US2907905A

US2907905A - Mercury vapor discharge device

Info

Publication number: US2907905A
Application number: US719576A
Authority: US
Inventors: Andrew J Humphrey
Original assignee: Reliance Electric and Engineering Co
Current assignee: Reliance Electric and Engineering Co
Priority date: 1958-03-06
Filing date: 1958-03-06
Publication date: 1959-10-06
Anticipated expiration: 1976-10-06

Description

Oct. 6, 1959 A. J. HUMPHREY 2,907,905

MERCURY VAPOR DISCHARGE DEVICE Filed March 6, 1958 3 Sheets-Sheet 1 INVENTOR.

ANDREW J. HUMPHREY Oct. 6, 1959 A. J. HUMPHREY MERCURY VAPOR DISCHARGE DEVICE 3 Sheets-Sheet 2 Filed March 6, 1958 FIG.Z

INVENTOR: ANDREW J. HUMPHREY Www; Mimi. my.

Oct. 6, 1959 A. J. HUMPHREY MERCURY VAPOR DISCHARGE DEVICE 3 Sheets-Sheet 3 Filed March 6, 1958 FIG.7

INVENTOR. AN DREW J. HUM PHR EY The discharge device 11 is of metal construction and includes generally a cylindrical outer shell 12, an anode 13, and a grid 14. The metallic outer shell 12 is closed by

end caps

15 and 16, which in this embodiment are chosen to be made from carbon or graphite. Being of carbon they are unlikely to condense mercury on their surface as a wetted coating. A cathode 17 is on the inner surface of the cylindrical shell 12 and hence the

end caps

15 and 16 are electrically connected to this cathode 17.

The anode 13 is mounted along the axis 20 of the cylindrical shell 12 and is supported by an anode shaft 21 electrically connected to a flexible cable 22 exterior of the device 11. The anode shaft 21 is mounted in a sleeve 23 connected by a glass seal 24 with another metal sleeve 25 connected to an end sleeve 27, in turn connected to the end cap 15. The end cap 15 has a cylindrical extension 26 relatively closely spaced to the anode shaft 21.

The grid 14 is a cylindrical perforated metal or graphite structure surrounding the anode 13 and generally parallel to the surface of the anode and coextensive with this surface. The perforated grid 14 is carried on a grid shaft 29 disposed on the axis 20 with this shaft 29 being supported by metal sleeves 30 and 31 and a glass seal 32 in a manner similar to the support of the anode shaft 21. An annular keep-alive anode 33 concentrically surrounds the grid shaft 29 and is positioned between the lower axial end of the grid 14 and the end cap 16. The keepalive anode 33 is supported by mounts and lead-in terminals 34 similar to the one shown and all insulated by glass seals similar to 35 from an end sleeve 42 connected to the end cap 16. A starting electrode 36 is movably carried by a bellows 37 and a glass seal 38 on a lead 39. This starting electrode 36 typifies the usual starting electrode which may be moved out of engagement with the cathode 17 to strike an are which may move to the keepalive anode 33 to maintain a small discharge within the device 11.

The cylindrical outer shell 12 has fixedly attached thereto as by brazing, soldering, or other suitable means a liquid coolant coil 40 which may be connected to an external cooling heat exchanger. The coolant coil 40 also may have an electrical terminal 41 for connection to the cathode 17.

The outer cylindrical shell 12 is normally of a base metal, but may be the metal desired to form the cathode 17. Typical metals in use to form the active cathode surface are the so-called refractory metals which are not destroyed by an arc discharge, such as molybdenum or tungsten. Such a refractory metal may not be necessary in all cases however, dependent upon the use of the device 11. Nickel or iron may be satisfactory for the base metal of the cathode 17 where long life of the tube is not essential. Examples of short life tube requirements could be for a surge current tube or a switching tube where the life is but a few operations. The cathode 17 is a prepared active surface on the inner metal surface of the shell 12 and is a surface wetted with mercury. Molybdenum and tungsten are metals which can be wet with a mercury film when such metting takes place during the forming operation of the discharge device 11 under action of an electric are or discharge between the cathode 17 and anode 13. The entire exposed inner cylindrical surface of the shell 12 may be wetted to form the cathode 17 or it may merely be of the type of metal which will be capable of being wetted during use. Normally the active cathode surface would consist of a thin sheet of rolled molybdenum or tungsten metal spot welded to the base metal container 11. Another possibility is a sprayed or electroplated layer of refractory metal.

