Зображення сторінки
PDF
ePub

THE TELEPHONE PATENT SITUATION.—III.

THE telephone receiver being free and a non-infringing transmitter possible, how may the the telephone be supported on its hook without infringing one or more of the telephone switch patents? There are more than one hundred patents on telephone switches, a large proportion of which are upon automatic switches and supports. The Bell company has had seventeen years' possession of the telephone field in which, leisurely and carefully, to make experiments, take out patents of its own and purchase the patents of others at practically its own price. In no department of the art, perhaps, has the company shown greater skill and better judgment than in the protection of the automatic telephone support. The most famous of the support patents, if not the most inclusive, is that of Hilborne L. Roosevelt, dated May 27, 1879, and numbered 215,837. This patent covers broadly the class of telephone supports by which the relations of circuits are changed through the action of the weight of the receiver when upon its support, against a spring-the circuit being in one condition when the telephone is in use and in another when it is hung up. The claims of this patent are as follows:

1. The combination, with a telephone, of a circuit closing or changing portion and screws or points, the circuit-closing portion being arranged to be placed in contact with one screw-point through the influence of the telephone when not being used, and to be placed in contact with the other screw or point when the spring is freed from the influence of the telephone, substantially as described.

2. The combination of a spring-switch, connecting-wire connected therewith, and a transmitting-instrument suspended thereto, substantially in the manner described, whereby the raising of the transmitting-instrument causes the spring-switch to make or break or alter the electric circuit.

3. The combination of a spring-switch and connecting-wire connected therewith, and a transmitting-instrument suspended thereto, combined and connected together, substantially as herein described, whereby a circuit is made through a signaling-instrument when the weight of the transmitting-instrument is on the switch, while the circuit is closed through the transmitting-instrument itself when its weight is removed from the switch.

4. A transmitting-instrument hung on a spring-switch, which spring-switch has two points, the lower one dead, the upper one making a contact with the ground, combined with another transmitting-instrument suspended on a similar switch, which switch has its lower point connected with a signaling-instrument, and its upper point connected to the transmitting-instrument, substantially as described.

5. The combination of a suspended transmitting-instrument, spring-switch, and connecting-cord independent of the connecting-wires, whereby the weight of the transmitting-instrument is taken from the wires, substantially as described.

6. The combination of two telephones, connecting-wire, and battery, and two spring-switches, connected and combined substantially as described, whereby when the weight of the telephones rests on the spring-switches a through-circuit is made by means of the battery through the signaling-instrument, while when the telephones are raised a circuit is made through the telephones and the battery is cut out.

7. The combination of a connecting-wire carrying an electric circuit, and attached to the spring-switch having contact-points, and a transmitting-instrument suspended to said spring-switch, connected and combined substantially as described, whereby the weight of the transmitting-instrument upon the switch causes the switch to complete a circuit through itself, and to a ground or a signaling instrument, while when the transmitting-instrument is raised a circuit is made through said transmitting-instrument.

8. A telephone having two connecting conducting-cords and one suspending non-conducting cord, the said non-conducting cord being shorter than the two conducting-cords, whereby the weight of the telephone is taken from the conducting cords and rests upon the non-conducting cord, substantially as required.

The patent of which the claims are quoted above has but two years to run from May 27, 1894-or in other words, it will expire on May 27, 1896. In the most important claims of this patent-the first, second, third and fourth-the term "transmitting instrument" is employed instead of "telephone" in all but the first claim. The intention of the patent, however, is entirely clear and it is doubtful whether splitting hairs on the part of those who would infringe or evade the patent on this ground would be successful before a Court. The next important and

broad patent upon telephone support switches is that of It will be noticed that while there are only three claims, no Geo. M. Phelps, of December 2, 1879, numbered 222,201. words are wasted, and the claims cover absolutely all that class of telephone supports in which a circuit-changing telephone switch is operated positively in both directions by the removal from, and replacement of, the telephone in its support. There are many subsequent patents subsidiary to this one just as there are many patents subsidiary to Roosevelt's. The following are the claims in full of the Phelps patent :

1. A circuit-changing telephone switch-lever actuated positively in both directions by the removal from or replacement of the telephone in its support, substantially as herein before set forth.

2. The combination, substantially as herein before set forth, of the telephone supporting hook, the pivoted forked switch-lever, and the circuit-changing switch-pieces or contact-springs mounted thereon.

3. The improved telephone-switch herein before described, consisting of the combination of the supporting-hook, the pivoted forked switch-lever, its contact-springs, and the circuit-wires, whereby the circuit-changing is positively controlled by the removal from or replacement of the telephone in its support.

