M 2 PHASE CHANGERS, ETC. [Hxr. 



pulsating into a non-pulsating transmission of power, or vice 

 versa. 



It is accordingly not possible, by means of transformers, to 

 draw single-phase current from a polyphase system and draw 

 from the several phases equally, so that the flow of energy is 

 non-pulsating. To accomplish such a transformation, use is 

 made of a motor-generator* consisting of a polyphase motor 

 driving a single-phase generator. The moving parts act as a 

 flywheel, storing and restoring kinetic energy, thus accounting 

 for the momentary difference between the pulsating output and 

 non-pulsating input of electric energy. This method is advo- 

 cated for running single-phase railway feeders from a polyphase 

 transmission line. 



3. Single-phase to Polyphase Transformation not Possible. 

 It is likewise not possible, by means of transformers, to change 

 a single-phase into a balanced polyphase system. This too can 

 be done by means of a motor-generator, or by running a poly- 

 phase induction motor on a single-phase circuit, a 2-phase or a 

 3-phase motor giving 2-phase or 3-phase currents. Various sta- 

 tionary phase-splitting devices will give difference in phase suffi- 

 cient for starting induction motors on single-phase circuits, but 

 such devices cannot give balanced polyphase currents. 



4. Polyphase Transformation Possible. It is possible, how- 

 ever, by various arrangements! of transformers to change from 

 one balanced polyphase system to any other balanced polyphase 

 system, the flow of energy in each system being uniform. This 

 is termed polyphase transformation and its study is the object 

 of this experiment. The various methods of polyphase trans- 

 formation are similar in principle, use being made of the fact$ 



* Such a motor-generator has been installed in the chemical laboratory 

 of Cornell University to supply 2,000 or 3,000 amperes of single-phase 

 current for the electric furnace. 



t(4a). Two transformers, only, are necessary; but more than two 

 are used in some arrangements, as Fig. 4. 



$ Fully discussed in Exp. 6-A. 



