THE ELECTRIC TRANSMISSION OF POWER.
Lecture delivered by Prof. Ayrton, F.R.S., at the Drill Hall, Bath, on Friday, September 7, 1888.
WHAT is power, and why should we wish to transmit it?
Power has one very definite meaning in science, and several rather vague meanings in practice. We speak of a powerful athlete, the power of the law; we sing of the power of love; we say knowledge is power, and so on, using the word in several different senses. Now, in spite of the fact that a general audience feels a little anxious as to what troubles may be in store for it when a lecturer begins by being painfully exact, my telling you that by power an engineer understands the rate of doing work will not, I hope, make you fear that my remarks will bristle with technicalities.
When you walk upstairs you exert power - only, perhaps, the one-twentieth of a horse when you go up slowly, talking to other people. But when you run upstairs because you have forgotten something that you intended to bring down, then your exertions represent, perhaps, the one-tenth of a horse-power. You only get to the top of the stairs in either case, but the breathless sensation of running fast upstairs tells you that the more quickly you go the harder you are working. A person exercises power in the engineer's sense when he exerts himself physically, and the greater the exertion the greater the power. The exercise of power by the ruling classes, however, is unfortunately not necessarily accompanied by any exertion, physical or mental.
Probably the most familiar example of exerting power at a distance - that is, of transmitting power - is pulling a handle and ringing a bell in another room. I pull the handle, exerting myself slightly, and as the result the bell at the other end of the platform rings. Were not this such a very familiar operation I would call it experiment No. I. You have doubtless all of you performed this experiment several times to-day, and - what is all important with an experiment - performed it successfully.
And yet it was not until just one hundred years ago that it dawned on people that if one person, A, wanted to attract the attention of another person, B, the place where the bell ought to sound was where B was, and not where A was. Indeed, in many English villages down to the present day the knocker principle of attracting attention is alone resorted to, with the result which you may remember happened when Mr. Pickwick was staying in Bath at lodgings in the Royal Crescent, and Mr. Dowler undertook to sit up for Mrs. Dowler, but "made up his mind that he would throw himself on the bed in the back room and think - not sleep, of course... Just as the clock struck three there was blown into the crescent a sedan-chair with Mrs.Dowler inside, borne by one short fat chairman and one long thin one... They gave a good round double knock at the street door... 'Knock again, if you please,' said Mrs. Dowler, from the chair. 'Knock two or three times, if you please.' The short man stood on the step and gave four or five most startling double knocks of eight or ten knocks a-piece, while the long man went into the road and looked up at the windows for a light. Nobody came - it was as silent and as dark as ever." But the tall thin man, you may remember. "kept on perpetually knocking double knocks of two loud knocks each, like an insane postman," till Mr. Winkle, waking up from a dream "that he was at a club where the chairman was obliged to hammer the table a good deal to preserve order," met with the catastrophe which the readers of "Pickwick" will remember.
This episode shows what comes of having plenty of power and no means of transmitting it.
But if some houses can still dispense with mechanical or other methods of transmitting power, even to ring bells, factories cannot. The looms, the lathes, or whatever the machinery used in the factory may be, must either be worked by hand or foot in the old style, or it must be connected with the steam-, gas-, or water-engine in the new. On entering a large factory you see lines of rapidly-rotating shafting, and a network of rapidly-revolving belting, all employed in transmitting power. As a contrast to this, I now throw on the screen a photograph of Sir David Salomon's workshop at Tunbridge Wells, in which every machine is worked by a separate electric motor, thus saving to a great extent the loss of power that usually accompanies the mechanical transmission.
In America there are 6000 electromotors working machinery; in Great Britain hardly 100.
But it is not only in transmitting the power from the steam-, gas-, or water-engine of a factory to the various machines working in it, that electricity can be utilized. An incredible amount of power is daily running to waste in this and other countries because many of the rapid streams of water are too far away from towns for their power to have been hitherto utilised.
The holiday tourist, when admiring the splashing water dashing over the stones, hardly realizes that the money loss is as if the foam were composed of flakes of silver.
If we take as a low estimate that a large well-made steam engine burns only 2 pounds of coal per horse-power per hour, the coal consumption which would be equivalent to the waste of power at Niagara would exceed 150,000,000 tons per annum, which at only 5s. or 6s. per ton means some £40,000,000 sterling wasted. And descending from big things to small, the River Avon, flowing through Bath, which, so far from being a roaring cataract, especially in dry weather, pursues its course with only a respectable orderly swish, still represents a certain amount of lost power. It has been estimated that from 25 to 130 horse-power runs to waste at the Bathwick Weir behind the Guildhall, depending on the season. If we take as an all-round average that the fall of this weir represents 50 horse-power, and that a steam-engine producing this power burns 150 pounds of coal per hour, it follows that with steam coal at 16s. per ton - the price at Bath - the waste at Bathwick Weir represents an income of £450 per annum, not a princely fortune, it is true, but too large to be utterly thrown away as at present.
This state of things will I hope, however, be shortly remedied, for, as you will see from the large map on the wall, it is proposed to put up eighty-one electric arc lamps throughout the streets of Bath, and to supply the 50 horse-power required for these lamps by the fall of the Bathwick Weir, supplementing the fall with a steam-engine at dry seasons.
The next large diagram shows the use that Lord Salisbury has made of the River Lea to electrically light Hatfield House, and to supply electric motive power to the various machines working on his estate. The following diagram shows the course of the Portrush electric railway, six and a half miles long, which is worked by the Bushmill Falls, situated at about one mile from the nearest point of the railway. And lastly, this working model on the table, kindly lent me by Dr.E.Hopkinson, as well as the diagram on the wall, represent the Bessbrook and Newry electric tramway, a little over three miles in length, which is also worked entirely by water power, the turbine and dynamo which convert the water power into electric power being at about three-quarters of a mile from the Bessbrook terminus. [Model electric railway shown in action.]
