THE INDUCTION MOTOR. 405 



the leakage flux on the scale of flux (the leakage flux 

 must evidently be in phase with the primary current, 

 since it is unaffected by the secondary winding, whereas 

 the rotor flux is due to the resultant action of both 

 primary and secondary currents). Then the triangle 

 A B will be the triangle of fluxes for the motor, since the 

 two sides A, OB, represent the primary and leakage 

 fluxes, which must have as their resultant the third 

 side A B, which will, consequently, represent the rotor 

 flux. 



z is the total leakage flux of the motor, and therefore 

 includes the rotor leakage. Hence, we can assume the 

 rotor winding to be non-inductive, as its self-induction 

 is already taken account of in the length of B. The 

 rotor current will, consequently, be in phase with the 

 E.M.F., which produces it ; that is, perpendicular in 

 phase to the rotor flux Z r . Draw B E r perpendicular to 

 B A to represent the induced rotor voltage. Draw D 

 perpendicular to B E r . The triangle O B D will then be 

 the triangle of primary, secondary, and magnetising 

 currents, drawn to a reduced scale, since the line O B ism 

 phase with the stator current, the line B D is in phase 

 with the rotor current, and the line O B, being perpen- 

 dicular to B D, and parallel to the line B A = rotor flux, 

 is in phase with the motor magnetising current. D 

 will always be perpendicular to B D and parallel to B A 

 at all loads, and represents the current which maintains 

 the flux in the magnetic circuit of the machine. 



The diagram obtained in this way represents the 

 relation between the most important quantities in an 

 induction motor. 



Heyland Diagram. By means of a Heyland diagram 



the relations between the quantities at all loads can be 



simply obtained. In Fig. 194, the line A B == Z r <x 



primary magnetising ampere turns magnetising current 



reluctance of magnetic circuit reluctance 



oc - where ^ = -- reluctance of magnetic circuit. 



Therefore -rrr) * W == constant. That is to say, the 



line A will always be cut at a definite point by the 

 line B D ; calling this point F, the line B D will 



