TRANSFORMERS 1 1 



the iron loss in watts per cubic inch for transformer No. H? 

 (c) What are the maximum flux density, the permeability, and 

 the iron loss in watts per cubic inch for transformer No. I ? 



48. A 100-kv.-a., 1 1 ,000 : 2200-volt, 60-cycle transformer has 

 primary and secondary resistances of 6.0 ohms and 0.24 ohm 

 respectively, and primary and secondary leakage reactances of 

 16 ohms and 0.64 ohm respectively. What is the maximum per- 

 centage change that can occur in the mutual flux from no-load to 

 full-load current? At what power factor would this occur? 

 Neglect the no-load current. 



49. A 500-kv.-a., 11,000 : 2300-volt, 60-cycle transformer has 

 primary and secondary resistances of 0.81 ohm and 0.0358 ohm 

 respectively, and primary and secondary leakage reactances of 

 3.7 ohm and 0.162 ohm respectively. With the low-tension wind- 

 ing short circuited what voltage should be impressed on the high- 

 tension winding so that the current will have its full-load value? 

 Neglect the no-load current. 



50. A 7.5-kv.-a., 2080 : 208-volt, 60-cycle transformer has the 

 following constants: 



ri = 7.53 ohms Zi = 14.2ohms 



r 2 = 0.0662 ohm z 2 = 0.l28 ohm 



Th<- core loss with 208 volts impressed on the secondary is 200 



watts. Neglect the exciting current, (a) What is the regula- 



tion of this transformer for full-load current at 0.8 power factor? 



b What is the efficiency of the transformer for this load? 



51. A 50-kv.-a., 30,000 : 440-volt, 50-cycle transformer has the 

 following constants: 



r l = 120 ohms .r, =428 ohms 



r, = 0.02r>s ohm x 2 = 0.092 ohm 



The iron loss at the rated voltage is 641 watts. Neglect the 

 exciting current, (a) What is the regulation of this fcnilS- 

 r a load of 40 kw., at 0.75 power factor? (b) What is 

 the efficiency of the Iran-former for thU load? 



52. A 500-kv.-a., 13,200 : 425- volt, 25-cycle transformer ha- 

 primary and x-condary resistances of 1.6 ohms and O.OOHili ohm 



tivrly, and primary and secondary leakage reactam 

 14.5 ohms and 0.0151 ohm respectively. At no load with 425 

 volts impressed on the low-tension winding the power 

 kw. and the kilovolt-amperes are 16.0. Neglect any change in 



