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EDISON'S DYNAMO WORK
Edison, His Life and Inventions, vol. 2 | ||
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EDISON'S DYNAMO WORK
AT the present writing, when, after the phenomenally rapid electrical development of thirty years, we find on the market a great variety of modern forms of efficient current generators advertised under the names of different inventors (none, however, bearing the name of Edison), a young electrical engineer of the present generation might well inquire whether the great inventor had ever contributed anything to the art beyond a mere type of machine formerly made and bearing his name, but not now marketed except second hand.
For adequate information he might search in vain the books usually regarded as authorities on the subject of dynamo-electric machinery, for with slight exceptions there has been a singular unanimity in the omission of writers to give Edison credit for his great and basic contributions to heavy-current technics, although they have been universally acknowledged by scientific and practical men to have laid the foundation for the efficiency of, and to be embodied in all modern generators of current.
It might naturally be expected that the essential facts of Edison's work would appear on the face of his numerous patents on dynamo-electric machinery, but such is not necessarily the case, unless they are carefully studied in the light of the state of the art as it existed at the time. While some of these patents (especially the earlier ones) cover specific devices embodying fundamental principles that not only survive to the present day, but actually lie at the foundation of the art as it now exists, there is no revelation therein of Edison's preceding studies of magnets, which extended over many years, nor of his later systematic investigations and deductions.
Dynamo-electric machines of a primitive kind had been
It seems almost incredible that only a little over thirty years ago the sum of scientific knowledge in regard to dynamo-electric machines was so meagre that the experts of the period should settle upon such a dictum as this, but such was the fact, as will presently appear. Mechanical generators of electricity were comparatively new at that time; their theory and practice were very imperfectly understood; indeed, it is quite within the bounds of truth to say that the correct principles were befogged by reason of the lack of practical knowledge of their actual use. Electricians and scientists of the period had been accustomed for many years past to look to the chemical battery as the source from which to obtain electrical energy; and in the practical application of such energy to telegraphy and kindred uses, much thought and ingenuity had been expended in studying combinations of connecting such cells so as to get the best results. In the text-books of the period it was stated as a settled principle that, in order to obtain the maximum
It was by no miracle that Edison was far and away ahead of his time when he undertook to improve the dynamo. He was possessed of absolute knowledge far beyond that of his contemporaries. This he ad acquired by the hardest kind of work and incessant experiment with magnets of all kinds during several years preceding, particularly in connection with his study of automatic telegraphy. His knowledge of magnets was tremendous. He had studied and experimented with electromagnets in enormous variety, and knew their peculiarities in charge and discharge, lag, self-induction, static effects, condenser effects, and the various other phenomena connected therewith. He had also made collateral studies of iron, steel, and copper, insulation, winding, etc. Hence, by reason of this extensive work and knowledge, Edison was naturally in a position to realize the utter commercial impossibility of the then best dynamo machine in existence, which had an efficiency of only about 40 per cent., and was constructed on the "cut-and-try'' principle.
He was also naturally in a position to assume the task he set out to accomplish, of undertaking to plan and-build an improved type of machine that should be commercial in having
As some account of Edison's investigations in this connection has already been given in Chapter XII of the narrative, we shall not enlarge upon them here, but quote from An Historical Review, by Charles L. Clarke, Laboratory Assistant at Menlo Park, 1880-81; Chief Engineer of the Edison Electric Light Company, 1881-84:
"In June, 1879, was published the account of the Edison dynamo-electric machine that survived in the art. This machine went into extensive commercial use, and was notable for its very massive and powerful field-magnets and armature of extremely low resistance as compared with the combined external resistance of the supply-mains and lamps. By means of the large masses of iron in the field-magnets, and closely fitted joints between the several parts thereof, the magnetic resistance (reluctance) of the iron parts of the magnetic circuit was reduced to a minimum, and the required magnetization effected with the maximum economy. At the same time Mr. Edison announced the commercial necessity of having the armature of the dynamo of low resistance, as compared with the external resistance, in order that a large percentage of the electrical energy developed should be utilized in the lamps, and only a small percentage lost in the armature, albeit this procedure reduced the total generating capacity of the machine. He also proposed to make the resistance of the supply-mains small, as compared with the combined resistance of the lamps in multiple arc, in order to still further increase the percentage of energy utilized in the lamps. And likewise to this end the combined resistance of the generator armatures in multiple arc
Among the earliest of Edison's dynamo experiments were those relating to the core of the armature. He realized at once that the heat generated in a solid core was a prolific source of loss. He experimented with bundles of iron wires variously insulated, also with sheet-iron rolled cylindrically and covered with iron wire wound concentrically. These experiments and many others were tried in a great variety of ways, until, as the result of all this work, Edison arrived at the principle which has remained in the art to this day. He split up the iron core of the armature into thin laminations, separated by paper, thus practically suppressing Foucault currents therein and resulting heating effect. It was in his machine also that mica was used for the first time as an insulating medium in a commutator.[10.1]
Elementary as these principles will appear to the modern student or engineer, they were denounced as nothing short of absurdity at the time of their promulgation—especially so with regard to Edison's proposal to upset the then settled dictum that the armature resistance should be equal to the external resistance. His proposition was derided in the technical press of the period, both at home and abroad. As public opinion can be best illustrated by actual quotation, we shall present a characteristic instance.
