US2899587A - Lightning arrester - Google Patents

Description

H. V. DRYER LIGHTNING ARRESTER Aug. ll, 1959 Filed Aug. l. 1956 lli - IN VEN TOR.

Heng Z/'fyer Mem, @gte 2,399,587 Patented Aug. l1, 1959 LIGHTNING ARRESTER Henry V. Dryer, South Milwaukee, Wis., assignor to McGraw-Edison Company, a corporation of Delaware Application August 1, 1956, Serial No. 601,480

1 Claim. (Cl. 313-182) The present invention relates to lightning arresters for protecting electric power lines and equipment, and is particularly directed to an improved spark gap assembly in combination therewith.

It has long been conventional practice to provide lightning arresters a spark gap assembly comprising a pile of spaced apart electrodes delining a plurality of series spark gaps. The electrode assembly is positioned to be in serial electrical arrangement with a valve element in the form of a non-linear resistance material, such as silicon carbide. The silicon carbide crystals may consist of individually molded blocks stacked in the arrester housing, or may be in the form of a solid mass molded directly to the housing, or, in certain cases, loose grain is packed into the housing. In any case, the spark gap assembly is conventionally provided to work under atmospheric pressure, except perhaps, for an hermetic seal provided to maintain a moisture-proof atmosphere internally of the arrester housing.

It is also appreciated that the prior art contains various spark gap assemblies arranged in evacuated envelopes. However, nearly all of the heretofore presented embodiments were self-contained to function on communication or other relatively low power electric lines where available power follow current was negligible when compared to current available in power distribution or transmission circuits. Obviously, no current limiting means was required for such purposes. In fact, in recent years the development of the modern signal type arresters has led away from evacuated embodiments to relatively loose fitting housings enveloping a simple set of gap electrodes with interposed ceramic insulators.

It is also to be noted that a very recent contribution to the lightning protection iield is disclosed as an evacuated spark gap assembly intended for protection of high voltage lines. However, no means is provided to limit available power follow current. A spark gap, no matter how formed, when not provided with some means for limiting this current, is in itself limited in application by the available short-circuit current. A spark gap assembly used alone is generally dependent upon back-up devices such as fuse cutouts or circuit breakers to handle power current interruption.

In addition, a spark gap assembly, even when working properly to interrupt follow current will add a momentary strain on all equipment during this abrupt action, unless such assembly is combined with a power follow current limiting means.

The present invention contemplates the provision of a lightning arrester spark gap assembly for use with a non-linear valve material, wherein at least the spark gap assembly is maintained under evacuated conditions. Under such conditions, it has been observed that even in the case of a single series gap, this gap will interrupt power follow currents of over three times the magnitude of conventional arresters having as many as 13 individual gaps defining a total air gap space of over 50 times the gap setting dimension of the single evacuated gap.

It is, therefore, a primary object of the present invention to provide an evacuated spark gap assembly for a lightning arrester.

Another object of the present invention is to provide a spark gap assembly for lightning arrester application, wherein said lightning arrester includes a non-linear valve element, and wherein at least the spark gap assembly is contained in an evacuated housing.

It is a further object of this invention to provide a single series spark gap in serial arrangement with a lightning arrester valve element or other means for limiting follow current, and wherein at leastthe spark gap portion is maintained under evacuated conditions.

Still another object of the present invention is to provide an improved lightning arrester including a spark gap assembly of relatively short length and minimum number of parts, thereby materially reducing manufacturing costs in fabrication andv assembly and further providing a unit ofcompact construction for ease in mounting with relation to equipment to be protected thereby.

A still'further-object of the presentv invention is to provide an improvedv lightning arrester including an evacuated spark gap assemblyin combination with-a nonlinear resistance valve element in which the inherent impedance of the arrester components regulates itself to current flowing'and thereby provides not only follow-current limitation, but also adequate voltage limitation when high lightning 'currents liow Athrough the arrester.

Referring now to the drawing:

Fig.v l is a vertical elevational view, partly in section, of a lightning arrester adopting yone embodiment of the present invention.

Fig. 2 is a vertical sectional view ofthe spark gap assembly portion, greatly enlarged, and removed from the housing.-

Fig. 3 is /a fragmentary sectional view of a portion of a spark gap assembly disclosing another embodiment of the present invention.

