US2858468A

US2858468A - Overvoltage protective device

Info

Publication number: US2858468A
Application number: US388498A
Authority: US
Inventors: Hedlund Roland Gustaf Magnus
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1953-10-27
Filing date: 1953-10-27
Publication date: 1958-10-28
Anticipated expiration: 1975-10-28

Description

United States Patent O i i $585463 ovERVoLTaGE Pnorucrlvr. nnvrcn Roland Gustaf Magnus Hsdiuadrliftseld, Mass, assiguor (ismael. Eletta? Campana .a sommation f New Application October 27, 1953, Serial No. 388,498 1.1 clams.. (Clsuf-.na

This invention relates to an overvoltage protective device, and moreparticularly, to an overv1tage"'protective device havinga liquid sparkfgap cbnstruction. '5

Spark gaps completely" submerged in an insulating liquid are well-known in the art.4 However, sincethe breakdown voltage of insulating liquids is generally very high, it isffnot feasible to completely submerge the spark gap in the liquid." Where the sparkVv gap is"co1`npletely submerged in the liquid close spacing and very accurate positioning'of ther electrodes deiinin'g the spark 'gap is necessary in order yto insun're a low and consistent sparkover voltage for'the spark gap. I have discovered that itfwould be better to make the spark gap are over or ignite c lose to the surface of the liquid and thus evaporate gases from the liquid Vwhich would either directly Vcool d'own, elongate, and blow ont-'the arc or forcea series gap to open up down in the liquid itself. Accordingly, it isfan object of this invention to provide a liquid spark gap construction wherein the spark gap is ignited close to the surface 'of the liquid. A My inventionV Acomprises a liquid spark gap constructionV comprising two spaced electrodes defining a spark gap therebetween, each ofsaid electrodes 'partially subl merged in a non-flammable insulating liquid, said spark gaperrtendingfbetween said electrodes along the surface f saidliquid( u My 'invention further comprises a protective device comprising an electrical circuit portie-n having two spaced electrodes therein defining an arc gap therebetween, each of `sai'delectrodes"partiaily submerged in a non-flammable insulating liquid, said gap extending between'said electrodes along the surface of said liquid, one of said electrodes comprising a movable rod-like member, one end of said rod-like member disposed in said liquid, a iixed contact insaid electrical circuit portion submerged in said liquid, said one end abutting said fixed contact, the other end of said rodllike member positioned above the surface of said liquid and having a hood attached thereto,`t`he other of said electrodes comprising an annular portion concentrically surrounding said rod-like member and spaced therefrom.

` The invention will be better understood by considering thefo-llowing description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawingjliig 1 is a side view, partly in section, of one form of my invention. Fig. 2 is a side View, partly in section, of another form of my invention. Fig; 3 isa side View, partly in section, of still another form of my invention. Fig. 4 is a side view, partly in section, of the protective device sho-wn in Fig; 3 with the parts shown in the positions they occupy when the device is interrupting'a heavy current.

Referring now to the drawing, and more particularly to Fig. 1, shown therein is a protective device adaptedV to protect a transmission line 1i? or other electrical apparatusfrom ligtning surges or the like. The protective device` or lightning arrester comprises a closed encasing 2,858,468 Patented Oct. 28,

ICC

means or tank 11 partially iilled with a non-tiammable insulating liquid 12, as perchlorethylen, fluorinated cydic ethers, or askarels. Disposed within encasing means 11 is a spark gap construction partially submerged within insulating liquid 12. The partially submerged spark gap construction comprises two arcing electrodes or

horns

13 and 14 defining a spark gap 1S therebetween along the surface of insulating liquid 12. The lower ends'of arcing

electrodes

13 and 14 which are immersed in insulating liquid 12`are substantially parallel and the upper ends of arcing

electrodes

13 and 14 which are positioned above the surface of dielectricliquid 12 diverge as the distance above the surface of the liquid increases whereby spark gap 15 extends between electrodes 13 and 141 along the surface of dielectric liquid 12.

