ALTERNATING-CURRENT TRANSMISSION 7 



of the high-tension apparatus increases disproportion- 

 ately fast, so that the voltage is seldom increased above 

 this figure, even for very long lines. For such long lines, 

 less than 1,000 volts per mile is usually used. In connec- 

 tion with this economical limit to the use of extremely 

 high voltage, it may be noted that some large capacity, 

 extra high voltage oil switches recently built occupied 

 1,200 cubic feet and weighed 14 tons each, and that the 

 following comment on them was made in an editorial of 

 The Electrical World: "The time seems almost to have 

 arrived in high-tension work at which the generators 

 and prime movers become comparatively insignificant." 

 Another evidence of the extreme cost of very high voltage 

 apparatus is given by the fact that some 5,800 Kva. 

 150,000 volt transformers could have been built, accord- 

 ing to an article in The Electric Journal of August, 1913, 

 for a rating of 30,000 Kva. at 22,000 volts, without in- 

 creasing the size. Plainly, electrical engineers are able 

 to utilize extremely high voltages, but the cost becomes 

 excessive. 



It has been shown that, as the distance of transmis- 

 sion is increased, it pays to increase the expenditure at 

 the line terminals in order to decrease the size or num- 

 ber of the conductors. This is usually done by using 

 higher voltage, and a limitation to this development is 

 being felt in the rapid increase in cost of the terminal 

 apparatus as the voltage is raised to an extreme amount. 

 But this need not put the final limit on the distance of 

 economical energy transmission, for the size of the con- 

 ductors can be decreased, without raising the voltage, by 

 installing synchronous phase modifiers and adopting the 

 constant-voltage system of line control. 