The newspapers of last week contained a long account of the spiral electric mountain railway that has just been opened to carry people up the Burgenstock, near Lucerne, and worked by the River Aar, three miles away, so that we see electric traction worked by distant water power is extending. But, splendid as are these most successful uses of water power to actuate distant electromotors, it is but a stray stream here and there that has yet been utilized, and countless wealth is still being squandered in all the torrents all over the world.
The familiarity of the fact makes it none the less striking, that, while we obtain in a laborious way from the depths of the earth the power we employ, we let run to waste every hour of our lives many many times as much as we use.
It is also a well-established, time-honoured fact that large steam-engines can be worked much more economically than small ones, and that therefore if it were possible to economically transmit the power from a few very large steam-engines to a great number of small workshops there would be a great saving of power, as well as a great saving of time from the workmen in these many small workshops having only to employ this power for various industrial purposes, instead of having to stoke, clean, repair, and generally attend to a great number of small, uneconomical steam-engines.
When delivering the lecture which I had the honour to give at the meeting of the British Association at Sheffield nine years ago, I entered fully into Prof. Perry's and my own views on this subject, and therefore I will not enlarge on them now. You can all realize the difference between the luxury of merely getting into a train instead of having to engage post-horses; of being able to send a telegram instead of employing a special messenger; or being able to turn on a gas tap and apply a match when you want a light, instead of having to purchase oil and a wick, and trim a lamp. Well, a general supply of power to workshops is to the manufacturer what a general supply of light or a general supply of post-office facilities is to the householder: it is all part of the steady advance of civilization that leads the man of to-day to go to the tailor, the shoemaker, the baker, the butcher, instead of manufacturing his own mocassins and lassoing a buffalo for dinner. And in case any of you may be inclined to think that we have gone far enough in these newfangled notions, and we are all perhaps prone to fall into this mistake as we grow older, let me remind you that while each age regards with justifiable pride the superiority of its ways to those of its ancestors, that very age will appear but semicivilized to its great-grandchildren. Let us accept as an undoubted fact that a general distribution of power would enable the wants of civilized life to be better satisfied, and therefore would greatly benefit industry.
There are four methods of transmitting power to a distance: (1) by a moving rope ; (2) by air compressed or rarefied at one end of a pipe operating an air motor at the other end; (3) by water forced through a pipe working a water motor; (4) by electricity.
We have an example of the transmission of power through a short distance by an endless belt or rope in the machine geared together by belts on this platform, and in the rotatory hairbrushes at Mr. Hatt's establishment in the Corridor, Bath. At Schaffhausen, and elsewhere in Switzerland, the principle is employed on a large scale. Spain and other countries use it in connection with their mining operations; and lastly, wire ropes replace horses on many hilly tramways. Do not look, however, for the wire rope of the Bath cable tramways, for cable is only to be found painted on the sides of the cars.
For short distances of a mile or so there is no system of transmitting power in a straight line along the open country so cheap to erect, and so economical of power as a rapidly-moving endless rope; but the other systems give much greater facilities for distributing the power along the line of route, are much less noisy, and far surpass wire rope transmission in economy when the rope must move somewhat slowly, as in tramway traction, or when the distance is considerable over which the power is transmitted, or when the line of route has many bends.
In the same sense that an ordinary house-bell may be considered as a crude example of the transmission of power by a moving rope, the pneumatic bell at the other end of the hall which I now ring by sending a puff of air through the tube is a crude example of the transmission of power by compressed air. [Pneumatic bell rung.] Compressed air is employed to work from a distance the boring-machines used in tunnelling. The continuous vacuum-brakes used on many of the railways are also probably familiar to you, and the pneumatic system of transmitting power to workshops is shortly to be tried on a fairly large scale at Birmingham.
But distribution of power by water pressure is the plan that has hitherto found most favour in this country. That little water motor at the other end of the platform rapidly revolves when I work this garden syringe, and serves as a puny illustration of the transmission of water pressure. [Experiment shown.] Pressure water has been employed for years on a large scale at Hull for distributing power; also by Mr.Tweddle, as a means of communicating a very large amount of power through a flexible tube to tools that have to be moved about; but the grandest illustration of this principle is the vast system of high-pressure mains that have been laid throughout London, as you will see from the photograph that I now project on the screen of the map kindly lent me by Mr.Ellington.
The economy of this system is so marked and the success that has attended its use is so great that, did I not feel sure that electricity offers a grander system still, it would be with fear and trembling that I should approach the subject of this evening, the "Electric Transmission of Power." Punch drew six years ago the giant Steam and the giant Coal looking aghast at the suckling babe Electricity in its cradle. That baby is a strong boy now; let the giant Water look to its laurels ere that boy becomes a man. For the electric transmission of power even now bids fair to surpass all other methods in (1) economy in consumption of fuel; (2) more perfect control over each individual machine, for see how easily I can start this electric motor, and how easily I can vary its speed [experiment shown]; (3) ability to bring the tool to the work instead of the work to the tool - this rapidly-rotating polishing-brush, with its thin flexible wires conveying the power, I can handle as easily as if it were a simple nail-brush; (4) in greater cleanliness, no small benefit in this dirty, smoky age; (5) and lastly, there is still one more advantage possessed by this electric method of transmitting power that no other method can lay claim to - the power which during the day-time may be mainly used for driving machinery can, in the easiest possible way, be used during the night for giving light. I turn this handle one way, and the electric current coming by one of these wires and returning by the other works this electromotor; now I turn the handle the other way, and the current which comes and returns by the same wires as before keeps this electric lamp glowing. [Experiment shown.]
