6 ARMATURE CONSTRUCTION 



alternating-current generator or synchronous motor, or for 

 an induction motor. In the case of an alternating-current 

 generator or synchronous motor, the internal rotor is a "field," 

 and does not come within the scope of this treatise. Strictly 

 speaking, this is equally true of the rotor of an induction motor, 

 when the primary winding is on the stator and the secondary is 

 on the rotor ; nevertheless, since the construction of such an induc- 

 tion motor " field " is utterly unlike the ordinary conception of the 

 " field " of a dynamo-electric machine, and is, in fact, practically 

 identical in most respects with the construction of a rotating 

 armature, it has been decided to include in this treatise the rotors 

 of induction motors. These as, of course, also all the above 



FIG. 6. Induction Motor Squirrel-cage Rotor. Almauna Svenska 

 Elektriska Aktiebolaget. 



types will be taken up in detail in the course of this treatise. 

 At this point it will suffice to refer to Figs. 6 and 7, in which two 

 typical examples of induction motor " rotors " (still often termed 

 " armatures ") are given. 



Fig. 6 has a short-circuited rotor winding commonly called a 

 " squirrel-cage " winding, which denomination is suggested by its 

 appearance. 



Fig. 7 represents a wound rotor for an induction motor in this 

 case, although this rotor would do equally well for the armature 

 of an alternating-current generator. 



The rotor of an induction motor may be regarded as an 

 armature by virtue of its having E.M.F.'s induced in it; and 

 hence it has been included, as well as the stator, in this treatise. 



For the purpose of making clearer the distinction between 

 the parts stator, rotor, armature, and field of dynamo-electric 



