CHAPTER IX 

 TRANSFORMERS, GENERAL 



1. A 10 to 1 transformer has the same length of turn and current 

 density in both coils. The secondary resistance is 0.01 and the 

 secondary turns are 80; required the primary resistance. With 

 110 volts and 2.2 kilowatts, given by the secondary, required the 

 primary e.m.f. and current (neglect drop and magnetizing current). 

 (1 min.) 



2. The resistance of the two coils of a transformer marked for 

 110-volts secondary are 0.3 and 0.012; if the current density and 

 length of turn are the same, for what primary voltage is the trans- 

 former designed? (1 min.) 



3. A 500-kv-a., 40,000-volt transformer with 2000-volts second- 

 ary, has 420 secondary turns; what would be the area of this 

 secondary conductor in square inches allowing 2000 circular mils 

 per ampere? Also the resistance if the mean length of a turn is 

 9.5 feet and the resistance of a circular-mil-foot be taken as 12.5? 

 Also required the primary turns, current and resistances with same 

 current density and length of turn in the two coils. (5 min.) 



4. In problem 2, if 2% drop, no load to full load is permitted, 

 what kilowatt output would be obtained (neglect leakage)? What 

 primary e.m.f. necessary for 110 volts on the secondary, at full 

 load? (3 min.) 



5. A 3-kv-a., 10 to 1 transformer giving 110 volts on the 

 secondary and having equal primary and secondary losses has 

 a regulation of 2%; what must be the resistance of each coil and 

 what is the drop in each? Neglect magnetic leakage and hence 

 the reactance of the coils. (3 min.) 



6. A transformer has two primary coils each of 900 turns and 

 two secondaries, each of 90 turns; with the former in series the 

 transformer is suitable for use on a 2200-volt system; for what 

 other e.m.f. can the primary coils be connected, and what secondary 

 e.m.f. 's can be obtained in each case? (1 min.) 



7. A transformer has 2 secondary coils made up each of 48 

 turns of No. 8 wire, the length of the turn being 2 ft. and the 



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