CONDUIT AND SURFACE-CONTACT TRAMWAY SYSTEMS
Roughly speaking, the arrangements for generating electricity,
distributing it, and utilising it on the car, remain the same in conduit
tramways and surface-contact tramways as on the overhead system. The
differences between the three systems are, as already indicated,
confined to the means of collecting the current for each car.
Both the conduit and the surface-contact system were suggested as a means of escape from the main objection to the overhead system—the exposure of 'live' wires in the street. The cable tramway, with its concrete trough and slot, gave an obvious hint. There would be no difficulty, apparently, in carrying wires on insulators in the trough or conduit, and utilising the slot for a 'plough' which would slide along inside the conduit, keeping contact with the wires, and so conveying the current to the car.
This was tried for the first time in Blackpool, where—in 1884—a length of conduit tramway was laid along the front street of the town. The conditions could hardly have been less favourable for the system, as the sea frequently washed over the roadway, flooding the conduit with water and sand. Further, the conduit was so shallow that children were able to get at the conductors with their metal spades. As the conduit carried the return wire, the effect of a metallic contact between the two conductors was to cause a 'short circuit,' with very entertaining fireworks but with no amusing results for the tramway engineer. After a heroic trial, the system had to be abandoned.
Bournemouth was the next British town to adopt the conduit. It did so as a token of its exceptional civic pride. Three times, in fact, the Bournemouth Corporation declared that it did not want tramways of any kind whatever within its gates. And when the pressure of public opinion forced its consent, the arrangement was made that no overhead wires should appear in the central district of the town. Several miles of conduit tramway were therefore constructed (the trolley system being used for the outer tramway routes); and as by that time a good deal of experience had been gained in conduit work both in America and on the Continent, the contractors were able to give the Corporation a conduit system built to endure. At first the Corporation was reconciled to the fact that the conduit sections had cost about twice as much per mile as the trolley lines, but as years went on, and as the financial results of the system continued to prove unsatisfactory, the Corporation's contentment became modified. An examination of the accounts showed that the conduit sections could be reconstructed on the overhead system at a cost equal to the annual expense of maintaining these sections in good working order. Since the public had got used to the overhead wires on the other sections, and since they had not got used to owning tramways which produced a heavy loss, the decision was made to abandon the conduit system altogether.
In London the conduit system was adopted by the London County Council for various reasons. One was that the Council felt that London ought to have the best, the very best, and nothing but the best. Another was that the streets were so congested with traffic, lamp standards, telegraph and telephone poles, and other obstructions, that trolley wires and trolley standards would be a great nuisance and a serious danger. Aesthetic reasons were also advanced, but it is difficult to realise that they had much weight in connection with the majority of metropolitan streets. Trolley wires were, in fact, freely erected in suburban streets where there was a certain amount of beauty worth preserving.
The main underlying reason, no doubt, was the feeling that London could afford the most costly system. In any ordinary city (and perhaps in London as well) the conduit must be regarded as a luxury. It involves a continuous road excavation so deep that a great deal of incidental work has frequently to be done in moving gas, water, and drain pipes out of the way. The conduit itself is a thick channel of concrete, strengthened at intervals of a few feet with heavy cast iron 'yokes' which support the 'rails' forming the lips of the slot through which the 'plough' of the car passes. Elaborate arrangements have to be made for draining the conduit, as any accumulation of mud or water in contact with the conductors, or the special insulators supporting them, would be fatal to the working of the system. And in practice the ordinary drainage has to be assisted by continual scraping of the conduit with special brushes and by repeated flushing during the hours when the cars are not running. Heavy rains and snowstorms are therefore liable to upset the working of the system; and the tramway manager has to employ quite an army of men simply to keep the conduit in working order.
Trouble is also apt to be caused by purely mechanical means. On one occasion a child's hoop fell through the slot and caused a short circuit. As the ordinary scrapers slipped over the hoop, its presence was not detected for a considerable time, during which the tramway service was at a standstill. Altogether there is a greater liability to interruption on the conduit system than on the overhead system.
Experience of these drawbacks led the London County Council to seek
an alternative to the conduit when constructing electric lines in the
north of London. Many of the borough councils, following the County
Council's own previous arguments, would not listen to the suggestion of
the overhead system; and a freshly-elected Council, pledged to a policy
of economy, determined to try the surface-contact system. How this trial
gave rise to a violent political controversy, leading to the
abandonment of the project and culminating in important libel actions,
forms a picturesque story which need not be told in detail here. Its
main interest lies, for the moment, in the emphasis which the incidents
give to a characteristic of the surface-contact system—its sensitiveness
to minute alterations in detail.
The surface-contact or 'stud' system is really a modification of the conduit system. It has, in fact, been called the 'closed conduit.' The electric wires are again placed in a channel or pipe underground, but instead of being accessible through a slot, contact can be made with them only through metal studs placed at intervals flush with the roadway. By special electro-mechanical devices in the stud and on the car, the stud is brought into contact with the 'live' underground wire only when the car is over it. That is to say, the studs covered and protected by the car will be 'live' and supplying power to the car through a sliding brush or 'skate,' while those not so protected will be 'dead' and therefore of no danger to the public.
