Electric automobileFig. 8. A modern electric automobile.—The electric battery is placed under the front half of the car, and the motors drive the back axle through chains. (British Electric Automobile Co., Ltd.)
Fig. 8. A modern electric automobile.—The electric battery is placed under the front half of the car, and the motors drive the back axle through chains. (British Electric Automobile Co., Ltd.)
Fig. 8. A modern electric automobile.—The electric battery is placed under the front half of the car, and the motors drive the back axle through chains. (British Electric Automobile Co., Ltd.)
Great hopes were once entertained of accumulator traction on tramways. The storage battery offered a means of escape from all the difficulty and expense of carrying electric mains overhead or underground. By fitting each car with a storage battery, it could be made an independent self-contained locomotive, capable of running a certain number of miles untilthe battery was approaching exhaustion. By providing centres where the batteries could be re-charged—or, to save time, replaced by batteries previously charged—a continuous service could be maintained on a tramway system.
The advantages of accumulator traction, apart from the saving in first cost, are the absence of obstruction and danger from overhead wires, and of the risk of a general stoppage of the service when the current at the generating station fails from any accidental cause. When accumulators are used, the conversion of a horse tramway to an electric tramway becomes a very simple matter. All that is required is to erect a generating station and provide each car with a storage battery and electrical equipment. This equipment, it may be mentioned, is substantially the same as with ordinary electric cars. The current flows from the accumulator through the controller and the motors back to the accumulator.
Many trials were made with this system in the early days of electric traction, but there are no survivals. The failures were due in part to weaknesses in the batteries and to the difficulty of handling them with proper care under the rough and ready conditions of tramway service. The main cause, however, was the inherent drawback of all locomotive systems—the fact that the tractor has to haul its own dead weight in addition to the weight of the car andpassengers. Lead being one of the heaviest of metals, this dead weight was a very serious item on accumulator tramcars. It proved to be a fatal item when the attempt was made to run large cars on heavy gradients. The rush of current demanded in starting such cars up-hill was in itself too severe a tax on the delicate structure of the batteries. In practice, moreover, the necessity of bringing each car back to the depot for re-charging, after a limited journey, proved very troublesome. The more extensive the system and the more frequent the service, the more troublesome this necessity became. Even the most enthusiastic advocate of the storage battery was at last forced to admit that it was not applicable to a system of transport, which demanded comparatively high speeds with large cars on all gradients and over a range of several miles from the centre of power.
After the admitted failure of accumulator tramways, the storage battery was for some time used only on river launches and small private vehicles. The conditions in both cases—and especially in the former—are very favourable to its operation. On a river launch the weight of the battery is not a serious item, as it serves to some extent in the place of ballast. Launches, moreover, are generally required for trips of a limited number of miles up and down the river from the boathouse or charging station of the owner. In contrast with the tramway, there isno demand for rapid acceleration at starting or for abnormal power at intervals. The batteries discharge slowly and fairly evenly, and are not subjected to serious vibration. The electrical equipment is extremely simple, as the motor is fixed on to the propeller shaft and operated by a controller on the deck close to the steering wheel.
However, if economy were the only consideration, it is doubtful whether the electric launch would have survived against the competition of steam and petrol launches. It has survived because the simplicity of the equipment, its silent running, and the absence of heat, smoke and fumes, make it the ideal thing for river work. The hire of an electric launch on the Thames costs more than that of a steam launch, but plenty of people are willing to pay the additional charge to avoid the drawbacks of steam propulsion on a small vessel.
Similar considerations underlie the extensive use of electric broughams in cities. Such vehicles are required only for travel within a restricted area and on streets where the gradients are seldom severe. Their carrying capacity is generally limited to two or four passengers, so that the batteries do not require to be unduly heavy. A maximum speed of 12 miles an hour is quite sufficient for city streets; and with careful treatment the batteries can be very economically used and will not deteriorate nearly sorapidly as they would under tramway conditions. Considerations of economy, on the other hand, do not weigh very heavily with the class of people who use private electric broughams. They are prepared to pay for the best available; and the electric brougham, with its noiselessness, its easy running, its absence of smell or other nuisance, is regarded as the ideal which other modes of city transport must do their best to approach.
In London a certain amount of business has been done for some years in hiring electric broughams for various periods on terms which include current, maintenance, garage facilities, driver's wages, and all other charges. The convenience of such an arrangement to the hirer need not be emphasised, since what is wanted in this case is a vehicle which is always ready at a telephone call. But the system has another important advantage, which bears upon the economic prospects of accumulator traction. By retaining the vehicles under its control the hiring company not only centralises the arrangements for storing and re-charging, but it is able to take care that the batteries are properly treated. Just as the success of the surface-contact system depends on minutiae of design, so the success of accumulator traction depends upon minutiae of treatment. Carelessness in driving the vehicles and in handling the batteries at the garage may transform a perfectlysatisfactory mode of city transport into an extravagant nuisance. Consequently the success of this class of business depends upon an organisation which permits of constant supervision over every vehicle and every driver.
A good deal of ingenuity has been exercised upon the electrical equipment of broughams; and it is probable that further improvements will be made. In some cases the front axle is driven by the motor; in some cases the back axle. The earliest cars used toothed-wheel gearing in order to reduce the speed of the small fast-running motor. Improved types on this principle still exist, but there are some interesting forms in which the motors are placed right at the hub of the wheels and effect speed reduction and control by electrical means, without any intermediate gearing.
