1. Course Title: Theory of Electrical Machines
Course Code: EE 359
Topic : D C Machines
Branch: ME Semester: V
Text Books:
S. Chapman, Electric Machinery Fundamentals, 4th Ed., McGraw-Hill, 2003.
R. K. Rajput, Electrical Machines, 3rd Ed., Laxmi Publications (P) Ltd., 2003

2. D.C Machine Introduction Construction Principle of Operation
Types of DC Machines
Characteristics
Applications

3. DC MACHINES
INTODUCTION
A DC machine is an electro-mechanical energy conversion device. It can convert Mechanical power into Electrical Power. When output electrical power is DC , it is called DC Generator. When it converts DC electrical power into mechanical power , it is known as DC Motor.

4. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
1. BODY OR MAGNETIC FRAME OR YOKE
2. POLE CORE AND POLE SHOES
3. FIELD or EXCITING COILS
4. ARMATURE CORE
5. ARMATURE WINDING
6. COMMUTATOR
MAIN CONSTRUCTIONAL FEATURES

5. 7. BRUSHES 8. END HOUSINGS 9. BEARINGS 10. SHAFT DC MACHINES
MAIN CONSTRUCTIONAL FEATURES

6. MAIN CONSTRUCTIONAL FEATURES
Bearing
Brush
Body / Yoke
Pulley
End Housing
Shaft
Armature
Commutator
Field Core
Brush
holder
Field Winding
MAIN CONSTRUCTIONAL FEATURES

7. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
YOKE
ARMATURE +
SHAFT
FIELD POLE
& COIL
BRUSH -
COMMUTATOR
MAIN CONSTRUCTIONAL FEATURES

8. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
1. MAGNETIC FRAME or YOKE :
The outer cylindrical frame to which main poles and inter poles are fixed and by means of the machine is fixed to the foundation is called YOKE.
MAIN CONSTRUCTIONAL FEATURES

9. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
1. MAGNETIC FRAME or YOKE :
It serves two purposes:
a) It provides mechanical protection to the inner parts of the machines.

10. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
1. MAGNETIC FRAME or YOKE :
b) It provides a low reluctance path for the magnetic flux.
The yoke is made of cast iron for smaller …
MAIN CONSTRUCTIONAL FEATURES

11. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
1. MAGNETIC FRAME or YOKE :
machines and cast steel or fabricated rolled steel for larger machines.
MAIN CONSTRUCTIONAL FEATURES

12. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
2. POLE CORE AND POLE SHOES :
The pole core and pole shoes are fixed to the yoke by bolts. They serves the following purpose :
a) They support the field or exciting coils.
POLE CORE
MAIN CONSTRUCTIONAL FEATURES

13. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
2. POLE CORE AND POLE SHOES :
b) They distribute the magnetic flux on the armature periphery more uniformly.
MAIN CONSTRUCTIONAL FEATURES

14. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
2. POLE CORE AND POLE SHOES :
c) The pole shoes have larger X- section, so, the reluctance of the magnetic path is reduced. The pole core
MAIN CONSTRUCTIONAL FEATURES

15. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
2. POLE CORE AND POLE SHOES :
and pole shoes are made of laminated steel assembled by riveting together under hydraulic pressure.
MAIN CONSTRUCTIONAL FEATURES

16. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
3. FIELD or EXCITING COILS :
Field coils or exciting coils are used to magnetise the pole core. Enameled copper wire is used for the construction of these coils.When direct
MAIN CONSTRUCTIONAL FEATURES

17. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
3. FIELD or EXCITING COILS :
current is passed through these coils/ winding, it sets up the magnetic field which magnetise the pole core to the reqd. flux.
MAIN CONSTRUCTIONAL FEATURES

18. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
4. ARMATURE CORE:
Armature is a rotating part of the DC machine, reversal of flux takes place, so hysteresis losses are produced. To minimise this loss, silicon steel is used for the construction.
MAIN CONSTRUCTIONAL FEATURES

19. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
4. ARMATURE CORE:
The rotating armature cuts the main magnetic field , therefore an e.m.f is induced in the armature core.This e.m.f circulates eddy currents in the core which results in eddy current loss in it.
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

20. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
4. ARMATURE CORE:
The armature core is laminated to reduce the eddy current loss.
Armature core serves the following purposes:
a) It houses the conductors in the slots.
b) It provides an easy path for magnetic flux
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

21. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
The no. of conductors in form of coils placed in the slots of the armature and suitably inter connected are called winding .
ARMATURE WINDING
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

22. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
This is the armature winding where conversion of power takes place i.e. in case of generator ,
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

23. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
mechanical power is converted into electrical power and in case of a motor, electrical
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

24. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
power is converted into mechanical power.
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

25. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
Depending upon the types of inter connection. of coils , the winding can be classified into two types;
i) Lap Winding;
The conductors/coils are connected in such a way that no of parallel paths are equal to no. of poles.
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

26. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
If machine has ‘P’ no. of poles and ‘Z’ no. of conductors, then there will be ‘P’ no. of parallel paths.And each path will have ‘Z/P’ no of conductors in series. Also the no. of brushes are equal to no. of parallel paths.
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

27. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
Out of which half of the brushes will be positive and remaining will be negative.
ii) Wave Winding;
The conductors are so connected that they are divided into two parallel paths only , irrespective of the no. of poles. If machines has ‘Z’ no. of …
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

28. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
conductors, there will be only two parallel paths and each will be having ‘Z/2’ no. of conductors connected in series with only two brushes.
Click here to study detailed contents of winding
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

29. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
6. COMMUTATOR
It is the most important part of a DC machine and serves the following purpose :- i) It connects …
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

30. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
6. COMMUTATOR
the rotating armature conductors to the stationary external circuit through the brushes.
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

31. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
6. COMMUTATOR
ii) It converts altering current induced in the armature conductors into unidirectional …..
COMMUTATOR
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

32. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
6. COMMUTATOR
current in the external load circuit in generating action and it converts alternating torque into unidirectional
COMMUTATOR
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

33. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
6. COMMUTATOR
COPPER SEGMENT
RISER
MICA INSULATION
END RING
ADJUSTING NUT
METAL SLEEVE
SHAFT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

34. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
6. COMMUTATOR
torque produced in the armature in motoring action.
The commutator is of cylindrical shape and is made of wedge shaped hard drawn copper segments.The segments are insulated from each ….
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

35. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
6. COMMUTATOR
other by a thin sheet of mica.The segments are held together by means of two V-shaped rings that fit into the V-grooves cut into the segments. Each armature coil is connected to the commutator segment through riser.
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

36. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
7. BRUSHES
Brushes are made of high grade carbon.They form the connecting link between armature winding and the external circuit. The brushes are held in particular position around the commutator by brush holders.
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

37. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
8. END HOUSINGS
They are attached to the ends of main frame and support bearing . The front housing supports …..
END HOUSING
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

38. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
8. END HOUSINGS
the bearing and the brush assembly whereas rear housing supports the bearing only.
END HOUSING
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

39. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
9. BEARINGS
The function of the bearing is to reduce friction between the rotating and stationary parts of the machines.These are fitted in the end housings. Generally, high carbon steel is used for the construction of the bearings.
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

40. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
10. SHAFT
The function of shaft is to transfer mechanical power to the machine or from the machine .
SHAFT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

41. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
10. SHAFT
Shaft is made of mild steel with maximum breaking strength. All the rotating parts like
SHAFT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

42. MAIN CONSTRUCTIONAL FEATURES
DC MACHINES
MAIN CONSTRUCTIONAL FEATURES
10. SHAFT
Armature core, ,commutator, cooling fan etc. are keyed to the shaft.
SHAFT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40

43. Principle of Operation

44. S N DC MACHINES FIELD YOKE WINDING BRUSH ARMATURE AXIS _ + BRUSH. + . +
BRUSH
AXIS
ARMATURE _ + + +
BRUSH
ARMATURE
CONDUCTORS + + + . +
FIELD
POLES . N +
MAIN FIELD AXIS
Fig. 1

45. DC MACHINES
The field windings are shown as excited from external source. The polarity of electro-magnetic field will depend upon the direction of field current as shown in the fig.

