US2917662A - Arc arrester spark gap - Google Patents

Description

Dec. 15, 1959 F. v. CUNNINGHAM 2,917,662

ARC mnssrm SPARK GAP Filed Jan. 7, 1958 2 Shuts-Shoot 1 ig INVENTOR.

Francis M Cwmn y/zam BY fin /Q 5L ATTO RN EY Dea. 15, 1959 F. v. CUNNINGHAM 2,917,662

mo ARRESTER SPARK GAP 2 Sheets-Shut 2 Filed Jan. 7, 1958 INVENTOR. l2 Franals M 'urmz'ryfiam BY fi s Q54 ATTORNEY United States Patent ARC ARRESTER SPARK GAP Francis v. Cunningham, Milwaukee, Wis., assignor to McGraw-Edison Company, Milwaukee, Wis., a corporation of Delaware Application January 7, 1958,. Serial No. 707,604

' 6 Claims; (Cl. 315-36) This invention relates. to an arc arresting spark gap and, more particularly, relates to an arc arresting spark gap assembly associated with a lightning arrester or the like.

Commercial lightning arresters presently in use generally have associated therewith a series of spark gaps which are in electrical series relationship to valve material, i.'e., negative resistance material and the like. These spark gaps presently in use for valve type lightning arresters have been of two main types, namely, a ladder gap where there are spaced metallic electrodes in series arrangement such as shown in my copending application entitled Spark Gap Assembly, filed March 14, 1956, and having Serial No. 571,543,- or the magnetic type wherein the arc is stretched or extended from the closest point between spaced electrodes by external magnetic means.

In lightning arreste'r spark gaps of the latter type, i.e., the magnetic type, extra space within the lightning arrester housing is needed to provide for the electromagnet coil or the permanent magnet which provides the magnetic flux for stretching the arc. Space within a lightning arrester housing is at a premium both from an initial cost standpoint and because of weight considerations occasioned by the fact that lightning arresters by their very nature are designed to be associated with electrical equipment which is often mounted in an elevated position.

It is an object of this invention to provide a magnetic spark gap wherein the are movement is accomplished without the aid of an external magnet or external electromagnet coil means which provide a magnetic flux to aid the interruption of the high follow current usually associated with the low discharge voltage or IR drop needed for the modern valve type lightning arresters.

It is an object of this invention to provide a magnetic type of spark gap assembly wherein the arc is stretched by the magnetic principles involved in a change of current direction and more particularly a change in current path direction of an are at its points of egress and ingress to an electrode, said change in direction giving rise to an inherent magnetic blowout effect.

It is a further object of this invention to provide a spark gap assembly of the type aforementioned wherein an arc extinguishing chamber surrounds the spark gap area such that there is are cooling and stretching afforded by the dual effects of thermal expansion of gas within said chamber, forcing the are away from the are initiating point as well asthe magnetic effect, both effects being coordinated to interrupt the arc in a minimum space and time.

It is a further object of this invention to provide a spark gap assembly of the type above described wherein spaced electrodes are so configured and disposed that the initial arcing takes place at one preselected place and extended arcing takes place at a different preselected place whereby prolonged arcing will not deleteriously effect the initial sparkovercharacteristics of the initial spark gap area.

It is another object of this invention to provide a series of spark gaps for a valve type lightning arrester which is made of a plurality of single plates or discs disposed in a stacked construction which may be used in any multiple depending upon the voltage rating desired.

It is a further object of this invention to provide a disclike construction as-above identified which iseasily'molded into a configuration such that 'two mating surfaces of adjacent discs within the stack form an arc extinguishing chamber or are chutes; Said discs may be formed of gas evolving material which aids the thermal expansion effect to quickly interrupt a power follow current are within a minimum space of time and within a minimum area.

It is a further object of this invention to provide a pair of spaced arcing electrodes of the type aforementioned wherein the arc initiating point between the electrodes and the are as it is traveling along the extended portions of each of theelectrodes leaves and enters each of said electrodes generally normal to the current direction in the electrode per se, the abrupt change in current direc tion providing. maximum intensity of the magnetic effect on said are to stretch the latter.

