US2793325A - High voltage rectifier - Google Patents

Description

May 21, 1957 R. H. WENZEL HIGH VOLTAGE RECTIFIER Filed Jan. 28, 1954 XNVENTOR ROBERT H. WENZEL ATTO RN EYS United States Patent HlGH VOLTAGE RECTIFIER Robert H. Wenzel, Temple City, Calif., assignor of twentyfive percent to Paul M. Rogers, Newport Beach, Calif.

Application January 28, 1954, Serial No. 406,696 9 Claims. (Cl. 315-246) This invention relates to high voltage rectifiers, and is particularly directed to the provision of an improved high voltage vacuum tube rectifier capable of withstanding exceptionally high inverse voltages, while at the same time having a high conductance in the forward direction. Thenew high voltage rectifier is characterized by the incorporation of a rotatable anode by which, in normal operation of the rectifier, the electron path length from cathode to anode is alternately increased and decreased with each change from the conducting to the nonconducting half of the cycle and back again.

The new high voltage rectifier of this invention comprises an evacuated envelope in which is mounted an electron-emissive cathode. An anode shaft also is mounted in the evacuated envelope for rotation therein, and it carries an anode which is so disposed as to be moved by rotation of the shaft alternately into close proximity with and widely spaced separation from the cathode. Means are provided for impressing a high alternating voltage between the cathode and anode, and a motor or equivalent means is provided for rotating the anode shaft in synchronism with the alternations of the anode to cathode voltage, so that the anode is brought into close proximity with the cathode during the conducting half cycle, and is brought into widely spaced separation from the cathode during the nonconducting half cycle. Owing to the long length of the electron path which is thereby established during the nonconducting half of each cycle, it is possible for the new rectifier to withstand extremely high peak inverse voltagesvoltages in the hundreds of kilovolts or even of the order of megavolts. 0n the other hand, during the conducting portion of the cycle, when rotation of the anode has reduced the length of the electron path between cathode and anode to a small fraction of the length prevailing during the nonconducting portion of the cycle, the rectifier is capable of passing, with little loss, a high current and a correspondingly large amount of power. 7 Advantageously, in some cases, acontrol grid is interposed in the electron path between the cathode and the anode of the new rectifier. The control grid may be used with advantage to limit the duration of the conducting portion of the cycle to less than the full half cycle during which the anode is positive with respect to the cathode; and it is of course of value when the new rectifier is employed in an inverter circuit.

structurally the anode of the new rectifier, which is rotatably mounted in the evacuated envelope,-has a current-receiving face disposed --eccentrically with respect to the axis of anode rotation, thus being rotatable in an orbit about such axis. The cathode then is mounted in close proximity to, but slightly beyond, the orbit of rotation of said current-receiving face. The sum of the angles subtended from the axis of anode rotation by the cathode and the current-receiving face of the anode is substantially less than 360, so that the-length of tl 1e electron path from cathode toanode is alternately increased and decreased as the anode face rotates in its orbit. The current-receiving face of the anode is preferably curved convexly and has a long dimension which extends substantially parallel to the axis of anode rotation; and the cathode is advantageously curved concavely toward such axis. It is desirable that each of these curved elements subtend an angle from the axis of anode rotation that is substantially less than so that the electron path length from cathode to anode is .increased substantially, from its minimum value, as the cathode polarity relative to the anode changes from negative to positive.

The foregoing and other features of the new rectifier are described below with reference to the accompanying drawings, in which Fig. 1 is a perspective, partially in section, of an advantageous embodiment of the new rectifier;

Fig. 2 is a cross section taken substantially along the line 2-2 of Fig. 1;

Fig. 3 is a perspective, partly in cross section, of a modified form of rectifier according to the invention; and

Fig. 4 is a section taken substantially along the line 4 i of Fig. 3, but with the anode rotated approximately 180 from the position shown in Fig. 3.

