224 THE MAGNETIC CIRCUIT [ART. 66 



the original paper and to the works mentioned at the end of 

 this article. 



Let there be C PPl conductors per pole per phase in the stator 

 winding; then the fictitious coil (Fig. 54) made up of the 

 primary and secondary conductors has C PP1 turns, when reduced 

 to the primary circuit. This is because the secondary winding 

 can be replaced by an equivalent winding with a " one to one " 

 ratio, that is, with the same number of conductors as the 

 primary winding. In this case, the secondary current is equal 

 to the primary current (Art. 446). Therefore, eq. (150) can 

 be made to give the equivalent inductance, including the pri- 

 mary inductance and the secondary inductance reduced to the 

 primary circuit, provided that the permeances of the paths 

 linking with the secondary conductors are included in the values 

 of (P"s. Such is naturally the case when the values are deter- 

 mined from a test with the rotor locked. 



Extended tests have shown that in a given line of machines 

 the permeance <P/ is inversely proportional to the peripheral 

 length of the equivalent leakage flux, that is, inversely proportional 

 to (r/m), where r is the pole pitch and m is the number of 

 primary phases. 1 This shows that the permeance per centi- 

 meter of peripheral length of the active layer is fairly constant, 

 in spite of different dimensions and proportions, as long as 

 these are varied within reasonable limits. Thus 



tP/-(P/7(r/m), 



where &" is the leakage permeance of the active layer in the 

 embedded part per one centimeter of axial length and per centi- 

 meter of the peripheral length of the path. Thus, the final 

 formula for the equivalent leakage inductance of an induction 

 machine, per pole per phase, reduced to the primary circuit, is 



L egPP =C pp *[(P i "l i /(T/m) + (Pj a + a(P e 'l e ]W-* henrys. (151) 



In this formula the following average values of unit per- 

 meance may be used for machines of usual proportions, unless 

 more accurate data are available. 



1 H. M. Hobart, Electric Motors (1910), table on p. 397. The values 

 for (Pi" given below have been computed from this table, and the results 

 multiplied by 2, because the table gives the values of the primary per- 

 meances only. 



