US2677072A - Lightning arrester - Google Patents

Description

t e o t espondinsly 'l Patented Apr. 27, 1954 UNITED ?ATE.NT OFFKCE LIGHTNING ARRESTER Eugene J, De Val, Pitcairn 2a., assignor to Westin hwss Ele ric C rp at n, t t s i -r h, Pa a eoxporation of Pennsylvania Application August 24, 1951, Serial No. 243,496

8 Claims.-

sent invent on rela to l h nin a resters, and more partieularlytap a eqlnpact and s mpl fie c nstr c an or i h nin arres e rs of the ex sion t e- E ulsie pe l h nin a re ars wa t semi u Q s Qs i lee rede di b se i in a ve ed i hamber:- wh eh is li te wi 9 cos a na. nsula ng ma i a bl o evo ins, u ant v iilwiQiiiZ a wh n; q s a an e t ic-,1 ar 1 Amen a schar e deca s be weea he e ectrodes. a ar e u nti Qi' s is evo d h eb s .BXPQIJBQ n b s th aus he ent b win out th are g s nd li law the are h a ext n ui e e hu in er up in the q er qa feni wh c nds t flaw th u h he ar estes tQ smtsd f l win the disch r e at l en nssu seth us a cen tmat an @t attssta of this im t at ambeli an ists 91 a tfib lai t etut f i m- 5 fit qr o hat suitable aas e ol ias ma eria i h el c rodes. d secssd at he ai Eli the tuba a leas we of the e ctm es xtemein h e, and at lea t use 0 the ele tr d s ts ve ed- A. lus: 0. fil sro sas-e qlvi-ne m ta' is u ually pl ced, in the take et e n i 2 sleea testtitt t a 9 1 sa s n 1a ne U the swam ell i et a tmviis a e en infqrceme t agaigist the g h bursti whieh eecus it; the t e at s. n to i na ic o imp o e the spa: .7121? chaitaqt ris t o the a r ster he pressing: his wnd c in shi on the @u siae @i he t at ground s tsnti l, mak s it nae ssaw t9 .vme. aqa ua e in t n betw en tbe'slii la and in? lin e e tm tbs atmstes ne? t9 pre ent o ty 9i ex n l fi h t M a a a- 1 its Prior p as i e, the news x i s lal .tlas sqmsiin'l s be me v ded, y lastsa .leagtll iii the tube abw th h el ui i s i9 m ies 19 2s en u h su ce bet een the up s x 92 o he shield a e n arest expased-part 9f h lin electrode to insure against exteg al. flasl pver. This methd 9 ta nia asisquats latipn is un ab e liows sr e? a 9? that gr t in eas eng h i the taba Win91; ali ses he ba rist r um desir b 191 a @2 41 bstantially srsa e the costbec use @i it h 9 gs e an hou ng r a an as a lectre ia c hi ld used to. obtain adequate insulation empleys a "reservoir of liqilid or semi-:liquid insulatiilg gum above the end of the shield with insulating barrier members containing the gum and sealing the structure. This construetion, however, requires a number of extra parts to contain the gum and form the necessary seal, and involves donsiclerable difficulty in assembly as well as reqaix ing increased length, all of which increase the cost of the arrester,

T e principal a ie t o h re en in en i is to provide an expulsion type lightning arrester in which adequate insulation against external fiashove is provided in a simple mar ner ithout increasing the length or cost of tl e arreste r.

Another object of the invention is to ptovicle an expuisien type lightning ar teste of minimum length and 10W 'cost, but Whiph has adequate insulation to prevent exter al flasbover oi the expulsion tube. A further object oi the inventiqg is to provide n u s n t e l htnirl r ste a in a m mum numbe of Pa m! a s m l es on tru n wh e sai ts t an ears-v sttmb rv th s substa l re ls s 5 9st a t l. li ct Qt. i2 1? iea, t Prov de arr s ba ias a 19s t d asale the "are s at 'i- 'e i is and advantages 9.? the. twee its aliasin embad a. in an .8

in is ad at ha sea pr a insulating material which is capable oi eve -vine substantially unaionized gas when exppsecl to an $1 3 ar Q W 11 1 1% ufi it i' T bal. ls sa; up e tlstir de mm??? 2 i @isnossfi -u er aria 0? tub Th sleeve illey fits t sieq in slaa ro me laz abstra ts f is hown tnin agrester,

thrust which occurs when the arrester operates. A lower electrode member 3 is provided at the lower end of the tube I. The lower electrode 3 is shown as a generally cylindrical steel member which fits against the lower end of the tube I, and which is provided with a plurality of vent openings 4 to permit discharge of the gas generated in the arrester during operation.

