QUESTIONS AND PROBLEMS 505 



34. Why is it difficult to break a high- voltage power arc in air? Discuss 

 briefly the construction of an oil switch for high voltages. Why is it neces- 

 sary that the case be designed to withstand high pressures? 



35. What special care must be used in carrying high-voltage lines into 

 stations? What care should be taken in the location of the various 



of apparatus? 



36. What are the economic necessities which have developed the outdoor 

 sub-station? In what way does the apparatus for such a station differ 

 from that of an indoor station? 



PROBLEMS ON CHAPTER XH 



143. Calculate the inductance per mile of a two-conductor distributing 

 line of 2/0 solid conductors spaced 2 ft. apart. What is the inductance if 

 the distance between the wires is 4 ft.? 



144. What is the reactance per conductor at 60 cycles of 4 miles of the 

 lines of problem 143? What is the maximum allowable current if it is 

 necessary that the reactive voltage drop shall not exceed 250 volts in the 

 two wires? What is the total impedance drop per wire? 



146. A three-phase distribution line consists of three 4/0 solid conductors 

 symmetrically spaced, the distance between conductors being 30 in. (a) 

 What is the reactance per wire per mile of this line when the frequ- 

 25 cycles per second? 60-cycles per second? (6) What is the impedance 

 under these conditions? 



146. What is the capacitance to neutral per mile of the line in problem 



lie charging current when there is 6,900 volts between con- 

 ductors and the frequency is 60 cycles per second? 



147. A 30-mile transmission line consists of two 4/0 conductors spaced 

 3 ft. apart, (a) What is the capacitance to neutral of this system? (6) 



- the 60-cycle charging current if the voltage is 26,400 volts between 

 conductors? 



148. Compute the capacitance to neutral per conductor and tl. 



current per conductor in problem 117. if the system is changed to a three- 

 phase system by the addition of a third conductor similar to the oth- 



lually spaced from them. The voltage between wires is the sum* m 

 both cases. 



149. The voltage at the receiving line with the 2-foot sparing in 

 problem 144 is 2,300 volte, when the load is KM) k\\. and the load power- 

 factor is unify. (a- What is the voltage at the generating end? (/> 



is the line regulation 1 .' (c What is the i tor at the generating end? 



: r^ing cur: 



150. Rep. -at problem 149 for a power-factor of 0.8, lagging urrent 



151. 149 for a power-factor of 0.8, leadin; 

 162. red to transmit 2,000 k w., single-phase, a distance 



with i loss I! I tage is 15,000 volto, the load j 



ffict.tr is 0.7. lamrink' Current, the ft- is 26 cycle* pP tecond, and the 



conductors are in on centers. Find (a) the voltage drop per 



