US2433181A - Ignitron - Google Patents

Description

J. E. WHITE Dec. 23, 1947.

IGNITRON Filed May 16, 1945 ATTORNEY Patented Dec. 23, 1947 IGNITRON John E. White, Bloomfield, N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a. corporation of Pennsylvania.

Application May 16, 1945, Serial No. 594,015

8 Claims. 1

This invention relates to ignitrons and has particular reference to conductors forming part of the ignltron entity.

Any current-carrying conductor has present, in addition to the current, a magnetic ux, whose intensity is proportional to the current. In the case of alternating current, the flux induces currents known as eddy currents in any conductor through which it passes. A heavy conductor carrying alternating current has induced in it voltages tending to produce eddy currents; the net result of this is to drive the circuit current to the surface of the conductor. Thus, a heavy conductor carrying alternating current, carries the current only in a. layer near the surface; this effect is called the skin effect. In this way, the effective resistance of a heavy conductor to A. C. is greater than to D. C. The depth of penetration of current into the surface of a large conductor can be shown mathematically to be inversely proportional to the square root of the product of frequency and ux density. Since carbon-steel and like magnetic materials may have a flux density about 2000 times as great as copper while carrying the same current, it is seen that the current in a heavy conductor may only penetrate about 1/40 as deep in a carbon-steel conductor as in a nonmagnetic conductor of otherwise simfiar characteristics. The non-magnetic materials most used for electrical conductors are copper and aluminum. In a practical example where a solid carbon-steel rod 11/2 inches in diameter is used as current conductor in an ignitron, all the current is carried in a layer 11g inch thick on the outside of the rod, while the effective resistance to A. C. is nearly twenty times as great as to D. C.

Accordingly, the practice has been followed in the art of providing copper or other non-magnetic material for the heavy-current conductors for alternating current in electrical equipment. In certain electronic tubes, however, especially ignitrons, it is desirable to make the major current-carrying conductor and certain other current-carrying parts of steel. This is because copper and other non-magnetic materials unfortunately have certain disadvantages; for instance, most are attacked by mercury, some are too weak mechanically; others are gassy or some too resistive to current flow, and so on. Stainless steel, a border-line material between magnetic and non-magnetic, but here classed as non-magnetic, introduces the disadvantages of expense and difculty of brazing. The advantages of ordinary or carbon-steel make it more desirable for use in ignitrons, and such desirability would be vastly increased if the draw-back of eddy currents were not present.

The primary object of the present invention is to overcome the objectionable characteristic of carbon-steel and enhance its use in ignitrons and the like.

A further object of the invention is to permit successful employment of carbon steel conductors.

and conductive parts in electronic devices having heavy alternating current flow.

Another object of the invention is to Substantially minimize eddy currents and skin effect losses in devices of the character indicated.

Still further objects of the invention will appear to those skilled in the art to which the lnvention appertains as the description progresses, both by direct recitation thereof and by implication from the context.

Referring to the accompanying drawing in which like numerals of reference indicate similar parts throughout the several views:

Figure 1 is a vertical section of an ignitron embodying the invention;

Figure 2 is a cross-section of the anode conductor on line II-II of Fig. 1:

Figure 3 is a similar cross-section of a conductor of modified construction;

Figure 4 is an underneath or lower end view of the device of Fig. 1;

Figure 5 is a cross-section of a part of the header on line V-V of Fig. 4; and

Figure 6 is a similar section view of a modified form header.

In the specific embodiment of the invention illustrated in said drawing, the reference numeral I0 designates the cylindrical metal body of an ignitron as the electronic device selected for disclosure purposes. Headers II, I2 close the top and bottom ends respectively of the body I0. said headers being cup shaped With the rim thereof welded vacuumtight to the margin ofthe body. The top header has a central hole therein with an upturned annular flange I3 thereat to which is sealed vacuumtight, a ring I 4 as an extension of the ange and to the upper edge of ring is sealed a glass or other dielectric collar I5 also extending axially upward and sealed at its upper margin to the lower margin of an inverted metallic cup I6 the end wall of which is centrally perforate to receive a coupling nipple I 1 therethrough. Said nipple provides a peripheral flange I8 engaging against and vacuum sealed to the end Wall of the cup and is screw threaded above and below the flange. The threads on thev nipple above the flange receive the hub portion a socket, to receive the end of the lead-in cable 2|. The periphery of the lower portion of the conductor is shown screw threaded as a means for attachment and support thereon of a carbon or other coaxial anode 22.

