THE MAGNETIC FIELD IN THE POLYPHASE MOTOR. 



In this equation to is the magnetizing current, n the number of con- 

 ductors per pole and phase, and A the air-gap in cm. The reluctance 

 of the iron is supposed to be negligible. 



From this equation follows 



(B 1.6 A 



(6) / = 7=- amperes. 



2 n . V 2 



22. If the reluctance of the iron is not negligible, the magnetic in- 

 duction ($> has to be determined point for point, which can easily be 

 done with the help of a magnetizing curve. It is of importance to note 

 that the maximum induction does not extend over a very large part 

 of the pole-pitch, hence it is not objectionable to have an induction 

 of 15,000 or 16,000 in the teeth, as this high induction hardly in- 

 creases the magnetizing current on account of its being limited to a 

 very small part of the surface of the pole. 



23. I have not entered upon a detailed consideration of the elemen- 

 tary phenomena in the polyphase motor, as they have been treated by 

 Gisbert Kapp* and Andre Blondel* with a lucidity and clearness 

 which it would be impossible for me to surpass. 



B. The Formulae for the Three-Phase Current 

 Motor. 



24. It remains to prove that the theory of the general alternating cur- 

 rent transformer is directly applicable to the polyphase motor. That this 

 is true, as long as the armature of the motor is standing still, is evident. 

 If the armature runs at synchronism, the number of its revolutions cor- 

 responds to the frequency of the feeding current ~i. If the arma- 

 ture runs slower than the field, the difference being ~! - 2 , then 



an e. m. f. is induced in the armature proportional to the slip ~i ~ r 

 If the armature resistance per phase is r t , then a current will flow 

 proportional to ~' ~*. The same current can be attained in the 

 transformer with the secondary at rest, if the resistance be thus 

 chosen that the relation exists 



'Electric Transmission of Energy, p. 304 and following, reprinted in Appen- 

 dix I. 



*L' 'Eclairagt Electriqitt, 1895. 



15 