An immense amount of ingenuity has been expended by many engineers in devising studs to act with absolute certainty under all conditions. In the laboratory or the workshop, and even on an experimental track, it was simple enough to arrange a mechanism which would 'make' and 'break' contact with admirable regularity. But when it came to putting the mechanism down on an ordinary roadway, to be covered with mud, pounded by heavy traffic, and subjected to the action of damp, frost, heat, and all sorts of unexpected influences, much less satisfactory results were obtained. Time and again the hopes of engineers were dashed by a succession of petty troubles—some of them obscure, most of them unforeseen. The weak points in nearly all the systems were the insulation of electrical parts and the road construction work. Lack of simplicity and rigidity led to the introduction of moisture and to the shifting of parts so that studs jammed and remained 'alive' after the car had passed over them. But even after the practical elimination of these troubles the success of the surface-contact system seemed as sensitive as the system itself.
One system was tried at Torquay, and discontinued after a protracted trial on a large scale. Another system—the Lorain system—was installed at Wolverhampton and is still in operation, but without imitators. A third system—the Griffiths-Bedell or G-B. system—was installed in 1905 at Lincoln, with satisfactory results. It was the G-B. system which was offered to the metropolitan borough councils as an alternative to the conduit and the trolley. A trial section was laid down in 1898 in the Bow Road, and a certain amount of trouble was experienced with live studs and with various parts of the equipment. Owing to the stud system having been suggested by the Moderate Party, the experimental difficulties were extensively advertised by members of the Progressive Party, who condemned the system as dangerous and unworkable. Public feeling was worked up to such a pitch that, in the face of expert advice in favour of the system in a somewhat modified form, the Council decided to abandon the experiment. Libel actions by the owners of the 'G-B.' patents followed, part of the plaintiffs' case being that the system as laid down was altered in a number of small but vitally important details by the Council's officers and was therefore not the 'G-B.' system proper.
The results with the 'G-B.' system at Lincoln prove that it is possible to construct surface-contact tramways at a cost about 10 per cent. more than that of trolley tramways, and to operate them, safely and with reliability, at a cost not appreciably more than the general working expenses of an overhead line. But this proof has not only been enfeebled for the special reasons just described, but it came at a time when the public had got quite accustomed to the trolley and also when most towns had already been equipped with electric traction. Ten or fifteen years earlier, such a proof might have changed the course of tramway development; now it can have no great material effect.
The upshot of the contest between the three systems has, therefore, been the survival of the one which was most despised at the outset.
Both the conduit and the surface-contact system were suggested as a means of escape from the main objection to the overhead system—the exposure of 'live' wires in the street. The cable tramway, with its concrete trough and slot, gave an obvious hint. There would be no difficulty, apparently, in carrying wires on insulators in the trough or conduit, and utilising the slot for a 'plough' which would slide along inside the conduit, keeping contact with the wires, and so conveying the current to the car.
This was tried for the first time in Blackpool, where—in 1884—a length of conduit tramway was laid along the front street of the town. The conditions could hardly have been less favourable for the system, as the sea frequently washed over the roadway, flooding the conduit with water and sand. Further, the conduit was so shallow that children were able to get at the conductors with their metal spades. As the conduit carried the return wire, the effect of a metallic contact between the two conductors was to cause a 'short circuit,' with very entertaining fireworks but with no amusing results for the tramway engineer. After a heroic trial, the system had to be abandoned.
Bournemouth was the next British town to adopt the conduit. It did so as a token of its exceptional civic pride. Three times, in fact, the Bournemouth Corporation declared that it did not want tramways of any kind whatever within its gates. And when the pressure of public opinion forced its consent, the arrangement was made that no overhead wires should appear in the central district of the town. Several miles of conduit tramway were therefore constructed (the trolley system being used for the outer tramway routes); and as by that time a good deal of experience had been gained in conduit work both in America and on the Continent, the contractors were able to give the Corporation a conduit system built to endure. At first the Corporation was reconciled to the fact that the conduit sections had cost about twice as much per mile as the trolley lines, but as years went on, and as the financial results of the system continued to prove unsatisfactory, the Corporation's contentment became modified. An examination of the accounts showed that the conduit sections could be reconstructed on the overhead system at a cost equal to the annual expense of maintaining these sections in good working order. Since the public had got used to the overhead wires on the other sections, and since they had not got used to owning tramways which produced a heavy loss, the decision was made to abandon the conduit system altogether.
In London the conduit system was adopted by the London County Council for various reasons. One was that the Council felt that London ought to have the best, the very best, and nothing but the best. Another was that the streets were so congested with traffic, lamp standards, telegraph and telephone poles, and other obstructions, that trolley wires and trolley standards would be a great nuisance and a serious danger. Aesthetic reasons were also advanced, but it is difficult to realise that they had much weight in connection with the majority of metropolitan streets. Trolley wires were, in fact, freely erected in suburban streets where there was a certain amount of beauty worth preserving.
