Construction of d.c. Machines & Classifi cation of Generators

Chapter 7.3 Construction of d.c. Machines

Fundamental Electrical and Electronic Principles Third Edition Book
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Summary of Contents

Fundamental Electrical and Electronic Principles Third Edition Book

  • 238Fundamental Electrical and Electronic PrinciplesWith a large number of armature coils the ripple on the resultant waveform will be negligible, and a smooth d.c. output is produced. 7.3 Construction of d.c. Machines The various parts of a small d.c. machine are shown separately in Fig. 7.8 , with the exception that neither the fi eld nor armature windings have been included. The frame shell (bottom left) contains the pole pieces, around which the fi eld winding would be wound. One end frame (top left) would simply contain a bearing for the armature shaft. Fig. 7.8 The other end frame (bottom right) contains the brushgear assembly in addition to the other armature shaft bearing. The armature (top right) construction has already been described. The slots are skewed to provide a smooth starting and slow-speed torque. 7.4 Classifi cation of Generators D.C. generators are classifi ed according to whether the fi eld winding is electrically connected to the armature winding, and if it is, whether it is connected in parallel with or in series with the armature. The fi eld current may also be referred to as the excitation current. If this current is supplied internally, by the armature, the machine is said to be self-excited. When the fi eld current is supplied from an external d.c. source, the machine is said to be separately excited. The circuit symbol used