98 PROBLEMS IN ALTERNATING CURRENT MACHINERY 



copper loss, (d) Calculate the relative outputs when both are 

 operating at 0.7 power factor. 



36. A 5-kilowatt single-phase rotary converter supplies power 

 on the direct-current side at 110 volts. It receives energy on the 

 alternating-current side through a transformer from a 2200-volt 

 circuit. What should be the transformer's ratio of transforma- 

 tion? If the rotary has an efficiency of 85 per cent, what should 

 be the current rating of the high-tension winding of the trans- 

 former? 



37. A 100-kilowatt, 4-phase rotary converter supplies power 

 on the direct-current side at 230 volts. It receives energy on 

 the alternating-current side through two single-phase trans- 

 formers from a 2-phase circuit. The voltage between adjacent 

 high-tension conductors is 1555 volts, and between alternate 

 conductors is 2200 volts. The high-tension windings of the 

 transformers are connected across the 2200-volt lines and the 

 low-tension windings are connected in star with the neutral 

 point grounded. The efficiency of the rotary at full load and 

 unit power factor is 94 per cent. What should be the full-load 

 current and voltage ratings of the high- and low-tension windings 

 of the transformers? 



38. A 4-phase, 50-kilowatt rotary converter supplies power on 

 the direct-current side at 220 volts. It receives energy on the 

 alternating-current side from a 2-phase line through two 

 single-phase transformers which have double primary and 

 secondary windings. The voltage between the adjacent high- 

 tension conductors is 1625 volts and between alternate conduc- 

 tors is 2300 volts. The high-tension windings of the transform- 

 ers are connected in star and the low-tension windings in mesh. 

 The efficiency of the rotary at full-load output and 0.90 power 

 factor is 90.2 per cent. What are the primary and secondary 

 currents and voltages when the rotary delivers its rated load at 

 0.90 power factor? 



39. A 4-phase 100-kilowatt rotary converter delivers power 

 on the direct-current side at 220 volts. It receives energy from 

 a three-phase, 11,000-volt circuit through Scott-connected trans- 

 formers. The low-tension windings are connected in star. The 

 efficiency of the rotary at full load and unit power factor is 92.5 

 per cent. What are the ratios of transformation of each of the 

 transformers? What are the full-load current ratings of the 

 primary and secondary windings of each transformer? 



