LIGHTNING ARRESTER SPARKGAP ASSEMBLY HAVING OPPOSED ELECTROMAGNETIC FIELD-GENERATING MEANS FOR CONTROLLING ARC MOVEMENT
United States Patent 3611045
A current-limiting sparkgap assembly of the type that utilizes a magnetic field to stretch arcs in the discharge circuit of the assembly thereby forcing the arcs against cooling surfaces to extinguish them, characterized by having an auxiliary electromagnetic field-generating means that selectively resists the arc-stretching movement of arcs in the assembly to delay the extinguishing operation of the assembly until the surge current has been completely discharged to ground.
US Patent References:
Spark gap type of surge arrestor for a d.-c. system
Lee - November 1966 - 3287588
Lightning arrester spark gap
Schultz - December 1964 - 3159765
Lightning arrester spark gap having arc-confining chamber walls of graded porosity
Stetson - November 1967 - 3354345
Spark gap type of surge arrestor for a d.-c. system
Lee - November 1966 - 3287588
Lightning arrester spark gap
Schultz - December 1964 - 3159765
Lightning arrester spark gap having arc-confining chamber walls of graded porosity
Stetson - November 1967 - 3354345
Application Number:
05/013317
Publication Date:
10/05/1971
Filing Date:
02/24/1970
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
361/128, 361/137
International Classes:
H01T1/04; H01T1/00; H02H1/00
Field of Search:
317/61.5,73,74,75,77 313/156 315/36
Primary Examiner:
Miller J. D.
Assistant Examiner:
Fendelman, Harvey
Claims:
What I claim and desire to secure by Letters Patent of the United States is
1. A current-limiting sparkgap assembly having a pair of horngap electrodes mounted in spaced-apart relationship therein to define a sparkgap, in combination with means for electrodynamically moving arcs outward from said sparkgap along said electrodes thereby to lengthen and accelerate extinction of the arcs, the improvement comprising electromagnetic means mounted on said assembly and operable to continuously resist, with a magnetic flux the strength of which is proportional to current in said discharge circuit, the movement of arcs outward from the sparkgap by said means for electrodynamically moving said arcs until said arcs pass a predetermined point on said electrodes, thereby to proportionately vary the rate at which the arcs are moved along said horngaps and lengthened.
2. The invention defined in claim 1 wherein said electromagnetic means is operative in response to a predetermined size of arcing current through the discharge circuit of the assembly to prevent movement beyond said predetermined point in the assembly of arcs driven by the means for electrodynamically moving said arcs and is further operable in response to an arcing current smaller than said predetermined size to allow movement of arcs beyond said predetermined point.
3. The invention defined in claim 2 wherein said electromagnetic means comprises a coil of wire electrically connected in series circuit relationship with the discharge circuit of the assembly and wherein said means for electrodynamic moving arcs comprises a second coil of wire mounted on the assembly around a horngap that is electrically connected in parallel with said second coil and in series with the discharge circuit, the coil of said electromagnetic means being wound and mounted on the assembly to develop a magnetic field that opposes the magnetic field developed by said second coil when current is passed through the discharge circuit of the assembly.
4. The invention defined in claim 3 wherein the number of turns of wire on the coil of the electromagnetic means has a turns ratio with respect to the large number of turns of wire on said second coil of one to at least 10.
5. The invention defined in claim 2 wherein the electromagnetic means comprises an arcuate conductor the ends of which are respectively connected in series circuit relationship with the discharge circuit of the assembly, and wherein said means for electrodynamically moving arcs comprises a coil of wire mounted on the assembly around a horngap that is electrically connected in parallel with said coil of wire and in series with the discharge circuit, the arcuate conductor being formed and mounted on the assembly to develop a magnetic field that opposes the magnetic field developed by said coil when current is passed through the discharge circuit of the assembly.
6. A sparkgap assembly comprising a plurality of insulating plates arranged in a stack, at least two pairs of main electrodes, each of said pairs of main electrodes being mounted respectively in spaced-apart relationship between different plates to form main sparkgaps between the electrodes of said pairs, a current-limiting sparkgap formed by a pair of horngap electrodes mounted in spaced-apart relationship between two of said insulating plates, a coil of electrical current-conducting wire mounted adjacent said current-limiting sparkgap to develop an arc-driving magnetic field that moves an arc formed between the horngap electrodes outward therefrom along the horns of the electrodes when current is passed through the coil, a pair of terminals mounted respectively adjacent opposite ends of said stack, circuit means connecting said main sparkgaps and said current-limiting sparkgap in a series circuit between said pair of terminals and connecting said coil in shunt circuit relationship with the current-limiting gap, the improvement comprising electromagnetic means mounted a predetermined distance away from the point of minimum spacing of the current-limiting gap for continuously resisting movement of an arc formed between the horngap electrodes of said current-limiting gap outward along the horns thereof.
