THE DYNAMO. 



6l 



Furthermore, the laminations of the armature core are separated 

 at intervals, thus forming air ducts from the interior to the ex- 

 terior of the armature core. Fig. 46 shows seven places where 

 the laminations are thus separated, and Fig. 50 shows one place 

 where the laminations are separated. The object of this thorough 

 ventilation of the armature is to avoid the high temperatures 



Fig. 51. 



which would otherwise be produced by the very considerable 

 heat which is generated in the armature core by eddy currents 

 and magnetic hysteresis, and in the armature windings by the 

 armature current. Fig. 5 1 is a view of a portion of the arma- 

 ture core showing two slots filled with conductors which are held 

 in place by wooden wedges, and also showing several of the 

 ventilating ducts between the sheet-iron laminations. The arma- 

 ture conductors shown in Fig. 5 1 consist of massive rectangular 

 bars of copper. Wire-wound armatures are, in general, used for 