In the Scientific American of October 18, 1879, there appeared an illustrated article by Mr. Upton on Edison's dynamo machine, in which Edison's views and claims were set forth. A subsequent issue contained a somewhat acrimonious
"It is not my intention to criticise the design or construction of the machine (not because they are not open to criticism), as I am now and have been for many years engaged in the manufacture of electric machines, but rather to call attention to the impossibility of obtaining the described results without destroying the doctrine of the conservation and correlation of forces. . . . . .
"It is stated that `the internal resistance of the armature' of this machine `is only ½ ohm.' On this fact and the disproportion between this resistance and that of the external circuit, the theory of the alleged efficiency of the machine is stated to be based, for we are informed that, `while this generator in general principle is the same as in the best well-known forms, still there is an all-important difference, which is that it will convert and deliver for useful work nearly double the number of foot-pounds that any other machine will under like conditions.' '' The writer of this critical letter then proceeds to quote Mr. Upton's statement of this efficiency: " `Now the energy converted is distributed over the whole resistance, hence if the resistance of the machine be represented by 1 and the exterior circuit by 9, then of the total energy converted nine-tenths will be useful, as it is outside of the machine, and one-tenth is lost in the resistance of the machine.' ''
After this the critic goes on to say:
"How any one acquainted with the laws of the electric circuit can make such statements is what I cannot understand. The statement last quoted is mathematically absurd.
"Does Mr. Edison, or any one for him, mean to say that [Description: Mathematical formula included in the second volume of Edison: His Life and Inventions: r/n. ] enables him to obtain nE, and that C is not = [Description: Mathematical formula included in the second volume of Edison: His Life and Inventions: E/((r/n)+R). ] ? If so Mr. Edison has discovered something more than perpetual motion, and Mr. Keely had better retire from the field.
"Further on the writer (Mr. Upton) gives us another example of this mode of reasoning when, emboldened and satisfied with the absurd theory above exposed, he endeavors to prove the cause of the inefficiency of the Siemens and other machines. Couldn't the writer of the article see that since [Description: Mathematical formula included in the second volume of Edison: His Life and Inventions: C=E/(r+R). ] that by [Description: Mathematical formula included in the second volume of Edison: His Life and Inventions: R/n. ] or by making R = r, the machine would, according to his theory, have returned more useful current to the circuit than could be due to the power employed (and in the ratio indicated), so that there would actually be a creation of force! . . . . . . .
"In conclusion allow me to say that if Mr Edison thinks he has accomplished so much by the reduction of the internal resistance of his machine, that he has much more to do in this direction before his machine will equal in this respect others already in the market.''
Another participant in the controversy on Edison's generator was a scientific gentleman, who in a long article published in the Scientific American, in November, 1879, gravely undertook to instruct Edison in the A B C of electrical principles, and then proceeded to demonstrate mathematically the impossibility of doing what Edison had actually done. This critic concludes with a gentle rebuke to the inventor for ill-timed jesting, and a suggestion to furnish authenticinformation!