It might be said that the transmission of power by coal-gas, which I have excluded from my list, fulfils this condition, but so also does the transmission of power by a loaded coal-waggon. In both these cases, however, it is fuel itself that is transmitted, and not the power obtained by burning the fuel at a distant place.
Let us study this electric transmission a little in detail. I pull this handle, and the bell at the other end of the room rings; but in this case there is no visible motion of anything between the handle and the bell. [Electric bell rung by an electric current produced by pulling the handle of a very small magneto-electric machine.] Whether I ring the bell by pulling a wire, or by sending an air puff, or by generating an electric current by the exertion of my hand, the work necessary for ringing the bell is done by my hand exactly as if I took up a hand-bell and rang it. In each of the three cases I put in the power at one end of the arrangement, and it produces its effect at the other. In the electric transmission how does this power travel? Well, we do not know. It may go through the wires, or through the space outside them. But although we are really quite in the dark as to the mechanism by means of which the electric power is transmitted, one thing we do know from experience, and that is this: given any arrangement of familiar electrical combinations, then we can foretell the result.
Our knowledge of electrical action in this respect resembles our knowledge of gravitation action. The only thing quite certain about the reason why a body falls to the ground is that we do not know it; and yet astronomical phenomena can be predicted with marvellous accuracy. I mention the analogy, since some people fancy because the answer to that oft-repeated question, "What is electricity?" not only cannot be given exactly, but can only be guessed at in the haziest way, even by the most able, that therefore all electric action is haphazard. As well might the determinations of a ship's latitude at sea be regarded as a mere game of chance because we have not even a mental picture of the ropes that pull the earth and sun together.
This power of producing an action at a distance of many yards, or it may be many miles, by the aid of electricity without the visible motion of any substance in the intervening space is by no means new. It is the essence of the electric telegraph; and electric transmission of power was employed by Gauss and Weber when they sent the first electric message. I am transmitting power electrically whether I now work this small model needle telegraph instrument, or whether I turn this handle and set in motion that little electric fan. [Experiment shown.]
But until about ten years ago the facility that electricity gave for producing signals almost instantaneously at a great distance was the main thing thought of. The electric power consumed for sending the telegraph messages was so small, the amount of power lost en route comparatively so valueless, that the telegraph engineer had no need to trouble himself with those considerations that govern us to-day when we are transmitting power large enough to work a factory or an electric tramway. Although there are as many as 22,560 galvanic cells at the Central Telegraph Office, London, which cost some thousands annually to keep in order, what is that compared with the salaries of all the 3089 superintendents, assistants, telegraph-clerks, messengers, and the maintenance of the 1150 telegraph lines that start from the Central Office?
In all the last three systems in my list some form of power, such as flowing water, or the potential energy stored up in coal, wood, zinc, or other fuel, has initially to be utilized. This power is given to some form of air, water, or electric pump, which transfers the air power to the air, water, or electricity, by which it is conveyed to the other end of the system. There it is re-converted into useful mechanical power by means of an air, water, or electric motor.
You will observe that I class together air, water, and electricity; by that I do not mean to imply that electricity is a fluid, although in many respects it acts like a fluid - like a fluid of very little mass, however; or, odd as it may seem, like a fluid moving extremely slowly, for electricity goes round sharp corners with perfect ease, and without any of the phenomena of momentum possessed by rushing water. But what I particularly wish to impress on you by classing air, water, and electricity together is that electricity is not, as some people seem to think, a something that can be burnt or in some way used up and so work got out of it. Electricity is no more a source of power than a bell-wire is, electricity is a marvellously convenient agent for conveying a push or a pull to a great distance, but it is not by the using up of the electricity that electric lights burn or that electromotors revolve. It is by the electricity losing pressure, exactly as water loses head when turning the miller's wheel as it flows down hill, that work is done electrically.
This model shows, in a rough, symbolical way, what takes place in the transmission of power whether by air, water, or electricity. [Model shown.] The working stuff, whichever of the three it may be, is first raised in pressure and endowed with energy, symbolized by this ball being raised up in the model: it then, gradually loses pressure as it proceeds along the tube or wire which conveys it to the other end of the system, the loss of pressure being accompanied by an increase of speed or by its giving up power to the tube or wire and heating it. This is shown in the model by the ball gradually falling in its coarse. At the other end there is a great drop of pressure corresponding with a great transference of power from the working stuff to the motor, and finally it comes back along the return pipe or wire, losing, as it returns, all that remains of the pressure given to it initially by the pump. The ball has, in fact, come back to its original level.
The problem of economically transmitting power by air, water, or electricity is the problem of causing one or other of these working stuffs - air, water, or electricity - to economically perform the cycle I have described.
In each of the four stages of the process - (1) transference of power to the working substance at the pump ; (2) conveyance of power to the distant place; (3) transference of power from the working substance to the motor at the distant place: (4) bringing back the working substance - there is a loss of power, and the efficiency of the arrangement depends on the amount of these four losses. The losses may be shortly called (1) loss at the pump; (2 and 4) loss on the road; (3) loss at the motor.
