Or/:>77o.Y> J.V7) PROBLEMS 



the speed field produce a rotating magnetic field? How does this in part 

 explain the operation of the single-pha.se induction mot 



12. What is the approximate ratio of weights of single-phase to poly- 

 phase induction motors of the same ratings? How may a three-phase 

 induction motor be operated single-phase? What is often the cause of a 

 polyphase motor over-heating when carrying its normal load? 



13. Describe the manner in which the initial starting torque of a single- 

 phase motor may be obtained by splitting the phase. What is the order of 

 magnitude of this starting torque? Show how the phase may be split by 

 the use of resistance and induct he use of resistance and capacitance. 



14. Discuss the operation of the "shaded-pole" as a method of starting 

 single-phase motors. How is the repulsion motor principle utilized ii. 



ing the Wagner Single-Phase Induction Motor? What operation converts 

 the motor from a repulsion motor to an induction motor? 



15. Upon what principle does the phase converter operate? What 

 advantage is derived by its use on railway locomotives? Make a diagram 

 of connections showing how the single-phase power received at high voltage 

 from the trolley is converted into low voltage three-phase power for use in 

 the motors of the railway locomotive. 



16. Make a diagram of connections showing the relation of field windings 

 to armature, etc., in the General-Electric Repulsion-Induction Motor. 

 How is this motor reversed? 



17. What unique feature is embodied in the armature of th? Wagner, typo 

 BK motor? What excellent operating characteristics are claimed for this 

 motor? 



QUESTIONS ON CHAPTER X 



1. Compare the design of the alternator with that of the synchronous 



motor. 



2. Show that at standstill the average torque of the singlo-pha- 

 chronous motor is zero and that in order to develop a continuous torque 

 either the moving conductor or the moving pole must cover a di.-tance equal 

 to one pole pitch every half cycle. What is the relation between speed, 

 frequency and number of jM)le8? 



3. What reaction occurs in the direct-current shunt motor which enables 

 it to take more current when additional load is applied? Show that the 



<n in the synchronous motor under similar condition- cannot be 

 exact! e as that of the -hunt motor. 



4. \\ t reaction which occur- \\lien load is applied to any 



'.' What resulting reaction follows in the case of the .yiichnnus 

 he current taken by a synchronous motor \\hen the 



angul of the rotor i> -Imhtlv retarded, is nio-tl\ MMTpf urrenf. 



6. What are tl hich follow an increa.se of tin n f a 



1:1' motor'.' Why cannot then reactions occur in a ayn- 

 chronou- mot 



6. \\ ut the syi 



ised abov 

 ire voltage can be numerically greater than the terminal voltage. 