In addition to these improvements, the storage battery itself has made a distinct advance in design and construction. It is more efficient, more durable, and more reliable now than ever it was before. The closer attention given to its treatment tends in the same direction; and the result is that storage-battery makers and engineers have a very accurate knowledge of what the accumulator will do at a certain cost under certain conditions. The conditions being the variable factors in the problem, and being in largemeasure determinable by choice, it is rather remarkable that the engineers and financiers should have selected, at the outset, the very conditions which were least suited to the peculiarities of the accumulator.
The attempt to adapt battery traction to tramway work is a conspicuous case in point, but it is not perhaps so conspicuous in the public memory as the efforts to organise electric cab and electric omnibus services in London and elsewhere. These efforts have been made so often and failed so regularly that they have made it difficult to obtain capital for any form of electric battery propulsion.
The electric omnibus has many of the drawbacks of the storage-battery tramcar, but they are not so serious in the case of an urban service, adequately met by small cars running at moderate speeds on short routes with moderate gradients. It is possible that if recent metropolitan electric omnibus enterprises had been as happy in their finance as in their engineering, they would have succeeded well enough. But even in their engineering they had to meet great difficulties. They sought to protect themselves against excessive costs by entering into maintenance agreements with the makers of the batteries; and although the terms of these agreements were satisfactory enough, their validity depended on careful treatment of the batteries by the drivers of the cars—a matter which it is rather difficult to guarantee. Moreover, the number of omnibuses put on the roadwas so small that the garage costs and other standing charges were proportionally very heavy. With a larger fleet and with efficient organisation, much better results might have been achieved in spite of the inherent difficulties of the situation.
Although the electric cab has the advantage of being a smaller vehicle and therefore more adapted to economical propulsion by storage batteries, the conditions of the cab service are not at all favourable to the system. The essential feature of a cab is that it should be available anywhere, to go anywhere at a moment's notice. An accumulator-driven vehicle, on the other hand, is tied by an invisible cord to the charging station. Even if charging stations were multiplied enormously, the electric cab would have no real freedom of action, since several hours are required for the process of re-charging. We have only to compare the limitations of the electric cab with the freedom of the petrol cab (which can renew its supply of petrol in a minute or two at any motor depot) to realise that the roving commission is not at all suited to the former.
In 1899 a very bold effort was made to establish an electric cab service in London. To inaugurate the service a procession of the cabs was formed, but it excited more ridicule than serious interest. The clumsy appearance of the cabs was against them;and their behaviour was not satisfactory enough—as to speed and reliability—to overcome the first unfavourable impressions. They soon disappeared, to add another failure to the long list of disappointments in connection with accumulator traction.
The private electric automobile remains, however, because it has been organised under conditions which suit the peculiarities of the storage battery. Its survival, in conjunction with the failure of a similar means of transit for tramway, omnibus, and public cab services, has pointed to another direction in which the electric automobile should be a commercial possibility. That is, in connection with the local distribution of goods from large stores and other centres.
The United States have given a very distinct lead in this matter. In New York, Chicago, Washington, and other large cities the electric automobile for private use is highly developed and there is also an extensive service of electric vehicles ranging in size from a small parcels van to a large lorry capable of carrying loads up to several tons. No doubt the local cost of other means of transport has something to do with this American development, which has, moreover, been strongly supported by the companies which supply electricity to the public. But the fundamental reason lies in the special character of the service demanded.
The vans belonging to a large store all start from a certain point and return to it after journeys oflimited range. Owing to the period occupied in loading up, and also to the pre-determined hours of most of the deliveries, there is no difficulty about affording the time required for re-charging the batteries, or in arranging each journey so that the vehicle returns before the batteries are exhausted. With a standardised fleet of vehicles, it is possible to remove the discharged batteries and replace them with charged ones in a few minutes. The whole arrangement, in fact, is like a private automobile garage, with the advantage that the probable demand can be forecast with a somewhat greater degree of certainty.
Steam and petrol-driven wagons run most economically on long steady journeys at fairly high speeds, and the electric automobile does not attempt to compete with them on these lines. But it offers competition within city limits for door-to-door delivery; and its prospects are particularly good for light parcel service, where the horse is still maintaining its position against the petrol vehicle. The advantages of the electric vehicle in neatness and noiselessness will certainly secure its success if the cost can be proved to be not appreciably greater than that of its rivals.
Apart from the necessity of careful organisation, the main essential of success in electric automobile work is a supply of cheap electricity. Owners of private electric launches have to pay anything from8d.to 2s.6d.per unit for re-charging their batteries, but these high prices are due to the intermittent character of the demand and also (in some cases) to the cost of providing machinery to supply current at special pressures for particular launches. An electric automobile garage, situated close to a public generating station and offering a larger and more regular demand, will of course obtain current much cheaper. And it is possible that arrangements may be made for supplying electricity to automobiles at a much lower rate even than that customary for general power demands. In the metropolitan borough of Marylebone, for instance, an electric garage may obtain current during the small hours of the night at 1/2d.per unit, which is half the standard rate for power purposes. This low price is offered because there is otherwise practically no demand at all for electricity during these hours. If, therefore, a garage arranges—and the arrangement is quite feasible—to charge its batteries overnight, the power bill may be divided by two.
The electric automobile has been used to some extent as a touring car, but although journeys up to 100 miles have been performed on a single charge, the time occupied in re-charging, and the difficulty of finding convenient charging stations, are fatal to any development in this field.
Between the petrol-driven vehicle and the electric automobile there is an interesting series of links provided by 'petrol-electric' systems.
At one end of the chain, electricity plays an important part in supplying power to drive the car. At the other end, electrical apparatus is introduced merely as a form of transmission gear between the petrol engine and the driving axle. The reason for attempting the petrol-electric combination will be most readily understood by considering the latter arrangement first.