The apparatus shown in Figs. 1 and 2 is of the high vacuum grid controlled rectifier tube type. It comprises an envelope 10 of glass or other suitable material, which is highly evacuated. The upper end of the envelope 10 is constricted to form a relatively narrow neck 11, and of lower end likewise is constricted to form a stem 12 of reduced diameter. A bearing assembly 13 capable of operation in high vacuum is mounted in the neck 11, and a similar bearing assembly 14 is mounted in axial alignment therewith in the lower portion of the stem 12.

An anode shaft comprising an upper section 15 and an axially aligned lower section 16 is mounted in the bearings 13 and 14 for rotation therein within the evacuated envelope 10. The anode shaft carries an anode structure 17 which geometrically is generally in the form of a rectangular hexahedron having itscorners and edges all smoothly rounded. As shown in Fig. 2, the anode body in a (horizontal) cross-sectional plane is of considerably greater length than width. The width in fact is not substantially greater than the diameter of the shaft 15, 16, but the length is preferably a considerable number of times greater than the shaft diameter. The anode is attached to the shaft so that the shaft extends in a (vertical) direction normal to the relatively long and narrow cross-sectional plane above referred to. In its third dimension (height), extending in a direction parallel to the axis of the anode shaft, the anode body advantageously is fairly high relative to its width. It may in fact be as high as or higher than it is long, although it is shown in Fig. 1 as being a little less high than long.

The anode body 17 is advantageously a metallic structure throughout, but in any event its end edge surfaces 18 which extend parallel to the shaft axis in eccentric relation therewith are metallic, for these surfaces constitute the current-receiving faces of the anode. The upper shaft section 15 likewise is metallic and is electrically connected to the anode current-receiving faces 18. The upper shaft section 15 is of course in electrical contact with the upper bearing structure 13, and this hearing structure is in turn electrically connected to a leadin conductor 19 which is sealed in the neck 11 of the envelope 10 and is in turn connected to an external cap terminal 20.

The lower shaft section 16 where it extends into the upper portion of the envelope stem 12 carries a rotor element 21 of a synchronous motor. The wound stator element 22 of the motor surrounds the rotor element 21 outside the stem 12. When the windings of the stator 22 are energized, the rotor 21 spins at a speed determined 3 by the frequency of the energizing current, and causes the anode shaft and the anode structure carried thereby to rotate within the evacuated envelope 10.

The cathode structure comprises a series of cathode elements 24 mounted in ceramic end blocks 25. Each cathode element 24 advantageously comprises a porous shell of tungsten, molybdenum or equivalent metal of high melting temperature which encloses a charge of barium or strontium oxide or equivalent material of pronounced thermionic emission properties. Suitable cathode elements (designated L cathodes) are described in Philips Technical Review, vol. II (June 1950) pp. 341 350. The several elements 24 which make up the complete cathode assembly are electrically connected together by a lead wire 26 which is sealed into the wall of the envelope and is connected to an external cathode terminal 27. Preferably, the cathode structure is curved concavely toward the axis of rotation of the anode shaft; and the cathode is positioned just a short distance beyond the orbit of rotation of the current-receiving faces 18 of the anode itself. The cathode is of course arranged parallel to the axis of anode rotation, and its height is advantageously about equal to or slightly greater than the height of the anode faces 18.

The particular form of cathode employed in the new rectifier is not in itself critical. A cathode of the character above described, using one or more L cathode elements, is advantageous for its ability to carry extremely high momentary current densities without becoming seriously damaged thereby. However, other cathode structures can be employed if desired.

The cathode structure shown in the drawing is of the indirectly heated type. It is heated to its thermionic emis sion temperautre by a more or less conventional heater winding 28, supported on lead wires 2d which are sealed into the wall of the envelope l0 and are connected to external heater terminals 30. Heat shields (not shown) of nickel or other metal may be disposed back of the cathode to minimize heat losses therefrom, as is conventional in the art.