It is a further object of this invention to provide a stacked disc-like construction as above identified wherein a pair of arci'n-g spaced electrodes are disposed within a chamber formed between each of two neighboring discs, each of said chambers so formed having an outlet, each of said outlets being spaced radially from the next adjacent upper and lower outlet to thereby prevent external flashover of the stack of discs when ionized gas formed by the arcing electrodes exhausts or empties from said outlets.

It is a further object of this invention to provide a stack of internal spark gaps of the type aforementioned which is exceedingly compact in axial and radial dimensions, is easy to manufacture, easy to store, easy to inventory, has high manufacturing tolerances, is self-locking in assembly and is otherwise welladapted for the purposes forwhich it was designed;

The novel features that are characteristic of the invention are set forth with particularity in the appended claims. The invention itself, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood by the following description of specific embodiment when read in connection with the accompanying drawings in which:

Fig. 1 is a top plan view of the single disc used in conjunction with other identical discs in a stacked relation;

Fig. 2 is a perspective view of the disc shown in Fig. 1 and rotated approximately 40' from the view in Fig. 1;

Fig. 3 is a side view of the disc shown in Figs. 1 and 2;

Fig. 4 is a perspective view similar to Figs. 1-3 above, the disc being rotated 40 from the position shown in Fig. 3;

Fig. 5 is a bottom view of the disc shown in Figs. 1-4, inclusive;

Fig. 6 is a cross section through two identical discs in stacked relation, the lower portion of the drawing being along lines 6A-6B of Fig. l and the upper disc being along lines 6C6D of Fig. 1;

Fig. 7 is an exploded perspective View of two discs in stacked relation to show the relative position of the arc chute and the electrodes on the bottom and top sides of the stacked discs respectively;

Fig. 8 is a fragmentary exploded perspective view, partially in section, showing the operating characteristics of the electrodes in a plurality of stacked discs;

Fig. 9 is a fragmentary view, partially in section, of a valve type lightning arrester embodying a series spark gap arrangement in accordance with the inventive concept and showing the relative position of the vents of the arc chutes when the discs are in stacked relation;

Fig. is a top view of an alternative form of construction embodying the principles of my inventive concept;

Fig. 11 is a front view of the embodiment shown in Fig. 10; and

Fig. 12 is a sectional view along lines 1212 of Fig. 10.

Returning now to the drawings and more particularly to Fig. 9, the reference numeral 9 represents a lightning arrester having a tubular porcelain housing 16, the lower end of which is grounded at 11 and the upper end of which is attached to equipment desired to be protected by a suitable conductor 12. An outer protective cap 13 is generally cup shape in configuration and fits down -over the top of the lightning arrester housing 10 and is held in place by suitable potting compound as shown. A metal conducting cap 14 is sealingly mounted on the top of the housing 10, there being gasket means 15 interposed around the peripheral edges of the housing to seal out .moisture to the interior of the arrester 9. A leaf-like spring 16 mechanically and electrically engages conducting cap 14 and serves both as a current carrying member and to bias and hold a stack of series gap discs 17 into the upright position at the top of the housing shown. A metal plate 19 is disposed in conducting engagement between the spring 13 and the upper most disc in the stack and a metal plate 20 is disposed intermediate the valve material 21 and the bottom most disc of the stack 17.

The individual disc 18 is shown in detail in Figs. 14, inclusive, the top side being denominated 22 and the .bottom side 23. The disc 18 may be formed of a glass and mica combination that is sold under the tradename .Mycalex or may be formed of suitable material of the gas evolving type such as horn fibre or the like. Mycalex is not ordinarily considered to be gas evolving; rather there is a thermal expansion of gas within the chamber which tends to seek the outlet from the chamber.

The top disc side 22 is formed with an upper raised electrode support portion 24 and a raised are chute wall portion 25, said portions 24 and 25 defining therebetween a depressed upper arc chute bottom wall portion 26. The depressed portion of the arc chute has a curvilinear sidewall portion 28 and a straight wall portion 28a formed as best shown in Figs. 2 and 7 of the drawings, there being outlet end 29 and electrode end 30 at the respective ends of the chute. A radial shoulder 27 is formed on the periphery of the disc 18 coplanar with the chute bottom wall 26. The shoulder 27 is adapted to mate with :1 depending portion 33 of the next adjacent disc as shall be explained more fully hereinafter.