The petrol engine is a high-speed engine, capable of working most satisfactorily when it runs at a uniform rate with a constant load. On the other hand, the speed of the driving axle of a car varies from a very much lower speed down to zero. It is therefore necessary, when driving a vehicle with a petrol engine, to arrange some forms of variablespeed-reducing transmission gear between the engine and the driving axle. The problem is further complicated by the fact that the petrol engine is irreversible, has practically no 'starting torque,' and has a very slight overload capacity. It has to be started running 'light' and then switched on to a low gear which gives sufficient power to overcome the inertia of the car. As the speed of the car rises, there have to be successive changes of gear. These difficulties are, of course, accentuated when dealing with the heavy weight of an omnibus.
Petrol-electric motor omnibusFig. 9. Elevation and plan of a petrol-electric motor omnibus equipped by W. A. Stevens, Ltd. Directly behind the front wheels is the petrol engine, driving a dynamo through a flexible coupling. The dynamo supplies current to the motor directly behind it; and the motor drives the rear wheels through a cardan shaft. The transmission of power between the engine and the shaft is electrical at all speeds.
Fig. 9. Elevation and plan of a petrol-electric motor omnibus equipped by W. A. Stevens, Ltd. Directly behind the front wheels is the petrol engine, driving a dynamo through a flexible coupling. The dynamo supplies current to the motor directly behind it; and the motor drives the rear wheels through a cardan shaft. The transmission of power between the engine and the shaft is electrical at all speeds.
Fig. 9. Elevation and plan of a petrol-electric motor omnibus equipped by W. A. Stevens, Ltd. Directly behind the front wheels is the petrol engine, driving a dynamo through a flexible coupling. The dynamo supplies current to the motor directly behind it; and the motor drives the rear wheels through a cardan shaft. The transmission of power between the engine and the shaft is electrical at all speeds.
Practically all the troubles with petrol motor omnibuses have resided in the gear; and even the most ardent enthusiast for the all-electric faith must admit that the motor engineer has overcome these troubles (in great part if not wholly) with remarkable skill and ingenuity. But the complications of an adjustable mechanical bridge between a high-speed engine and a varying low-speed axle are so great that an electrical bridge was proposed as a substitute. By coupling the engine direct to a dynamo and by using the current so generated to drive variable-speed motors geared to the driving axle, the electrical engineer hoped to get better working results from the petrol motor than could be obtained with any mechanical transmission gear.
The most conspicuous advantage, apart from the quietness of running at all speeds, lies in the ease and smoothness with which the petrol-electric motor can start and gain speed. In this respect the combination system is practically on the same level as (or even superior to) the electric tramcar or the electric automobile. There is an entire absence of the jerks and jarring noises which usually accompany the starting of a motor omnibus. The same facility of control is of advantage in adjusting speed to suit the other traffic on the road, and also in negotiating hills.
In one class of petrol-electric vehicles the electric transmission gear is continuously used. In another, it is used at all speeds except the highest, when the engine is coupled directly (by a magnetic clutch) to a mechanical driving gear. In a third class the arrangement is more complicated, as it involves the use of storage batteries as an auxiliary to the power provided directly by the petrol engine. The Fischer type of petrol-electric vehicle uses electric transmission solely and has a fairly large battery to supplement the engine-produced current when steep hills are being negotiated. At ordinary speeds on level roads the surplus power produced by the engine goes to charge the battery.
The 'Automixte' type is peculiar in using the mechanical transmission gear all the time. The dynamo coupled to the engine supplies current to a small battery when surplus power is available; thesame dynamo may be driven as a motor by current from the battery when such assistance is wanted at starting or on steep hills. The electric part of the equipment thus acts first as a generator and then as a motor, the change taking place automatically.
These different petrol-electric devices are very attractive from the engineering point of view, but at the present time it is uncertain whether they will realise the hopes of their inventors. The additional weight of the electric equipment is against them; and in some cases there appears to be a lower all-round efficiency. So that the motor-omnibus world, as a whole, continues to fix its faith upon the improved forms of mechanical transmission.
The underlying idea of the petrol-electric system has, however, been suggested for marine propulsion with a somewhat better prospect of success.
There is a partial analogy between the conditions of motor omnibus working and of ship propulsion with turbines. The steam turbine is, like the petrol engine, essentially a high-speed machine. The screw propeller, on the other hand, works most efficiently at low speeds. Therefore the marine engineer has to try and find some common denominator between an engine which runs most efficiently at high speeds and a propeller which is at its best when revolving comparatively slowly.
Steamship with 'Paragon' systemFig. 10. Diagrammatic section of a steamship which has been 'converted' from the ordinary method of propulsion to the 'Paragon' system of electric main marine propulsion. The reciprocating engine has been replaced by a steam turbine, coupled direct to an electric generator which supplies current to a motor attached to the propeller shaft. The tests carried out with this vessel will indicate the advantages of the electric method of propulsion even with the usual long length of shaft. The vessel has a gross tonnage of 1241, and its speed is 9 knots. The engines replaced ran at 78 revolutions per minute and gave 500 brake horse power. The turbine now installed runs at 2500 r.p.m., and develops 630 brake horse power. (Illustration reproduced by courtesy ofThe Electrician.)
Fig. 10. Diagrammatic section of a steamship which has been 'converted' from the ordinary method of propulsion to the 'Paragon' system of electric main marine propulsion. The reciprocating engine has been replaced by a steam turbine, coupled direct to an electric generator which supplies current to a motor attached to the propeller shaft. The tests carried out with this vessel will indicate the advantages of the electric method of propulsion even with the usual long length of shaft. The vessel has a gross tonnage of 1241, and its speed is 9 knots. The engines replaced ran at 78 revolutions per minute and gave 500 brake horse power. The turbine now installed runs at 2500 r.p.m., and develops 630 brake horse power. (Illustration reproduced by courtesy ofThe Electrician.)
