447,921
ALTERNATING-ELECTRIC-CURRENT GENERATOR - Nov 15, 1890
UNITED STATES PATENT OFFICE
NIKOLA TESLA, OF NEW YORK, N. Y.
Nikola Tesla Patent 447,921 ALTERNATING-ELECTRIC-CURRENT GENERATOR
SPECIFICATION forming part of Letters Patent No. 447,921, dated March 10, 1891.
Application filed November 15, 1890. Serial No. 371,554. (No model.)
To all whom it may concern:
Be it known that I, NIKOLA TESLA, a subject of the Emperor of Austria, from Smiljan, Lika, border country of Austria-Hungary, residing at New York, in the county and State of New York, have invented certain new and useful Improvements in Alternating-Current Machines, of which the following is a specification, reference being had to the accompanying drawings.
In the systems of distribution of electrical energy from alternating-current generators in present use the generators give ordinarily from one to three hundred alternations of current per second. I have recognized and demonstrated in practice that it is of great advantage, on many accounts, to employ in such systems generators capable of producing a very much greater number of alternations per second—say fifteen thousand per second or many more. To produce such a high rate of alternation, it is necessary to construct a machine with a great number of poles or polar projections; but such construction, on this account, in order to be efficient, is rendered difficult. If an armature without polar projections be used, it is not easy to obtain the necessary strength of field, mainly in consequence of the comparatively great leakage of the lines of force from pole to pole. If, on the contrary, an armature-core formed or provided with polar projections be employed, it is evident that a limit is soon reached at which the iron is not economically utilized, being incapable of following without considerable loss the rapid reversals of polarity. To obviate these and other difficulties, I have devised a form of machine embodying the following general features of construction.
I provide a field-magnet core made up of two independent parts formed with grooves for the reception of one or more energizing-coils. The energizing coil, or coils, is completely surrounded by the iron core, except on one side, where occurs the opening between the polar faces of the core, which opening is made as narrow as the conditions of the machine will permit. The polar faces of the core of the field are not smooth, but formed with a great many projections or serrations, the points of which is one side or polar face are preferably exactly opposite those in the other. Between the faces so formed I mount or support the armature coil or coils and provide either for rotating the field-magnet or the armature, or both, and I arrange the said armature-coil or conductor so that it will be symmetrically disposed with respect to the field—that is to say, so that when one portion of the conductor is passing through the strongest portion of the field the other portion, which forms the return for the former, is passing through the weakest points or parts of the field. The strongest points of the field, it will be understood, are those between the projections or points on the polar faces, while the weakest points lie midway between them.
A field-magnet, when constructed as above described, produces, when the energizing-coil is traversed by a continuous current, a field of great strength, and one which may be made to vary greatly in intensity at points not farther distant from one another than the eighth of an inch. In a machine thus constructed there is comparatively little of that effect which is known as “magnetic leakage,” and there is also but a slight armature reaction. Either the armature-conductor or the field-magnet may be stationary while the other rotates, and as it is often desirable to maintain the conductors stationary and to rotate the field-magnet I have made a special modification of the construction of the machine for this purpose, and with a view in such case of still further simplifying the machine and rendering it more easy to maintain in operation I arrange the armature-conductors and the frame or supports therefor so as to support also a fixed coil or coils for energizing the rotating field-magnet, thus obviating the employment of all sliding contacts.
In the accompanying drawings I have illustrated the two typical forms of my machine above referred to.
Figure 1 is a vertical central section of the machine, taken on lines x x of Fig. 2; and Fig. 2 is horizontal section on line y y of Fig. 1. The machine in these two figures is one in which the armature-conductor and the field-coil are stationary while the field-magnet core revolves. Fig. 3 is a vertical central section of a machine embodying the same plan of construction, but having a stationary field-magnet and rotating armature. Fig. 4 is a diagram illustrating the peculiar configuration of the polar faces and the relation of the armature conductor or conductors thereto.