Until 1870 the pump most generally employed for pumping up electricity and giving it pressure was the galvanic battery - scientifically an extremely efficient converter of the energy in fuel into electric energy, only unfortunately the only fuel a battery will burn is so expensive. A very perfect fire place, in which there was very complete combustion, and very little loss of heat, but which had the misfortune that it would only burn the very best wax candles, would be analogous with a battery. The impossibility of using zinc as fuel to commercially work electromotors has been known for the last half-century, and the matter was very clearly put in an extremely interesting paper "On Electro-magnetism as a Motive Power," read in 1857 by Mr. Hunt before the Institution of Civil Engineers, a copy of which has been kindly lent me by Dr. Silvanus Thompson. Prof. William Thomson (Glasgow) - I quote from the discussion on the paper - put the matter very pithily by showing that, even if it were possible to construct a theoretically perfect electromotor, the best that could be hoped for, if it worked with a Daniell's battery, would be the production of a one horse-power by the combustion of 2 pounds of zinc per hour, whereas with a good actual steam-engine of even thirty years ago, one horse-power could be produced by the combustion of exactly the same weight of the much cheaper fuel coal. This argument against the commercial employment of zinc to produce electric currents is irresistible, unless - and this is a very important consideration, which is only beginning to receive the attention it deserves - unless, I say, the compound of zinc formed by the action of the battery can be reduced again to metallic zinc by a comparatively inexpensive process, and the zinc used over and over again in the battery. If the compound of zinc obtained from the battery be regarded as a waste product, then it would be much too expensive to work even theoretically perfect electromotors, if they were existent, by consuming zinc. Suppose, however, a process be devised by means of which burnt zinc can be unburnt with an expenditure comparable with the burning of the same weight of coal, then it might be that, although coal would still form the basis of our supply of energy, the consumption of zinc batteries might be an important intermediary in transforming the energy of coal, economically, into mechanical energy.
While, then, some experimenters are aiming at possibly increasing the working power of a ton of coal to eight times its present value by earnestly seeking for a method of converting the energy it contains directly into electric energy without the intervention of a wasteful heat engine, it should not be forgotten that in the cheap unburning of oxidized metal may lie another solution.
The solution of this latter problem is quite consistent with the principles of the conservation and dissipation of energy, since the heat required to theoretically unburn 1 pound of zinc is only one-seventh of that given out by the burning of 1 pound of coal. Further, it involves no commercial absurdity like that found in the calculations given in the prospectuses of many primary battery companies, which are based on zinc oxide, a material used in the manufacture of paint, maintaining its present price even if thousands of tons were produced. Unless all those who use primary batteries on this expectation intend to have the painters doing up their houses all the year round, they will find themselves possessed of the stock-in-trade of an oil and colourman on a scale only justified by a roaring business in paint.
Now about waste No. 3, the waste of power at the motor. That also is gone into fully in the discussion on Mr. Hunt's paper, and Mr. Robert Stephenson concluded that discussion by remarking "that there could be no doubt, from what had been said, that the application of voltaic electricity in what ever shape it might be developed was entirely out of the question commercially speaking... The power exhibited by electro-magnets extended through so small a space as to be practically useless. A powerful electro-magnet might be compared for the sake of illustration to a steam-engine with an enormous piston, but with an exceedingly short stroke. Such an arrangement was well known to be very undesirable."
And this objection made with perfect justice against the electromotors of thirty years ago might also have been made to all the machines then existing for the mechanical production of electric currents. I have two coils of wire at the two sides of the platform joined together with two wires. I move this magnet backwards and forwards in front of this coil, and you observe the magnet suspended near the coil begins to swing in time with my hand. [Experiment shown.] Here you have in its most rudimentary form the conversion of mechanical power into electric power, and the re-conversion of electric power into mechanical power; but the apparatus at both ends has the defects pointed out by Mr.Hunt and all the speakers in the discussion on his paper - the effect diminishes very rapidly as the distance separating the coil from the moving magnet increases.
As long as electromotors as well as the machines for the production of electric currents had this defect, the electric transmission of power was like carrying coals to Newcastle in a leaky waggon. You would pay at least 16s. a ton for your coals in Bath, lose most of them on the way, and sell any small portion that had not tumbled out of the waggon for, say, 2s. a ton at Newcastle - a commercial speculation not to be recommended.
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A very great improvement in electromotors was made by Pacinotti in 1860, but although his new form of electromotor was described in 1864 it attracted but little attention, probably because any form of electromotor, no matter how perfect, was commercially almost useless until some much more economical method of producing electric currents had been devised than the consumption of zinc and acids. Pacinotti's invention removed from motors that great defect that had been so fully emphasized by the various speakers at the reading of Mr.Hunt's paper in 1857. When describing his motor in the Nuovo Cimento in 1864, he pointed out that his principle was reversible, and that it might be used in a mechanical current generator. This idea was utilized by Gramme in 1870, who constructed the well-known Gramme dynamo for converting mechanical into electric power - a machine far more efficient than even Pacinotti had contemplated - and gave the whole subject of electrical engineering a vigorous forward impulse. Every subsequent maker of direct-current dynamos, or motors, has followed Gramme's example in utilizing the principle devised by Pacinotti, which was as follows. In all the early forms of dynamos or motors there were a number of magnets and a number of coils of wire, the magnets moving relatively to the coils, or the coils relatively to the magnets, as you see in this rather old specimen of alternate-current dynamo. To produce magnetism by a large number of little magnets is not economical, and Pacinotti's device consisted in arranging a number of coils round a ring in the way shown in the large wooden model [model shown], so that they could all be acted on by one large magnet. Instead of frittering away his magnetism, Pacinotti showed how it could be concentrated, and thus he led the way to dynamos and motors becoming commercial machines.
Pacinotti's science, engineered by Gramme, not only made electric lighting commercially possible, but led to electricity being used as a valuable motive power. It was in their work that the electric transmission of power in its modern sense sprang into existence.
Quite recently an improvement in the same direction has been introduced into alternate-current dynamos by Mr.W.N.Mordey, for he has replaced the many magnets of the ordinary alternate-current dynamos with one large magnet, and so with his alternator weighing 41 hundredweight, which you see in this hall, he has succeeded in obtaining at a speed of 650 revolutions per minute an output of 53.6 horse-power with a high efficiency.
