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Pennsylvania railway and on the Norfolk and Western lines, where the traffic is very heavy. There is a marked difference between the types of locomotives and of motors developed in America and those developed in other countries, and it is possible that the direction along which designers have gone in the United States has not on the whole been the most favourable for the single-phase system. At the same time it would be wrong to assume that America as a whole is in favour of the continuous-current system. The use of 165 cycles in Europe as compared with 25 cycles in America has been much to the advantage of the former continent in single-phase work.

Italy. Italy was one of the first countries in Europe to consider and adopt the electrification of its railways. At that time (1902) the three-phase system was practically the only one available for main lines, the position in this respect being somewhat akin to that on the Brighton railway when the single-phase system was chosen. The one serious drawback to the three-phase system is the need for two overhead wires at different potentials, which makes the overhead construction at points and crossings very complicated. Also the profile of certain tunnels renders the adoption of this system difficult. One undesirable result of the overhead complications is the limita- tion of the pressure to 3,000 volts. The objectionable double over- head potential and the choice of two other satisfactory systems have prevented the extension of the three-phase system to other countries. At the same time it should not be supposed that less success has been obtained with this system than with either of the others indeed, the whole technical world must view with admiration the ability shown by the Italian engineers in carrying out the system. Many important State lines are now worked electrically, among which may be mentioned the pioneer Valtellina line (opened in 1902), the Giovi tunnel and the Mont Cenis tunnel lines. For mountain lines the three-phase system is peculiarly well adapted, because of the auto- matic regenerative braking action which occurs as soon as the motors run above synchronous speed. The original locomotives had two speeds obtained by the cascade arrangement of two motors; while the newer locomotives have four speeds, the cascade con- nexion being combined with pole-changing devices. The power for the Italian lines is obtained from hydraulic stations, the use of water- power being important in a country without native coal.

Switzerland. To Switzerland belongs the credit of much pioneer work in railway electrification ever since the Oerlikon Co. equipped an experimental line from Seebach to VVettingen. The piercing of the Simplon tunnel in 1907 was followed by the adoption of the three-phase system so as to utilize available plant as far as possible. This tunnel is 14 m. long (from Brigue in Switzerland to Iselle in Italy), and insulation difficulties were experienced with both over- head conductors and locomotives on account of the hot springs, which produced a very humid, warm atmosphere. On a cold day, a locomotive entering the tunnel from Brigue became rapidly covered with moisture. The earlier locomotives were provided with slip-ring induction motors, two speeds being obtained by changing the number of poles ; the later locomotives have squirrel-cage rotors and are arranged for four speeds, the stators being provided with two- pole changing windings. The three-phase electrification has now been extended to Sion in the Rhone valley. In 1912 the Loetschberg railway from Berne to Brigue (Simplon tunnel) was opened and from the outset this line was operated electrically. The system chosen was the single-phase system at 15,000 volts and 15 cycles. (This may be changed later to 165 cycles, the frequency used on the Federal rail- ways.) After the initial difficulties had been overcome, both in the overhead system and in the locomotives, the Swiss Government decided to apply the same system on the St. Gothard railway. In this connexion mention may be made of the important official com- mission which was appointed in 1904 to study the electrification of the Swiss railways. Several reports were issued by this commission, the labours of which were concluded in 1914. It has been claimed that the economy and efficiency of the single-phase system are greater than those of other systems, and this was particularly the case on the Loetschberg railway, where the single-phase overhead line is fed directly from the single-phase generating station at Spiez at the working voltage without transformers. Not only did the commission report strongly in favour of the single-phase system, but also advocated the generation of single-phase power at railway frequency (163 cycles) rather than 3-phase generation at the indus- trial frequency of 50 cycles and conversion to single-phase at rail- way frequency. If the over-all cost of energy delivered to the locomotive, including attendance, be reckoned as unity when the current is converted from one system to another, this may be reduced to about 0-6 when conversion is dispensed with, and the latter figure can again be reduced still further when the intermediate link of trans- formers is eliminated. Extensions have been made on the lines adjoining the Loetschberg line as far as Berne, and the St. Gothard line (Lucerne-Chiasso) is now working electrically from Erstfeld to Bellinzona. Several of the lines subsidized by the 'Canton of Berne have recently been electrified and linked up with the Loetschberg railway, while many other important projects are also under con- sideration. It is estimated that about 30 per cent of the Swiss railways are now worked electrically.

