US3377576A - Gallium-wetted movable electrode switch - Google Patents

Description

April 1968 E. LANGBERG ETAL 3,377,576

GALLIUM-WETTED MOVABLE ELECTRODE SWITCH 2 Sheets-Sheet 1 Filed May 5, 1965 A ril 9, 1968 E. LANGBERG ETAL GALLIUM'WETTED MOVABLE ELECTRODE SWITCH 2 Sheets-Sheet 2 Filed May 3, 1965 United States Patent Ofiice 3,377,576 GALLIUM-WETTED MOVABLE ELECTRODE SWITCH Edwin Langberg, Lexington, and Louis W. Roberts, Boston, Mass, assignors to Metcom, Inc., Salem, Mass, a corporation of Delaware Filed May 3, 1965, Ser. No. 452,811 6 Claims. (Cl. 335-496) This invention pertains to electrical switching devices; more particularly, it pertains to large power capacity switches which embody arc suppressing features.

Switches in high voltage large current capacity service are subject to arcing between the open switch electrodes. Such arcing phenomenon itself causes undesired RF signals, increases switching time, disturbs line balance heightening undesired line transients, and is destructive of the switching equipment per se.

The hold-off voltage of a switch is defined as the voltage which the switch is capable of withstanding with out breakdown or arcing between electrodes when the switch is in an open position. The breakdown phenomenon is caused primarily by ionization of gas molecules in the electric field between the electrodes. A second breakdown phenomenon, which may be described as electron field emission from the cathode switch eledtrode, occurs at higher voltages and also acts to limit switch hold-off voltage.

At the instant of the contact electrodes separating or closing, when the separation distances are 10 cm. or less, a very large valued electric field is created. The cathode, whether it be a solid or liquid electrode, emits some ionized metal vapor along with substantial thermionic and field emission electron flow sutficient to initiate arcing. If the vapor pressure of the electrode metal is high enough, the are initiated by the breaking of the contacts will continue even after the electrodes are separated to their full distances.

Switch arcing pits solid metal electrodes by melting small regions of the electrode surfaces and vaporizing or splattering the molten elect-rode material. The pitted contact electrodes exhibit during switching action increased field electron emission due to regions of intense concentration in the electrical field above the roughened pitted electrode surfaces. The pitted contact electrodes have higher junction resistance because of the reduced area of contact. Excessive electrode pitting renders switches useless due to heightened electron emission, overheating and increasingly inefiicient switching action.

Liquid metal or self-healing switch electrodes offer some advantage over solid metal electrodes in that electrode pitting and consequent electrode deterioration are avoided. Heretofore, mercury has by far been the preferred liquid metal electrode substance for switch applications. While mercury through the range of ambient temperatures, the vapor pressure of mercury is much too high for use with high voltage systems. The presence of mercury vapor increases arcing due to gas ionization between the electrodes. De-

switches, earlier workers in high power capacity switch technology have not dis-closed practical self-healing electrode switches for high voltage, large current capacity service.

One technique extensively employed to increase switch hold-off voltage and to suppress switch arcing is to encase the contact electrodes and the region the-rebetween in an evacuated envelope. The contact electrodes are moved into and out of contact by mechanical linkages which interconnect through the vacuum seal. A remarkably reduced arcing between contact electrodes may be achieved by reducing the presence of ionizable gas in the envelope is normally in the liquid state r 3,377,576 Patented Apr. 9, 1968 to a pressure below 10 mm. of Hg. As a result, gas ionization breakdown is greatly reduced, however, the field emission arcing effects remain unchanged or may even increase in an evacuated environment. Thus, solid electrode pitting is not controlled by use of vacuum alone.

Although operation of a high power switch in vacuum achieves a marked reduction in electrode arcing, the mechanical motion of the electrodes in vacuum introduces heretofore unsolved mechanical problems. Mechanical linkages interconnected through vacuum seals are notoriously troublesome. Previously available mechanical linkages operated through vacuum seals exhibit only short useful life expectancy.

Still another problem exists in actuating mechanical linkages to close or to open vacuum encased power switches. The mechanical movement of one metallic member against another in high vacuum under conditions of large current flow through the moving parts has been a continuous source of switch malfunction. Lubrication of the moving parts in a vacuum is restricted to very low vapor pressure substances. The configuration of the switch linkages often requires that the lubricant be conductive for the switch to function properly. Heretofore, none of the earlier high voltage large capacity vacuum switches has satisfactorily avoided, with practical inexpensive mechanical means, the disadvantage of dry non-lubricated sliding junctions between current conducting switch linkage elements.

