14 PROBLEMS IN ALTERNATING CURRENT MACHINERY 



64. The resistance of the high-tension winding (a-c) see Fig. 

 1 of a 50-kv.-a., 440 : 110-volt auto-transformer is 0.02156 ohm 

 and that of low-tension winding (b-c) is 0.00216 ohm. The 

 leakage reactance of the winding (a-b) is 0.068 and that of the 

 low-tension winding is 0.00756 ohm. If the high-tension winding 

 is short-circuited, what voltage should be impressed on the low- 

 tension winding in order that there will be full-load current in 

 the windings? What power would be supplied? 



65. Calculate the regulation of the auto-transformer described 

 in problem 63 for a load of 22 kw. at 0.80 power factor on the 

 low-tension side. If the core loss at the rated voltage is 288 

 watts what is the efficiency of the transformer at this load? 



66. Calculate the regulation of the auto-transformer described 

 in problem 64 for a load of 46 kw. at 0.87 power factor on the 

 low-tension side. If the core loss is 512 watts at the rated 

 voltage what is the efficiency of the transformer at this load? 



AUTO-TRANSFORMER DATA 



67. Calculate the regulation of the auto-transformer No. A for 

 a load of 10 kw. at unit power factor on the low-tension side. 

 What is the efficiency of the transformer at this load? 



68. Calculate the regulation of the auto -transformer No. B 

 for a load of 16 kw. at 0.78 power factor on the high-tension side. 

 What is the efficiency of the transformer at this load? 



69. Calculate the regulation of the auto-transformer No. C 

 for a load of 22 kw. at 0.80 power factor on the high-tension 

 side. What is the efficiency of the transformer at this load? 



70. Calculate the regulation of the auto-transformer No. D. 

 for a load of 55 kw. at unit power factor on the low-tension side. 

 What is the efficiency of the transformer at this load? 



71. Calculate the regulation of the auto-transformer No. E 

 for a load of 93 kw. at 0.87 power factor on the low-tension side. 

 What is the efficiency of the transformer at this load? 



1 The low-tension winding is short-circuited and voltage is applied to the 

 high-tension winding so that there is full-load current in the windings. 



