Triggering circuit for spark gap assemblies

Abstract

A plurality of series connected main spark gaps are connected in shunt circuit relation with a voltage grading impedance network which includes a trigger gap that is connected though frequency responsive coupling means in shunt relation with approximately one-half of the series connected main spark gaps. The trigger gap is operative, as a substantially linear function of a voltage impressed across the series connected gaps, to cause the main gaps to spark over in cascade fashion. The triggered control network allows use of a large number of main gaps but with a controlled total sparkover very much less than the sum of the sparkover of the individual main gaps, thus, providing a desirably high ratio of reseal voltage to sparkover voltage for the main gap series circuit.

What we claim as new and desire to secure by Letters Patent of the United States is: 
     
       1. A spark gap assembly comprising.[.means defining.]..Iadd.: .Iaddend. a plurality of main spark gaps electrically connected in a first .Iadd.and a second .Iaddend.series circuit, a trigger gap connected in shunt relation with .[.a first portion of.]. said first series circuit.Iadd., said first and second series circuits .Iaddend.including a predetermined number .Iadd.of pairs .Iaddend.of said main spark gaps, .Iadd.each pair of said main gaps being shunted by a first linear resistor and a first nonlinear resistor in series, .Iaddend.impedance means electrically connected in series with said trigger gap .[.in said shunt circuit relation,.]. whereby a .[.predetermined proportional increment of a.]. voltage across said first series circuit is impressed across said trigger gap, said trigger gap having a sparkover voltage substantially higher than the sparkover voltage of one of said main gaps and substantially lower than the sparkover voltage of .[.the.]. .Iadd.said .Iaddend.first series circuit when it is not triggered.Iadd., said first linear and nonlinear resistors being selected to provide a uniform distribution of voltage across said mains gaps. .Iaddend. .[.   
     
     
       2.  A spark gap assembly as defined in claim 1 wherein said predetermined number of main gaps comprises at least two of said gaps..]. 
     
     
       3. A spark gap assembly as defined in claim 1 wherein said predetermined number of main gaps is approximately one-half of the total number of gaps in said plurality of main spark gaps. 
     
     
       4. A spark gap assembly as defined in claim 3 wherein the sparkover voltage of said trigger gap is equal to approximately one-quarter the untriggered sparkover voltage of said first series circuit. .[.5. A spark gap assembly as defined in claim 2 including means for grading a voltage across said first series circuit to distribute substantially equal voltages across 
     
     
        each of said main gaps at their desired reseal voltage rating..]. 6. A spark gap assembly as defined in claim 1 including preionizing means to preionize said trigger gap, and means to energize said preionizing means in response to a voltage across said first series circuit such that said 
     
     
        trigger gap is ionized at a voltage lower than its sparkover voltage. 7. A spark gap assembly as defined in claim 6 wherein said preionizing means comprises a preionizer spark gap disposed adjacent the trigger gap and adapted to sparkover at a voltage lower than the sparkover voltage of said trigger gap, and means electrically connecting said preionizer gap in shunt relation with said first series circuit. .[.8. A spark gap assembly as defined in claim 2, in combination, with an insulating lightning arrester housing, a nonlinear resistance material disposed in said housing, means for mounting said spark gap assembly in said housing, electric terminals disposed adjacent opposite ends of said housing, and means electrically connecting said first series circuit of said spark gap assembly in series with said nonlinear resistance material between said 
     
     
        terminals..]. 9. The invention defined in claim 8 including electromagnetic means for driving arcs formed between said main spark gaps toward the periphery of the spark gap arcing chambers in said housing. 
     
     
            The invention defined in claim 9 wherein said electromagnetic means comprises at least one conducting coil disposed around the spark gap assembly and electrically connected in series with said first series circuit through said assembly, and including protective means shunting 
     
     
        said coil to prevent it from being damaged by an overvoltage surge. 11. A spark gap assembly as defined in claim 1 wherein, said impedance means is voltage responsive and adapted to offer a relatively low impedance to high 
     
     
        voltages and to offer a relatively high impedance to low voltages. 12. A spark gap assembly as defined in claim 5 wherein said means for grading voltage comprises an impedance network including a plurality of series connected ionizer capacitances, each of said series connected ionizer capacitances respectively being shunt connected across one of said main 
     
     
        spark gaps. 13. In a lightning arrester, a plurality of spark gap assemblies, each of said assemblies comprising.Iadd.: .Iaddend. a plurality of main spark gaps electrically connected in a first .Iadd.and second .Iaddend.series circuit, means electrically connecting each of said first .Iadd.and second .Iaddend.series circuits in series to form a larger series circuit, at least one trigger gap connected in shunt circuit relation with .[.at least one portion of said larger.]. .Iadd.said first .Iaddend.series circuit, said trigger gap having a sparkover voltage substantially higher than the sparkover voltage of one of said main gaps and substantially lower than the sparkover voltage of said .[.larger.]. .Iadd.first .Iaddend.series circuit when it is not triggered, a .[.block of nonlinear resistance material,.]. .Iadd.valve resistor and .Iaddend.a pair of terminals disposed respectively adjacent opposite ends of said arrester, means electrically connecting said .[.larger.]. .Iadd.first .Iaddend.series circuit in series with said .[.block of nonlinear resistance material.]. .Iadd.valve resistor .Iaddend.between said terminals, .[.and means forming.]. a voltage grading circuit between said terminals .Iadd.comprising a first linear and a first nonlinear resistor across said first series circuit and a second nonlinear and a second linear resistor across said second series circuit .Iaddend.whereby a predetermined portion of a voltage impressed across said terminals is applied across said trigger gap when at least some of said main spark gaps   
     