The

end caps

15 and 16 are electrically connected to the shell 12 and cathode 17; however, these are preferably formed from a material which is not wetted, an example being the use of carbon or to use any common.

. 4 7 metal with the surface prepared so that it will not be easily wetted. If the metal be molybdenum, for example, it may be oxidized because molybdenum oxide is not easily wetted. A more common metal may be used for economy, for example, one of the ferrous metals, and in such case the inner surface of the

end caps

15 and 16 and of the cylindrical extension 26 may be covered with a colloidal graphite emulsion to prevent wetting of these exposed surfaces. The

end caps

15 and 16 may also be an insulator, such as ceramic. This construction establishes that no portion of the envelope or of metal electrically connected to the cathode and capable of emission from a condensed mercury layer has access to the field of the anode except through the grid 14.

In operation, the device 11 is evacuated and sealed with a mercury vapor atmosphere established within the envelope formed by the shell 12 and

end sleeves

27 and 42. During the manufacture of the device, the inner surface of the shell 12 is wetted at least in part with a film of mercury and this mercury film is that which establishes the mercury atmosphere within the device 11. This mercury film is maintained upon the wetted area by the equilibrium between the vapor pressure of mercury in the atmosphere inside the envelope and the vapor pressure from the wetted surface. This equilibrium will always be maintained despite changes of temperatures of the parts of the device as long as the temperature of the cathode does not get too much higher than that of other parts. It is believed that the mercury film on the cathode is a form of amalgam or at least a surface amalgam which has exposed on the surface not only mercury molecules but also molecules of the cathode metal, such as molybdenum. The cathode can thus be at a somewhat higher temperature than the anode or grid and yet maintain this equilibrium of vapor pressure in the envelope and pressure of vapor over the cathode film to cause a maintenance of mercury film on the cathode for proper continued operation of the device. This would also remain true during storage periods or non-operating periods of the device.

Under operating conditions the starting electrode 36 may be used to strike an arc which will be transferred to the keep-alive anode 33 and be maintained at the lower end of the device 11. When the operating positive potential is applied to the anode 13, the customary discharge will occur between the anode and cathode as controlled by the grid 14. The construction of the device 11 is such that a very short discharge path is maintained between the anode 13 and cathode '17 without any intervening bafiles. This is especially desirable in devices operating on voltages under 1500. For higher voltage operation bafiling may be used, but for the normal voltages of one hundred to fifteen hundred volts no baflies are required. The natural configuration of the device 11 is such that heat within the device 11 maintains the anode 13 at a higher temperature than that of the cathode 17, thence, there will be no mercury condensation on the anode 13 nor on the grid 14. The coolant coils 40 connected to a heat exchanger permit extraction of heat from the device 11 so as to aid the natural temperature differential of. elements of the device 11 so that the anode 13 will always be maintained warmer. This makes certain thatthe film of mercury on the cathode '17 will always be maintained to sustain the electric discharge. The lack of requirement for a pool of mercury anywhere within the device 11 eliminates random vapor jets which could strike the anode 13 and thus cause failure or improper operation, and this permits a much closer spacing between the anode and cathode. The close spacing minimizes the voltage drop in the are or electric discharge; hence, less wattage loss is incurred in the operation of the device '11, thus increasing the efliciency. The baffies formerly used in prior art devices between anode and cathode increase the length of the arc discharge path and hence increase the voltage drop therein, ipcrgase the wattage losses, decrease the efiiciency', and aggravate the cooling problems. By the present construction of a wetted film cathode, the natural configuration of a tubeor' tank discharge devicemay' be utilized to best advantage. This also permits operation of the tube in my attitude or position, even changing positions as in a moving vehicle, and it. is not required to take into account the action of gravity on any of the parts for proper operation as was true'in the prior art mercury pool type of discharge device. With the device 11 mounted with the axis 20 vertically, the entire cathode surface 17 is vertical as is the active'surface of the anode 13. If the "device 11 were operatedon its side, the active surface of the cathode'17 would'have two portions, one of which was'horizontal and'one of which was vertical. These would be two surface portions which are mutually perpendicular, yet the device 11 would function normally with a big advantage over the prior art mercury pool types which'could be operated'in only one position.

