US3515947A - Inclined arc chamber for a spark gap - Google Patents

Description

' June 2, 1970 E. sTETso-N 3,515,947

INCLINED ARC CHAMBER FOR A SPARK GAP Filed Feb. 29, 196s 2 sheets-sheet 2 ,ffii/275i? 2%/ www, y a@ P ya United States Patent O 3,515,947 INCLINED ARC CHAMBER FOR A SPARK GAP Earl W. Stetson, Pittsield, Mass., assignor to General Electric Company, a corporation of New York Filed Feb. 29, 1968, Ser. No. 709,284 Int. Cl. H02h 1/00, 9/06 U.S. Cl. 317-61 16 Claims ABSTRACT OF THE DISCLOSURE An arcing chamber for a spark gap, such as those utilized in current limiting lightning arresters, characterized by having an inclined or curvilinear arc-lengthening passageway that functions to maintain the path of movement of an arc forced into the arcing chamber substantially perpendicular to the curvilinear lines of tiux of a magnetic eld established in the chamber for driving an are from the spark gap into the chamber. Thus, maximum arc moving eiciency and maximum arc voltage is attained in utilizing the magnetic eld.

Reference is made to my copending United States patent application, Ser. No. 706,911, tiled Feb. 20, 1968, which is assigned to the assignee of the invention described herein. That application discloses and claims the improved electrode structure and electrode positioning means shownherein.

The invention described herein relates to arcing chambers of the type utilized in lightning arresters, and more particularly, to an arcing chamber for a lightning arrester spark gap which has a magnetic eld established therein for moving an arc from the spark gap into the chamber; wherein the chamber is characterized 'by having an arclengthening passageway that is inclined along its length to maintain the direction of motion of an arc in the passageway substantially perpendicular to the lflux lines of the magnetic iield.

It is well known to use various types of spark gap structures and associated arcing chambers in the construction of lightning arresters. The primary object of a lightning arrester is to discharge surges of voltage, which may result from lightning striking equipment protected by the arrester or "which may be induced in a protected system by switching surges. This protective function is altorded by providing a path to ground through the lightning arrester for discharging transient and surge voltages from a protected system, through the arrester, to ground. Of course, lightning arresters must be constucted so that they form a discharge circuit to ground only when a predetermined magnitude of surge voltage is impressed on the arrester, and once the circuit has performed its discharge function, it must be quickly interrupted to prevent power-follow current from the protected system from following the discharge path through the arrester to ground. These operating characteristics are conventionally obtained by combining some type of spark gap structure in a series circuit with a nonlinear resistance valve material between suitable terminals mounted on an insulating lightning arrester housing. The spark gaps in these structures are designed to arc over at a predetermined voltage which is above the normal operating voltage of the system, but -below the limit of voltage levels which would damage the electrical equipment or insulation of the system 'being protected. The nonlinear resistance valve material presents a relatively high resistance to the normally low operating voltages of the system being protected, and presents a much lower resistance to the higher voltages resulting from transient surges. Therefore, when a high voltage surge is impressed across such lightning arresters, the spark gaps arc over and a rela- 3,515,947 Patented June 2, 1970 ICC tively low resistance path is provided through the nonlinear resistance valve material to discharge the surge voltage to ground. After the surge has been dissipated it is necessary, as noted above, to return the arrester t0 its normal open circuit condition as rapidly as possible to prevent the continuous discharge of normal line current, or power-follow current, through the arrester to gound. This result is accomplished by the combined effect of the arcs formed across the arc gaps being quickly extended and by the increased resistance presented to the power-follow current by the valve resistance material at the lower voltages.

