2. Lecturer Mr.PARTHASARATHY P
Dept. of EEE

3. KIRAN GEORGE AKKARA MEB1314
KISHORE KUMAR P MEB1315
MAHADEVAN L MEB1316
MANIKANDAN MEB1317

5. Mechanical Characteristics
Speed (N) Vs Torque (T)
Electromechanical Characteristics
Torque (T) Vs Armature Current (Ia )
Speed (N) Vs Armature Current (Ia)

6. Whenever a current
carrying conductor is
placed in a magnetic field,
the conductor experiences a
force tending to move it

8. IL Ia
Ish IL = Ia + Ish

9.  Electrical
characteristics
 T ∞ φ Ia
Torque T
Ta Tsh
 T ∞ Ia Armature Current Ia

10. Armature Current Ia
Speed N
Speed equation of DC motor is N = K
V-IaRa
φ
N = K(V- Ia Ra )
•The speed is nearly constant
•Applications
Machine tools
Lathes
Driving Shafting
Wood working machines

11.  T ∞ Ia
From above equation

N∞( v -T Ra )
Torque T
Speed N

12. IL
Ise
Ia
IL = Ise = Ia

13. T ∞ φ Ia
Φ ∞ Ia
T ∞ Ia
2 (before saturation)
T ∞ Ia (after saturation)
2
T ∞ Ia
Armature Current Ia
Torque T
T ∞ Ia
At light load the Ta increases as square of
current
and hence the curve is parabola
After saturation the flux is constant ,
hence T ∞ Ia
therefore it becomes straight line

14. Armature Current Ia
Speed equation of DC motor is N = K
V-IaRa
φ
N = K
V-IaRa
Ia
(φ = Ia)
N ∞
Eb
Ia
Speed N
oSpeed decreases when armature current is increased
oIf motor is started without some load the speed increases to a
dangerous value and hence destroys it

15.  T ∞ Ia
 N ∞
Torque T
Speed N
Eb
T

16. The characteristics of a
compound motor
depends on whether
the series and shunt
field windings are
assisting each other
(cumulative) or
opposing each other
(differential)
Speed N
Differential
Shunt
cumulative
series
Armature Current Ia

17. TORQUE - SLIP
CHARACTRISTICS
The curve drawn between torque and
slip is known as torque slip
characteristics of induction motor.
Torque equation
T ∞ sE2
2 R2
R2
2+(sX2)2
T ∞ sR2 Eb =
constant
2 + (sX2)2
R2

18. The Torque – Slip characteristics
consists of three regions ,
1) Stable Operating Region.
2) Unstable Operating Region.
3) Normal Operating Region.

20. In stable region, the slip value is very
small
T ∞ sR2
R2
2
T ∞ s (R2 = constant)
Therefore the graph is straight line

21. When slip is further increased the region is
unstable.
The slip value is high
T ∞ s
(sX2)2
T ∞ 1 (X2 is constant)
S
Hence the curve is rectangular hyperbola

22. The region AC is also known as operating
region
From the curve we can understand the
following terms
1. Starting torque
2. Maximum torque or pull out torque
3. Full load torque

23. Starting torque
In torque-slip characteristics, the slip is 1 and speed is
0. At this time the torque is called starting torque.
• Maximum torque
The torque at slip s = sm is called maximum torque.
It is also known as breakdown torque or pull out torque
Full load torque
In the curve the point c is called full load torque of
motor. Normally full load torque is less than the
maximum torque.

25. This curve is divided into regions according
to slip value
 Motoring Region (0 ≤ s ≤ 1)
Generating Region (s < 0)
 Plugging Region (1.0 ≤ s ≤ 2.0)

26. Motoring Region (0 ≤ s ≤ 1)
Induction motor rotates in the same direction as
that of the field.
The speed decreases and torque increases till
breakdown torque is reached.
In this region the air gap flux is nearly constant.
After breakdown torque Tmax, torque decreases
and slip increases.

27. Generating Region (s < 0)
The machine operates as a generator.
The rotor rotates at a speed greater than
synchronous speed in the same direction
as that of the rotating magnetic field.
Due to super synchronous speed the slip
becomes negative, creating negative, or
regeneration torque.

28. Plugging Region (1 ≤ s ≤ 2)
The slip becomes greater then unity
This region occurs only when the stator field is reversed
and also the rotating direction.
The change in direction results to come to rest and
hence it is known as braking torque.
The torque is positive, but the speed is negative.
This method of braking is known as plugging.