The Figure 2 shows a modified form of the invention to illustrate that the invention may be utilized in different forms of discharge devices. Figure 2 shows a discharge device 50 which is principally or at least partially of glass construction as opposed to the metal construction of Figure 1. The anode 13 is'again supported on an anode shaft 21 in this case mounted and carried in the glass end cap 51. A metal shell 52 is sealed in and forms a partof the envelope formed by the glass end cap 51 and another glass end cap 53. The metal shell 52 is treated on the inside to be wetted with a mercury film to form the cathode 17; and hence, the metal shell 52 may be conveniently made of a refractory metal'wettable with mercury such as molybdenum or tungsten. An anode shield 54 is closely spaced to the anode shaft 21 and upper end oftheanode 13, and is either electrically floating or tied to the cathode through a resistor. This shield 54 establishes that the cathode 17 is not exposed to the field of the anode 13 except through the structure of the grid 55. This grid may be identical to the grid 14 of Figure 1 but has been shown in a slightly different configuration.

A keep-alive anode 56 has been shown as an annular or cylindrical perforated metal or graphite shield surrounding the grid 55 and generally coextensive therewith. The keep-alive anode 56 is supported by mount and lead-in terminals 57. A starting electrode 58, a portion of which is magnetic, is mounted on a pivot 59 and may be operated by an external electromagnet 60 to move the electrode 58 away from the cathode 17 for initiating an electric discharge. Air cooling fins 61 are attached directlyto the outside of the cylindrical shell 52 radially for ellicient heat transfer to the ambient atmosphere. The operation of the discharge device 50 is essentially the same as that of the device of Figure 1, the keep-alive anode 56 permitting discharge at any point between the cathode 17 and keep-alive anode '56 which is most favorable.

The Figures 3-7 show a multi-electrode mercury vapor discharge device 70. This device 70 is contained within a metal tank 71 supported on electrical insulators 72. Figure 3 is a horizontal section through this tank 71 showing a plurality of hollow rectangular cathodes 73 and anodes 74. Grids 75 are electrically and physically connected to the tank 71 and surround the anodes 74.

Figure shows a vertical section through one of the cathodes 73 which is of hollow rectangular construction containing baffles 76 and supported by two

hollow terminals

77 and 78. These terminals are supported in metal sleeves 79 and glass seals 80 to the tank 71 and a terminal connecting portion 81 may be fastened to the

hollow terminals

78 or 77. A coolant liquid may be circulated through the hollow terminal 78 and directed by the'baffles 76 for efficient cooling of the cathode73 and exit through the hollow terminal 77. A starting electrode 82 movable with respect to the cathode 73 may be provided as well as a keep-alive anode 83.

Figure 6 shows a vertical section through one of the anodes 74 again of hollow construction containing baflies 76 for directing of coolant from one hollow terminal 84,

anything; suitable such as molybdenum or tungsten fastened to a base metal 88. Another surface 89 is a nonwetted surface prepared by any suitable means such as oxidation or covering with-colloidal graphite emulsion. The thickness of the mercury film on the wettable surface is-not shown separately but may bein the nature of a few molecules in thickness.

