CHAPTEE XVI. 



Different Systems of Transmission of Energy Comparison of Costs of 

 Transmission Lines with Different Systems. 



TRANSMISSION OF ENERGY. 



123. In the transmission of electrical energy over long distances, 

 it is of importance to consider the cost of the line, which, unless 

 clue precaution is taken, may be such as to make the outlay pro- 

 hibitive. 



If energy is transmitted by continuous currents at E volts, we 



have 



EI = W (1) 



where W is the power in watts transmitted, and / the current in 

 amperes. 



It is seen, therefore, that the higher the voltage, the less the 

 current for a given power transmitted. Thus, to economically 

 transmit power over long distances with a reasonable efficiency 

 demands that the voltage of transmission should be as high as 

 possible consistent with other controlling conditions, the chief of 

 which is the quality of the insulation attainable. 



124. To further illustrate the case, suppose that it is desired 

 to transmit W kilowatts over a distance x centimetres with an 

 efficiency of transmission ij. Let us compare the cost of the trans- 

 mission lines according as the transmission is effected (1) by con- 

 tinuous currents, (2) by mono-phase alternating currents, (3) by 

 di-phase currents with four wires, (4) by di-phase currents with 

 three wires, one being a common return, (5) by tri-phase currents 

 mesh- grouping, and (6) by tri-phase currents star-grouping. 



Since the efficiency is rj, if we let E be the voltage at the 

 generating end of the line, that at the receiving end will be r\E, 

 and the watts lost in the line will be 



(2) 



