484 ELEMENTS OF ELECTRICAL ENGINEERING. 



the elevator motor is taking its maximum current of 150 am- 

 peres, and () when the battery is nearly charged and the elevator 

 motor is taking no current at all. Ans. (a) 35.9 amperes; (b) 

 14.7 amperes. 



Note. Assume that the voltage of the booster is proportional to its net field exci- 

 tation, 10 volts for each n ampere-turns. 



The student may calculate the values of the current corresponding to (a) and (b] 

 on the supposition that the winding, S', is connected as shown in Fig. 150, 3 being 

 the field excitation due to S' when the voltage between the terminals of S / is no 

 volts. The answers in this case are : (a) 32.9 amperes ; and (b} 17.5 amperes. 



CHAPTER IX. ELECTRIC DISTRIBUTION AND WIRING. 



147. Five hundred glow lamps each taking one-half an am- 

 pere at no volts are supplied with current from a ii5.5-volt 

 generator at a distance of 1,000 feet from the lamps. Find : (a) 

 The size of copper wire required, (b) the total weight of the wire, 

 and (c) the total cost of the wire at 16 cents per pound. Ans. 

 (a) 982,000 circular mils ; (b) 5,950 pounds ; (c) 953 dollars. 



148. Five hundred glow lamps each taking one-half an am- 

 pere at no volts are supplied with current from a 231 -volt gen- 

 erator at a distance of 1 ,000 feet from the lamps. The Edison 

 three-wire system is used and the system is balanced. Find : 

 (a) The size of copper wire required for the outside mains ; (b) 

 the total weight of all three mains, the middle main having one- 

 half the sectional area of either outside main ; and (c) the total 

 cost of the three mains at 16 cents per pound. Ans. (a) 245,- 

 500 circular mils ; (b) 1,860 pounds ; (c) 298 dollars. 



149. The three-wire system of problem 148 supplies 300 

 lamps (150 amperes) on one side and 200 lamps (100 amperes) 

 on the other side, all at a distance of 1,000 feet from a 231 -volt 

 generator. A balancer is used in the station to take care of the 

 current in the middle main and to keep the voltage between the 

 middle main and each outside main equal to 115.5 volts. Find : 

 (a) The voltage across the set of 300 lamps ; and (b) the voltage 

 across the set of 200 lamps. Ans. (a) 104.5 volts; (b) 115.5 

 volts. 



