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ELECTRICAL MACHINERY 



in strength and oscillate across the pole face, but also pro- 

 duces a weakening of the main field, the amount of weaken- 

 ing depending upon the magnitude of the current in the 

 armature and upon the power factor of the load, and being 

 greater the less the power factor. 



Single-phase Armature Reaction with Leading Armature 

 Current. In case the alternator is furnishing current to 

 a load having a leading power factor, the locus of the arma- 

 ture m.m.f. is a circle but is rotated backward from the 

 position it had for a non-inductive load. This condition 

 is shown in Fig. 152. A study of this figure shows that 



FIG. 152. Locus of Armature Reaction of a Single-phase Generator, 

 Leading Current. 



for the single-phase alternator, furnishing a leading current, 

 the armature reaction results in a periodic pulsation in the 

 strength of the main field, an oscillation of the field across 

 the pole face from the leading to the trailing pole tips and 

 back, and a strengthening of the main field, which is pro- 

 portional to the armature current and dependent upon the 

 power factor, being greater the less the power factor. 



Reaction of an Actual Multiple-coil Winding. The 

 previous analysis has been carried out for an armature 

 having a single coil; however, any ordinary single-phase 

 winding produces an effect nearly the same as though the 

 armature had but one turn, there being such a current 



