TWELVE-PHASE CONVERTER 



253 



148. Twelve- phase Converter 



For the purpose of operating a twelve-phase converter from 

 three-phase transformers, the arrangement recently patented by 

 A. D. Lunt, of Schenectady, N.Y., may be used.* This is shown 

 diagrammatically in Figs. 155 (a) and (b). The armature winding 

 is, as before, represented by a circle, and the points of connection 

 to the twelve slip-rings are marked A, D, C', etc. It will be noticed 

 that the voltages corresponding to the nine dotted lines in the diagram 

 fall into three groups, such that those corresponding to any one group 

 (e.g. AB, FK, A'B', which are all represented by parallel lines) are 



' * * 



w 



FIG. 155. Connections of Twelve-phase Converter. 



all derivable from secondaries of the same transformer; hence all 

 the nine voltages may be supplied by means of only three transformers, 

 each transformer having three distinct secondary windings, as shown 

 in Fig. 155 (&). The two groups ABC and A'B'C' of secondary 

 windings are arranged precisely as for a six-phase converter, and 

 are mesh-connected. Each of these groups contains the same 

 number of turns. The third set of windings, DG, FK, and HE, 

 Fig. 155 (6), consists of coils having a larger number of turns than 



the coils of the other two groups, in the ratio of -rt and these 



* Western Electrician, vol. xxxv. p. 306 (1904). 



t For a sine wave of magnetic flux distribution. >. = -7= = 1-155. 



At/ V 



