100 PROBLEMS IN ALTERNATING CURRENT MACHINERY 



three single-phase transformers from a three-phase, 13,200- 

 volt transmission line. The transformers are connected in Y on 

 the high-tension side and diametrically on the low-tension side. 

 In order to maintain a constant line voltage of 13,200 volts at the 

 substation the rotary is over-compounded so that when delivering 

 15 per cent, overload current at 650 volts it operates at 0.85 power 

 factor with an efficiency of 92.7 per cent. What is the ratio of 

 transformation for each transformer? What should be the 

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

 the transformers? 



46. A six-phase, 1000-kw., rotary converter receives power 

 through three transformers from a three-phase, 11,000-volt circuit. 

 The rotary delivers power at 650 volts to a railway system. The 

 transformers are connected in Y on the high-tension and in double 

 delta on the low-tension side. What should be the current and 

 voltage ratings and the ratio of transformation for each of these 

 transformers? In determining the rating neglect the losses. 



47. A 6-phase, 2000-kw., rotary converter receives power from 

 a 3-phase, 13,000-volt transmission line. The transformers are 

 connected in delta on the high-tension and in double Y on the 

 low-tension side. The rotary delivers power at 650 volts to a 

 railway system. It has an overload current capacity of 20 per 

 cent, and an efficiency of 92.8 per cent, when delivering this load 

 and operating at 0.85 power factor. What should be the over- 

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

 windings of the transformers? What should be their ratio of 

 transformation? 



48. A 12-phase, 3000-kw., 650-volt rotating converter receives 

 power from a three-phase transmission line through three single- 

 phase transformers, whose high-tension windings are connected 

 in Y and whose low-tension windings are connected in double 

 chord. The high-tension line voltage is 22,000 volts. Neglect- 

 ing the losses what should be the current and voltage ratings of 

 the high- and low-tension windings of the transformers? 



49. l A 6-phase, 25-cycle, 600-volt rotary converter has an 

 efficiency of 92.5 per cent, when delivering 750 kw. and operating 

 at 0.90 power factor. The armature winding has 4 inductors 



1 In calculating the armature reaction do not neglect the distribution of 

 the winding, and assume that the constant usually given as 0.707 is 0.00. 

 This makes an approximate correction for the effect of the ratio of pole ;u < 

 to pole pitch. 



