184 GENERAL DIAGRAMS FOR SYNCHRONOUS MOTORS 



the axis OX; and the currents corresponding to increasing loads will 

 be represented by the distances Bd, BD', BD", etc. Let D", for 

 example, represent the normal load condition for which there is no 

 lag (r=o). The vectors Cd, C'D', C"D", which measure the corre- 

 sponding reactive currents, increase extremely fast at light loads; 

 and, since the scale of current-values is very small, owing to the fact 

 that Z is very small, it is seen that the reactive currents at light loads 

 would be very large. On the other hand, in the case represented 

 by Fig. 6, owing to the fact that the load-lines are no longer perpen- 

 dicular to OB, it is easy to find, with a constant E.M.F. E, and with 

 small active currents, load-points, C, C', C", corresponding to points 



0' o' o & B<t A' \p' Y 



*' 



FIG. 7. 



O, O', O", which are displaced to the left, and, consequently cause 



/t.\ 



an increase in the voltage I -r I at the brushes. 



It is seen, thus, that it is possible to obtain economically a voltage- 

 regulation giving constant or rising voltage, as the load increases, 

 only when the circuit contains a certain amount of reactance. 



This point being established, it is easy to note the influence of 

 reactance, by supposing that the " no lag " condition is made to 

 correspond always to the same load, i.e., to the same value of the 

 active current, I w . In fact (Fig. 8), all the load-points corresponding 

 to that condition are found to be located at distances, ZI W , from the 

 point B, which are proportional to the impedances Z=\/R 2 X 2 ; 

 hence, if we measure off, on OB prolonged, a distance BK, equal 

 to RI W , all the points G, corresponding to different reactances X, 

 will be located on the right line KP perpendicular to OK. Likewise, 