A generally cylindrical plug or filler of insulating, gas evolving material, such as hard flber, is preferably inserted in the bore of the tube 1 between the electrodes 2 and 3 to restrict the arc path. Any suitable type of filler may be used but it is preferred to utilize the type of filler disclosed and claimed in my copending application Serial No. 182,994, filed September 2, 1950, and assigned to the Westinghouse Electric Corporation. As more fully explained in that application, the filler 5 is generally cylindrical and has a helical groove 5 in its surface extending from end to end of the filler. When the arrester operates, the gas evolved from the tube and filler flows through the groov and forces the arc into a helical path, elongating the arc and increasing the arc voltage, to facilitate its interruption. While this helically grooved type of filler is preferred because of the improved current-interrupting ability and increased life obtained, it will be apparent that any other type of filler, either loose or fixed in position, might be used if desired.

A conducting shield and reinforcing member I is disposed on the outside of the tube I. The shield I is preferably a steel sleeve which fits tightly over the tube I, and which is held in position by annular indentations or crimps 8 which engage corresponding annular depressions on the tube I to prevent axial displacement between the tube and shield. The lower electrode 3 is provided with an annular recess 9 and the lower end of the shield is crimped or rolled into this recess to retain the electrode 3 in position and to efiect electrical contact between the shield and the lower electrode. The shield 1 extends from the lower end of the tube I towards the upper end and, as shown in the drawing, it preferably extends far enough to overlap the upper electrode 2a substantial distance, so that the shield I functions to lower the critical spark-over voltage of the arrester by concentrating the voltage stress adjacent thelower; end ofltheelectrodezl immediately before breakdown.

It will be evident that since th shield] exn wa ds t eere d. 02t u thi prq aine n @Qp g tern flashover on the outside of the tube between the electrode 2 and the shield I. This result has sometimes been accomplished heretofore by extending the tube I above theend of the shield I for a greatenough distance to provide the necessary insulation, but this construction requires an extremely long tube, and is unsatisfactory because of the increased cost of such a tube and of the required housing, andbecause it results in an undesirably long arrester. Another construction which has been used involves the use of a liquid, or semi-liquid, insulating gum surrounding the upper end of the tube I above the shield, with insulating barrier members to contain the gum and to seal it inplace, but this type of construction results in a complicated structure requiring numerous exti'a' parts and considerable difilculty in assembly of the device, as well as undesirably increasing the length.

In accordance with th present invention, adequete insulation between the shield and the upportion III of the tube I.

per electrode is obtained in a. simple and inexpensive manner. For this purpose, the upper end of the tube I above the shield I is externally tapered, as indicated at I0 and an insulating member or barrier II is provided which encloses the tube I and extends axially over the shield I toward the lower tnd of the tube, the barrier being made long enough to provide the necessary insulation. The insulating barrier II is shown as being generally cylindrical and is internally tapered at its upper end to engage th tapered The insulating barrier II may be made of any suitable plastic insulating material which has some flexibility or resilience, polyethylene being a very suitable material for this purpose. The internally tapered upper end of the insulating barrier I I is designed to have an appreciable interference fit with the tapered end III of the tube I, that is, it is designed so that its internal dimensions are slightly smaller than the external dimensions of the tapered part of the tube I.

In assembling the device, a thin layer of insulating gum is applied to the tapered surface III of th tube I and the insulating barrier H is then placed over the tube I and forced into place, the insulating gum serving to exclude any air between the'engaging tapered surfaces so that a tight sealing engagement is obtained. A washer I2 is placed on top of the barrier I I and a nut I3 is threaded on the upper end of the electrode 2 to clamp the insulating barrier II in place on the tube I. The insulating barrier II thus surrounds and encloses the tube I and shield I and extends axially over the shield towards the lower end of the tube, providing a long insulating path between the upper electrode 2, ad associated conducting parts, andthe nearest exposed part of the shield I. The lower part of the barrier I I may be tapered in thickness, as shown, to facilitate manufacture and reduce the cost, since it is not necessary for this part of the barrier to have great mechanical strength. I

It will be seen that adequate insulation is provided to prevent xternal flashover of the tube" I, but that the length of the structure is not increased over that required by the necessary length of the internal arc path. Thus, an arrester is provided which is of minimum length and of simple, ldw cost construction, and which can readily be assembled without difficulty.

