CHAPTER XII. 



PROBLEMS. 



Many who are efficient in carrying out standardized experi- 

 ments are not so efficient in carrying out experiments for which 

 no instructions are given. It is very important to possess such 

 ability and it can be acquired only by attacking problems which 

 demand initiative and responsibility. 



It is futile to prepare a schedule of problems of this sort with 

 any expectation of its being adequate or complete; some of the 

 problems here given, however, may prove useful or suggestive. 



Various reference books and periodicals should be consulted 

 in most cases before proceeding with experimental work. A 

 familiarity with original sources and the ability to give proper 

 weight to different authorities is highly desirable. 



i. Given an over-compounded D.C. generator. Determine a shunt 

 to go in parallel with the series coils to produce a definite regulation 

 (as flat compounded or, say, 5 per cent, over compounded) for a cer- 

 tain speed and voltage. Determine how the result would be affected, 

 and the cause for it, if the generator is operated at the same speed, 

 but at a different voltage (say 100 instead of 125 volts) ; or at the 

 same voltage but different speed. If the source of power is an induc- 

 tion motor, how will its slip enter into the problem? 



2. Determine the relation between electromotive force and speed 

 in a separately excited generator and in a self-excited shunt generator. 



3. Determine the relation between line voltage and speed in a 

 shunt motor. 



4. Operate two D.C. generators in parallel, first as shunt and then 

 as compound machines, and ascertain how any desired division of the 

 load is obtained. In the case of compound generators, an equalizing 

 bus-bar is necessary connecting the two brushes (one on each 

 machine) to which the series coils are connected. 



5. Explore the field of a dynamo-electric machine by determining 

 the distribution of the flux in the air gap. 



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