It may be convenient to mention at this stage the very valuable work that has been done by the Drs.Hopkinson, Mr.Crompton, Mr.Kapp, and others, in the improving of dynamos and motors by applying scientific principles in the construction of these machines. Were I lecturing on dynamos and motors instead of on the electric transmission of power, I would explain to you how, by putting more iron into the rotating armature, as it is called, and less wire on it, by shortening the stationary magnet, and generally by concentrating the magnetic action, these constructors have raised the commercial efficiency of these machines to actually as high as between 93 and 94 per cent.; further, how, by recognizing the force of the general principles laid down by Prof. Perry and myself, as to the difference that should exist in the construction of a motor and a dynamo, Messrs.Immisch have succeeded in constructing strong, durable electromotors weighing not more than 62 pounds per effective horse-power developed.
The subject is so entrancing to me, the results commercially so important, that I am strongly templed to branch off, but the inexorable clock warns me that I must concentrate my remarks as they have concentrated the magnetic action.
87 1/2 per cent. of the power put into an Edison-Hopkinson dynamo has actually been given out by the motor spindle when 50 horse power was being transmitted. How does this compare with the combined efficiencies of an air-pump and an air-motor, or of a water-pump and a water-motor? I understand that in either of these cases 60 per cent, is considered a very satisfactory result. As far, then, as the terminal losses are concerned, electric transmission of power is certainly superior to air or water transmission.
The next point to consider is the loss of power on the road between the dynamo at the one end and the motor at the other. This problem was perhaps seriously attacked for the first time in the discussion of a paper read by Messrs.Higgs and Brittle at the Institution of Civil Engineers in 1878, and that problem was considered in some detail theoretically and experimentally at the lecture I gave during the meeting of the British Association in Sheffield in the following year. It was then shown that, since the power developed by the generator and motor depended on the product of the current into the electric pressure, while the loss when power was transmitted through a given wire depended on the square of the current and was independent of the electric pressure, the economical transmission of power by electricity on a large scale depended on the use of a very large electric pressure and a small current, just as the economic transmission of much power by water depended on the use of a very large water pressure and a small flow of water. At that time it was not thought possible to construct a small dynamo to develop a very large electric pressure, or potential difference as it is technically called, and therefore it was proposed to join up many dynamos in series at the one end and many lamps or electromotors in series at the other, and to transmit the power by a very small current, which passed through all the dynamos and all the lamps in succession, one after the other.
You have an example to-night of the realization of this principle in the fifteen arc lamps that are all in series outside this Drill Hall, and are worked with a small current of only 6.8 amperes, as indicated in the wall diagram; and a further example in the thirty arc lamps at the Bath Flower Show, which are also all worked in series with the small current passing through them; but it is known now how to produce a large potential difference with a single dynamo, so that a single Thomson-Houston dynamo belonging to Messrs.Laing, Wharton, and Down supplies the current for each of the two circuits.
The electric pressure, or potential difference, between the terminals of any arc lamp is not high, but it is between the main wires near the dynamo as well as between these wires and the ground. How far does this lead to the risk of sparks or unpleasant shocks? That is a point that can be looked at in a variety of ways. First, there is the American view of the matter, which consists in pointing out to people exactly what the danger is, if there be any, and training them to look out for themselves: let ordinary railway trains, say the Americans, run through the streets, and let horses learn to respect the warning bell. Next, there is the semi-paternal English system, which cripples all attempts at street mechanical locomotion, because we are conservative in our use of horses, and horses are conservative in their way of looking at horseless tramcars. Lastly, there is the foreign paternal system, which, carried to its limit, would prohibit the eating of dinners because some people have at some time choked themselves, and would render going to bed a penal offence because it is in bed that most people have died.
We laugh a good deal at the rough-and-ready manner adopted on the other side of the Atlantic. The Americans, no doubt, are very ignorant of the difficulties that properly-minded people would meet with, but is a blissful ignorance where it is folly to be wise. Every English electrician who has travelled in America comes back fully impressed with their enterprise and their happy-go-lucky success. They have twenty-two electric tramways, carrying some 4,000,000 passengers annually, to our four electric tramways at Portrush, Blackpool, Brighton, and Bessbrook. Why, New York city alone, Mr. Rechenzaun tells me, possesses 300 miles of ordinary tramway track, and Philadelphia 430 miles, so there is more tramway line in these two cities than in the whole of the United Kingdom put together. Now there would be no difficulty in proving, to anyone unfamiliar with railway travelling, that to go at 50 miles an hour round a curve with only a bit of iron between him and eternity would be far too risky to be even contemplated. And yet we do go in express trains, and even 80 miles an hour is beginning to be considered not to put too great a demand on the funds of life insurance companies. The American plan of basing a conclusion on experience rather than on anticipations is not a bad one; and if we follow that plan, then, taking into account that there are 75,000 arc lights alight every night on the Thomson-Houston high-potential circuits throughout the world, and the comparatively small number of people that have suffered in consequence (not a single person, I am assured, outside the companies' staffs) we are compelled to conclude that high potential now is what 30 miles an hour was half a century ago - uncanny rather than dangerous.
But it is possible to use a very large potential difference between the main wires by means of which the electric power is economically conveyed a considerable distance, and transformed into a very small potential difference in the houses where it is utilized. An electric transformer is equivalent to a lever, or wheel and axle, or any other of the so-called mechanical powers. You know that a large weight moving through a small distance can raise a small weight through a large distance; there is no gain in the amount of work, but only a transformation of the way in which the work is done. A large weight moving through a small distance is analogous with a high potential difference and a small current, while a small weight moving through a large distance is analogous with a small potential difference, and a large current, and an electric transformer is for the purpose of effecting the transformation with as little loss as possible, so that what is lost in potential difference may, as far as possible, be all gained in current.
