TRANSFORMERS 17 



side is 0.202 ohm. Assume that the leakage reactances of the 

 windings vary as the square of the number of turns in them. 



(a) If the high-tension winding of the regular transformer has 

 186 turns how many turns are there in each of the other windings 

 of the regular and auto- transformer? 



(b) The regular transformer is rated to deliver 25 kw. at 110 

 volts. If the losses at full load are the same for both transformers 

 what is the kilovolt-ampere rating of the auto-transformer? 



(c) What is the regulation and efficiency of each transformer 

 when it is delivering its rated fulHoad current at 0.83 power fac- 

 tor and its rated voltage? 



80. Two transformers, one connected as a regular, and the 

 other as an auto-transformer, have identical magnetic cores and 

 the same amount of copper in their windings. Each of these 

 transformers gives a ratio of transformation of 550:220 volts and 

 the windings are so designed that the volts per turn are the same 

 for each. With 25 volts impressed on the high-tension winding 

 of the regular transformer and with the low- tension winding 

 short circuited the current and power are 91 amperes and 665 

 watts. At the rated voltage the core loss in the regular trans- 

 former is 641 watts. Assume that the resistances and leakage 

 reactances of all of the windings vary as the square of the number 

 of turns in them. 



(a) The regular transformer is rated to deliver 50 kv.-a. at 

 220 volts. If the losses at full load are the same for both 

 transformers, what is the kilovolt-ampere rating of the auto- 

 transformer? 



(b) What are the regulation and efficiency of each transformer 

 when it is delivering its rated full-load power at 0.9 power fa< t.i ' 



81. Two transformers, one connected as a regular and tin- 

 other as an auto-transformer, have identical magnetic cores and 

 the same amount of copper in their windings. Each of these 

 transformers gives a ratio of transformation of 440:110 v>h<. 

 and the windings are so designed that the volts per turn are tin- 

 Bame for each. With 14 volts impressed on the high-tni-inn 

 winding of the regular transformer and with the low-im-inn wind- 

 ing short circuited the current is 227 amperes and the pm\< T i< 

 1004 watts. The core loss of this transform, i MI rated impreed 

 voltage is 1010 watts. Assume that the resistances and leakage 

 reactances of all of the windings vary as the square of the mimlu r 

 of turns in tln-m. 



