US2623197A - Spark gap device - Google Patents

Description

J. W. KALB SPARK GAP DEVICE Filed Jan. 22, 1951 Dec. 23, 1952 IN V EN TOR.

JOHN H. K ALB ATTORNEY Patented Dec. 23, 1952 sPnRmGAP DEVICE 1 JohmW. Kalb',- Barberton, Ohio; assignorgto The; Ohio. Brass Company, Mansfie1d,-.0hio, a, .0011- poratiol'iioflNew. Jersey.

Applieationflanuar e 22, 1951;"Serial 1N6; 207518.3

Thisitinventio'rr. relatesrto; an;.-imp1;o.ved;;spa;1c.;- ductin -.po inez-l:' f oa e ted gape device. fonia :lightning:arresteriiotzthe. like; with. onerele tr de-o i heeanpd vice andya dlfi rw and:anzimprovedelementforause therein;

Sparleagap. devices; ;are:.:-forme.d .ot metal-.xelecz material. connected with it). is. placedcontlguous trodes;+.usua;l1y; brassr'which carezspaced.:.by;an .5 to the exposed surface-ofthe spacer,, sothat insulating;.materiahwhichimay:heppotcelainzorz it is. separatedfrom the conducting; material.105g v titaniumrdioxide;...(rutile:),...et Some sparkegamsz devices :includez,-inziaddition;:.to;- the; spacers;. .ine. sulatingmaterialin the; formoiayrod. or; the .likes f whichthe-yspacer is composei; whena hig-hm.

surface of the spacer adjacent. then-pointer, contiguity causing; rapid. and consistentbreakdown of the gap. Insteadot coatingthesurface oi;-

electnodesgiromnm :endcof Lthe spark-gap deyice; to .the, liotherz:

The-sparkegaps device; is idesignedzso. that; when: connected- -betweerna dine: and the; gmund; .1the.;; linei'wi'l'li;carmz:anyzusual;voltagehtiis designed" 15 10W 5! be fi l h 'a conductin l; P6 1 1? to carry; and;theasparlezgapsrwilll; pretentzzthisag. Other y of low nc curnent'fnom fiowingjnto;.the.-gro11nd;.;.l-lowever Also, according this ti Stance when lightning: strikesy...or;when..for .anyzsothenc; reason .thenecisian .electricrsurae of high voltages. adjacent Several electrodes Operating difi l throughzxthee:lineg. thez;;c11rr.ent:wilLdischargexZO em P maintain in a m m P 5 1 36?? acrossfjthe :gaps into theagmlmdu manner the difference in potential of the portions;

Generallyspeaking,:theimorflmipwlyiad51337111325.. of the insulating material nearestuthe differentgap,device-discharges:the.moreasatisfactory;itis P fi m t thereby to lessen thevefiecti f t e It iswineco m th t t gasinjhe s a 1on1z1ng tips in. inducingon theinsulating ma.- betweenfthfl electrodes: ofa ank an irsziomzedwg5 terial the, potentials 'ofthe respectiveeeleotrodes: therspank; gaps; dischareescrapidly' whencrsube from which they Project jected to.aihighiyqltaggmnpulse'i;. 3 isdflisghangeij To,.illustrat.e,. referenceis had to a cylindrical Occurs;.ahajmimmumwltage:Whm jnmdictabla: vporcelain rod located. in the centra1=- opening and cnnsistenh. a m orderitofiionizeithgampn gash through. a. plurality of electrodes with. one; ioniza it hasvfbeennpmposed to h .i i tig tipsxofiigo mg tip from. each electrodeadjacent the surface: conducting.material pnoiectqfromxthe.:e1ect11odes;;.. of the It is to bemnderstood of agsparkhgapganda-m lfqcatieijthem "figment-fin? electrodesare shaped sothat. inganiarea away; sulafing mammal WhereD thezsvoltagg. iidifiemnt; from the centralwopening spark gansare; formed: fromithecvolwgeiofiutheamspectgiqmzaltionctmsr... between them.. The voltage of eachofrthe-telece-l- Thewnearnessrofranionization o the insulat 3. trodes- Wm'be induced ing material. may influence th, voltage 1.0. :the latter. by tendine o bringgit tohe: oltage. of... the; electrode to whichthe ionization tip. 315 comb the length of ro'dasjriom one of nected. Thevv greater thev areatof-theionization: sparkggp m 0- the nit-hen Assmnmgothai? tip adjacent the insulating material.lthefigxeatgrvw theportion of each electrode adjacentlthe"central v thetendency to bringitswoltage-to .theevoltagee QPemng; perfectly andthat-theiomza'tion therelctmde-n tips projecting from the electrodes. ane..-contig;--