The bottom side 23 of the disc 18 is formed with an an arc chute wall portion 32. The bottom wall portion 41 is defined by a curvilinear side wall portion 36 and straight wall 36a. It will be observed that the arc chutes, electrodes, wall portions, etc., on the top 22 and bottom 23 are disposed 90 from each other.

Each disc 18 is adapted to have two electrodes 37-38 mounted thereon which have common current carrying pins interconnecting the same, said pins being denominated 39 and 40. The electrodes 37-38 are generally U-shaped in configuration, each being formed with base portions 37b and 38b, arms 37a-38a, 37c38c and portions 37d-38d. The arm portions 37a38a of the electrodes are electrically connected by the aforementioned conducting pins 39-40. The base portions 37b--38b are disposed at substantially right angles to arm portions 37a-38a and arm portions 37c38c, the two arms on each electrode being parallel to each other for space saving reasons. The free ends of arms 37c38c are formed with an arcing extension 370! which curves back around the ends of arms 37a38a, the configuration shown being very compact.

It will be observed that when two discs such as 18a and 18b as shown in Fig. 7 are placed in stacked relation, the depending lug 34 fits into the end portion 30 opposite from outlet portion 29 of the arc chute bottom wall 26. This disposition serves to locate electrode 38 on disc 131') relative to electrode 37 on disc 18a and to locate the upper and lower arc chute bottom wall surfaces 26 and 41, respectively, relative to the assembly as shown in Fig. 6. Thus, a chamber is formed between discs 18 and 18b having therein first and second spaced electrodes, i.e., 37 and 38, the electrodes having base portions 37b38b generally opposite each other to form a gap. When the discs are molded in the configurations shown (particularly refer to the sectional view of Fig. 6) the long planes of electrodes 37 and electrode 38 are offset from each other slightly in the axial direction. This ofiset aids in causing the are formed therebetween to contact the walls forming the arc chute and to be cooled thereby. It will be apparent that the electrodes may be set in a parallel plane if such is desired and the same cooling effect may be had by tapering the walls of the chute.

The initial arcing point 42 (see Fig. 8) of the electrodes '3738 is at the confluence of portions 37b37c and 3Sb-3Sc respectively. The are path at the initiating point 42 is such that it is generally normal to the direction of the current path in the individual electrodes at that point, i.e., as shown in Fig. 8, the arc path 43a at points 42 on electrodes 37-38 is substantially normal to the current path within electrodes 37-38 at the rounded confluence of portions 37b-37c and 38b38c. The inherent magnetic effect of the curent flow itself in the path shown will tend to cause the arc at 42 to move outwardly along portions 37c and 380, respectively, as shown by reference numerals 43b and 430. The are may continue until it reaches arcing tips 38d and 37d as shown in Fig. 8. There may also be times when the arc is extinguished and current flow ceases before the arc reaches its full extension as shown by 43d. (On A.C. circuits this would depend on just what point in the voltage wave the power follow current was initiated by the surge.) If extended arcing takes place at this point, i.e., 37d38d, it will be observed that it will not effect the characteristics of the initial point of sparkover, i.e., point 42. It will also be observed that the arc path at all times is substantially normal to the current path within the electrodes, i.e., arc path 431) and 430 are normal to the current path in electrode portions 37c38c and are path 43d is normal to portion 37d38d.

As the arc travels outwardly along the electrodes 37--38 as shown in Fig. 8 (reference numbers 43a43d) it is put into engagement with the surfaces of the arc chutes 41 and 26 which will tend to cool same. Note that no external magnetic effect is used or needed to move the arc outwardly along portions 37c38d of the electrodes; the movement is caused by the change in current direction at the points of ingress and egress. The arcing at point 42 causes a great thermal expansion of the gas within the arcing chamber formed by the discs. This tremendous expansion of gas tends to move toward the outlet area and carries the arc therealong. Of course, if gas evolving material is used, this blast effect is heightened by the addition of more gas.

