214 ELECTRICAL ENERGY. 



although alternating arc lamps are used to a limited extent, yet the 

 number is not increasing, and in some cases continuous-current arc 

 lamps have been substituted for the alternating. Under these condi- 

 tions the load on the station is even more variable than in the case of a 

 continuous-current supply where motors may be employed, and the 

 constant loss due to the large number of small transformers used 

 places this system at a disadvantage as compared with the continuous- 

 current system. The great advantage it possesses lies in the increased 

 area of distribution rendered possible by the high voltages that are 

 used, together with the possibility of locating the stations where power 

 can be cheaply made. Abroad in the last few years most of the new 

 stations that have been built use continuous currents, although some 

 years ago the greater proportion of them were alternating-current sta- 

 tions, It is also the custom abroad to use substations with large trans- 

 formers for distribution, thus doing away with a considerable part of 

 the constant loss due to the small transformers used here. It is not 

 possible, at the present time, without greatly complicating the system, 

 to obtain a steady load on the station, and the only question that arises 

 is the value of substations, and the possibility of using some form of 

 alternating current other than the single-phase. 



METHODS OF ELECTRICAL TRANSMISSION. 



Coming to the question of transmission of electrical energy as distin- 

 guished from the supply to customers from distributing centers, there 

 have been great advances made in the last few years, and these mainly 

 through the introduction of multiphase alternating currents. Single- 

 phase alternating currents permit the transmission of power to long 

 distances and its distribution for lighting purposes. It is also possible 

 to supply power from such circuits to large motors working under a 

 steady load. It is not possible, however, to distribute power econom- 

 ically for ordinary uses. As most long-distance transmission schemes 

 contemplate the substitution of electric motors for steam engines, and 

 as their success will, in many cases, depend upon the possibility of such 

 substitution, single- phase alternating currents are not at present able 

 to comply with the conditions imposed by the desired service. The 

 introduction of multiphase alternating systems, where two or more 

 alternating currents are employed, the currents differing in phase, has 

 completely changed the situation with respect to long-distance trans- 

 mission. I shall consider briefly the possibilities of such systems and 

 their value as compared with any direct-current system. 



CONTINUOUS-CURRENT TRANSMISSION. 



The first long.-distance transmission plant was operated by the con- 

 tinuous-current system, and even now plants are being built in which 

 continuous currents of high potential are used to transmit energy to dis- 

 tances up to 15 miles. As compared with transmission by means of 

 alternating currents, we will find that the continuous-current system 



