294 ELEMENTS OF ELECTRICAL ENGINEERING. 



is the supply voltage, n is its frequency, and n' is the speed of 

 the rotor in revolutions per second (two-pole model assumed). 



(a) A pulsating flux 4>, Fig. 253, is produced by the stator 

 winding, and the electromotive force induced in the stator wind- 

 ing by this pulsating flux just balances the supply voltage E '. 



(fr) The moving rotor rods cut the flux <3>, and an * electro- 

 motive force, A r , Fig. 254, is induced in the regions A and 

 A' of the rotor winding. This electromotive force A r has the 

 same frequency as <, it is in phase with <E>, and it produces 

 up-flowing currents at A' and down-flowing currents at A, 

 Fig- 2 53- These currents are magnetizing currents (M a in Fig. 

 254) and they produce a cross-flux <3> c which pulsates at the pri- 

 mary frequency. The pul- 



* sations of this cross-flux 



induce an electromotive 



B r force, A pt in the rotor rods 



I' at A and A', and this 



electromotive force bal- 



~M~ ~^A ^" ances the electromotive 



~m ? x 



force A r . 



(c) The pulsations of <I> 

 produce an electromotive 



p force B p in the rotor rods 



^c in the regions B and 



FIg>254 ' B', Fig. 253, and the 



cutting of the cross-flux 4> c induces an electromotive force B r 

 in the same rods. When the rotor runs at synchronous speed 

 (n f equals ri), then B p is exactly balanced by B r , no currents 

 flow in the rotor rods in the regions B and B f ', and therefore 

 nothing but magnetizing current flows in the stator. When the 



* A squirrel-cage rotor presents a multiplicity of circuits, and to speak of the elec- 

 tromotive force or the current in the rotor, depends upon a scheme which is described 

 in a subsequent part of this article. In speaking of an electromotive force or cur- 

 rent in the rotor the electromotive force or current in a stationary group of the 

 moving rotor rods is understood. New rods are, of course, coming into such a group 

 continuously on one side and leaving the group continuously on the other side. An 

 electromotive force induced by pulsation is indicated by a subscript p, and an electro- 

 motive force due to the cutting of lines of force by rotation is indicated by a subscript r. . 



