AND PROBLEM* 17!) 



12. Why is it necessary to brace very strongly the coil ends in alternators 

 of large capacity'.' 



13. Sketch the shape of two common types of alternator slot. State the 

 advantages and disadvantages of each type. 



14. Show that with large units, even when operating at very high efficiency, 

 the amount of energy to be dissipated per minute is very large. What 

 method is used to carry the resulting heat away from the machine? 



15. Into how many classes are the rotating-field structures of alternators 

 divided? Give reasons why different designs of field structure are neces- 

 sary. What is the general construction of the field cores in all types of 

 salient-pole alternators? How are these field cores held in position? 



16. Describe the field spiders for (a) very slow-speed machines of large 

 rapacity; (6) moderately high-speed water-wheel generators. Why is it 



-si Me to use salient poles in high-speed turbo-alternators? 



17. Describe the construction of (a) the parallel-slot type of rotor; 

 (6) the radial-slot type of rotor. Why must the end-flanges be of non- 

 magnetic material? Under what conditions are these types of rotor used? 



18. Describe the method of conducting the field current into the field 

 winding. What different methods are used for supplying excitation? 

 What precautions are often taken to insure continuity of excitation? 



19. Derive from a fundamental relation the equation of the induced 

 electromotive force in an alternator. What is meant by "breadth factor" 

 and "pitch factor"? 



20. What relation exists between the flux distribution and the shape of 

 the electromotive force wave per conductor? How may the shape of the 

 actual electromotive force wave of a generator be made nearly sinusoidal 

 even though the electromotive force wave in the individual conductors 

 differs considerably from a sine wave? 



21. Sketch the flux distribution curve for a distributed field winding. 

 Kxplain why such machines usually have a better wave shape than machines 

 of the salient-pole type. 



22. State the procedure in phasing out the coils of a three-phase alter- 

 r so that they may be Y-connected. 



23. Repeat for a machine which is to be delta-connected. 



24. I'INHI what factors does the rating of an alternator depend'.' Why 

 is a kilovolt-ampere rating more rational than a kilowatt rating? Upon 

 which rating does the rating of the prime mover depend'.' 



PROBLEMS ON CHAPTER V 



66. Draw a single-phase, full-pitch, four-pole lap winding in which 

 ire four slots per pole and the winding and slots occupy only 60 per 



66. Kepe.-it problei: wave winding. 



67. Draw a single-phase, single-range, spiral winding for an armature 

 having eight ^lote per pole, t he winding oeeup\ ing l-ut i\ of 1 hcae slot*. 



68. Draw a two-phase, chain winding for a six-pole alternator having 1'J 

 slots per pole, utih/.ing all the slote. 