Electrical transformation may be effected by (1) alternate current transformers, (2) motor-dynamos, (3) accumulators, or secondary batteries, (4) direct-current transformers. Of these apparatus, the eldest by far is the alternate-current transformer, as it is merely the development of the classical apparatus invented by Faraday in 1831, and familiar to many of you as the Ruhmkorff, or induction-coil. A combination of a motor and dynamo was suggested by Gramme in 1874. Accumulators are the outcome of Plante's work, while direct-current transformers are quite modern, and not yet out of the experimental stage.
After studying the literature on this subject, it appears, as far as I have been able to judge, that the first definite proposal to use a high potential difference in the street mains, and transform down to a low potential difference in the houses, was made in the lecture given by me at the meeting of the British Association in Sheffield in 1879, on which occasion I explained and showed in action the motor-dynamo principle suggested by Prof. Perry and myself. The apparatus on the platform is not unlike that shown on the former occasion: an Immisch motor working at 500 volts, and with a current of 6.8 amperes, is geared direct to a Victoria Brush dynamo giving five times that current, and we will now use this larger current to produce an electric fire. [Experiment shown.] Messrs.Paris and Scott have combined the motor and dynamo into one machine, which they have kindly lent me, and by means of which we are now transforming about 700 volts and 6.8 amperes into 100 volts and about 40 amperes used to light that group of sunbeam incandescent lamps or work these motors. [Experiment shown.]
Lastly, here is a working illustration of the double transformation proposed by MM. Deprez and Carpentier in 1881, by means of which - while the potential difference between the mains may be 2000 or 10,000 volts, if you like - not merely is the potential difference in the house so low that you could hardly feel anything if you touched the wires, but, in addition, there is the same security against shocks in the dynamo-room. This alternate-current machine is producing about 50 volts, which is transformed up to 2000 volts by means of this transformer. At the other end of the platform, by means of a similar transformer, the 2000 volts is transformed down again to 50 volts, employed to light that cluster of low-voltage incandescent lamps. [Experiment shown.] For the use of this apparatus I am indebted to the kindness of the Anglo-American Brush Company.
In this experiment there is, as a matter of fact, still more transformation than that I have yet mentioned, because, whereas in actual practice the alternate-current dynamo, as well as the small dynamo used to produce the current for magnetizing the electromagnets in the alternate-current dynamo, would be worked by steam, gas, or water engine, I am working them both by electromotors, since a steam-engine or a water-wheel would be an unsuitable occupant of the Drill Hall. Practically, then, a steam-engine on the land belonging to the Midland Railway Company, on the other side of the Lower Bristol Road, is driving a Thomson-Houston dynamo; this is sending a small current working these high-voltage constant-current Immisch motors. The motors being geared with low-voltage dynamos the potential difference is transformed down, the first alternate-current transformer transforms it up again, and the second alternate-current transformer transforms it down again, so that there are in fact three transformations taking place in this experiment on the platform before you. For the benefit of the electricians present, I may mention that the two motors are running in series, and that their speed is kept constant by means of a centrifugal governor which automatically varies the number of the convolutions of the field magnet that are being utilized at any moment. In fact, since the dynamo maintains the current constant that is passing through each motor, the function of the governor may be regarded as that of proportioning the potential difference maintained at the terminals of either motor to the load on the motor at any moment.
A vast district in London, extending from Regent's Park on the north to the Thames on the south, from the Law Courts on the east to Hyde Park on the west, has over 20,000 incandescent lamps scattered over it all worked from the Grosvenor Gallery in Bond Street by means of alternate-current transformers which convert the 2000 volts maintained between the street mains into 100 volts in the houses, and this London Electric Supply Company have arranged for a vast extension of this system to be worked from Deptford.
In America, alternate-current transformers are, due to the remarkable enterprise of Mr. Westinghouse, used to light 120,000 incandescent lamps in sixty-eight towns. In fact the electric lighting of a whole town from a central station begins to excite less astonishment than the electric lighting of a single house did ten years ago.
The efficiency of a well-made alternate-current transformer is very high, being no less than 96.2 per cent. when the transformer is doing its full work, and 89.5 per cent. when it is doing one-quarter of its full work, according to the experiments made by our students. It certainly does seem most remarkable, and it reflects the highest praise on the constructors of electrical machinery, that motive power can be converted into electrical power, electrical power at low pressure into electrical power at high pressure, or electrical power at high pressure into electrical power at low pressure, or, lastly, electrical power into motive power, in each case with an efficiency of not less than 94 per cent.
As a further illustration of the commercial importance of this electric transformation I will show you some experiments on electric welding, one of the latest developments in electrical engineering. To weld a bar of iron one square inch in section requires a gigantic current of some 13,000 amperes. To convey this current even a few yards would be attended with a great waste of power; consequently, while an enormous current is passed through the iron to be welded, only a comparatively small current is transmitted along the circuit from the dynamo to the welding apparatus. Mr. Fish, the representative of Prof. Elihu Thomson, of America, to whom this apparatus is due, will be so kind as to first show us the welding together of two bars of square tool steel, the edge of each bar being 3/4 of an inch, and the operation is, as you see, entirely completed in some fifteen seconds. For this experiment an alternate current of 20 amperes will be produced by the dynamo at the other side of the Lower Bristol Road, and this current will be converted by the transformer on the platform into one of 9000 amperes, large enough for 12,000 of these incandescent lamps if they were placed in parallel and the current divided among them. He will next try welding some thicker bars, and lastly he proposes welding together two pieces of aluminium which it is extremely difficult, if not impossible, to weld in any other way. The bars, as you see, are in each case pressed together end on, and, in consequence of the electric resistance of the very small gap between the bars being much higher than that of the bars themselves, the current makes the ends of the bars plastic long before it even warms the whole bar, so that I can, as you see, hold the bar at a distance of three or four inches from where the weld has been made without experiencing any marked sense of warmth. The heat is, in fact, applied exactly where we require it, the temperature can be adjusted with the greatest nicety so as not to burn the steel, and the softening of the bar is effected throughout its entire cross-section. Hence a very good weld indeed can be made by end pressure. We have to think Mr. Fish, not merely for showing us these most interesting experiments on electric welding, but for supplying the electric power for many of the experiments I have been showing you, and for the electric lighting of the Drill Hall.