The next stroke of genius on the part of the Bell Company-or rather Western Electric Company-in the matter of supports was in securing control of the patent of Ezra T. Gilliland, of May 31, 1881, No. 242,195. After the patents of Roosevelt and Phelps there seemed to be only one important variety of hook to be covered, and that was the fixed hook in which the telephone when supported was shunted out of circuit by the mere contact of the eye carried by the receiver with its support when hung thereon. The claims of this patent, however, do not seem to be quite so inclusive as those of its two predecessors. There are forms of hook support not covered by these claims, which, it would seem, might as well have been included as not. The claims are as follows:

1. A telephone apparatus comprising, in combination with a telephone and its support, one or more contact-pieces carried by the telephone and electrical connections, as indicated, whereby, when the telephone is on its support, the current passes through the latter without passing through the telephone, substantially as described.

2. The combination of a telephone, an eye or equivalent device carried by the telephone and electrically connected with one or both the binding-posts, and a supporting hook or pin, substantially as described.

3. The combination of an electrical circuit, a transmitter, a hand telephone, a support for the hand-telephone, a contactpiece carried by the telephone, and electrical connections, substantially as described, whereby the hanging of said telephone on its support cuts both itself and the transmitter out of the circuit, as set forth.

4. A telephone provided with an eye or equivalent device electrically connected with one or both binding-posts, as set forth.

It will be noticed that a telephone carrying a contact piece which is not in electrical connection with either of the binding posts is clear of the second and fourth claims. Again, if the telephone so arranged hangs upon its support in such a manner that the current is divided, say, equally between the support and the telephone, the device is also obviously clear of the first claim, which definitely specifies that when the telephone is on its support the current passes through the latter without passing through the telephone. In order to be clear of the remaining hook patents, however, the transmitter used must employ no induction coil for the reason that the device would then fall under the shadow of the great patent of Thomas A. Watson, of January 9, 1883, No. 270,522, the claims of which are as follows:

1. In combination with suitable contact-points and springs electrically connected with the call-circuit and the primary and secondary circuits of a transmitter, the latter circuit including the hand-telephone, a lever electrically connected with the main line in a telephone-circuit, substantially as described, to bring in the hand-telephone and transmitter and break the call-circuit, or to cut out the hand-telephone and transmitter and establish the callcircuit, accordingly as the lever is moved in one direction or the other.

2. In combination with suitable contact-points and springs

electrically connected with the call-circuit and the primary and secondary circuits of a transmitter, the latter including a handtelephone, a lever electrically connected with the main line and provided with a hook to support the hand-telephone, and a spring tending to overcome the weight of the hand-telephone, substantially as described, to bring in the hand telephone and transmitter and break the call-circuit, or to cut out the hand-telephone and transmitter and establish the call-circuit, accordingly as the handtelephone is removed from or hung upon said hook.

3. In combination with suitable stops connected with the primary and secondary circuits of a transmitter, the latter including the circuit through the hand-telephone, a lever electrically connected with the main line and adapted to support the hand-telephone, and provided with a spring tending to overcome the weight of the hand-telephone, substantially as described, to complete the local circuit through the transmitter, and at the same time connect with the main line the secondary circuit through the transmitter and hand-telephone by taking the hand-telephone from the hook.

4. In combination with a magneto-generator, a main-line telephone-circuit and a shunt-circuit passing through the magnetogenerator, the push-button U to break the shunt-circuit, substantially as described.

5. A switch-lever and contacts for connecting with the linewire either a telephonic circuit or a call-circuit, according to the position of the switch-lever, in combination with the magnetogenerator, its shunt and push-button, the said magneto-generator being connected with the call-circuit, substantially as described.

6. In a telephonic circuit, the spring-hook D, adapted to support the weight of the hand-telephone, in combination with the contact-springs s1, s2, and s3, connected with the transmitter handtelephone and a signaling-circuit, substantially as described, for the purpose specified.

7. In a telephonic circuit, the spring-hook D, adapted to support the weight of the hand-telephone, in combination with contact-springs s1s and their connections, substantially as described, to automatically establish the primary local circuit through the transmitter, and at the same time bring into the main line the circuit through the hand-telephone and the secondary circuit through the transmitter by taking the telephone from the hook.

8. A switch-lever connected with the main line of a telephonic circuit and movable in either direction, in combination with the contact-springs, s1 s2 83, the transmitter, the hand-telephone, a signaling-circuit and suitable connecting-wires, substantially as described.

This patent, especially in connection with those of Roosevelt, Phelps and Gilliland, has been responsible for many sleepless nights to many inventors. The first claim of the Watson patent would seem to be especially productive of insomnia. The specifications and drawings would indicate that an automatic switch only was intended to be covered, yet in the first claim the inventor seems absentmindedly not to have mentioned the fact. Those inventors and manufacturers who are preparing to go into the telephone business and who propose to use magneto call-bells may profitably direct their attention to the 4th and 5th claims of this patent.