46. v DC MACHINES S  TL N ( MOTOR ) A B S _ N + Te           
MECHANICAL LOAD +   Te     DC
SUPPLY v  TL  N 
Fig. 2

47. DC MACHINES
The armature carries conductors in side the slots.Two brushes are placed at the right angle to the main field axis. The brushes are stationary whereas armature is free to rotate.
APPLICATION CONCEPT OF ALIGNMENT OF TWO MAGNETIC FIELDS

48. DC MACHINES
When the armature is rotated in the magnetic field, an e.m.f will be induced in the armature conductors.The direction of the induced e.m.f can be found by applying Fleming’s Right Hand Rule.
APPLICATION CONCEPT OF ALIGNMENT OF TWO MAGNETIC FIELDS

49. DC MACHINES
The direction of induced e.m.f will depend upon the direction of rotation of armature , if polarity of field poles to be kept unchanged.When load is connected across the armature terminals , the current will flow through the armature circuit.

50. DC MACHINES
The direction of current will be same as that of induced e.m.f. The armature will now be considered as electro-magnet and its polarity is shown in the fig The electro-magnetic torque Te will be developed in the anti-clock wise direction as shown in the fig. no. 1 and 2.

51. DC MACHINES
The magnitude of Te will depend on the strength of the field poles and armature field which further depends upon the currents flowing through the respective windings. As the external load on the generator is increased, the magnitude of Te increases.

52. DC MACHINES
As Te acts in the opposite direction to the applied mechanical torque, more torque will be required through the prime mover to maintain the speed of armature .

53. DC MACHINES
The direction of currents in the upper conductors in the armature are indicated by ‘dots’ and conductors in lower half of armature are indicated by ‘cross’ .

54. DC MACHINES
The brush ‘B’ will collect dot currents and brush ‘A’ will collect cross currents as the armature continues to rotate in clockwise direction. In the out put circuit, across terminals ‘A’ and ‘B’, current will flow in one direction.

55. DC MACHINES
The dc machine shown in fig. 2 is working as Generator. The same machine will work as motor , if the armature is provided with electric supply as shown in fig. 3.

56. DC MACHINES S   N ( GENERATOR ) A B S _ N + Te Tm         
MECHANICAL INPUT N +   Te      Tm
ELECTRICAL
LOAD   N 
Fig 3

57. DC MACHINES
The armature is connected across a supply voltage ‘V’ and the field windings are excited from the same supply or from any external dc source. The magnetic polarities due to the current in armature winding will be as shown in fig.3.

58. DC MACHINES
The electro-magnetic torque Te will be developed in the anti-clockwise direction as opposite poles of armature field and main field will attract each other. The armature will rotate in anti-clockwise direction due to Te .

59. DC MACHINES
To reverse the direction of rotation of armature, either the direction of current in the field winding or armature winding will have to be reversed.If the direction of currents in both the windings are reversed, direction of rotation of armature will be unchanged.

60. DC MACHINES
As the mechanical load on the armature i.e. rotor shaft represented by load torque TL is increased, more and more electro-magnetic torque will be developed by the armature to balance the mechanical torque requirements for which the armature will draw more current from the supply mains.

