1. DC motors use direct current and are used where wide speed variation is required like in vehicles. The types are separately excited, shunt, and series motors. 2. Speed in DC motors can be controlled by adjusting the field resistance, armature voltage, or inserting series resistance in the armature circuit. Adjusting field resistance allows control above base speed while armature voltage controls below base speed. 3. Compounded DC motors combine features of series and shunt motors, providing higher starting torque than shunt motors but less than series motors. Cumulatively compounded motors have torque characteristics between the two.

1. CHAPTER 8
DC MOTORS AND GENERATORS

2. Types of Electrical Motors
Electric Motors
Alternating Current (AC)
Motors
Direct Current (DC)
Motors
Synchronous Induction
Three-Phase
Single-Phase
Self Excited
Separately
Excited
Series Shunt
Compound

3. DC maotors:
• use:
• cars, trucks, aircraft
• where wide variation of speed required
• Speed regulation
• SR =
• in rev/min and rad/sec
• assumption; input voltg constant

4. Recall Voltage Regulation

5. SPEED REGULATION

6. TYPES OF DC MOTORS

7. EQUIVALENT CIRCUIT: input voltage DC
motor assumed constant

8. Simplified Equivalent Circuit

9. MAGNETIZATION CURVE:

10. Relating IF andEA
For a given speed at wo, DC m/g operate at kneept or satu for max power:
If in DC m produces mmf; fairly large inc. in If produce small increase in Ea

11. Magnetization curve
• Ea proportional to
• since If prop. to mmf
• therefor plot of graph for Ea vs If for given w0
• operate at saturation pt. at f.l.

12. 1. Equivalent circuit of separately excited
DC motor:
“IF” supplied from separate const. Voltg

13. Equivalent circuit of shunt DC motor:
“IF” gets power directly across the armature terminals

14. KVL eq. for Armature circuits of these
motors:

15. Terminal Characteristics of Shunt DC
motor: plot of o/p quantities; Torque vs
speed

16. • Ld inc T load exceed T ind
• Slows down,
• so “w” decreased;
• Ea dec.; Ea=K.ph.w
• Ia inc; Ia = (Vt-Ea)/Ra
• So T ind inc. => Tind=K. ph. Ia
• Finally T ind= T ld. At lower “w”

17. Terminal Characteristics or output
characteristics of Shunt DC motor

18. Terminal Characteristics of Shunt DC
motor: eqn. with –ve slope

19. T-S characteristics
• Speed varies with Torque linearly; other terms in equation
constant therefore VT assume to be constant
• Armature Reaction ; as load increases, flux-weakening
effect increase motor speed, use of compensating winding
(see curve dotted)

20. Torque speed characteristics with armature reaction:
“NoAR” due to Compensating Winding, since when ld. Inc., flux
weakening, hence increase speed (withAR)

21. Example 8.1:
Due to compensating winding, Flux is constant regardless of load;
speed can be calculated at different values of load

22. Figure

23. Solution

24. Solution: i. at no load
ii. At 100A

26. iii. At 200A

27. iv. At 300A

28. Corresponding Torques:

30. Torque-Speed X-tics

31. Speed control of shunt DC motor

32. Speed control of shunt DC motor

33. 1. Adjusting Field Resistance ;RF

34. Adjusting Field Resistance ;RF

35. Summary of points; Change in RF value

36. Adjusting Field Resistance:
(No load to Full Load)

37. Adjusting Field Resistance X

38. Adjusting Field Resistance: Entire range;
(from No-Load to Stall)

39. Important points; Adjusting RF
• from graph b, increase in Rf decreases speed of motor
(towards stall)
• small dc m operate near stall
• Unpredictable; shouldn't be used

40. Ex 8-3: RF variation

42. RF variation

43. RF variation

45. 2. Adjusting Armature Voltage; VA

47. Summary of points; VA adjust

48. Adjusting Armature Voltage

49. Ex 8-4: VA variation

53. 3. Series Resistance with Armature
Circuit; Ra X

54. Inserting series R in arm cct. X
• insertion, slope inc. as shown Fig 9-15(8-15)
• wasteful method of speed control
• inc in IF, dec speed

55. Series Resistance with Armature Circuit
X

56. Discussion X
• Rated (speed; Vt; power) is base speed; nbase
• Rf control speed above base speed not below
• Vt(Armature Voltg) control speed below base speed nbase not
above
• so combine two speed techniques to get a wide range of
speed-control
• Limiting factor either case is heating of armature
conductors place upper limit on Ia