In Figs. 1 and 2, A A designate two cylindrical castings provided with bracket-arms B B, in which latter are bushings C for the rotating shaft. The conductor in which the currents are induced may be constructed or arranged in various ways; but I prefer to form it in the following manner: I take an annular plate of copper D and by means of a saw or other cutting-tool cut in it radial slots from one edge nearly through to the other, beginning alternately from opposite edges. In this way a continuous zigzag conductor is formed. To the inner edge of this plate are secured two rings of non-magnetic metal E, which are insulated from the copper conductor, but held firmly thereto, as by means of bolts F. Within the rings E is then placed an annular coils G, which is the energizing-coil for the field-magnet. The conductor D and the parts attached thereto are supported by means of the cylindrical shell or casting A A, the two parts of which are brought together and clamped by bolts F' to the outer edge of the conductor D. The conductor D is also insulated from the shell A.
The core for the field-magnet is built up of two circular parts H H, formed with annular grooves I, which, when the two parts are brought together, form a space for the reception of the energizing-coil G. The central parts or hubs of the cores H H are trued off, so as to fit closely against one another, while the outer portions or flanges which form the polar faces J J are reduced somewhat in thickness to make room for the conductor D, and are serrated on their faces or provided in any other convenient way with polar projections. The two parts of the core H H are mounted on and fixed to the shaft K, and are bound together by bolts L. The number of serrations in the polar faces is arbitrary; but there must exist between them and the radial portions of the conductor D a certain relation, which will be understood by reference to Fig. 4, in which N N represent the projections or points on one face of the core of the field, and S S the points of the other face. The conductor D is shown in this figure in section, a a' designating the radial portions of the conductor, and b the insulating-divisions between the same. The relative width of the parts a a' and the space between any two adjacent points N N or S S is such that when the radial portions a of the conductor are passing between the opposite points N S, where the field is strongest, the intermediate radial portions a' are passing through the widest spaces midway between such points and where the field is weakest. Since the core on one side is of opposite polarity to the part facing it, all the points or projections of one polar face will be of opposite polarity to those of the other face. Hence, although the space between any two adjacent points on the same face may be extremely small, there will be no leakage of the magnetic lines between any two points of the same name; but the lines of force will pass across from one set of points to the other. The construction followed obviates to a great degree the distortion of the magnetic lines by the action of the current in the conductor D, in which it will be observed the current is flowing at any given time from the center toward the periphery in one set of radial parts a and in the opposite direction in the adjacent parts a'.
In order to connect the energizing-coil G with a source of continuous current, I have found it convenient to utilize two adjacent radial portions of the conductor D for connecting the terminals of the coil G with two binding-posts M. For this purpose the plate D is cut entirely through, as shown, and the break thus made is bridged over by a short conductor c.
At any convenient point the plate D is cut through to form two terminals d, which are connected to binding-posts N.
The core H H, when rotated by the driving-pulley P, generates in the conductors D an alternating current, which is taken off from the binding-posts N. It will be observed that from the nature of the construction described this machine is capable of producing an alternating current of an enormously high rate of alternations.
When it is desired to rotate the conductor between the faces of a stationary field-magnet, I adopt the construction shown in Fig. 3. The conductor D in this case is or may be made in substantially the same manner as above described by slotting an annular conducting-plate and supporting it between two heads O, held together by bolts o and fixed to the driving-shaft K. The inner edge of the plate or conductor D is preferably flanged to secure a firmer union between it and the heads O. It is insulated from said head. The field-magnet in this case consists of two annular parts H H, provided with annular grooves I for the reception of the coils. The flanges or faces surrounding the annular groove are brought together, while the inner flanges are serrated, as in the previous case, and form the polar faces. The two parts H H are formed with a base R, upon, which the machine rests.
S S are non-magnetic bushings secured or set in the central opening of the cores.
The conductor D is cut entirely through at one point to form terminals, from which insulated conductors T are led through the shaft to collecting-rings V.
