Lost gas indicator for gas tube lightning arrestors
United States Patent 1 1 1111 3,875,465 Riedel 1 Apr. 1, 1975 [5 1 LOST GAS INDICATOR FOR GAS TUBE 2,064,369 12/1936 Biggs 313/221 2,429,420 10/1947 McMaster 313/221 LIGHTING ARRESTORS Inventor: Charles E. Riedel, Villa Park, 111.  
 Assignee: GTE Automatic Electric Laboratories Incorporated, Northlake, 111.  
 Filed: Oct. 18, 1973 Appl. No.: 407,685  
 U.S. Cl. 317/61, 317/62 int. Cl. H02h 3/22 Field oi Search 317/61, 61.5, 62; 313/220,  
 313/221, DIG. 5; 117/97, 95  
 References Cited UNITED STATES PATENTS Primary Examiner-J. D. Miller Assistant ExaminerPatrick R. Salce Attorney, Agent, or FirmRobert J. Black [57] ABSTRACT Agas tube lightning arrestor includes a glass or ceramic envelope upon the ends of which are disposed disk-type electrodes and upon the interior surface of which is deposited a coating of a dessicant electrolyte. During normal operation, the electrolyte remains inert, but upon the occurence of gas leakage, atmospheric moisture is able to leak into the envelope and react with the electrolyte rendering the same conductive, such phenomena causing talking noise and/or excessive loop conductance, the latter conditions being detectable by conventional means during the course of normal plant operations.  
 8 Claims, 2 Drawing Figures LOST GAS INDICATOR FOR GAS TUBE LIGHTING ARRESTORS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to gas tube lightning arrestors and more particularly to an improved gas tube lightning arrestor which provides an electrical indication of the leakage and loss of the pressurized, inert gaseous atmosphere within the arrestor.  
 2. Description of the Prior Art While several different types of lightning arrestors, such as for example, the carbon-block type and air-gap type, have been utilized in the past as means of protecting subscriber and office equipment from electrical surges, modern telephonic systems are employing gas tube lightning arrestors with ever increasing frequency, the primary reason being the increased service life, that is, the number of repeated surges of average magnitude which a device can withstand without failure.  
  However, caution must be exercised when employing gas tube lightning arrestors for should the arrestor gastight integrity fail, the rare gas would be lost and the internal pressure altered to substantially that of the ambient atmosphere, the breakdown voltage of the device being increased by several thousand volts and consequently the arrestor can no longer function usefully in protecting the particular associative equipment. A structural failure within such arrestors could occur for example, within the vicinity of the glass-to-metal seal existing between the glass tubing and the metallic electrodes. Whenever two such radically different materials must be joined in a gas-tight sealing arrangement that is designed to last for years, various factors, such as for example, improper bonding and unequal rates of expansion associated with the metal and insulator components, could eventually result in structural fatigue and failure.  
  In view of the foregoing, companies utilizing gas tube lightning arrestors must conduct periodic tests of the individual devices in order to determine if they are still providing the requisite protection. Such means of detecting gas leakage however is inconvenient and sometimes impossible within telephone plants and telephonic systems.  
 SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved gas tube lightning arrestor which will eliminate the aforementioned problems and disadvantages.  
  Another object of the present invention is to provide an improved gas tube lightning arrestor which will automatically indicate the loss of inert gas from the lightning arrestor.  
  Still another object of the present invention is to provide an improved gas tube lighting arrestor which will provide an electrical indication of when the inert gas pressure is lost from the arrestor, such indication being detected by conventional means.  
  The foregoing objectives are achieved according to the present invention through the provision of a gas tube lightning arrestor which includes a glass or ceramic envelope upon the ends of which are disposed disk-type electrodes and upon the interior surface of which is deposited a coating of a dessicant electrolyte. During normal operation, the electrolyte remains inert,  
 but upon the occurence of gas leakage, such as for example, during a lightning induced arc, upon cessation of the are, atmospheric moisture is able to leak into the envelope and react with the electrolyte rendering the same conductive, such phenomena causing talking noise and/or excessive loop conductance, the latter conditions being detectable by conventional means during the course of normal telephonic plant operations.  
 BRIEF DESCRIPTION OF THE DRAWINGS Various other objects, features, and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description when considered in connection with the accompanying drawings, in which like reference characters designate like or corresponding parts throughout the several views, and wherein:  
  FIG. 1 is a perspective view of a section of glass or ceramic tubing having a dessicant electrolyte coated upon the interior surface thereof; and  
  FIG. 2 is a perspective view of the tubing of FIG. 1 having suitable electrodes sealed thereto so as to form a gas tube lightning arrestor in accordance with the present invention.  
 DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, the gas tube lightning arrestor of the present invention is generally indicated by the reference character 10 and is seen to include an envelope 12 which may be either glass or ceramic tubing, disk-type metallic electrodes I4 being disposed upon the end portions thereof and adapted for connection to appropriate circuitry. In the instance that glass tubing is employed, the interior surface of the tubing is initially etched or frosted in order to render the same sufficiently coarse and adherent so as to be able to retain coated material thereon, such processes being unnecessary in the case of ceramic due to the fact that such material is inherently coarse to the requisite degree.  