There remains, then, an unfulfilled need for a large current capacity. high hold-off voltage switch which simultaneously embodies the advantages of self-healing electrodes, high vacuum environment suppression of ionized gas arcing and fully lubricated mechanical motion of the switch electrodes.

Accordingly, one object of the present invention is to provide an improved high hold-off voltage, large current capacity switch.

Another object of this invention is to provide a high voltage vacuum switch with self-healing contact electrodes:

Still another object of this invention is large power capacity, high voltage vacuum switch having lubricated sliding mechanical contacts.

Another object of this invention is to provide in a high voltage vacuum switch system an improved means of communicating switch motion through a vacuum seal.

Another object of this invention is to provide a high voltage, large power capacity switch with a superior arc suppression capability.

Still another object of this invention is to provide a longlife, highly reliable high voltage, high power capacity switch.

These and other objects and advantages of our invention will be evident from the following illustrations, specification and claims.

FIGURE 1 is a partly cut away view of a first preferred embodiment of our invention.

FIGURE 2 is a cross section view of a fragment of the embodiment of our invention shown in FIGURE 1.

FIGURE 3 is a partially cut away view of a second preferred embodiment of our invention.

FIGURE 4 is a partially cut away view of a variation of .the embodiment of our invention illustrated in FIG- URE 3.

FIGURE 5 is a URE 4 but showing two sliding electrodes.

Referring now to the figures, a first preferred emb0di ment of our invention illustrated in FIGURES l and 2 is adapted for interruption of high voltage, large current capacity power mains. Stationary switch electrodes 10 and 12 are mounted coaxially in a spaced relationship within a gas tight electrically insulating envelope 14. The

to provide a partially cut away view similar to FIG-- envelope is comprised of metal end caps 16 and 18, each having a central aperture 20 and 22 through which the stationary electrodes and 12, respectively, are mounted. The apertures and 22 are each provided with a flange 24 and 26 that provides a surface suitable for metallurgically bonding to the respective stationary electrodes 10 and 12.

A high dielectric material cylindrical tube 30 is sealed to the edges 32 and 34, respectively, of the end caps 16 and 18 and provides the side walls of the gas tight envelope.

The electrical power main bus bars 36 and 38 are connected, respectively, by conventional mechanical means to the portion of the stationary electrodes 11) and 12 which extend outside the gas tight envelope 14. In the embodiment shown in FIGURE 1, the stationary electrodes 10 and 12 are inserted through close fitting apertures in the bus bars 36 and 3-8.

Movable electrodes 40 and 42, comprised of high relative magnetic permeability metallic cylinders, are each respectively mounted coaxially over the stationary electrodes 10 and 12. The movable electrodes 40 and 42 are sized to readily slide coaxially along the stationary electrodes with only a small clearance. In addition, the movable electrodes are sufiiciently long so that when extended coaxially beyond the respective stationary electrodes 10 and 12, the two movable electrodes 40 and 42 will readily make contact with one another in the space between the stationary electrodes without slipping off the supporting stationary electrodes; and when the movable electrodes are retracted from the ends of the stationary electrodes, a substantial space exists between the two ends thereof. The relative position of the two movable electrodes 40 and 42 in the closed switch position is illustrated in FIGURE 2, and the open switch position is illustrated in FIGURE 1.

The movable electrodes 40 and 42 are normally held in the open switch positions, such as illustrated in FIG- URE 1, by means of two tension springs 44 and 46 respectively mounted coaxially over the stationary electrodes 10 and 12. The spring 44 is connected at a first end to the moving electrode 40 and at the second end rigidly connects by means of a collar 48 to the end cap' 16. A groove is provided in the movable electrode 12 and in the collar 48 into which one coil at each end of spring 44 rests for purposes of securing the spring at either end. Similarly, the moving electrode 42 is normally held in a retracted or open switch position by means of the spring 46 one end of which is fixed by a groove, shown in the illustrations, to the end cap 18 by means of rigidly mounted collar 50.

FIGURE 2 illustrates the detailed structure of the movable electrodes 40 and 42. The fixed electrodes 10 and 12 are made of copper and have at the forward tips a flame spray tungsten coating 10a and 12a. The movable electrodes 40 and 42 are made of ferromagnetic material such as 420' stainless steel, a high magnetic permeable stainless steel. The movable electrodes are similarly provided with flame spray tungsten coatings 40a and 42a on those surfaces through which current may be required to pass. The tungsten coating furnishes a high wear resistant surface to the underlying copper electrode. The electrical resistivity of tungsten is much greater than that of copper, however the flame spray coating may be as shallow as a few thousandths of an inch. Hence, in the arrangement shown in the illustrations, a relatively large area of the tungsten coating is available through which the current passes and only negligible resistances losses are encountered.