In the light of facts, as they were and are, this article is so full of humor that we shall indulge in a few quotations It commences in A B C fashion as follows: "Electric machines convert mechanical into electrical energy.... The ratio of yield to consumption is the expression of the efficiency of the machine.... How many foot-pounds of electricity
The would-be critic then goes on to tabulate tests of certain other dynamo machines by a committee of the Franklin Institute in 1879, the results of which showed that these machines returned about 50 per cent. of the applied mechanical energy, ingenuously remarking: "Why is it that when we have produced the electricity, half of it must slip away? Some persons will be content if they are told simply that it is a way which electricity has of behaving. But there is a satisfactory rational explanation which I believe can be made plain to persons of ordinary intelligence. It ought to be known to all those who are making or using machines. I am grieved to observe that many persons who talk and write glibly about electricity do not understand it; some even ignore or deny the fact to be explained.''
Here follows his explanation, after which he goes on to say: "At this point plausibly comes in a suggestion that the internal part of the circuit be made very small and the external part very large. Why not (say) make the internal part 1 and the external 9, thus saving nine-tenths and losing only one-tenth? Unfortunately, the suggestion is not practical; a fallacy is concealed in it.''
He then goes on to prove his case mathematically, to his own satisfaction, following it sadly by condoling with and a warning to Edison: "But about Edison's electric generator! . . . No one capable of making the improvements in the telegraph and telephone, for which we are indebted to Mr. Edison, could be other than an accomplished electrician. His reputation as a scientist, indeed, is smirched by the newspaper exaggerations, and no doubt he will be more careful in future. But there is a danger nearer home, indeed, among his own friends and in his very household.
". . . The writer of page 242'' (the original article) "is probably a friend of Mr. Edison, but possibly, alas! a wicked partner. Why does he say such things as these? `Mr. Edison claims that he realizes 90 per cent. of the power applied to this machine in external work.' . . . Perhaps the writer
"Mr. Edison has built a very interesting machine, and he has the opportunity of making a valuable contribution to the electrical arts by furnishing authentic accounts of its capabilities.''
The foregoing extracts are unavoidably lengthy, but, viewed in the light of facts, serve to illustrate most clearly that Edison's conceptions and work were far and away ahead of the comprehension of his contemporaries in the art, and that his achievements in the line of efficient dynamo design and construction were indeed truly fundamental and revolutionary in character. Much more of similar nature to the above could be quoted from other articles published elsewhere, but the foregoing will serve as instances generally representing all. In the controversy which appeared in the columns of the Scientific American, Mr. Upton, Edison's mathematician, took up the question on his side, and answered the critics by further elucidations of the principles on which Edison had founded such remarkable and radical improvements in the art. The type of Edison's first dynamo-electric machine, the description of which gave rise to the above controversy, is shown in Fig. 1.
Any account of Edison's work on the dynamo would be incomplete did it omit to relate his conception and construction of the great direct-connected steam-driven generator that was the prototype of the colossal units which are used throughout the world to-day.
In the demonstrating plant installed and operated by him at Menlo Park in 1880 ten dynamos of eight horse-power each were driven by a slow-speed engine through a complicated system of counter-shafting, and, to quote from Mr. Clarke's Historical Review, "it was found that a considerable percentage of the power of the engine was necessarily wasted in friction by this method of driving, and to prevent this waste and thus increase the economy of his system, Mr. Edison conceived the idea of substituting a single large dynamo for the several small dynamos, and directly coupling it with the driving engine, and at the same time preserve the requisite high armature speed by using an engine of the high-speed
FIG. 1
[Description: Drawing of Edison's first dynamo-electric machine.]The construction of the first one of these large machines was commenced late in the year 1880. Early in 1881 it was
With the experience thus gained, Edison began, in the spring of 1881, at the Edison Machine Works, Goerck Street, New York City, the construction of the first successful machine of this type. This was the great machine known as "Jumbo No. 1,'' which is referred to in the narrative as having been exhibited at the Paris International Electrical Exposition, where it was regarded as the wonder of the electrical world. An intimation of some of the tremendous difficulties encountered in the construction of this machine has already been given in preceding pages, hence we shall not now enlarge on the subject, except to note in passing that the terribly destructive effects of the spark of self-induction and the arcing following it were first manifested in this powerful machine, but were finally overcome by Edison after a strenuous application of his powers to the solution of the problem.
