112 SYNCHRONOUS HONORS 



ing having taps connected to contacts, over which moves the switch 6. 

 The two ends, A, B, of the winding are connected to the source of 

 current-supply, while the motor is connected to the end B and the 

 switch b. 



The winding operates like a potentiometer by which any fraction 

 whatever of voltage can be obtained at will. At the beginning, very 

 low voltage is obtained by placing the switch handle to the right-hand 

 side. The handle is then moved gradually toward the left in pro- 

 portion as the speed increases, and gradually raising the voltage applied 

 to the motor, while reducing the current consumed by it. The 

 current /i taken from the supply-source is a fraction of the current 

 12, consumed by the motor, which is represented by the inverse ratio 

 of voltages 



The winding of the transformer is traversed by the current /i, 

 between A and D, and by the current I^Ii, between D and B. 



In the case of polyphase apparatus it is sufficient to install as many 

 transformers with commutating switches as there are phases. All 

 the levers of these switches are operated by one handle. An arrange- 

 ment of this kind was utilized with polyphase current in the power- 

 transmission installed for Messrs. Menier, at Noisiel in 1893 (Power- 

 Transmission to Noisiel, Lumiere Electrique, May, 20, 1894). 



Starting of Single-Phase Machines. These machines can also be 

 started by the first two methods, i.e., by means of an auxiliary D.C. 

 motor, or by a small induction-motor which starts by means of an 

 auxiliary phase such as, for example, " shaded pole " single-phase 

 motors. It is desirable to be able to increase the speed of the machine 

 gradually while keeping constant the speed of the small auxiliary motor, 

 because the latter would be stalled if it were made to slow-up. To 

 overcome this difficulty the motor is mounted on guides, and it transmits 

 power to the larger machine by means of a friction-cone bearing 

 against a large disk mounted on the shaft of the machine itself. The 

 motor is gradually shifted on the guides in such manner that the fric- 

 tion-cone approaches the center of the disk until the moment when 

 synchronism is attained. 



The starting of the machine as an induction -mo tor is more difficult, 

 but it can be accomplished by transforming temporarily the armature 

 into a two-phase armature, by means of a second winding suitably 