The several anodes-74* maybe connected in parallel externally of the tank 71 as well as the several cathodes '73. This paralleling permits high current operation of the entire device which limits the amperage required'to be carried by each'particular anode. The grid being electrically connected to the tank 71 shields each of the anodes 74- from the cathodes on eitherside thereof and the insulators 72 for the tank 71 permit maintenance of thegrid potential at otherthan ground potential.

The lower surface ofthe cathode 71 is preferably activated or at least'permitted to be wetted by a mercury film as are the other refractory metal surfaces, and thus the construction of Figures 3-7 showsa mercury discharge device which has three mutually perpendicular cahode surfaces which are active and which may support an electric discharge between the. cathode 73 and the anode 74. This is true regardless of the attitude of the tank 71.

The invention shows several constructions of mercury vapor discharge devices which permit close spacing of the anode and cathode with a minimum of bathing therebetween for" minimum voltage drop and hence higher eficiency. The'structure of Figures 3-7 is preferably operated so that the heat exchanger connected to the liquid coolant of the cathode is more efficient or at least maintains'thecathodes 73 at a lower temperature than that of the anodes 74. This assures that the -mercury film on the cathodes 73 will be maintained and that mercury will not condense on the anodes 74. The rectangular construction'of Figures 3-7 permits a maximum utilization of space within the tank 71 for a'multi-electrode structure and permits large active areas of both anode and cathode with these surfaces beingsubstantially parallel and coextensive.

Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to Without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

l. A mercury vapor discharge device comprising, an

anode, a cathode cooperating with said anode, insulating means mutually insulating said anode and cathode, substantially perpendicular mercury film wettable surface portions on said cathode disposed substantially parallel to and coextensive'with surface portions of said anode, and a perforate grid substantially coextensive with said wettable surface portions on said cathode.

2. In a mercury vapor discharge device, an anode, a cathode cooperating with said anode, substantially perpendicular mercury fihn wettable surface portions on said cathode forming a discharge area disposed substantially parallel to and opposite corresponding surface portions of said anode.

3. A mercury vapor discharge device comprising, a sealed envelope, an anode, a cathode, and a grid supported in said envelope in mutually insulated relationship with said grid shielding said anode from the cathode, a substantially verticalsurface on each said anode and cathode disposed substantially coextensive and parallel, means establishing said vertical surface of said cathode as wetted by mercury, said mercury wetted surface establishing a mercury vapor atmosphere within said envelope, heat exchange means connected to one of said anode and said cathode to maintain a mercury vapor pressure equilibrium to favor maintenance of a mercury film on said cathode wetted surface whereby said wetted vertical surface of said cathode is that from which the space discharge to the anode takes place, and said grid having a perforate surface substantially coextensive and parallel with said anode and with said cathode wetted surface.

4. A mercury vapor discharge device comprising, a sealed envelope at least partially of metal and having an upper wall, an anode electrically insulated from said envelope and supported from said upper wall, a cathode supported within said envelope, a grid shielding said anode from the cathode, insulator means mutually insulating said grid, anode and cathode, said anode and cathode being relatively closely spaced with only the grid therebetween, heat exchange means connected to one of said anode and said cathode to maintain said cathode cooler than said anode during operating conditions, first and second surface portions substantially mutually perpendicular on said cathode, first and second surface portions on said anode disposed substantially coextensive with and parallel to said first and second surface portions of said cathode, a keep-alive anode within said envelope disposed adjacent said cathode, a starting electrode disposed within said envelope for cooperation with said cathode, means forming a mercury film on said first and second surface portions of said cathode, said mercury film establishing a mercury vapor atmosphere within said envelope portions, and said grid having a perforate surface substantially coextensive and parallel with said anode and with said cathode wetted surface.

