SUBJECT: ELECTRO-MAGNETIC THEORY
: Submitted By :
Rajvi Trivedi (131039)
Shailaja Sampat (131046)
What is an Electric Motor?
Electric motor has brought one of the biggest advancements
in the fields of engineering and technology ever since the
invention of electricity.
Electric Motor is a simple device that produces rotational
force or more generally Electric Motor is an electro-magnetic
device that converts electrical energy into mechanical energy.
Electric Motor Symbol
Electric motor works on the principle of a magnetic
interaction between a current-carrying conductor and an external
magnetic field to generate rotational motion.
Current carrying coil placed in electro-magnetic field rotates
continuously due to torque acting on the coil. When the coil
rotates, the shaft attached to it also rotates and thus it can result
in doing mechanical work.
Electric Motor – Timeline :
electrical energy into
mechanical energy by
The most primitive
expensive and not
used for practical
First electrical motor
which was capable of
rotating at a constant
speed under a varied
range of load
Frank Julian Sprague
Electric Motor - Timeline
Electric Motor – Parts :
Electric motor consists mainly with five parts;
Armature or Rotor
Armature is a rectangular coil made up of insulated
copper wire wound on a soft iron core. It is placed between the
Commutator is a copper ring split into two parts C1 and
C2. They rotate along with the coil. Battery is connected to the
rings by brushes in-between.
Brushes (B1 and B2)
Two small strips of carbon, known as brushes are used
to connect power source with Commutator.
Operational Principle- Fleming’s left hand rule :
Fleming’s left hand rule- Place index finger, middle finger
and thumb of our left hand in such a way that the electric current
carrying wire is placed in a magnetic field (index finger) and
perpendicular to the direction of current (middle finger), then the
conductor experiences a force in the direction (represented by
the thumb) mutually perpendicular to both quantities.
Working of Electric Motor:
Due to applied external DC source, electric current starts
flowing through the Armature. As the conductor is carrying
current inside a magnetic field, the left side of the armature is
pushed away from the left magnet and drawn towards the right
causing rotation. It will experience a force and torque which tends
to rotate the Armature.
Rotation of a coil due to torque
When the coil turns through 900
, the Brushes lose contact
with the Commutator and the current stops flowing through the
coil however the coil keeps turning because of its own
Now when the coil turns through 1800
, the sides get
interchanged. As a result the Commutator ring C1 is now in
contact with brush B2 and Commutator ring C2 is in contact with
brush B1. Therefore, the current continues to flow in the same
We can find magnitude of Force by F= ILB sinө and direction
by applying Fleming’s Left hand Rule. At any instance of time,
forces experienced by the conductors are in such a direction that
they tend to rotate the Armature due to forces of same
magnitude but opposite direction.
Fl = ILB Sin (90°) = BIL (Force on left part of Armature)
Fr = (− I) LB Sin (90°) = − BIL (Force on right part of Armature)
Types of Electric Motor :
DC: driven by Direct Current
AC: driven by Alternate Current
Synchronous motor: always runs at synchronous speed.
Induction motor / Asynchronous motor: whose speed is
governed by varying the slip.
3 phase induction motor: contains 3 phase supply and runs
on the principal of e.m.f. induction due to flux.
Single phase induction motor: contains single phase supply
and runs on the principal of established theories, namely the
Double Revolving field theory and the Cross field theory.
AC MOTOR DC MOTOR
INDUCTION MOTOR /
3 Phase INDUCTION
Shunt: field windings are shunted to, or are connected in
parallel to the armature.
Compound: field windings are connected in series to the
Applications of electric motors :
3 phase Induction motor: conveyers, crushers, cranes,
elevators, compressors, blowers, fans, machine tools,
centrifugal pumps etc.
Single phase Induction motor: domestic applications mainly
used in Hair dryers, fans, washing machine, ac fans, dairy
machinery, small power tools, small farming equipment,
vacuum cleaner, mixers etc.
3 phase Synchronized motor: variable speed applications
such as high power and high speed compressors, blowers
Special Types of Motors :
Reluctance motors - electric clocks timers, signaling devices,
recording devices etc.
Hysteresis motors - electric clocks and timing devices
Permanent magnet DC motor – portable vacuum cleaner,
Servomotors - robotics, radars, computers, machine tools,
DC motors - DC series motor is also used in lifts, fans etc.
DC Shunt motors - mill machines, conveyors.