In connection with the subject of support patents, a good story is told of an enthusiastic inventor who called recently at the office of an electrical journal, asking the opinion of one of the staff upon his invention. The newspaper man complimented the inventor upon his ingenuity but observed, "I see that you use an automatic gravity switch which, if placed upon the market, will infringe the Roosevelt patent; I would suggest that you change your device so that it will be clear of this patent and also of the other patents upon telephone supports." "Very good," the inventor replied, "I shall do so; this evening I shall take up the matter and think it over." "If you can spare the time," suggested the newspaper man, "you might think it over a little to-morrow evening also."

NOTE.-In the first section of this article [ELECTRICAL ENGINEER January 17, p. 45] Phelps's telephone patent was referred to as No. 222,201, Dec. 2, 1879. The reference should have read: No. 220,209, Sept. 30, 1879.

ELECTROLYTIC POLARITY TEST PAPER.

WE have received from Dr. Durand Woodman, analytical and technical chemist, No. 80 Beaver street, New York, some strips of electrolytic test paper for determining the polarity of electric circuits. The current from two or three Leclanché cells, or say, a a potential of about 4 volts up, is sufficient to produce a violet red color at the negative pole. Specimens of this paper can be obtained from Dr. Woodman.

SYSTEMATIC NOMENCLATURE,

A LETTER appearing in Nature by Prof. Geo. F. Fitzgerald and Mr. F. T. Trouton contains the following interesting remarks on the above subject.

If once for all some system of termination was settled upon (as in chemistry, for the increasing oxidation results, &c.), the coinage of words as fresh needs arose would proceed automatically on rational lines.

This might very well form the object of a special committee of the British Association.

Mr. Oliver Heaviside's system for electromagnetic matters has much to recommend itself for adoption, also, in general physics.

For example, after the plan (1) conduction, (2) conductance, (3) conductivity, we would have, in the case of radiant energy, (1) radiation, (2) radiatance, (3) radiativity.

The first is for reference in a general way to the phenomenon in question; the second refers to its amount in appropriate units in any individual case; while the third is suitable for expressing the peculiar action or factor in the phenomenon possessed by different kinds of bodies. Thus the radiatance from a hot kettle would be the total quantity of energy lost per second. The radiativity would be the quantity of this per square centimetre.

With a view of examining the feasibility of this system, the following list is subjoined. Many of the words appear at first as if they would prove most awkward in practice, but remembering similar fears (which subsequently proved groundless) in electromagnetic matters, one is afraid to say they are due to more than unfamiliarity.

[blocks in formation]

As regards the future of electricity as an economical agent, Prof. Edwin J. Houston in the January McClure's Magazine says: "In the nearer foreground I see a practical method for the production of electricity directly from the burning of coal. This achieved, there necessarily follows the universal adoption of the electric motor as a prime mover; the relegation of the steam engine to the scrap heap, and the almost immediate realization of the airship as a means of transportation.

"Assuming the cause of chemical affinity to lie in the unlike electric charges of the combining atoms, I see the practical realization of electric synthesis, whereby wholesome food products will be directly formed under the potency of electric affinities. I see, too, a marked advance in electro-therapeutics, whereby human life will be prolonged and its sufferings alleviated. Diagnosis and prognosis will be profoundly aided by exact electrical measurements of the various organs of the human body as regards their electromotive force and resistance. The electro therapeutist of the future will employ electric charges and currents for restoring the normal charges and currents of the body, as well as for the stimulation of nervous or muscular tissues.

"Back of these achievements I discern a practical apparatus for seeing through a wire-i. e., a device for looking into a receiver at one end of a metallic wire and seeing therein a faithful reproduction of whatever optical images are impressed on a transmitter at the other end-even though thousands of miles intervene. I see the possible use of the step-down transformer for the preparation of a road bed or road surface by the vitrification, in situ, of clay or other suitable soil, by the intense heating power of enormous currents of electricity.

"These things I believe I see with fair distinctness. In the further background I faintly see, dimly outlined through the clouds, an apparatus for the automatic registration of unwritten, unspoken thought, and its accurate reproduction at any indefinite time afterward."

This dream of man's future is full of brightness.

MISCELLANEOUS.

THE ELECTRICAL TRANSMISSION OF POWER FROM NIAGARA FALLS.-VII.

BY PROF. GEORGE FORBES.