  In preparing the envelope 12 for use within the assembled lightning arrestor 10, a solution, not necessarily aqueous, of a dessicant electrolyte material is deposited within the tubing and subsequently dried whereupon the entire interior surface of the tubing is able to be coated therewith, as noted at 16. Sections of tubing of several feet in length may be so coated by dipping the same in a saturated solution, repetition of the dipping and drying processes resulting in an increase in the coating thickness, as a saturated solution will not dissolve previous coating layers.  
  The exterior surfaces of the tubing sections are then washed and the sections severed so as to provide smaller tubing sections of such length as is desired in formulating lightning arrestors in accordance with the present invention. The electrodes 14 are then mounted upon the end portions of the envelopes l2 and the assemblies placed within a vacuum chamber whereupon the air being evacuated, the desired noble, inert gases, such as for example, argon, are introduced therewithin to a pressure of approximately one-fourth atmosphere.  
  In order to provide rapid arrestor breakdown during the occurence of fast-rising surges, the inert gas may contain minute traces of a radioactive element which serves to partially ionize the gas, the low pressure within the arrestor, in addition to the use of the radioactive material, permitting the arrestor assemblies to exhibit breakdown voltages equal to conventional carbon&#39;block arrestors while the electrode spacing is considerably greater than that existing within such conventional arrestors. As a result of such electrode spacing, the likelihood of electrode fragments being severed from the electrodes and becoming lodged within the spacing or gap and thereby grounding the arrestor, is substantially lessened.  
  Subsequent to the introduction of the inert gas within the envelope l2, suitable sealing means, such as for example, boron nitride, may be utilized to seal the envelopc relative to the electrodes 14, whereupon the assembly may be cured at temperatures approximating 300C in the instance of boron nitride. During normal arrestor operation, the dessicant electrolyte [6 remains inert, and the coating thickness is such that resistance between the electrodes 14 may be in excess of l megohm, the thickness of course being adjustable so as to result in any other desired resistance value.  
  If gas leakage should occur during a lightning induccd arc, the elevated temperature and pressure within the envelope normally attending a lightning surge prevents the admission of air therewithin and consequently moisture within the air is not able to react with the electrolyte l6 and normal protector operation occurs. Upon the occurence of quiescent conditions however, the temperature and pressure within the envelope I2 is sharply decreased and atmospheric moisture is able to enter the envelope and react with electrolyte 16 rendering the same electrically conductive. The protector resistance is decreased to a value well below I megohm within a time period ranging from minutes to hours, such resulting in the generation of talking noise and/or excessive loop conductance, both phenomena being capable of detection by conventional means during normal plant operation. The defective arrestor may then of course be replaced.  
  It should be noted that during power line crossing conditions wherein a high current are is maintained within the arrestor for several seconds or minutes, the dessicant electrolyte may tend to fuse and react with the glass or ceramic envelope l2 and under such conditions, conventional solder-pellet failsafe structures provided within such gas tube protectors are expected to operate so as to short-circuit the line, whereupon the protector must also be replaced. Since certain somewhat unknown levels of power cross current could fuse the dessicant electrolyte but not cause gas leakage nor solder-pellet operation, it is additionally important to select an envelope. material which softens near and slightly below the fusing temperature of the dessicant electrolyte. As a result of such selection, gas leakage and its electrical indication, is insured prior to the destruction of the arrestor assembly.  
  Examples of dessicant electrolytes which may be employed within the gas tube lightning arrestor of the present invention are as follows:  
  Thus, it may be seen that the gas tube lightning arrestor of the present invention has important advantages over the known prior art structures in that the arrestor provides an automatic electrical indication of gas leakage therefrom and defective protection thereby, which may be readily detected by conventional means, such improved arrestors thereby eliminating the need for conducting periodic testing of individual lightning arrestors within protector systems.  
  Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is to be understood therefore, that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.  
  What is claimed as new and desired to be secured by Letters Patent of the United States is:  
 l. A gas tube lightning arrestor comprising:  
 a tubular envelope;  
 a pair of electrodes respectively sealed upon the end portions of said tubular envelope;  
 an inert, pressurized gas disposed within said envelope; and  
 means within said envelope for automatically indicating leakage of said gas from said envelope comprising a dessicant electrolyte coated upon the interior surface of said envelope and which during normal operation of said arrestor remains inert but upon the occurrence of leakage of said gas from said envelope and admission of air within said envelope, atmospheric moisture is able to react with said electrolyte rendering the same electrically conductive.  
  2. A gas tube lightning arrestor as set forth in claim I, wherein the thickness of said coating of said electrolyte may be adjusted so as to attain a particular resistance value between said electrodes.  
  3. A gas tube lightning arrestor as set forth in claim 1, wherein said tubular envelope is ceramic.  
  4. A gas tube lightning arrestor as set forth in claim I, wherein said tubular envelope is etched glass.  
  5. A gas tube lightning arrestor as set forth in claim 1, wherein said tubular envelope is frosted glass.  
  6. A gas tube lightning arrestor as set forth in claim 1, wherein said inert gas is argon.  
  7. A gas tube lightning arrestor as set forth in claim 1, wherein said dessicant electrolyte is CaCl 8. A gas tube lightning arrestor as set forth in claim 1, wherein said dessicant electrolyte is in electrical contact with each of said pair of electrodes.