A' line 16 extending from transmission lin e 170 is electrically connected to the upperV end lof electrode 13 through an insulated terminal or bushing 17. Another line lsfconnected to ground is electrically connected to the upper c nd of electrode 1lithrough an insulated terminal or bushing 19.

' When a high voltage surge, such as lightning, ,strikes the transmission line" 10 the surge will pass' fror'rrtr'ansmissionrline 1 0 toline 16 and thence down to arcingelec# trode 13, The gap 15 between

arcing electrodes

13 and 14*r will b e ignitedby the overvoltage whereby the current due to the lightning surge will pass from arcing electrode 1 3 across gaplS to arcing electrode 14 and then to ground. No rc'will be ignited between the lower spaced submerged ends" of

main arcing electrodes

13 and 14 inasmuch as the lower ends of sparking electrodes V13 and 14 are spaced and insulated from each by insulating liquid 12 which has a higher insulating strength than spark gap 1'5.'v After sparkgap 15 has been ignited by the lightning surge the electrical circuit portion from transmission line v10 to grounded line 18 has been completed whereby the power'follow current from transmission line 1() will also ilow togrbund.v The electrical arc across spark gap 1S initially is forced by the'magneticfield due to the closed electrical circuit' portion comprising arcing electrode 13, spark gap 15, and arcing electrode 14 to stay along the surface of liquid 412 or either go further 'down into' the insulating liquid 12 itself at least at the first instant. However, the heat of the arc across spark gap 15 which was ignited close to the surface of liquid 12, and which may have been forced down into the liquid 12, will evaporate gases from liquid 12. The gases liberated by the arc will be stronger after a` few microseconds than the magnetic field and'will blow the arc in an upward direction thus cooling and extending it. The blast of gases resulting from the vaporized liquid due tothe electrical are across'spark gap 15 will progressiveiy move the electricalarc further towards the diverging ends of arcing electrodes 15% and 14 a's'illustrated by the progressively longer arc-'like broken lines between arcing electrodes 13 and' 14. Thus, 'the blast of evaporated gases from liquid 12 besides' cooling the electrical arc also elongates the electrical arc. When the power follow current reaches current zero spark gap will be so deionized that the are will not restrike.

Referring now to Fig. 2, shown therein is another formof my invention wherein the protective` device is adapted to protect a transmission line 29 or other electrio al apparatus from lightning surges or the like. The protective device or lightning arrester shown in Fig; 2 operates on the same principle as the protective' device shown in Fig. 1. That is, the' spark gapV is ignited close` tothe surface 'of the liquid and thus evaporates gases from the liquid which will directly cool down, elongate, and blow out the arc; However, the form of my inven-V tion shown in Fig. 2 has an additional function wherein if; the power follow current is of such magnitude that itl 3 cannot be interrupted by the gas blast resulting from the electrical arc across the surface of the liquid said gases will force a series gap to be opened down in the liquid itself wherein the power follow current will be interrupted.

The protective device or lightning arrester shown in Fig. 2 comprises a tank or encasing means 21 partially filled with a non-flammable insulating liquid 22. The partially submerged spark gap construction comprises electrodes 23 and 24 defining a spark gap 25 therebetween along the surface of liquid 22. Electrode 23 comprises an axially movable rod-like member, the bottom end of which is submerged in liquid 22. Rod-like member 23 is movably mounted in an insulated bushing or guide 26 whereby rod-like member 23 can move axially. A fixed contact 27 disposed within the electrical circuit portion of the protective device, and as will appear more clearly hereinafter, is adapted to be abutted by the lower end of rod-like electrode 23. Fixed contact 27 is submerged within liquid 22 and is connected by a line 28 to ground.4

The upper end of rod-like member 23 protrudes beyond the surface of insulating liquid 22 and has attached thereto an umbrella-like hood 29. The hood 29 preferably is constructed out of an insulating material so that the arc struck across electrodes 23 and 24 will not spark over from electrode 24 to the hood 29. The skirt or flange 30 of hood 29 is shown as extending down into the insulating liquid 22. However, my invention will operate successfully even though the umbrella-like hood 29 does not form a closed chamber above the insulating liquid 22. Between the cover or lid 31 of tank 21 and the hood 29 is disposed a spring 32 which continuously urges the rod-like member 23 downward whereby the lower end of electrode 23 will contact the fixed contact 27. i

Electrode 24 comprises an annular portion which is partially submerged within insulating liquid 22 and conv centrically disposed about the upper end of rod-like'member 23 and spaced therefrom by annular spark gap 25. Fixed annular portion or electrode 24 is positioned beneath umbrella-like hood 29. A line 33 is electrically connected to transmission line and is electrically connected to annular electrode 24 through an insulated terminal or bushing 34.