According-Ito this invention conductingfmaafl uoustothe porcelain rod in the respectivezplanesterila'ljjss-ljempldyed n combination with h i 5" OI thesefiat -DQItiDI1S .Of thevelectrodewthe :YQlti-- sulatir'rg material .tdlihcireasathe; voltage diff-em ential "between it land. ,one... or.. more ionization. tip contiguous to; it.i.by..maintaini'ng.,.th insu -e. lating material; atJa different. voltageilevel. than. a it wouldhavei'f. the conducting .material'lwere gaps,. there willbethe same-voltage ,dr -op over-2.

trode from which the. .tipprojects. Assuming: that the electrodes are all. of. the same, construe:

spacer or'insulating' rod; etc; malstiloiel holIowlecht and the} sunfagehof no'w g lain rod, there willbe a...voltage drop between thei conductingumateflal'g B-ause Qfvflthe) high?v each tw electrodes, and the,..intermediate:=porr-- trons of, the rodwill.beatavoltage intermediate cap-acityg'between [this inner coated. surfacev :andl the-exposed surface '.,of .the.,spacer theilattenis .55 thevoltaigfi m esm maintained at'torcneargth'e; .vol-tage, .ofethe con However if Odie-i5 rhbllownfor afi i n' Oi I ent electrode; of. the gap structure (or:conducting;;.;

only. a. thin partition of the; insulating- 'materiaL- voltage surge is. impressed acrossithe gap [device which extendsi through a:centra1:..opening;in.athelo corona discharge willv f m- O r h exnosedw the hollow with a conducting ,matergial; the; 1101-.

material is associated with insulating mateniais' high voltage surgeis discharging; over the-spa k 45 age "of the rod adjacent each of, the ionization" tips will be the same .as. thehvoltage of the .elec-i tion anduniformly spaced 1 from 0ne:-another,-,, notfpresent For instance, the tope-of a-"gapw 1 t Ionization tips'iarei an of Same size and all bear the. same relation. to. the porce its length, and the surface of the hollow is coated with some conducing material as contemplated by this invention, and that conducting material is connected with one of the electrodes, e. g., the top electrode of the entire spark-gap device, the conducting material will be maintained at the voltage of the top electrode, and likewise, the entire portion of the rod which surrounds this conducting material will tend to be maintained at the voltage of the top electrode. The presence of the other electrodes in the vicinity of the rod will tend to lower the voltage of the rod step by step in the vicinity of each succeeding electrode, but the voltage of the rod in the plane of each electrode will be higher than the voltage of that electrode. Thus, each ionization'tip, although in the plane of its electrode, will be contiguous to porcelain which is at a different voltage from the electrode to which the tip is connected, and consequently at a different voltage from the ionization tip. It follows, that when a high voltage surge is impressed upon the spark-gap device, corona discharge will form over the surface of th porcelain rod around each ionization tip and ions will radiate from it. The presence of such ions in the space between the electrodes of several or all of the spark gap-s will facilitate the discharge of electricity, making a much faster spark than would otherwise be obtainable, and this discharge will occur at a minimum voltage.

Various embodiments of the invention are possible and a few of these are illustrated in the drawings. In the drawings- Fig. 1 is a vertical section through the top of a spark-gap device;

Fig. 2 is a horizontal section on the line 2-2 of Fig. 1;

Fig. 3 is a vertical section through an intermediate portion of an alternative spark-gap device;

Fig. 4 is a section on the line 4-4 of Fig. 3;

Fig. 4A is a section similar to the section shown in Fig. 4, but showing a modified type of spacer;

Fig. 4B is a vertical section through the modified spacer;

Fig. 5 is a vertical section through a modification of the device shown in Fig. 3;

Fig. 6 is a section on the line 66 of Fig. 5;

Fig. 7 is a vertical section through an alternative spark-gap device; and

Fig. 8 is a section on the line 8-8 of Fig. 7.

Figure 1 shows the upper end of a spark-gap device which includes pairs of electrodes I9 and II separated by annular spacers I2. The electrodes are all of the same size and shape but alternate ones are inverted so that the annular dished portion I 5 of the upper electrode H] of each pair approaches the corresponding dished portion of the lower electrode i I to form a spark gap. A spacer l2 separates the two electrodes IE! and l I of each spark gap.

