Aug. ll, 1959 H. V. DRYER 2,899,587 LIGHTNING ARRESTER Filed Aug. l. 1956

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~ IN VEN TOR. Heng» Z/'ßf‘y‘er .. Mem, @gâte 2,399,587 Patented Aug. l1, 1959

2 It is, therefore, a primary object of the present inven tion to provide an evacuated spark gap assembly for a lightning arrester. 2,899,587 Another object of the present invention is to provide LIGHTNING ARRESTER a spark gap assembly for lightning arrester application, wherein said lightning arrester includes a non-linear valve Henry V. Dryer, South Milwaukee, Wis., assignor to element, and wherein at least the spark gap assembly is McGraw-Edison Company, a corporation of Delaware contained in an evacuated housing. Application August 1, ‘1956, Serial No. 601,480 It is a further object of this invention to provide a 10 single series spark gap in serial arrangement with a light 1 Claim. (Cl. 313-182) ning arrester valve element or other means for limiting follow current, and wherein at least- the spark gap por tion is maintained under evacuated conditions. Still another object of the present invention is to pro The present invention relates to lightning arresters for vide an improved lightning arrester including a spark protecting electric power lines and equipment, and is par gap assembly of relatively short length and minimum ticularly directed to an improved spark gap assembly in number of parts, thereby materially reducing manufac combination therewith. turing costs in fabrication andv assembly and further pro It has long been conventional practice to provide light viding a unit ofïcompact construction for ease in mount ning arresters a spark gap assembly comprising a pile of 20 ing with relation to equipment to be protected thereby. spaced apart electrodes delining a plurality of series spark A still'further-object of the presentv invention is to gaps. The electrode assembly is positioned to be in serial provide an improvedv lightning arrester including an evac electrical arrangement with a valve element in the form uated spark gap ass‘emblyin combination with-a non of a non-linear resistance material, such as silicon car linear resistance valve element in which the inherent im bide. The silicon carbide crystals may consist of indi 25 pedance of the arrester components regulates itself to cur vidually molded blocks stacked in the arrester housing, rent flowing'and thereby provides not only follow-current or may be in the form of a solid mass molded directly limitation, but also adequate voltage limitation when to the housing, or, in certain cases, loose grain is packed high lightning 'currents liow Athrough the arrester. into the housing. In any case, the spark gap assembly Referring now to the drawing: is conventionally provided to work under atmospheric 30 Fig.v l is a vertical elevational view, partly in section, pressure, except perhaps, for an hermetic seal provided to of a lightning arrester adopting yone embodiment of the maintain a moisture-proof atmosphere internally of the present invention. arrester housing. Fig. 2 is a vertical sectional view ofthe spark gap as It is also appreciated that the prior art contains various sembly portion, greatly enlarged, and removed from the spark gap assemblies arranged in evacuated envelopes. 35 housing. However, nearly all of the heretofore presented embodi Fig. 3 is /a fragmentary sectional view of a portion ments were self-contained to function on communica of a spark gap ­assembly disclosing another embodiment tion or other relatively low power electric lines where of the present invention. available power follow current was negligible when com The embodiment of Figs. 1 and 2` of Athe present arrester pared to current available in power distribution or trans 40 comprises a spark' gap? assembly denoted generally by mission circuits. Obviously, no current limiting means the reference numeral 1, and which‘may be accommo was required for such purposes. In fact, in recent years dated to alightning 'arresterofanyof the conventional the development of the modern signal type arresters has types. However, it'is shown herein» as being enclosed led away from evacuated embodiments to relatively loose in the chamber of a porcelain housing 2 which is pro fitting housings enveloping a simple set of gap electrodes vided with a series of axially spaced skirts or petticoats 45 with interposed ceramic insulators. 3, and includes'conducting metal end caps 4 Iand 5. The It is also to be noted that a very recent contribution porcelain housing 2 is‘l sealed at= each4 end by means of to the lightning protection iield is disclosed as an evac compressing and retaining av heavy resilient gasket 6 be uated spark gap assembly intended for protection of high tween ‘the housing and a conducting -cap 7, which is spun voltage lines. However, no means is provided to limit 50 in place over the'annular'flange portion 8 of the housing available power follow current. A spark gap, no mat while the assembly is under pressure in a hydraulic press. ter how formed, when not provided with some means The end‘caps are held in place adjacent the housing by for limiting this current, is in itself limited in applica means of a cement'9r poured between the end cap and tion by the available short-circuit current. A spark the housing. gap assembly used alone is generally dependent upon 55 The electric line 10 to be protected by the lightning back-up devices such as fuse cutouts or circuit breakers arrester