CHAPTER V 

 ARMATURE WINDINGS AND SLOT INSULATION 



21. Introductory. The object of this chapter is to explain 

 the essential points which the designer must keep in mind when 

 determining the number of slots, the space taken up by insula- 

 tion, the cross-section of the copper windings, and the method 

 of connecting the individual conductors so as to produce a finished 

 armature suitable for the duty it has to perform. It is assumed 

 that the reader is familiar with the appearance of a D.C. machine 

 and understands generally the function of the commutator. 

 For this reason it is proposed to omit such elementary descrip- 

 tive matter as may be found in every textbook treating of elec- 

 trical machinery. On the other hand, the practical details of 

 manufacture and much of the nomenclature used in the design 

 room and shops of manufacturers will also be omitted, because 

 space does not permit of the subject being treated exhaustively; 

 but if the reader will exercise his judgment and rely upon his 

 common sense, he will be able to design a practical armature 

 winding to fulfil any specified conditions. 



The direction of the generated e.m.f. will depend upon the 

 direction of the flux through which the individual conductor is 

 moving, and it is therefore a simple matter so to connect the 

 armature coils that the e.m.fs. shall be additive. It does not 

 matter whether the machine is bipolar or multipolar, ring- or 

 drum-wound, it is always possible to count the number of con- 

 ductors in series between any pair of brushes and thus make 

 sure that the desired voltage will be obtained. 



Closed-coil windings will alone be considered, because the 

 open-circuit windings: as used in the early THOMSON-HOUSTON 

 machines and other generators for series arc lighting systems 

 are now practically obsolete. Another type of machine, known 

 as the homopolar or acyclic D.C. generator, although actually 

 used and built at the present time, has a limited application 

 and will not be considered here. The absence of the com- 

 mutator is the feature which distinguishes this machine from the 



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