There is a central opening I! in each electrode and the openings in all of the electrodes are directly above'one another. The rod I8 is located in these openings. Figure 2 shows that the central openings in the electrodes are circular; but they may be serrated or have an otherwise irregular edge. The rod 18 need not be in contact with the electrodes as shown in Figs. 1 and 2 but there may be a very small space between them.

The spacers l2 and the rod l8 are made of porcelain or rutile or other insulating material. The electrodes are ordinarily stamped from sheet brass but may be made of any suitable metal. If the rod 18 were of uniform composition and construotion throughout, the portion continguous to each electrode would have the voltage of the electrode induced upon it.

When such a spark gap is subjected to an electric surge, the voltage drop from the top of the column to the bottom of the column is the same as the voltage drop between the two terminals of the spark-gap device. However, the column is not of uniform composition and its construction is not uniform throughout. The upper end is hollowed out and the wall of this hollow portion 20 is coated with a thin coating 2| of brass or other metal. This coating may be applied to the surface of the hollow by electroplating, spraying, applying a conducting glaze or in any other manner. There is a metallic end disc 25 which cover-s the top of the pile of spark-gap units in a customary manner. It lies upon or is held against the top electrode Ii. 'lhe metallic spring 26 is fastened to the end disc by the bolt 21. As is customary, the end disc 25 is maintained at the voltage of the line or other conductor to which the top of the spark-gap device is connected. Through its contact with this disc the spring 26 is maintained at this same voltage. This spring is formed with several narrow, depending arms which are pressed into contact with the coating 2| in several places. tained at the same voltage potentia1 as the end disc 25. The coating 2| covers a large surface of the column and the voltage of this coating has a greater influence on the voltage of the column than the line contact of the various electrodes.

When an electric surge is discharged through the spark-gap device there is no voltage differential between the surface of the rod and the top electrode H which contacts the end disc 25. However, there is a substantial differential between each of the next four electrodes and the area of the rod contiguous to each. As a consequence of the difference in potential a corona discharge occurs over the outer surface of the hollow portion of the rod adjacent the inner edge of each of these four electrodes. The electrons produced radiate into the adjacent gap space and ionize the air. As a consequence the upper three gaps break down almost immediately when a surge occurs, and they spark over at a minimum voltage which is always the same. There is no corona discharge over the surface of the lower portion of the rod below the hollow 20, because there the voltage of the rod is that induced by the adjacent electrodes. These electrodes and the adjacent surface of the rod are at the same. voltage. However, the rapid discharge over the top three gaps increases the voltage drop over each of the other gaps, and this increase may be sufiicient to hasten the discharge over the balance of the gaps. For instance, if the spark-gap device of Figs. 1 and 2 contains a total of no more than thirty gaps, rapid discharge of an electric surge over the top three gaps, will ordinarily cause the other gaps to discharge substantially simultaneously. This depends upon the design of the device. By providing the metal-coated hollow at one end of the rod, thus insuring ionization of the air in a. sufiicient per cent of the gaps, all of the gaps discharge rapidly, and at a consistently low and predictable potential.

The electrodes I0 and l I contact the opposite surface of the wall of the insulating material from that coated with the conducting material.

If the electrode and conducting material contacted the same side of the insulating material In this manner the coating 2| is main- I terial;- The spark: gapsrarelformed betweenrflat;

electrodesi 35 and; dished electrodes 3 6 and 31,; each; ofl whichgis. formed from afiat. :disc; Alternatezdished; electrodesware inverted so thatreach ofihczloweryelectrodes136 forms: aspark gap with:

The: a

the: flat; disc 35 below it, and: each: of: the upper electrodes 31 forms a spark gap with the:;fiat electr'odezflfi abovesit: Ionizing tips '38 arebent upwardly -fromgthez fiat zelectrodes r and c ionizing; tips: 39- are; bent downwardly therefrom: The.

tips:. 38 contact: the inner; wall of the hollow DOT-r tionlof the adjacent spacer 30. Becauseof the large areasof the conducting. surface 32 on the hollow in' the spacer; and the factthat this coatingiisrinwcontact with one of the lower electrodes 36, .the voltageof the-inner surfaceof the spacer contiguousr-to the ionization tips 38 is the same as, orta1most the same as, the voltage of the lower electrodec36. Because of this difference .in potential. between the; ionization tips .38 and'the contiguoussurf'ace. of the spacer, whenever an electric surge is impressed-upon; thev spark-gap device's corona:discharge ccurs around the tips 38:?- The electrons; produced radiate into .the spark gap. space and it breaks down at a low and consistent value.

