PROBLEMS ON TRANSFORMERS. 125 



PROBLEMS ON CHAPTER XII. 



1. Calculate the lengths, cross-sections, and resistances of the primary and 

 secondary windings of a transformer whose output is 50 kilowatts, the trans- 

 formation ratio being 2000 to 100 volts, the copper losses 1*25 per cent, of the 

 output, and the current density being 150 amperes per square centimetre. 



Answers. ^ = 52,188 cms. ; ff l 0'167 sq. cm. ; r l = 0*5 ohm 



l z = 26,039 cms. ; <r 2 = 3-333 sq. cms. ; r 2 = 0-00125 ohm 



2. If the frequency is 50 cycles per second, and the induction 3500 lines 

 per square centimetre, and the rest being the same as in Question 1, complete 

 the design as a transformer of the Mordey type, and calculate the full-load 

 efficiency. 



3. Calculate the lengths, cross-sections, and resistances of the primary and 

 secondary windings of a transformer whose output is 10 kilowatts, the transfor- 

 mation ratio being 500 to 200 volts, the copper loss 4 per cent, of the output, 

 and the current density being 150 amperes per square centimetre. 



Answer. 7 t = 41,667 cms. ; <r 1 = 0'133 sq. cm. ; r t = 0'5 ohm 

 1 2 = 16,667 cms. ; <r. 2 = 0'333 sq. cm. ; r 2 = 0'08 ohm 



4. If the frequency is 80 cycles per second, and the induction 4000 lines 

 per square centimetre, and the rest the same as in Question 3, what is the total 

 weight of the transformer, the iron losses being 5 per cent, of the output, and 

 the thickness of the stampings 15 mils.? 



Ansiuer. 913 Ibs. 



