THE TRANSFORMER. 



227 



the required electromotive force E r Similarly, the electromo- 

 tive forces E 2 and E y Fig. 193, may be produced each by a 

 pair of properly proportioned secondary coils. Therefore, the 

 two-phase three-phase transformer consists of two transformers with 

 their primary coils supplied from the two-phase system, and having, 

 in general, six secondary coils which are connected in pairs in series, 

 each pair supplying one of the three-phase voltages. Such an 

 arrangement can be used to change from two-phase to three-phase 

 or to change from three-phase to two-phase. 



The Scott transformer. The general type of two-phase three- 

 phase transformer above described may be greatly simplified, 

 and the simplest arrangement is that due to Chas. F. Scott. 



P 



/ \ 



Fig. 195. 



Fig. 196. 



To understand the Scott transformer it is necessary to consider 

 an even more general type of two-phase three-phase transformer 

 than that described above, and to make use of the following propo- 

 sition : Consider three units of any kind, alternators, or combina- 

 tions of transformer secondaries, a b and c, which are Y-con- 

 nected to three mains I, 2 and 3, as shown in Fig. 195 ; if the 

 lines a, b and c, Fig. 196, which represent the electromotive 



