Spark gap and discharge control apparatus

Feb. 17, 1970 τ. r. connell 3,496,409

SPARK GAP AND DISCHARGE CONTROL APPARATUS Filed Oct. 11. 1966 2 Sheets-Sheet 1

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FIG. 4

INVENTOR THOMAS R. CONNELL tn b.

ATTORNEY

Feb. 17, 1970

T. R. CONNELL

3,496,409

SPARK GAP AND DISCHARGE CONTROL APPARATUS

Filed Oct. 11, 1966

Sheets-Sheet 2

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ATTORNEY

3,496,409

Patented Feb. 17, 1970

United States Patent

3,496,409 SPARK GAP AND DISCHARGE CONTROL APPARATUS

Thomas R. Connell, Wadsworth, Ohio, assignor to The Ohio Brass Company, Mansfield, Ohio, a corporation ⁵of New Jersey

Filed Oct. 11,1966, Ser. No. 585,846

Int. Cl. H02h 3/22, 9/06

U.S. Cl. 315—36 10 Claims ¹⁰

This invention relates to spark gaps and preionizing and control devices for lightning arresters and overvoltage discharge devices and the like.

A principal object of the invention is to provide spark gaps for lightning arresters and overvoltage discharge devices and the like having constant breakdown voltages.

Another object of the invention is to improve the operating reliability of lightning arresters and the like for switching surges.

Another object of the invention is to provide a spark ²⁰gap and. preionizer arrangement in which the breakdown voltage, is within a predetermined range of voltages from the design breakdown voltage over a long operating lifetime.

Another object of the invention is to provide a spark ²⁵gap and preionizer arrangement in which the effect of production variations in dimensions of the gap parts and spacing of the gap electrodes on the breakdown voltage is minimized.

In lightning arresters and the like, it is known to il- ³⁰luminate the main gap by an auxiliary or preionizing gap which serves as a source of ions for imparting a conductivity to the atmosphere between the main gaps. The auxiliary gap is arranged to fire at relatively low current densities so that the spacing between the electrodes is ³⁵maintained within close size and dimensional tolerances throughout the life of the arrester. Such arrangements are useful since the auxiliary gap is not in the main discharge path of the arrester and may be designed and constructed with precise parts and manufactured to within ⁴⁰close tolerances and at relatively low cost. This result could not be achieved economically by design of the main gap.

However, the problem is of some complexity since, in order to achieve proper operation, it is necessary to ⁴⁵insure response of the auxiliary gap to excess voltages in the circuit to which the arrester is connected and to insure operation of the main gap after the auxiliary gap is fired. Further, it is necessary to provide the electrical functioning a limited space and in the proper relation to the main gap of the arrester.

The present invention relates to a spark gap and a discharge control and preionizing apparatus, in which a novel arrangement of auxiliary switching gaps and voltage grading means is associated with the main gaps of ⁵⁵the lightning arrester. The main gaps, auxiliary gaps, and grading means are arranged in a plurality of stages for cascade operation in which a first main gap is fired and then the other main gaps are fired in a sequence determined by the upset of voltage division between the ⁶⁰various stages produced by the firing of the switching main gaps. Novel structural arrangements are provided for incorporating the main gaps, auxiliary gaps, and grading devices in a compact unitary assembly in a lightning arrester. 65

The invention, together with further objects, features, and advantages thereof, will be understood from the following detailed specification and claims and the appended drawings, in which:

FIG. 1 is a side elevation view of a spark gap apparatus 70 embodying the invention;

FIG. 2 is a schematic diagram showing an overvoltage discharge circuit embodying the novel gap and discharge control and preionizing circuit;

FIG. 3 is a plan view of a gap plate, taken along the line 3—3 in FIG. 1 and showing the arrangement of electrodes and grading resistors on the gap plates;

FIG. 4 is a section view of the gap plate of FIG. 3, taken in the direction 4—4 in FIG. 3; and

FIG. 5 is a schematic diagram of a spark gap embodying an alternative arrangement of a discharge control circuit.

Referring to FIG. 1, there is shown the physical construction of the spark gap 10, in which a plurality of gap plates 11, 12, 13, and 14 cooperate with associated center plates 15 and 16 to define spark gaps, associated arc chambers, and control and discharge circuits of the gap control stages SI, S2, S3, and S4 of FIG. 2. The plates 11, 12, 13, and 14 cooperate with associated center plates 15 and 16 along peripheral ridge and recess means and interengage the end faces of a plate member 17 which carries a magnetic coil 18 at the center position of the four gap plates. The entire assemblage is arranged in the form of a stack, and the elements are connected in series with two end plates 19 and 20 which function to connect the gap assembly to the terminals of the arrester housing, to the line conductor, and to the valve resistor, as the case may be.