The arrester is contained in a generally cylindrical housing I4 of porcelain, brother suitable we'a.therresistant insulating material. The lower end of the housing is closed by a metal washer I5 which surrounds the lower electrode 3 and engages an external shoulder on the electrode, and

which is clamped against an internal shoulder in the housing I4, a gasket I6 being interposed between the washer I5 and housing I4 to seal the interior of the housing. The washer I5 has an extending lugv I I on one side which is bent downward and carries a terminal device I8, of any suitable type, for connection of a ground lead to the lower electrode 3. The housing I4 preferably has a recess or opening I9 for the terminal device It so that it is accessible but is substantially enclosed within the housing.

.A series spark gap is always utilized with expulsion type lightning arresters so that the fiber tube will not be continuously subjected to the normal line voltage. Any suitable type of series gap may be used with the arrester of the present invention, and the drawing shows a semi-enclosed gap of the type disclosed and claimed in my copending application Serial No. 243,497, filed August 24, 1951. This gap device is contained in a porcelain housing which consists of two-members and 2| glazed, or otherwise joined together, to form a unitaryhousing. A threaded stud 22 .extends through a central opening in the lower housing member 20 and an electrode member 23 is threaded on the upper end of the stud 22 within the gap housing. A nut 24 clamps the stud and electrode to the gap housing. The lower end of the stud 22 is threaded into a tapped hole in the top of the upper electrode 2 of the expulsion assembly, to secure the gap housing in place and to eifect electrical connection between the electrode 23 and the electrode 2. A gasket25 is prei- Y erably interposed between the top of the housing i4 and the bottom of the gap housing, and when the stud 22 is threaded into the electrode 2 and tightened, the gap housing is firmly secured on the-housing l4 and the washer I5 is drawn tightly against the housing I4.

The upper electrode of the series gap consists of a threaded stud 26 extending-through a central opening in the upper part 2| of the gap housing and positioned by means of a U-shaped retain-' lng member 21 which engages a slot in one side of the stud 26 and is seated in a recess in the housing 2!. The upper gap housing part 2'! has openings 28 to permit visual inspection of the gap between the electrodes 23 and 26, the gap bein sufliciently enclosed, however, to prevent accidental bridging or contact, as more fully explained in my above-mentioned copending application. A nut 29 is threaded on the upper end of the stud 26 to retain it in position, and suitable terminal means 30 are provided on the stud for clamping a line lead thereto, so that the stud 26 serves as a line terminal device for the arrester.

It is highly desirable that all live parts of the arrester be enclosed to prevent accidental contact.

The electrodes of the series gap are enclosed in the gap housing, as described, and a cap member 3i provided for enclosing the arrester terminal and line lead. Cap members have been used heretofore for enclosing the terminals of lightning arresters, and other electrical devices, but the caps which have been available have been unsatisfactory where the cap must be capable of being removed and replaced. Previous devices have usually required some type of metallic spring to also because of the relatively hard, brittle material which previously had to be used for such caps, which made it relatively easy to break them in the course of handling. In accordance with the present invention, a cap member is provided for covering the terminal and line lead which avoids these disadvantages and which can readily be applied and removed without risk of breakage.

The cap 3| is made of a flexible, or somewhat resilient, plastic insulating material, the preferred material being polyethylene. The cap 3| is a generally cup-shaped member with slots or recesses in opposite sides for entrance of the line lead. A central boss or enlargement 33 is formed on the inside surface of the top of the cap and has a central opening which is designed to have an interference fit on the terminal stud 26. The boss 33 is preferably split on opposite sides, as indicated at 34. It will be apparent that the cap 3! can readily be applied by forcing the central opening over the top of the terminal stud, so

gagement of the sides of the boss 33 with the stud, and that the cap can readily be removed by pulling it off without damaging the cap. There are no metallic .parts to corrode, and polyethylene, which is the preferred material, has good weath ering properties, so that its life is very long, and is sufliciently flexible to avoid any risk of breakage. Thus, a terminal cover has been provided which is simple and readily applied, and which can be produced at low cost, and avoids the disadvantages of the previous types of terminal covers which have been available.

It should now be apparent that a construction has been provided for lightning arresters of the expulsion type which provides a compact and lowcost arrester of simple construction but with fully adequate insulation to prevent any possibility of external flashover. The new arrester can readily be assembled and provides a desirable type of construction in that all live parts are fully enclosed, so that there is no risk of accidental contact or of accidentally bridging the series gap. The terminal cove which encloses the line terminal and lead is a simple, low-cost member which is not subject to breakage and which is easily applied and removed.

It will be apparent that although a particular embodiment of the invention has been shown and described for the purpose of illustration, various other embodiments and modifications are possible within the scope of the invention, and it is to be understood that the invention is not limited to the specific details of construction shown, butin its broadest aspects, it includes all equivalent embodiments and modifications which come within the scope of the appended claims.