In order to quickly limit the power-follow current and extinguish the arcs formed between the spark gaps following a transient Voltage surge, it is common practice in the lightning arrester field to provide arcing chambers adjacent the respective spark gaps for lengthening the arcs formed between the gaps thereby to increase the arc resistance to a level such that the system Voltage will be incapable of maintaining the arc. In general the more rapidly an arc can be moved into an arcing chamber and the higher its arc voltage, the 4better are the lightning arresters discharge and re-seal characteristics, because a smaller value of nonlinear resistance can be utilized in such arresters. A known technique for rapidly moving an arc into an arcing chamber is to provide a magnetic eld in the chamber to drive the arc from the spark gap into the chamber. 4One way of developing such a magnetic field in an arcing chamber is shown in U.S. Pat. No. 2,566,895, issued Sept. 4, 1951 to l. W. Kalb for a Protective Device, and assigned to the same assignee as the present invention. As disclosed in that patent, a coil is provided in series with a main spark gap so that when the spark gap arcs over the coil is energized and a magnetic eld is created in the arcing chamber and spark gap to move the arc from the gap into the chamber. From the earliest use of such coils in lightning arresters, the practice of shunting the coil with either a coil gap or a resistance to limit the voltage across the coil and thus protect it from ilashover and insulation damage was common practice. This shunting feature is also shown in the above-referenced Kalb patent.

While prior art lightning arresters of the type generally described above function in a suitably reliable manner, it is desirable to improve their operating characteristics and reduce their size, so that more accurate system parameters can be reliably designed based on the improved operating characteristics, and so that more economical arresters can be constructed. One major problem inherent in present day lightning arresters which employ an electromagnetic coil, of the type described above, to accelerate the movement of an arc into an arcing chamber, results from the fact that the respective arc voltages across the several series arcs formed in the lightning arrester tend to vary relatively widely. Most of this voltage differential between the respective arcs is attributable to the variation in effective arc moving magnetic flux present in the various arc chambers. A second difficulty presented by some present-day arcing chambers stems from the fact that arcs stretched into the chambers act to ionize the spark gap disposed in the chamber so that there is a tendency for this gap to re-strike a second arc after the initial arc has been extinguished. Of course, such re-strikes are objectionable because they lengthen the time required to clear the power-follow current through the arrester.

Although it is obvious that the resistance of an arc can be increased by lengthening the arc to produce a greater voltage drop across it thus limiting power-follow current, as described above, it is usually desirable to minimize the physical size of a lightning arrester housing. Heretofore, a step toward optimized operation in these conflicting areas has been achieved by providing a tortuous arcstretching passageway in the arcing chamber adjacent the peripheral wall thereof, so that the effective arc-stretching length of the wall is increased without increasing the outside diameter of the chamber. An advantage of my invention is that further optimization of the results in these two areas is provided by the inclined-pasageway arc chambers constructed pursuant to the invention.

One object of my invention is to provide an arcing chamber for a spark gap which has a magnetic arc moving field established therein; in which the chamber is arranged to confine an arc in a path that is substantially perpendicular to the lines of flux of the magnetic eld over substantially the entire length of the arc. Thereby maximizing the speed of arc movement and the arc voltage produced.

Another object of the invention is to provide better equalization of arc voltages across the respective arcs formed between a plurality of series connected spark gaps in a lightning arrestei housing.

A further object of the invention is to provide an arcing chamber having an inclined arc-stretching passageway therein that serves to obscure a portion of an extended arc from a line-of-sight View of a spark gap disposed in the chamber, thereby to limit ionization of the gap and thus reduce the probability of an arc re-striking.

Still another object of the invention is to provide an arcing chamber of a predetermined minimized diameter with an increased arc-lengthening passageway that serves to increase the arc voltage drop as an arc is stretched into the passageway.

Further objects and advantages of the invention will become apparent as the following description of it proceeds. In the preferred form of the invention described in detail herein, arcing chambers incorporating the inclined arc-lengthening passageways of my invention are shown with respect to a lightning arrester that incorporates several such arcing chambers in series.

The invention will be better understood from the following description taken in connection with the accompanying drawings n which:

FIG. 1 is a side elevation, partly in cross section, of a lightning arrester incorporating the improved arc chamber structure taught by my invention.

FIG. 2 is a top plan View, partly in phantom, of the spark gap and associated arcing chamber structure of the lightning arrester shown in FIG. 1. The phantom View is taken along the plane 2-2 in FIG. l.

FIG. 3 is a side elevation of the structure shown in FIG. 2.

FIG. 4 is an exploded perspective view showing the component parts in one of the main spark gaps and arcing chambers of the lightning arrester shown in FIG. 1.

FIG. 5 is an exploded perspective view showing the component parts of the coil gap and associated arcing chamber of the lightning arrester shown in FIG. l.