The rectifier shown in Fig. 1 is provided with a control grid 31 which is mechanically supported by wires 32 at tached to the ceramic cathode end frames 25. The grid is preferably curved correspondingly to the cathode and is interposed, in close proximity to the cathode, in the electron path between the cathode and the anode. The grid is electrically connected to a grid lead wire 33 which is sealed into the wall of the envelope 1t and is connected externally to a grid terminal 34.

An elementary half-wave rectifier circuit is shown in Fig. l in conjunction with the above-described apparatus, to illustrate operation of the rectifier. One side of a high voltage single-phase power line 35 is connected to the cathode terminal 27 of the rectifier tube, and the other side of the power line is connected through a high voltage D. C. load L to the anode terminal 20. The windings of the synchronous motor stator 22 are also connected to the power line 35, through a transformer 36, thereby assuring rotation of the anode structure 17 in synchronisrn with the alternations of the voltage impressed between anode and cathode of the rectifier tube. The motor stator 22 is angularly positioned on the stem 12 of the tube, so that when the cathode is at its maximum negative voltage with respect to the anode, one of the anode current-receiving faces 18 is positioned in geometrically centered relation with respect to the cathode structure and is in its position of closest proximity thereto, as shown by the solid lines in Fig. 2. At this instant, a high current flow takes place from cathode to anode, and because of the close proximity of these electrodes, the conductance of the tube is at its maximum.

. The motor stator 22 is designed to rotate the anode shaft one-half revolution per cycle, and accordingly a half cycle following the moment of maximum conductance, when the'cathode has come to its highest positive potential with respect to the anode, the anode has been rotated to the position (shown by dotted lines in Fig. 2) where the electron path from cathode to anode is of maximum length. With the anode in this position, the rectifier is capable of withstanding a very high peak inverse voltage. It will be noted (as indicated in Fig. 2) that the angle a subtended by each current-receiving face of the anode, and the angle b subtended by the cathode, each from the axis of rotation of the anode shaft, is each substantially less than and in fact (in the tube of Figs. 1 and 2, wherein the anode has two current-receiving faces disposed 180 apart) the sum of these angles is less than lSO". Thus the electron path length from anode to cathode is elfectively increased by a substantial amount as the anode rotates from the position shown in full lines to the position shown in dotted lines in Fig. 2.

The smoothly rounded corners and edges of the anode body 17 are formed to minimize regions of inordinately high electrical stress in the electron path adjacent the anode, thereby to increase the ability of the rectifier to withstand breakdown due to field-induced emission of electrons from the anode under very high inverse voltages, and also to avoid small areas when damagingly high current densities may develop on the anode during the conducting portions of each cycle.

It is apparent from the foregoing that during the conducting half of each cycle of operation of the rectifier, while current is passing from anode to cathode, the length of the electron path therebetween is at a minimum, and the conductance of the tube is at its maximum. Conversely, during the nonconducting half-cycle, the length of the electron path from anode to cathode is maximum, and the voltage gradient in the field between anode and cathode is at its minimum, so that under these conditions the tube is capable of resisting breakdown even though the numerical value of the voltage from anode to cathode may be very large.

In the elementary circuit shown in Fig. l, a negative biasing voltage is applied to the grid 31;, relative to the cathode, by a biasing battery 37. The biasing voltage may be selected so that the conducting portion of the half cycle during which the cathode is negative with respect to the anodeis reduced to substantially less than 180 electrical degrees. A control of this character is of particular value when a number of rectifier tubes are connected together in a multiphase rectifying circuit. The grid, moreover, is a particularly advantageous element for incorporation in the rectifier assembly when the tube is to be employed in a rectifier type of inverter circuit.

Although only an elementary half-wave single-phase rectifier circuit is protrayed in Fig. 1, it is understood that the new rectifier can be incorporated in all types of fullwave and polyphase rectifier circuits, and inverter circuits, in the same manner as high vacuum rectifier tubes with conventional fixed anode-to-cathode spacing.

