THE INDUCTION MOTOR. 407 



work in either limiting condition. The amount of the 

 primary current is consequently determined in either 

 case by the reluctance of the magnetic path (which is 

 different for the two cases, being in one case the usual 

 path through rotor and stator cores., and in the other case 



o 



FIG. 195. SIMPLE HEYLAND DIAGRAM. 



the leakage path), through which the primary current has 

 to force the constant flux of Z K lines. Consequently, 

 if R = reluctance of main magnetic circuit through stator 

 and rotor, and r = reluctance of leakage paths 



Primary current at still-stand 



Primary current at synchronism 



reluctance of leakage path_ 



reluctance of main circuit 



= in Fig. 195. 



The reciprocal of this ratio is often called the leakage 

 factor, and is denoted by the letter v, since it determines 

 the magnetic leakage of the motor. 



The importance of the diagram given in Fig. 195 

 for our present purpose is that two simple measurements 

 on a motor enable us to determine the primary current 

 at still-stand and at synchronism, and from these 

 measurements the diagram can be drawn. 



Diagram for Commercial Motor. In the simple diagram, 

 Fig. 195, the losses in the motor are neglected. In the 

 commercial motor the losses to be considered are 



(a) Iron and mechanical losses ; 



(6) Copper losses due to resistance of rotor and stator 

 windings. 



The sum of losses (a) is approximately constant at 

 all loads, for a constant voltage applied. They form the 