Heretofore, anode conductor 20 has been a solid metallic rod which, and both in the present showing and in the prior art, is required to conduct heavy alternating current electrical power. Use of non-magnetic material, such as copper, has been preferred in the prior art for this anode conductor 20, in view of the fact that skin effect losses in steel are very high; but steel conductors have been used'in many cases, despite the high losses, because of the attack of mercury on copper. The present invention reduces the skin-effect losses, and thus makes use of carbon steel more advantageous.

In the showing or Figures 1 and 2, the anode conductor is shown as a hollow tube threaded internally at its upper end to attach to the threads of the nipple and threaded on its outer periphery next its lower end for mounting the anode. Said conductor is preferably split longitudinally for its entire length, as by slit 23 thereby establishing a discontinuity to rotationally inclined magnetic flux. By virtue of this discontinuity, current can now flow in both the outer and inner surface layers of the conductor, thus substantially doubling the conducting surface area, reducing the A. C. resistance by a factor of 2, approximately, and reducing power losses also to half their previous value. Additional splits of the same type would still further reduce the A. C. resistance of this conductor.

It is deemed within the scope of the present invention to provide a conductor presenting circular discontinuity attained otherwise than by a, hollow and split tube. For instance, as shown in Figure 3, the conductor may be composed of a plurality of longitudinal and parallel laminations 24 of carbon steel or other magnetic material. These laminations preferably extend the full length of the conductor and present circular discontinuity equivalent to the split of the previously described construction. The discontinuity is obtained by spacing the laminations apart, as indicated at 25, as a prevemative to eddy current; the unfilled spacing serves adequately and effectively for the purpose. However, to provide a more solid structure and one which will make good screw-thread mounting from the nipple and for the anode, a solid material having a. radically different permeability than the laminations, and acting toward the eddy currents as a dielectric 26, such as graphite, lava, Micalex and the like, may be interposed between the laminations. This laminated construction is more effective than a single split, and can be made to give an A. C. resistance practically as low as the D. C. resistance. Approach to this desideratum is accomplished by increasing the number cf laminations and thereby increasing the eective current-carrying surface and decreasing the ineffective body of the conductor included within the surfaces. More technically expressed. the ob- `iective is attained by 'an increase of area active in skin eect.

Usual construction of ignitrons utilizes. the bci;-

tom header I2 as a support for the mercury pool 2B which constitutes the cathode. The said header therefore is subject to heavy alternating current and to eddy current losses. The invention is likewise applicable to the header, which is also in the category of an electrode conductor. The header is preferably made from carbon steel or other magnetic material,` and in this invention as shown best in Figures 4 and 5, has a plurality of approximately pie-shaped metallic trays 21 also of carbon steel or other magnetic material each with a peripheral rim or flange. Adjacent flanges of contiguous trays are parallel and separated by air or other material having radically different permeability than the magnetic material of the trays. The trays are similarly separated from the overlying header by material having radically different permeability than the magnetic material of the trays and header. It may be here noted that this difference in permeability of the interposed material, which may be a dielectric, but preferably is a non-magnetic solder or brazing material such as copper or silver, sets up the discontinuity necessary and desirable in accordance with the present invention for interrupting the eddy current path and thereby preventing eddy current flow and increasing the effective current-carrying surface or skin. Therefore, while these trays give mechanical support for the headers, they present the desired discontinuity from one tray to the next and to the header by virtue of the radical difference in permeability of the interposed material and thus offer the desired interference to generation of eddy currents, minimize the adverse influence of skin effect, and minimize eddy current loss in the headers.

In Figure 6 the discontinuity for header supports is shown accomplished by a relatively thick carbon steel or other magnetic material plate 28 beneath the header i2, said plate having radial or otherwise located grooves 29 in the under side adequately deep to constitute a discontinuity and interrupt the flux lines, increase the effective current-carrying surface and thereby minimizing eddy current loss.