A rectifier having a modified form of anode structure is shown in Fig. 3. This rectifier, like that shown in Fig. 1, comprises an evacuated envelope 40 of glass or other material, which is formed with a neck 41 of reduced diameter, and a stem 42, also of reduced diameter. Bearings 43 and 44 suitable for high vacuum operation are mounted in axial alignment in the neck 41 and in the lower portion of the stem 42, and an anode shaft indicated generally at 45 extends between these bearings and is rotatably supported thereby.

The anode shaft carries a pair of spaced collars 46. Attached to these collars, and spanning between them, is an anode 47 which bows outwardly from the shaft 45 and is formed with a current-receiving face 48 positioned eccentrically with respect to the axis of the shaft 45. When the shaft 45 is rotated, the anode face 43 is caused thereby to rotate in an orbit about the axis of the shaft. The collars 46 carry, balancing weights 49, to counterbalance the anode 47 and form a dynamically balanced rotatable assembly.

The upper end 50 of the shaft 45 is metallic and is electrically connected to the anode 47. It is of course in electrical contact with the bearing 43, and this latter in turn is electrically connected to a lead-in 51 sealed into the upper end of the envelope 40. An anode terminal 52 is electrically connected to the lead-in 51 externally of the envelope.

The central section 53 and lower section 54 of the anode shaft 45 are of electrically nonconducting material such as glass. The lower section 54 carries a synchronous motor rotor 55, which is positioned interiorly of the upper end portion of the envelope stem 42. A wound synchronous motor stator 56 surrounds the rotor 55, outside the envelope stem 42; and the rotor is caused to rotate when the stator windings are energized by connecting the motor lead wires 57 to a suitable A. C. power source.

The cathode structure of the rectifier shown in Figs. 3 and 4 is the same as described above in connection with Fig. 1. It comprises L cathode elements 58 supported in ceramic or other nonconducting end frames 59. The cathode elements 58 are all electrically connected together and to an external cathode element 60 by means of a lead wire 61 which is sealed into the wall of the envelope 40 and which thereby provides mechanical support for the cathode structure. A cathode heater winding 62 is provided to heat the cathode to its electron emission temperature, and is connected to and supported by lead wires 63 which are sealed into the wall of the envelope 40 and are connected to external heater terminals 64. Heat shields (not shown) may be provided if desired.

No grid is shown in the form of tube portrayed in Figs. 3 and 4. However, a grid could be as well provided in a tube of the design here shown, as in the design shown in Figs. 1 and 2. It is of course apparent that the inclusion of a grid in a rectifier of the character provided by this invention is optional. The rectifier shown in Figs. 3 and 4 operates in essentially the same manner as described above in connection with the form of rectifier shown in Figs. 1 and 2. One major difference in the design of these two types is that the motor 55, 56, by which the anode shaft 45 is rotated in a tube of the design shown in Fig. 3, must serve to rotate the anode shaft one full revolution per cycle, rather than only one-half revolution per cycle. This follows from the fact that in the geometry of the tube shown in Fig. 3, maximum separation of the anode from the cathode requires rotation of the anode shaft through a full 180 from the position in which the anode-to-cathode spacing is at a minimum.

An advantage of the structure shown in Fig. 3 is that a large difference between maximum and minimtun anode-to-cathode spacings, and thus a large change in the length of the electron path between anode and cathode, can be achieved in a tube of physically more compact form than with the tube design shown in Fig. 1. On the other hand, the design shown in Fig. 3 suffers from the disadvantages that dynamic balancing of the rotating anode assembly is more difiicult than with the symmetrical anode and anode shaft assembly shown in Fig. 1. A further disadvantage of the design shown in Fig. 3, relative to that shown in Fig. 1, is that it is much more difficult to configure the anode face 47 and other metallic parts of the anode structure to minimize sharp corners or short radii of curvature and the accompanying high electrical field stresses which encourage field-induced emission of electrons from the anode when a high inverse voltage is impressed between anode and cathode. In spite of these disadvantages, the advantage of compactness to which the design of Figs. 3 and 4 lends itself can be of considerable value, especially for tubes that are intended to operate only at moderately high peak inverse voltages (e. g. 100 or 200 kilovolts).