61. MAGNETIC FIELD A B  A A Q P B
LOAD 0o

62. MAGNETIC FIELD A B  A Q + _ P B e
LOAD
30o t

63. MAGNETIC FIELD A B  A Q + _ P B e
LOAD
60o t

64. MAGNETIC FIELD A B  Q A B + _ P e
LOAD
90o t

65. MAGNETIC FIELD A B  A B Q + P _ A e
LOAD
120o t

66. MAGNETIC FIELD B A  B A Q + P _ A e
LOAD
150o t

67. MAGNETIC FIELD B A  B A Q + P A e
LOAD
180o t

68. MAGNETIC FIELD B A  B Q + _ P A e
LOAD
210o t

69. MAGNETIC FIELD B A  B Q + _ P A e
LOAD
240o t

70. MAGNETIC FIELD B A  Q B A + _ P e
LOAD
270o t

71. MAGNETIC FIELD A B  A A Q + _ P B e
LOAD
300o t

72. MAGNETIC FIELD A B  A A Q + _ P B e
LOAD
330o t

73. MAGNETIC FIELD A B  A A Q P B e
LOAD
360o t

74. TYPES OF DC Machines
Depending upon the type of excitation to the field winding. The dc machine can be classified into three categories:
Machines with permanent field,
Separately excited
Self excited type
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

75. TYPES OF EXCITATIONS ( DC MOTORS )
Dc motors with permanent magnetic field, are manufactured for small rating applications such as toys, cassette tape recorders etc.large rating dc motors …
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

76. TYPES OF EXCITATIONS ( DC MOTORS )
are constructed with electro-magnetic field i.e field winding is placed on the field core and this winding is supplied with dc current called excitation. Depending upon the type of connections to the field winding for ….

77. The dc motors can be classified into two categories ;
TYPES OF DC MOTORS
The dc motors can be classified into two categories ;
1) Separately excited dc motors
2) Self excited dc motors.
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

78. SEPARATELY EXCITED DC MOTORS+ Ia + Rf A F FF M E V If
Supply Ra _ AA
VDC _ + _
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

79. SEPARATELY EXCITED DC MOTORS
The field winding is excited from a supply which is not connected to the armature winding. It may be noted that current flowing through the field winding is independent of load and is equal to V / Rf , where Rf is the….
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

80. SEPARATELY EXCITED DC MOTORS
field circuit resistance. The flux produced is proportional to the field current i.e. Ø  If

81. SELF EXCITED DC MOTORS ( DC SHUNT MOTORS )+ Ia If IL F A V M E
SUPPLY Ra FF AA _
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

82. SELF EXCITED DC MOTORS ( DC SHUNT MOTORS )
In this type of excitation , armature and field windings are connected across a constant source of supply. The field current If is drawn from the same source as that of armature current. As shown in fig.
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

83. SELF EXCITED DC MOTORS ( DC SERIES MOTORS )YY Y + Ia +
ISE IL A V M E
SUPPLY Ra _ AA _

84. SELF EXCITED DC MOTORS ( DC SERIES MOTORS )
The field winding is connected in series with the armature so that If = Ia = IL . Therefore field winding is made up of thick winding wire of less no. of turns as compared to that of shunt field winding so that armature current can ...
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

85. SELF EXCITED DC MOTORS ( DC SERIES MOTORS )
flow through it without overheating. In case of dc series machine , Ø  If  Ia .. The relationship between induced e.m.f. and terminal voltage is as follows ; …..
See Fig.
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

86. SELF EXCITED DC MOTORS ( DC SERIES MOTORS )
V = E + Ia Ra + Ia Rse or
E = V - Ia ( Ra + Rse )
Ia = Ise = IL
and
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

87. SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )
ISh YY Y + Ia IL
ISE A Z
Rsh
SUPPLY M E V Ra ZZ AA _
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

88. SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )
There are two field windings , namely a shunt field winding and a series field winding. The shunt field winding is connected in parallel with the armature and series field winding is connected in series with the combination .
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

89. SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )
Series field winding will carry a large armature current Ia or IL and therefore it is made of wire of large cross section and has a few turns only. The resistance of series field winding is very small.
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

90. SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )
The shunt field winding is made up of wires of small cross section and has high resistance. Since the resistance of shunt field winding is high , the current flowing through it is very small as compared to that of series field winding
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

91. SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )
or armature current Ia . The main magnetic field flux is produced by the shunt field current / winding but it is modified by the field of series winding. A compound machine therefore combines the best features of dc shunt machines and dc series machines.
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

92. SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )
Depending up on the connections of shunt field winding in the combination of armature and series field winding, dc compound generators can be named as
i) Short shunt compound generators.
ii) Long shunt compound generators.
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

93. SHORT SHUNT TYPE ( DC COMPOUND MOTORS )
ISh YY Y + Ia IL
ISE A Z
Rsh
SUPPLY M E V Ra ZZ AA _
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

94. SHORT SHUNT TYPE ( DC COMPOUND MOTORS )
i) SHORT SHUNT DC COMPOUND MOTORS
In this case the shunt field winding is connected across the armature winding only as shown in the fig of slide no.
Ise = IL = Ia + Ish
V = E + Ia Ra+ Ise Rse
= E + Ia Ra+ ( Ia + Ish ) Rse
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

95. LONG SHUNT TYPE ( DC COMPOUND MOTORS )YY Y + Ia IL Z
ISE A
Rsh
SUPPLY M E V
ISh Ra AA ZZ _
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

96. LONG SHUNT TYPE ( DC COMPOUND MOTORS )
ii) LONG SHUNT DC COMPOUND MOTORS
In this case the shunt field winding is connected across the combination of armature and series field winding as shown in the fig.
Ise = Ia and IL= Ia + Ish
V = E + Ia Ra+ Ise Rse
= Ish Rsh
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

97. SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )
Depending upon the direction of flow of current through series field, we can classify dc compound motors into two categories namely ;
I) Cumulative compound dc motors
II) differential compound dc motors
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

98. CUMULATIVE TYPE ( DC COMPOUND MOTORS )
ISh YY Y + Ia IL
ISE A Z
Rsh
SUPPLY M E V Ra ZZ AA _
Ø = Øsh + Øse
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

99. CUMULATIVE TYPE ( DC COMPOUND MOTORS )
The direction of current in the series field winding is such that magnetic field produced by it is in the direction to that of shunt field. Total magnitude of the field is the sum of shunt field and series field so that Ø = Øsh + Øse. .
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

100. DIFFERENTIAL TYPE ( DC COMPOUND MOTORS )
ISh + YY Y Ia IL A Z
ISE
Rsh
SUPPLY M E V Ra ZZ AA _
Ø = Øsh - Øse

101. DIFFERENTIAL TYPE ( DC COMPOUND MOTORS )
The direction of current in the series field winding is such that magnetic field produced by it is in the opposite direction to that of shunt field. Total magnitude of the field is the difference of shunt field and series field so that
Ø = Øsh - Øse.
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )

102. FACTORS DETERMINING THE SPEED OF DC MOTOR
The expression for back e.m.f. developed in the armature of a dc motor is given as follows :
P Ø Z N
…..(i)
E =
60 A
E =
V - Ia Ra
…..(ii)
FACTORS DETERMINING THE SPEED OF DC MOTOR

103. FACTORS DETERMINING THE SPEED OF DC MOTOR
Comparing expressions (i) and (ii)
P Ø Z N =
V - Ia Ra
60 A OR
K Ø N =
V - Ia Ra
V - Ia Ra N =
K Ø

104. FACTORS DETERMINING THE SPEED OF DC MOTOR
Where K is the constant of proportionality and equal to PZ / 60 A
Now in the above expression for speed, the speed can be varied by varying the applied voltage ‘V’ , field flux Ø and resistance of the armature .
FACTORS DETERMINING THE SPEED OF DC MOTOR

105. FACTORS DETERMINING THE SPEED OF DC MOTOR
It is clear that speed is directly proportional to the supply voltage ‘V’. So the speed increases with increase in voltage ‘V’ and vice versa.
The speed is inversely proportional to the field flux Ø . So speed decreases as the Flux Ø increases and vice versa.
FACTORS DETERMINING THE SPEED OF DC MOTOR

