394 ELEMENTS OF ELECTRICAL ENGINEERING. 



current in each armature winding, when the alternator is A-con- 

 nected to the mains, and the mains are Y-connected to three sim- 

 ilar receiving circuits, each one of which has a resistance of 4 

 ohms and a reactance of 3 ohms. Ans. (a) 11.55 amperes, (&) 

 same as (a), (c) 100 volts, (d) 6.67 amperes. 



73. Find (a) the current in each receiving circuit, (b) the cur- 

 rent in each main, (c) the voltage between mains, and (d) the 

 current in each armature winding, when the generator specified 

 in problem 72 is Y-connected to the mains and the mains are 

 A-connected to the given receiving circuits. Ans. (a) 34.64 

 amperes, (ft) 60 amperes, (c) 173.21 volts, (d) 60 amperes. 



74. The electromotive force developed in each winding of a 2- 

 phase alternator is 100 volts. What is the electromotive force 

 given by the two windings connected in series? Ans. 141 volts. 



75. The electromotive force developed in each winding of a 

 3 -phase alternator is 100 volts. What is the electromotive force 

 developed by the three windings in series ? Ans. 200 volts, or 

 zero. 



76. Two watt-meters are arranged as shown in Fig. 105 to measure the power 

 delivered to three similar receiving circuits each having a power factor equal to o. 75- 

 The total power delivered to the three circuits is 20 kilowatts. Find the reading of 

 each watt-meter. Draw a vector diagram similar to Fig. 1 06 representing the relation- 

 ship between voltages and current. 



Note. This problem is based on the assumption that the electromotive forces and 

 currents are harmonic. 



CHAPTER VII. VOLTAGE AND VOLTAGE REGULATION OF 

 ALTERNATORS. 



77. The alternator represented in Fig. 107, Chapter VII, is a 

 4-pole single-phase machine having 8 conductors in the 8 slots, 

 as specified on page 120. The speed of the machine is 30 revo- 

 lutions per second and the flux emanating from each pole is 

 1,000,000 lines. Calculate the effective value of the electro- 

 motive force generated by the machine. Ans. 1 1.03 volts. 



78. Assuming the field flux of an alternator to be harmonically 

 distributed, as explained on page 121, calculate the phase con- 



