234 ELECTRICAL ENGINEERING 



its maximum value is Vs E and its effective value is 



Similarly the e.m.f. between B and C is 



e BC = e 2 - e 3 = EQ {sin (0 - 120) - sin (0 - 240) j 



= \/3 # sin (0 - 90) . (235) 



of maximum value V3 E and effective value Vs #. 



ABC 



FIG. 201. Star or "Y" connection. 



The e.m.f. between C and A is 



CCA = e 3 - i = EQ {sin (0 - 240) - sin 0\ 



= V 3 E Q sin (0 + 150) (236) 



of maximum value A/3 E Q and effective value A/3 E. 



Thus the three e.m.f. 's between terminals are equal to one 

 another and are displaced in phase by 120 degrees. 



A fourth terminal is usually connected to the neutral point 

 and it may be grounded. 



If a third harmonic exists in the e.m.f. wave of each phase it 



will not appear in the e.m.f. between terminals in the "Y" con- 



A,. 



FIG. 202. Grounded neutrals. 



nection since this e.m.f. is the difference of two e.m.f. 's at 120 

 degrees to one another or the sum of two e.m.f. 's at 60 degrees, 

 the third harmonics will be combined at 3 X 60 = 180 and will 



