SYNCHRONOUS MACHINERY 235 



therefore neutralize one another. If, however, the neutral is 

 connected to ground at both the generator and receiver end, as 

 shown in Fig. 202, a third harmonic of current may flow in the 

 neutral supplied from the three phases. 



Alternators should, whenever possible, be connected in "Y" 

 instead of "A" to reduce the danger of circulating currents. 



142. E.M.F.'s, Currents and Power in Three-phase Circuits. 

 Fig. 203 shows a " A "-connected three-phase system. 



FIG. 203. 

 The e.m.f. in phase 1 is 



e\ = EQ sin 0, effective value E\ = ~= \ 



v2 



the e.m.f. in phase 2 is 



E 



e 2 = EQ sin (0 120), effective value E 2 = ^ J 



V2 



the e.m.f. in phase 3 is 



e 3 = EQ sin (0 - 240), effective value # 3 



V2 



The effective values of the e.m.f. 's in the three phases are equal 

 and are the terminal e.m.fs. of the alternator or the e.m.fs. between 

 lines, 



*~ 3 " Vl* 



The current in phase 1 is 



ii = IQ sin (0 0), effective value /i = =; 



V2 



the current in phase 2 is 



i z = IQ sin (0 0120), effective value 7 2 = 



/o . 



/- 



V2 



the current in phase 3 is 



iz = IQ sin (0 240), effective value 7 3 = 



/o 