(Discussion.)

motors he would find he had a whole lot of consuming devices on his circuit to take up lagging current. Capacity in the mains was very much like putting a redressed circuit round the field-magnets. Mr. Crompton and he went into the question of frequency some years ago, and they advocated about the same frequency as Prof. Forbes-about 20. But on looking into the matter they found they were wrong. In the first place, the transformers came out outrageous. In the second place, a point which Prof. Forbes had not mentioned, there was the heating of the field-magnets. If they were going to use very low frequency their pole-pieces would be very broad; the peripheral angle covered was large, and if the pole-pieces were not laminated they would get very hot. If they were laminated in the direction of movement they got over the difficulty of heating due to the Foucault currents in it, but they did not get over the difficulty of the enormous hysteresis loss, and he was not sure that this was not going to be a serious difficulty. MR. S. F. WALKER said with reference to the winking of incandescent lamps, if they used thick filaments they could make the frequency as little as they pleased. He would like to know what the cost of the culvert which Prof. Forbes described was going to be. It appeared to him that town distribution would have to come to that. At present they buried their cables, and they could not be certain what was going to happen to them. Sooner or later faults would be generated; experience in connection with telegraph lines would bear that out. Therefore, he felt confident that sooner or later subways would have to be made for town work, and the conductors would have to be carried so that a man could walk upright and examine them. Of course, the subways might be used for a good many other things. The only question was one of cost, and it was important to know what that would be. The revolving parts in Prof. Forbes's dynamos were very heavy, and the speed seemed to him to be high. He had folfowed the designs for the bearings and so on very carefully. They could provide for the speed, for the centrifugal force, and the twisting strain on the spindle, which was a most important matter, but there was a big difficulty when they came to provide a steel spindle which was very large, as it would have to be to stand the enormous twisting strain; they could never be quite certain what they got inside. He believed he was correct in saying that,

MR. J. SWINBURNE said the first thing that struck him on reading the Paper was not a purely electrical question, but a commercial one, and that was, what was this power going to cost? What was it going to be sold at, who wanted it, and what were they going to do with it? The cost of the power was not given in the Paper. In time it must become public property, and he could not be asking Prof. Forbes any secret, because villages and cities were being built and factories started, and he hardly imagined the 'cute Yankee was ready to build villages and start factories without knowing what the power was going to cost. This was rather a curious question, and a rather surprising one when they went into it. In most industries the power used was quite a small proportion of the cost of running a factory, whatever it might be. In others, of course, it was a very large proportion. But in such cases, for instance, as flour milling, the cost of power was really a very small proportion, and it would hardly pay to remove a flour mill to a place where power could be had cheap from a place where labor was cheap. In other cases, such as tearing up wood pulp, of course the cost of power was a much more serious matter. But in dealing with very large power plants it generally came out, unless the load factor was very good indeed, that the cost of coal was not such a serious item as they might expect. Some time ago he worked out a scheme for transmitting power from the Midlands to London, and he found it was very largely a matter of interest, for he found that the interest upon capital was so enormous when compared with the cost of coal that the cost of coal was hardly a factor to be considered at all. There was also another important question in connection with this. They wanted to know who was going to use the power. The problem was entirely different according to whether they wanted to supply small users who required one tenth of a horse power, or to run printing machines in a district like Fetter-lane, with 2 or 3 H. P., or to drive aluminum works, where they would want hundreds or thousands of horse-power. The difficulty with medium powers was to start the motors. That did not come in with large powers; it was a small detail then. Referring to the extra output from a double current, there was something in that undoubtedly, and as a matter of interest he would like to mention that the question of the transmission of power for long distances by means of double alternating current was really before electrical engineers as early as 1887. He had nothing to do with it himself, so he had all the more pleasure in mentioning that at Messrs. Crompton's they had an inquiry for a large power transmission in Australia, and they discussed a method and decided that it should be alternating. Mr. R. B. Rogers, then his (Mr. Swinburne's) assistant, suggested that the right way to do it was by double current, winding the armature all over with wire. In fairness to Mr. Tesla and others he must say that he did not think Mr. Rogers realized that this double-current plant would be self-starting, but he quite realized other advantages. But the extra output, which was one of the features mentioned by Mr. Rogers, with a little illusory when they dealt with very large machines. The next thing he ought to remark was the very high infrequency which Prof. Forbes used, an infrequency of 0.04 sec. per period. He would like to add to what Mr. Mordey and others had said about transformers. Everybody who had done much practical designing would wish to protest against the large amount of general statement in the Paper "all other things being equal," and so on. The whole gist of the matter was in the "all other things being equal." In making a radical alteration such as that the whole comparison turned on the other things." He protested also against the introduction into a scientific Paper of "well-known facts." Whenever an author said a thing was a well-known fact he was sure to be wrong. As to the flickering of lights, one rather important point ought to be threshed out. Helmholtz was the first, he believed, to investigate the frequency which worries the eye; whether Helmholtz quoted or investigated he was not sure. Helmholtz was concerned with the frequency that worried the ear, and went on from that to the frequency that worried the eye, which he found to be a frequency of 25. It must be borne in mind that the frequency of the flickering in the lamp was always double the frequency of the current. so that would mean, according to Helmholtz, that the eye would stand an alternate current frequency of 122. It was very curious that Helmholtz's and Forbes's results did not agree. Prof. Forbes observed a flickering at a frequency of 48, or a frequency in the lamp of 96, whereas Helmholtz said the point of limit was 25, so that there was a very large discrepancy between the observations of electrical engineers and the observations of Helmholtz. As to capacity, Prof. For es took a great deal of trouble to eliminate capacity from his system. He (Mr. Swinburne) could not help thinking he was wrong there. As soon as Prof. Forbes had in all these triple and double-current

in this country, at any rate, all machines which had such heavy moving masses as this revolved at a very much lower speed, something like one-tenth.