Fig. 10. Diagrammatic section of a steamship which has been 'converted' from the ordinary method of propulsion to the 'Paragon' system of electric main marine propulsion. The reciprocating engine has been replaced by a steam turbine, coupled direct to an electric generator which supplies current to a motor attached to the propeller shaft. The tests carried out with this vessel will indicate the advantages of the electric method of propulsion even with the usual long length of shaft. The vessel has a gross tonnage of 1241, and its speed is 9 knots. The engines replaced ran at 78 revolutions per minute and gave 500 brake horse power. The turbine now installed runs at 2500 r.p.m., and develops 630 brake horse power. (Illustration reproduced by courtesy ofThe Electrician.)
The gulf between the two has been narrowed by the improved design of propellers. Some engineers assert that continued improvements will bridge the gulf completely. Others have sought the solution in the same way as the motor engineer—by the use of mechanical change-speed gears. The suggestion has also been made to employ hydraulic gear as an intermediary; and in some recent vessels reciprocating engines with comparatively low-speed turbines driven by exhaust steam have been adopted.
In the electric system the turbine is coupled direct to an electric generator and may run continuously at the highest economical speed. The propeller shaft may be quite short and is driven by a slow speed motor connected by cables to the generator. Various arrangements for controlling the supply of current to the motor (with appropriate design of generator and motor) have been devised by Mr Durtnall, Mr Mavor, and other workers in this field; but whatever the details of these arrangements may be, they all give a wide range of speed both ahead and astern. The direct drive with the steam turbine has really only one speed—full speed ahead; and as the turbine is irreversible, 'astern' turbines have to be installed in addition. These limitations and complications are removed entirely when electrical transmission is adopted.
Moreover, the electric system can be so arranged that the control gear may be operated from thebridge itself. The facility in manoeuvring is, in fact, so marked that it would recommend electric marine propulsion even if that system offered no advantages on the score of economy in weight, space, and steam consumption over the existing systems. The steam turbine, it may be noted, has been adopted so far only in high-speed vessels; and it is generally recognised that its extension to vessels which run at 12 or 16 knots depends upon its adaptation to slow-speed propellers. Advocates of electric marine propulsion claim that they hold the most efficient solution of this problem.
It may also be pointed out that a considerable section of marine engineers look forward to the use of internal combustion engines (driven by oil or gas) on board ship. For naval purposes especially it would be a great advantage to do away with funnels and so leave the decks more free for gun mountings. As internal combustion engines are irreversible, the electric system offers a means of escape from a fundamental drawback to their use at sea. Here again the perfection of manoeuvring power, especially with twin screws (either of which may be controlled from the bridge through a wide range of speed ahead or astern), gives the electric system a strong claim for consideration by the naval authorities.
It is hardly necessary, except as a matter of curiosity, to refer to the suggestions made, from timeto time, of accumulator-driven ocean steamships. Some wonderful pictures have been published of large vessels with tons of ballast in the form of storage batteries. They are likely to remain in this ideal condition, for although the driving of a large vessel by stored electricity is quite possible, it is also about the most expensive method which has ever been proposed.
Electric power from storage batteries has been used as an auxiliary in the propulsion and manoeuvring of submarines. In aerial navigation electricity has so far been employed to a very limited extent. Small airships have been designed to carry electric accumulators connected with various motor-driven propellers for raising, lowering, going ahead or astern, and steering. The switches which control the passage of the current to these propellers are connected with a wireless telegraph receiver, so that each operation may be started or stopped by a particular ether wave or series of waves. Demonstrations of such 'wireless-controlled' airships have been given in theatres; their field of usefulness, if any, is in connection with war on land or sea. Whether they will have any better fate than other devices for dropping bombs over the enemy's camps or ships remains to be seen.
One inventor has, I believe, suggested a means of direct electrical propulsion for aeroplanes, thecurrent being derived from a petrol-driven generator and carried to motors attached to propellers so arranged as to give certain advantages in stability and manoeuvring. As yet, however, the probability of electricity being applied to locomotion in the air as well as on land and on sea is somewhat remote.
Electric tramways have reached a period of middle age in which they are more concerned about their internal economy than the prospect of enterprise in new directions. Such development as they feel capable of making under present legislative conditions is only by proxy and tentatively, with the aid of the trolley omnibus.
Electric railways, however, have still many worlds to conquer. They are now in much the same position as electric tramways held about the year 1896. That is to say, they have already given practical proof of their capabilities and enabled engineers to point out the directions along which they are certain to develop. In the railway world there is a growing conviction that the adoption of electric traction on all suburban and inter-urban railways must be simply a matter of time. For main line traffic the possibilities of using electricity are as yet only an article of faith among electrical engineers.
Although the earliest experiments in electric traction were made in the railway form, the first electric lines could hardly be regarded as railways in the ordinary sense. They were really light railways, in which the traffic conditions approximated to those of tramways. The routes were short, the cars small, and the traffic of modest dimensions. They contained the germ of both the tramway and the railway; but, in the case of the railway, many years of technical development had to pass before the problem of applying electricity to the handling of large masses of traffic under standard railway conditions was solved.
