Ms. Nishkam Dhiman
Assistant Professor -EEE Deptt.
Chitkara Institute of Engg. & Technology
1. Series Motor
2. Shunt Motor
1. Induction Motors
2. Synchronous Motors
When current flows in a conductor it produces a magnetic
field about it.
◦ when the current-carrying conductor is within an externally
generated magnetic field, the fields interact and a force is
exerted on the conductor.
Therefore if a conductor lies within a magnetic field:
◦ motion of the conductor produces an electric current
◦ an electric current in the conductor will generate motion
The reciprocal nature of this relationship means that, for
example, the DC generator above will function as a DC motor
1) Stator – The static part that houses the field windings and
receives the supply and
2) Rotor – The rotating part that brings about the mechanical
3) Yoke of dc motor.(cast iron or steel, provides protective cover)
4) Poles of dc motor.(cast iron, slotted)
5) Field winding of dc motor.(copper wire)
6) Armature winding of dc motor.( Copper wire)
7) Commutator of dc motor. (copper segments stacked together, it
commutates or relay the supply current from the mains to the armature
windings housed over a rotating structure through the brushes of dc
8) Brushes of dc motor. The brushes of dc motor are made with carbon
or graphite structures, making sliding contact over the rotating
commutator. The brushes are used to relay the electric current from
external circuit to the rotating commutator form where it flows into the
Sh u n
Percent of Rated Torque
Percent of rated Speed
Series Motor: Armature and field connected in a series circuit.
Apply for high torque loads that do not require precise speed
regulation. Useful for high breakaway torque loads.
locomotives, hoists, cranes, automobile starters
300% to as high as 800% of full load torque.
Shunt Motor: Field coil in parallel (shunt) with the armature.
Current through field coil is independant of the armature.
Result = excellent speed control.
Apply where starting loads are low
fans, blowers, centrifugal pumps, machine tools
125% to 200% full load torque (300 for short periods).
Performance is roughly between series-wound and shuntwound
Moderately high starting torque
Moderate speed control
Inherently controlled no-load speed
safer than a series motor where load may be
AC motors can be divided into two main forms:
◦ synchronous motors
◦ induction motors
High-power versions of either type invariably operate
from a three-phase supply, but single-phase versions
of each are also widely used – particularly in a
As its name indicate stator is a stationary part of induction
motor. A three phase supply is given to the stator of
The rotor is a rotating part of induction motor. The rotor is
connected to the mechanical load through the shaft. The
rotor of the three phase induction motor are further
• Squirrel cage rotor
• Slip ring rotor or wound rotor or phase wound rotor
Advantages of squirrel cage induction rotor
1. Its construction is very simple and rugged
2. as there are no brushes and slip ring, these motors requires less
Squirrel cage induction motor is used in lathes, drilling
machine, fan, blower printing machines etc
Slip ring or wound three phase induction motor : In this type
of three phase induction motor the rotor is wound for the same
number of poles as that of stator but it has less number of slots
and has less turns per phase of a heavier conductor.The rotor
also carries star or delta winding similar to that of stator
winding. The rotor consists of numbers of slots and rotor
winding are placed inside these slots.
Advantages of slip ring induction motor
1. It has high starting torque and low starting current.
2. Possibility of adding additional resistance to control
Slip ring induction motor are used where high starting
torque is required i.e in hoists, cranes, elevator etc
When a 3 phase electric conductors are placed in a certain geometrical positions (In
certain angle from one another) there is an electrical field generate.
The rotating magnetic field rotates at a certain speed, that speed is called
Now if an electromagnet is present in this rotating magnetic field, the
electromagnet is magnetically locked with this rotating magnetic field and rotates
with same speed of rotating field.
Synchronous motors is called so
because the speed of the rotor of
this motor is same as the rotating
magnetic field. It is basically a fixed
speed motor because it has only
one speed, which is synchronous
speed and therefore no intermediate
speed is there or in other words
it’s in synchronism with the supply
frequency. Synchronous speed is given by
Synchronous motor is a doubly excited machine i.e two
electrical inputs are provided to it. It’s stator winding which
consists of a 3 phase winding is provided with 3 phase
supply and rotor is provided with DC supply.
The 3 phase stator winding carrying 3 phase currents
produces 3 phase rotating magnetic flux. The rotor carrying
DC supply also produces a constant flux.
At a particular instant rotor and stator poles might be of
same polarity (N-N or S-S) causing repulsive force on rotor
and the very next second it will be N-S causing attractive
force. But due to inertia of the rotor, it is unable to rotate in
any direction due to attractive or repulsive force and remain
in standstill condition. Hence it is not self starting.
• Synchronous motor having no load connected to its shaft is
used for power factor improvement. Owing to its
characteristics to behave at any power factor, it is used in
power system in situations where static capacitors are
• Synchronous motor finds application where operating speed
is less (around 500 rpm) and high power is required. For
power requirement from 35 kW to 2500KW, the size, weight
and cost of the corresponding induction motor is very high.
Hence these motors are preferably used. Ex- Reciprocating
pump, compressor, rolling mills etc
Servomotor is normally a simple DC motor which is controlled
for specific angular rotation with help of additional
servomechanism (a typical closed loop feedback control system).
A Servo is a small device that incorporates a three wire DC
motor, a gear train, a potentiometer,an integrated circuit, and
an output shaft bearing (Shown in Figure). Of the three wires
that stick out from the motor casing, one is for power, one is
for ground, and one is a control input line. The shaft of the
servo can be positioned to specific angular positions by
sending a coded signal. As long as the coded signal exists on
the input line, the servo will maintain the angular position of
the shaft. If the coded signal changes, then the angular position
of the shaft changes.
Servos are constructed from three basic
pieces; a motor, a potentiometer (variable
resister) that is connected to the output
shaft, and a control board. The
potentiometer allows the control circuitry to
monitor the current angle of the servo motor.
The motor, through a series of gears, turns the
output shaft and the potentiometer
simultaneously. The potentiometer is fed into
the servo control circuit and when the control
circuit detects that the position is correct, it
stops the motor. If the control circuit detects
that the angle is not correct, it will turn the
motor the correct direction until the angle is
correct. Normally a servo is used to control
an angular motion of between 0 and 180
degrees. It is not mechanically capable
(unless modified) of turning any farther due
to the mechanical stop build on to the main
The amount of power applied to the
motor is proportional to the distance it
needs to travel. So, if the shaft needs
to turn a large distance, the motor will
run at full speed. If it needs to turn
only a small amount, the motor will
run at a slower speed. This is called
A very common use of servo motors is in Radio
Controlled models for controlling direction of motion
like cars, airplanes, robots, movement of the tray of a
CD or DVD player and puppets. They are also used
in powerful heavy-duty sail boats.