MR. FERRANTI said it was well known that dynamo contractors and designers from all the world over had submitted plans to the Niagara Company. It seemed to him that it would be very hard to design a dynamo which was not in every way the best from the knowledge which the gentlemen of the Cataract Construction Company had had put before them. There were, however, several important features in which the dynamo proposed was novel. One of them was the method of insulating the coils. He had not heard of any other public proposition except that of Prof. Forbes for doing it in that way. It might be interesting to know that in the provisional specification of a patent he (Mr. Ferranti) had abandoned, occurred a passage describing a very similar arrangement. He let that drop, and he thought wisely so. He had had the pleasure lately, even since the last discussion, as well as before the Paper was read, of going round some of the works on the Continent, much as Prof. Forbes and the other engineers of the Cataract Construction had done. Although he thoroughly disagreed with the general design of the machine, he recognized some details of value in it, but these were embodied in the designs sent in by Mr. C. E. L. Brown, of Baden, perhaps the man who had done most towards high-pressure work and long-distance transmission. With regard to the cooling of the bearings, it was a very general practice amongst English and Continental engineers to circulate water continually in the jacket round the bearing, which of course was preferable to throwing water on from a hose according to marine practice, but in this case he should say it would be very effective if water were always left on. There should surely be enough water at Niagara to make this possible. He considered the exciting a large plant like that in series was anything but the best arrangement; he believed the old parallel method of exciting, had many points in its favor. The question of transforming up was in practice a very awkward one. It led to many objectionable results, and was especially bad where it was combined with other dynamos working direct on the circuit at high pressure. He believed it was contemplated to make those dynamos of higher pressure than 20,000 volts; then, he supposed, the old ones would have to be rewound, remodeled, or worked on this objectionable plan. There was, he thought, a very great difference, which might not appear at first sight, between designing dynamos and building them; in fact, a thing which one made one's ordinary daily business, was very different from getting together a collection of all the information which was available in the world, and, then, without any previous knowledge of dynamo design, and especially building, and more e pecially running, to design a machine which was hoped to fulfil great expectations. With regard to the next point, that of the construction of the line and the voltage to be used, as he understood it, it was proposed to use an electromotive force of 20,000 volts on the assumption that, as at Deptford, there had been used an electromotive force of 10,000 volts; 10,000 volts

with one pole to earth, so the safety would be equally great with 20,000 volts, and both poles insulated. He thought this was a great fallacy. If they had two cables both insulated from earth and charged in this way, it was exceedingly unstable and dangerous. If they adopted the safest method of conveying electricity, namely, by concentric cables, then the outer conductor took the same potential as that of the earth. If the two cables were separate they were liable by any accident which might occur in practice to have one put to earth. Then they would have a reversal of strains, the whole theory of 20,000 volts being as easy as 10,000 being upset. and they would have conditions which they had not provided for. Taking this pressure of 20,000 volts, the question was how to insulate it. He read in the paper that a subway had been partly built to carry the cables. The first impression upon his mind, and also the last after carefully considering it, was that that subway would be a very hot place; 10,000 volts was quite alarming enough when it got out of control; 20,000 with big horse-power at the back would, he thought, be worse. He thought it was quite possible if any fault did occur in the subway it would cause a very serious state of affairs in the whole of that subwav, or, at any rate, through a considerable portion of it, and it would probably lead to the complete breakdown of the system. Next they had the question of periodicity. He could not agree with the periodicity of 163 per second, or even with a periodicity of 25. He was sure there must be a considerable amount of lighting to be done. Why should this lighting be sacrificed? Was there going to be a proportionate gain in the general working of the system by using such a low periodicity? He did not think there would be. He believed the system adopted by Ganz at BudaPesth was a more satisfactory one to work at, somewhere about 40.

It certainly rendered both arc and incandescent lighting possible, and was somewhere about the happy medium. With regard to the higher periodicity which they had heard spoken of in connection with this Paper, there were enormous difficulties in working with it. It had been spoken of as though it really was not an important thing; but there were very serious effects. In the first place, the capacity effects were much worse where they had to deal with capacity at this high periodicity, and what was much worse than that again was the magnetic retardation due to the field excited round the conductors. This would be alluded to fully in a Paper shortly to be read, and he would not further touch upon it, except to say that it was a very grave difficulty. He ventured, however, to say that so high a periodicity as 100, or even 86, as at Deptford, would be fatal to an economical working of the system. They came now to a most interesting question— how was electricity to be transmitted to a very great distance, by what method was it going to be done? Was it going to be done by alternating currents or by continuous current? He must say he did not see the faintest chance of its being done with the continuous with the present knowledge; but, at the same time, he saw very grave difficulties in the way of doing it by alternating currents.