The fact that the first electric railway in the United Kingdom was constructed at the Giant's Causeway (in 1883) is significant. The Giant's Causeway is one of the few places in our islands where water power is available close to a district with a demand for traffic facilities. In 1885 another electric railway deriving its energy from water-driven turbines was built between Bessbrook and Newry. At that period it was considered that waterfalls provided the only really feasible source of cheap electricity on a large scale. Even yet the impression survives that electric power stations using steam cannot produce current so cheaply as those which 'harness' waterfalls. Many people, in fact, are inclined to attribute the comparative backwardnessof electrical development in Great Britain, not to legislative conditions, but to the lack of large waterfalls.
There might have been more active progress in the pioneering days if the presence of water power at convenient points had encouraged electrical engineers to repeat the experiments at Portrush and Bessbrook. But at an early stage in electrical history it became clear to engineers that coal was just as feasible a source of cheap power as water. The idea that a waterfall provides power 'for nothing' is one of those superficial conceptions which make the hardiest of fallacies. To 'harness' a waterfall requires a heavy expenditure of capital on conduits, pipe-lines, dams, and other works. The interest upon that capital is a heavy item, apart from the cost of maintenance and repairs. Waterfalls are situated in mountainous country, generally remote from the centres of industry; the water-power station, therefore, has to face the cost of transmission mains and the loss of energy involved in conveying the power to the place where it is wanted. Further, waterfalls and the adjacent ground belong either to individuals or to the State; and payment is generally exacted for the right to use them.
All these items have to be covered in the price charged for current to the public or to railway undertakings. Nature may provide the 'head' ofwater 'free,' but man has to spend money in utilising it, just as he has to do in mining and in obtaining heat from the coal which is also provided 'free.' Anything which is obtained 'for nothing' is generally worth nothing.
The full economies of generating electricity by steam power are not, however, realised until business is done on a large scale. As the first essential of a successful electric railway is a plentiful supply of cheap power, development from the experimental stage of Portrush had to wait until engineers mastered the art of producing electricity from large generators. They gained the necessary experience with electric tramways and in electric lighting. We have seen how, as regards tramways, legislation delayed and hampered progress. A similar cause was at work in connection with electric lighting. In 1882 an Act was passed regulating electric lighting on lines modelled upon the principles of the Tramways Act, 1870. Capitalists declined to work under this Act; and it was not until after 1888, when the Act was amended, that any money could be found in Great Britain for electric lighting schemes. This delay was a serious handicap not only to electric lighting but to the business of British electrical manufacturing, as there was, comparatively speaking, no demand for electrical plant for over six years. Meanwhile, matters had been advancing on normallines in other countries; and when the demand came at last, the manufacturers on the Continent and in America were the only ones organised and ready to meet it.
These points must be touched upon in order to understand why so long a period elapsed between the pioneer electric railways and the real electric railway movement as we know it to-day. They also serve to explain the prominent part which American and German firms took in electrical developments here. Engineering and legislative conditions combined to retard electric railway enterprise so that it did not begin to take firm root in Great Britain until about 1890, and did not attain to any conspicuous growth until the beginning of the twentieth century.
Until after 1890 the only electric railways in Great Britain taking power from steam dynamos were those at Brighton Beach, Ryde Pier (Isle of Wight) and Southend Pier, opened in 1883, 1886 and 1890 respectively. These were all, of course, of short length. The Brighton Beach railway, designed and constructed by Mr Magnus Volk, was a unique piece of work. The rails were laid on heavy concrete blocks below high-water mark; and the cars were platforms raised on a light iron structure. Power was conveyed to the cars from wires hung on posts like the standards of a tramway on the trolley system. The unusual sensation of travelling over the waterwas enjoyed by hundreds of people until the difficulty of maintaining the track (owing to the erosive action of the waves) led to the railway being abandoned and another line of more ordinary character being laid on the level of the undercliff roadway.
The first indication of the genuine electric railway movement was given in 1893, when the Liverpool Overhead Railway was opened. This line was constructed to afford communication along the line of docks fringing the Mersey. The track was carried on a continuous bridge in order to avoid obstruction between the docks and the streets behind; and being overhead, there were serious disadvantages attached to the use of steam locomotives. Electric locomotives were therefore employed.
In this case, it should be noted, electricity was not adopted because it was more economical or efficient than steam. The reason lay with the peculiar situation of the railway. A similar reason decided the promoters of the City and South London Railway to try electric locomotives on their line. This railway, which was opened in 1890, was the first deep level or 'tube' railway in the world. Moreover, it was constructed and equipped throughout by British engineers, and at a time when the art of tunnelling was much less advanced than it is now. In the later and more imposing development of tube railways in London, the foresight and enterprisedisplayed by the pioneers of the City and South London Railway are apt to be overlooked. It was, however, the success of the original line from the Monument to Clapham which made it possible to raise capital for the Central London Railway (opened in 1900) and for the extensive tube railway system organised by the Underground Electric Railways Company of London.
On a deep-level railway, steam is, of course, out of the question. Even on the old 'Underground,' built close to the surface and furnished with frequent openings at the stations, and by means of ventilating shafts, the atmospheric conditions were abominable. The sulphurous fumes were indeed recommended for asthma and other complaints, but on a tube railway they would have been sufficient to cure every human ailment. Therefore the choice lay between electric traction and haulage by cables, compressed air, or some other innocuous system. Within these limits electricity was chosen on its merits.
The first railway in Great Britain to undertake conversion was one in which both the physical and economic troubles were exceptionally serious. The Mersey Railway is little more than a tunnel under the river, and it is distinguished by heavy gradients and by the continuous necessity of pumping out the water which drains into it. With steam traction the difficulty of ventilating the tunnel was an addedtrouble. Owing to these various causes the working expenses were abnormally heavy, and led ultimately to a receivership. Electric traction was adopted as the only possible cure. The pumping and ventilation arrangements were both reorganised for electric power; and the trains were equipped with electric traction on the 'multiple-unit' system, an arrangement—to be described in the next chapter—which is well suited to the economical handling of steep gradients. The practical result was a great increase in traffic, with a marked decrease in the proportion of expenses to receipts.