I claim as my invention:

1. A lightning arrester comprising a tubular structure having an internal surface of material capable of evolving gas when exposed to an electric are, electrode means disposed at opposite ends of said tubular structure, at least one of said electrode means extending into the tubular structure to establish an internal discharge path between the electrodes, and at least one end of the tubular structure being vented, a conducting shield extending over a substantial part of the outer surface of the tubular structure, and an enclosing insulating member directly engaging one end of the tubular structure adjacent the end of the shield and extending axially over said shield.

2. A lightning arrester comprising a tubular structure having an internal surface of material capable of evolving gas when exposed to an electric arc, electrode means disposed at opposite ends of said tubular structure, at least one of said electrode means extending into the tubular structure to establish an internal discharge path between the electrodes, and at least one end of the tubular structure being vented, a conducting shield disposed on the outside of the tubular structure and extending from one end thereof toward the other end, and an enclosing insulating member directly engaging said other end of the tubular structure adjacent the end of the shield and extending axially over said shield.

3. A lightning arrester comprising a tubular structure having an internal surface of material capable of evolving gas when exposed to an electric arc, electrode means disposed at opposite ends of said tubular structure, at least one of said electrode means extending into the tubular structure to establish an internal discharge path bestructure having an internal surface of material capable of evolving gas when exposed to an electric arc, electrode means disposed at opposite ends of said tubular structure, at least one of said electrode means extending into the tubular struc ture to establish an internal discharge path between the electrodes, and at least one end of the tubular structure being vented, a conducting shield disposed on the outside of the tubular structure, said shield being in electrical contact with the electrode means at one end of the tubular structure and ext-ending toward the other end thereof, said other end of the tubular struc ture being tapered, and an enclosing insulating member having an internally tapered end portion engaging the tapered end of the tubular structure, said insulating member extending axially over said shield.

5. A lightning arrester comprising a tubular structure having an internal surface of material capable of evolving gas when exposed to an electric arc, electrode means disposed at opposite ends of said tubular structure, at least one of said electrode means extending into the tubular structure to establish an internal discharge path b tween the electrodes, and at least one end of the tubular structure being vented, a cylindrical conducting shield fitting tightly on the outside of the tubular structure, one end of the tubular structure being tapered, and a cylindrical insulating member having an internally tapered end portion engaging the tapered end of the tubular structure with a tight, sealing engagement, said insulating member extending axially over the shield.

6. A lightning arrester comprising a tubular structure having an internal surface of material capable of evolving gas when exposed to an electric arc, electrode means disposed at opposite ends of said tubular structure, at least one of said electrode means extending into the tubular structure to establish an internal discharge path between the electrodes, and at least one end of the tubular structure being vented, a cylindrical conducting shield fitting tightly on the outside of the tubular structure, one end of the tubular structure being tapered, and a cylindrical barrier member, said barrier member being made of a plastic insulating material having substantial resilience, the barrier member having an internally tapered end portion engaging the tapered end of the tubular structure with a tight, sealing engagement and extending axially over the shield.

7. A lightning arrester comprising a tubular structure having an internal surface of material capable of evolving gas when exposed to an electric arc, electrode means disposed at opposite ends of said tubular structure, at least one of said electrode means extending into the tubular structure to establish an internal discharge path between the electrodes, and at least one end of the tubular structure being vented, a cylindrical conducting shield fitting tightly on the outside of the tubular structure, said shield being in electrical contact with the electrode means at one end of the tubular structure and extending toward the other end thereof, said other end of the tubular structure being tapered beyond the end of the shield, and a cylindrical insulating member having an internally tapered end portion engaging the tapered end of the tubular structure with a tight, sealing engagement, said insulating member extending axially over the shield.

8. A lightning arrester comprising a tubular structure having an internal surface of material capable of evolving gas when exposed to an electric arc, electrode means disposed at opposite ends of said tubular structure, at least one of said electrode means extending into the tubular structure to establish an internal discharge path between the electrodes, and at least one end of the tubular structure being vented, a cylindrical conducting shield fitting tightly on the outside of the tubular structure, said shield being in electrical contact with the electrode means at one end of the tubular structure and extending toward the other end thereof, said other end of the tubular structure being tapered beyond the end of the shield, and a cylindrical barrier mem her, said barrier member being made of a plastic insulating material having substantial resilience, the barrier member having an internally tapered end portion engaging the tapered end of the tubular structure with a tight sealing engagement and extending axially over the shield.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,338,479 Ackerman Jan. 4, 1944 2,385,663 Wade Sept. 25, 1945

Images