The
electric motor is a device which converts electrical energy to mechanical
energy. There are mainly threetypes
of electric motor.
1)DC
Motor
2)Induction
Motor
3)Synchronous
Motor.
All of these motors work in more or less same principle.Working
of electric motormainly depends upon the interaction of
magnetic field withelectric
current.
Now we will discuss the basic operatingprinciple
of electric motorone
by one for better understanding the subject.
Working of DC Motor
Working
principle of DC Motormainly
depends uponFleming
Left Hand rule. In a basicdc
motor, an armature is placed in between magnetic poles. If thearmature
windingis
supplied by an external dc source,electric
currentstarts
flowing through the armature conductors. As the conductors are carrying current
inside a magnetic field, they will experience a force which tends to rotate the
armature. Suppose armature conductors under N poles of the field magnet, are
carrying current downwards (crosses) and those under S poles are carrying current
upwards (dots). By applyingFleming’s
Left hand Rule, the direction of force F, experienced by the
conductor under N poles and the force experienced by the conductors under S
poles can be determined. It is found that at any instant the forces experienced
by the conductors are in such a direction that they tend to rotate the
armature.
Again, due this rotation the conductors under N – poles come under S – pole and
the conductors under S – poles come under N – pole. While the conductors go
form N – poles to S – pole and S – poles to N – pole, the direction of current
through them, is reversed by means of commutator. Due to this reversal of
current, all the conductors come under N – poles carry current in downward
direction and all the conductors come under S – poles carry current in upward
direction as shown in the figure. Hence, every conductor comes under N – pole
experiences force in same direction and same is true for the conductors come
under S – poles. This phenomenon helps to develop continuous and unidirectional
torque.
Working of Induction Motor
Working
of electric motor in the case of induction motor is little bit different fromdc
motor. In single phase induction motor, when a single phase supply
is given to the stator winding, a pulsating magnetic field is produced and in athree
phase induction motor, when three phase supply is given to three
phase stator winding, a rotating magnetic field is produced. The rotor of an
induction motor is either wound type or squirrel cadge type. Whatever may be
the type of rotor, the conductors on it are shorted at end to form closed loop.
Due to rotating magnetic field, the flux passes through the air gap between
rotor and stator, sweeps past the rotor surface and so cuts the rotor
conductor. Hence according toFaraday’s law of
electromagnetic induction, there would be a induced current
circulating in the closed rotor conductors. The amount of induced current is
proportional to the rate of change of flux linkage with respect to time. Again
this rate of change of flux linkage is proportional to the relative speed
between rotor and rotating magnetic field. As perLenz
lawthe
rotor will try to reduce the every cause of producing current in it. Hence the
rotor rotates and tries to achieve the speed of rotating magnetic field to
reduce the relative speed between rotor and rotating magnetic field.
Working of synchronous Motor
Insynchronous
motor, when balanced three phase supply is given to the stationary
three phase stator winding, a rotating magnetic field is produced which rotates
at synchronous speed. Now if an electromagnet is placed inside this rotating
magnetic field, it is magnetically locked with the rotating magnetic field and
the former rotates with the rotating magnetic field at same speed that is at
synchronous speed.
This Page is a little effort to make you Sharing of some own materials .This is just a Kick-Start to make the aware of Practical World !!! Best of luck.-DHRUVANG SUTHAR
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