220 ELECTRICAL ENERGY. 



It will be seen that the longest transmission is at Fresno, Cal., the 

 distance being about 35 miles. The highest alternating voltage used is 

 13,000 volts, at Zurich, Switzerland. The highest direct potential is 

 15,000 volts, at Brescia. 



All of these plants are working successfully, and this fact will lead 

 to still longer transmission and higher voltages. No limit of either 

 distance or potential has yet been reached. If we consider the record 

 of the present transmission plants, we can safely say that it would not 

 be going outside of the safe limit of development to transmit at least 

 50 miles at a potential of 20,000 volts, provided the energy could be 

 delivered at such a price as to be considerably lower than the cost of a 

 corresponding amount of energy obtained from a steam plant. This, of 

 course, is a matter of local condition entirely, and the commercial value 

 of such a transmission will depend upon local conditions. 



LONG-DISTANCE TRANSMISSION FOR RAILROAD WORK. 



The possibility of long-distance electric-railroad lines is intimately 

 connected with the possibility of long-distance transmission of power. 

 We have seen that it is possible to transmit considerable distances from 

 a single station. The current so distributed is not, however, such that 

 it can be applied directly to railroad motors, but it must be transformed 

 at points along the line, the distance apart of these points of distribu- 

 tion depending upon the system that is employed. At present con- 

 tinuous current motors are used, and considerations of safety would 

 lead us to use line potentials not greater than 700 volts. By distrib- 

 uting rotary transformers at distances of 5 or 6 miles apart, we would 

 be able to supply motors with current without any great investment in 

 copper. The amount of copper required could be still further reduced 

 by using rotary transformers with storage batteries thus keeping a 

 constant load on the transmission line. It will be found, however, that 

 on any long-distance railroad line, the load on any section of the line 

 is exceedingly variable and the discharge rate of the batteries will have 

 to be very high in order to prevent excessive cost for our reducing 

 stations. It is doubtful whether we have reached a point in battery 

 construction that this system of transmission would be economical. It 

 is certain, however, that when the distances are comparatively short, 

 say within 15 miles, and where the traffic is not evenly distributed, that 

 rotary transformers, with, or without batteries, can be economically 

 employed for railroad work. 



CONCLUSIONS. 



My conclusions, subject always to the influence of local conditions, are 

 as follows : 



1. In both direct current lighting and traction systems, where the 

 power is generated in or near the area of distribution, it is best to use 

 one station situated at the most economical point for producing power. 