106. CHARACTERISTICS OF DC MOTORS
The important characteristics of dc motors are :
1) Speed - armature current ( Load ) characteristics
2) Torque - armature current ( Load ) characteristics
3) Speed - Torque characteristics
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

107. CHARACTERISTICS OF DC MOTORS
It is very much important to know the characteristics mentioned above for different types of dc motors because it enables the selection of a specific type of dc motor for specific purpose.
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

108. CHARACTERISTICS OF DC SHUNT MOTORS+ Ia If IL F A V M E
SUPPLY Ra FF AA _
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

109. CHARACTERISTICS OF DC SHUNT MOTORS
FULL LOAD Ia
( Amps)
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

110. CHARACTERISTICS OF DC SHUNT MOTORS
1. Speed - Armature current (Load ) characteristics
For a dc motor , we know that ; N Ia
FULL
LOAD
( Amps)
V - Ia Ra
N =
K Ø
A dc shunt motor is connected across the mains having supply voltage ‘V’ .

111. CHARACTERISTICS OF DC SHUNT MOTORS
Speed - Armature current (Load ) characteristics
This supply voltage is assumed to be constant.The field winding is connected across the armature as shown in Fig. The magnetic flux Ø produced by field current If will be constant as V remains constant.
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

112. CHARACTERISTICS OF DC SHUNT MOTORS
1. Speed - Armature current (Load ) characteristics
But in actual practice, the air gap flux is slightly reduced due to the effect of armature reaction. From the expression for the speed mentioned earlier, it is evident that as the armature current Ia …...
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

113. CHARACTERISTICS OF DC SHUNT MOTORS
1. Speed - Armature current (Load ) characteristics
increases , speed will decrease by a small amount due to an increase in Ia Ra drop is very small as compared to V . The speed verses armature current characteristics is shown in Fig.

114. CHARACTERISTICS OF DC SHUNT MOTORS
1. Speed - Armature current (Load ) characteristics
The shunt motor being thus more or less a constant speed motor , can be used in the applications such as driving of line shafts, lathes conveyors etc.
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

115. CHARACTERISTICS OF DC SHUNT MOTORS
2. Torque - Armature current (Load ) characteristics T Ia
( Amps)
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

116. CHARACTERISTICS OF DC SHUNT MOTORS
2. Torque - Armature current (Load ) characteristics
The equation for torque can be written as follows ;
T = kt Ø Ia
If flux Ø is taken as constant, the torque T becomes directly proportional to armature current (Load current) Ia . It is a straight line passing through the origin.
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

117. CHARACTERISTICS OF DC SHUNT MOTORS
3. Speed - Torque characteristics N T
( N-m)
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

118. CHARACTERISTICS OF DC SHUNT MOTORS
3. Speed - Torque characteristics
The relation between T and Ia and N and Ia are as under ;
T = kt Ø Ia
V - Ia Ra
N =
K Ø
And The relationship between speed and torque can be drawn as shown in Fig .
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

119. CHARACTERISTICS OF DC SERIES MOTORSYY Y + Ia +
ISE IL A V M E
SUPPLY Ra _ AA _
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

120. CHARACTERISTICS OF DC SERIES MOTORS
1. Speed - Load characteristics N Ia
( Amps)
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

121. CHARACTERISTICS OF DC SERIES MOTORS
1. Speed - Load characteristics
V - Ia Ra
From the expression ;
N =
K Ø
It is seen that the speed N is inversely proportional to flux Ø
For a dc series motor ,magnetic flux Ø is proportional to Ia.