7. A sparkgap assembly as defined in claim 6 wherein said electromagnetic means comprises an arcuate conductor mounted on one side of the current-limiting gap and insulated therefrom by one of said insulating plates, said arcuate conductor being formed and mounted to develop a magnetic field that opposes the magnetic field developed by said coil in the current-limiting gap when current is passed through said series circuit.
8. A sparkgap assembly as defined in claim 7 in which said arcuate conductor develops a relatively weak magnetic field at the sparkover area of the horngap electrodes and develops a much stronger magnetic field at a given point between the horns of said horngap spaced a predetermined distance outward from its sparkover area, whereby an arc formed between the horngap electrodes is allowed to move outward therefrom under the arc-moving force of the flux developed by said coil without encountering strong resistance to such movement from the magnetic field developed by the arcuate conductor until the arc reaches said given point.
9. A sparkgap assembly as defined in claim 7 wherein the arcuate conductor is connected in series with the main sparkgaps so that all current discharged through the main sparkgaps also passes through the arcuate conductor, whereby the strength of the magnetic field developed by the arcuate conductor to resist movement of arcs in the coil gap is directly proportional to the size of current discharged through the main sparkgaps.
10. A sparkgap assembly as defined in claim 9 wherein said arcuate conductor is extended to form a coil having at least one complete turn thereon, and wherein the turns ratio of turns on said arcuate-conductor coil to turns on the coil around the current-limiting gap is one to at least 10.
1. A current-limiting sparkgap assembly having a pair of horngap electrodes mounted in spaced-apart relationship therein to define a sparkgap, in combination with means for electrodynamically moving arcs outward from said sparkgap along said electrodes thereby to lengthen and accelerate extinction of the arcs, the improvement comprising electromagnetic means mounted on said assembly and operable to continuously resist, with a magnetic flux the strength of which is proportional to current in said discharge circuit, the movement of arcs outward from the sparkgap by said means for electrodynamically moving said arcs until said arcs pass a predetermined point on said electrodes, thereby to proportionately vary the rate at which the arcs are moved along said horngaps and lengthened.
2. The invention defined in claim 1 wherein said electromagnetic means is operative in response to a predetermined size of arcing current through the discharge circuit of the assembly to prevent movement beyond said predetermined point in the assembly of arcs driven by the means for electrodynamically moving said arcs and is further operable in response to an arcing current smaller than said predetermined size to allow movement of arcs beyond said predetermined point.
3. The invention defined in claim 2 wherein said electromagnetic means comprises a coil of wire electrically connected in series circuit relationship with the discharge circuit of the assembly and wherein said means for electrodynamic moving arcs comprises a second coil of wire mounted on the assembly around a horngap that is electrically connected in parallel with said second coil and in series with the discharge circuit, the coil of said electromagnetic means being wound and mounted on the assembly to develop a magnetic field that opposes the magnetic field developed by said second coil when current is passed through the discharge circuit of the assembly.
4. The invention defined in claim 3 wherein the number of turns of wire on the coil of the electromagnetic means has a turns ratio with respect to the large number of turns of wire on said second coil of one to at least 10.
5. The invention defined in claim 2 wherein the electromagnetic means comprises an arcuate conductor the ends of which are respectively connected in series circuit relationship with the discharge circuit of the assembly, and wherein said means for electrodynamically moving arcs comprises a coil of wire mounted on the assembly around a horngap that is electrically connected in parallel with said coil of wire and in series with the discharge circuit, the arcuate conductor being formed and mounted on the assembly to develop a magnetic field that opposes the magnetic field developed by said coil when current is passed through the discharge circuit of the assembly.
6. A sparkgap assembly comprising a plurality of insulating plates arranged in a stack, at least two pairs of main electrodes, each of said pairs of main electrodes being mounted respectively in spaced-apart relationship between different plates to form main sparkgaps between the electrodes of said pairs, a current-limiting sparkgap formed by a pair of horngap electrodes mounted in spaced-apart relationship between two of said insulating plates, a coil of electrical current-conducting wire mounted adjacent said current-limiting sparkgap to develop an arc-driving magnetic field that moves an arc formed between the horngap electrodes outward therefrom along the horns of the electrodes when current is passed through the coil, a pair of terminals mounted respectively adjacent opposite ends of said stack, circuit means connecting said main sparkgaps and said current-limiting sparkgap in a series circuit between said pair of terminals and connecting said coil in shunt circuit relationship with the current-limiting gap, the improvement comprising electromagnetic means mounted a predetermined distance away from the point of minimum spacing of the current-limiting gap for continuously resisting movement of an arc formed between the horngap electrodes of said current-limiting gap outward along the horns thereof.
