REGULATION OF ALTERNATORS 



309 



the point / on the short-circuit current curve is obtained. By 

 repeating the construction for any other assumed value of the 

 current it will be seen that so long as E' g lies on the linear portion 

 of the no-load characteristic, the relation between the 'short- 

 circuit current and the field-pole excitation is also linear. When 

 the field excitation is OL, giving a pressure OE on open circuit, 

 the short-circuit current will be LK. 



FIG. 128. Method of constructing curve of armature current on short-circuit. 



108. Regulation on any Power Factor. Unless the effects of 

 cross-magnetization are taken into account, it is impossible to 

 predetermine the regulation accurately when the power factor 

 differs appreciably from zero, but by the intelligent use of vector 

 quantities (involving as they do the assumption of simple 

 harmonic curves) very satisfactory results can be obtained. The 

 best method known to the author by which the load saturation 

 curve for any power factor may be drawn, without resorting to 

 flux distribution and wave-shape analysis, is that given by 

 PROFESSOR ALEXANDER GRAY/ and recently embodied in the 

 Standardization rules of the American Institute of Electrial En- 

 gineers. A. E. CLAYTON 2 has also suggested a similar method. 



X A. GRAY. "Electrical Machine Design." 

 z Electrician, vol. 73, p. 90, 1914. 