The ability of the rectifier herein described to operate successfully under conditions of extremely high voltage, and to pass high currents with minimum conductance loss, makes iteminently suitable for rectifying very high voltage A. C. power for purposes of long distance'transmission on D. C. transmission lines. The new rectifier, when provided with a control grid, can be incorporated in inverter circuits at the receiving end of the D. C. transmission line, to produce high voltage alternating current for transformation to lower voltages and for use by A. C. power consuming equipment. In addition to such use of the new rectifier in the power transmission field, it is of course apparent that it can also be used with ad vantage for other high voltage rectification and inverter purposes.

While the invention has been described herein with particular reference to a structure in which the cathode is fixed in relation to the envelope and the anode is mounted on a shaft for rotation in the envelope, it is of course feasible to reverse these parts, making the cathode the rotatable electrode and making the anode the fixed electrode. The appended claims must therefore be construed with the understanding that a device having a rotatable cathode and a fixed anode is the full equivalent, for purposes of this invention, of a device having a rotatable anode and a fixed cathode. An advantage of mounting the anode in fixed relation to the envelope is that in very high-power rectifiers it then becomes a relatively simple matter to provide water-cooling or other forced cooling for the anode, by coolant pipes or tubes extending through the envelope to a hollow anode structure. A disadvantage is that more than one electrical connection generally must be made to the rotating cathode structure, to provide both for heating and for the cathode lead. However, provision for such electrical connections can be made, at some expense for making a more complex structure, and the disadvantage of doing so can be more than offset by the advantage of forced anode cooling in large and high-power rectifiers according to this invention.

I claim:

1. A high voltage rectifier comprising an evacuated envelope, a plate-like, electron-emissive cathode mounted in said envelope, an anode shaft mounted in said envelope for rotation, said anode shaft being substantially parallel to the median surface of said cathode, an anode mounted on said shaft in position to be moved by rotation thereof alternately into close proximity with and widely spaced separation from said cathode, means for impressing a high alternating voltage between said cathode and said anode, means coupled to said anode shaft for rotating it in synchronism with the alternations of said impressed voltage to alternately bring the anode into close proximity with the cathode when the cathode is negative with respect to the anode, and into widely spaced separation from the cathode when the cathode is positive with respect to the anode, and means for taking off a rectified voltage from the anode.

2. A high voltage rectifier comprising an evacuated envelope, a plate-like, electron-emissive cathode mounted in said envelope, an anode shaft rotatably mounted in said envelope, said anode shaft being substantially parallel to the median surface of said cathode, an anode mounted on said shaft in position to be moved by rotation thereof alternately into close proximity with and widely spaced separation from said cathode, a control grid interposed in the electron path between the cathode and the anode, means for impressing a high alternating voltage between said cathode and said anode, means coupled to said anode shaft for rotating it in synchronism with the alternations of said impressed voltage, to alternately bring the anode into close proximity with the cathode when the cathode is negative with respect to the anode, and into widely spaced separation from the cathode when the cathode is positive with respect to the anode, and means for taking off a rectified voltage from the anode.

3. A high voltage rectifier comprising an evacuated envelope, an anode shaft rotatably mounted in said envelope, an anode mounted on said shaft for rotation therewith, said anode having a current-receiving face substantially parallel to the axis of said shaft and disposed laterally a substantial distance therefrom, an elect'ron-emissive cathode mounted in said envelope substantially parallel to said anode shaft, said cathode being substantially parallel to the current-receiving anode face and being positioned slightly farther from the axis of the anode shaft than said face, said anode face and said cathode each subtending an angle substantially less than 180 from the axis of the anode shaft, means coupled to the anode shaft for rotating it to alternately increase and decrease the length of the electron path from cathode to anode, and means for taking off a rectified voltage from the anode.