FIG. 6 is a cross sectional view taken through the plane 6*6 of FIG. 2 showing an enlarged view of one of the main spark gaps and its associated arcing chamber in an expanded relationship.

FIG. 7 is a fragmentary perspective view showing a portion of one of the main arcing chambers and depicting the detailed structural features of one of the main spark gap electrodes utilized in the lightning arrester shown in FIG. 1.

Referring now to the drawings in which like reference numerals are used to indicate similar parts throughout the various figures illustrated, and making particular reference to FIG. 1, there is shown a lightning arrester 1 comprising an annularinsulated housing 2, which may be formed of porcelain or other suitably strong insulating material. The arrester 1 is shown with respect to a power line conductor 3 that is connected by a second conductor 4 to a metallic terminal 5 sealed in any suitable manner to the top of lightning arrester housing 2. For example, a sealing resin `6 may be used to seal the terminal 5 to the housing 2. The end terminal 5 has a metallic conductor 7 electrically connected to it and extending into the interior of housing 2 where its lower end is flared to engage compression spring 8, which serves to resiliently bias the operating components of the lightning arrester into an electrical conducting relationship. The operating components of the lightning arrester 1 comprise a spark gap assembly 9 stacked in electrically conducting relationship with a nonlinear resistance valve element 10. The resilient spring 8 urges these members into electrical conducting relationship with each other and with a metalic contact member or plate 11 sealed to the bottom of housing 2 by a washer of resinous material 12 disposed around the periphery of the contact plate 11 and the housing 2. Plate 11, in turn, forms an electrical contact with the lower terminal 13 of the arrester which is provided with a contact 14 for facilitating electrical connection of the arrester 1 in a protective circuit, suh as in contact with a conductor 15 that completes the series circuit from the protected line 3 through the arrester 1 to ground.

The spark gap assembly 9 and nonlinear resistance valve element 10 of the arrester 1 operates in a generally conventional manner when a high voltage surge appears on transmission line conductor 3. Such a high Voltage surge causes the respective spark gaps (not shown) in the spark gap assembly 9 to arc over, thus allowing current to flow through the valve member 10 to the lower terminal 13 and thence to ground. After the surge voltage has been discharged, the power-follow current then flowing through the arrester 1 is interrupted by the interaction of the spark gap assembly 9' and the valve resistance element 10. The structural details and operation of the spark gap assembly 9 and its associated arcing chambers will be described in more detail below.

-Referring now to FIGS. 2 and 3 of othe drawings, a preferred embodiment of the spark gap assembly 9 is illustrated to depict the functional parts thereof. The spark gap assembly 9 comprises a housing formed of a plurality of porous discs A, B, C, D, E and F, each of which are provided with interlocking ridges and matching detents to position them in operating relationship. A pair of metallic terminals 16 and 17 are positioned on the upper and lower ends of the assembly 9, respectively. The terminal 16 is fastened in any suitable manner, such as by brazing, to an integral link 18 on a spark gap electrode 19. The other half of the spark gap is formed by a second electrode 20` which, in turn, is electrically connected by an integral link 21 to another spark gap electrode (not shown in FIG. 2, but seen as electrode 34 in FIG. 7) in an arcing chamber disposed between the porous housing members B and C. A second electrode forming the unseen spark gap between housing discs B and C is electrically and mechanically connected to one end of coil 22 by coil lead 22 and also by integral link 23 to coil gap electrode 24 seen in FIG. 5. Thus, a parallel circuit arrangement is formed placing the coil spark gap defined by electrode 24, and a secondpcoil gap electrode 25, across' the electromagnetic coil 22. The opposite end of coil 22 (not shown) and link 26 on coil gap electrode 25 are both electrically and mechanically connected to still another electrode of a main series spark gap disposed in an arcing chamber defined by the porous housing members D and E. This main spark gap is, in turn, series connected, in the manner described above with regard to the spark gap defining electrodes 1-9 and 20 and the spark gap disposed between housing members B and C, to a final spark gap formed by electrodes disposed in an arcing chamber between the housing members E and F. The endmost electrode of the spark gap between the housing members E and F is connected by an integral link that is brazed to metallic terminal 17 so that a completed series electrical circuit is formed between the two metallic terminals 16 and 17 on the upper and lower ends of spark gap assembly 9 when a high volt-age surge is impressed across these terminals causing the intervening spark gaps to arc over.