is connected to the conducting end cap 4 by to handle power current interruption. means of-conventional connectors (not shown) received In addition, a spark gap assembly, even when working in an aperture in one of the integral >laterally projected properly to interrupt follow current will add a momen ears 11. Connection with ground G may be made in like tary strain on all equipment during this abrupt action, manner with a projecting ear» 12 of the conducting end 60 unless such assembly is combined with a power follow cap 5. Contained within the housing 2 is a conventional current limiting means. valve material 15 of suitable quantity and generally com The present invention contemplates the provision of prising valve blocks or a solid mass of negative resistance a lightning arrester spark gap assembly for use with a material, such as silicon carbide. non-linear valve material, wherein at least the spark gap Although the spark gap-assembly 1 has been shown 65 assembly is maintained under evacuated conditions. Un as being mounted’ at‘one end of the lightning arrester, der such conditions, it has been observed that even in it is1wi'th'in- thefprovince of the present invention to provide the case of a single series gap, this gap will interrupt assemblies at either or at both ends thereof, or in inverted power follow currents of over three times the magnitude relationship'from the> position shown, ifso desired. of conventional arresters having as many as 13 individual _ In detail, the spark gap assembly lvof'the arrester ern gaps defining a total air gap space of over 50 times the 70 bodiment disclosed-in‘Figs. l and 2, comprises-a glass gap setting dimension of the single evacuated gap. shell 20 with its external surface preferably being cor-v 2,899,587 3 4 rugated, as shown, to provide an extended creepage and tance effects provided by a coiled spring conductor under flashover distance between terminal connections. The surge current conditions. „ glass shell is closed at its upper end as shown in Fig. 2, The second embodiment of the present invention is dis by means of a cup-shaped terminal cap 21, which is closed in detail in Fig. 3, and provides a non-adjustable formed with an annularinwardly disposed ñange 22 to spark gap assembly for use in lightning arresters capable provide stress relief as a means of minimizing the effects of being mass-produced at selected voltage ratings. That of corona discharge. A conventional metal-to-glass seal is, in the embodiment of Figs. l and 2, the spark gap is provided between the shell 20 and the cap 21 with the setting 30 is adjustable by means of the nut 31 engaging aid of an annular ring 23 externally of the shell and hav the threaded portion of the axially movable electrode ing a flanged margin contacting the cap 21. 10 29. Thus, factory adjustment may be made for a par The lower end of the shell 20, as shown in Fig. 2, is ticular arrester from previously fabricated and stocked also provided with a cup-shaped cap 24 also having an spark gap assemblies 1. annular flange portion 22 extending towards the cap 21 However, in the embodiment of Fig. 3, it will be ap to complete the relief of stresses occurring during any parent that the various components of the spark gap as corona discharge. The glass shell 20 also engages a con 15 sembly are substantially identical, except for the fact ducting sleeve-like fitting 25 at its lower end, and is sealed that the electrode 50 is statìonarily secured to the fitting thereto with a conventional metal-to-glass seal aided by 51 to provide a preselected and non-adjustable gap setting. the ring-like member 23. In the present case, the upper Again the shield or tube 35 is provided and has a baliie spark gap electrode 26 is stationarily secured to the re for condensing metal vapor which is adapt to lessen the cessed portion 27 of the cap 21 and is in electrical Contact 20 ñashover distance of the shell 20. The shell 20 is sealed therewith. It will be apparent from Fig. l that the cap at its lower end to the cup-shaped cap 24 and is retained 21 is conducting and electrically engages the spun cap 7 in place by the ring 23. The construction is again evacu of the arrester to complete the circuit through the end ated to the greatest extent possible, which at this time cap 4 to line 10. The electrode member 26 is preferably is in the neighborhood of about 0.1 micron of mercury. of tungsten, or may be of a steel rod having a tungsten 25 As an illustration of the unexpected and successful arcing portion 28 to provide a lesser expensive construc operation of the arrester, various tests were conducted tion than of a rod composed entirely of tungsten. with a selection of gap spacings. Both 60-cyc1e and front The opposed or lower gap electrode 29 is preferably of-wave sparkover tests were run. of similar material as the electrode 26 and is adjustable Tests conducted on the samples with the fixed gap set as shown in the embodiment of Figs. 1 and 2 and pro 30 ting in the range of approximately 0.01" to 0.1" indicated vides a variable spark gap 30 with the electrode 26. The that even with a single high vacuum gap with a spacing electrode 29 is axially slidable relative to the sleeve-like of between 0.01” and 0.015", this gap could readily fitting 25, and is preferably threaded at the end to engage interrupt follow currents of over 400 amperes with 15 an adjusting stop nut 31, abutting the projecting fitting kv. applied 60­cycle voltage. This is compared