When lightning strikes transmission line 20 the current resulting from said lightning strike will pass through line 33 and bushing 34 to the annular electrode 24. The gap between electrodes 23 and 24 will break down whereby the lightning current surge will pass through electrode 23 and fixed contact 27 to line 28 and thence to ground. The arc ignited between spaced electrodes 23 and 24 along the surface of insulating liquid 22 will evaporate said liquid whereby gases will be liberated from the liquid to elongate, cool down, and blow out the arc across spark gap 25. If the blast of gases liberated from insulating liquid 22 and directed across the arc is unable to extinguish the arc additional evolution of gases underneath hood 29 will move hood 29 and electrode 23 upwardly whereby the lower end of electrode 23 will be removed from contact with fixed contact 27. When the lower end of rod-like member 23 is removed from fixed contact 27 an electrical arc is established therebetween within the insulating liquid 22 and the liquid 22 will deionize said arc and extinguish it. After interruption of the arc across the series gap between the lower end of movable electrode or contact 23 and fixed contact 27 the spring 32 will move movable electrode 23 back to its original position.

The insulated guide or bushing 26 is shown as being dome-shaped. However, it will be obvious that other types of bushings or guides can be used to steadythe movable electrode or contact 23. The chamber formed by insulated bushing or guide 26 within which the lower end of electrode 23 and fixed contact 27A are disposed has apertures or openings 35, only one of which isl disclosed, whereby the gases evolved by the arc across the series spark gap between the lower end of electrode 23 and fixed contact 27 can escape from said chamber.

Referring now to Figs. 3 and 4, shown therein is still another form of my invention. The Figs. 3 and 4 protective device utilizes the two principles disclosed in the Fig. 2 protective device. That is, the Figs. 3 and 4 device uses a gas blast means and a series spark gap means to insure that the power follow current is inten rupted. However, in the third form of my invention a third effect or means is introduced to interrupt the power follow current if the other two mentioned means fail. The third means or principle is an expansion effect.

The protective device or lightning arrester shown in Figs. 3 and 4 comprises a tank or encasing means 40 having insulating material side walls and a metallic bottom and cover. The side walls of tank 40 are constructed out of insulating material so that a short circuit will not be formed from transmission line 41, line 42, and the metallic cover of tank 40 to the metallic bottom of tank 40 and then to grounded line 43 around the partially liquid immersed spark gap and series gap structure within tank 40.

A solid rod-like guide 44 is attached at one end thereof to the cover of tank'40 and insulated therefrom, and extends down towards the bottom of tank 40. A movable hollow rod-like electrode 45 is guided or carried by solid rod-like guide 44. The lower end of rod-like electrode 45 is submerged within a non-flammable insulating liquid 48 within tank 40 and is adapted to abut a fixed contact 46 which can be formed as an integral part of the metallic bottom of tank 40. The movable rod-like electrode 45 is tubular and can slide up and down on the rod-like guide 44. The upper end of electrode 45 protrudes above the surface of dielectric liquid 48 and has connected thereto or integrally formed therewith an unbrella-like hood 47. A coil spring 49 surrounding the upper end of guide 44 is insulatedly disposed between the cover of tank 40 and the hood 47 whereby the axially movable electrode 45 is continuously urged into electrical contact with fixed grounded contact 46.

