230 



ELECTRICAL ENGINEERING 



The form factor of a rectangular wave is 1.00 and for all other 

 waves is greater than 1.00. For a sine wave the form factor is 



E 



^ = V2 



i TV rn 



2V2 



1.11. 



140. Two-phase or Quarter-phase Alternator. When two 

 similar single-phase windings are placed on an armature spaced 

 at 90 electrical degrees to one another the winding is called a 

 two-phase winding and two e.m.f. 's are generated displaced in 

 phase by 90 degrees. Fig. 195 shows a two-phase winding. 



A B C D 



FIG. 195. Two-phase alternator winding. 



Phase 1 starts at Si and ends at /i and phase 2 starts at s^ and 

 ends at /2. 



The e.m.f. generated in phase 1 is 



T7 



e\ = EQ sin 0, effective value E = 



the e.m.f. generated in phase 2 is 



e 2 = EQ sin (0 90), effective value E = ^ 5 



and they are represented by the two waves or the two vectors in 

 Fig. 196. 



The two windings are usually entirely separate and their ends 

 are brought out to four terminals A, B, C, D. 



If any two terminals as B and C are joined the e.m.f. between 

 A and D is 



= ei - e 2 = E Q sin - EQ sin (0 - 90) 



= EQ (sin + cos 0) 



= V2# sin (0 + 45), (233) 



