US2933635A - Vacuum-tight electrode lead-in assembly for mercury vapor rectifiers - Google Patents

Description

Apnl 19, 1960 A. LANG EI'AL 2,933,635

VACUUM-TIGHT ELECTRQDE LEAD-IN ASSEMBLY FOR MERCURY VAPOR RECTIFIERS Flled July 11, 1958 INVENTORS Lia MW M ATTORNEYS United States Patent VACUUM-TIGHT ELECTRODE LEAD-IN ASSEM- BLY FOR MERCURY VAPOR RECTIFIERS Andi- Lang and Ernst Zantop, Wettingen, Switzerland, assignors to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a company of Switzerland Applicafion July 11, 1958, Serial No. 747,881

Claims priority, application Switzerland July 13, 1957 2 Claims. (Cl. 313-331) This invention relates generally to an electrode lead assembly structure for mercury vapor rectifiers having an insulator arranged around the lead-in pin.

Electrode leads, particularly the anode lead of a mercury vapor mutator, generally exhibit a structurally-difficult form. Atmospheric pressure exists on the outside of the lead-in and consequently to achieve a high voltage strength, a large insulation path along the upper surface of the insulator and also in the air spark-over path is required. A very low pressure exists on the inside of the unit. In order to be below the breakdown minimum of the Paschen curve, the product of the gas pressure times the spark-over path must be kept as small as possible. These oppositely directed requirements create diificulties for the construction of the anode leads.

Also the danger arises of a leakage path formation on the inside of the insulator due to mercury condensation. When the temperature of the insulation surfaces is lower than the steam vapor temperature of the gas discharge tube an intensive mercury condensation will occur on the insulator. Thus an upper surface conduction will be generated and the insulation strength will be so reduced that electrical discharges could readily arise.

Furthermore, so-called secondary ignitions arise by current discharges particularly upon the occurrence of too low gas pressure-Le, cathode spot formations on the metallic wall of the gas discharge tube-by which an evaporation of the metallic wall material results. This vaporized metal diffuses radially from the evaporated spot to all sides where it condenses thereon and forms a more or less conductive deposit on the insulator surfaces. Such deposits reduce the surface leakage-current strength of the insulator and are therefore particularly undesirable on the anode leads. This formation of metal deposits on the insulators and subsequent reduction of insulation strength is commonly referred to in the art as aging.

Thus the primary object of the present invention is to provide a vacuum-tight electrode tube lead-in arrangement of conductors and insulators which will be resistant to aging.

The invention is characterized by the provision of a narrow long spacing or gap in the area of the cool part of the electrode lead between the inner surface of the insulator and the lead-in pin.

Thus there are formed long, narrow substantially tubular spaces between the lead-in pins and the inner contact area of the insulator. This contact area lies predominately in the cold part of the electrode lead and consequently in the turned away part of the heated electrode of the electrode lead. Thus these inner insulation surfaces are spaced from the spark-over discharge and are also removed from the source of the secondary ignition, so that only a small amount of metal vapor will arrive at the narrow gap and will be precipitated there without appreciably reducing the insulation strength of the resulting long leakage path. A particularly high sparkover strength will be obtained with the provision of an auxiliary tubular insulator arranged around the lead- 2,933,635 Patented Apr. 19, 1960 in pin. Thus an insulated covering of the metal lead-in pins will be obtained whereby the resulting gap through the insulation surfaces will be formed.

These small gaps may be advantageously employed also near an envelope of the main anode with a grid basket whereby the insulation may be fitted on the insulated lead-in pins with light pressure. From this point of contact the sleeve will continue with a reversed flange along the insulator with'a small gap therebetween and thus good dust protection will also be achieved. The insulator may have the form of a bell with a lengthened outer discharge path, which insures a high voltage strength.

Other objects and advantages of our invention will become more apparent from a study of the following specification when taken in conjunction with the accompanying drawings in which:

Fig. 1 is a partly sectioned view of an electrode leadin assembly for a grid or an anode;

Fig. 2 is a partly sectioned view of an electrode leadin asembly for an auxiliary anode; and

Fig. 3 is a partly sectioned view of an electrode leadin assembly for a main anode having an auxiliary anode.