A carbon steel or other magnetic material leadin connection may be made to the header l2 supporting the cathode pool. As shown, the lead connection comprises a plurality of parallel plates 30, of such material. shown spaced with a gap 3l therebetween so as to be separated by air or other dielectric or material of radically different permeability than the plates, said plates being each welded or otherwise secured at one edge to the under face of the header. The laminated construction thus obtained increases the surface area or skin for the lead-in connection, reduces the eddy current losses which would otherwise be instigated in the magnetic material resultant from passage of heavy alternating current therethrough, and thus permits use of that material to gain the advantages offered thereby without suffering from its detrimental characteristic.

I claim:

1. An electrode electrical connection comprising a body conductive of high power electrical current longitudinally thereof, said body comprising a magnetic material thereby susceptible to high flux intensity productive of eddy current losses, said body having a transverse and longitudinal discontinuity interrupting circumferential paths sought by magnetic flux,

2. An electrode electrical connection comprising a body conductive of high power electrical current longitudinally thereof, said body comprising carbon steel and thereby susceptible to high ilux intensity productive of eddy current losses, said body having a transverse and longitudinal discontinuity interrupting circumferential paths sought by magnetic ilux.

3. An electrode electrical connection comprising an electrically uniiied longitudinal body conductive of high power alternating electrical current through the body in its longitudinal direction, said body comprising a magnetic material rendering said body highly susceptible to magnetic flux in a path transverse to the alternating current flow, and said body in its electrically uniiled length providing a discontinuity in the path sought by the magnetic ilux.

4. An electrode electrical connection comprislng a body conductive of high power alternating electrical current through the body in one direction, said body comprising a magnetic material rendering said body highly susceptible to magnetic flux in a path transverse to the alternating current ilow, and said body having means of radically different permeability therefrom extending in a direction parallel to the said direction of flow of the alternating current thereby interposing a discontinuity in the path of ilow sought by the magnetic flux.

5. An electrode electrical connection comprising a substantially cylindrical hollow body conductive of high power alternating electrical current through the body longitudinally thereof, said body comprising a lmagnetic material rendering said body highly susceptible to magnetic flux in a circular path transverse to the alternating current flow, and said body having a longitudinal slot from the hollow interior to the exterior thereof parallel to the said direction of flow of the alternating current thereby interposing a discontinuity in the circular path of ow sought by the magnetic ilux Ifor substantially reducing eddy current flow and skin effect loss in said body.

6. An electrode electrical connection comprislng a. cylindrical body consisting of a plurality of longitudinal laminations of magnetic material juxtaposed faces whereof are spaced from each other to present a .transverse discontinuity flux. and said laminations having material in the spaces therebetween o! radically different permeability than the material of said laminations.

7. An electrode electrical connection comprising a header of magnetic material and a plurality of plates secured each along an edge thereof to a face of said header and projecting perpendicularly therefrom, said plates likewise comprising magnetic material, and said plates being spaced apart and presenting a discontinuity to circulation of flux across the space and peripherally 'of the group of the several plates.

8. An electrode electrical connection comprising a header of magnetic material and a plurality of inverted tray-like members flatwise contiguous thereto and edgewise contiguous to each other, said members being likewise of magnetic material and separated from each other and from the header by material having a radically different permeability from the magnetic materials of said header and members and thereby presenting a discontinuity to circulation of magnetic flux.

JOHN E. WHITE.4

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,251,631 Mayer Aug. 5, 1941 2,093,711 Dallenbach Sept. 21, 1937 1,900,600 Emanueli Mar. 7, 1933 1,088,902 Hunter Mar. 3, 1914 FOREIGN PATENTS Number Country Date 249,576 Italy July 30, 1928 640,818 France Apr. 3, 1928 708,162 France Apr. 27, 1931 243,378 Great Britain Apr, 15, 1926 22,923 Great Britain Dec. 13, 1892 435,536 Germany Oct. 18, 1926 182,381 Germany e Feb. 4, 1907

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