POLYPHASE CIRCUITS 107 



from the mains 1, 2 and 3 respectively of a three-phase, 220-volt 

 circuit to a common point. If Fi 2 leads F 23 by 120 degrees, (a) 

 what are the line currents? (b) What is the total power absorbed? 

 C What i< the voltage between the " common point" and the 

 true neutral of the system? 



15. In problem 14 if F 23 leads F i2 by 120 degrees a what are 

 the line currents? (b) What is the total power absorbed? (c) 

 What is the voltage between the " common point" and the true 

 neutral of the circuit? 



16. Three impedance units which are represented by the ex- 

 pressions Zi = lQ+jQ, z z = Q+jlO, z 3 = jlO, are connected in 

 Y from the mains 1, 2 and 3 respectively of a three-phase, 

 220-volt circuit to a common point. If Fi 2 leads F 23 by 120 de- 

 grees (a) what are the line currents? (b) What is the total power 

 absorbed? (c) What is the voltage between the " common point" 

 and the true neutral of the system? 



17. In problem 16 if F 23 leads Fi 2 by 120 degrees (a) what are 

 the line currents? (b)What is the total power absorbed? (c) 

 What is the voltage between the " common point" and the true 

 neutral of the system? 



18. Three voltmeters are connected in Y from the mains of a 

 three-phase, 220-volt circuit to a common point. The resistances 

 of the voltmeters are Ri ohms and R* ohms and R 3 ohms respec- 

 tively. What does each instrument indicate? 



19. Three unequal lamp loads are connected between the 

 mains and neutral conductor of a three-phase transmission line. 

 The mains and neutral conductor each have a resistance of 0.1 

 ohm and negligible reactance. The resistances of the lamp 

 loads are 1.0 ohm, 1.5 ohms and 2.0 ohms respectively. At 

 the generating station the line voltages are each 220 volts and the 

 voltages between the mains and neutral conductors are equal. 

 (a) What are the line and neutral currents? (b) What is the 

 voltage across each lamp load? (c) What is the efficiency of 

 transmission? 



20. Three unequal lamp loads are connected in delta at the 

 end of a three-phase transmi in line which has a resistance of 

 0.1 ohm per conductor and netji^il.lr reactance. The resistances 

 of the lamp loads are 1.0 ohm. !.."> nlmi- and 'J.O ohms respectively. 

 If the lino voltages at the generating station an ea< h 220 volts, 

 (a) what are the line currrn >> What are the line voltages at 

 the load? (c) What is the efficiency of ti on? 