Referring now to Fig. 1, on the electrode supporting plate 1 is arranged the tubular insulator 2 concentrically about the lead-in pin 3. The lead-in pin has an enlarged head portion 3a in the region of the upper cooled part of the electrode lead-in assembly. The outer diameter of the lead-in pin 3 is less than the internal diameter of the insulator sleeve 2 so that the long narrow space 4 Will be provided. This space has a length of at least two centimeters and a Width less than five millimeters. This spacing efiiciently prevents the penetration of fine electrical ignition and conductive substances and the formation of leakage paths at the anode and grid conductors. Thus the insulator is arranged in the cool part of the electrode lead-in assembly to avoid the danger that the insulating material should become a semi-conductor due to high temperature. The cool part of the electrode lead-in assembly thus Will not be adversely affected when the conductor is further heated by an additional heating element, for example the resistance coil 10, and by this means mercury vapor condensation is prevented. The temperature will advantageously be confined above the saturated steam temperature of the mercury vapor in a vacuum.

Referring now to Fig. 2, an electrode lead-in assembly is illustrated having an auxiliary anode around which is positioned a protective shell 7. Similar parts in the figures have been given the same reference numerals for clarity. Arranged about the lead-in pin 3 is an additional tubular insulator 5. This insulator creates two long narrow gaps 4, 6 between the outer surface of the pin 3 and the internal surface of the auxiliary insulator 5 and between the outer surface of insulator 5 and the internal surface of the insulator 2. The risk of leakage path formation by deposition of electrical ignition and conducting substances on the insulators is effectively impeded by means of the double spacings.

Fig. 3 shows an electrode lead-in arrangement for a main anode wherein the insulator 2 has a bell-shaped configuration. Concentrically arranged about and spaced from the auxiliary tubular insulator 5 is a grid shell 8 which has a reverse flange 8b at its upper end. The shell 8 contacts the bell-shaped insulator 2 at its upper extremity 8a. Between the flange 8b and the inner surface of the bell-shaped insulating sleeve 2 an additional protective space 9 is provided by means of which the protective spacing operation is further improved. The remotely-arranged grid terminals 13 are provided with grid insulators 12 in a manner similar to the arrangement of Fig. 1 to provide intermediate protective spacings.

illustratedand described the best embodiments of our invention now known to us, it will be apparent to those skilled in the art that other changes and embodiments maybe made in the apparatus described without deviating from the scope of our invention as set forth in the following claims.

We claim: V 3

l. A vacuum-tight electrode lead-in assembly for mercury vapor rectifiers comprising a horizontal electrode supporting plate having an aperture therein, an electrode lead-in pin extending vertically through and spaced from the walls of the aperture in said supporting plate, said lead-in pin having an enlarged head portion at the upper end thereof, a first electrode secured to the lower end of said lead-in pin, a bell-shaped insulating sleeve mount ed concentrically about and spaced from the upper portion of said lead-in pin, said insulating sleeve being contiguous at its lower extremity to the upper surface of the supporting plate and contiguous at its upper extremity to the lower surface of the head portion of the lead-in pin to support the lead-in pin'and the electrode connected thereto, said bell-shaped insulating sleeve having a configuration converging upwardly from a larger internal diameter at its lower end to a smaller internal diameter 4. s s at its upper end, a conductive lead-in shell concentrically mounted about said lead-in pin and the electrode connected thereto, said lead-in shell being intermediate and spaced from the lead-in pin and the walls of the aperture in the supporting plate, said lead-in shell extending at its lower end below said first electrode, an auxiliary electrode secured to said lead-in shell below said first electrode, said lead-in shell at its upper end having a generally downwardly extending outer reversed flange portion, the upper extremity of said lead-in shell being contiguous with a portion of the inner surface of the bellshaped insulating sleeve, means for supporting said leadin shell from said supporting plate, and a tubular insulator concentrically mounted about and spaced from said lead-in .pin, said tubular insulator being spaced from the upper portion ofsaid bell-shaped sleeve and the upper portion of said lead-in shell. s

2. Apparatus as defined in claim 1 and further including heating means concentrically mounted about and spaced from said bell-shaped insulating sleeve for preventing condensation of mercury on the inner surface thereof.

References Cited in the file of this patent nruren STATES PATENTS 2,522,902 Shamos Sept. 19, 1950

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