7. A sparkgap assembly as defined in claim 6 wherein said electromagnetic means comprises an arcuate conductor mounted on one side of the current-limiting gap and insulated therefrom by one of said insulating plates, said arcuate conductor being formed and mounted to develop a magnetic field that opposes the magnetic field developed by said coil in the current-limiting gap when current is passed through said series circuit.
8. A sparkgap assembly as defined in claim 7 in which said arcuate conductor develops a relatively weak magnetic field at the sparkover area of the horngap electrodes and develops a much stronger magnetic field at a given point between the horns of said horngap spaced a predetermined distance outward from its sparkover area, whereby an arc formed between the horngap electrodes is allowed to move outward therefrom under the arc-moving force of the flux developed by said coil without encountering strong resistance to such movement from the magnetic field developed by the arcuate conductor until the arc reaches said given point.
9. A sparkgap assembly as defined in claim 7 wherein the arcuate conductor is connected in series with the main sparkgaps so that all current discharged through the main sparkgaps also passes through the arcuate conductor, whereby the strength of the magnetic field developed by the arcuate conductor to resist movement of arcs in the coil gap is directly proportional to the size of current discharged through the main sparkgaps.
10. A sparkgap assembly as defined in claim 9 wherein said arcuate conductor is extended to form a coil having at least one complete turn thereon, and wherein the turns ratio of turns on said arcuate-conductor coil to turns on the coil around the current-limiting gap is one to at least 10.
Description:
It is common practice in the lightning arrester field to utilize lightning arrester sparkgap assemblies that incorporate current-limiting horngaps, in combination with arc-driving electromagnetic coils, to rapidly move arcs formed in the sparkgaps of the arrester's discharge circuit outward from their respective points of initiation on the horngap electrodes into contact with arc stretching and cooling surfaces of insulated arc-confining chambers so that the arcs will be quickly extinguished to clear the arrester and seal it against power-follow current, that would otherwise be discharged through the arrester for an undesirably extended period of time. One suitable prior art circuit arrangement for attaining such an electrodynamic arc moving and extinguishing action involves connecting an electromagnetic coil in shunt circuit relationship with a sparkgap that is electrically connected in series with the lightning arrester sparkgap assembly's discharge circuit. In such an arrangement as an arc is moved outward on the horngap electrodes of the sparkgap shunted across the electromagnetic coil, the coil voltage is rapidly increased so that the arc-driving magnetic field produced by the coil becomes proportionately stronger and more quickly extinguishes the arcs by forcing them against the arc-confining chamber walls of the assembly.
Current-limiting lightning arrester circuits of this prior art design have proven to be very satisfactory in use with electric power transmission lines designed for the commercial transmission voltages that are conventional today. However, it has been found that when such prior art arresters are used with the extra high transmission voltages now planned for the near future, and particularly in those instances where direct current is used on the protected transmission system, such current limiting arrester circuits can produce undesirable voltage peaks on the system. For example, it has been found that the arc-driving and extinguishing force produced by the combined action of sparkgap assembly, horngap electrodes and arc-driving electromagnetic coils mounted on an arrester sparkgap assembly are capable of moving a high-current discharge arc into engagement with the arc-cooling walls of the sparkgap assembly of the arrester to extinguish it. Frequently, such operation has at least three major disadvantages. First, since the arc is extinguished while relatively large surge current is being discharged through the arrester, an undesirably high-peak voltage is impressed on the protected transmission system. Such peak voltages may easily damage the insulation that the arresters are primarily intended to protect, which of course would be an unsatisfactory result. A second disadvantage of extinguishing high-current arcs prematurely is that such arc extinction frequently damages the interior of the arc-confining chambers extensively, thus shortening the normal operating life span of the arrester. A third disadvantage of such high-current arc extinction is that frequently the interrupted arc restrikes because the premature extinguishing operation has resulted in overheating and ionization of the materials within the arc-confining chambers of the assembly and this condition, in combination with the high voltage still impressed on the terminals of the arrester, causes reinitiation of a discharge circuit through the arrester.
A primary object of the present invention is to provide an improved sparkgap assembly for a lightning arrester that will overcome the above-mentioned disadvantages occuring from premature extinction of high-current arcs within the arrester assembly.
