Introduction OF AC Motors
A motor which is operated by an alternating current AC is
called an AC motor. AC motor consists of many parts and the basic parts of AC
motor are stator and rotor. Stator consists of coils and are supplied by
Alternating current to produce a rotating magnetic field. These coils are
wrapped to the magnetic poles of the motor which are present on the cover of
the AC motor. The rotor is attached to the shaft to produce second rotating
magnetic field. The rotor magnetic field is produced with permanent magnets or
with an exciter.
Classification of AC Motor
AC motors are classified into so many groups which are as
follows:
According to the Principle
of Operation
1.
Synchronous motor
Synchronous motor further divides into following types:
- Plain
- Super
2.
Asynchronous motor
Asynchronous motor further divides into two types:
- Induction motor
Induction motor further divides into two types:
- Squirrel cage motors
- Slip ring motors
Induction motor
types according to rotor
- Polyphase cage rotor motors
- Polyphase wound rotor motors
Induction motor
types according to phases
- · Single phase induction motors
- Single phase induction motor further divides into many types
- Shaded pole motor
- Reversible shaded pole motor
- Split phase motor
Split phase motor is further divided into its following
types
- Capacitor start motor
- Resistance start motor
- Permanent split capacitor motor
- Three phase induction motors
3.
Commutator motor
These are further divides into six types
- Series motors (single phase or universal)
- Compensated commutator motors (conductively or inductively)
- Shunt motors (simple or compensated)
- Repulsion motors (straight or compensated)
- Repulsion start induction motors
- Repulsion induction motors
According to current
1.
Single phase motors
2.
Three phase motors
According to speed
1.
Constant speed motors
2.
Variable speed motors
3.
Adjustable speed motors
According to their
structures
1.
Open type motors
2.
Enclosed type motors
3.
Semi enclosed type motors
4.
Ventilated type motors
5.
Pipe ventilated type motors
6.
Reverted frame type motors etc.
Other AC Motors
1.
Universal motor
2.
Repulsion motor
3.
Exterior rotor
4.
Sliding rotor motor
5.
Electronically commutated motor
6.
Watt hour meter motor
7.
Slow speed synchronous timing motor etc.
Working Principle of AC Motor
In the operation of the ac motor, the working of rotor and
stator must be discussed because these are the main and basic parts of AC motor
by which an AC motor operates. As we discussed above that there are the two
main and basic parts of AC motor, one is stator and the other is rotor. The
stator consists of a coil which is wrapped up on the main and auxiliary poles
of ac motor and poles are attached on the inner side of the cover of AC motor.
These poles are also called stator poles. The stator is the stationary part of
AC motor and the rotor is the rotating electrical component. Rotor consists of
electromagnets arranged around the cylinder, with the poles facing towards
stator poles. The rotor is located inside the stator and is fixed on the shaft
of the AC motor. This is because when the rotor rotates and the shaft also
rotates and the shaft will provide us mechanical energy. The rotation will
occur because of the magnetic phenomenon. The magnetic phenomenon is that
unlike magnetic poles attract each other and like magnetic poles repel each other.
When we change the polarity of the stator poles by giving the ac supply to the
stator winding or stator coils then a combined magnetic field occurs which will
give a force to the rotor to rotate and as a result the rotor will follow the
direction of magnetic field and starts rotating with the magnetic field of the
rotor.
How to
produce the rotating magnetic field on the stator of an AC motor?
There is only a one way to produce rotating magnetic field
on the stator of an AC motor is that by giving the three-phase ac supply to the
stator coils. The connection of the stator coils is with a sequence and the
sequence is that each coil of a pole is connected to the next pole coil in
opposite direction and so on. For further understanding see the figure shown
below.