Doubtless one of the chief causes of the success of the single-phase system in Switzerland arises from the successful development of the single-phase commutator motor for traction work. In Europe there

has always been a tendency to use fewer and larger motors and to mount them higher in the locomotive than is the case in America. Though this construction has introduced new problems with connect- ing and coupling rods, it has permitted the logical development of the single-phase motor. Of all the different types of commutator motor the repulsion motor with fixed and movable brushes (Deri motor), 'the repulsion motor with phase compensation (Winter Eich- berg Latour motor as used on the London, Brighton and South Coast railway), and the various forms of series repulsion motor the suc- cessful survivor is doubtless the compensated series motor, the excitation required to give the E.M.F. to neutralize the transformer E.M.F. in the coils short-circuited by the brushes being obtained by suitable winding on auxiliary poles. Though such motors can be built for low terminal pressures only (200 to 500 volts) and therefore necessitate step-down transformers on the locomotive, advantage is taken of this to obtain economical and ample speed control by provid- ing suitable tappings on the secondary of the transformer.

Germany. Tn Germany the single-phase system has also been adopted where main lines have been electrified. The chief elec- trified lines are the Dessau-Bitterfeld section of the Magdeburg Hall line, the Silesian mountain lines and the Wiesental railway in Baden. Early in the present century trials had been made on the Berlin Zossen experimental line, and it would appear that the single-phase system at 15,000 volts, l6 cycles, will be adopted as the standard system for the German railways. The power for several of these lines is generated at 60,000 to 80,000 volts in steam stations. The electrification of the Dessau-Bitterfeld line was the alternative chosen in preference to quadrupling the tracks in order to cope with the increasingly heavy demands on this section.

Many different types of electric locomotive have been built in Germany, some of which were in accordance with the specifications of the railway engineers. Much adverse criticism was raised owing to important troubles in several constructions, arising mainly from failures in the driving mechanism. Many problems, both in Germany and Switzerland, concerning vibrations set up by the natural frequency of the system, deformation of the several parts and the play in the bearings, had to be investigated before successful solu- tions were found. In some cases it was found that an elastic member between the driving and the driven parts proved effective in damp- ing the oscillations.

Sweden, like Italy and Switzerland, is a country without coal but with ample water-power. The first important electrification in Sweden was the Riksgriins railway, the most northerly railway in the world, situated entirely within the Arctic Circle. This railway ex- tends from Lulea in the Bothnian Gulf to Narvik, an ice-free port on the Norwegian coast, and is used for transporting mineral ores to the latter place for export. Since the original electrification was carried out in 1910 extensions have been made, and it is hoped that the whole line will shortly be worked electrically.

The high price and great scarcity of coal towards the end of the war, and afterwards, made the consideration of the utilization of water-power extremely urgent. The expert commission appointed to study the question confined its attention to the problem of imme- diate urgency the Stockholm-Gothenburg line. A careful com- parison was made between the continuous-current system at 3,000 volts and the single-phase system at 15,000 volts, and it was shown that the latter was slightly better from an economic standpoint, in addition to which the Swedish railway administration and manu- facturing firms were fairly well acquainted with the actual working of the single-phase system. The proposals for this scheme were accepted by the Riksdag in 1920.

France. A commission was also set up in this country to study the electrification of the French railways. Before the war certain short sections had been electrified on the single-phase system, but as a result of a post-war visit to the United States, the commission appeared to be whole-heartedly in favour of the continuous-current system, at a pressure of 1,500 volts in this respect agreeing with the findings of the British advisory committee. It is intended to make use of the waterfalls for supplying energy to the railways.

Austria. Prior to the war, the Mittenwald railway between Austria and Bavaria had been electrified, and it has now been de- cided to adopt electrification on a general scale. The system adopted is the single-phase at l,ooo volts and i6 cycles. Locomotives were ordered in 1920, and it was hoped to commence running in 1925.

General. As general problems connected with electric traction on railways may be mentioned interference with communication cir- cuits, regenerative braking and speed control.

In most countries telegraph and telephone lines run alongside the track, and all systems have created disturbances in these circuits from electromagnetic or electrostatic influence. Some of these dis- turbances are periodic and traceable to harmonics in the current in the power circuit ; others, perhaps the most violent, arise from pres- sure surges, earths, short circuits, etc. Numerous remedies have been adopted, most of which are more or less costly. Thus the avoidance of close parallels by removing the communication circuits to a distance or placing them in underground cables is an expensive expedient. To say, as is usual, that the single-phase system causes worse disturbances than the continuous-current system could not be accepted as a general statement ; some of the most troublesome cases have occurred in continuous-current systems fed from rotary