Referring now to FIG. 2, the spark gap apparatus 10 comprises four main gaps 21, 22, 23, and 24 connected in series and having certain associated gaps, resistors, and capacitors connected in parallel therewith to constitute four switching control stages, referred to generally as SI, S2, S3, and S4, all connected in series with a coil 25 associated with the gaps 21 to 24. The apparatus 10 is connected in series circuit 26 which includes a nonlinear valve resistor 27, a powerline conductor 28, and a ground 29, and constitutes a protective circuit or lightning arrester for the powerline 28.

The coil 25 comprises a means for generating a magnetic field to elongate the arcs in the several gaps 21 to 24. Two fixed gaps 30 and 31 are connected in shunt with the coil 25 and function during initial discharge of energy from the line 28 to the ground 29 through the gaps 21 to 24. After a sufficient time interval, current flow, in the coil 25 extinguishes the arcs in the gaps 30 and 31 so that an increasing magnetic field is generated by the coil for moving the arcs in the gaps 21 to 24. The gaps 30 and 31 may be replaced by arrangements of nonlinear resistors, as is described in U.S. Patents 2,825,008 and 3,019,367 to J. W. Kalb, or by arrangements of arc elongating electrodes, within the contemplation of the invention.

In the apparatus 10, the gap control stage SI is constituted by the gap 21, a switching gap 32 having series connected switching resistors 33 and 34, and a grading resistor 35. Gap control stage S2 comprises the gap 22, a switching gap 36 with series switching resistors 37 and 38, and a grading resistor 39. The gap control stage S3 comprises the gap 23, a grading capacitor 40, and a grading resistor 41. The gap control stage S4 comprises a switching gap 42 with series resistors 43 and 44, and a grading resistor 45. The described parts are connected in a parallel circuit to constitute the designated stage.

The stages SI, S2, and S4 have the same grading resistances, that is, the grading resistors 35, 39, and 45 are equal, whereas the resistance of the grading resistor 41 of stage S3 is small relative to resistors 35, 39, and 45. The switching gaps 32, 36, and 42 are designed and adjusted to sparkover at substantially the same voltage, less than the breakdown voltage of the mains gaps, but the associated series resistors, that is, the resistors 33 and 34 of the gap 32, the resistors 37 and 38 of the gap 36, and the resistors 43 and 44 of the gap 42, are progressive3,496/ 3 ly smaller for the successive stages so that an unequal voltage division exists as between the main gaps 21, 22, and 24 after the switching gaps have fired.

The switching gaps 32, 36, and 42 are small gaps having precisely dimensioned electrodes positioned adjacent 5 the main gaps 21, 22, and 24. The switching gaps function as preionizers for the main gaps as well as a switching means for the several switching stages, and are adapted for discharge in a narrow, predetermined range of voltages over the range of design tolerances. In pro- 10 duction, one of the gaps 32, 36, and 42 is selected to spark over at a voltage close to the design voltage, and minor production variations in the remaining switching gaps do not materially alter the overall functioning, inasmuch as the gap 32 determines the firing sequence of the stages 15 because of the larger values of resistors 33 and 34.

The functioning of the apparatus 10 is dependent upon the nature of the overvoltage on the conductor 28. The functioning for line overvoltages which have slowly rising wave fronts or switching surge voltages, so called, is as follows:

The line voltages are divided between the several mam gaps 21 to 24 in the same proportions as the resistance of the individual grading resistors 35, 39, 41, and 45 to the total grading resistance constituted by the four re- 25 sistors. Accordingly, with the grading resistances heretofore described and, prior to discharge of the switching gap 32, the line voltage is divided with equal voltages across stages SI, S2, and S4 and a much lesser voltage across S3. . ®

Upon the occurrence of an overvoltage on line conductor 28, the switching gaps 32, 36, and 42 spark over and connect the switching resistors 33 and 34 in parallel with the grading resistors 35, the switching resistors 37 and 38 in parallel with the resistor 39, and the switching 35 resistors 43 and 44 in parallel with the grading resistor 45. The resistors 33 and 34 are substantially larger than the resistors 37 and 38, which are in turn substantially larger than resistors 43 and 44. Accordingly, after the switching gaps 32, 36, and 42 have fired, the distribu- 40 tion of line voltage as between the stages SI, S2 and S4 is altered so that a greater proportion of the line voltage appears across the gaps 21, 22, and 24, in that order, in accordance with the inequality between the parallel resistances of the stages SI, S2, and S4. Accordingly, the gap 21 fires first, followed by the gap 22 and the gap 24, whereupon all the line voltage appears across the gap 23 which is fired last. This completes the firing sequence and initiates the discharge sequence in which transient energy is discharged from the line conductor 28 to the ground 29, through the valve resistor 27. In the discharge sequence, the coil 25 functions to elongate the arcs of the main gaps 21 to 24 to terminate the discharge, all as described in the patents heretobefore referred to.

