ADVANTAGES AND DISADVANTAGES 31 



the distance of 120 miles over a comparatively flat 

 plateau of 14,000 feet elevation. This place is called the 

 roof of the world, and is up in the Andes Mountains, in 

 Peru. The load on this system is mostly motors driving 

 copper-mining machinery to the extent of about 10,000 

 horse-power, requiring a conductor of No. i size cable. 

 The motors are divided up between synchronous and 

 induction in such a way that the power-factor will be 

 under complete control by means of automatic voltage 

 regulators adjusting the excitation of the synchronous 

 motors." The description further states that owing to 

 the small size of conductor and the great altitude, the 

 phenomenon of corona loss prohibited the use of a higher 

 voltage than 50,000 volts, which is seen to be in agree- 

 ment with Table V. As 50,000 volts is a very low volt- 

 age for a 120-mile transmission line, the above case is 

 an unusually favorable one for the constant-voltage 

 method. 



Wherever there is a large number of scattered cus- 

 tomers, each requiring a substation on the transmission 

 line or net-work, the reluctance to using very high voltage 

 will also be apparent. A 6o,ooo-volt substation costs 

 very much less than one designed for 100,000 or 150,000 

 volts. 



For detailed examples showing the savings in cost, 

 at a certain voltage, made by installing synchronous 

 phase modifiers, see Chapter X. 



The increase in carrying capacity of a transmission 

 line due to the use of phase modifiers is greatest for large 

 sizes of conductors, as is shown by an inspection of Figs. 

 5 and 6. With varying voltage, it is not economical to 

 use a larger size of conductor than about No. oooo cop- 