No other British railways, happily, were in so desperate a condition as the Mersey line, but all of them were, at the end of last century, feeling the effect of certain disquieting tendencies. These tendencies were most marked in connection with suburban and short-distance inter-urban traffic, which is quite distinct in character from the main-line traffic. We talk glibly enough of railway traffic as if it were a unity, but it is clear that very different considerations govern the traffic on a main line between, say, London and Glasgow, and those which control the traffic on London suburban routes or on a railway connecting the adjacent towns of the Potteries. Some railways have to deal with all three classes at the same time and occasionally on the same lines of rails. Electric traction has, so far, made itself felt only where thesuburban or similar inter-urban traffic has been separable from the main line traffic.
The growth which took place in suburban traffic before and after the end of the century ought to have brought increased prosperity to the railway companies, but it did not always do so. Competition between the various companies led to a reduction in fares; Parliament, by establishing workmen's fares, forced the companies to carry an ever-increasing number of passengers at a loss, or at least without profit; wages tended to increase and hours of working to decrease—both affecting the cost of operation; rates and taxes became heavier and heavier with the growth of municipal expenditure; and a higher standard of comfort and efficiency was demanded by the public. In some instances the situation was aggravated by the competition of electric tramways along routes parallel to the railways. This competition was limited to point-to-point traffic, its maximum range being about three miles; but it was a grievance against which the railway companies protested very loudly, especially when the tramways were owned by local authorities to which the railways paid large sums in rates.
The general effect of all these factors was to reduce the margin of profit on which the railways were working. We have seen, in the case of tramways,how easy it is for a slight change in a frequently-recurring expense to have a serious effect in the aggregate. Railways are in much the same position; and the various influences at work upon the suburban traffic brought them face to face with the importance, if not the necessity, of finding some means of dealing with larger volumes of traffic on a basis more economical than that provided by steam locomotives.
This means they found in electric traction; but it may be noted that even railway engineers took some time to realise exactly what electric traction offered them. They were looking for something to reduce their annual expenses; and when they made calculations about electric traction they found that, when the expense of providing the electrical equipment was taken into account, the total cost of hauling the trains electrically on the existing schedule might be greater instead of less than the cost of steam haulage. They were therefore inclined to look upon the economic benefits of electric traction as an illusion.
In course of time, however, it came to be recognised that the function of electricity is not to act like a blue pencil on the debit side of the revenue account. Its essential purpose is to increase the volume of traffic. From the public point of view this is very much more valuable. Passengers are not directly concerned with means of reducing working expenses, but they are closely interested in the improvement of the frequency and speed of the service. Theadoption of electricity on suburban lines has really been dictated by the demand for increased facilities. At the 'rush' hours of the morning and evening, when the great tide of workers flows and ebbs, the capacity of the steam lines was taxed to the utmost. And with the growth of population the difficulty of running sufficiently frequent trains became almost insuperable.
Apart from these particular necessities, the general features of railway economics point to the supreme advantage of increasing the volume of traffic in every possible way. In a railway, as in a tramway, the preponderating item is the cost of construction and maintenance; and unless a certain minimum of traffic is carried, the most economical working in the world will not secure a profit. The standing charges fall upon the idle hours as well as upon the busy; for every minute that a line of rails stands empty there is a loss of money. Railway progress depends upon reducing the proportion of idle hours; and that can only be done where there is scope for the growth of traffic, and where there is means—such as electric traction—of dealing with that growth on an economical basis.
In the succeeding chapter it is explained how electric traction enables a more frequent service to be run with advantage even on systems which were worked to the maximum limit possible under steam conditions. But in the meantime it will be interesting to trace the effect itself on a railway which soon followed the Mersey Railway in making the change from steam to electricity—the Metropolitan District Railway.
Electric trainFig. 11. An electric train on the Metropolitan District Railway, equipped by the British Thomson Houston Company. The front and rear cars and one intermediate car are equipped with electric motors, all controlled from the 'cab' at the end of the train. The controller handle may be seen close to the nearest window of the first car. The rail immediately in front of the foot of the guard is the conductor rail which conveys the current to the train. The rail between the track rails carries the return current.
Fig. 11. An electric train on the Metropolitan District Railway, equipped by the British Thomson Houston Company. The front and rear cars and one intermediate car are equipped with electric motors, all controlled from the 'cab' at the end of the train. The controller handle may be seen close to the nearest window of the first car. The rail immediately in front of the foot of the guard is the conductor rail which conveys the current to the train. The rail between the track rails carries the return current.
Fig. 11. An electric train on the Metropolitan District Railway, equipped by the British Thomson Houston Company. The front and rear cars and one intermediate car are equipped with electric motors, all controlled from the 'cab' at the end of the train. The controller handle may be seen close to the nearest window of the first car. The rail immediately in front of the foot of the guard is the conductor rail which conveys the current to the train. The rail between the track rails carries the return current.
Throughout the steam age the finance of the District Railway Company was as unattractive as the physical conditions of the railway itself. No dividend was ever paid on the ordinary shares; and even with the growth of London there was little prospect of any dividend ever being paid. When—about ten years ago—the late Mr C. T. Yerkes came over from America and obtained a controlling interest in the District Railway Company with a view to converting it to electric traction, he was regarded as a philanthropic enthusiast. Many of the shareholders themselves were reluctant to give their assent to the change; they preferred to bear the ills they knew than fly to others which might be introduced by an American financier.