To Mr. Snell, the representative of Mr.Immisch, our best thanks are due for his having devoted several days in arranging the two high-voltage, constant-current motors, to drive the dynamo with that constancy of speed which you observe. This ingenious telpher model, to which I shall refer presently, is the handy work of Mr.Bourne, and considering that it has had to be hastily taken to pieces, and hastily put together again, it is surprising that it works as well as it does. An ordinary watch is a very trustworthy, steady-going machine, but if one had to take it to pieces hastily, and as hastily to put it together again one might expect it to lose. Indeed, if you or I had to do it we should not be surprised if it did not go at all, and so be only right twice every twenty-four hours.
For the arrangements of the models and the smaller experiments, as well as for the admirable execution of many of the diagrams, our best thanks are due to Mr. Raine.
Did time allow I should like to describe to you to what perfection the system of economical distribution with accumulator originally proposed by Sir William Thomson in 1881 and shown in its very simplest form in the wall diagram, has been brought by Mr. King, the engineer to the Electrical Power Storage Company; how the cells when they are fully charged are automatically disconnected from the charging circuit, and electrically connected with the discharging circuit; how the electric pressure on the discharging or house mains is automatically kept constant, so that the brightness of the lamps is unaffected by the number turned on; and how cells that are too energetic have their ardour automatically handicapped, and not allowed to give more current than is being supplied by the less active ones.
During the last few months fierce has been the battle raging among the electricians, the war-cry being "alternate-current transformers versus accumulators," while the lookers-on, with the better view of the contest that they are proverbially said to possess have decided that the battle is a drawn one. Neither system the better under all circumstances: if the district to be lighted is a very scattered one, use alternate-current transformers by all means; but if the houses to be lighted are clustered together a distance from the supply of power, then the storing property possessed by accumulators, which enables the supply of electric power to far exceed the capacity of the dynamos and engines the busiest part of the twenty-four hours, will win the battle of accumulators. Any direct-current system of distribution such is furnished by accumulators has also the very great advantage that it lends itself to the use of the very efficient electromotor which I have been using this evening. Alternate-current motors do exist, but they are still in the experimental stage, and are not yet articles of commerce.
Secondary batteries have caused much heart-burning, for the users, from the apparent fickleness of their complex chemical action, yet but imperfectly understood. But we have at length been taught what is good and what is bad treatment for them: and after years of brave persevering application on the part of the Electrical Power Storage Company, that forlorn hope the secondary battery has become one of the most useful tools of the electrical engineers; and secondary cells, some of which, than to the kindness of that Company, I am using here tonight supply power for lamps and motors, may now be trusted have a vigorous long life. That Company, I learn, undertake henceforth to keep their cells in order, when used for central station work, for 12 1/2 per cent. per annum, and I understand that they have such confidence in them that they anticipate making no little money by incurring this insurance office responsibility. It is not, then, surprising that the Chelsea Supply Company have decided to use secondary batteries on a large scale for the economical distribution of light and power in the district.
Oliver Goldsmith said, more than a hundred years ago, in his "Life of Richard Nash, Esquire": "People of fashion at Bath... when so disposed, attend lectures on the arts and science which are frequently taught in a pretty superficial manner, so as not to tease the understanding, while they afford the imagination some amusement." I want not to be superficial, yet must not tease your understanding, and so we will not lose our selves in technical details. If, however, my remarks have led you to appreciate the vast economical importance of using very large electric pressures, and to grasp that, by substituting 2000 volts for 50 volts, when transmitting a certain amount of electric power, the current can be reduced to the one-fortieth part, and the waste of power, when transmitted along a given length of a given wire to the one fortieth of the one-fortieth - that is, to the one sixteenth-hundredth part - your imagination will have been kindled as well as amused.
With a loss on the road of only 11 per cent., M.Deprez has, by using 6000 volts, transmitted 52 horse-power over a distance of about 37 miles through a copper wire only one-fifth of an inch in diameter. A piece of the actual conductor he employed I hold in my hand: the copper wire is coated with an insulated material, and then with a leaden tubing, so that the outside may be touched with perfect impunity, in spite of the high potential difference employed. M. Deprez's dynamo and motor were not nearly as efficient as he could make them now, so that his terminal losses were unnecessarily great, and the efficiency of the whole arrangement, wonderful as it was, was not so startling as it would otherwise have been. I have told you that the loss in dynamo and motor has actually been reduced to only 12 1/2 per cent.; so that, if a dynamo and motor of this efficiency had been used by M. Deprez, the total loss in the whole transmission over 37 miles would have been under 25 per cent. Indeed, by using only 1250 volts, Mr. Brown has succeeded in transmitting 50 horse-power supplied by falling water at Kriegstetten to Solothun, in Switzerland, five miles away, with an entire loss in the dynamo, motor, and the five miles of going and returning wire of only 25 per cent.; so that three-quarters of the total power supplied by the water at Kriegstetten was actually delivered to machinery at Solothun, five miles away.
