134 PROBLEMS IN ALTERNATING CURRENT MACHINERY 



(a) If three equal lamp loads, each of which has a resistance of 

 .5 ohms, are connected in delta across the 3-phase lines what 

 current does each take? 



(b) If three equal lamp loads, each of which has a resistance of 

 3 ohms, are connected in Y across the 3-phase lines what current 

 does each take? 



38. In problem 37 three equal air-core reactors, each of which 

 has a resistance of 5 ohms and an inductance of 7.5 mil-henrys, 

 are connected in delta across the 3-phase lines. What current 

 does each take? What is the line current? 



(b) If these reactors are connected in Y what current will 

 each take? 



39. In problem 37 three equal impedance units, each con- 

 sisting of a resistance of 20 ohms in series with a condenser 

 of 50 microfarads' capacity, are connected in delta across the 3- 

 phase lines. What current does each unit take? What is the 

 line current? 



(b) If these impedance units are connected in Y what current 

 will each take? 



40. In problem 37 three hypothetical impedance units are 

 connected in delta across the 3-phase lines. The values of these 

 units at 60 cycles may be represented in the complex notation by : 

 Zi = 10+jO, 2 2 = 0+jlO, 2 3 = 0-jlO. What current does each 

 unit take? What are the line currents? 



41. In problem 37 the smaller transformer is tapped at a 

 point two-thirds from its line terminal to give a neutral on the 

 3-phase side. The three hypothetical impedance units described 

 in problem 40 are connected in Y between the lines and neutral. 

 What are the line currents? What is the neutral current? 



42. A 3-phase, 60-cycle alternating-current generator supplies 

 power to a transmission line through step-up transformers whose 

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

 windings are connected in delta. These transformers are rated at 

 3333 kv.-a. , and have a voltage ratio of 3,800 to 80,000 volts. With 

 the high-tension winding short-circuited and with 162 volts at 60 

 cycles impressed on the low-tension winding full-load current 

 exists in each winding and 18.85 kw. is supplied. The neutral 

 points of both the generator and the low-tension windings of the 

 transformers are connected to the same ground bus. When the 

 transformers are delivering no load on the high-tension side and 

 the excitation of the generator is adjusted so that its terminal 



