THE SINGLE-PHASE MOTOR. 



series, but in such a manner that an observer looking at the fields in 

 the direction of the axes of the rotors, would call the one revolving 

 clockwise, the other counter-clockwise. The armatures of both mo- 

 tors are rigidly connected.! The field I would then try to turn the 

 armatures in a clock-wise direction, while the field II, if left to itself, 

 would try to turn them in a counter-clockwise direction. The motor 

 / would take the larger share of the voltage, since we have seen that 

 the reactance of a polyphase motor is great for a small slip, and small 

 for a great slip. Hence, the voltage which is necessary to drive the 

 current, that comes from motor 7, through motor II, is small in com- 

 parison with that consumed by motor /. 



97. In order, then, to draw a diagram of the single-phase motor we 

 should have to find out by trying how the voltage is distributed be- 

 tween the two motors. This is a very wearisome procedure. We ar- 

 rive at a sufficiently accurate and simple solution if we remember 

 that the resultant magnetic field in motor II will always, with very 

 little inaccuracy, coincide with the impressed magnetic field of mo- 

 tor 7. But this means nothing else than that the effect of motor // may 

 be taken into account by considering it as an apparent increase of the 

 primary leakage field of motor I. 



98. According to the above considerations it is clear that currents 

 will be induced by the field // in the armature, even if running almost 

 synchronously. Synchronism, of course, can never be reached by the 

 armature unless an external force is applied to its shaft. These ar- 

 mature currents react upon the primary and must, obviously, about 

 double the magnetizing current; in other words, the single-phase 

 motor running idle, takes a current about twice as large as the mag- 

 netizing current. The accurate relation between magnetizing cur- 

 rent and "idle current" depends upon the leakage factor, and can be 

 calculated as follows. Each of the motors / and // receives one-half 



the idle current t. is the magnetizing current in motor I, and the 



tThe author is indebted for this helpful comparison to a conversation with Mr. 

 Herrmann Cahen in 1895. 



55 