In less than twenty years, then, from Gramme's practical realization of Pacinotti's invention, we have power transmitted over considerable distances by electricity with only a total loss of 25 per cent., whereas the combined loss in an air-pump and air-motor or in a water-pump and water-motor is 40 per cent., irrespective of the additional loss by friction or leakage that occurs en route. We cannot help feeling that we are rapidly arriving at a new era, and that it will not merely be for the inauguration of the quick transmission of our bodies by steam, or the quick transmission of our thought by telegraph, but for the economical transmission of power by electricity, that the Victorian age will be remembered.
I showed you a little while ago an electric fire. Was that a mere toy, or had it any commercial importance? To burn coal, to work dynamos, and to use the electric current to light your houses and your streets is clean and commercial; to use the current to warm your rooms clean but wasteful, on account of the inefficiency of the steam-engine. But when the dynamos are turned by water power which would otherwise be wasted, the electric current may be economically used, not merely to give light, but also to give heat. And when the electric transmission of power becomes still more perfect than at present, even to burn coal at the pit's mouth where it is worth a shilling a ton may, in spite of the efficiency of the steam-engine being only one-tenth, be the most economical way of warming distant towns where coal would cost 20s. a ton. Think what that would mean! - no smoke, no dust, a reform effected commercially which the laws of the land on smoke prevention are powerless to bring about, a reform effected without the intervention of the State, and therefore dear to the hearts of Englishmen.
I am aware that this idea of burning coal at the pit's mouth and electrically transmitting its power has quite recently been stated to be commercially impracticable. But is that quite so certain? - for in 1878 it was stated that, although telephones might do very well for America, they certainly would never be introduced into Great Britain, as we had plenty of boys who were willing to act as messengers for a few shillings a week. The phonograph was also declared to be worked by a ventriloquist, and electric lighting on a large scale was proved to be too expensive a luxury to be ever carried out. Putting a Conservative drag on the wheels is a very good precaution to take when going down hill, but it is out of place in the up-hill work of progress.
To-day the electric current is used for countless purposes. Not only is it used to weld, but by putting the electric arc inside a closed crucible, smelting can be effected with a rapidity and ease quite unobtainable with the ordinary method of putting the fire outside the crucible. If one had pointed out a few years ago that it was as depressing scientifically to put a fire outside a crucible when you wanted to warm the inside, as Joey Ladle, the cellarman, found it depressing mentally "to take in the wine through the pores of the skin, instead of by the conwivial channel of the throttle," who would have believed that in 1888, a 500 horse-power dynamo would be actually employed to produce an electric arc inside a closed crucible in the manufacture of aluminium bronze.
But, of all the many commercial uses to which the electric current may be put, probably, after the electric light, electric traction has most public interest. The English are a commercial people, but they are also a humane people; and when, as in this case, their pockets and their feelings are alike touched, surely they will be Radicals in welcoming electric traction, whatever may be their political sentiments on other burning topics of the day. It is not a nice thing to feel that you are helping to reduce the life of a pair of poor tramway horses to three or four years: it would be a very nice thing to be carried in a tramcar for even a less fare than at present. Now, while it costs 6d. or 7d. to run a car one mile with horses, it only costs 3d. or 4d. to propel it electrically. Indeed, from the very minute details that have recently been published of the four months' expenses of electrically propelling thirty cars at 7 1/2 miles an hour along a 12-miles tramway line in Richmond, Virginia, it would appear that the total cost - inclusive of coal, oil, water, engineers, firemen, electricians, mechanicians, dynamo and motor repairers, inspectors, linemen, cleaners, lighting, depreciation on engine, boiler, cars, dynamos, and line-work - has been only 1 1/4d. per car per mile. This is indeed a low price; let us hope that it is true. The tramway is, no doubt, particularly favourable for propelling cars on the parallel system (that is, the system in which the current produced by the dynamo is the sum of the currents going through all the motors on the cars) without a great waste of power being produced by a very large current having to be sent a very long distance, because the tramway track is very curved, and the dynamo is placed at the centre of the curve, with feeding-wires to convey the current from the dynamo to all parts of the track. But even in the case of a straight tramway line with a dynamo only at one end, it is quite possible to obtain the same high economy in working by employing a large potential difference and by sending a small current through all the trains in series, instead of running the trains in parallel, as is done on the Portrush, Blackpool, Brighton, and Bessbrook tramways.
This series system of propelling electric trains was oddly enough entirely ignored in all the discussions that have taken place this year at the Institution of Civil Engineers, and at the Institution of Mechanical Engineers, regarding the relative cost of working tramways by horses, by a moving rope, and by electricity; and yet this series system is actually at work in America, as you will see from an instantaneous photograph which I will now project on the screen, of a series electric tramway in Denver, Colorado; and a series electric tramway 12 miles long, on which forty cars are to be run, is in course of construction in Columbus, Ohio. The first track on which electric trams were run in series was the experimental telpher line, erected in Glynde in 1883 under the superintendence of the late Prof. Fleeming Jenkin, Prof. Perry, and myself, for the automatic electric transport of goods. A photograph of this actual line is now projected on the screen. The large wall diagram shows symbolically, in the crudest form, our plan of series working: the current follows a zigzag path through the contact pieces, and when a train enters any section the contact piece is automatically removed, and the current now passes through the motor on that train, instead of through the contact piece. The Series Electrical Traction Syndicate, whom we have to thank for the model series tramway on which the two cars are now running, are now developing our idea, but it has received its greater development in the States, where the Americans are employing it, instead of spending time proving, a priori, that the automatic contact arrangements could never work. Mental inertia, like mechanical inertia, may be defined in two ways. Inertia is the resistance to motion - that is the English definition: but inertia is also the resistance to stopping - that is the American definition.
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