The particular structure above described is particularly Well adapted for a stacked relationship of gaps in that no additional magnetic effect is involved. Thus, a very short or compact axial dimension between spark gaps may be maintained.

The offsetting of the arc chutes relative to one another on the tops and bottoms of the individual discs changes the radial disposition of the outlets 35, thus making the outlet otfset 90 ineach individual disc of the stack from its next adjacent neighbor. This offsetting of outlets 35 is important in that the gases evolved during the arcing when exhausted throughv the outlets will be prevented from flashing over the entire stack 17.

An alternative embodiment is shown in Figs. 10-12, inclusive. The same principles of arc movement are used, i.e., the. dual effects of thermally expanding gas and the magnetic principles of a current path direction change. The alternative embodiment shown is semidiagrammatic and is similarly formed of two opposing discs 44 and 45 which are formed with hollowed out are chamber portions 46 and 47 having a common outlet 48. This embodiment can also be stacked in any desired number, i.e., more than one pair of electrodes may be used depending on system voltage rating of the arrester desired. The electrodes 50 and 49 are respectively connected to the equipment to be protected at 51 and to ground at 52. The electrodes 49 and 50 are each of a general boomerang shape, the first portion 50b being substanitally otfset relative to portion 50a and portion 49b being similarly disposed relative to portion 49a. The are will initiate at the confluence of the portions on each electrode and will move outwardly through the chamber to the outlet 48. Inthis embodiment, the discs are shown as composed of horn fibre to increase the influence of the blast effect on the arc.

Although specific embodiments of the invention have been shown and described, it is with full awareness that many modifications thereof are possible. The invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

What is claimed as the invention is:

1. A spark gap assembly comprising walls formed of a dielectric material defining an arc extinguishing chamber having an outlet, first and second electrodes each having a first and second portion, said first portion afiording a first electrical current path direction therewithin and second portion affording a second current path direction therewithin, said first and second electrodes being spacedly disposed in said chamber such that the are initiating path therebetween is at a confluence of each of said first and second portions of each electrode and generally normal to the current path in said electrodes so that the arc cretaed upon breakdown of the arc initiating path creates a self generated magnetic repulsion relative to the current in the current path in the electrode immediately adjacent thereto to provide a magnetic movement of the are along the second portion of said electrodes, said outlet of said chamber being spaced from said are initiating path between said electrodes and generally disposed normal to said path.

2. A spark gap assembly comprising walls formed of dielectric material defining an arc extinction chamber having an outlet, first and second spaced electrodes disposed Within said chamber each having a configuration afiording a first and second electrical current path direction therewithin, said first and second electrodes being disposed such that the shortest gap path therebetween is at a point requiring an abrupt change of current direction from said first current direction upon breakdown of the gap so that the are created upon breakdown of the arc initiating path creates a self generated magnetic repulsion relative to the current in the curent path in the electrode immediately adjacent thereto to provide a magnetic movement of the are along the second portion of said electrodes, said outlet of said chamber being spaced from said shortest gap path between said electrodes and generally disposed normal thereto.

3. Lightning arrester spark gap comprising walls formed of a delectric material defining an arc extinction chamber having an outlet, first and second electrodes each having first and second portions, said first portion afiording a first electrical current path direction" therewithin and second portion afiording a second current path direction therewithin, said first and second electrodes being spacedly disposed in said chamber such that the arc initiating path therebetween is .at a confluence of each of said first and second portions of each electrode and generally transverse to the current path in said electrodes so that the arc-created upon breakdown of the arc initiating path creates a self generated magnetic repulsion relative to the current in the current path in the electrode immediately adjacent thereto to provide a magnetic movement of the are along the second portion of said electrodes, said second portions of each electrode being so disposed as to have an arc move outwardly therealong away from the arc initiating path to elongate the arc, the direction of curren flow of the arc path during said movement being generally normal to each of the said second portions at the points of egress and entrance thereto, said outlet of said chamber being spaced from said are initiating path between said electrodes and generally disposed normal thereto.