The main underlying reason, no doubt, was the feeling that London could afford the most costly system. In any ordinary city (and perhaps in London as well) the conduit must be regarded as a luxury. It involves a continuous road excavation so deep that a great deal of incidental work has frequently to be done in moving gas, water, and drain pipes out of the way. The conduit itself is a thick channel of concrete, strengthened at intervals of a few feet with heavy cast iron 'yokes' which support the 'rails' forming the lips of the slot through which the 'plough' of the car passes. Elaborate arrangements have to be made for draining the conduit, as any accumulation of mud or water in contact with the conductors, or the special insulators supporting them, would be fatal to the working of the system. And in practice the ordinary drainage has to be assisted by continual scraping of the conduit with special brushes and by repeated flushing during the hours when the cars are not running. Heavy rains and snowstorms are therefore liable to upset the working of the system; and the tramway manager has to employ quite an army of men simply to keep the conduit in working order.
Trouble is also apt to be caused by purely mechanical means. On one occasion a child's hoop fell through the slot and caused a short circuit. As the ordinary scrapers slipped over the hoop, its presence was not detected for a considerable time, during which the tramway service was at a standstill. Altogether there is a greater liability to interruption on the conduit system than on the overhead system.
Fig. 5. The upper portion of the illustration shows
a section of a typical conduit system of electric tramway traction.
This section is taken at one of the cast-iron 'yokes' which support the
rails forming the slot through which the 'plough' passes from the car to
make contact with the conductor rails.
The lower illustration gives a longitudinal and
transverse section of the 'G-B.' system of surface-contact tramway
traction. The rope-like cable carries the current and is supported on
insulators. When the collector on the car covers the stud, the action of
the magnet draws the lower part of the stud into contact with the
cable, thus supplying current to the car. After the car has passed, the
lower part of the stud rises by the action of a spring and, breaking
contact with the 'live' cable, becomes dead. (In actual practice contact
would be made under the conditions shown in the left-hand diagram.)
The surface-contact or 'stud' system is really a modification of the conduit system. It has, in fact, been called the 'closed conduit.' The electric wires are again placed in a channel or pipe underground, but instead of being accessible through a slot, contact can be made with them only through metal studs placed at intervals flush with the roadway. By special electro-mechanical devices in the stud and on the car, the stud is brought into contact with the 'live' underground wire only when the car is over it. That is to say, the studs covered and protected by the car will be 'live' and supplying power to the car through a sliding brush or 'skate,' while those not so protected will be 'dead' and therefore of no danger to the public.
An immense amount of ingenuity has been expended by many engineers in devising studs to act with absolute certainty under all conditions. In the laboratory or the workshop, and even on an experimental track, it was simple enough to arrange a mechanism which would 'make' and 'break' contact with admirable regularity. But when it came to putting the mechanism down on an ordinary roadway, to be covered with mud, pounded by heavy traffic, and subjected to the action of damp, frost, heat, and all sorts of unexpected influences, much less satisfactory results were obtained. Time and again the hopes of engineers were dashed by a succession of petty troubles—some of them obscure, most of them unforeseen. The weak points in nearly all the systems were the insulation of electrical parts and the road construction work. Lack of simplicity and rigidity led to the introduction of moisture and to the shifting of parts so that studs jammed and remained 'alive' after the car had passed over them. But even after the practical elimination of these troubles the success of the surface-contact system seemed as sensitive as the system itself.
One system was tried at Torquay, and discontinued after a protracted trial on a large scale. Another system—the Lorain system—was installed at Wolverhampton and is still in operation, but without imitators. A third system—the Griffiths-Bedell or G-B. system—was installed in 1905 at Lincoln, with satisfactory results. It was the G-B. system which was offered to the metropolitan borough councils as an alternative to the conduit and the trolley. A trial section was laid down in 1898 in the Bow Road, and a certain amount of trouble was experienced with live studs and with various parts of the equipment. Owing to the stud system having been suggested by the Moderate Party, the experimental difficulties were extensively advertised by members of the Progressive Party, who condemned the system as dangerous and unworkable. Public feeling was worked up to such a pitch that, in the face of expert advice in favour of the system in a somewhat modified form, the Council decided to abandon the experiment. Libel actions by the owners of the 'G-B.' patents followed, part of the plaintiffs' case being that the system as laid down was altered in a number of small but vitally important details by the Council's officers and was therefore not the 'G-B.' system proper.
The results with the 'G-B.' system at Lincoln prove that it is possible to construct surface-contact tramways at a cost about 10 per cent. more than that of trolley tramways, and to operate them, safely and with reliability, at a cost not appreciably more than the general working expenses of an overhead line. But this proof has not only been enfeebled for the special reasons just described, but it came at a time when the public had got quite accustomed to the trolley and also when most towns had already been equipped with electric traction. Ten or fifteen years earlier, such a proof might have changed the course of tramway development; now it can have no great material effect.
The upshot of the contest between the three systems has, therefore, been the survival of the one which was most despised at the outset.
By ADAM GOWANS WHYTE, B.Sc.
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