It will be understood that additional spark gaps can be added in series with those illustrated in the preferred embodiment of the invention in order to form a lightning arrester spark gap assembly having a higher voltage rating than the rating inherent in the assembly depicted, as is well known in the lightning arrester field. Furthermore, those skilled in the art will understand that when the coil 22 is energized by having a relatively low frequency electric current pass through it an electromagnetic field will be established around the coil 22 having lines of flux concentration that are generally circular in form. These magnetic flux lines intersect the respective arcs formed between the various spark gaps when a surge voltage is impressed on arrester 1, and act to electrodynamically drive the arcs outwardly from the sparks gaps into their associated arcing chambers in a manner well known in the lightning arrester field.

Since each of the four main spark gaps and their associated arcing chambers are essentially identical in structure and function in the preferred spark gap assembly 9 of the invention, only one of these main spark gaps and arcing chambers will be described in detail. For purposes of this description, I have chosen to describe the arcing chamber between housing elements A and B containing the spark gap defined by electrodes 19 and 20.

Referring to FIG. 4, there is shown an exploded view of the arcing chamber and spark gap arrangement disposed between the porous housing elements A and B. Both housing -members A and B, as well as the remainder of the housing members C, D, E, and F, are formed of porous insulating material, which in the preferred embodiment of the invention, comprises a mixture of aluminum oxide granules and a suitable binding material. These housing members are formed in a precast die and then heat treated to harden them into their respective configurations. A major feature of my invention resides in the particular configurations of the primary arcing cha-mbers, such as chamber 27, defined between housing members A and B when they are disposed in their operative position abutting one another.

Referring to FIG. 6, it will be seen that the arcing charnber 27 is formed to incorporate a generally planar wafershaped portion 27 adjacent the spark gap defined by electrodes 19 and 20, and a second portion 27" that is inclined to obscure a substantial part of its length from a line of sight view of the spark gap. One of the desirable benefits realized by having the arcing chamber 27 inclined to form the arc-lengthening passageway with its planar portion 27 intersected at a predetermined angle by the inclined portion 27, is that a major portion of the entire passageway will thus lie in a plane that is perpendicular, over a substantial portion of its extent, to the magnetic lines of flux established in the arcing chamber 27 by current fiowing through coil 22.

For illustrative purposes, the magnetic lines of flux established by coil 22 when current is passed therethrough are shown schematically by dotted lines 28 in FIGS. 3 and 6. It will be understood that the flux concentration of the magnetic fields these lines 28 represent will vary from a high degree of concentration in the Window of coil 22 to a less concentrated field on the outer side of the coil 22. Also, the circular configuration of coil 22 will cause the flux lines 28 to vary from a nearly vertical plane, or`path parallel to the longitudinal axis of asembly 9, near the center of the coil window, to a substantially horizontal plane at the circumference of assembly 9. Of course, as an arc moves through these lines of ux along electrodes 19 and 20, a driving force is applied to the arc by the magnetic Ifield. Accordingly, if the arc is allowed to travel in a path that intersects fiux lines 28 at a right angle, it

