74 ELECTRICAL MACHINERY 



elementary outline and analysis of some of the various 

 forms employed in different c-c. generators. By the 

 term " armature winding " is meant the group of con- 

 ductors placed on the armature core, which revolve with it 

 and cut the magnetic field. The different ways in which 

 these conductors may be placed on the armature core and 

 interconnected, leads to innumerable winding schemes. 

 The armatures of motors and generators are wound in 

 exactly the same way; the same factors have to be kept 

 in mind no matter whether the armature is to be used 

 for one purpose or the other. We shall speak of the dif- 

 ferent windings as generator windings but they serve just 

 as well for a motor armature. 



Classification of Armature Windings. The armature 

 windings for alternating current generators are quite 

 different from those intended for a c-c. generator; we 

 shall consider here only the c-c. windings, the first two 

 general divisions of which are the ring winding and the 

 drum winding. 



Ring Winding. In the ring winding the coils are wound 

 around the armature in such a way that half of the coil 

 is on the inside of the armature core. This may be seen 

 by reference to Fig. 38, which shows the armature of an 

 early type of generator. The winding of these armatures 

 is not as easy as the winding of a drum armature but a 

 more important objection is the amount of " dead wire " 

 on the armature. 



Disadvantage of the Ring Winding. The conductors 

 on the inside of the core do not cut any flux as the arma- 

 ture revolves and hence they can generate no e.m.f. This 

 extra wire is detrimental to the machine not only because 

 of the extra cost for wire but because the resistance of the 

 armature winding is much larger than it should be; this 

 high resistance means high PR and a high heat loss in the 

 generator. As a result the efficiency is lowered. 



The ring winding is used very little at present and we 



