TRANSFORMERS, GENERAL 



83 



are to be plotted directly from inspection of the projections of the 

 "T" vectors. (12 min.) 



38. Two 1100- to 110- volt transformers of the usual type and 

 operated on a 1100-volt, 2-phase line can have the secondaries 

 connected in two different ways to produce unbalanced 3-phase 

 systems in which two of the e.m.f.'s are equal. By revolution of 

 tihe appropriate diagrams, construct the e.m.f. curves for these 

 two cases. (30 min.) 



39. The hysteresis curve of a sample of steel containing 0.184% 

 silicon is given by the following points: 



If a transformer is built of this steel having a maximum density 

 of 11,500, a length of magnetic circuit of 50 centimeters and 100 

 primary turns; also if the impressed e.m.f. is a sine curve; plot the 

 curves of primary current for no load and for a non-inductive load 

 of 10 amperes. (30 min.) 



40. On the no-load test of a transformer; the voltmeter is con- 

 nected inside of the ammeter and takes 0.05 ampere. The test 

 shows 20 watts iron and instrument loss and the e.m.f. is 100; find 

 the magnetizing current if the current read on the ammeter is 

 3 amperes. (5 min.) 



41. Construct the sine waves for the component 3-phase parts 

 of the 2-phase e.m.f. 's obtained by the connection described in 

 problem 35 and by combining these derive the 2-phase sine curves. 

 The 3-phase e.m.f. 's are each 100 volts. (30 min.) 



