TRANSFORMERS 21 



The ratios of transformation are slightly different. These 

 transformers take a combined power of 960 kw. at 0.92 power 

 factor from a 12,800-volt circuit. 



(a) What is the current in each transformer? 



(b) If the ratios of transformation are made equal by removing 

 a few turns from the high-tension winding of the shell-type trans- 

 former what is the current taken by each transformer for this 

 load? Assume that the short-circuit data would be unchanged. 



92. Consider the transformers described in problem 82. 

 They are operating in parallel on both the high- and low-tension 

 sides. What are the least values of resistance and reactance that 

 should be added to each transformer on the low-tension side in 

 order that the currents supplied by the transformers shall be in 

 phase and in proportion to their capacities? 



(b) For a given load on the transformers compare the total 

 heating in the transformers and reactors with that in the trans- 

 formers alone before the addition of the reactors. 



93. Consider the transformers described in problem 83. 

 They are operating in parallel on both the high- and low-tension 

 sides. 



(a) Compare the sum of their rated outputs with the kilovolt- 

 ampere load they can deliver without overloading either of them. 



(b) A reactor of negligible resistance is added on the low- 

 tension side of one transformer of such a value that the resultant 

 impedance volts of the transformer and reactor on short circuit 

 with full-load current is the same as that of the other transformer 

 alone when it also carries full-load current. What is the imped- 

 ance of this reactor? By what amount can the combined output 

 of the transformers be increased by the addition of this reactor 

 without overloading either transformer'.' 



94. ('nn-iilrr the transformers described in problem 84. 

 They are operating in parallel on both the high- and low-ten-ion 

 sides. 



(a) ( 'mil pa re the sum of their rated outputs with the greatest 

 kilovolt-ampere load they can deliver wit limit overloading either 

 of them. 



(b) A reactor of negligible resistance is added on the low-ten- 

 sion side of one transform- r of such a value that the resultant 

 impedance volts of the transformer and reactor on short circuit 

 wit h full-load current is t he same as that of the other transformer 

 alone when it also carries full-load current. What is the imped- 



