US3496409A

US3496409A - Spark gap and discharge control apparatus

Info

Publication number: US3496409A
Application number: US585846A
Authority: US
Inventors: Thomas R Connell
Original assignee: Ohio Brass Co
Current assignee: Ohio Brass Co
Priority date: 1966-10-11
Filing date: 1966-10-11
Publication date: 1970-02-17
Anticipated expiration: 1987-02-17
Also published as: CH470775A; BE704385A; GB1173685A; DE1588607A1

Description

Feb. 17, 1970 'r. R. ICONNELL 3,

SPARK GAP AND DISCHARGE CONTROL APPARATUS Filed 001;. 11, 1966 2 Sheets-Sheet 1 Ili'l/ FIG. 3

INVENTOR THOMAS R. CONNELL ATTORNEY 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 of New Jersey Filed Oct. 11, 1966, Ser. No. 585,846 Int. Cl. H02h 3/22, 9/06 US. Cl. 315-36 10 Claims 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 gap 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 gap 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 illuminate 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 maintained 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 close 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 insure 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 the 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 various 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.

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 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 t0 define spark gaps, associated arc chambers, and control and discharge circuits of the gap control stages S1, 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 S1, 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 US. Patents 2,825,008 and 3,019,367 to I, W. Kalb, or by arrangements of arc elongating electrodes, within the contemplation of the invention.

In the apparatus 10, the gap control stage S1 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 S1, 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 progressively 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 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 production, 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 because of the larger values of

resistors

33 and 34.

The functioning of the apparatus 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 main 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 resistors. 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 S1, 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 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 distribution of line voltage as between the stages S1, 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 S1, 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 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 S1, 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:

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 40, or the com bined impedances of the capacitor and the grading resistor 41, for the stage S3 or the resistance of the

grading resistors

35, 39, and 45 for the stages S1, 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 S1, S2, and S4, so that, for impulsive voltages having a sufiiciently 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, th 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 are 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

mem bers

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 S1, 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, gen erally 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.

As shown in FIG. 5, the *

rnain gaps

66, 67, 68, and 69 are connected in parallel with associated

grading resis tors

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. p

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 l 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 US. Patents 2,825,008 and 3,019,367, and features of copending applications 624,275 filed Mar. 20, 1967, and 598,467, filed Dec. 1, 1966, used the following values:

Grading resistorsR35, R39, R45, 15 megohms; R41, 0.5 megohm.

Switching resistors and switching gapG32, R33, R34, 10 megohms.

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

Grading capacitorC40, 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, inwhich 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 firedG77, 4.5 megohms.

Grading capacitors-C75, 200 mmfd.; C76, 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.

I claim:

1. Spark gap and discharge control apparatus comprising a plurality of gap electrodes and grading means therefor, said gap electrodes and grading means constituted as a plurality of stages of parallel connected elements in series connection, stage by stage, each stage comprising two electrodes constituting a main gap, a first resistive grading means in parallel with the main gap, the said first resistive grading means of the said several stages dividing voltages between the stages, and a switching gap and series switching resistor connected in parallel with the main gap, the switching gap of each stage having electrodes positioned adjacent the associated main gap electrodes and communicating with the main gap to constitute a preionizer therefor, the resistance of the series switching resistor and switching gap being unequal in the several stages to constitute a second voltage grading means for preferentially firing the main gap of one of the stages prior to the main gaps of the remaining stages.

2. Spark gap and discharge control apparatus in accordance with claim 1, in which the resistance of the series switching resistor and switching gap of the said one stage is greater than the resistance of the series switching resistor and switching gap of each of the remaining stages and is less than the resistance of the first resistive grading means of the said one stage, all for predetermining the preferential firing of the main gap of the said one stage independent of firing sequence of the switching gaps.

3. Spark gap and discharge control apparatus in accordance with claim 2, in which the main gap of the said one stage is critically spaced to predetermine the breakdown voltage thereof, the remaining main gaps being relatively independent of small variations in the spacing of the electrodes thereof.

4. Spark gap and discharge control apparatus comprising a plurality of gap electrodes and grading means therefor, said gap electrodes and grading means constituted as a plurality of stages of parallel connected elements in series connection, stage by stage, each stage comprising two electrodes constituting a main gap, a first resistive grading means in parallel with the main gap in each of the stages, the said first resistive grading means of the said several stages dividing voltages between the stages, a

switching gap and series switching resistors connected in parallel with the main gap in at least one of the stages, the switching gap having electrodes positioned adjacent the main gap electrodes and communicating therewith to constitute a preionizer, all for firing the main gap in response to overvoltages having slow wave fronts, and capacitive grading means connected in parallel with the main gap in at least one of the stages for firing the main gaps of the remaining stages in response to overvoltages having fast wave fronts, and all providing predetermined firing sequences of the main gaps for a wide time spectrum of overvoltages.

