ELEMENTS OF ELECTRICAL ENGINEERING. 



The field flux, the trend of which is shown by the closed dotted 

 lines 4>^>, is produced by a field winding ZZ which is fixed to the 

 inside of the hollow cylindrical yoke, and surrounds the rotating 



Fig. 62. 



cylindrical armature A. There are two sets of positive brushes 

 which are arranged to rub upon the extreme ends of AA, and 

 two sets of negative brushes which are arranged to rub on AA 

 at any convenient place inside of YY. The leads which connect 



to the brushes inside of YY 

 pass through a series of holes 

 through YY, which are shown 

 by the short dotted lines.* 



The low electromotive force 

 of the unipolar dynamo is due 

 to the fact that the armature con- 

 sists necessarily of a single ele- 

 ment in which electromotive 

 force is induced. To obtain a 

 high electromotive force there- 

 fore, a number of distinct machines must be connected in series, f 

 These distinct machines may have, however, a common mag- 



* A modified form of unipolar dynamo is described by H. E. Heath in the Elec- 

 trical World and Engineer, February 10, 1900, Vol. 35, p. 210. 



fSee paper, "Acyclic Homopolar Dynamos," by T. E. Noeggerath, Trans. A. 

 I. E. E., January 27, 1905. 



Fig. 63. 



