

GENERAL DIAGRAMS FOR SYNCHRONOUS MOTORS 189 



the particular case where the voltage must be constant, we must 

 s'= s, or =o, and the expression for i Q 2 reduces to the simple form 



which gives, substantially, 



R 



and 



Q=R . 



or, practically, XQ= 



NOTE 2. In the particular case where to=/ u , and tan 0=i, for- 

 mulas (7) and (7') will no longer apply, and they must be replaced by 

 the following formulas, deduced from Eq. (4): 



Regulation of Voltage at Terminals by Variation of the Supply 

 E.M.F. In what precedes it has been supposed that the E.M.F. E 

 of the source of current is constant at all loads. This necessitates a 

 reactive current at light loads. 



It is possible to compound or to regulate automatically the excita- 

 tion of the alternator in such manner that its E.M.F., E, will increase 

 with the load. This compounding will obviate all necessity for any 

 reactance; and the line of reference in the diagram can be the line 

 OB prolonged, if there is no other loss of voltage than that due to 

 ohmic drop. This solution is obviously the most perfect one, theoret- 

 ically, but it cannot be realized exactly otherwise than in the excep- 

 tional case where the rotary converters are supplied individually by 

 separate alternators. It is not possible otherwise to establish a 

 correlation between the load of the converters and that of the lines 

 when they supply current at the same time to other apparatus. 



An approximation to this method of regulation can be made by 

 supplying the converters with current through transformers whose 