5. Spark gap and discharge control apparatus in accordance with claim 4, in which there are four gap stages connected in series and comprising three stages, similar to the described one stage, having switching gap electrodes connected in parallel with the main gap electrodes thereof, and one stage having a capacitor connected in parallel with the main gap thereof.

6. Spark gap and discharge control apparatus in accordance with claim 4, in which there are four gap stages connected in series and comprising two stages having switching gap electrodes connected in parallel with the main gap electrodes thereof, and two stages having capacitors connected in parallel with the main gap electrodes thereof.

7. Spark gap and discharge control apparatus in accordance with claim 4, in which there are two stages having switching gaps and switching resistances in parallel with the main gaps thereof and at least one stage having a capacitor connected in parallel with the main gap thereof, and the first-named two stages have equal time constants for control of the main gaps in response to overvoltages having fast wave fronts.

8. Spark gap and discharge control apparatus comprising a plurality of gap plates and a magnetic coil in stacked arrangement and a plurality of gap electrodes and grading means carried by the said gap plates, the said gap electrodes and grading means constituted as a plurality of stages of parallel connected elements in series connection, stage by stage, and in series with the magnetic coil, each stage comprising two electrodes constituting a main gap having electrodes with divergent arc faces positioned in the field of the magnetic coil, a first resistive grading means in parallel with the main gap, the said first resistive grading means of the several stages dividing voltages between the stages, a switching gap and series switching resistors connected in parallel with the main gap in at least one of the stages for upsetting the voltage division produced by the first grading means, the switching gap having a breakdown voltage less than the breakdown voltage of the main gap and having electrodes positioned adjacent the main gap electrodes and communicating therewith to constitute a preionizer, all for firing the main gap in response to overvoltages having slow wave fronts, and capacitive grading means connected in parallel with the main gap for firing the main gaps of the remaining stages in response to overvoltages having fast wave fronts, and all providing a predetermined firing sequence of the said main gaps and initiating current flow in the magnetic coil.

9. Spark gap and discharge control apparatus in accordance with claim 8, in which the switching gap electrodes comprise cylindrical members of resistive material constituting the series switching resistors, and means supporting the switching gap electrodes in spaced relation adjacent the electrodes of the main gap.

10. Spark gap and discharge control apparatus in accordance with claim 9, in which the main gap electrodes are carried by a gap plate, and the means supporting the switching gap electrodes is carried by the gap plate.

References Cited UNITED STATES PATENTS 2,623,197 12/1952 Kalb 315-36 2,825,008 2/1958 Kalb 315-36 X 3,076,114 1/1963 Hicks 315-36X 3,377,503 4/1968 Osterhout 315-36 JOHN W. HUCKERT, Primary Examiner I. R. SHEWMAKER, Assistant Examiner U.S. Cl. X.R. 313-326

Claims

1. SPARK GAP AND DISCHARGE CONTROL APPARATUS COMPRISING A PLURALITY OF GAP ELECTRODES AND GRADING MEANS THEREFOR, SAID GAP ELECTRODES AND GRADING MEANS CONSTITUTED AS A PLURALITY OF STAGES OF PARALLEL CONNECTED ELEMENTS IN SERIES CONNECTION, STAGES BY STAGE, EACH STAGE COMPRISING TWO ELECTRODES CONSTITUTING A MAIN GAP, A FIRST RESISTIVE GRADING MEANS IN PARALLEL WITH THE MAIN GAP, THE SAID FIRST RESISTIVE GRADING MEANS OF THE SAID SEVERAL STAGES DIVIDING VOLTAGES BETWEEN THE STAGES, AND A SWITCHING GAP AND SERIES SWITCHING RESISTOR CONNECTED IN PARALLEL WITH THE MAIN GAP, THE SWITCHING GAP OF EACH STAGE HAVING ELECTRODES POSITIONED ADJACENT THE ASSOCIATED MAIN GAP ELECTRODES AND COMMUNICATING WITH THE MAIN GAP TO CONSTITUTE A PREIONIZER THERE-