A solenoid 54 is mounted exterior of the envelope 14 about a high magnetic flux capacity core 56. The core 56 is in turn mounted between two magnetic flux conductors 58 and 60 which in turn are connected respectively to the stationary electrodes 10 and 12. When a direct current is passed through the solenoid coil 54, a magnetic flux is induced in the core 56 and transmitted through the magnetic flux conductors 58 and 60 to the stationary electrodes 10 and 12 and finally to the movable electrodes 40 and 42. The polarity of the magnetic field transmitted to the first movable electrode 40, by the above-described arrangement, will always be opposite to that transmitted to the second movable electrode 42; thus, a strong magnetic field of opposite polarity may be induced between the two movable electrodes. Amagnetic field of suitable strength will draw the movable electrodes together, overcoming the spring tension which holds the two electrodes in normally separated position.

With the application of a large current to the solenoid 54, the movable electrodes 40 and 42 may be brought together with considerable force. To prevent damage to the stationary electrode mountings, cushion springs 62 and 64 are mounted at the ends of the stationary electrodes 10 and 12 to absorb the impact momentum incurred by the magnetic field force closing and the spring loaded opening of the movable electrodes.

Large current at high voltage must pass through the stationary electrodes 10 and 12 and the moving electrodes 40 and 42. By placing a film 66 and 68 of liquid gallium metal over the stationary electrodes, a low viscosity, low vapor pressure, high conductivity contact surface is maintained between the sliding metal electrodes. The gallium metal film provides a low friction lubricant having high conductivity and readily healed electrode action. Moreover, the vapor pressure of liquid gallium metal is lower than that of solid silver and compares favorably with copper alloys. Accordingly, vacuum of 10- mm. Hg or better may be readily maintained within the envelope 14. The physical properties of gallium metal will not be described in detail here, but the reader is referred to the numerous places in the literature which set forth the full physical data.

By the above-described switch, large current at high voltages may be readily and economically interrupted without appreciable arcing between electrodes or without excessive wear between sliding electrode members.

Gallium melts at 30 C. Only a small quantity of heat need be applied to the switch before start-up to assure that the gallium metal is melted and is lubricating the moving electrode parts. After being in high voltage, large current service for a short period of time, ample heat is normally generated within the electrodes to assure liquification of the metallic gallium lubricant and electrode surfaces.

Referring now to FIGURE 3, a variation of our invention shown in FIGURES 1 and 2 is illustrated. The actuation of the movable electrodes in the embodiment shown in FIGURE 3 is controlled by solenoidal magnetic fields applied directly to the movable electrodes, as will be readily understood from the following description.

Power main bus bars and 82 terminate on fixed electrodes 84 and 86. The fixed electrodes are elongated and mounted in spaced relationship but in coaxial alignment. A vacuum tight envelope 88 is hermetically sealed about an intermediate point on fixed electrodes 84 and 86 so that a portion of each electrode extends into the interior of the envelope 88, which is made of high dielectric, nonmagnetic material. The electrodes may be made of any low resistance metal, copper being preferred. Movable electrodes 90 and 92, comprised of hollow cylindrical tubes, are fitted over the fixed electrodes respectively and adapted to readily slide therealong. The movable electrodes are made of a ferromagnetic, electrically conductive metal such as magnetic stainless steel. Coil springs SP4 and 96 are mounted over the respective fixed electrodes and secured at each first end of the respective springs to a movable electrode and at the respective second ends of the springs to the respective fixed electrodes. The coil springs 94 and 96 will normally hold the movable electrodes 90 and 92 in retracted positions; that is, out of contact with one another.

Solenoids 98 and 100 are positioned exterior of the envelope 88 and transversally about the portion of the fixed electrodes 84 and 86 which extend into the interior of the envelope 88.

A film of liquid gallium metal is coated onto the fixed electrodes 84 and 86 and onto the surfaces of the movable electrodes 90 and 92. The gallium metal readily wets other metal surfaces and liquefies at 30 C. A small quantity of heat from an external source or from a heating element 102, inserted permanently within the envelope, may be required to liquefy the gallium metal electrode surfaces and lubricant prior to use of the switch.

The solenoids 98 and 100 are powered by direct current, the polarity of which determines the polarity of the resultant magnetic field. If the polarity of the solenoid magnetic fields from coils 98 and 100 are opposite in sign, the two movable electrodes 90 and 92 will have induced therein magnetic fields of opposite polarity and exert a strong attraction upon one another. Such attraction between the movable electrodes will abruptly close the switch. The coil springs 94 and 96 separate the movable electrodes, thereby opening the switch upon the removal of the solenoidal magnetic fields.