What I claim is—
1. The combination, in an annular field of force formed by opposing polar faces with radial grooves or serrations and with said poles, of a connected series of radial conductors so disposed with relation to the serrations that while one portion of the radial conductors is passing between the strongest parts of the field, or the points where the two poles most nearly approach, the adjacent or intermediate conductors will pass through the weakest parts of the field, or the points where the two poles are most remote, as set forth.
2. The combination, with a connected series of radial conductors forming an annular coil, of a stationary two-part supporting-frame clamped to and insulated from the outer ends of said conductors, a ring formed in two parts clamped to the inner ends of the same, an energizing-coil contained in said ring, and field-core made in two parts and enclosing said energizing-coil and presenting annular polar faces to the series of radial conductors, as described.
3. The combination, with the annular conducting-plate slotted to form a connected series of radial conductors, a sectional supporting-frame secured to and insulated from the outer edge of the slotted plate, a sectional ring secured to and insulated from the inner edge of said plate, a hollow energizing-coil contained in said ring, and a field-core composed of two parts bolted together and recessed to enclose the energizing-coil, said cores being mounted in a rotating shaft, as set forth.
4. The combination, with two annular polar faces of opposite magnetic polarity and formed with opposite points, projections, or serrations, of a conductor turned back upon itself in substantially radial convolutions and mounted in the annular field, whereby a rotation of the field or said conductor will develop therein an alternating current, as set forth.
5. The combination, with a polar face of given polarity formed with grooves or serrations, of a polar face of opposite polarity with corresponding grooves or serrations, the two polar faces being placed with their grooves opposite to each other, and a conductor or coil mounted between said faces with the capability of movement across the lines of force in a direction at right angles to that of the grooves or serrations, as set forth.
6. In a magneto-electric machine, the combination of a sectional frame, a field-magnet core composed of two connected parts, a rotating shaft on which said core is mounted, a conductor in which currents are to be induced, the convolutions of which are radially disposed between the polar faces of the field-core and secured to and supported by the frame, and an energizing-coil for the field-core supported by the induced-current coil and contained in an annular recess formed by grooves in the faces of the two sections of the field-core.
7. The combination, with opposing field-magnet poles formed with projections or serrations in their faces, the highest parts or prominences of one face being opposite to those of the other, of a conductor the convolutions of which are adapted to pass at right angles through the magnetic lines between the opposing prominences, as set forth.
8. The combination, with a rotating field-magnet core having two opposing and annular polar faces with radial grooves or serrations therein systematically disposed, so that the highest parts or prominences of one face lie opposite to those of the other, of a stationary conductor with radial convolutions and mounted between the polar faces, as set forth.
NIKOLA TESLA
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Source File: US Patent 447,921 - pdf
Chapter XXIX - The Martin Book
Thomas Commerford Martin
Nikola Tesla's Alternating Current Generators for High Frequency, in Detail
The machine above described was only one of many such types constructed. It serves well for an experimental machine, but if still higher alternations are required and higher efficiency is necessary, then a machine on a plan shown in Figs. 204 to 207, is preferable. The principal advantage of this type of machine is that there is not much magnetic leakage, and that a field may be produced, varying greatly in intensity in places not much distant from each other.
In these engravings, Figs. 204 and 205 illustrate a machine in which the armature conductor and field coils are stationary, while the field magnet core revolves. Fig. 206 shows a machine embodying the same plan of construction, but having a stationary field magnet and rotary armature.
The conductor in which the currents are induced may be arranged in various ways; but Mr. Tesla prefers the following method: He employs an annular plate of copper D, and by means of a saw cuts in it radial slots from one edge nearly through to the other, beginning alternately from opposite edges. In this way a continuous zigzag conductor is formed. When the polar projections are 1/8 inch wide, the width of the conductor should not, under any circumstances, be more than 1/32 inch wide; even then the eddy effect is considerable.
To the inner edge of this plate are secured two rings of non-magnetic metal E, which are insulated from the copper conductor, but held firmly thereto by means of the bolts F. Within the rings E is then placed an annular coil G, which is the energizing coil for the field magnet. The conductor D and the parts attached thereto are supported by means of the cylindrical shell or casting A A, the two parts of which are brought together and clamped to the outer edge of the conductor D.
