SYNCHRONOUS MACHINERY 



225 



(b) The revolving field type illustrated in Fig. 191 and Fig. 

 192, is almost universal for all sizes and voltages. The armature 

 is the stationary part and the field poles revolve. This type has 

 many advantages over the revolving armature type. (1) It only 

 requires two slip rings even for polyphase machines and these 



Generator 



FIG. 190. Single-phase alternator, revolving armature type. 



slip rings carry only the small current supplied to the field wind- 

 ing, while the load current is taken off from stationary terminals. 

 (2) There is much more space for the armature windings and 

 they are relieved from all centrifugal strains. They can, there- 

 fore, be much better insulated and ventilated. The field wind- 

 ings are made of copper strap and the revolving member is very 



Armature Winding 



FIG. 191. Single-phase alternator, revolving field type. 



rugged and is not affected by strains due to rotation; thus, much 

 higher peripheral speeds may be used than with type (a), with 

 consequent increase in economy of material. 



(c) The inductor alternator is almost obsolete. In these 

 machines the field and armature windings are both stationary 

 and a part of the iron of the magnetic circuit revolves, producing 



