QUESTIONS AND PROBLEMS 



489 



the transformer steps up tin- voltage one to ten, what is the approximate 

 value of the secondary voltage? 



106. A 50-kv-a., 2,200/600-volt transformer has the following constants: 



Hi^li iil- r stance, 0.7 ohm; low-side resistance, 0.052 ohm; equivalent 



reactance referred to the high side, 1.7 ohms. Determine the regulation 



transformer at unity power-factor and at 0.7 power-factor, lagging 



and leading current. 



106. Determine the efficiency of the transformer of problem 10.") at '. 

 K, J^, rated, and :> 4 -kv-a. load at unity power-factor. Plot a curv 

 currrnt as abscissas. The no-load core loss is 500 watts. 



107. Repeat problem 106 for 0.8 power-factor, lagging current. 



108. The following are the data taken from open- and short-circuit teste 

 of a 10-kv-a., 2,080 208-volt, 60-cycle transformer: 



High side open, instruments on low-voltage side: 



E= 208 / = 2.8 amp. P = 124 watts 



Low side short-circuited, instruments on high side: 



E = 110 / = 6.3 P = 370 watte 



Ohmic Resistance: High side, 4.85 ohms. Low side, 0.0381 ohm. 



(a) Determine the regulation of this transformer at unity power-factor 

 and at 0.8 power factor, lagging and leading current. 



(6) Determine the transformer efficiency under each of the above 

 conditions. 



(c) What is the ratio of effective to ohmic resistance in this transformer? 



I 



150 Volts 



Fio. 109A. 



Flo. 



109. A 20-kv-a., 1,100/110-volt transformer is connected as shown in 1 IK 

 109 A so that it acte as a booster to raise the line voltage from 1,100 \ ..Its 

 to 1,210 volte. Neglecting the voltage drops in the transformer, determine: 



power received by the system; (6) the power delivered by the system; 



B power transform' . po\\er which flows through without 



mi at ion; (n if the efficiency of ti,< :ner is 97 per cent., what 



>f the entire system? In the ai.ove problem the transformer 



nte must not exceed tin- values iriven l.\ the transformer nting. 



110. Repeat problem 109 with the secondary reversed so that the ultimate 

 voltage is 990 volte. Which coil i> the primary and which is the secondary 

 under these conditions? 



111. 1 i IT in 1 11 A showsa compensator reducing the voltage from 

 150 volts to 120 volte for a 10k \\ i,..,, mdu- Indicate all tl 

 rente and all the voltages existing m the svstem. H..\\ much power is trans- 



1 and how much pawes through without transformation? Neglect 