Another object of the invention is to provide a sparkgap assembly having at least two electromagnetic field-generating means for controlling the arc-extinguishing movement of arcs within the assembly to resist extinction of high-current arcs and to accelerate extinction of low-current arcs.
Yet another objective of the invention is to provide means for selectively controlling the movement of arcs in a discharge circuit of a lightning arrester sparkgap assembly so that arc movement is made directly responsive to the size of discharge current passed through the arrester.
A still further object of the invention is to provide a self-regulating, automatic control circuit for regulating the movement and resultant voltage increase of arcs formed in the discharge circuit of a sparkgap assembly for a lightning arrester.
In one preferred embodiment of the invention, a sparkgap assembly having a plurality of main sparkgaps electrically connected in series with a current-limiting horngap, which is shunted across an electromagnetic coil to provide arc-driving magnetic flux, is provided with an auxiliary electromagnetic field-generating means that selectively opposes the magnetic field generated by the arc-driving coil. The auxiliary electromagnetic means is connected in series with the main discharge circuit of the assembly so that the strength of its magnetic field is directly proportional to the size of discharge current. Accordingly, the auxiliary electromagnetic means develops a strong magnetic field when large currents are being discharged through the assembly, and it develops a substantially weaker magnetic field when relatively smaller currents are discharged through the assembly. The form and position of the auxiliary electromagnetic means are adjusted to selectively resist arc-lengthening movement of the arc produced between the electrodes of the sparkgap shunted by the primary magnetic coil so that this arc is prevented from moving beyond a given point when arc discharge currents in excess of a predetermined size are passed through the discharge circuit of the assembly. Therefore, the voltage across the primary coil is maintained relatively low while such high discharge currents are flowing. Conversely, when relatively smaller discharge currents pass through the assembly, the auxiliary electromagnetic means does not retard the arc, therefore, it lengthens and rapidly increases the voltage across the primary coil, which in turn develops a strong magnetic field that accelerates arc movement and extinguishes the arcs in all of the sparkgaps of the assembly.
Further objects and advantages of my invention will become apparent to those skilled in the art from the following description of preferred embodiments of it taken in conjunction with the appended drawings in which:
FIG. 1 is a perspective view of a sparkgap assembly for a lightning arrester that embodies one preferred form of my invention.
FIG. 2 is an exploded perspective view of the sparkgap assembly illustrated in FIG. 1 showing the unique component parts of this embodiment of my invention as they are associated with a primary arc-driving electromagnetic coil and a pair of horngap electrodes connected in parallel with the coil.
FIG. 3 is a circuit diagram of a lightning arrester assembly that incorporates a sparkgap assembly similar to that illustrated in FIGS. 1 and 2 of the drawing.
FIG. 4 is a top elevation view of the sparkgap assembly illustrated in FIG. 2 taken along the plane 4--4 shown therein and including a phantom view of an auxiliary electromagnetic means that is formed and mounted relative to the other component parts of the assembly pursuant to the teaching of my invention.
Referring now to FIG. 1 of the drawing, there is shown a sparkgap assembly 1 comprising a plurality of insulating plates 2, 3, 4, 4', 5, 6 and 7 that are arranged in interlocking engagement, respectively, in the stack to define a plurality of arc-confining chambers between each pair of juxtaposed plates 2-7 in any suitable well-known manner. For example, the stacking arrangement may be similar to the assembly that is more fully described in U.S. Pat. No. 3,354,345 -- Stetson, which issued on Nov. 21, 1967 and is assigned to the assignee of the present invention. As explained in that patent, and as is illustrated schematically in the circuit diagram shown in FIG. 3 hereof, a plurality of pairs of main horngap electrodes 8--8', 9--9', 10--10' and 11--11' are mounted respectively in spaced-apart relationship between different pairs of plates 2-7 of assembly 1 to form four main sparkgaps between the electrodes of the pairs. It will be understood by those skilled in the art that a greater or lesser number of main sparkgaps may be utilized in order to vary the voltage rating of the assembly 1 as desired. However, with the embodiment of the invention described herein, at least two pairs of main electrodes should be utilized to form main sparkgaps on each side of series connected electromagnetic coil 12, which is formed of any suitable electrical current conducting wire. In addition to the main sparkgaps, operating components of assembly 1 comprise a pair of horngap electrodes 13 and 13' that are mounted in spaced apart relationship between insulating plates 4' and 5 to form a current limiting sparkgap 13--13' that is shunt connected across coil 12, as shown in FIG. 3. Also connected in series with the main sparkgaps and coil 12 is a unique electromagnetic means that is operative to selectively resist movement of an arc outward from its point of initiation between the horngap electrodes of current limiting gap 13--13'. In the embodiment of the invention illustrated in FIG. 2 the electromagnetic means 14 is formed of an arcuate copper conductor that is mounted above the current limiting sparkgap 13--13' in a chamber between insulating plates 4 and 4'. As shown in the circuit diagram of FIG. 3, circuit means are provided in the assembly 1 to connect the main sparkgaps 8--8', 9--9', 10--10', 11--11' in series circuit relationship with an arcuate conductor 14', which is shown in the form of a small coil in the circuit diagram since such a coil may be substituted for the arcuate conductor 14 pursuant to one form of my invention. Also, the primary arc-driving coil 12 is connected in series with the main sparkgaps to complete a series circuit between a pair of terminals 15 and 16 that are mounted, respectively, in any conventional manner adjacent opposite ends of the stacked components of assembly 1. (The terminal 15 is also illustrated in FIG. 1) As is well known in the lightning arrester field, at least one block of nonlinear resistance valve material 17 is ordinarily mounted in a lightning arrester and connected in this series circuit to form a discharge circuit through the arrester that possesses suitable sparkover and reseal characteristics.
