APPENDIX B. 



14. The split-pole rotary converter.* The discussion of the 

 electromotive force relations of the synchronous converter in Art. 

 90 of Chapter IX is based on the assumption that the direct- 

 current brushes of the machine are fixed permanently in the neu- 

 tral axis. Under these conditions, the voltage ratio of a rotary 

 converter is very nearly fixed in value as shown in the table on 

 page 184. A possible method for controlling the voltage be- 

 tween the direct-current brushes of a rotary converter (with un- 

 varying voltage between the alternating-current terminals of the 

 machine) would be to shift the direct-current brushes from the 

 neutral axis. In this way the voltage between the direct-current 

 brushes could be reduced from its normal value, as given in the 

 table on page 184, to zero. This method of voltage control is, 

 however, impracticable because of the sparking which is pro- 

 duced at the direct-current brushes when the brushes are shifted 

 from the neutral axis. To overcome this difficulty Mr. J. L. 

 Woodbridge has proposed the split-pole converter in which each 

 field pole is split into two (or three) parts. One of these parts is 

 permanently excited and it produces the fringe of field which is 

 necessary for sparkless reversal, as explained on page 162 of the 

 first volume of this text. The other portion (or portions) of each 

 pole piece is arranged so that its excitation may be increased or 

 decreased at will, thus shifting the resultant axis of the field with 

 respect to the stationary direct-current brushes. The result is 

 equivalent to the shifting of the direct-current brushes in so far as 

 the voltage relations of the converter are concerned. This type 

 of rotary converter is manufactured by the General Electric 

 Company. 



* See paper by Comfort A. Adams, Proceedings of Am. Inst. Elec. Eng. , June, 

 1908, pp. 899-925. 



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