4. Lightning arrester spark gap comprising walls formed of a dielectric material defining an arc extinction chamher having an outlet, first and second electrodes each having a first and second portion, said first portion affording a first electrical current direction therewithin and second portion affording a second current direction therewithin, said first and second electrodes being spacedly disposed in said chamber such that the arc initiating path therebetween is at a confluence of each of said first and second portions of each electrode and generally transverse to the current path in said electrodes so that the are created upon breakdown of the arc initiating path creates a self generated magnetic repulsion relative to the current in the current path in the electrode immediately adjacent thereto to provide a magnetic movement of the are along the second portion of said electrodes, said second portions or" each electrode being spaced from each other a greater distance than said are initiating path and adapted to receive extended arcing without deleteriously eifecting the operating characteristics of the initial path, said outlet of said chamber being spaced from said are initiating path between said electrodes and generally disposed normal to said path.

5. Lightning arrester spark gap assembly comprising a plurality of stacked discs formed of a dielectric material, said discs having, when in stacked relation, mating hollowed out portions defining an arc extinction chamber having an outlet, first and second cooperating spaced electrodes disposed within said chamber and each being fixedly mounted on a different disc within said stack with an air gap therebetween, each individual electrode having a configuration afiording a first and second electrical current path direction therewithin, said first and second electrodes each being disposed such that the shortest electrical path across the air gap therebetween is at a point requiring an abrupt change of current direction from said first current path direction in the electrode upon breakdown of said gap so that the are created upon breakdown of the arc initiating path creates a self generated magnetic repulsion relative to the current in the current path in the electrode immediately adjacent thereto to provide a magnetic movement of the are along the second portion of said electrodes and said outlet of said chamber being spaced from said shortest air gap between said electrodes and generally disposed transverse thereto.

6. Lightning arrester spark gap assembly for valve type lightning arresters comprising a plurality of stacked discs formed of a dielectric material, each of said discs having, when in stacked relation, an upper and a lower mating hollowed out portion defining with the next adjacent lower and upper hollowed out portion respectively of the adajcent discs, an arc extinction chamber having an outlet on a peripheral edge of the disc, first and second cooperating spaced electrodes disposed within said chamber and each being fixedly mounted on a different disc within said stack with an air gap therebetween, each individual electrode having a configuration aflfording a first and second electrical current path direction therewith, said first and second electrodes each being disposed such that the shortest electrical path across the air gap therebetween is at a point requiring an abrupt change in current direc tion from said first current path direction in the electrode upon breakdown of said gap so that the arc created upon breakdown of the arc initiating path creates a self generated magnetic repulsion relative to the current in the cur- 10 2,825,008

rent path in the electrode immediately adjacent thereto to provide a magnetic movement of the arc along the second portion of said electrodes, and said outlet of said chamber being spaced from said shortest air gap between said electrodes and generally disposed transverse thereto.

References Cited in the file of this patent UNITED STATES PATENTS Hedlund Feb. 25, 1958 Kalb Feb. 25, 1958 UNITED .STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,917,662 December 15, 1959 Francis V0 Cunningham It is herebfi certified that error appears in the -printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 47, claim 1, for "creteed" reed created line 66, claim 2, for "cnrent" read s current column 6;; line 15, 01am 3, for "curren" read current column '7, line 3 claim 6, for "therewith" read me therewithin Signed and sealed this 7th day of June 1960.,

Attest:

KARL E. Attesting Officer ROBERT C. WATSON Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION No, 2,917,662 December 1959 Francis V0 Cunningham It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line if), l, for "cre'taed" reed cr eeted g llne 66, claim 22,, for "cur'ent" read f;ur1"6'nb column 6,, 1.1118 15, clam 3, for "CYLIITGI'I" read current column '7, line 3, claim 6, for "therewlth" road w tlQeTeWitI-Tin Signed and sealed this 7 h day of June 19600 Attest:

EL ROBERT C. WATSON Attesting Officer Commissioner of Patents

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