In order to more fully understand my invention, it must be appreciated that arcuate conductor 14 is positioned over the arc-lengthening path of the coil-shunting, current limiting sparkgap 13--13' in a position similar to that best seen by the phantom view of arcuate conductor 14 in FIG. 4. Also, it should be understood that the wire on coil 12 is wound and connected in such a manner in relation to arcuate conductor 14 that the magnetic field developed by coil 12 is opposed to the magnetic field developed by the arcuate conductor 14 when current is passed through the sparkgap assembly series circuit from terminal 15 to terminal 16. More specifically, it will be noted that by positioning the arcuate conductor 14 a predetermined distance away from the point of minimum spacing 18 of horngap electrodes 13--13', in the area depicted in FIG. 4, the conductor 14 will selectively resist movement of an arc initiated at point 18 when it is moved outward therefrom under the electrodynamic arc-driving influence of the horns 13a and 13a' acting in combination with the electromagnetic field developed by current flowing through coil 12. At this given point, which is shown by the schematically illustrated arc 19, the relatively stronger magnetic field developed by arcuate conductor 14 in the limited area within its curvature arrests further movement of arc 19 as long as discharge current through the series discharge circuit of the assembly 1, and thus through conductor 14, remains in excess of a given predetermined size. When the surge current that is being discharged through the assembly 1 finally falls below this predetermined size, the magnetic field developed by arcuate conductor 14 weakens proportionately and allows the arc formed between horngap 13--13' to be moved further outward on the horns 13a and 13a' thereby lengthening the arc to further increase its voltage. Of course, this increase in voltage is applied directly across coil 12 due to the shunt relationship, illustrated in FIG. 3, between coil 12 and current limiting horngap 13--13' so that the electromagnetic field developed by coil 12 is rapidly increased in strength and forces the arc to move outward into contact with arc-stretching and cooling walls of the arc-confining chamber defined by insulating plates 4 and 5.
It will be apparent to those skilled in the art, from the preceding description of the operation of my invention, that the arcuate conductor 14 may be replaced by other suitable magnetic means, such as the small conductive coil of wire 14' mentioned above with reference to the circuit diagram of FIG. 3. When such a modification is made in the invention, I have found it is desirable to maintain the turns ratio between coil 14' and coil 12 such that there are at least ten times as many turns on coil 12 as there are on coil 14'. By maintaining such a ratio, when a large portion of the discharge current flows in coil 12, due to movement of an arc more than the above-mentioned predetermined distance from the point of arc initiation 18 outward on horns 13a, 13a' of the coil gap 13--13', a very strong arc-driving magnetic field will be developed by coil 12 to overcome the relatively weaker field produced by coil 14' and rapidly move the relatively small-current discharge arc into contact with the arc-confining walls of chamber plate member 5 to extinguish the arc. It will be seen by those skilled in the art that the given point at which the magnetic field developed by arcuate member 14, or coil 14', arrests the movement of an arc outward from arc initiation point 18 can be varied as desired by either moving the position of arcuate member 14 relative to horngap 13--13', or by changing the strength of the magnetic field developed by this electromagnetic arc movement resisting means. Therefore, the discharge characteristics of assembly 1 can be changed as needed for various surge voltage arresting applications. With such flexibility of design, it is possible to utilize my invention to overcome all of the disadvantages cited at the outset hereof. For example, with the invention, current-limiting voltage buildup in the sparkgaps of assembly 1 is prevented for an automatically regulated period sufficient to allow all of a high-current surge to be discharged to ground before the assembly is cleared; therefore, damage to the arc-confining walls of the arc chambers is minimized and restriking of arcs is avoided.