The embodiment of Figs. 1 and 2` of Athe present arrester comprises a spark' gap? assembly denoted generally by the reference numeral 1, and whichmay be accommodated to alightning 'arresterofanyof the conventional types. However, it'is shown herein as being enclosed in the chamber of a porcelain housing 2 which is provided with a series of axially spaced skirts or petticoats 3, and includes'conducting metal end caps 4 Iand 5. The porcelain housing 2 isl sealed at= each4 end by means of compressing and retaining av heavy resilient gasket 6 between the housing and a conducting -cap 7, which is spun in place over the'annular'flange portion 8 of the housing while the assembly is under pressure in a hydraulic press. The endcaps are held in place adjacent the housing by means of a cement'9r poured between the end cap and the housing.

The electric line 10 to be protected by the lightning arrester is connected to the conducting end cap 4 by means of-conventional connectors (not shown) received in an aperture in one of the integral laterally projected ears 11. Connection with ground G may be made in like manner with a projecting ear 12 of the conducting end cap 5. Contained within the housing 2 is a conventional valve material 15 of suitable quantity and generally comprising valve blocks or a solid mass of negative resistance material, such as silicon carbide.

Although the spark gap-assembly 1 has been shown as being mounted atone end of the lightning arrester, it is1wi'th'inthefprovince of the present invention to provide assemblies at either or at both ends thereof, or in inverted relationship'from the position shown, ifso desired.

In detail, the spark gap assembly lvof'the arrester ernbodiment disclosed-inFigs. l and 2, comprises-a glass shell 20 with its external surface preferably being cor-v rugated, as shown, to provide an extended creepage and flashover distance between terminal connections. The glass shell is closed at its upper end as shown in Fig. 2, by means of a cup-shaped terminal cap 21, which is formed with an annularinwardly disposed ange 22 to provide stress relief as a means of minimizing the effects of corona discharge. A conventional metal-to-glass seal is provided between the shell 20 and the cap 21 with the aid of an annular ring 23 externally of the shell and having a flanged margin contacting the cap 21.

The lower end of the shell 20, as shown in Fig. 2, is also provided with a cup-shaped cap 24 also having an annular flange portion 22 extending towards the cap 21 to complete the relief of stresses occurring during any corona discharge. The glass shell 20 also engages a conducting sleeve-like fitting 25 at its lower end, and is sealed thereto with a conventional metal-to-glass seal aided by the ring-like member 23. In the present case, the upper spark gap electrode 26 is stationarily secured to the recessed portion 27 of the cap 21 and is in electrical Contact therewith. It will be apparent from Fig. l that the cap 21 is conducting and electrically engages the spun cap 7 of the arrester to complete the circuit through the end cap 4 to line 10. The electrode member 26 is preferably of tungsten, or may be of a steel rod having a tungsten arcing portion 28 to provide a lesser expensive construction than of a rod composed entirely of tungsten.

The opposed or lower gap electrode 29 is preferably of similar material as the electrode 26 and is adjustable as shown in the embodiment of Figs. 1 and 2 and provides a variable spark gap 30 with the electrode 26. The electrode 29 is axially slidable relative to the sleeve-like fitting 25, and is preferably threaded at the end to engage an adjusting stop nut 31, abutting the projecting fitting 25, for moving the electrode in an axial direction to provide a predetermined gap setting.

The electrode 29 is provided with an hermetically sealed bellows 32, which is preferably of bronze, and terminates at one end in sealed relationship with the sleeve-like fitting 25. The bellows permits axial movement of the electrode 29 without breaking the vacuum within the chamber of the shell 20. The shell 20 is evacuated in the conventional manner to provide a very hard vacuum in the neighborhood of 0.1 micron of mercury, or as low as available high vacuum technique will provide. The bellows 32 is sealed at its upper end to a disk-like cap 33 providing an air tight seal with the movable electrode 29.

The use of tungsten or similar high melting temperature and refractory metals as the gap electrodes minimizes vaporization of the electrodes during arcing. It is impossible, however, to prevent all vaporization of electrode metal. Without a baffle or barrier means of some kind, the vaporized metal condenses on the inside surface of the glass shell 20, and builds up thereon a conducting layer which eventually will develop into a short between the electrodes. This is prevented for the most part by surrounding the gap 30 with a member of vitreous material such as a glass baffle or shieldtube 35. The tube 1s supported by the shell at its upper end and includes an aperture 36 at its lower end so as to provide an extended leakage path between the electrodes. The tube 35 1s also preferably provided with an annular groove 37 for further constricting the member in the vicinity of the gap 30 .to act as a means of accelerating the dispersion of any arclng gases or metal vapor away from the gap.

