232 ELECTRICAL ENGINEERING 



The effective value of each of the four e.m.f. 's is 



E 



141. Three-phase Alternator. If three similar windings are 

 placed on the same alternator armature displaced 120 electrical 

 degrees from one another, Fig. 199, and the ends of the windings 



FIG, 199, Three-phase alternator winding. 



are brought out to terminals, the machine is a three-phase alter- 

 nator. The e.m.f. J s generated in the three windings are dis- 

 placed 120 degrees. 



The e.m.f. in phase 1 is e\ = E sin 6, effective value E = jL ; 



v 2 



the e.m.f. in phase 2 is e z = E Q sin (6 120), effective value E = ^ ; 

 and the e.m.f. in phase 3 is e 3 = E Q sin (6 240), effective value 



: Vz' 



The windings may be interconnected in two ways. (1) Join 

 /i to s 2 , /2 to s 3 and / 3 to i, and connect the three junctions to 



ABC 



FIG. 200. Delta connection. 



the terminals A, B and C. (Fig. 200.) This is called the "delta" 

 connection or ring connection and is represented by A. 