But Mr Yerkes and those who worked with him had something more in view than the improvement of traffic on the District Railway. They acquired control of several tube railway schemes and obtained powers for new lines, so as to organise a comprehensive system of underground electric transport in London. They had sufficient faith in the traffic possibilities of London to find the enormous capital required toconstruct these tube railways and also to convert the whole District Railway to electric traction. The constructional work occupied several years; and after the lines were opened one by one, arrangements had to be developed for through-bookings among the various lines and between them all and the existing underground railways like the Central London Railway, the Metropolitan Railway (closely linked with the Metropolitan District) and the City and South London Railway. A systematic attempt was also made to develop the travelling habit in London by persistent advertising of the railway services and by increasing the frequency and rapidity of the trains. From these points of view the organisation of the network of lines comprehensively known by the title of 'Underground' is certainly unsurpassed.
The difficulties which had to be overcome in this great work were enormous, but there has been no break in the thread of progress. The 'tubes' are paying dividends which, though modest, are an encouragement to further developments. The finance of the District Railway has lost its element of chronic despair. Considered as a whole, the results prove that where there is the potentiality of large traffic, electricity is the instrument which must be applied. During the steam days, the most crowded part of the District Railway (the 'Inner Circle') carried a maximum of 16 trains per hour. With electrictraction that figure has been raised to 40 trains per hour. And the remarkable thing is that with each increase in the service the traffic grows. Many people welcomed the electrification of the District as a measure of relief from the overcrowding on the steam trains during the busy hours. But with a service of trains more than doubled in frequency and also increased in capacity per train, overcrowding continues and the 'straphanger' has become an established institution.
It may be accepted as substantially proved that, on suburban and inter-urban railways in populous districts, electric traction is a means of increasing traffic and diminishing the proportion of working costs. Moreover, these results have been achieved in conjunction with substantial reductions in fares and with marked improvements in the comfort of travelling.
The engineering aspect of these changes has now to be considered.
When electric railways were first considered, the natural tendency of engineers was to follow the existing model and merely substitute electric locomotives for steam locomotives. In point of fact, however, the engineering method now adopted is an evolution from the tramway model, not from that of the typical railway.
A certain advantage was, of course, to be gained by replacing steam locomotives by electric ones. The greater 'starting torque' of the electric locomotive enables it to get a train up to full speed more quickly; and the capacity of the electric motor for taking heavy overloads assists the electric train in surmounting heavy gradients. Some advantage was also gained by producing all the power at a central source, instead of having a large number of steam locomotives, which are really power stations on wheels. But the electric locomotive had still to be made heavy enough to get sufficient grip of the rails; it had to haul itsown dead weight; and it had to be made powerful enough to tackle a full-sized train on the steepest gradient with its complement of passengers, although the general demand upon it might be considerably less than that maximum.
The electric locomotive, in short, was an advance upon the steam locomotive, but it did not get past the essential drawbacks of the locomotive system. A locomotive is most economical when hauling full trains for long distances at a uniform speed; it is essentially a long-distance machine. The first demand for electrification came, however, from suburban railways, where the stations are close together and where, therefore, the speed is constantly varying from zero up to a maximum and back to zero again. The traffic also fluctuates between extreme limits; and there is obvious waste in having to run heavy locomotives and trains backwards and forwards during the slack hours. There was therefore a demand for some method of propulsion which would enable the length of trains and the consumption of power to be adjusted more closely to the variations in the traffic.
A step in the right direction was taken when the locomotive equipment was placed on a car, thus utilising the weight of the passengers to increase the adhesion on the rails. But the full advantages of electric traction were not realised until what is known as the 'multiple-unit' system was adopted.
The idea underlying this system is quite simple. If, instead of concentrating the motive power on a single locomotive or driving unit, we distribute it among the cars forming a train, we get the multiple-unit system. An electric tramcar and a trailer attached to another tramcar and trailer, with a third tramcar behind, would form a model for a multiple-unit train. By connecting the electrical equipments on the three tramcars—front, middle, and rear—it would be possible to control the train from either end or from the middle.
This is the principle upon which all the electric railways in Great Britain are now worked, with the exception of the City and South London Railway, where locomotives are still used and where the trains are comparatively short and light.
It will be seen that each multiple-unit train is readily divisible. A single motor car may be run, or a car with one or two trailers, or a long train made up of as many motor cars and trailers as the platforms will accommodate. And whether the trains are long or short, the power absorbed is in proportion to the length of the train and the load of passengers. By this simple means power is economised, and the railway engineer is able to reduce the proportion of idle rolling stock.
The adjustment of the length of trains to the fluctuations of the service is made easier by theabsence, in the multiple-unit system, of the necessity of shunting at the termini. As a multiple-unit train can be controlled from either end, a more frequent as well as a more flexible service can be run. With steam traction the number of trains which may enter or leave a terminus is limited by the time occupied in shunting and by the necessity of leaving lines of rails free for that operation. With an electric train on the multiple-unit system, no more time is lost than the few seconds necessary for the driver to walk from the front of the train to the rear, which then becomes the 'front.' No lines have to be kept open for shunting locomotives, so that the available accommodation for trains is considerably increased. Some of the London railway companies have spent enormous sums in enlarging their terminal accommodation and have found that it is still inadequate to the demands of the 'rush' traffic. Electric traction therefore offers them an improvement of enormous value without the expenditure of a penny on station alterations.
The crowning advantage of electric traction lies, however, in the more rapid acceleration which it affords. We have already seen how important this item is on tramways. It is still more important on suburban railways, where a high average speed, in spite of frequent stops, is a vital matter.