The core for the field magnet is built up of two circular parts H H, formed with annular grooves I, which, when the two parts are brought together, form a space for the reception of the energizing coil G. The hubs of the cores are trued off, so as to fit closely against one another, while the outer portions or flanges which form the polar faces J J, are reduced somewhat in thickness to make room for the conductor D, and are serrated on their faces. The number of serrations in the polar faces is arbitrary; but there must exist between them and the radial portions of the conductor D certain relation, which will be understood by reference to Fig. 207 in which N N represent the projections or points on one face of the core of the field, and S S the points of the other face. The conductor D is shown in this figure in section a a' designating the radial portions of the conductor, and b the insulating divisions between them. The relative width of the parts a a' and the space between any two adjacent points N N or S S is such that when the radial portions a of the conductor are passing between the opposite points N S where the field is strongest, the intermediate radial portions a' are passing through the widest spaces midway between such points and where the field is weakest. Since the core on one side is of opposite polarity to the part facing it, all the projections of one polar face will be of opposite polarity to those of the other face. Hence, although the space between any two adjacent points on the same face may be extremely small, there will be no leakage of the magnetic lines between any two points of the same name, but the lines of force will pass across from one set of points to the other. The construction followed obviates to a great degree the distortion of the magnetic lines by the action of the current in the conductor D, in which it will be observed the current is flowing at any given time from the centre toward the periphery in one set of radial parts a and in the opposite direction in the adjacent parts a'.
In order to connect the energizing coil G, Fig. 204, with a source of continuous current, Mr. Tesla utilizes two adjacent radial portions of the conductor D for connecting the terminals of the coil G with two binding posts M. For this purpose the plate D is cut entirely through, as shown, and the break thus made is bridged over by a short conductor C. The plate D is cut through to form two terminals d, which are connected to binding posts N. The core H H, when rotated by the driving pulley, generates in the conductors D an alternating current, which is taken off from the binding posts N.
When it is desired to rotate the conductor between the faces of a stationary field magnet, the construction shown in Fig. 206, is adopted. The conductor D in this case is or may be made in substantially the same manner as above described by slotting an annular conducting-plate and supporting it between two heads O, held together by bolts o and fixed to the driving-shaft K. The inner edge of the plate or conductor D is preferably flanged to secure a firmer union between it and the heads O. It is insulated from the head. The field-magnet in this case consists of two annular parts H H, provided with annular grooves I for the reception of the coils. The flanges or faces surrounding the annular groove are brought together, while the inner flanges are serrated, as in the previous case, and form the polar faces. The two parts H H are formed with a base R, upon which the machine rests. S S are non-magnetic bushings secured or set in the central opening of the cores. The conductor D is cut entirely through at one point to form terminals, from which insulated conductors T are led through the shaft to collecting-rings V.
In one type of machine of this kind constructed by Mr. Tesla, the field had 480 polar projections on each side, and from this machine it was possible to obtain 30,000 alternations per second. As the polar projections must necessarily be very narrow, very thin wires or sheets must be used to avoid the eddy current effects. Mr. Tesla has thus constructed machines with a stationary armature and rotating field, in which case also the field-coil was supported so that the revolving part consisted only of a wrought iron body devoid of any wire and also machines with a rotating armature and stationary field. The machines may be either drum or disc, but Mr. Tesla's experience shows the latter to be preferable.
In the course of a very interesting article contributed to the Electrical World in February, 1891, Mr. Tesla makes some suggestive remarks on these high frequency machines and his experiences with them, as well as with other parts of the high frequency apparatus.
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This machine was discussed by Nikola Tesla in his lecture: Experiments With Alternate Currents of Very High Frequency And Their Application To Methods of Articifical Illumination, May, 1891.
In the above referenced lecture, Tesla specifies the frequency output of this particular patented technology was 2 million cycles per minute, or 33,300 cycles per second. We call this 33 kilohertz. We can document that this equipment was used by Tesla to power the first tuned wireless transmitters.
