GENERAL DIAGRAMS FOR SYNCHRONOUS MOTORS 177 



. produces a magnetizing effect. The variations in the condi- 

 tions of the external circuit, therefore, constitute an indirect process 

 for making the field-excitation of the rotary vary, though this variation 

 is often contrary to what is wanted. 



I. CONDITIONS OF ELECTRIC-CURRENT SUPPLY TO ROTARY 



CONVERTERS 



From what precedes, it is important to know, quite precisely and 

 quantitatively, the manner in which the reactive current varies with 

 the conditions of the current-supply to the converters, especially with 



the constants of the circuit and with the impressed E.M.F. This 

 question will now be discussed. 



Fundamental Diagram. We can start from the usual diagrams 

 for alternators, made with two scales, one for currents, and the other 

 for E.M.F.'s. 



Assuming 2= the secondary (D.C.) voltage at the terminals, let 

 e=OB (in Fig. 2) represent the primary voltage, which is substantially 

 proportional to 2, owing to the low internal resistance of the arma- 

 ture. 



Let E=OC=the E.M.F. of the alternator supplying current to 

 the converter (or the voltage of the distribution-system, according to 

 the case). Unless otherwise stated OC will be assumed constant at 

 all loads. 