FIGURE 4 illustrates still another embodiment of our invention. Two nonmagnetic, fixed electrodes 110 and 112 are mounted to extend into a high dielectric nonmagnetic material envelope 114. The fixed electrodes are mounted in coaxial alignment but in a spaced arrangement so that a space is provided between the fixed electrodes within the envelope. The envelope is preferably vacuum tight and capable of maintaining vacuum of mm. Hg or greater.

A solenoid 116 is mounted on the exterior of the envelope 114 and when energized is positioned to induce a magnetic field within the envelope having a fixed polarity.

The fixed electrode 112 is provided with a cylindrical hollow recess 118 into which a movable electrode 120 may be inserted. A coil tension spring 122 secured at the end of the recess 118 is inserted into the recess 118 beneath the movable electrode 120. The second end of the spring 122 is secured to the end of the movable electrode as shown in the illustration.

The movable electrode 120 is hollow and made of a nonmagnetic conducting metal such as copper. Sealed mechanically within the electrode 120 is a permanent elongated maget 124 positioned so that the permanent magnet field is coaxial with the movable electrode 120. The permanent magnet may be made of any hard ferromagnetic material.

A film of gallium metal applied to the movable electrode 120 wets the exterior of the electrode 120 and the surfaces of the recess 118. The gallium film when liquefied provides a low friction lubricant suitable for relatively high vacuum environment between the moving electrode 120 and the surfaces of the fixed electrode 112. Moreover, the liquid gallium film provides a highly conductive self-healing interelectrode contact surface between the moving electrode parts.

When the solenoid 116 is energized, the resulting magnetic field reacts on the permanent magnet 124 causing the movable electrode 120 to slide partially out of the recess 118 and make contact with the first fixed electrode 110. This action closes the switch. When the sole noid 116 is de-energized, the movable electrode 120 is abruptly retracted by the coil spring 122. This latter action opens the switch. A variation of FIGURE 4 is set forth in FIGURE 5. As shown, FIGURE 5 illustrates a second sliding electrode controlled by a second solenoid, the parts of which are designated by the same numerals as the sliding electrode and solenoid in FIGURE 4 but with a sutfix a. The structure and function of each of the two sliding electrodes in FIGURE 5 are similar to the structure and function of the single sliding electrode assembly shown in FIGURE 4.

As a variant of this embodiment, the fixed electrode can be replaced with a second sliding electrode assembly including a solenoid, such assembly being similar to the single assembly illustrated. The tips of the two sliding electrodes will preferably be formed int-o complementary shapes for proper physical contact. In the resulting switch, the two movable electrodes will readily make contact with one another in the space between the stationary electrodes Without slipping out of the recesses therein; and when the movable electrodes are retracted from the ends of the stationary electrodes, a substantial space exists between the two ends thereof.

Numerous variations and alternative combinations of the detailed construction of embodiments of our invention fall within the scope of our invention. The abovedescribed and illustrated preferred embodiments of our invention are intended as merely illustrative of our invention, the scope of which is set forth in the following claims.

We claim:

1. An electrical switch comprised of an evacuated high dielectric material envelope; a first and a second elongated fixed electrode mounted in coaxially aligned spaced relationship within the envelope; a first and a second hollow cylindrical sliding electrode mounted, respectively, coaxially about the first and second fixed electrodes, the sliding electrodes being made of relatively high magnetically permeable material; a lubricating selfhealing film of gallium metal wetting the electrode surfaces; and solenoids mounted exterior to the envelope and transversally of the fixed electrodes; whereby, electrical contact between the fixed electrodes may be made and broken by alternately axially moving the sliding electrodes into and out of contact in the space between the fixed electrodes.

2. An electrical switch comprised of an evacuated high dielectric material envelope; a first and a second elongated fixed electrode mounted in coaxially aligned spaced relationship within the envelope; a first and a second sliding electrode mounted, respectively, to and coaxially with the first and second fixed electrodes, the sliding electrodes having means for mounting a permanent magnetic polarity; a lubricating self-healing film of gallium metal wetting the electrode surfaces; heating means for liquefying the gallium metal mounted within the envelope; and magnetic means mounted exterior of the envelope for positioning the sliding electrodes along the fixed electrodes; whereby, electrical contact between the fixed electrodes may be made and broken by moving the sliding electrodes into and out of contact in the space between the fixed electrodes.

