GENERAL DIAGRAMS FOR SYNCHRONOUS MOTORS 185 



the point of zero-load, d, will be on the perpendicular kd corresponding 

 to a segment Bk=Rj . We will compare, for various cases, the values 

 of the reactive current io corresponding to this no-load condition. 



This reactive current is obtained by drawing through d the right 

 line dF, perpendicular to BG, until it crosses the circle of radius E. 

 In order to make this cur- 

 rent-value comparable with 

 BK, it is only necessary 

 to reduce also the segment 



R 



dF in the proportion , 



which can be done by pro- 

 jecting it on KG. The 

 segment d'F' then meas- 

 ures the value Rio, while 

 Bk measures RI W . By 

 this process all the current FlG g 



values are referred to one 



and the same scale, io, whatever may be the value of Z. On making 

 the diagram anew for cases corresponding to various angles of the line 

 of reference BG, it is found that the reactive current, which is very 



large for very small " lags " 

 diminishes, rapidly at first, 

 then more slowly. 



In order to follow more 

 easily the law of variation, 

 let us suppose the active 

 current to vanish at zero- 

 load, i.e., let us assume 

 jo=o, which makes d coin- 

 cident with D (Fig. io). 

 The reactive current io is 

 then proportional simply 

 to the distance FH. 

 If the point G be raised gradually on the vertical line KG, starting 



T> T^ 



from the point K, the reactive current is at first equal to - (Fig. 9), 



K 



and it will then decrease; for example, for the point G (Fig. io), it 

 will decrease to FH. When G is very high, it is seen that an addi- 

 tional rise, G'G", for example, will increase almost proportionally the 



F IG . 9 . 