5. A mercury vapor discharge device, comprising, an evacuated envelope having an axis, an anode disposed centrally on said axis, an annular grid substantially axially coextensive with and surrounding said anode, an annular cathode substantially axially coextensive with said anode and forming a part of said envelope to surround said grid, and an active surface on the interior of the axially coextensive part of said cathode to establish an area for mercury vapor discharge beween said cathode and said anode through said annular axially coextensive grid, said cathode as part of said envelope operating at a temperature to establish a mercury vapor pressure in the envelope favoring maintenance of a mercury film on said cathode.

6. A mercury vapor discharge device, comprising, a generally cylindrical evacuated envelope having an axis, a cylindrical anode disposed centrally on said axis, means supporting and establishing electrical connection to said anode, a cylindrical shell cathode substantially axially coextensive with said anode and forming a part of said envelope, said anode being relatively closely spaced to said cathode without baffles therebetween, means form ing a wetted mercury surface on the interior of said cathode to establish an area for mercury vapor discharge between said cathode and anode, and a cylindrical perforated grid substantially axially coextensive with and surrounding said anode, and substantially axially coextensive wtih said wetted cathode surface said cathode as part of said envelope having good heat transfer relationship with the ambient atmosphere, whereby said cathode operates at a temperature not higher than that of said anode.

7. A mercury vapor discharge device, comprising, a generally cylindrical evacuated envelope having an axis and first and second ends, a cylindrical main anode disposed centrally on said axis, a cylindrical perforated grid substantially axially coextensive with and surrounding said anode, first support and terminal means axially extending into said envelope from said first end to support said anode and provide electrical connection thereto, second support and terminal means axially extending into said envelope from the second end thereof to support said grid and provide electrical connection thereto, a cylindrical shell cathode substantially axially coextensive with said anode and surrounding said grid and forming a part of said envelope, a keep-alive anode within said envelope and cooperating with said cathode, a movable starting electrode within said envelope and cooperating with said cathode, said main anode being relatively closely spaced to said cathode Without baffles therebetween, a mercury film on a substantial part of the interior portion of said cathode which is parallel to said anode to establish an area for mercury vapor discharge between said cathode and main anode, a mercury vapor atmosphere in said envelope established by said mercury film, and a mercury film non-wettable surface on portions of said cathode and of said envelope which are other than parallel to surfaces of said anode, said perforated grid being substantially axially parallel and coextensive with said mercury film cathode surface, said discharge area of the cathode being formed of a dense member of arc-resisting metal and as part of said envelope having an envelope external surface for good heat transfer relationship with the ambient atmosphere, whereby said cathode operates at a lower temperature than said main anode.

8. A mercury vapor discharge device, comprising, a generally cylindrical evacuated metal envelope having an axis and first and second ends, a cylindrical main anode disposed centrally on said axis, a cylindrical perforated grid substantially axially coextensive with and surrounding said anode, first support and terminal means axially extending into said envelope from said first end to support said anode and provide electrical connection thereto, second support and terminal means axially extending into said envelope from the second end thereof to support said grid and provide electrical connection thereto, a cathode formed from that portion of said metal envelope which is substantially axially coextensive with said anode, a keep-alive anode within said envelope and cooperating with said cathode, a movable starting electrode cooperating with said cathode, said main anode being relatively closely spaced to said cathode without baffies therebetween, means forming a wetted mercury surface on the interior of the axially coextensive part of said cathode to establish an area for mercury vapor discharge between said cathode and main anode, means including said wetted mercury surface establishing a mercury vapor atmosphere in said envelope, and liquid cooling conduits connected directly to the outer surface of said envelope at said cathode portion thereof, whereby said cathode operates at a lower temperature than said main anode.

