CHAPTER VII 

 FLUX DISTRIBUTION OVER ARMATURE SURFACE 



An experienced designer may go far and obtain good results 

 without resorting to the more or less tedious process of plotting 

 flux-distribution curves; but occasions arise when his experience 

 and judgment fail him, and when a reasonably accurate method 

 of predetermining the distribution of flux density over the sur- 

 face of the armature would give him all necessary information. 

 A method of designing electric machinery whether continuous- 

 current dynamos or alternating-current generators which in- 

 volves the plotting of the flux distribution curves, has much to 

 recommend it, not only to the student, but also to the professional 

 designer. The advantage from the student's point of view is 

 that a more accurate conception of the operating conditions 

 can be obtained than by using empirical formulas, or making 

 the unscientific assumptions which are otherwise necessary. 

 The designer will be glad to avail himself of a practical method 

 of plotting flux curves when departures have to be made from 

 standard models, or when it is desired to investigate thoroughly 

 the effects of cross-magnetization upon commutation or pressure 

 regulation. 



36. Air-gap Flux Distribution with Toothed Armatures. 

 The determination of the flux densities in all parts of the tooth 

 and slot for various values of the average air-gap flux density 

 is so difficult and complicated that it is safe to say no correct 

 mathematical solution may be looked for, although empirical 

 rules and formulas of great practical value may serve the 

 purpose of the designer. 



The reluctance of the magnetic paths between pole face and 

 armature core can be calculated with but little error for the two 

 extreme cases of very low and very high average flux density 

 over the tooth pitch; but for intermediate values the designer 

 has still to rely on his judgment, based on familiarity with the 

 laws of the magnetic circuit. 



To calculate the permeance of the air paths over one slot 

 pitch at the center of the pole face, when the density is low, the 

 magnetic lines are supposed to follow the paths indicated in 



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