From the foregoing description of my invention, it will be apparent that any suitable circuit means may be used to electrically connect the arcuate member 14 or a suitable coil 14' in series circuit relationship with the electrode 9' of main sparkgap 9--9' and with one of the end terminals of coil 12. In the embodiment of my invention depicted in FIGS. 2 and 4, these circuit means comprise a copper pin 20 that is screwed into arcuate member 14 and extends through an aperture in insulating plate 4 to engage electrode 9' (seen in FIG. 3). The other end of arcuate member 14 is electrically connected in the series circuit by a wire 21 that is soldered to the member 14 and also to pin 22 that extends through an aperture in plate 4' and is mounted on electrode 13 of current limiting sparkgap 13--13'. As is best seen in FIG. 4, the electrode 13 is also connected by one end 12a of the wire in coil 12. The other end 12b of the wire in coil 12 is connected to electrode 13' so that the coil is thereby shunted as shown schematically in FIG. 3.
Those skilled in the art will realize that various other modifications and improvements may be made in my invention without departing from the true spirit and scope thereof and all such embodiments of the invention are intended to be encompassed within the scope of the appended claims.
Current-limiting lightning arrester circuits of this prior art design have proven to be very satisfactory in use with electric power transmission lines designed for the commercial transmission voltages that are conventional today. However, it has been found that when such prior art arresters are used with the extra high transmission voltages now planned for the near future, and particularly in those instances where direct current is used on the protected transmission system, such current limiting arrester circuits can produce undesirable voltage peaks on the system. For example, it has been found that the arc-driving and extinguishing force produced by the combined action of sparkgap assembly, horngap electrodes and arc-driving electromagnetic coils mounted on an arrester sparkgap assembly are capable of moving a high-current discharge arc into engagement with the arc-cooling walls of the sparkgap assembly of the arrester to extinguish it. Frequently, such operation has at least three major disadvantages. First, since the arc is extinguished while relatively large surge current is being discharged through the arrester, an undesirably high-peak voltage is impressed on the protected transmission system. Such peak voltages may easily damage the insulation that the arresters are primarily intended to protect, which of course would be an unsatisfactory result. A second disadvantage of extinguishing high-current arcs prematurely is that such arc extinction frequently damages the interior of the arc-confining chambers extensively, thus shortening the normal operating life span of the arrester. A third disadvantage of such high-current arc extinction is that frequently the interrupted arc restrikes because the premature extinguishing operation has resulted in overheating and ionization of the materials within the arc-confining chambers of the assembly and this condition, in combination with the high voltage still impressed on the terminals of the arrester, causes reinitiation of a discharge circuit through the arrester.
A primary object of the present invention is to provide an improved sparkgap assembly for a lightning arrester that will overcome the above-mentioned disadvantages occuring from premature extinction of high-current arcs within the arrester assembly.
Another object of the invention is to provide a sparkgap assembly having at least two electromagnetic field-generating means for controlling the arc-extinguishing movement of arcs within the assembly to resist extinction of high-current arcs and to accelerate extinction of low-current arcs.
Yet another objective of the invention is to provide means for selectively controlling the movement of arcs in a discharge circuit of a lightning arrester sparkgap assembly so that arc movement is made directly responsive to the size of discharge current passed through the arrester.
A still further object of the invention is to provide a self-regulating, automatic control circuit for regulating the movement and resultant voltage increase of arcs formed in the discharge circuit of a sparkgap assembly for a lightning arrester.
In one preferred embodiment of the invention, a sparkgap assembly having a plurality of main sparkgaps electrically connected in series with a current-limiting horngap, which is shunted across an electromagnetic coil to provide arc-driving magnetic flux, is provided with an auxiliary electromagnetic field-generating means that selectively opposes the magnetic field generated by the arc-driving coil. The auxiliary electromagnetic means is connected in series with the main discharge circuit of the assembly so that the strength of its magnetic field is directly proportional to the size of discharge current. Accordingly, the auxiliary electromagnetic means develops a strong magnetic field when large currents are being discharged through the assembly, and it develops a substantially weaker magnetic field when relatively smaller currents are discharged through the assembly. The form and position of the auxiliary electromagnetic means are adjusted to selectively resist arc-lengthening movement of the arc produced between the electrodes of the sparkgap shunted by the primary magnetic coil so that this arc is prevented from moving beyond a given point when arc discharge currents in excess of a predetermined size are passed through the discharge circuit of the assembly. Therefore, the voltage across the primary coil is maintained relatively low while such high discharge currents are flowing. Conversely, when relatively smaller discharge currents pass through the assembly, the auxiliary electromagnetic means does not retard the arc, therefore, it lengthens and rapidly increases the voltage across the primary coil, which in turn develops a strong magnetic field that accelerates arc movement and extinguishes the arcs in all of the sparkgaps of the assembly.