Theilower ionizing tips 39 are contiguous to theilnextxlower spacertat a pointopposite the coatednhollow inits lower-end. The coating on this hollow portion is in contactxwithan upper electrode 3'! so that the-potential of that portion of-the spacer which is contiguous to the tips 39 is-substantially the same asthe' potential of the upper electrode-31. When the spark-gap device is subjected to an electric surge, a corona discharge likewise occurs over the surface of this spacer-about the tips39 with a result comparable to that producedby thecorona discharge about thetips'38'.

There may'be any desired number. of individual spark gapsinaspark-gap device of the type shown in Figs; 3'and 4'. One end of each of the spacers may be'hollowed'out and coated, or only a few of the spacersfor example, ten per cent-- may-"beconstructed irr-this manner.- Those so constructedimay'be located adjacent 'onesanother in the spark-gap device,- or they may be spaced from--one-another; Figure 3"illustrates sucha construction a with the uppermost spacers 30 shown as not hollowed out. The flat electrodes used'iibetween such spacers 3ll may be of the same construction as the. electrodes 35, and it is immaterial whether their ionization tips '38 and 39L-arercontiguous to surfacesaof the spacers 30 of widely difierent voltage from thertips-or subare used; the. flatelectrodes between the spacers 30 'may...be made -without ionization tips; For mass: production it will ordinarily be desirable to have all ofcthe. electrodes-of the same construction;. Iti-:.is-for@this-reason that all of the flat electrodes .in Fig; '3: are shown 1 with ionization tips 38 and 39.

Figures missus; section tthrough r aspark gap 1 a graphite paste 32 a,torother low" resistancermak terial such, as: silicon carbide; carbon-,1 etca, Thea upwardlypointing ionization tips 3flazcontactsthei;

inner: surface-of the spacer: oppositexthe several-1. filled LhOHOWSi'i The": downward-1y" projectingctipss 3 9a.:areccontiguoustthesexpo'sed inner: surface I v the-nextrlowen spacer; andladja'centreach ofltltese is; a .l hollow-r filled.:.with1- low "resistance material: Ifathe ionizationzpoints are staggered;the-spauzers mustztlikewisef-b'er staggered,; as 1 indicated; sothatl: there is only;a:- thirr partitiorr:of the insulating; material: ofs thes spacer" "between the: -io'ni'zatioii pointzandatherlow resistan'ce'materiaia Alternatively;- the' hollows m'ay extend entirelythrough the; spacer. In this type iof- 'spacer the hollows :must be filled with 7 high resistancema teria1,. such as carbon, .graphite; silicon carbi e grains, etc; to prevent :the electrodes '.h'eing'-'short circuited. through the spacers;

In an alternativetype -of' spacer, an annular band ofhigh resistance materialextendsdrom the top to: thebott'om ofthe spacer. This is bounded on each side by a thin annular-walletporeclai'nor other insulating materia'l- Such high resistance prevents the spacer from short circulating the gap. By providi ng anannula-r layer: of high resistance material; the spa'cer' is uniform throughout, and in -building-up a sparkgapx device it'is not necessary t0-arrange-thespacers sothat pockets of resistance"material are opposite the ionization points; because therearetno such pockets."

Figures 5 and 6 illustrate a-somewhat'similar construction; but in this'd'evice the-portions 4'9 andh ll 0f the-fiat disc electnides-lll whichare-- bent upwardly and downwardly to: contact theinnersurface of the spacers 43 are not-pointed,- but make: line contactwith the-spacers.- The= spacers are made-0f insulating material: Such line contact might be objectionable if 'the spacers: were not hollowed out at one end and-li-nedwith a metal coating 44 which contacts the electrodes; because. the'linecontact might be sufficient-to induce in-v the spacer a potential substantiallythesame as the potential of the-flat disc-elec troda That would prevent: the formationof corona discharge over the surface of the spacer;-