It may be of interest, however, to mention some of its dimensions and electrical characteristics, quoting again from Mr. Clarke: "The field-magnet had eight solid cylindrical cores, 8 inches in diameter and 57 inches long, upon each of which was wound an exciting-coil of 3.2 ohms resistance, consisting of 2184 turns of No. 10 B. W. G. insulated copper wire, disposed in six layers. The laminated iron core of the armature, formed of thin iron disks, was 33 ¾ inches long, and had an internal diameter of 12 ½ inches, and an external diameter of 26 7/16 inches. It was mounted on a 6-inch shaft. The field-poles were 33 ¾ inches long, and 27 ½ inches inside diameter The armature winding consisted of 146 copper bars on the face of the core, connected into a closed-coil winding by means of 73 copper disks at each end of the core. The cross-sectional area of each bar was 0.2 square inch their average length was 42.7 inches, and the copper end-disks were 0.065 inch thick. The commutator had 73 sections.
The student may find it interesting to look up Edison's United States Patents Nos. 242,898, 263,133, 263,146, and 246,647, bearing upon the construction of the "Jumbo''; also illustrated articles in the technical journals of the time, among which may be mentioned: Scientific American, Vol. XLV, page 367; Engineering, London, Vol. XXXII, pages 409 and 419, The Telegraphic Journal and Electrical Review, London, Vol. IX, pages 431-433, 436-446; La Nature, Paris, 9th year, Part II, pages 408-409; Zeitschrift fur Angewandte Elektricitäatslehre, Munich and Leipsic, Vol. IV, pages 4-14; and Dredge's Electric Illumination, 1882, Vol. I, page 261.
The further development of these great machines later on, and their extensive practical use, are well known and need no further comment, except in passing it may be noted that subsequent machines had each a capacity of 1200 lamps of 16 candle-power, and that the armature resistance was still further reduced to 0.0039 ohm.
Edison's clear insight into the future, as illustrated by his persistent advocacy of large direct-connected generating units, is abundantly vindicated by present-day practice. His Jumbo machines, of 175 horse-power, so enormous for their time, have served as prototypes, and have been succeeded by generators which have constantly grown in size and capacity until at this time (1910) it is not uncommon to employ such generating units of a capacity of 14,000 kilowatts, or about 18,666 horse-power.
We have not entered into specific descriptions of the many other forms of dynamo machines invented by Edison, such as the multipolar, the disk dynamo, and the armature with two windings, for sub-station distribution; indeed, it is not possible within our limited space to present even a brief digest of Edison's great and comprehensive work on the dynamo-electric machine, as embodied in his extensive experiments
FIG. 2
[Description: Illustration of electric generator.]Although he has not given any attention to the subject of generators for many years, an interesting instance of his incisive method of overcoming minor difficulties occurred while the present volumes were under preparation (1909). Carbon for commutator brushes has been superseded by graphite in some cases, the latter material being found much more advantageous, electrically. Trouble developed, however, for the reason that while carbon was hard and would wear away the mica insulation simultaneously with the copper, graphite, being softer, would wear away only the copper, leaving ridges of mica and thus causing sparking through unequal contact. At this point Edison was asked to diagnose the trouble and provide a remedy. He suggested the cutting out of the mica pieces almost to the bottom, leaving the commutator bars separated by air-spaces. This scheme was objected to on the ground that particles of graphite would fill these air-spaces and cause a short-circuit. His answer was that the air-spaces constituted the value of his plan, as the particles of graphite falling into them would be thrown out by the action of centrifugal force as the commutator revolved. And thus it occurred as a matter of fact, and the trouble was remedied. This idea was subsequently adopted by a great manufacturer of generators.
The commercial manufacture of built-up sheets of mica for electrical purposes was first established at the Edison Machine Works, Goerck Street, New York, in 1881.
Had Edison in Upton's Scientific American article in 1879 proposed such an exceedingly low armature resistance for this immense generator (although its ratio was proportionate to the original machine), his critics might probably have been sufficiently indignant as to be unable to express themselves coherently.
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EDISON'S DYNAMO WORK
Edison, His Life and Inventions, vol. 2 | ||