rotating magnetic field to
produce a starting torque.
A synchronous motor is not a self-starting motor because torque is only
developed when running at synchronous speed.
A synchronous motor may be started by a DC motor on a common shaft or by
a squirrel-cage winding imbedded in the face of the rotor poles.
Keeping the same load, when the field excitation is increased on a synchronous
motor, the motor operates at a leading power factor. If we reduce field excitation,
the motor will operate at a lagging power factor.
The induction motor is the most commonly used AC motor in industrial
applications because of its simplicity, rugged construction, and relatively low
Single-phase motors are used for very small commercial applications such as
household appliances and buffers.
Synchronous motors are used to accommodate large loads and to improve the
power factor of transformers in large industrial complexes.