ELECTRIC POWER 



2848 



ELECTRIC POWER 



now obtained solely by the aid of 

 hydro-electric power ; and the 

 manufacture of artificial fertilisers 

 by the fixation of the nitrogen of the 

 atmosphere, which is now being 

 carried out on a considerable scale 

 in Scandinavia, the product as pre- 

 pared for agricultural use being 

 known as nitrolime. 



The useful properties of elec- 

 tricity together with the increasing 

 cost of coal are now compelling 

 attention to the possibility of using 

 other and new sources from which 

 to obtain the energy. Natural oil 

 offers no appreciable advantages 

 over coal in this connexion, though 

 low classes of oil are now being 

 used in Diesel engines (q.v.) for the 

 development of electricity. It has 

 been predicted that we shall one 

 day cultivate oil-yielding plants 

 specially for the purpose of provid- 

 ing fuel to be used in such classes of 

 engines for the development of elec- 

 tric power. It is possible that the 

 tides, especially where they run to 

 considerable heights, may one day 

 be utilised ; and in tropical and 

 subtropical regions, the direct rays 

 of the sun. Edison has studied the 

 possibility of constructing a voltaic 

 cell in which the latent energy of 

 coal, much the larger part of which 

 is now wasted in the most economi- 

 cal systems of power development, 

 would be directly converted into 

 electric power. Sir Oliver Lodge 

 looks ultimately to the liberation of 

 atomic energy ; while Sir Charles 

 Parsons, reviving an old project, 

 would obtain energy from the in- 

 ternal heat of the earth. 



Utilisation of Natural Steam 



Meanwhile the most remarkable 

 electric power development system 

 in the world is to be found in Italy, 

 where the internal fires are actually 

 being utilised. The soffioni of 

 Tuscany are well known and have 

 long been a principal source of 

 borax. They are openings in the 

 crust of the earth through which, 

 from time immemorial, volumes of 

 steam have poured day and night. 

 Prince Gironti-Conti, on whose 

 estate soffioni occur, has now tapped 

 some of this natural steam before it 

 comes to the surface by driving 

 pipes into the ground, and is 

 using it as the heating agent in 

 special steam boilers for thedevelop- 

 ment of electric power by turbo- 

 generators. 



TRANSMISSION AND DISTRIBU- 

 TION. Since the earliest days of the 

 present industrial era, even before 

 the inventions of James Watt gave 

 so great a stimulus to industrial de- 

 velopment, the transmission of 

 power, mechanical energy particu- 

 larly, has always been a branch of 

 applied engineering of the highest 

 importance. Until the modern de- 



velopments in electricity, transmis- 

 sion was effected chiefly by shaft- 

 ing and gearing, belts and ropes, 

 and in some cases by wire cables 

 running over pulleys. All these 

 systems, even the latter, were ex- 

 tremely limited in their scope. 

 Here and there the attempt has 

 been made to transmit power over 

 considerable distances by means of 

 steam, water, or air carried in pipes 

 underground. None of these agents, 

 however, can compare with elec- 

 tricity in regard to the facility with 

 which convertible energy can be 

 transmitted over long distances. 

 Telegraphic Power Transmission 

 Electric transmission may be 

 considered under three heads, 

 factory, local, and long distance. 

 The principles involved are the 

 same in all ; the differences lie 

 chiefly in the scale on which those 

 principles are applied. The 

 medium mostly employed to-day 

 for transmission, and for distribu- 

 tion, is copper wire, though alu- 

 minium is now being used to some 

 extent, and may ultimately dis- 

 place copper ; weight for weight it 

 is a much better conductor, and 

 therefore at equal cost and equal 

 durability would be the more eco- 

 nomical medium. For telegraphic 

 power transmission, galvanised iron 

 wire is mostly used, being permis- 

 sible because of the relatively small 

 amounts of current which need to 

 be transmitted. In all cases of 

 electric transmission a medium for 

 the return of the current to the 

 source of generation is required 

 the circuit must be complete. This 

 medium may be provided by a 

 separate wire, by the rails of a 

 tramway or railway, or by a system 

 of separate rails or T bars, or by 

 the earth, which is a universal 

 conductor and equaliser. 



Transmission and distribution, in 

 the case of factories where the elec- 

 tricity is generated on the pre- 

 mises, present no difficulties. The 

 current is usually continuous or 

 direct and the voltage compara- 

 tively low, 200 to 250 volts, and 

 rarely over 500. In large estab- 

 lishments with many buildings and 

 much machinery a separate system 

 for lighting, and heating, may be 

 installed ; otherwise the lighting 

 distribution will be taken off the 

 same mains which supply the 

 electric motors for driving the 

 machinery. The mains or con- 

 ductors will be encased so as to 

 avoid risk of personal contact or 

 short circuiting, exposure to 

 moisture, accidental injury, as by 

 the driving in of a nail, or any con- 

 ditions likely to cause personal 

 injury or fire. 



A question that may call for 

 careful consideration will be as to 



whether the machines shall be ar- 

 ranged to be operated in series or in 

 parallel, that is to say whether the 

 current shall pass through one 

 machine to the next, or each take 

 its own supply independently from 

 the main. Arc lamps are largely 

 operated in series ; and some 

 economy in cost of installation 

 may be secured by adopting that 

 system, but as the system involves 

 the addition to each machine or 

 lamp of a shunt device which will 

 automatically cut out a lamp or 

 machine from the circuit if it 

 goes wrong, and pass the current 

 round it on to the next, and as, 

 further, it is practically inapplicable 

 to incandescent or glow lamps, the 

 balance of advantage lies with the 

 system of working in parallel, 

 under which the failure of one lamp 

 or machine does not necessitate 

 any disturbance of the remainder. 

 Local transmission and distri- 

 bution represents a much larger, 

 more complex, and difficult prob- 

 lem. The work is in the hands 

 either of a municipal authority or 

 of a public company ; in either 

 case it may assume a four-fold 

 aspect the provision of light and 

 heat to domestic and business 

 users, public lighting, the provision 

 of power to workshops, and lastly 

 power for electric traction. The 

 supply of private light and heat 

 will usually be the first considera- 

 tion, and two antagonistic factors 

 will present themselves. The or- 

 dinary domestic incandescent or 

 glow lamp cannot take current at 

 more than 200 volts ; large numbers 

 still in use must be supplied with 

 current at a much lower pressure. 

 Cost of Installation 



On the other hand, the conductors 

 for transmission and the distribut- 

 ing lines, whether of copper or of 

 aluminium, are costly, and the only 

 way by which the cost of instal- 

 lation can be kept within reason- 

 able limits is to generate the cur- 

 rent, and put it into the main at as 

 high a pressure as may be permis- 

 sible. As in the case of steam the 

 higher the pressure the larger the 

 amount that may be passed through 

 a given size of pipe ; so with electric- 

 ity the higher the pressure volt- 

 age the smaller may be the size of 

 the mains for the transmission of a 

 given quantity. Thus the conditions 

 at one end require a low voltage ; 

 at the other end a high voltage ; 

 and a compromise will have to be 

 adopted having regard to all the 

 conditions of the district to be 

 served. 



Voltages as low as 1 00 are in use 

 in the stations of Great Britain, but 

 the newer installations will usually 

 be arranged for voltages between 

 250 and 550. Hence the current put 