57. Safe range of armature voltage
flux constant X

58. Safe Range of Filed current X

59. Safe range of armature voltage: power
and torque limits X

60. as Rf inc, speed inc, if Rf infinite, speed uncontrolled-
rise, Runaway condition X

61. 4. The Series DC motor
• Field winding consist of very few turns
• Field winding connected in series with Armature cct.
• IA= IF= IL (all same)

62. Circuit for Series DC M

63. Applications:
Gives more Torque as compared any other DCm
• Starter motors in car
• Elevator motors
• Tractor motors

65. Eliminate phi to get Torque vs w

66. T-S curve for un-saturated series motor:
Never run motor unloaded; speed goes very
high
Series DCm: Ex 8-5

67. Speed control:
“VT” controlled through solid state
control
“RA” not commonly used

68. THE COMPOUNDED DC MOTOR
Motor with both Series and Shunt field
• Dots and square symbols have same meaning as for a
Transformer
• Cumulatively compounded
• Currents flowing into dots on both sides, armature and field
coils, produce +ve mmf, called cumulatively compounded
where mmfs add
• Differentially compounded
• Currents flowing into square of one coil and out of square
from other coil produce -ve mmf, called differentially
compounded, the resulting mmf subtracts long shunt
connection and short shunt connection

69. Short-shunt connection- Cumulatively
Comp. M

70. Long-Shunt connection conection:
Cumulatively Comp. M

71. Equations for Cumulatively/
Differentially Compounded Motors

73. T-S characteristics of Cumulatively
Compounded DC M
• Higher starting Torque than Shunt DC M; but less than
Series DC M
• So combines best features of both
• At higher loads behave like Shunt DC M
• At low loads behaves like Series DC M

74. Full load rating comparison

75. No load rating comparison

77. Differentially Compounded DC M
• Shunt mmf and series mmf subtract each other
• When :
• load inc.
• Ia decrease
• and speed inc.
• Due to unstable condition, runaway, not used

78. Torque speed characteristics of
Differentially Compounded motor.

79. Speed controls of Cumulatively
Comp DC M:
•
• Change of Rf, Va, and Ra

80. 5. Permanent Magnet DC motor
Poles are permanent magnet ( Shunt DCm electro-mag
poles)
Advanatages:
• No copper loss
• Smaller size as no field winding
Disadvantages:
• Not high flux, low Tind per ampere of IA compared Shunt
DCm same size
• Risk of demagnetization:
• if IA becomes verly large, amature mmf may demagnetize the
poles
• If the temperature rise, it also creats demagnetization

81. Typical magnetic curve of Ferromagnetic
material

82. Magnetization curve for Perm. Mag.:
based on B res and Large Coerc Hc

83. PMDCm
• So large B res and Hc required, not same as Electromag
poles based
• New magnetic materials found; ceramic ferrite, rare earth
mag mat comparison with conventional Alnico5
• Speed Control:
• No speed control by If
• Only Va and Ra based control

84. DC GENERATOR

85. Gn vs M

86. VR vs SR

87. Eq cct. DC G

88. Simplified diagram of shunt DC Gen

89. 1 Separately Excited: G

90. Compare; Sep Excited M

91. Terminal xtic-DC G

92. 2 Shunt DC Gen

93. Terminal X-tics Shunt DC G

94. Compared;Terminal Shunt DC motor

95. Voltg control vs Speed Control
Motor(sep/ shunt) Gen (sep/ shunt)
• Change speed of rotation
(w)
• Change RF i.e. Field
current (IF)

96. Next-Comparison for:
• Series DC G/M
• Compounded DC G/M
 Differentially and Cumutatively Comp

97. The Series DC Generator

98. Terminal X-tics of Series DC G

99. Compare DC Series motor

100. The Compounded DC G
1 Cumulatively Compd
• Long shunt
• Terminal xtics

101. Cumulatively Compd. DC G
• Short Shunt

102. Compare with Cumulative DC M
• Long shunt
• Fill yourself
• Short shunt
• Fill yourself

103. 2 Differentially Compd. DC G-
Compare to Diff. Comp DC M-do it

104. Ex and End prob.: ?
• Ex 1, 3 , 4, 5
• Ex8-9
• Prob.s 1-12
• 22,23,24