The other electrode of the partially liquid immersed spark gap construction comprises an annular portion 50 which is concentrically disposed with respect to electrode 45 and spaced therefrom by an annular spark gap 51. Connected to or integrally formed with annular portion 50 is a dome or funnel-shaped portion 52. The converging or narrow end portion of funnel-shape portion 52 is directed towards the annular spark gap 51, and the diverging or wide end portion of funnel-shaped portion 52 is adapted to abut an annular insulating material gasket 53 connected -to the bottom of tank 40 whereby a pressure chamber 54 is formed enclosing the lower or contact end. of movable electrode 45 and fixed grounded contact 46. Integrally formed with and between annular portion 50 and the neck of funnel-shaped portion 52 is a flange 55 which extends laterally beyond hood 47 and towards the side walls of tank 40. Disposed conductively between the cover of tank 40 and the ange 55 is a coil spring 56 whereby the diverging or mouth end portion of funnelshaped portion 52 will be continuously urged into contact with annular insulating material gasket 53.

4When lightning strikes transmission line 41 Ithe current resulting therefrom will pass along line 42 to the top of tank 40 and then through spring 56 and flange 55 to annular portion or electrode 50. The spark gap 51 will. break down whereby said current will pass through movable electrode 45 and fixed contact 46 yto grounded line 43. The power follow current will follow the same path, and the arc established across the spark gap 51 will liberate some gases from liquid 48 which will be blasted across the arc to cool, elongate, and extinguish it. The bottom surface of hood 47 has an annularly extending domelike configuration and electrode 50 is positioned off center with respect to the centerline of said dome-like configura,

tion towards electrode 45 whereby when a blast of gas is directed across the arc said arc will pivot about electrode 50 and be 4elongated as it nioves upwardly along said dome-like configuration. If the current is too high to be interrupted', by'said gas blast, additional gases will be evolvedfom liquid 484 to move'hood 47 and the lower 'endv of electrode 4'5 out of contact with xed grounded ontact'46. After the electrode"45l is separated `from fixed contact 46, la'n' arc will be established across this series gap which may be interrupted by the'liquid 48 inasmuch as this second-mentioned arc is t-otally submerged within liquid 48. Also, the arc across the separated electrode 45 and contact 46 causes the evolution of gases and an increase in pressure within chamber 54 whereby said gases and some of the liquid within chamber 54 will be funneled towards the annular spark gap 51 and be blasted across the arc between spaced electrodes 50 and 45 to interrupt said arc. -If this additional blast of gases does not interrupt the arc across electrodes 4S and 50, and if the arc across the series spark gap persists, additional gases will be evolved within chamber 54 after which funnel-shape portion 52 will be driven upwards to separate the lower diverging end of funnel-shaped portion 52 from insulating material gasket 53. After the bottom of the funnel-shaped portion 52 is opened the high pressure within expansion chamber 54 is rapidly relieved and a strong cooling eiect is obtained due to this rapid decrease in pressure or expansion to extinguish the arc across the series spark gap between spaced electrode 45 and fixed contact 46. After interruption of the power follow

current springs

49 and 56 will move the moving parts of the system back to their original positions.

While there have been shown and described particular embodiments of the invention, it will be obvious to those skilled in the art that changes .and modifications may be made without departing from the invention, and that it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A spark gap construction comprising two-spaced electrodes defining an unobstructed arc gap therebetween, each of said electrodes partially submerged in a nonfl-ammable vaporizable insulating liquid, said arc gap extending between said electrodes along the surface of said liquid.

2. An arc gap construction comprising, in combination, a container, a non-iiammable vaporizable electrical insulating liquid partially filling said container, a pair of spaced electrodes extending through the surface of said liquid, the spacing between said electrodes above the surface of said liquid being a minimum at the surface of said liquid and increasing progressively as the distance above said surface increases, said electrodes below said surface having a predetermined spacing wherein the arcover voltage of said gap is determined by the electrode spacing at said surface.

3. A lightning arrester having two spaced electrodes defining an are gap therebetween, each of said electrodes partially submerged in a non-flammable vaporizable insulating liquid, said arc gap extending between said electrodes along the surface of said liquid, and said electrodes having a predetermined spacing whereby an electrical arc will be established lbetween said electrodes across said arc gap along said surface in response to a lightning surge.