Howeventhe influence of the metal coatingnover 1 the large surface ofthe-hollow of the electrode isrsufiicientto maintain the hollow portion-of the spacer contacted by theionization flanges ortips. 49 and M -at a potential-substantially=-that of the dished electrodes-45. Thus, w'hen-arrelectric: surge is impressed upon the-spark-gap device there is a voltageadifierential between thetips40 and 4] andthezcontiguous surfacesof the spacers... Corona; dischargeitoccurs;alongs'i= the line .ofv contact and. ,over' the 'surfacemof-t the; spacers, and electrons radiateinto. withev gapzspacei anduassure r pid spark.over;. at: minimumrrpmaa V, tentialtfl Although generally the hollow of the manor; spacer will be coatedwithv as, conducting; terial, as illustrated in; Figs. 1 6, alternatively the :hollow mayrbeyfilled with axpastewor 'other. i bodyof. low resistances For example;,a carbonz.v or; graphite powderxor. pastemayi beflused I'f'ahigh. resistance material were-.used there. would be a voltage drop within thehollow; and there would be; lesscvoltage differentialbetween the tmaateria1: .zwith'im the; hollow-and theionizatiom 7 tip, etc. contiguous to the outer surface of the rod or spacer.

Figures 7 and 8 illustrate a different construction. There are flat disc electrodes 50 and also electrodes and 52 the inner portions of which are dished to form annular spark gaps with the disc electrodes 50. The electrodes 5| and 52 are identical in construction, one being inverted with respect to the other. They are arranged in pairs between spacers 53 which are made of insulating material. The upper electrode 52 of each such pair forms an annular spark gap with the flat disc electrode 50 immediately above it, and the lower electrode 5| in each pair forms a similar spark gap with the flat disc electrode 50 immediately below it. There is a central opening through the spark-gap device in which the hollow rod 55 is located. This rod is thin-walled porcelain, rutile or the like, and is filled with high resistance material such as a carbon resistance element, graphite or silicon carbide grains or the like, designated 56. This filling of resistance material is in contact with an end plate 51 at both the top and bottom of the rod. Thus there is a surface gradient along the outer surface of the rod, the same as though a plain rod were used. However, the potential of the rod is maintained in a more positive manner. It is not so easily affected by contiguous ionization tips.

The tips need not terminate in a point. Fig. 8 shows the inner edge of the disc electrode 50 slit at six places, and the segments 58 thus formed are bent alternately up and down. The inner edges of the segments are contiguous to the rod a short distance above or below the plane of the disc 50. Here the potential of the rod is diiferent from the potential of the electrode, and the resistance filling within the rod inhibits the potential of a segment from being induced in the portion of the rod contiguous to it. Thus a difference in potential is maintained which causes corona discharge over the surface of the rod when an electric surge is impressed upon the spark-gap device.

As shown in the drawing, ionizing tips or flanges 58 project both upwardly and downwardly from the flat electrodes 58. Alternatively, the ionizing tips might project only upwardly or only downwardly from these fiat electrodes. The tips are blunt and, as shown in Fig. 8, they form a line contact with the surface of the rod which is sixty degrees in length. The voltage gradient over the length of the rod is not greatly affected even by such line contact because of the filling 55, whereas without the filling the voltage of the respective electrodes would be induced in the rod, lessening the differential in voltage between each tipand the rod. When an electric surge is impressed upon the spark-gap device, corona discharge occurs over the surface of the rod about each tip. Ions produced by these discharges radiate into the annular gap spaces between the electrodes 50 and the dished electrodes 5|. The presence of these ions causes a rapid discharge over the gap space at a minimum and constant potential.

The foregoing are merely illustrative of constructions which produce ions which radiate into the gap spaces between the eelctrodes. Hollow spacers may be filled with resistance material to lessen the effect of contiguous ionization tips on the potential of the spacer. Many other modifications are possible.

The wordfcontiguous is used herein to mean touching, and also near althoushnot in contact.

The invention is defined in claims.

What I claim is:

1. A spark-gap device formed in part of an element of insulating material and having at least two electrodes therein with a spark gap between them, a portion of one of the electrodes being contiguous to one surface of the element of insulating material, the opposite surface of the said element being contacted by conducting material connected to a conductingelement of the spark-gap device maintained at a different 1 potential. from said electrode portion when an electric surge is impressed upon the spark-gap device.

2. A spark-gap device formed in part of insulating material and having a plurality of electrodes therein with at least one spark gap between them, an ionization tip projecting from i an electrode and terminating contiguous to the surface of the insulating material, the insulating material being contacted by conducting material which is in contact with a conducting element of the spark-gap device through which current flows at a voltage level substantially different from the voltage level of the electrode from which the ionization tip projects, when an electric surge is impressed upon the spark-gap device, whereby the voltage of the insulating material contiguous to the ionization tipis made to approach the voltage of said conducting element and to produce a voltage differential be: tween the ionization tip and the contiguous surface of the insulating material so that corona distrodes adapted to be maintained at different voltages, conducting material unitarily united with one surface of a thin portion of the in-,

sulating material and connected with conducting material in the spark-gap device which is at a different voltage from one electrode, said electrode being contiguous to the other surface of the thin portion of the insulating material.