The resistor 41 is chosen so that its resistance is less than the parallel grading and switching gap resistances of the stages SI, S2, and S4 with the switching gaps fired, so that the main gap 23 is fired only after the main gap firing sequence, gap 21, gap 22, gap 24, is completed. Resistor 41 is small in relation to the individual grading resistances 35, 39, and 45, which insures that the switching gaps 32, 36, and 42 are fired before the main gap 23 is fired.

The functioning of the discharge control circuit for line overvoltages which have rapidly rising wave fronts, impulse voltages so-called, is as follows: ⁶⁵

The impulse voltages are divided between the several main gaps in proportion to the impedance of a given stage, as the impedance of the capacitor 48, or the combined impedances of the capacitor 40 and the grading resistor 41, for the stage S3 or the resistance of the 70 grading resistors 35, 39, and 45 for the stages SI, S2, and S4 to the series impedance of the combined stages. The capacitor 40 has a capacitance which is large in comparison with the distributed capacitances across the stages SI, S2, and S4, so that, for impulsive voltages having 75 a sufficiently high rate of increase, the proportional impedance of the stage is low and the impressed voltage is divided substantially between the main gaps 21, 22, and 24. Accordingly, the main gaps 21, 22, and 24 fire, although not necessarily in that order, whereupon the impressed voltage is applied directly across the stage S3 to fire the main gaps 23.

The firing sequence just described is dependent primarily upon the voltage upset between the stages produced by the fast wave front impulses applied to the grading capacitor 40 and is not substantially determined by the functioning of the switching gaps. The firing order as between the main gaps 21, 22, and 24 will, generally speaking, be indeterminate rather than determined as to the gap 21 by the firing of the switching gap 32.

In both embodiments of the invention, the voltage at which the switching gaps lose control of main gaps, that is, cease to determine the firing order, is dependent primarily upon the rate of rise of the impulse voltage, and the control function may be retained for faster impulses by equalizing the time constants of the stages.

Referring now FIG. 3 and FIG. 4, the construction of the stage S4 of the apparatus 10 is illustrated by the construction of the gap plate 14. The plate 14 comprises a circular plate formed of arc resistant ceramic material and having a circumferential ridge 50 and an interior surface 51 of the plate defining an arc chamber 52. Two main gap electrodes 53 and 54, comprising the main gap 24, are carried by the plate 14 and secured thereto and to the plate 16 by means such as epoxy adhesives and associated rivets 55 and 56. Two ceramic barrier members 57 and 58 integral with the plate 14 define the extremities of the arc chamber 52 and the limit of elongating arc movement from the adjoining arcing faces .of the electrodes 53 and 54 along the diverging extremities thereof and toward the radially outward extremities of the arc chamber under the influence of the magnetic field generated by the coil 18.

A separate member 60 formed of ceramic material is secured to the surface of the plate 14 between the members 57 and 58. The member 60 supports two electrodes 61 and 62 which constitute the switching gap 42 and have the bodies formed of resistive material to constitute the switching resistors 43 and 44. The electrodes 61 and 62 are formed as cylindrical bodies of resistive material which are received in cylindrical openings in elevated portions of the member 60 and have the interior ends closely spaced at a predetermined distance to constitute the gap 42. A resistor 63 is disposed between the radially outward extremity of the member 60 and the peripheral rim 50 of the plate 14 and constitutes the grading resistor 45 of FIG. 1. The lead wires of the resistor 63 are connected to the electrodes 61 and 62 and to the electrodes 53 and 54 to constitute the parallel circuit arrangement of stage S4.

The gap plates 11, 12, and 13, comprising the stages SI, S2, and S3, may be constructed in the same way as the stage S4, just described. The stage S3 may be constituted by substituting a resistor corresponding to the resistor 41 for the two electrodes 61 and 62 and a capacitor corresponding to the capacitor 40 for the resistor 63 or, conversely, substituting the resistor 41 for the resistor 63 and the capacitor 40 for the electrodes 61 and 62.

In the embodiment of FIG. 2, selection of main gaps for critical spacing is important only for the main gap 21 and the remaining gaps 22, 23, and 24 are relatively tolerant of production variations in spacing.

The spark gap apparatus 65 of FIG. 5 comprises an arrangement of main gaps and a discharge control and preionizing circuit in four stages S5, S6, S7, and S8, generally similar in construction and functioning to the spark gap and discharge control apparatus of FIG. 1 and FIG. 2. However, the apparatus 65 incorporates a symmetric arrangement of stages S6 and S7 with respect to the stages S5 and S8 so that the gap plate assembly 11, 15, 12 is identical with the gap plate assembly 13, 16, 14.