On the District Railway the rate of accelerationin the old steam days was about 6 inches per second per second. It was, in fact, so low that the trains could not reach a fair speed before the brakes had to be applied to bring the train to a stop at the next station. With electric traction the rate of acceleration has risen to about 18 inches per second per second. On the Liverpool Overhead Railway a rate of 36 inches per second per second was reached in certain tests. Heavy starting currents are, of course, necessary to bring a train from rest to full speed at such a rapid rate, but it is quite possible for the electrical engineer, without being unduly extravagant in current, to accelerate a train more quickly than the passengers would find comfortable.
The practical result of rapid acceleration (combined with rapid braking) is not only to give a higher average speed but also to enable a more frequent service to be run. Owing to the block system on railways it is impossible for trains to follow each other closely in the manner of tramcars; and it is therefore of cardinal importance that no train should occupy a block for one second more than is necessary. Rapid acceleration becomes all the more important in this respect because of the difficulty of setting down and picking up passengers quickly. This difficulty is overcome in part by using saloon carriages with middle and end doors, in place of compartment carriages. At first the District Railwaytried to help matters by operating these doors pneumatically, but the mechanism became unpopular after a number of late-comers had been pinched by closing doors. The management has reverted to hand operation; and it has probably achieved more by educating the public to move quickly than it would have gained with its too-perfect mechanical system.
London travellers have become so accustomed to entering and leaving trains quickly that it is possible for an observer to distinguish strangers by their slower movements on an underground railway. Thus the passenger, as well as the service, has been 'speeded-up.' The more frequent service of trains with a higher average speed would not have been possible, however, without an improvement upon the old methods of signalling. There is no need to dwell upon the weakness of the human element in railway signalling; and it will be clear even to the layman that the strain of handling traffic with a headway of one minute and a half, or less, would be more than men could stand. Automatic signalling had therefore to be adopted to obviate the risk of disaster.
Each train, as it leaves a block or section, 'clears' the signals for that block; and when any train attempts to enter a block against signals, the current is automatically switched off and the brakes applied. The system is so perfect that, in spite of the enormous traffic worked under it, there has been no failure andno accident. It is, of course, costly to install; and its cost can be justified (financially) only when the traffic is very heavy—that is to say, when the conditions make it almost a necessity.
The supply of electric power to electric railways is organised on practically the same lines as in the case of tramways. That is to say, current is generated at a central station, transmitted at high pressure to various sub-stations, and supplied from there at working pressure through 'feeders' to each section of the system. In the case of the 'Underground' system, most of the power is taken from a single huge electric station at Chelsea. Current from that station drives trains as far west as Wimbledon, Hounslow, and Ealing, as far north as Highgate and Golder's Green, and as far east as Barking.
This is a magnificent example of the concentration which gives economy. If each of the underground railways forming the system had erected its own generating station, the total initial outlay, on land, buildings, and machinery, would have been greater, and the cost of current would have been higher, owing to the smaller output and the more irregular demand which a single railway affords. The ideal electric power station is one which is constructed with the largest generating units and produces current at its maximum capacity throughout the twenty-four hours of each day. The Chelsea power station is nearer theideal than a smaller one supplying a short railway could be. And a station of the latter class is, it may be noted, nearer the ideal than the arrangements on a steam railway, where the sources of power are scattered in hundreds of locomotives.
The concentration of power is therefore one of the many factors which have enabled electric railways to give a vastly improved service at lower fares.
With two exceptions—to be considered in the next chapter—the electric railways of Great Britain are constructed on the 'third-rail' system. They are thus a reversion to—or, rather, a survival of—the original type adopted by Siemens in 1879. The 'third-rail' is carried on insulators a few inches outside the track rail; and the motor cars are provided with a 'brush' or 'shoe' which slides along it and collects the current. In the centre of the track there is generally a second insulated rail to carry the return current, as it is more convenient, under railway conditions, to have a conductor independent of the track rails than to follow the tramway plan of using the rails 'bonded' together. In stations and at crossings the third or 'live' rail is protected by a wooden board in order to reduce the risk of shock to anyone falling on the line or walking upon it. The board is placed high enough over the rail to allow the shoe to pass freely.
As regards the motor equipment on the cars,tramway models have been followed very closely. The 'series-parallel' system of control is again adopted in order to get the high starting torque which gives rapid acceleration with moderate current consumption. The course of the current is again from the live rail, through the controller, through the motors, and thence to the return rail. The controller itself is more or less on the tramway principle; and the main modification in it is the arrangement which enables all the motors on a multiple-unit train to be operated by a single controller. This is done by connecting the controllers electrically and using electric power so that they all work in unison. Some companies use, for this purpose, compressed air controlled by electricity instead of electric power alone, but in both cases the principle is essentially the same.
Considered as a whole, the difference between a tramway and an electric railway on the third-rail system is a difference in degree, not in kind. The traffic is greater and the speeds higher, but both serve the purposes of comparatively short-distance transit. Indeed, within certain limits they compete with each other.
There remains to be considered another type of British electric railway which points the way to the extension of the new mode of traction to main line railways.
On tramways, automobiles, and 'third-rail' lines, the electric current used belongs to the type described as 'continuous' or 'direct,' because the flow is always in the same direction. The other type of current is known as 'alternating,' as it flows backwards and forwards many times per second. There are several kinds of alternating current—single-phase, two-phase, three-phase, and polyphase—each produced from generators designed in a particular way.
It is not possible to give any adequate account of these different kinds of alternating current without going rather deeply into the theory of electricity. The ultimate practical point is that in transmitting alternating currents the circuits increase in number with the phases. Thus, three-phase current requires three wires, two-phase current three or four wires, and single-phase current a single circuit like that of continuous current[1].