224 



ELEMENTS OF ELECTRICAL ENGINEERING. 



A and B, the magnetic circuits of both being completed through 

 the portion c of the core. When used* for two-phase step-up 

 or step-down transformation, transformer A is used for one phase 

 and transformer B for the other phase. In this case the magnetic 

 flux in core a as in phase-quadrature with the magnetic flux in 

 core b, and the return flux in core c is related to the fluxes in 

 a and b as shown in the clock diagram in Fig. 1 90. 



Fig. 189. 



Fig. 190. 



Fig. 192. 



Figure 191 shows what may be called a three-phase trans- 

 former. It consists of three similar transformers A, B and C, 

 with a single core-structure as shown. When used for three- 

 phase step- up or step-down transformation, transformer A is 

 used for one phase, transformer B for another phase, and trans- 

 the third phase. In this case the magnetic fluxes 

 , b and c are 1 20 apart in phase, as shown in the clock 

 of fluxes, Fig. 192, and each core may be looked upon as 

 path for the flux in the other two. 



