An AC motor operates using the interaction between a rotating magnetic field in the stator created by AC current and a magnetic field in the rotor. The stator is the stationary part containing windings that generate the magnetic field, while the rotor is the rotating part. Induction motors are the most common type and have a wound stator and rotor. In an induction motor, currents induced in the rotor by the stator create rotation, while in a synchronous motor the rotor carries its own magnetic field from a separate DC source and locks to the rotating magnetic field frequency. Synchronous motors have constant synchronous speed regardless of load but require an external starting mechanism, while induction motors have self-starting torque but a speed that decreases slightly with increasing load

1. (2) AC MOTORS

2. AC MOTORS
BASIC PRINCIPLE
An AC motor is an electric motor driven by an alternating current (AC)
 Principle of operation for all AC motors relies on the interaction of a revolving
magnetic field created in the stator by AC current, with an opposing magnetic field
either induced on the rotor or provided by a separate DC current source.
 Resulting interaction produces usable torque, which can be coupled to desired
loads throughout the facility in a convenient manner.
The AC motor is made up of two parts
 Stator -The stationary section that contain the windings (magnetic field)
 Rotor – The rotating section that contains the conductors
Advantages of AC Motor
 Low cost
 Speed variation
 High power factor
 Reliable operation
Disadvantages of AC Motor
 Inability to operate at low speeds
 Poor positioning control
 AC will produce eddy currents due to the production of a back emf.

3. (1) INDUCTION MOTOR
Induction motors are the most common motors used for various equipments in
industry.
Induction ac motors are the simplest and most rugged electric motor and consists of two basic
electrical assemblies: the wound stator and the rotor assembly.
 The induction ac motor derives its name from currents flowing in rotor that are induced by
alternating currents flowing in the primary member (stator).
 The combined electromagnetic effects of the stator and rotor currents produce the force to
create rotation
Induction motors can be classified into two main groups:
Single-phase induction motors:
These only have one stator winding, operate with a
single-phase power supply.
Three –phase induction motors:
 A three phase supply is given to the stator of induction motor.
Figure 1/single phase ac motor

4. (2) SYNCHRONOUS MOTOR
 The stator in this type of motor is identical to that used in an induction motor, except the rotor
alternatively carries its own magnetic field windings,which are supplied from a DC source.
 Synchronous motors are not self starting as The rotor gets locked to the RMF, so They require
some external means to bring their speed close to synchronous speed before they are
synchronized.
 The speed of operation of is constant irrespective of load condition related to frequency of
supply .
 Difference between Induction Motor and Synchronous Motor
BASIS OF DIFFERENCE SYNCHRONOUS MOTOR INDUCTION MOTOR
Supply System Its armature winding is energized from an AC
source and its field winding from a DC source.
Its stator winding is energized from
an AC source.
Speed It always runs at synchronous speed. The
speed is independent of load.
If the load increased the speed of the
induction motor decreases. It is always
less than the synchronous speed.
Starting It is not self starting. It has to be run up to
synchronous speed by any means before it
can be synchronized to AC supply.
Induction motor has self starting
torque.
Usage It can be used for power factor correction
in addition to supplying torque to drive
mechanical loads.
An induction motor is used for
driving mechanical loads only.
Efficiency It is more efficient than an induction
motor of the same output and voltage
rating.
Its efficiency is lesser than that of
the synchronous motor of the same
output and the voltage rating.
Cost A synchronous motor is expensive than an
induction motor of the same output and
voltage rating
An induction motor is cheaper than
the synchronous motor