20 



DISCOVERY 



station equipment has somewhat upset the balance 

 in the advantages of the systems that we have been 

 discussing. It is now possible to employ contact line 

 pressures up to 3,000 or even 5,000 volts. This system 

 is in use in this country on the Manchester-Bury line 

 of the Lancashire and Yorkshire Railway, and on the 

 Shildon-Newport line of the North Eastern Railway. 

 The same system working at 2,400 and 3,000 volts is 

 also in use in America and elsewhere. 



The high-tension continuous-current system is con- 

 sequently now a formidable competitor of the single- 

 phase system, and the near future should see great 

 extensions in its use. It has already been adopted as 

 the standard for extensions of electric railway working 

 in France, and is being used for important schemes in 

 South Africa and elsewhere. The high line pressure 

 enables the number of sub-stations to be reduced, and 

 recent developments of automatic switch gear enable 

 these to run without continuous attention. The 

 converting sets in any particular sub-station are 

 started up automatically as the line requires power in 

 the section in question, and are stopped when no 

 longer required, their control being effected by the 

 variations in the pressure in the line according to the 

 demand upon it. By this means, not only are labour 

 costs substantially reduced, but greater economy in 

 working is secured. 



Standardisation of one System Unlikely 



Although standardisation of system is an ideal worthy 

 of sacrifice to attain, every system is worth examina- 

 tion on its own merits. There is no " best " system 

 in every circumstance. In different countries the 

 opinions of experts differ. As said before, the three- 

 phase system appears to suit the conditions in northern 

 Italy, for the Italian engineers still remain true to it, 

 while the single-phase system is being actively extended 

 in Switzerland, and has been accepted as the standard 

 in Germany, Norway, and Sweden. On the other 

 hand, in France, America, and in various parts of the 

 British Empire the high-tension continuous-current 

 system is making rapid headway. 



A good example of modern American practice in 

 this direction is presented by the 3,000-volt continuous- 

 current locomotive recently built for the mountain 

 sections of the Chicago, Milwaukee, and St. Paul 

 Railway by the General Electric Company (of America), 

 which is illustrated in Fig. 2 (reproduced from a 

 photograph kindly supplied by the British Thomson- 

 Houston Co., Ltd.). This locomotive is 76 ft. in 

 length overall, and has no less than fourteen axles. 

 The total weight is 265 tons, of which 229 tons are 

 borne by the twelve pairs of driving wheels. The 

 motors are arranged to be used three, four, six, or twelve 



in series on the 3,000-volt circuit. They can develop 

 2,760 h.p. continuously, or much more for short 

 periods, and the locomotive, which is designed to 

 pull a load of 900 tons at 25 miles an hour up a 2 per 

 cent, gradient, and can exert a drawing force up to 

 56,500 lb. There are a number of interesting points 

 about their mechanical as well as their electrical 

 design which render locomotives of this class suitable 

 for high speeds, at which they can travel with an 

 efficiency and steadiness exceeding that of geared 

 locomotives of approximately this size. 



In Northern Italj', where conditions are peculiarly 

 suitable for the electrification of railways owing to the 

 ample water-power available in a mountainous district, 

 Messrs. Brown, Boveri & Co. have recently supplied a 

 locomotive foruse on the line from Turin to Ceres, which, 

 contrary to the recent preference in Italy for three-phase 

 working, has been equipped for continuous current at 

 a maximum line pressure of 4,000 volts, and is supplied 

 through a single sub-station for the whole 26 miles. 

 Each motor is rated at 140 h.p. for one hour, and the 

 locomotive is capable of a maximum tractive effort 

 of about 9-3 tons and a maximum speed of 40-5 miles 

 per hour. 



The extent to which railway electrification is already 

 an accomplished fact may be gathered from the follow- 

 ing figures of the route mileage of main lines in different 

 countries already worked electrically, or actually in 

 process of conversion : United States, 1,522 miles ; 

 Austria, 489 miles ; Italy, 466 miles ; Switzerland, 

 462 miles ; and Sweden, 272 miles. 



Advantages of Electrification 



Speaking generally, and assuming that the most 

 suitable system has been chosen to meet the particular 

 circumstances, the advantages to be gained by the 

 substitution of electric for steam traction are : 

 (i) increased available average speed of trains ; 

 (2) increased carrying capacity of the lines and 

 greater economy in fuel consumption per train-mile ; 

 and (3) the great advantages of cleanliness in tunnels 

 and in urban areas. These advantages are really those 

 inherent upon power centralisation, but there are 

 other advantages, due to the simplicity and reliability 

 of electrical apparatus, which bring with them a 

 reduction of maintenance and operating costs as com- 

 pared with the steam locomotive. The increased 

 carrying capacity is mainly due to the much greater 

 accelerating power obtainable because an electric 

 train has all the resources of a large station at its 

 disposal, while a locomotive has only its own. It is 

 this increased acceleration which is of such great 

 value in heavy suburban traffic, where the advantages 

 of electric traction with modern systems of 



