86 ELECTRICAL ENGINEERING PROBLEMS 



netizing current is 0.8 ampere, the iron loss 200 watts; ri is 0.9, 

 r 2 is 0.1; with 300 volts induced e.m.f. on the primary and 20 

 amperes in the secondary find graphically the impressed primary 

 e.m.f. and the primary current with its lag; and also the secondary 

 induced and terminal e.m.f. 's for the following cases: (a) With the 

 current lagging 15 degrees behind the induced e.m.f., (b) in phase 

 with it, and (c) leading it by 15 degrees. (26 min.) 



17. A transformer has 200 secondary and 400 primary turns; 

 iron losses, 250 watts; FI, 1.2 and r 2 , 0.35 ohm; magnetizing 

 current, 0.6; primary reactance, 2.4 ohms and secondary, 0.6. 

 With 500 volts induced e.m.f. in the primary, construct diagrams 

 for a secondary current of 20 amperes; (a) in phase with the 

 secondary terminal e.m.f., (b) lagging 30 degrees; (c) leading 30 

 degrees, relative to the terminal e.m.f. Also determine the actual 

 ratio of transformation in each case. (50 min.) 



18. The secondary induced e.m.f. of a transformer is 200 and 

 maintained constant; r" equals 0.2, x" equals 0.6, with a constant 

 current of 200 amperes. Determine the secondary terminal e.m.f. 

 for lags of 90, 60, 30 and degrees behind the induced e.m.f. and 

 leads of the same amounts. (10 min.) 



19. A 2 to 1 transformer with constant primary impressed e.m.f. 

 of 100 volts has a secondary resistance of 0.02 ohm and reactance 

 of 0.06 ohm. Neglect iron loss and reluctance and transfer the 

 primary impedance drop to the secondary winding; then determine 

 the regulations for a load of 100 amperes with lags of 0, 30, 60 

 and 75 degrees behind the revolved primary terminal e.m.f. ; also 

 for 30- and 60-degree lead, and for unity power factor of the 

 outside circuit. Lines may be used to represent the primary and 

 secondary impedance drops. (30 min.) 



20. The same as problem 19, except that the resistance is 0.06 

 ohm and the reactance 0.02 ohm. Compare the results obtained 

 with those of problem 19. (30 min.) 



21. Given a transformer designed to transform from 300 to 

 100 volts, r" = 0.1, x" = 0.2, no-load current neglected. Draw 

 diagrams for the following cases: (a) No load, and (b) a load of 

 50 amperes lagging 30 degrees behind the induced e.m.f. Under 

 (b) make both regular diagrams and revolved diagrams with all 

 resistance and reactance referred to the primary. Assume (1) 

 primary terminal e.m.f. raised to keep induced e.m.f. 's same as 

 at no load; (2) ditto to keep secondary terminal e.m.f. same as at 