Further objects and advantages of my invention will become apparent to those skilled in the art from the following description of preferred embodiments of it taken in conjunction with the appended drawings in which:
FIG. 1 is a perspective view of a sparkgap assembly for a lightning arrester that embodies one preferred form of my invention.
FIG. 2 is an exploded perspective view of the sparkgap assembly illustrated in FIG. 1 showing the unique component parts of this embodiment of my invention as they are associated with a primary arc-driving electromagnetic coil and a pair of horngap electrodes connected in parallel with the coil.
FIG. 3 is a circuit diagram of a lightning arrester assembly that incorporates a sparkgap assembly similar to that illustrated in FIGS. 1 and 2 of the drawing.
FIG. 4 is a top elevation view of the sparkgap assembly illustrated in FIG. 2 taken along the plane 4--4 shown therein and including a phantom view of an auxiliary electromagnetic means that is formed and mounted relative to the other component parts of the assembly pursuant to the teaching of my invention.
Referring now to FIG. 1 of the drawing, there is shown a sparkgap assembly 1 comprising a plurality of insulating plates 2, 3, 4, 4', 5, 6 and 7 that are arranged in interlocking engagement, respectively, in the stack to define a plurality of arc-confining chambers between each pair of juxtaposed plates 2-7 in any suitable well-known manner. For example, the stacking arrangement may be similar to the assembly that is more fully described in U.S. Pat. No. 3,354,345 -- Stetson, which issued on Nov. 21, 1967 and is assigned to the assignee of the present invention. As explained in that patent, and as is illustrated schematically in the circuit diagram shown in FIG. 3 hereof, a plurality of pairs of main horngap electrodes 8--8', 9--9', 10--10' and 11--11' are mounted respectively in spaced-apart relationship between different pairs of plates 2-7 of assembly 1 to form four main sparkgaps between the electrodes of the pairs. It will be understood by those skilled in the art that a greater or lesser number of main sparkgaps may be utilized in order to vary the voltage rating of the assembly 1 as desired. However, with the embodiment of the invention described herein, at least two pairs of main electrodes should be utilized to form main sparkgaps on each side of series connected electromagnetic coil 12, which is formed of any suitable electrical current conducting wire. In addition to the main sparkgaps, operating components of assembly 1 comprise a pair of horngap electrodes 13 and 13' that are mounted in spaced apart relationship between insulating plates 4' and 5 to form a current limiting sparkgap 13--13' that is shunt connected across coil 12, as shown in FIG. 3. Also connected in series with the main sparkgaps and coil 12 is a unique electromagnetic means that is operative to selectively resist movement of an arc outward from its point of initiation between the horngap electrodes of current limiting gap 13--13'. In the embodiment of the invention illustrated in FIG. 2 the electromagnetic means 14 is formed of an arcuate copper conductor that is mounted above the current limiting sparkgap 13--13' in a chamber between insulating plates 4 and 4'. As shown in the circuit diagram of FIG. 3, circuit means are provided in the assembly 1 to connect the main sparkgaps 8--8', 9--9', 10--10', 11--11' in series circuit relationship with an arcuate conductor 14', which is shown in the form of a small coil in the circuit diagram since such a coil may be substituted for the arcuate conductor 14 pursuant to one form of my invention. Also, the primary arc-driving coil 12 is connected in series with the main sparkgaps to complete a series circuit between a pair of terminals 15 and 16 that are mounted, respectively, in any conventional manner adjacent opposite ends of the stacked components of assembly 1. (The terminal 15 is also illustrated in FIG. 1) As is well known in the lightning arrester field, at least one block of nonlinear resistance valve material 17 is ordinarily mounted in a lightning arrester and connected in this series circuit to form a discharge circuit through the arrester that possesses suitable sparkover and reseal characteristics.