4. A device as in claim 3, wherein one end of each said electrodes is submerged in said liquid, the other ends of said electrodes positioned above the surface of said liquid and increasingly spaced from each other in proportion to the distance above thersurface of said liquid.

5. A lightning arrester comprising two spaced electrodes defining an unobstructed spark gap therebetween, each of said electrodes partially submerged in a non- 6 flammable' vaporizable vinsulating liquid 'whereby 'an electrifcal-arc can be ignited acro'sssai'd spark gap between said two spaced electrodes along 'the' surface of said liquid in response to a lightning surge, said arc causing 'some of said liquid to vaporize whereby ablastof gas isdirected across said arc to extinguishv saidarc.

6. A lightning arrester comprising two generally upright spacedoand diverging horn electrodes defining a spark gap' therebetween, the closely spaced ends of said electrodes submerged within a non-flammable vaporizable insulating liquid and the widely spaced ends of said electrodes protruding beyond the surface of said liquid whereby an electrical arc can be established between said electrodes along the surface of said liquid.

7. A lightning arrester comprising an axially movable upright rod-like electrode and an yannular electrode concentrically disposed about said rod-like electrode and spaced therefrom defining an annular spark gap therebetween, each of said two spaced electrodes partially submerged within a non-ammable vaporizable insulating liquid whereby an electrical arc can be ignited across said spark gap between said two spaced electrodes along the surface of said liquid, the upper end of said rod-like electrode protruding beyond the surface of said liquid and having an umbrella-like hood attached thereto, a contact submerged in said liquid, and means urging said axially movable rod-like electrode downward for engagement of the lower end thereof with said contact.

S. A lightning arrester as in claim 7, wherein an axially movable funnel-shaped portion submerged within said liquid is concentrically disposed with respect to said rodlike electrode, a narrow open end portion of said funnelshaped portion disposed adjacent to and directed towards said annular spark gap, means urging said funnel-shaped portion downward for engagement of a wide open end portion of said funnel-shaped portion with a closure member whereby said wide open end portion is closed with said rod-like electrode lower end and contact disposed therein, an electrical arc struck across said series spark gap vaporizing some of said liquid.

9. A lightning arrester comprising an axially movable upright rod-like electrode and an annular immovable electrode concentrically disposed about said rod-like electrode and spaced therefrom defining an annular spark gap therebetween, each of said two spaced electrodes partially submerged within a non-flammable vaporizable insulating liquid whereby an electrical arc can be ignited across said spark gap between said two spaced electrodes along they surface of said liquid, the upper end of said rod-like electrode protruding beyond the surface of said liquid and having an umbrella-like hood attached thereto, a contact submerged in said liquid, and means urging said axially movable rod-like electrode downward for engagement of the lower end thereof with said contact.

l0. In a lightning arrester having two spaced electrodes which dene an arc gap therebetween, each of said electrodes being partially submerged in a non-flammable vaporizable insulating liquid, said arc gap extending between said electrodes along the surface of said liquid, and said electrodes having a predetermined spacing whereby an electrical arc will be established between said electrodes across said arc gap along said surface in response to a lightning surge, one of said electrodes comprising an axially movable rod-like member, one end of said rod-like member being disposed in said liquid, a fixed contact which is submerged in said liquid, said one end abutting said fixed contact, the other end of said rod-like lmember being positioned above the surface of said liquid and having a hood attached thereto, and the other of said electrodes comprising an annular member which surrounds said rod-like member and is spaced therefrom, said annular member being positioned beneath said hood.

ll. A device as in claim l0 wherein an axially movable funnel-shaped member is submerged in said liquid, said funnel-shaped member having a converging portion adjacent one end thereof and a diverging portion adjacent another end thereof, said funnel-shaped member surrounding said rod-like'member and being spaced therefrom said converging portion being directed towards said annular portion, and closure means engageable with said diverging portion whereby said rod-like member one end and said xed contact are enclosed within said diverging portion.

References Cited in the file of this patent UNITED STATES PATENTS