3,496,409

As shown in FIG. 5, the -main gaps 66, 67, 68, and 69 are connected in parallel with associated grading resistors 70, 71, 72, and 73 and associated switching gap 74, grading capacitor 75, grading capacitor 6, and switching gap 7 to constitute the stages S5, S6, S7, and S8, respectively. The several stages are connected in series with each other and with a magnetic coil 78 having parallel connected gaps 79 and 80, as in the apparatus 10 of FIG. 1.

The grading resistances 70 and 73 are equal and the grading resistances 71 and 82 are equal, with the resistances 70 and 73 much larger than the resistances 71 and 72. Accordingly, line voltages and transient overvoltages impressed on the apparatus 65 are divided unequally between the main gaps 66 and 69 and main gaps 67 and 68. The resistors connected in series with the switching gaps 74 and 77 are unequal, the resistors of the gap 74 being larger than .the resistors of the gap 77 so that a transient overvoltage fires both of the switching gaps 74 and 77, which in turn causes the main gap 66 to fire and then the main gap 69. With gaps 66 and 69 conducting, the entire line voltage is impressed upon the main gaps 67 and 68 which causes them to fire. The gaps 67 and 68 fire simultaneously if resistors 71 and 72 are equal. If resistors 71 and 72 are unequal, as in a preferred embodiment hereof resistor 71 is 1 megohm and resistor 72 is 2 megohms, the gaps 76 and 75 fire in that order. In general, inequality of the grading resistors 71 and 72 equalizes the time constants of the two stages S6 and S7.

The functioning of the apparatus 65 for overvoltages with rapidly rising wave fronts is such that the grading capacitors 75 and 76 impress a substantial proportion of the line voltage across the main gaps 66 and 69 and the associated switching gaps 74 and 77. Accordingly, these gaps are fired, and the line voltage is then impressed across the main gaps 67 and 68 which are fired to initiate the discharge sequence. The capacitances of the capacitors 75 and 76 may be in the order of 20 times the distributed capacitance, in practical devices, to impress more than 90 percent of the line voltage across the stages S5 and S8. Accordingly, the embodiment of FIG. 5 produces improved sparkover performance for impulse voltages as well as for switching surges.

The capacitors 75 and 76 may be made unequal and/or the grading resistors 71 and 72 may be made unequal to determine a voltage upset and preferential firing order of the stages S6 and S7.

A lightning arrester utilizing the circuit arrangement of FIG. 2 as a gap control and embodying the features of U.S. Patents 2,825,008 and 3,019,367, and features of copending applications 624,2'75 filed Mar. 20, 1967, and 598,467, filed Dec. 1, 1966, used the following values:

Grading resistors—R35, R39, R45, 15 megohms; R41, 0.5 megohm.

Switching resistors and switching gap—G32, R33, R34, 10 megohms.

Switching gap fired—G36, R37, R38, 6 megohms; G42, R43, R44, 1 megohm.

Grading capacitor—C40, 100 mmfd.

The apparatus, including spark gaps and magnetic coil, were incorporated in the gap assembly of FIG. 1 and utilized at a nominal operating voltage of 4.5 kilovolts. Tests demonstrated consistent sparkover performance for long duration surges and for impulse voltages.

The arrangement of the above described embodiments, in’which the resistance of the series combination of switching gap and two switching resistors, when the switching gap is fired, is less than the resistance of the associated grading resistor, is preferred to arrangements in which the resistance of the switching gap and switching resistors is greater than the resistance of the associated grading resistor.

One advantage of the spark gap arrangements described herein, and particularly of the embodiment of FIG. 5, is that very high values of grading resistances may be utilized for determining the initial voltage distribution between the stages, or may be omitted entirely without affecting the order in which the main gaps are fired. Thus, in one embodiment of the apparatus of FIG. 5, the resistors 70 and 73 were omitted entirely and the remaining components had the following values:

Grading resistors—R71, 0.5 megohm; R72, 1.0 megohm.

Switching resistors and switching gap—G74, 8.5 megohms.

Switching gap fired—G77, 4.5 megohms.

Grading capacitors—C75, 200 mmfd.; C76, 100 mmfd.

Tests demonstrated consistent sparkover characteristics for long duration surges and for impulse voltages. In another embodiment of the apparatus of FIG. 5, the grading resistors R70 and R73 are each 15 megohms, and the other components having the same magnitudes.

One feature of the new spark gap apparatus is that a much larger gap electrode spacing may be utilized for a given breakdown voltage while maintaining a consistent sparkover function. Increase in gap spacing reduces the effect of variations in dimensions of the gap electrodes.

The term “time spectrum” is used to refer to the range of rise times or of delay times of the impressed wave of overvoltage or both.

It is to be understood that the foregoing description is not intended to restrict the scope of the invention and that various rearrangements of the parts and modifications of the design may be resorted to. The following claims are directed to combinations of elements which embody the invention or inventions of this application.