There was one side of the question which he thought was much more important to the Institution than the periodicity, or the electromotive force, or the design of the dynamo. It was the general principle upon which the Cataract Construction Company had obtained its information. They proceeded in an exceedingly clever way. They formed a Commission, asked the greatest scientists of the day to join them, got a room at the City and Guilds Institute at South Kensington, and gave the Commission power to offer prizes, very small ones, and used other means, in fact any means, by which they could draw and collect information. He had had the pleasure of meeting some of the people who had sent in specifications. He himself did not send any. Various schemes were sent in. There were those great scientists, men they would not think of questioning, to give the thing perfect legality, and everybody thought it was a good thing. The information was not sent in by amateurs, but by people who had to make their living by building dynamos or some such articles. One firm spent at least £1,000 in doing it, and they might take it that that money did not represent the whole cost nor the value of the brains of those able men who had been engaged in working out a scheme. Nothing sufficiently satisfactory having been obtained, what was the next step? The engineers of the company were sent round to the different works on the Continent to gain information, the Company knowing full well all the time that that information was not going to be used to the benefit of those who gave it, or be adequately recompensed. It was upon the information so obtained that the designs and schemes which had been put before the Institution had been got out; it was upon the work of the world, the electrical world, unrecompensed, that the undertaking would be carried out at Niagara. He did not blame Prof Forbes, but it had been beautifully worked out by the Company, and nearly everbody had fallen into the trap.

THE DESIGN OF SWITCH CONTACTS AND BREAKS.

I HAVE been searching for some time past for rules for the design of switch contacts and breaks to suit various currents but have found no articles as yet on this subject. Can any of your readers give me any information or references on this subject? V.

THE THEORY AND DESIGN OF THE CLOSED COIL CONSTANT CURRENT DYNAMO.—II.

BY PROF. HENRY S. CARHART.

THREE METHODS OF GOVERNING.

Assuming still practically constant speed, we next inquire into the methods employed to maintain a constant current without appreciable sparking by rocking the brushes round the commutator cylinder.

In one machine the brushes are moved automatically by means of a small electric motor and at the same time field coils are successively cut out as the brushes rock forward with a light load. A pair of brushes is used on each side and they are kept at a fixed distance apart. By these combined means the machine can be run on short-circuit with normal current and without sparking.

Another system leaves the field coils constantly in circuit but employs two pairs of brushes and varies the angular distance between the members of each pair when the brushes are moved. The movement of the brushes is effected mechanically in response to any change in the main current till the current is brought back to the normal value. In these machines the spread of each pair of brushes, or what is sometimes called the overlap of the brushes, is lessened as they rock forward toward the polar centres. Very satisfactory results are secured in this way.

In the third class of machines only one pair of brushes is used which lap over about two or three commutator sections and the regulation of the current is effected solely by the movement of this one pair without change of overlap and without disturbance of the ampere turns on the field. The brushes are moved mechanically by means of an automatic regulating device. No less satisfactory results appear to be secured by this method than by the others, while the mechanism as a whole is somewhat simpler. I have described these three methods for the purpose of pointing out their bearing on the theory and design of closed-coil Gramme rings for constant currents. The important question is not how to get the necessary E. M. F. with such a dynamo, but how to vary the E. M. F. in response to the varying demands of the external circuit, without injurious sparking at the brushes.

The E. M. F. is controlled in all three of these methods by rocking the brushes, and the other differences in the devices are made necessary for the supression of the sparking. This brings us to a consideration of the most intrinsically interesting topic of the paper, viz., the conditions necessary to suppress sparking and the features of design required to furnish them.

SUPRESSION OF SPARKING.

If we assume that the armature is well balanced electrically and magnetically and that the brushes have a proper bearing in contact with the smooth commutator, the conditions required to commute the current without sparking are known to be as follows: With a two pole dynamo, the current is divided through the armature, one half going from brush to brush through one side and the other half through the other side. Hence when an armature coil is carried past the brush it is transferred from the one circuit throughout the armature to the other, and at the same time the current through it reverses its direction. This constitutes the act of commutation. But the sudden decay of a current through a coil in one direction and its growth to an equal value in the other gives rise to an E. M. F. of self-induction opposing the change. This E. M. F. will prolong the flow of the current on one side of the brush and will oppose it rise on the other side. Hence if the coil is short-circuited by the brush lapping over the two consecutive commutator segments to which its ends are connected, even when the coil passes the neutral plane of the dynamo, the E. M. F. of self-induction produces a local current through this coil; and when the one end of the coil slips past the brush and becomes a part of the other half of the divided circuit the current which should reverse through it meets the opposing current and breaks over the gap to the brush with a spark. Hence the commutation must not take place at the neutral plane but in advance of it, and in a field where the induced E. M. F. in the coil shall be just sufficient to offset the self-induction, and in addition reverse the current in the coil while it is passing through the brush or pair of brushes, and cause it to grow to the normal value at the instant when one end of it passes out from under the brush. The induction from the field must be sufficient to bring the one current to zero and to set an opposite one of equal value flowing in the coil, during the time it is under the brush. Then the commutation will be sparkless.