     
        are not sparked over. 14. The invention defined in claim 13 wherein the portion of said larger series circuit shunted by the trigger gap comprises one of said first series circuits. .[.15. The invention as defined in claim 14 wherein the number of said plurality of spark gap assemblies 
     
     
        comprises two of said assemblies..]. 16. The invention as defined in claim 13 wherein said plurality of spark gap assemblies comprises an even number of such assemblies, and wherein the portion of said larger series circuit 
     
     
        shunted by the trigger gap includes one-half of said assemblies. 17. The invention defined in claim 13 with preionizer means electrically connected between said pair of terminals and disposed adjacent said trigger gap, said preionizer means being operative to ionize said trigger gap at a voltage lower than the sparkover voltage of said trigger gap in response to a predetermined voltage being impressed across said pair of terminals. 
     
     
         8. The invention defined in claim 13 with a plurality of impedance networks for controlling the voltage distribution of the main spark gaps in each of said assemblies when they are not sparked over, each of said impedance networks being electrically connected to form a second series circuit shunting said first series circuit in each of said respective 
     
     
        assemblies. 19. The invention defined in claim 18 with a frequency responsive coupling circuit electrically connected in series with the 
     
     
        shunt circuit including said trigger gap. 20. The invention defined in claim 18 with capacitive grading means in each of said assemblies for further controlling the voltage distribution of the main spark gaps in said assemblies, each of said capacitive grading means including a plurality of electrical capacitances of various predetermined size connected to form a third series circuit through its respective spark gap 
     
     
        assembly hunting the second series circuit in that assembly. 21. The invention as defined in claim 20 wherein each capacitance in said plurality of electrical capacitances comprises a preionizer means electrically connected and mechanically positioned such that each of the main spark gaps is shunted respectively by a different preionizer means 
     
     
        disposed in ionizing relation thereto. 22. The invention as defined in claim 21 with a frequency responsive coupling circuit electrically connected in series with said trigger gap in the circuit establishing its shunt relation with said predetermined portion of the larger series circuit, and including preionizer means electrically connected between said pair of terminals and disposed adjacent said trigger gap, said preionizer means being operative to ionize said trigger gap at a voltage lower than its sparkover voltage in response to a predetermined voltage 
     
     
        being impressed across said pair of terminals. 23. The invention defined in claim 13 wherein the predetermined portion of voltage impressed across said spark gap is a linear function of the voltage between said terminals 
     
     
        when at least some of said main spark gaps are not sparked over. 24. The invention defined in claim 23 wherein the means forming a voltage grading circuit for impressing a voltage across the trigger gap comprises a second series circuit between said terminals shunting said larger series circuit and including series connected linear and nonlinear impedances, said trigger gap being shunt connected across a predetermined number of said 
     
     
        impedances. 25. A lightning arrester comprising.Iadd.: .Iaddend. at least one .[.nonlinear resistance element.]. .Iadd.valve resistor .Iaddend.electrically connected in series with a plurality of series connected spark gap assemblies, a predetermined number of said assemblies comprising.[.:.]. a plurality .Iadd.of pairs .Iaddend.of main spark gaps electrically connected in a first .Iadd.and a second .Iaddend.series circuit, .Iadd.each pair of said main gaps being shunted by a linear resistor and a nonlinear resistor, .Iaddend.at least one trigger gap connected in shunt circuit relation with .[.a predetermined number of said main spark gaps,.]. .Iadd.said first series circuit, .Iaddend.said trigger gap having a sparkover voltage substantially higher than the sparkover voltage of one of said main gaps and substantially lower than the sparkover voltage of said first series circuit when it is not triggered.[.,.]. .Iadd.said linear and nonlinear resistors being selected to provide a uniform distribution of voltage across said main gaps .Iaddend.and means for energizing said trigger gap in response to a predetermined voltage being impressed across said lightning arrester.   
     
     
        .[.  .  A spark gap assembly as defined in claim 25 in combination with modular mounting means in each of said assemblies for mounting said trigger gap and means for energizing said trigger gap in a predetermined relatively fixed relation with respect to said first series circuit..]. .[.27. A lightning arrester comprising a plurality of spark gap assemblies electrically connected to form a discharge circuit, a predetermined number of said assemblies being provided with control means for accurately regulating the sparkover voltage of the assembly, whereby the sparkover voltage of said discharge circuit is accurately regulated..]. .[.28. A lightning arrester as defined in claim 27 wherein said control means comprises a trigger gap and means for energizing said trigger gap in response to a predetermined voltage being impressed across said arrester, said trigger gap being adapted when energized to cause cascaded sparkover of its assembly..]. .[.29. A lightning arrester as defined in claim 27 wherein the unregulated sparkover voltage of each of said assemblies may vary between wide tolerances, and wherein the regulated sparkover voltage of each of said assemblies is maintained within substantially narrower tolerances by said control means..]. .[.30. A lightning arrester as defined in claim 27 wherein a predetermined number of said assemblies include a nonlinear valve resistance element electrically connected in series with said discharge circuit..]. .[.31. A lightning arrester as defined in claim 27 in combination with at least one nonlinear resistance element electrically connected in series with said discharge circuit..].