As wlll be seen from Fig. 1, the assembly is mounted 1n serial arrangement with the valve element 15 and rests on a conducting plate 40, being held in compressive relationship therewith by means of the coiled spring 4I lnterposed' therebetween.A The spring 41 is preferably shunted by a conducting flexible braid, or as shown, by means of a conducting exible strap 42. The Shllllf eliminates any problem of introducing any'illdlgtive reactance effects provided by a coiled spring conductor under surge current conditions.

The second embodiment of the present invention is disclosed in detail in Fig. 3, and provides a non-adjustable spark gap assembly for use in lightning arresters capable of being mass-produced at selected voltage ratings. That is, in the embodiment of Figs. l and 2, the spark gap setting 30 is adjustable by means of the nut 31 engaging the threaded portion of the axially movable electrode 29. Thus, factory adjustment may be made for a particular arrester from previously fabricated and stocked spark gap assemblies 1.

However, in the embodiment of Fig. 3, it will be apparent that the various components of the spark gap assembly are substantially identical, except for the fact that the electrode 50 is statonarily secured to the fitting 51 to provide a preselected and non-adjustable gap setting. Again the shield or tube 35 is provided and has a baliie for condensing metal vapor which is adapt to lessen the ashover distance of the shell 20. The shell 20 is sealed at its lower end to the cup-shaped cap 24 and is retained in place by the ring 23. The construction is again evacuated to the greatest extent possible, which at this time is in the neighborhood of about 0.1 micron of mercury.

As an illustration of the unexpected and successful operation of the arrester, various tests were conducted with a selection of gap spacings. Both 60-cyc1e and frontof-wave sparkover tests were run.

Tests conducted on the samples with the fixed gap setting in the range of approximately 0.01" to 0.1" indicated that even with a single high vacuum gap with a spacing of between 0.01 and 0.015", this gap could readily interrupt follow currents of over 400 amperes with 15 kv. applied 60cycle voltage. This is compared to a conventional arrester gap structure employing 13 individual gaps with total air gap space of approximately 3A, which is only capable of interrupting follow currents on the order of 50 to 150 amperes at l5 kv.

Although the electrodes 26 and 29 and 50 have been illustrated in their preferred rod-like embodiment, it is within the Yscope of the present invention to provide them in any of many known forms such as plates or disk-like members with supporting spacers (not shown). Other shell configurations and changes in operating components will also occur to one skilled in the art without departing from the broad aspects of this invention.

It will also be readily appreciated that it is within the scope of this invention to provide separate housing members, structurally independent of one another, but arranged for electrical connection with one another; one housing to contain the evacuated gap electrodes, while the other would contain the Valve element. Such construction would readily lend itself to providing an adjustable gap which may be stocked by a manufacturer for use with a variety of arrester valve housings, the gap to be adjusted for use with a certain size valve housing member.

It will be apparent that the present invention has provided an improved lightning arrester of simplified and compact construction, which in its preferred form, provides a single spark gap setting in an evacuated atmos` phere and capable of interrupting power follow currents of much higher magnitude than conventional arresters having a plurality of gaps together defining a relatively large total gap spacing.

I claim:

A lightning arrester for heavy duty power circuit use including an elongated housing of dielectric material, connector end caps cooperating with said housing to deiine a closed elongated chamber, a non-linear resistance valve element positioned in one end of said chamber, and a removable spark gap unit positioned in the other end of said chamber, said unit including an evacuated envelope of dielectric material having conducting terminal caps at opposite ends thereof, one of said terminals being in electrical ponpection with a connecting end cap and the other of said terminals being in electrical connection with said valve element, a pair of opposed elongated spark gap electrodes each respectively in engagement with a conducting terminal cap, one of said electrodes being adjustably movable toward and away from the other to vary the dimension of the spark gap, an elongated vitreous shield surrounding said electrodes and said spark gap inside of said evacuated envelope, said shield being open at at least one end with the movable electrode extending through said open end, means to adjust and x the movable electrode in a selected adjusted position, and an hermetically sealed bellows in operable association with said adjusting means whereby said adjustable electrode may be moved while maintaining the evacuated condition of said envelope.

References Cited in the le of this patent UNITED STATES PATENTS

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