282 ELECTRICAL EQUIPMENT 



in a three-phase system, under current the Y-current or current 

 per line and under voltage the A- voltage or voltage between lines 



FIG. 152. Three-phase Alternating Current. 



wires is understood. This subject is covered more fully in the 

 section on " Armature Connections." 



The e.m.f. induced in the armature circuit is determined by 

 the following formula: 



E g = 2Xk f Xk s Xk v ,XfXnX<t>Xl(T 8 ', 



in which k f = wave form factor; 

 fc, = slot factor; 

 ku, = winding pitch factor; 

 /= frequency in cycles per second; 

 n = number of armature conductors connected in series 



per phase (twice the number of turns per 



phase) ; 

 <t> = flux per pole in maxwells. 



The form factor of an e.m.f. wave is defined as the ratio 



effective voltage , . . , , . , 



= , and for a sine wave this value is equal to 1.11. 



average voltage 



The armature winding is generally distributed, that is, the 

 armature conductors are placed in more than one slot per pole per 

 phase. The principal advantages of such a distribution is the 

 closer approximation toward a sinusoidal wave form, while, on the 

 other hand, the total radiating surface of the coils is increased. 



With a distributed winding the e.m.f. will, however, be some- 

 what reduced because the voltage induced in the conductors in 