will do so, because this is the path of minimum resistance. On the other hand, if an arc is not allowed to follow such a path, but rather is confined in a plane that, for example, is perpendicular to the longitudinal axis of the assembly 9, the component of force from the magnetic field acting to drive the arc toward the periphery of chamber 27 is greatly reduced. Accordingly, with such a structure the arc is moved toward the periphery of chamber 27 at -a relatively slow rate and with a relatively low rate of increase in arc voltage. It will be seen that with my invention by forming the arc-lengthening passageway 27 so that its outermost peripheral portion 27 'is inclined at a predetermined angle such that it intersects the lines of fiux passing through this portion of the chamber at essentially a degree angle, a maximum driving force is maintained on the moving arc in the chamber 27 over its entire path of movement; therefore the arc is driven at maximum speed to the periphery of chamber 27 where it develops maximum are voltage. Since the fiux lines 28 bend sharply from a nearly vertical plane toward a horizontal plane in traversing arc chamber 27 from its center to its periphery, it is apparent that maximum overall electrodynamic motive force could be applied to an arc formed in the spark gap defined by electrodes 19 and 20, as it moved toward the tortuous arc stretching perimeter of the arcing chamber 27. if a smoothly curvilinear arc-lengthening passageway were formed between the lateral extremity of the arcing chamber 27 and the spark gap. Such an optimum arcing chamber structure is clearly within the intent and teaching of my invention, as are other structural modifications that utilize the teachings of my invention; however, in the preferred embodiment of the invention illustrated herein, I have elected to utilize an inclined arcing passageway 2727, having a single angular disruption therein. This simplified embodiment of my invention is preferred because it maintains a lengthened arc in the arcing chamber passageway 27-27l in a plane that is substantially perpendicular to the magnetic lines of flux 28 over a major portion of its length and, thus, affords a suitably high operating efiiciency, while at the same time allowing reasonable standardization of the various component parts of the spark gap assembly 9. Moreover, although it will be apparent to those skilled in the art that a slightly different curvilinear or bent angular configuration from that employed to form portion 27" of the outboard chambers between plates A and B, and E and F, would be necessary for the arc-lengthening passageway defined by the arcing chamber formed between the inboard housing members B and C, and D and E to obtain maximum electrodynamic driving action due to the fact that the magnetic lines of fiux 28 intersects these arcing chambers at a more nearly perpendicular angle than they intersect the outboard arcing chambers, I also prefer to utilize the same standardized dimensions for these inboard arcing chambers. Of course, it will again be understood that other chamber configurations that will increase the electrodynamic arc-driving force of the magnetic field on an arc formed between the spark gaps in these chambers is well within the scope of my invention.

In addition to satisfying the desirable objective of increasing the electrodynamic driving force of the magnetic eld estabilshed by coil 22, it will be noted that the unique curvilinear, or angular, configuration of the inclined arcing chamber 27 constructed pursuant to the teaching of my invention affords still another desirable result. Namely, referring to FIG. 6, it will be seen that as an arc is lengthened outwardly from electrodes 19 and 20 toward the perimeter 27" of the arcing chamber, it is extended in both a horizontal and vertical direction in the inclined portion 27 of the arcing chamber 27; thus, an added lengthening dimension is provided within a predetermined limit diametrical size housing member, such as members A and B. This -added arc-lengthening effect is magnified due to the fact that the teeth 29, 30, 31 etc. (see FIG. 2) serve to force an extended arc to move in a twisted, tortuous path around the peripheral portion 27 of the 7 arcing chamber 27 so that the vertical component of the arc distortion is doubled by each tooth.

From the foregoing description, an understanding of the enhanced arc-moving and arc-lengthening features of my invention can be obtained; however, the invention also embodies further unique and notable features, which are described and claimed in my contemporaneously filed application noted above in the first paragraph following the Abstract of the Disclosure. Referring to FIG. 4, it will be seen that electrodes 19 and 20 are positioned respectively on bosses 32 and 33. These bosses, 32 and 33, are integrally molded in the surface of housing member B and serve to precisely position electrodes 19 and 20 so that a spark gap of predetermined dimensions is formed by the electrodes without having to measure and then affix the terminals, 19 and 20, in position with some more conventional technique such as by gluing them or riveting them into position. In addition to facilitating the manufacture and assembly of the spark gap structure 9, the use of bosses 32 and 33 makes it possible to utilize standardized electrode assemblies that can be mass produced and consequently inexpensively made.

One such standardized electrode assembly is shown in detail in FIG. 7 of the drawing and it should be understood that these standardized units are employed in all of the main spark gap structures of the spark gap -assembly 9. Only the coil gap structure formed between electrodes 24 and 25, and one-half of the spark gap electrodes in the immediately adjacent arcing chambers, are formed by differently shaped electrodes. For purposes of illustration, the standardized electrode shown in FIG. 7 may be regarded as electrode 20, which is disposed between housing members A and B, joined by integral link 2.1 to a second integral electrode 34, which is positioned in the arcing chamber between housing members B and C in the preferred embodiment of the invention depicted in FIG. 3.