In order to more fully understand my invention, it must be appreciated that arcuate conductor 14 is positioned over the arc-lengthening path of the coil-shunting, current limiting sparkgap 13--13' in a position similar to that best seen by the phantom view of arcuate conductor 14 in FIG. 4. Also, it should be understood that the wire on coil 12 is wound and connected in such a manner in relation to arcuate conductor 14 that the magnetic field developed by coil 12 is opposed to the magnetic field developed by the arcuate conductor 14 when current is passed through the sparkgap assembly series circuit from terminal 15 to terminal 16. More specifically, it will be noted that by positioning the arcuate conductor 14 a predetermined distance away from the point of minimum spacing 18 of horngap electrodes 13--13', in the area depicted in FIG. 4, the conductor 14 will selectively resist movement of an arc initiated at point 18 when it is moved outward therefrom under the electrodynamic arc-driving influence of the horns 13a and 13a' acting in combination with the electromagnetic field developed by current flowing through coil 12. At this given point, which is shown by the schematically illustrated arc 19, the relatively stronger magnetic field developed by arcuate conductor 14 in the limited area within its curvature arrests further movement of arc 19 as long as discharge current through the series discharge circuit of the assembly 1, and thus through conductor 14, remains in excess of a given predetermined size. When the surge current that is being discharged through the assembly 1 finally falls below this predetermined size, the magnetic field developed by arcuate conductor 14 weakens proportionately and allows the arc formed between horngap 13--13' to be moved further outward on the horns 13a and 13a' thereby lengthening the arc to further increase its voltage. Of course, this increase in voltage is applied directly across coil 12 due to the shunt relationship, illustrated in FIG. 3, between coil 12 and current limiting horngap 13--13' so that the electromagnetic field developed by coil 12 is rapidly increased in strength and forces the arc to move outward into contact with arc-stretching and cooling walls of the arc-confining chamber defined by insulating plates 4 and 5.
It will be apparent to those skilled in the art, from the preceding description of the operation of my invention, that the arcuate conductor 14 may be replaced by other suitable magnetic means, such as the small conductive coil of wire 14' mentioned above with reference to the circuit diagram of FIG. 3. When such a modification is made in the invention, I have found it is desirable to maintain the turns ratio between coil 14' and coil 12 such that there are at least ten times as many turns on coil 12 as there are on coil 14'. By maintaining such a ratio, when a large portion of the discharge current flows in coil 12, due to movement of an arc more than the above-mentioned predetermined distance from the point of arc initiation 18 outward on horns 13a, 13a' of the coil gap 13--13', a very strong arc-driving magnetic field will be developed by coil 12 to overcome the relatively weaker field produced by coil 14' and rapidly move the relatively small-current discharge arc into contact with the arc-confining walls of chamber plate member 5 to extinguish the arc. It will be seen by those skilled in the art that the given point at which the magnetic field developed by arcuate member 14, or coil 14', arrests the movement of an arc outward from arc initiation point 18 can be varied as desired by either moving the position of arcuate member 14 relative to horngap 13--13', or by changing the strength of the magnetic field developed by this electromagnetic arc movement resisting means. Therefore, the discharge characteristics of assembly 1 can be changed as needed for various surge voltage arresting applications. With such flexibility of design, it is possible to utilize my invention to overcome all of the disadvantages cited at the outset hereof. For example, with the invention, current-limiting voltage buildup in the sparkgaps of assembly 1 is prevented for an automatically regulated period sufficient to allow all of a high-current surge to be discharged to ground before the assembly is cleared; therefore, damage to the arc-confining walls of the arc chambers is minimized and restriking of arcs is avoided.
From the foregoing description of my invention, it will be apparent that any suitable circuit means may be used to electrically connect the arcuate member 14 or a suitable coil 14' in series circuit relationship with the electrode 9' of main sparkgap 9--9' and with one of the end terminals of coil 12. In the embodiment of my invention depicted in FIGS. 2 and 4, these circuit means comprise a copper pin 20 that is screwed into arcuate member 14 and extends through an aperture in insulating plate 4 to engage electrode 9' (seen in FIG. 3). The other end of arcuate member 14 is electrically connected in the series circuit by a wire 21 that is soldered to the member 14 and also to pin 22 that extends through an aperture in plate 4' and is mounted on electrode 13 of current limiting sparkgap 13--13'. As is best seen in FIG. 4, the electrode 13 is also connected by one end 12a of the wire in coil 12. The other end 12b of the wire in coil 12 is connected to electrode 13' so that the coil is thereby shunted as shown schematically in FIG. 3.
Those skilled in the art will realize that various other modifications and improvements may be made in my invention without departing from the true spirit and scope thereof and all such embodiments of the invention are intended to be encompassed within the scope of the appended claims.