CHAPTER VII. 



VOLTAGE AND VOLTAGE REGULATION OF THE 

 ALTERNATOR. 



61, Electromotive force of the alternator, its dependence upon 

 speed and flux. The electromotive force of a direct current gen- 

 erator depends in a very simple way upon the magnetic flux <l> 

 per pole, upon the number of armature conductors Z*, and upon 

 the armature speed n. The electromotive force (effective) of an 

 alternator, however, depends not only upon <, Z y and n, but 

 also upon the width and shape f of the pole pieces of the field 

 magnet, and upon the extent to which the windings are spread 

 over the surface of the armature. 



The average value f of the electromotive force induced in one 

 armature conductor is always equal to p3>n abvolts, where / is 

 the number of field magnet poles, <I> is the magnetic flux from 

 one pole, and n is the armature speed in revolutions per second. 

 This is evident when we consider that a given armature conductor 

 cuts <i> lines of force in ifp of a revolution or in ifpn of a 

 second, so that the average rate of cutting lines of force is <E> 

 divided by I jpn which is equal to p3>n. 



Concentrated versus distributed armature windings. When the 

 armature conductors are grouped in / equidistant slots, / being 

 the number of field magnet poles, the armature winding is said to 

 be concentrated / when the armature conductors are spread out in 

 p broad bands or in / groups of slots, the winding is said to be 

 distributed. 



In a concentrated winding the same electromotive force e is 



* Number of armature conductors per path. 



f This is intended to include everything which affects the distribution of flux around 

 the armature. 



\ Whenever the average value of an alternating electromotive force or current is 

 spoken of, the average value during a half-cycle is always meant. 



117 