Figure 125 is the classic Tesla iron-core wireless power transmitter circuit. The circuit diagram below Figure 125 shows how the circuit was set up and tuned, with both an adjustable capacitance and adjustable primary inductance. The abreviated circuit diagrams frequently omit the capacitor, and fail to show either the capacitance or the inductance as adjustable. In practice the capacitor was always applied, and the values of both the capacitance and primary inductance were carefully adjusted to bring the circuits into tune.
US Patents: 447,920 - 405,858 - 424,036
Figure Credit: G. Peterson, tfcbooks.com
When used as a transmitter, as shown in the circuit development diagram above, these high-frequency alternators where directly shaft driven by powerful synchronous motors driven with isochronous generators.
Related Patent
447,920
Method of Operating Arc Lamps - Oct 1, 1890
Tesla had transmitters that worked well based on 447,920 - and - 447,921, but he was extremely limited in the power levels that could be developed with iron-shaft generators outputting between 3000 and 30,000 cycles per second. These generators had good wave forms for transmission purposes, but you could not scale them up economically without industrial support... What Tesla designed and patented was at the edge of the practical engineering limits of the time, and that is a small machine limited to about 10-25 kilowatts maximum output. If you want more output with this technology you would have to test and improve the material science and construction techniques, and then mass produce many component assemblies, like armature disks, and then synchronize them on a common shaft... It's an engineering nightmare.
By 1893 Tesla had given up development of high-frequency shaft-driven alternators for wireless transmission. He began a parallel research path into electrical oscillators, capacitive discharge power processing. The first path of development was into small desktop oscillators that operated at very low frequency, and served as working models of a global transmitter. The second development path was into the circuit controllers and the capacitors required to scale up the desktop models to a powerful high-voltage machine of many horsepower for a global transmitter.
Beginning in 1904, years after Tesla had gone with Harmonic oscillator technology, General Electric provided industrial support to electrical engineers like Ernst F. W. Alexanderson, who was influenced by the alternating current theories and mathematics of Charles Steinmetz, and whose work was actively promoted by Reginald Fessenden. Alexanderson, with General Electric industrial support, the nod by Steinmetz, and the promotion of Fessenden, developed high frequency motor driven alternators in the 50-60 kilowatt range which were used for transatlantic "long wave" wireless communications. These units took years to develop through trial and error, required material science improvements, and long hard thought into the construction techniques required. The end result were massive machines standing about 4-1/2 feet tall on the cast iron equipment mounts, about 12 feet long with the drive motor and gear box, and supported with pressurized cooling and lubrication systems. A progression of machines were built and installed at New Brunswick, NJ, and the transmitter there, operated by the U.S. Navy, broadcast reliably with up to 200 kilowatts output in 1918.
To the Archive Page Discussion on Tesla's Technology
Lab-Tesla disclosures on the technology just presented
Tesla's Cymatic Research
Steam Powered Isochronous Acoustic Oscillators & Generators
Tesla Transmitters
Wireless Transmission of Electrical Energy
Self-Exciting Dynamos and Alternators
Rectification, Energy Conversion
ROTATIONAL RECEPTION OF ISOCHRONOUS WAVES
Angular Displacement Receivers
EXPERIMENTS WITH ALTERNATE CURRENTS OF VERY HIGH FREQUENCY AND THEIR APPLICATION TO METHODS OF ARTIFICIAL ILLUMINATION
Lecture by N. Tesla before the American Institute of Electrical Engineers at Columbia College, N.Y., May 20, 1891
TESLA'S ALTERNATING GENERATORS FOR HIGH FREQUENCY
The Electrical Engineer, March 18, 1881; pp 338-340
The True Wireless
Electrical Experimenter, May, 1919
PHENOMENA OF ALTERNATING CURRENTS OF VERY HIGH FREQUENCY
Electrical World, Feb 21, 1891
THE TESLA EFFECTS WITH HIGH FREQUENCY AND HIGH POTENTIAL CURRENTS
