PHASE TKANSFOKMEKS. 



173 



proportional to the ratio of one-third of the whole number of turns 

 to the number of turns between the tappings corresponding to one 

 phase of the secondary. 



A method of transforming from di-phase to tri-phase currents 

 was subsequently given by Mr. C. F. Scott, of the Westinghouse 

 Company, by the use of two specially wound transformers, as 

 depicted in Fig. 73. 



FIG. 73. 



The primaries of the transformers are connected to the terminals 

 of a di-phase generator. In the transformers used by Mr. Scott, 

 one secondary CB was made equal to 100 turns, and was tapped 

 at its middle point, giving 50 turns on each side. The other 

 secondary had 87 turns (= 50\/3). One end of it was connected 

 with the middle point of the secondary of the first transformer, 

 and the three free terminals then A, B, C, gave tri-phase E.M.F.s. 



The methods given above do not include the most important 

 case from a practical point of view, viz. that of transforming mono- 

 phase currents to di-phase or tri-phase. Although methods of 

 achieving this have been theoretically propounded, they do not 

 seem to have been realized in practice by any stationary trans- 

 former. 



BOTARY CONVERTERS. 



118. A rotary converter is a machine with but one armature 

 winding, .which transforms alternating currents of any number of 

 phases into continuous current, or vice versa. 



This definition excludes such combinations as alternating- 

 current motors coupled to direct-current generators, which are 

 called Motor Generators. 



