102 'HIE MAGNETIC CIRCUIT [Au. ;,s 



kiloampero-t urns per centimeter. Then, if all the flux densities 

 are in kilomax wells per square centimeter, 



B a -l.25H. 



Substituting this value of B a into the preceding equation we 

 obtain, after division by A if 



B app ^B real + \.2^(A a /A-)H ..... (54) 



The ratio A a /Ai can be expressed through the dimensions of 

 the machine as follows: Ai = tt n where t is the width of the tooth, 

 and l n is the net axial length of the laminations, without the air- 

 ducts and insulation. A a = Xl g tl n , where A is the tooth pitch 

 (Fig. 20), and l g is the gross length of the armature core. Hence, 



-l. . : . . . (55) 



In eq. (54) the flux density B app and the ratio AJAi are known 

 in any particular case, and the problem is to find B real and H. 

 The other equation which connects B rcal and H is the magnetiza- 

 tion curve of the material, and the problem can be solved in a simi- 

 lar manner to problem 11 in chapter II (see also problem 4 below). 



Professional designers use curves like those shown in Fig. 2S, 

 which give directly the relation between B app and B real within the 

 range of values of A a /Ai which occur in practice. The curves are 

 plotted point by point by assuming certain values of B real and cal- 

 culating the corresponding B app from eq. (54). For instance, for 

 # reaZ =24, the saturation curve shown in Fig. 28 gives H= 1.33, so 

 that for A a /Ai=2, we have: app = 24 + 1.25X2Xl.33 = 27.33. 

 This determines one point on the curve marked " Ratio of air to 

 iron = 2." In using these curves one begins with the known value 

 of B app on the lower axis of abscissae, and follows the ordinate to 

 the intersection with the curve for the desired ratio AJ A^ this 

 gives the value of B real . By following the horizontal line from the 

 point so located to the intersection with the B-H curve, the corre- 

 sponding value of H is read off on the upper axis of abscissae. 



The curves in Fig. 28 are completely determined by the shape 

 of the B-H curve, so that, if the material to be used for the arma- 

 ture core differs considerably from that assumed in Fig. 28, new 

 curves of B real versus B app ought to be plotted, or else the method 