9. A mercury vapor discharge device, comprising, a generally cylindrical evacuated partially glass envelope having an axis and first and second ends, a cylindrical main anode disposed centrally on said axis, a cylindrical perforated grid substantially axially coextensive with and surrounding said anode, first support and terminal means axially extending into said envelope from said first end to support said anode and provide electrical connection thereto, second support and terminal means axially extending into said envelope from the second end thereof to support said grid and provide electrical connection thereto, a cylindrical shell cathode substantially axially coextensive with said anode and sealed in as part of said envelope with said cathode having an exposed exterior metal surface, a cylindrical perforated keep-alive anode substantially axially coextensive with and surrounding said grid and disposed adjacent said cathode, a movable starting electrode cooperating with said cathode, said main anode being relatively closely spaced to said cathode without baflles therebetween, means forming a wetted mercury surface on the interior of the axially coextensive part of said cathode to establish an area for mercury vapor discharge between said cathode and main anode, means including said wetted mercury surface establishing a mercury vapor atmosphere in said envelope, and air cooling fins directly connected to said exposed exterior metal surface of said cathode, whereby said cathode operates at a lower temperature than said main anode.

10. A mercury vapor discharge device comprising, a rectangular metal tank having upper and bottom walls, a hollow anode and a hollow cathode within said tank, first and second hollow electrical terminals insulatedly carried in said upper wall supporting said anode electrically insulated from said tank, third and fourth hollow electrical terminals insulatedly carried in said upper wall supporting said cathode electrically insulated from said tank, a grid electrically connected to said tank and surrounding said anode to shield said anode from the cathode, insulator means insulating said tank and grid from ground, liquid coolant inlet and outlet means through the two terminals of each said anode and cathode, means to circulate liquid coolant through said anode and said cathode to maintain said cathode cooler than said anode during operating conditions, first and second substantially vertical surfaces on each said anode and cathode disposed substantially coextensive and parallel, said cathode having a lower surface adjacent the bottom of said tank, a keep-alive anode within said tank disposed adjacent said cathode, a starting electrode disposed within said tank for cooperation with said cathode, means forming a mercury film at least on portions of said first and second vertical and lower surfaces of said cathode, and means including said mercury film establishing a mercury vapor atmosphere within said tank.

11 A multi-electrode mercury vapor discharge device comprising, a rectangular metal tank having upper and bottom walls, a plurality of hollow anodes and cathodes within said tank, first and second hollow electrical terrninals insulatedly carried in said upper wall supporting each said anode electrically insulated from said tank, third and fourth hollow electrical terminals insulatedly carried in said upper wall supporting each said cathode electrically insulated from said tank, said anodes and cathodes being alternately spaced in said tank, a series of grids electrically connected to said tank and surrounding each of said anodes to shield each anode from the cathodes on either side thereof, insulator means insulating said tank and grids from ground, baffles within each said anode and cathode to provide a lengthened coolant path, liquid coolant inlet and outlet means through the two terminals of each said anode and cathode, means to circulate liquid coolant through said anodes and said cathodes to maintain said cathodes cooler than said anodes during operating coditions, first and second substantially vertical surfaces on each said anode and cath ode disposed substantiallycoextensive and parallel, each of said cathodes having a lower surface adjacent the bottom of said tank, a keep-alive anode within said tank disposed adjacent at least one of said cathodes, a starting electrode disposed within said tank for cooperation with at least one of said cathodes, means forming a mercury film on said first and second vertical and lower surfaces of each said cathode, andmeans including said mercury film establishing a mercury vapor atmosphere within said tank.

12. A mercury vapor discharge device, comprising, an evacuated envelope having an axis, an anode disposed centrally on said axis, an annular perforated grid substantially axially coextensive with and surrounding said anode, means supporting and establishing electrical connection to said anode and said grid, an annular cathode substantially axially coextensive with said anode and forming a part of said envelope, a coaxial portion of said cathode having a mercury wettable refractory metal active surface to establish an area for mercury vapor discharge between said cathode and anode through said grid, said cathode as part of said envelope having good heat transfer relationship with the ambient, whereby said cathode operates at a temperature not sufiiciently higher than that of said anode to prevent maintenance of a mercury film on said cathode.

References Cited in the file of this patent UNITED STATES PATENTS