to a con 25, for moving the electrode in an axial direction to pro 35 ventional arrester gap structure employing 13 individual vide a predetermined gap setting. gaps with total air gap space of approximately 3A”, which The electrode 29 is provided with an hermetically is only capable of interrupting follow currents on the sealed bellows 32, which is preferably of bronze, and order of 50 to 150 amperes at l5 kv. terminates at one end in sealed relationship with the Although the electrodes 26 and 29 and 50 have been sleeve-like fitting 25. The bellows permits axial move 40 illustrated in their preferred rod-like embodiment, it is ment of the electrode 29 without breaking the vacuum within the Yscope of the present invention to provide them within the chamber of the shell 20. The shell 20 is in any of many known forms such as plates or disk-like evacuated in the conventional manner to provide a very members with supporting spacers (not shown). Other hard vacuum in the neighborhood of 0.1 micron of mer shell configurations and changes in operating components cury, or as low as available high vacuum technique will will also occur to one skilled in the art without departing provide. The bellows 32 is sealed at its upper end to a from the broad aspects of this invention. disk-like cap 33 providing an air tight seal with the It will also be readily appreciated that it is within the movable electrode 29. ‘ scope of this invention to provide separate housing mem The use of tungsten or similar high melting tempera~ bers, structurally independent of one another, but ar ture and refractory metals as the gap electrodes minimizes 50 ranged for electrical connection with one another; one vaporization of the electrodes during arcing. It is im housing to contain the evacuated gap electrodes, while the possible, however, to prevent all vaporization of elec other would contain the Valve element. Such construc trode metal. Without a baffle or barrier means of some tion would readily lend itself to providing an adjustable kind, the vaporized metal condenses on the inside surface gap which may be stocked by a manufacturer for use with of the glass shell 20, and builds up thereon a conducting 55 a variety of arrester valve housings, the gap to be ad~ layer which eventually will develop into a short between justed for use with a certain size valve housing member. the electrodes. This is prevented for the most part by It will be apparent that the present invention has pro surrounding the gap 30 with a member of vitreous mate vided an improved lightning arrester of simplified and _rial such as a glass baffle or shield- tube 35. The tube compact construction, which in its preferred form, pro 1s supported by the shell at its upper end and includes 60 vides a single spark gap setting in an evacuated atmos` an aperture 36 at its lower end so as to provide an ex phere and capable of interrupting power follow currents of much higher magnitude than conventional arresters tended leakage path between the electrodes. The tube having a plurality of gaps together defining a relatively 35 1s also preferably provided with an annular groove 37 for further constricting the member in the vicinity of the large total gap spacing. 65 I claim: gap 30 .to act as a means of accelerating the dispersion of A lightning arrester for heavy duty power circuit any arclng gases or metal vapor away from the gap. use including an elongated housing of dielectric material, _ As wlll be seen from Fig. 1, the assembly is mounted connector end caps cooperating with said housing to deiine 1n serial arrangement with the valve element 15 and a closed elongated chamber, a non-linear resistance valve rests_on a conducting plate 40, being held in compressive 70 element positioned in one end of said chamber, and a _relationship therewith by means of the coiled spring 4I removable spark gap unit positioned in the other end of lnterposed' therebetween.A The spring 41 is preferably said chamber, said unit including an evacuated envelope of shunted by a conducting flexible braid, or as shown, by dielectric material having conducting terminal caps at means of a conducting ñexible strap 42. The Shllllf opposite ends thereof, one of said terminals being in eliminates any problem of introducing any'illdlgçtive reac 75 electrical ponpection with a connecting end cap and the 2,899,587 6 other of said terminals being in electrical connection with may be moved while maintaining the evacuated condition said valve element, a pair of opposed elongated spark gap of said envelope. electrodes each respectively in engagement with a con ducting terminal cap, one of said electrodes being ad References Cited in the ñle of this patent justably movable toward and away from the other to vary UNITED STATES PATENTS the dimension of the spark gap, an elongated vitreous 1,024,555 Chapman ______.___ Apr. 30, 1912 shield surrounding said electrodes and said spark gap 1,111,453 Giles ______.. Sept. 22, 1914 inside of said evacuated envelope, said shield being open ' 2,163,697 Mittelstadt ______June 27, 1939 at at least one end with the movable electrode extending 2,414,308 Kalb ______Jan. 14, 1947 through said open end, means to adjust and íìx the mov 10 2,511,338 Jennings ______June 13, 1950 able electrode in a selected adjusted position, and an hermetically sealed bellows in operable association with FOREIGN PATENTS said adjusting means whereby said adjustable electrode 418,964 Great Britain ______Nov. 2, 1934