3. An electrical switch comprised of an evacuated high dielectric material envelope; a first and a second elongated fixed electrode mounted in coaxially aligned spaced relationship within the envelope, the first such fixed electrode being characterized by having a hollow central recess having an aperture opening into the space between the fixed electrodes; a sliding cylindrical electrode slidably mounted within the recess, such sliding electrode being of relatively high magnetically permeable material; a lubricating self-healing film of gallium metal wetting the electrode surfaces; and magnetic means for positioning the sliding electrode along the first fixed electrode and relative to the second fixed electrode, being mounted to the envelope; whereby electrical contact between the fixed electrodes may be made and broken by alternately moving the sliding electrode into and out of contact with the second fixed electrode.

4. An electrical switch comprised of an evacuated high dielectric material envelope; a first and a second elongated fixed electrode mounted in coaxially aligned spaced relationship within the envelope; a first and a second sliding electrode having a hollow tubular configuration mounted respectively coaxially on the first and second fixed electrodes, the sliding electrodes being made of relatively high magnetically permeable material; a lubricating self-healing film of gallium metal wetting the electrode surfaces; and magnetic means for positioning the sliding electrodes along the fixed electrodes; whereby, electrical contact between the fixed electrodes may be made and broken byalternately axially moving the sliding electrodes into and out of contact in the space between the fixed electrodes.

5. An electrical switch comprised of an evacuated high dielectric material envelope; a first and a second elongated fixed electrode being mounted in coaxially aligned spaced relationship within the envelope'and having each a hollow central recess with an aperture opening into the space between the fixed electrodes; a first and a second sliding electrode having cylindrical rod configuration, the first and second sliding electrodes being mounted respectively coaxially within the first and second fixed electrodes, the sliding electrodes being made of relatively high magnetically permeable material; a lubricating selfhealing film of gallium metal wetting the electrode surfaces; and magnetic means for positioning the sliding electrodes along the fixed electrodes; whereby, electrical contact between the fixed electrodes may be made and broken by alternately axially moving the sliding electrodes into and out of contact in the space between the fixed electrodes.

6. An electrical switch comprised of an evacuated high dielectric material envelope; a first fixed electrode, and a second fixed electrode, the second fixed electrode having hollow cylindrical tubular configuration, the first and second fixed electrodes being mounted in coaxially aligned spaced relationship within the envelope; a'sliding electrode mounted coaxially within the'second fixed electrode, the sliding electrode being made of relatively high magnetically permeable material; a lubricating self-healing film of gallium metal wetting the electrode surfaces; and magnetic means for positioning the sliding electrode along the second fixed electrode; whereby electrical contact may be made and broken by alternately axially moving the sliding electrode into and out of contact with the first fixed electrode in the space between the fixed electrodes.

References Cited UNITED STATES PATENTS 1,948,687 2/1934 Swinne 200-166 X 2,732,464 1/1956 Ohl 200166 2,749,402 6/1956 Tancerd 2.0087 3,150,901 9/1964 Esten et al. 308241 OTHER REFERENCES German Printed Appl., Wessel et al., 1,116,816, Nov. 9, 1961.

BERNARD A. GILHEANY, Primary Examiner.

B. DOBECK, J. J. BAKER, R. N. ENVALL, JR.,

Assistant Examiners.

Claims (1)

1. 3. AN ELECTRICAL SWITCH COMPRISED OF AN EVACUATED HIGH DIELECTRIC MATERIAL ENVELOPE; A FIRST AND A SECOND ELONGATED FIXED ELECTRODE MOUNTED IN COAXIALLY ALIGNED SPACED RELATIONSHIP WITHIN THE ENVELOPE, THE FIRST SUCH FIXED ELECTRODE BEING CHARACTERIZED BY HAVING A HOLLOW CENTRAL RECESS HAVING AN APERTURE OPENING INTO THE SPACE BETWEEN THE FIXED ELECTRODES; A SLIDING CYLINDRICAL ELECTRODE SLIDABLY MOUNTED WITHIN THE RECESS, SUCH SLIDING ELECTRODE BEING OF RELATIVELY HIGH MAGNETICALLY PERMEABLE MATERIAL; A LUBRICATING SELF-HEALING FILM OF GALLIUM METAL WETTING THE ELECTRODE SURFACES; AND MAGNETIC MEANS FOR POSITIONING THE SLIDING ELECTRODE ALONG THE FIRST FIXED ELECTRODE AND RELATIVE TO THE SECOND FIXED ELECTRODE, BEING MOUNTED TO THE ENVELOPE; WHEREBY ELECTRICAL CONTACT BETWEEN THE FIXED ELECTRODES MAY BE MADE AND BROKEN BY ALTERNATELY MOVING THE SLIDING ELECTRODE INTO AND OUT OF CONTACT WITH THE SECOND FIXED ELECTRODE.

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