CHAPTER IX 



THE MAGNETIC CIRCUIT DESIGN OF FIELD 

 MAGNETS EFFICIENCY 



65. The Magnetic Circuit of the Dynamo. Once the total 

 flux per pole necessary to develop the required voltage is known, 

 it is an easy matter to design the complete magnetic circuit and 

 provide it with a suitable winding in order that the required 

 flux shall enter the armature. The method of procedure is 

 similar to that adopted in the design of a horseshoe lifting magnet 

 (see Art. 16, Chap. Ill), and for this reason the subject will be 

 dealt with very briefly in this chapter. 



SECTION THROUGH 



A-B 



FIG. 71. Magnetic circuit of multipolar dynamo. 



Fig. 71 shows the flux paths in a multipolar dynamo. If we 

 know the flux density in the iron at all parts of the magnetic 

 circuit and the average lengths, y, c, and a, of the flux paths per 

 pole in the yoke, pole cores, and armature, respectively, we can, 

 by referring to the B-H curves of the materials used in the con- 

 struction, easily calculate the ampere-turns necessary to over- 

 come the reluctance of these portions of the magnetic circuit. 

 The greatest part of the total reluctance is in the air gap and 



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