CHAP. VI] 



EXCITING AMPERE-TURNS 



109 



flanks or sides of the pole shoes perpendicular to the shaft; (d) 

 between the flanks of the pole cores. In the calculations which 

 follow, the permeances are computed between a pole and the planes 

 of symmetry, MN, between the two poles, the permeance of the 

 other half of each path being the same. All these leakage paths 

 are in parallel with respect to the pole, so that the total leakage 



(c) 



FIG. 29. The leakage flux between field poles. 



permeance is equal to their sum. Knowing this total perm, 

 and the in. in. f. between the pole and the plane M \ the leakage 

 tfl found, and knowing this llux and the useful llu\ per pole 

 the leakage factor < ..!< ul. 



We shall now est i mate the permeances of cadi of the four above 

 mentioned paths of leakage. 



(</) Between the adjacent pole-tips. Estimate .the average 

 cross-section A of the path, in square centimeters, and the 



