CHAPTER I. 

 DIRECT CURRENT GENERATORS. 



EXPERIMENT i-A. Generator Study and Characteristics of a 

 Series* Generator. 



PART I. GENERATOR STUDY. 



I. Faraday discovered (1831) that when a conductor cuts 

 lines of force an electromotive force is generated in the conductor 

 proportional to the rate at which lines are cut, and all dynamos 

 (or generators as they are now commonly called) operate on this 

 principle. To generate an electromotive force, it is essential there- 

 fore to have a conductor (or several conductors combined by 

 various winding schemes) forming the armature as one member; 

 and to have lines of force or magnetic flux set up by field mag- 

 nets which form the second member. For operation it is neces- 

 sary also to have a source of mechanical powerf by which either 

 one of these members can be given a motion with respect to the 

 other. A generator may havej a stationary field and revolving 

 armature; or, a revolving field and stationary armature, desig- 

 nated as the revolving field type. Although the latter is useful 

 for large alternators, serious objections to it have been found 

 in direct current machines, for with the commutator stationary 

 the brushes must revolve, which leads to difficulties in construc- 

 tion and operation. It is the custom, therefore, to build all 



* Where a series generator is not available, this study may be taken 

 without experimental work or in connection with Part I. of Exp. i-B. 



f Power is required to overcome friction and other losses, and to over- 

 come a counter torque ( 1-3, Exp. 2-A) which varies with the load. 



$ Outside of this classification is the inductor alternator which has a 

 stationary armature, a stationary field winding and a revolving inductor of 

 iron ; its study should be taken up later under alternators. 



2 I 