122. CHARACTERISTICS OF DC SERIES MOTORS
1. Speed - Load characteristics
Thus , if V is constant, N is inversely proportional to Ia. The N verses Ia characteristics is therefore a rectangular hyperbola as shown in Fig . It is seen from the characteristics that ….
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

123. CHARACTERISTICS OF DC SERIES MOTORS
1. Speed - Load characteristics
the speed decreases as the load on the motor increases. At a very low load , the speed is dangerously high . Thus if a dc series motor is allowed to run on very light load or at No- Load , its speed will become much higher than its ……..
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

124. CHARACTERISTICS OF DC SERIES MOTORS
1. Speed - Load characteristics
normal speed which may cause damage to the motor. For this reason , dc series motors are never started on No- Load and are not used in the applications where there is a chance of Load being completely removed , when the motor ...
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

125. CHARACTERISTICS OF DC SERIES MOTORS
1. Speed - Load characteristics
remains connected to the supply. The load on the dc series motor is connected through the gears and not through the belt pulley arrangement.This is because, in case of failure of belt , the load will be removed from the motor and thereby the
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

126. CHARACTERISTICS OF DC SERIES MOTORS
1. Speed - Load characteristics
motor will attain a dangerously high speed . In case of load connected through the gears, however in the event of an accidental release of load, gears will provide some load on account of the frictional resistance of the gear teeth.
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

127. CHARACTERISTICS OF DC SERIES MOTORS
1. Torque - Load characteristics
SATURATION OF
SERIES FIELD CORE T Ia
( Amps)
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

128. CHARACTERISTICS OF DC SERIES MOTORS
1. Torque - Load characteristics
The equation for the torque for dc motor is given by ; T = kt Ø Ia
The magnetic flux for a dc series motor is proportional to armature current Ia. Thus the torque T = kt Ia Ia.
Or T  Ia2
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

129. CHARACTERISTICS OF DC SERIES MOTORS
1. Torque - Load characteristics
The relationship between torque and armature current , is therefore of the form of a parabola . With increase in Ia , the field flux increases linearly but due to saturation of the core, beyond a certain magnitude of Ia the increase in flux is
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

130. CHARACTERISTICS OF DC SERIES MOTORS
1. Torque - Load characteristics
negligible.. Thus T is proportional to the square of Ia up to the saturation point beyond which T varies linearly with Ia. From the torque load characteristics , it can be observed that a dc series motor ..
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

131. CHARACTERISTICS OF DC SERIES MOTORS
1. Torque - Load characteristics
started on-load , develops a very high starting torque.
Hence dc series motors are used in applications where high starting torque is required such as in electric trains , hoists, trolleys etc.
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

132. CHARACTERISTICS OF DC SERIES MOTORS
1. Torque - Speed characteristics N T
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

133. CHARACTERISTICS OF DC SERIES MOTORS
1. Torque - Speed characteristics
From the characteristics shown in slide no. , it can be seen that for low speeds , the torque is high and for high speeds the torque is very small. This is why dc series motor is widely used in the … ..
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

134. CHARACTERISTICS OF DC SERIES MOTORS
1. Torque - Speed characteristics
applications where motor is to be started on bulk loads such as electric loco- motive.
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

135. CHARACTERISTICS OF DC COMPOUND MOTORS
ISh YY Y + Ia IL
ISE A Z
Rsh
SUPPLY M E V Ra ZZ AA _
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

136. CHARACTERISTICS OF DC COMPOUND MOTORS
1. Speed - Load characteristics
DIFFERENTIAL
COMPOUND N
SHUNT
CUMULATIVE
COMPOUND Ia
( Amps)
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

137. CHARACTERISTICS OF DC COMPOUND MOTORS
1. Speed - Load characteristics
In cumulative compound motors , series field winding is connected in such a way that magnetic flux produced by it helps the flux produced by shunt field winding. Series field is directly proportional to the load current , ….. . … .
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

138. CHARACTERISTICS OF DC COMPOUND MOTORS
1. Speed - Load characteristics
therefore total flux increases with increase in load current / armature current due to the series field in addition to the voltage drop in the armature winding.The speed of dc motor is inversely proportional to the
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

139. CHARACTERISTICS OF DC COMPOUND MOTORS
1. Speed - Load characteristics
total main flux Ø . Therefore speed drops more sharply as compared to dc shunt motor.Refer Fig.
See Fig.
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