Now if the current is kept constant in strength the field induction required to accomplish the results described is approximately the same, whether the coil is short-circuited at one angle or another in advance of the neutral plane. It would appear at first thought that, unless the induction in every part of the field from the neutral plane to a point nearly 90 degrees in advance of it is substantially uniform. terrific sparking must result when the brushes are shifted far forward to vary the electric pressure to suit the requirements of the circuit; for, if the induction is in excess of the requirements to accomplish the result described in the commuted coil, then the current will circulate through it during

the short-circuit, and the rupture of this on leaving the brush will cause sparking. I have illustrated this action in the following manner: Separately excite the field magnets of a machine, which can run on short-circuit even. with a forward displacement of the brushes without sparking. Then, leaving the armature on open circuit, rock the brushes forward; the sparking will increase with each advance till it becomes terrific and endangers the machine. The induction to which each coil is subjected in an excited field produces a large current in it while it is under the brush, since there is less self-induction in the coil to offset the induction from the field than there is when the machine is self-excited and working in the normal way. There is another reason to be described later.

Considerations of this kind have lead some writers to say that sparkless commutation for any position of the brushes can be accomplished only when the induction in the field is made uniform. The Statter constant current machine in England is made on this principle. Portions of the pole pieces are laboriously cut away at such points as to make the density of the lines of force entering the armature over a given angle equal. Of course a machine built in this way will permit of shifting the brushes through a considerable angle in order to vary the potential difference without introducing sparking, but while a uniform field accomplishes the result, no such uniformity is required; the same result may be secured in other ways. The first method already described weakens the field when the brushes move forward by cutting out ampere-turns in the field magnet. This reduces the induction to the proper amount at each point without changing the overlap of the brushes. It is made necessary by the very high saturation of the armature core in this machine. It has the advantage of greater economy with small loads because field resistance is cut out, but it requires a more complex arrangement of parts on the machine than suffices for the mere movement of the brushes.

THE NORTHWESTERN ELECTRICAL ASSOCIATION. The annual meeting of the Northwestern Electrical Association was held at the Hotel Pfister, Milwaukee, on January 17, 18 and 19, as noted in our columns last week.

At the evening session Mr. W. N. Stewart, of the Siemens & Halske Electric Company, read a paper on the "Advantage of Direct Connection." describing his idea of a model central station, his plans being based on the methods employed in several European cities.1

Prof. D. C. Jackson of the Wisconsin University, read an interesting paper on "Essential Station Instruments" that is worthy of careful perusal.

On Thursday President Paige called the members to order at 10 o'clock, and a ballot was taken resulting in the selection of St. Paul as the city in which the semi-annual meeting would be held on the third Wednesday in July. Of the 27 members voting, 20 favored the city named.

MR. WILL W. Low, president of the Electrical Appliance Company, Chicago, then read a paper on "The New Things in Electricity," holding that from the central station-man's point of view the very complete catalogues and discount sheets, together with the salesmen possessing consciences, are the best among the new things in the supply business. Mr. Low then briefly referred to the inherent excellent qualities to be found in an insulated wire, a new transformer, an alternating arc lamp, and an incandescent lamp which his company is handling, and of the merits of which natural modesty forbade him saying more. As all but one of the supply-men present,- -a gloomy individual answering to the name of Bunce,-claimed to have a conscience, the paper was not discussed.

MR. W. FORMAN COLLINS followed with a thoughtfully prepared paper on the "Economical use of Transformers," dealing more especially with the theoretical side of the question, and maintaining that the highest economy is secured when the transformers are large and few in number.

MR. PARMELEE J. MC FADDEN, of the staff of the General Electric Company followed with some interesting practical details,1 so clearly and concisely presented that little was left for discussion.

