190 GENERAL DIAGRAMS FOR SYNCHRONOUS MOTORS 



ratio of transformation is made variable by means of " taps " on the 

 the secondary winding connected with suitable switching apparatus. 

 The fundamental diagram (Fig. 12), or the formula (fl), will deter- 

 mine the values which should be given to E for each value of the E.M.F. 

 e, and of the load ZI W , measured off along the line BY corresponding 

 to the fixed reactance of the circuit. The most suitable value for the 

 reactance is, in this case, evidently, the lowest value, X=o, when 

 possible; because this value reduces to a minimum the values of the 

 E.M.F. E required. Therefore, no supplementary reactance should 

 be included in the circuit. Under these circumstances BY becomes 

 the prolongation of OB in the diagram. 



FIG. 12. 



Regulation of Voltage at Terminals by Variation of Reactance. 

 It is also possible to neutralize the lag at all loads more simply by keep- 

 ing the supply E.M.F. E constant (and equal to that required to 

 insure the necessary voltage at the terminals with full load without 

 reactive current), and then reduce this voltage at lighter loads by the 

 introduction of suitable reactances in the circuit. 



Fig. 13 explains this method of regulation in the case where the 

 E.M.F. E is constant; and it enables the characteristic features of this 

 case to be studied. 



Let BK = RI W , represent the loss of voltage by ohmic drop in the 

 circuit, with full load. The segment BK can serve to represent the 

 acti e current. 



Let BK,' BK," etc., represent intermediate current values; and 

 let the corresponding perpendiculars KG, K'G,' K"G" be drawn. 

 Their points of intersection G, G,' G", with the circle of radius E, 