140. CHARACTERISTICS OF DC COMPOUND MOTORS
2. Torque - Load characteristics T
CUMULATIVE
COMPOUND
SHUNT
DIFFERENTIAL
COMPOUND Ia
( Amps)
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

141. CHARACTERISTICS OF DC COMPOUND MOTORS
2. Torque - Load characteristics
The torque developed by a cumulative compound motor increases with sudden increase in load and at no-load , it has a definite speed. Cumulative compound motors are therefore, suitable where there is sudden application
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

142. CHARACTERISTICS OF DC COMPOUND MOTORS
2. Torque - Load characteristics
of heavy loads like sheers, punches, rolling mills etc. The speed of differential compound motors remains more or less constant. With increase in load but its torque decreases with load. Since the dc shunt motor develops a good torque and
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

143. CHARACTERISTICS OF DC COMPOUND MOTORS
2. Torque - Load characteristics
its speed does not vary appreciably with increase in load, differential compound motors are not preferred over dc shunt motors and hence are rarely used.
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

144. CHARACTERISTICS OF DC COMPOUND MOTORS
3. Speed - Torque characteristics
DIFFERENTIAL
COMPOUND N
CUMULATIVE
COMPOUND T
(N-m)
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS

145. APPLICATIONS OF DC MOTORS
(a) DC SHUNT MOTORS
(i) Shunt motors are used in situations, such as driving a line shafting etc. where the speed as to be maintained approximately constant between no-load and full-load.
APPLICATION OF DC MACHINES

146. APPLICATIONS OF DC MOTORS
(a) DC SHUNT MOTORS
(ii) In situations where variable load is to be driven at different speeds but at each load, the speed is to be kept constant. Such as driving a lathe.
APPLICATION OF DC MACHINES

147. APPLICATIONS OF DC MOTORS
(b) DC SERIES MOTORS
DC Series Motors are used in applications such as driving hoists, cranes, trains, etc., as in these cases a large starting torque is required. They are also used where the motor can be permanently coupled to the load, such as
APPLICATION OF DC MACHINES

148. APPLICATIONS OF DC MOTORS
(b) DC SERIES MOTORS
Fans , whose torque increases with speed. Where constancy in speed is not essential, the decrease of speed with increase of load has the advantage that the power absorbed by the motor does not increase as rapidly as the torque .
APPLICATION OF DC MACHINES

149. APPLICATIONS OF DC MOTORS
(b) DC SERIES MOTORS
Series motors acquire very high speed at no-load or at very light load . That is why they should not be used for a belt drive where there is a possibility of the load decreasing to very small value.
APPLICATION OF DC MACHINES

150. APPLICATIONS OF DC MOTORS
(c) DC COMPOUND MOTORS
DC Compound Motors are used in application where large starting torque are required but where the load may fall to such a small value that a series motor would reach a dangerously high speed.
APPLICATION OF DC MACHINES

151. APPLICATIONS OF DC MOTORS
(c) DC COMPOUND MOTORS
Where the supply voltage may fluctuate , for instance on a traction system, the series winding reduces the fluctuation of armature current partly by its inductance and partly by its influence on the value of
APPLICATION OF DC MACHINES

152. APPLICATIONS OF DC MOTORS
(c) DC COMPOUND MOTORS
flux and therefore on that of the induced e.m.f.
When the load is of a fluctuating nature , e.g. for driving stamping processes, etc. the shunt excitation prevents the speed …
APPLICATION OF DC MACHINES

153. APPLICATIONS OF DC MOTORS
(c) DC COMPOUND MOTORS
Becoming excessive on light load, and the decrease of speed with increase of load enables the flywheel, usually fitted to such a machine, to assist the motor in in dealing with the peak load by giving
APPLICATION OF DC MACHINES

154. APPLICATIONS OF DC MOTORS
(c) DC COMPOUND MOTORS
up some of its kinetic energy.
* THANKS *
APPLICATION OF DC MACHINES