8 4 



SYNCHRONOUS ALTERNATORS. 



[Exp. 



Strike an arc from A as a center, with a radius o, cutting 

 the line OB at O, thus giving* OB = E T . 



20. Power Factor Less than Unity, Current in Advance. 

 This case is shown in Fig. 5. The triangle ABC is drawn as be- 

 fore, and OB is laid off making an angle with BC, so that cos 

 equals the power factor of the load. The current I, for this 

 case, is 30 in advance of ET. 



(a) Given ET = 

 by computation, 



, we find by construction = 508; or, 





Eo= . 



= V( T cos 6 + Riy+ (E T sin Xiy, 



= V(575 X .866 + 7.4) 2 + (575 X .5 233.9) 2 = 508. 



The regulation is 12 per cent. 



(b) Given ; the 

 terminal voltage ET is 

 found, as before, by 

 striking an arc from A 

 as a center, with a ra- 

 idius EO, cutting the line 

 OB at 0. 



For a leading current, 

 the terminal voltage is 



CM 



i always greater than for 

 a lagging current or for 

 unity power factor, and 

 ^ may even be equal to or 



FIG. 5. Electromotive force diagram, at greater than the no-load 

 power factor 0.866 ; current 30 in advance voltage. 



CM 0*1 



of terminal voltage. 



21. Special Case of 



Zero Pozver Factor. At zero power factor, cos = 



sn = 



* ( iga). The graphical construction for this case will usually be pre- 

 ferred ; an analytical expression for Ei, derived from the figure, is 

 ET = Vo z (XI cos ffRI sin 0) a (RI cos 9 -f XI sin 0). 



