1. Electric Machinery DC Machines A.E. Fitzgerald Charles Kingsley, Jr.
Sixth Edition
A.E. Fitzgerald
Charles Kingsley, Jr.
Stephen D. Umans
DC Machines

2. 7.1 INTRODUCTION

3. 7.1 INTRODUCTION

4. 7.1 INTRODUCTION

5. 7-4 7.1 INTRODUCTION Current in external armature circuit
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7.1 INTRODUCTION
Current in external armature circuit
Constant determined by the design of windings
Direct axis air-gap flux per pole
7-4

6. 7.1 INTRODUCTION
Rectified coil voltages and resultant voltage between brushes in a dc machine.
Power
Speed voltage
Angular speed

7. Typical form of magnetization curves of a dc machine.
7.1 INTRODUCTION
Typical form of magnetization curves of a dc machine.

8. Equivalent Circuit (Not in the textbook):
7.1 INTRODUCTION
Equivalent Circuit (Not in the textbook):
For steady-state, current is dc, therefore Lf and La can be neglected.

9. 7.1 INTRODUCTION
Field-circuit connections of dc machines: (a) separate excitation, (b) series, (c) shunt, (d) compound.

10. Volt-ampere characteristics of dc generators.
7.1 INTRODUCTION
Volt-ampere characteristics of dc generators.

11. Speed-torque characteristics of dc motors.
7.1 INTRODUCTION
Speed-torque characteristics of dc motors.

12. Ea Ra Rf Vt EXAMPLE (Final Exam 2006) :
Assume that a 240 V self-excited shunt motor is supplied by a line current of A when it is loaded with a full load at a speed of 1000 rpm. The armature-circuit resistance and the shunt-field circuit resistance of the motor are 0.1 ohm and 100 ohm, respectively. Assume that a breaking resistor of 1.05 ohm is used for dynamic braking (breaking means that voltage source is removed and immediately a resistor is connected to the terminals of the DC machine) and determine the following.
a)The value of counter emf Ea.
b)The full-load torque of the motor
c)The value of the armature winding current at the time of initial breaking.
d)The value of initial dynamic breaking (initial torque during breaking) Ea Ra Rf Vt

13. The End of This Chapter

14. Dc machine armature winding with commutator and brushes
Dc machine armature winding with commutator and brushes. (a), (b) Current directions for two positions of the armature.
Figure 7.7

15. Waveform of current in an armature coil with linear commutation.
Figure 7.8

16. Armature-mmf and flux-density distribution with brushes on neutral and only the armature excited.
Figure 7.9

17. Flux with only the armature excited and brushes on neutral.
Figure 7.10

18. Armature, main-field, and resultant flux-density distributions with brushes on neutral.
Figure 7.11

19. Motor or generator connection diagram with current directions.
Figure 7.12

20. Short-shunt compound-generator connections.
Figure 7.13

21. Magnetization curves for a 250-V 1200-r/min dc machine
Magnetization curves for a 250-V 1200-r/min dc machine. Also shown are field-resistance lines for the discussion of self-excitation in Section
Figure 7.14

22. Equivalent circuit for analysis of voltage buildup in a self-excited dc generator.
Figure 7.15

23. Cross section of a typical permanent-magnet motor
Cross section of a typical permanent-magnet motor. Arrows indicate the direction of magnetization in the permanent magnets.
Figure 7.17

24. (a) Dimension definitions for the motor of Fig. 7. 17
(a) Dimension definitions for the motor of Fig (b) approximate magnetic equivalent circuit.
Figure 7.18

25. Equivalent circuit of a permanent-magnet dc motor.
Figure 7.20

26. Section of dc machine showing compensating winding.
Figure 7.22

27. Schematic connection diagram of a dc machine.
Figure 7.24

28. Series-connected universal machine.
Figure 7.25

29. Typical torque-speed characteristics of a series universal motor.
Figure 7.26

30. 1200 r/min magnetization curve for the dc generator of Problem 7.4.
Figure 7.27

31. Series crane motor (Problem 7
Series crane motor (Problem 7.22): (a) hoisting connection and (b) lowering connection.
Figure 7.28