Finally, it should be understood that an important operating advantage of the spark gap structure of my invention stems from the fact that when an arc is extended into the tortuous, inclined portion 2 of the arcing chamber 27, it is obscured from a line of sight view of the spark gap electrodes, eg., electrodes 19 and 20. Therefore, when the arc is lengthened and extinguished by being cooled on the peripheral wall of chamber 27, the amount of radiation from the wall, which has been heated to near incandescence by the arc, tending to ionize the spark gap for a restrike is limited to that formed by the portion of the teeth 29, 30, 31, etc. extending to the innermost edge of inclined portion 27". Accordingly, the probability of an undesirable arc restrike is substantially diminished.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made therein Without departing from the invention and, therefore, it is intended by the appended claims to cover all such modifications and changes 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 chamber including means adapted to establish a relatively short arc and means defining a passageway adapted to receive said arc when it is lengthened, said passageway comprising a first portion that is disposed generally in a single plane, and a second portion that is disposed in at least one other plane that intersects said first plane at a predetermined angle such that a major part of said second portion is obscured from a line-of-sight view of said means adapted to establish a relatively short arc, said second portion of the passageway having a radial extend outward from said means adapted to establish an arc that is at least twice as long as the means vertical height of said passageway.

2. A spark gap chamber as defined in cliam 1 wherein said predetermined angle is less than 90 degrees.

3. A spark gap chamber as defined in claim 1 including means for establishing a magnetic field that forms generally curvilinear lines of magnetic flux through said chamber, wherein said second portion of said passageway is disposed in one or more planes each of which is substantially perpendicular to said lines of fiuX.

4. A spark gap assembly comprising means defining an p arcing chamber, a pair of separate electrodes disposed in spaced-apart relation within said chamber to define a spark gap therebetween, means for establishing a magnetic field that forms generally curvilinear lines of flux through said chamber, said magnetic field being effective to move an arc formed between said electrodes toward a wall of said chamber, means defining a curved passageway in said chamber between said electrodes and Said one wall of the chamber, a predetermined portion of said passageway adjacent said wall being obscured from a line-of-sight View of said electrodes, said curved passageway having at least one angular bend formed therein that is spaced from said wall a distance at least twice as great as the minimum length of said sparkgap.

5. A spark gap assembly as defined in claim 4 wherein said means for establishing a magnetic field comprises a coiled electrical conductor disposed adjacent said chantrber.

6. A spark gap assembly comprising an insulating housing having an arcing chamber therein, a pair of separate electrodes disposed in spaced apart relation within said chamber to define a spark gap therebetween, means for connecting said electrodes in an electrical circuit, an electrical coil disposed around said housing and adapted when electrically energized to establish a magnetic field in said chamber, means for energizing said coil, said magnetic field being effective to establish curvilinear lines of magnetic flux in said chamber that serve to move an arc formed between said electrodes into the chamber, said chamber being formed to define a generally wafer-shaped space with its major axis extending laterally from one side of said spark gap in a curved surface that is generally perpendicular to each of said curvilinear lines of flux at their respective points of intersection with said surface over substantially the entire extent thereof.

7. A spark gap assembly as defined in claim 6 including a second arcing chamber formed in said housing, a second pair of separate electrodes disposed in spaced apart relation to define a spark gap therebetween within said second arcing chamber, means for connecting the spark gaps defined by the respective pairs of electrodes in series, said electrical coil being effective when electrically energized to establish a magnetic field in said second chamber that acts to move an arc formed between the second electrodes into said seco-nd chamber, said second chamber being formed to define a generally wafer-shaped space having a major axis extending laterally from one side of said second pair of electrodes in a curved surface that is generally perpendicular over substantially itsentire extent to the magnetic lines of flux formed by the magnetic field in said chamber at each of the respective points of intersection between said surface and said flux lines.

8. A spark gap assembly as defined in claim 7 wherein said coil is disposed between said arcing chambers and the respective curved surfaces defined by the wafer-shaped chambers curve towards each other at their lateral extremities.

9. A spark gap assembly as dened in claim 7 including a plurality of additional spark gaps and associated arcing chambers, each of said additional spark gaps being electrically connected in series with the other two pairs of spark gaps.

