MOTOR
Motor is an
electrical machine where AC motor works only in AC supply and DC motor only works in DC supply. There are many different
types of motor in the world. Generally the motor works in the form of
interaction between magnetic fields and winding current.
Motor’s
History :
The first
electric motor is simple electrostatic device, which is invented by Scottish
monk in the year 1740. Following the old one Andre-Marie Ampere was discovered
the interaction of electric current and magnetic field in the year 1820. This
interaction is called as Ampere’s Force Law.
Electrical
energy into mechanical energy conversion by Electromagnetic was discovered by
the British scientist Michael Faraday in the year 1821. Jedlik was a scientist
who introduced the three main parts of the DC Motor. The three main parts of
the DC Motor are Stator, Rotor, Commutator. Now a days, the motor which is
manufactured by using these three parts.
Principle of
Motor :
A Motor is a Electrical Machine which
converts an electrical energy into mechanical energy. It works in the
principle, when current carrying conductor is placed in a magnetic field, it
results in mechanical force. And its
direction is given by Fleming Left Hand Rule.
Types of
Motor :
Generally
the Electric motor is classified into two types. They are
1. AC Motor
2.
DC Motor
AC Motor:
It is an
electric machine which works only in AC i.e., Alternating current. AC motor
consists of two main components. They are Stator and Rotor. Stator is a outside stationary part of the
motor which consists of coils supplied with AC voltage to produce a magnetic
field by rotating. Inside Rotor is used to produce a second rotating magnetic
field by attached to the output shaft.
DC Motor
:
Basically DC
Motor is splited , one is Brushed DC
Motor and another is Brushless DC motor. A Brushed DC motor producing a torque
from DC source. The Stator field was formed by the stationary permanent
magnets. By using Lorentz Force, a force experienced by an external magnetic
field using current carrying conductor. A Brushless DC Motor uses rotating
magnet in a rotor and in stator stationary current(coil) magnets is used.
There are
some of the classifications in both AC and
DC motors.
The types of
AC motors are :
1. Synchronous Motor
2. Induction Motor.
The types of
DC motors are :
1. Separately Excited DC
motor
2. Self Excited DC motor.
In this two
types of DC motor, Self Excited motor consists of three. They are shunt motor,
series motor, and compound motor.
Here the
types of AC and DC types of motors have been explained in the below.
1.Synchronous Motor :
It’s the motor which is developed in the year
1925. The other name of this motor is Selsyn Motor. Here the
basic of this
motor will be explained .
Construction :
The construction of this motor is
similarly as same as salient pole alternator. The synchronous motor which only
runs in alternating current. Synchronous motor which always runs in constant
speed at any stage such as motor with load and without load. When this motor is
operating under certain conditions, the low power factor of an inductive load can be corrected
easily. Synchronous motor has been designed in
many sizes in different horse power. This motor is designed in both single
phase and also in thre phase.
Working :
The Stator
phase of the motor are mentioned by three wounded windings, which is placed in
the angle of 120 degree. The Rotor consists of field winding, Damper
winding, which is placed under the poles
of rotor. The field windings and the damper windings are placed under the poles
of rotor and center of the rotor. To represent the path of induced the rotor
current, the two damper windings are short circuited. Mostly the Synchronous
motors are operated as a generator where the positive stator current flows out
from the machine. Thereby the positive electromagnetic torque represents to the
operation of generator and the negative electromagnetic torque represents to
the operation of motor.
Advantages :
- Synchronous motor is mechanically more stable, since it has been constructed with large air gaps than the induction motor.
- The electromagnetic power varies linearly gets changes in synchronous motor according to the voltage.
- Normally synchronous motor works with more efficiency, specially in unity power factor and low speed compared to Induction motor.
- The main application of synchronous motor is to control the power factor. Synchronous motor can be operated in parallel to Induction motor which have leading power factor. The other lagging power factor improves the system power factor.
Disadvantages :
- Continuous maintenance of Collector rings and brushes are more important.
- Synchronous motor is not eligible for frequent starting and high starting torque.
- The synchronism among stator and rotor, lost its magnetic field and comes to rest position at the time of working beyond its capacity.
- Synchronous motor doesn’t gets started when the load is connected to it.
- The cost of a single KW is high compared to induction motor.
- Synchronous motor needs some arrangements for starting and it is not self starting motor.
2. Induction Motor :
Induction
motor is a electrical machine, and it is one of the type of AC motor. This the
motor which is cheaper and the maintenance is easy and low compared to other
types of alternating motor. It is widely used in homes, offices, workshops. The
cost of this motor is low and the maintenance is less , and the construction of
this motor is very simple.
Generally induction
motor is differentiated into two category. They are single phase induction
motor and three phase induction motor.
Construction : (Single phase induction motor)
The
construction of single phase induction motor is similarly as same as three
phase induction motor. Instead if squirrel cage, stator is wound in a motor.
Starting windings are provided for Stator windings, starting windings are used
only for initial purpose only.
Induced
current is produced in the rotor bars, when AC flows through rotor windings.
The alternating flux is also produced by induced current. Though there is two
alternating flux produced, it doesn’t start rotation. It requires some external
force to initiate the motor, after initiating the motor it reaches the maximum
speed and there will be continuous motion.
Construction : (Three phase induction motor)
This motor
also consists of stator and rotor. The stator will be in stationary part and
the rotor will be a rotating part. There will be some air-gap which is produced
in-between the stator and rotor. Stator
is made up of steel and the steel laminations are kept inside the iron frame.
The rotating magnetic field is produced when AC supply is passed. By the same
way while AC supply is allowed to pass through the rotor, then the rotating
magnetic field will be produced.
Working : (Three phase
induction motor)
As
mentioned, that the single phase motor is not a self starting but the three
phase induction motor is a self staring motor. There is no external force to
start the this machine. Here the three phase lines are placed in 120 degree
phase difference. Hence the rotating magnetic field will have the same phase
difference which makes the rotor to move. Consider the three phase X,Y,Z and if X phase is magnetized then the rotor
will move towards the phase winding X. after a moment Y gets magnetized and the
rotor will gets attracted by phase Y. Then this process will continues foe Z
also.
Advantages :
- In absence of slip rings, commutator, and brushes cost of construction is less.
- The maintenance cost of this motor is less since it doesn’t consists of brushes.
- Induction motor can be use in any of the polluted places and environment as it does not consist of brushes which causes sparks.
- Three phase induction motor does not consists of any external force for staring the motor
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