ADVANTAGES AND DISADVANTAGES 33 



This, together with a large diameter of conductors, very 

 considerably reduces the possibility of corona loss. Thus 

 a line designed to carry as much power as possible, ac- 

 cording to the constant-voltage system, may be operated 

 at a considerably higher voltage than one of more usual 

 construction, owing to the limitation of voltage imposed 

 on the latter line by the phenomenon of corona. For 

 example, No. oooo cable at 12 feet spacing has a corona 

 limit of voltage of 135,000 volts, while 300,000 circular 

 mil cable at 20 feet spacing has a limit of 171,000 volts. 

 See Table V. 



Thus the constant- voltage system, by increasing the 

 power rating of a given line, and by allowing the use of 

 larger conductors and of higher voltages, extends to a 

 marked degree the distance to which electric power may 

 economically be transmitted, since this depends largely 

 on the line cost for a certain amount of power. 



Another advantage of the constant-voltage method 

 of control is that it encourages the use of high reactance 

 in all the different kinds of apparatus making up the 

 transmission system. Without power-factor control, a 

 line has its power-rating directly reduced when the re- 

 actance of any part is increased, since the voltage varia- 

 tion, which determines the power-rating of the line, is 

 thereby increased. But the addition of reactance has a 

 less effect on the power-rating of a constant-voltage line. 

 This has been already mentioned in connection with the 

 high reactance resulting from wide spacing of the conduc- 

 tors. The same fact is true as regards increasing the 

 reactance of the transformers and generators, and es- 

 pecially as regards using protective coils of very high 

 reactance. The value of high reactance in all parts of a 