4. A spark-gap device which includes spaced electrodes having an opening therethrough, the electrodes forming spark gaps therebetween, a

rod composed of insulating material extending through the opening with its surface contiguous to the surrounding electrodes, that portion of said rod which extends through the planeof several of the electrodes being hollow, the surface of said hollow being contacted by a conducting material which is connected to other conducting material which, when an electric surge is impressed upon the device, is at a different voltage potential from at least some of said electrodes.

5. The spark-gap device of claim 4 inwhich the conducting material contacting the surface of the hollow is united thereto.

6. The spark-gap device of claim 4' in which the hollow does not extend through the rod.

7. The spark-gap device of claim 4 which includes an electrode the plane of which does not intersect the hollow, this electrode serving as the other conducting material with which the conducting material which contacts the hollow is connected.

8. A spark-gap device whichincludesa spark I the appended gap formed of two electrodes spaced by an insulating spacer which embodies conducting material which is nearer one of the electrodes than the other, said conducting material being in contact with other conducting material in the spark-gap device which when an electric surge is impressed upon the device is at a voltage different from the voltage of said other electrode, a portion of said other electrode being contiguous to the spacer.

9. The spark-gap device of claim 8 in which one end of the spacer is hollow and is coated with the conducting material which is said to be embodied in the spacer.

10. The spark-gap device of claim 8 in which the said electrode is at one end of the spacer and the conducting material which is at a different voltage therefrom is the electrode at the other end of the spacer.

11. A spark-gap device which includes spaced electrodes having an opening therethroufih. the electrodes forming spark gaps therebetween, a hollow rod of insulating material extending through the opening with its outer surface contiguous to the surrounding electrodes, the hollow containing resistance material which at opposite ends of the rod is connected to conducting materials in the spark-gap device which are maintained at different potentials when an electric surge is impressed upon the spark-gap device.

12. The spark-gap device of claim 11 in which the hollow is filled with the resistance material.

13. A rod of insulating material adapted for use in a spark-gap device, the rod being hollow from one end to the other with conducting material in contact with the surface of the hollow.

14. The rod of claim 13 in which the conducting material is an integral coating on the surface of the hollow.

15. A rod of insulating material adapted for use in a spark-gap device, one portion of the rod being hollow and the balance not being hollow, with conducting material in contact with the surface of the hollow.

16. The rod of claim 14 in which the conducting material is an integral coating on the surface of the hollow.

17. A rod of insulating material adapted for use in a spark-gap device, the rod being hollow from one end thereof to the other, there being resistance material in the hollow which is continuous from one end of the hollow to the other.

18. The rod of claim 16 in which the hollow is filled with the resistance material.

19. An insulating spacer for a spark gap, in one end of which spacer there is at least one hollow, the spacer including conducting material 10 (which may be material of low resistance) which is in contact with the surface of said hollow.

20. The spacer of claim 18 in which the conducting material forms a coating on the surface of the hollow.

21. An insulating spacer for a spark gap containing high resistance material therein separated from the outer wall of the spacer by a thin partition of the insulating material of which the spacer is largely composed, said high resistance material extending from the top to the bottom of the spacer.

22. A spark-gap device comprising a plurality of spaced electrodes forming spark gaps therebetween, thin porcelain means extending at right angles to the plane of the electrodes, at least one electrode of each pair of adjacent electrodes which form a gap being provided with ionizing means contiguous to the outer surface of the porcelain means, the portion of the porcelain means opposite the said ionizing means being provided with conducting means, whereby there is capacity between said conducting means and the surface of the porcelain means contiguous to the ionizing means.

23. A spark-gap device comprising a plurality of spaced electrodes forming a spark gap between adjacent pairs of electrodes, porcelain means associated with the electrodes, the porcelain being hollow for at least a part of the length thereof, means projecting from one or more electrodes in contiguous relation to the porcelain means, and conducting means within the hollow connected with another of said electrodes, whereby there is capacity between said conducting means and the surface of the porcelain means contiguous to the projecting means.

24. A rod of insulating material adapted for REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date McFarlin Mar. 5. 1940 Number

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