4. A high voltage rectifier comprising an evacuated envelope, an anode rotatably mounted in said envelope, said anode having a current-receiving face disposed eccentrically with respect to the axis of anode rotation and thereby being rotatable in an orbit about said axis, a plate-like, electron-emissive cathode mounted substantially parallel to said anode shaft in said envelope in close proximity to but slightly outside the orbit of rotation of said anode face, the sum of the angles subtended by said cathode and said anode face from the axis of anode rotation being substantially less than 360, means coupled to said anode shaft for rotating it to alternately increase and decrease the length of the electron path from cathode to anode.

5. A high voltage rectifier comprising an evacuated envelope, an anode rotatably mounted in said envelope, said anode having a convexly curved current-receiving face extending substantially parallel to the axis of anode rotation, said convexly curved anode face being disposed eccentrically with respect to the axis of anode rotation and thereby being rotatable in an orbit about said axis, an electron-emissive cathode mounted in said envelope in close proximity to but slightly beyond the orbit of rotation of said anode face, means for impressing a high alternating voltage between said cathode and anode, and means coupled to said anode shaft for rotating it, said cathode being curved concavely toward said orbit and extending substantially parallel to the axis of anode rotation, said anode face and said cathode each subtending an angle substantially less than 180 from the axis of anode rotation, whereby the length of the electron path from cathode. to anode is alternately increased and decreased as the anode face rotates in its orbit, and means for taking off a rectified voltage from the anode.

6. A high voltage rectifier according to claim 4, in

which a control grid is interposed in the electron path between the cathode and the anode.

7. A high. voltage rectifier having, an evacuated envelope, an anode comprising a body which in. a crosssectional plane is of considerably greater length than width, and an anode shaft secured to said anode and extending in a direction normal to said cross-sectional plane, said anode being geometrically symmetrical, with respect to and dynamically balanced about the axis of said shaft, and means coupled to said anode, shaft for rotating said shaft with the anode thereon within said envelope.

8. A high voltage rectifier comprising, an evacuated envelope, a spaced pair of bearings positioned in said envelope, an anode shaft having its ends rotatably mounted in said bearings and extending therebetween, and an anode mounted on said shaft and having a current-receiving face disposed eccentrically with respect to the shaft between the bearings, one end portion of said shaft being metallic and being electrically connected to the current-receiving face of the anode, and the other end portion of said shaft being of electrically insulating material.

9. A high voltage rectifier comprising an'evacuated envelope, at least two electrodes comprising respectively an anode and an electron-emissive cathode mounted in said envelope, a shaft mounted for rotation in said envelope, one of said electrodes being plate-like, the shaft being substantially parallel to the median surface of said plate-like electrode, one of said electrodes being mounted in fixed relation to said envelope and the other of said electrodes being mounted on said shaft in position to be moved by rotation thereof alternately into close proximity with and widely spaced separation from said fixed electrode, means for impressing a high alternating voltage between said electrodes, means coupled to said shaft for rotating it in synchronism with the alternations of said impressed voltage, whereby the electrodes are brought into close proximity with each other when the cathode is negative with respect to the anode, and are brought into widely spaced separation from each other when the cathode is positive with respect to the anode, and means for taking off a rectified voltage from the anode.

References Cited in the file of this patent UNITED STATES PATENTS 798,954 Francis Sept. 5, 1905 943,969 De Forest Dec. 21, 1909 1,192,706 Thomson July 25, 1916 2,078,672 Knowles Apr. 27, 1937 2,225,032 Carbonara Dec. 17, 1940 2,315,176 Zacharia Mar. 30, 1943 2,467,243 Tillman Apr. 12, 1949

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