Following the opening of the discussion, MR. JOHN SCHUETTE, the well-known banker of Manitiwoc, related his experience in dealing with the question of transformation of currents, and his remarks were listened to with interest. He believed that the only point to consider was how to get the best results from the equipment now comprised in their plants. MR. E. L. DEBELL, of Sheboygan, believed that for business houses where the load seldom varied, the individual transformer is the more economical, but for residences the best results are secured by using large units. The European practice of employing a bank of transformers was referred to; a suggestion made that inventors be asked to produce a practical device that would automatically cut out a single transformer when not in service, and prevent the loss following the employment of many transformers after midnight. Then the relative merits of the five-wire direct current system versus transformers were discussed. MR. W. N. STEWART was in favor of

1. An abstract of this Paper will appear in our columns.-Eps. E. E. 2. See page 97.

the method comparatively new in this country but which the Siemens-Halske Company, employ in several of its European stations. Mr. Stewart maintained that there was scarcely a town represented in this association standing in need of a transformer system, that the price of copper was no longer the bugbear to be dreaded, and that the limited area covered by the present circuits would, in many cases, render it a profitable investment were the present systems displaced by the five-wire. Mr. Stewart asked the very pertinent question why the General Electric Company had not brought out and developed the merits of the five-wire system they owned and which was an extension of the three-wire system: "Five wires," he said, "can be installed more cheaply than transformers." Then followed a ploughing up of the old danger field, and many hypothetical cases of death following the handling of lamp_sockets on alternating current circuits, were referred to. MR. FORMAN COLLINS and MR. MCFADDEN explained how almost impossible was the likelihood of the primary current passing in on the secondary mains, as the secondary coil would burn out if the secondary fuse did not blow, which it had always been known to do. Mr. GEORGE MAYO thought that if there was the slightest danger to life from handling lamp sockets on alternating circuits it certainly would have been manifested long ago, for there were several hundred thousand such lamps in service. Mr. Debell referred to an accident resulting in a severe shock and burn, but admitted that the transformer was not of an improved type, but had a wooden base on which moisture often collected. Mr. McFadden explained the facts of a case wherein a defective socket and a grounding of the primary current caused serious trouble, but admitted that it was a very rare occurrence. MR. W. H. THORPE Suggested methods for overcoming some of the difficulties mentioned. MR. THOMAS GRIER stated that it was his practice to install transformers on a basis of an overload of 33% per cent. and that this method had proved satisfactory. MR. P. H. KORST referred concisely to the practice in several stations, and PROF. D. C. JACKSON stated that some of the troubles referred to might have been prevented had attention been paid to wellknown laws of engineering, the transgression of which always reacts unpleasantly on both pocket and physical comfort; that, usually, the better plan to follow when contemplating changes would be to call in engineering talent in each special branch of electrical work. These remarks were heartily endorsed.

At 2.30 P. M. the members again assembled and remained in session until 6 P. M. Following the call to order Mr. E. L. DEBELL of Sheboygan, read an interesting paper on "Corliss compound engines for Electric Light Work." 1

MR. H. C. THOM, of Madison, then stated that he had intended to prepare a paper on the subject "How Shall Members buy Supplies," but, with the permission of the president he would read two letters he had received and then follow with a paper entitled "The Trend of Electrical Investment." 1

Hardly had Mr. Thom ceased speaking when a discussion began that lasted for two hours. MR. W. F. COLLINS believed that the real blame for having non-paying plants rests on the men who endeavored to save the cost of the services of a competent consulting engineer, and that in some cases it might prove profitable to employ an experienced electrical engineer to overhaul the entire plant and place it on a paying basis. MR. NORCROSS believed that only business principles should prevail in this, the crowning industry of the future; then there would be no non-paying lighting. plants. MR. STEWART referred to the fallacy of cutting rates. SENATOR MERRILL referred to the lack of knowledge regarding the cost of a horse-power hour; PROF. JACKSON suggested the wisdom of first determining what the current costs at the dynamo or the switch board. Then the discussion drifted off into the keeping of station accounts and the proper rate to charge for arc and for incandescent lighting, and on motion, Prof. Jackson was requested to prepare a paper "On_the_Best Methods of Keeping Central Station Accounts." This Prof. Jackson promised to do provided the members would send to him copies of the forms now used and such data as would assist in the preparation of the paper. 3

MR. JOHN SCHUETTE made an observation to the effect that his superintendent files a daily report, and at the end of each six months Mr. Schuette declares the dividends and divides the surplus profits among the stockholders. The appointment of a committee to recommend a schedule of prices for arc and incandescent lights was discussed and on motion carried.

The following committees were then announced, several new members added, the business closed up, and an adjournment carried.

Committee on Legislation.-H. C. Thom, Geo. Merrill, George Grimm.

Committee on Transporation.-I. P. Lord, Pliny Norcross, O. M. Race.

Committee on Entertainment.-J. C. Woodward, W. B. Baker, L. E. Debell.

Committee on Special Legislation for Underwriter's Rules.— H. C. Thom, Pliny Norcross, J. A. Andrews.

3. It will materially add to the value of Prof. Jackson's paper if every cen tral station manager who may read this summary of the proceedings, will send a set of forms and any suggestions that would aid in formulating a standard system to Prof. D. C. Jackson, Madison, Wis.

« НазадПродовжити »