10. A spark gap assembly as defined in claim 9 wherein each of said additional arcing chambers respectively defines a wafer-shaped space having a major axis extending laterally from one side of the spark gap therein in a curved surface that is generally perpendicular over a major portion of its entire extent to magnetic flux lines 9 formed by a magnetic field established therein when said coil is energized.

11. A lightning arrester comprising a housing of insulating material having a first metallic terminal at one end thereof and a second metallic terminal at an opposite end thereof, means defining a plurality of series connected spark gaps disposed respectively in separate arcing chambers in said housing, a nonlinear resistance material mounted within said housing, an electrically conducting coil mounted within said housing, means electrically connecting said nonlinear resistance material in series with said coil and said plurality of spark gaps between said first and second metallic terminals, said coil being effective when electrically energized to establish a field of magnetic lines of flux in each of said arcing chambers to drive arcs formed in said spark gaps into said chambers, each of said arcing chambers being formed to define a passageway extending laterally from the spark gap in said chamber and adapted to receive an extended arc formed in the respective spark gaps and driven into the chamber by said magnetic field, each of said passageways being inclined at predetermined points along their lateral extent in a manner such that an arc confined by said passageway is maintained in a path that is substantially perpendicular to said magnetic lines of flux at their respective points of intersection therewith over a major portion of its length.

12. A lightning arrester as defined in claim 11 wherein said arcing chamber passageway are formed to define a generally wafer-shaped space bounded by closely spaced substantially parallel inclined surfaces that are in juxtaposition respectively with opposite sides of the means defining the spark gap in said chamber.

13. A lightning arrester as defined in claim 12 wherein the angle of inclination in at least one of said passageways is of such a magnitude with relation to the spacing of said bounding parallel surfaces that a substantial portion of the length of the passageway adjacent one end thereof is obscured from a line-of-sight view of the spark gap adjacent the opposite end thereof.

14. A lightning arrester as defined in claim 11 wherein the means defining a plurality of series connected spark gaps disposed respectively in separate arcing chambers comprises; a plurality of porous, molded insulating members having interfitting bosses and detents thereon for retaining said members in a predetermined closely spaced aligned relationship when they are in assembled position, said members being shaped respectively such that a plurality of stacked isolated arcing chambers are defined thereby, a plurality of electrode members each comprising a pair of electrodes integrally formed with an electrically conducting link therebetween, one electrode of one of said electrode members being electrically connected to said first metallic terminal and one electrode of another of said electrode members being electrically connected to said second metallic terminal, the remainder of the electrodes of said electrode members being disposed respectively in adjacent arcing chambers in a manner such that a spark gap is formed in each chamber between electrodes comprising an integral part respectively of separate electrode members, whereby a series of spark gaps are formed by said electrodes and electrically connected in series between said first and second metallic terminals by the integral conducting links of each of said electrode members.

15. A lightning arrester as defined in claim 14 including electrode-positioning bosses integrally molded on the respective surfaces of each arcing chamber and adapted to tightly engage the electrodes disposed therein thereby to position them in a predetermined spaced-apart relation such that a spark gap of predetermined length is formed between said electrodes.

16. In a lightning arrester, an arcing chamber, a pair of arc forming electrodes in said chamber, said arcing chamber comprising a first generally planar region adjacent said electrodes and a second region remote from said electrodes formed to define a tortuous passageway adapted to lengthen and cool an arc forced into it, electromagnetic means for driving an arc formed between said electrodes into the region of said chamber containing said tortuous pasageway, the tortuous passageway in said second region of the chamber being arranged in at least one planethat intersects said first generally planar region at a predetermined angle thereby to cause an arc driven from said electrodes into said second region to be bent around said angle, whereby the arc is lengthened in both a horizontal and vertical direction as it is forced into said tortuous passageway.

References Cited UNITED STATES PATENTS 2,917,662 12/1959 Cunningham 315-36 3,259,780 7/1966 Stetson 317-36 X 3,273,010 9/1966 Sacer 317-36 3,354,345 11/1967 Stetson 317-74 X JAMES D. TRAMMELL, Primary Examiner U.S. Cl. X.R.

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