222 



ALTERNATING CURRENTS 



a = 9 2 = tan" 1 -^- 2 . We may now complete the primary vector 



diagram by drawing BO = pM.1% in a direction at right angles to OD. 

 The vector 00 then corresponds to the constant stator phase p.d. V. 

 The triangle of secondary e.m.f.'s, ODE, may now be completed.* 



Having thus obtained our vector diagram, we proceed to trans- 

 form it just as we did in dealing with a motor ( 109), and so 

 establish the circle diagram for an induction generator. 



131. Generalized Circle Diagram 



The circle representing the locus of the extremity of the primary 



FIG. 142. Generalized Circle Diagram. 



current vector is identical with the circle obtained for the machine 



* If we wish to regard the rotating triangle ODE as giving us, by the projection of 

 its sides on a fixed straight line, the instantaneous values of the three e.m.f. components, 

 then we must suppose the rotation to be clockwise, that of OABC being counter-clock- 

 wise. This is due to the fact that the motion of the stator field relatively to the stator 

 conductors is opposed to its motion relatively to the rotor conductors. 



