Presentation on Induction Motor

1. WELLCOME
Equivalent Circuit for an Induction Motor
Introduction
WorkingProduce
Equivalent
Circuit
Circuitwithreferred
tothestator
Approximate
EquivalentCircuit
PowerRelationof
EquivalentCircuit
Submitted by
Azizul Hakim Roman
ID-192010057
Batch- 192
Section: EA
Department: EEE (Evening)

2. Introduction
WorkingProduce
Equivalent
Circuit
Circuitwithreferredto
thestator
Approximate
EquivalentCircuit
PowerRelationof
EquivalentCircuit
An induction motor or asynchronous
motor is an AC electric motor in which
the electric current in the rotor needed to
produce torque is obtained by
electromagnetic induction from the
magnetic field of the stator winding. An
induction motor can therefore be made
without electrical connections to the
rotor. An induction motor's rotor can be
either wound type or squirrel-cage type.

3. Introduction
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WorkingProduce
EquivalentCircuit
Circuitwithreferred
tothestator
Approximate
EquivalentCircuit
PowerRelationof
EquivalentCircuit
An induction motor is a well-known device which works on the principle of transformer.
So it is also called the rotating transformer. That is, when an EMF is supplied to its
stator, then as a result of electromagnetic induction, a voltage is induced in its rotor. So
an induction motor is said to be a transformer with rotating secondary. Here, primary of
transformer resembles stator winding of an induction motor and secondary resembles
rotor.
The induction motor always runs below the synchronous or full load speed and the
relative difference between the synchronous speed and speed of rotation is known as slip
which is denoted by s.
Where, Ns is synchronous speed of rotation which is given by-
Where, f is the frequency of the supply voltage.
P is the number of poles of the machine.

4. Introduction
Working
Produce
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Equivalent
Circuit
Circuitwithreferred
tothestator
Approximate
EquivalentCircuit
PowerRelationof
EquivalentCircuit
Equivalent Circuit of an Induction Motor
The equivalent circuit of any machine shows the various parameter of the
machine such as its Ohmic losses and also other losses.
The losses are modelled just by inductor and resistor. The copper losses are
occurred in the windings so the winding resistance is taken into account.
Also, the winding has inductance for which there is a voltage drop due to
inductive reactance and also a term called power factor comes into the
picture. There are two types of equivalent circuits in case of a three-phase
induction motor-
Here, R1 is the winding resistance of
the stator.
X1 is the inductance of the stator
winding.
Rc is the core loss component.
XM is the magnetizing reactance of the
winding.
R2/s is the power of the rotor, which
includes output mechanical power and
copper loss of rotor.

5. Introduction
Working
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Equivalent
Circuit
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Circuitwithreferred
tothestator
Approximate
EquivalentCircuit
PowerRelationof
EquivalentCircuit
If we draw the circuit with referred to the stator then the circuit
will look like-
Here all the other parameters are same
except-
R2’ is the rotor winding resistance with
referred to stator winding.
X2’ is the rotor winding inductance with
referred to stator winding.
R2(1 – s) / s is the resistance which
shows the power which is converted to
mechanical power output or useful
power. The power dissipated in that
resistor is the useful power output or
shaft power.

6. Introduction
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Circuit
৫
Circuitwithreferred
tothestator
Approximate
EquivalentCircuit
PowerRelationof
EquivalentCircuit
Approximate Equivalent Circuit
The approximate equivalent circuit is drawn just to simplify our calculation by
deleting one node. The shunt branch is shifted towards the primary side. This has
been done as the voltage drop between the stator resistance and inductance is less
and there is not much difference between the supply voltage and the induced voltage.
However, this is not appropriate due to following reasons-
The magnetic circuit of induction motor has an air gap so exciting current is larger
compared to transformer so exact equivalent circuit should be used.
The rotor and stator inductance is larger in induction motor.
In induction motor, we use distributed windings.
This model can be used if approximate analysis has to be done for large motors. For
smaller motors, we cannot use this.

7. Introduction
Working
Produce
Circuit
Circuitwithreferredto
thestator
Approximate
EquivalentCircuit
PowerRelationof
EquivalentCircuit
ation of Equivalent Circuit
r to stator- 3 V1I1Cos(Ɵ).
s the stator voltage applied.
rent drawn by the stator winding.
e stator power stator.
=
t- Stator copper and iron losses.
er loss = Slip × power input to the rotor.
Power = (1 – s) × Rotor input power.