US3448337A

US3448337A - Gaseous discharge device with keep-alive fifctrodes

Info

Publication number: US3448337A
Application number: US697274A
Authority: US
Inventors: Chester J Kawiecki
Original assignee: Joslyn Manufacturing and Supply Co
Current assignee: Joslyn Manufacturing and Supply Co
Priority date: 1967-12-21
Filing date: 1967-12-21
Publication date: 1969-06-03
Anticipated expiration: 1986-06-03

Description

GASEOUS DISCHARGE DEVICE WITH KEEP-ALIVE ELECTRODES Sheet Filed Dec. 21, 1967 CHESTER J. KAWlECKI lNl/ENTOR BUCKHOR/V, BLORE, KLAROU/ST 8 SPAR/(MAN June 3, 1969, c. J.-KAWIECKI 3,448,337 GASEOUS; DISCHARGE DEVICE WITH KEEP-ALIVE ELECTRODES Filed Dec. 21. 19 7 Sheet 2 of 2 POWER SOURCE LOAD FIG. 5

BUG/(HORN, BLORE, KLAPOU/ST 8 SPARKMA/V ATTORNEYS US. Cl. 315-238 23 Claims ABSTRACT OF THE DISCLOSURE A spark-gap device includes a pair of toroidal principal electrodes including annular permanent magnets therewithin providing a magnetic field for causing movement of an arc discharge around the principal electrodes. A pair of closely spaced starter electrodes, connected substantially in parallel with the principal electrodes, are disposed adjacent the outer periphery of the principal electrodes to form a starter gap adapted to break down at a predetermined voltage to illuminate and ionize the region of the gap between the principal electrodes. The principal gap then immediately breaks down into an arc discharge. According to another embodiment of the present invention, a substantially continuous arc discharge is established between the aforementioned starter electrodes for continuously illuminating and ionizing the region of the gap between the principal electrodes. The principal gap then responds more rapidly when a predetermined voltage is reached thereacross and will break down sooner in response to the occurrence of a fast rising transient surge.

This application is a continuation-in-part of my application Ser. No. 537,981, filed Mar. 28, 1966, now abandoned, entitled Spark-Gap Device, and assigned to the assignee of the present invention.

Background of the invention Spark-gap devices are frequently employed as transient protectors across a voltage supply line for protecting electrical equipment from transient surges. For example, such a spark-gap device may be employed as a lightning arrester providing a breakdown path from line to ground when a lightning surge occurs. Therefore, the surge does not reach and destroy electrical equipment also connected to the line. A suitable device of this type is described and claimed in Yonkers et al. Patent 3,154,718. The advantageous construction of the latter device includes a ring-shaped electrode having a circular arcing surface and having means for providing a magnetic field parallel to the arcing surface. When an arc strikes between the spark-gap electrodes, motor action due to the magnetic field tends to cause circular movement of the are around the ring-shaped electrode tending to minimize pitting on the electrode surface. However, even with this electrode construction, pitting along the electrode surfaces with continued use renders the breakdown voltage of the gap less and less predictable as the gap continues to United States Patent ice carry heavy follow currents. Therefore, protection of the line to which the spark-gap device is connected is hampered since the gap cannot be precisely set for a particular breakdown voltage.

Moreover, a spark-gap device designed to break down at a predetermined static breakdown voltage is usually not responsive at the same voltage value in the case of a fast-rising transient surge. In the instance of a fast rising spike of voltage across the gap, breakdown may not occur until the spike reaches a voltage value several times the designated static breakdown, due, for example, to the fact that ionization of the gap requires a finite period of time. The protection which the spark-gap device provides may therefore be seriously hampered and a high voltage transient may reach and damage equipment on the line.

It is, therefore, an object of the present invention to provide an improved spark-gap device having a predictable and preset breakdown voltage.

It is another object of the present invention to provide an improved spark-gap device capable of carrying large follow currents and thereafter continuing to render substantially accurate transient protection.

It is a further object of the present invention to provide an improved spark-gap device capable of breakdown in response to a fast rise time voltage transient at a more predictable voltage value.

Summary of the invention In accordance with an embodiment of the present invention, a spark-gap device includes annular ringshaped principal electrodes having a substantially constant spacing therebetween. The device preferably includes magnetic means tending to move an are along these principal electrodes. This spark-gap device is also provided with a pair of starting electrodes in parallel physical and electrical relation with the principal electrodes, connected between line and ground, and defining a starting gap therebetween which is aligned with but spaced laterally from the principal gap between the principal electrodes. The starting gap is adjacent the outer edge of the annular principal electrodes. However, the starting gap spacing is smaller than the spacing between the principal electrodes whereby the starting gap breaks down first to illuminate and ionize the region on at least one side of the gap between the principal electrodes causing substantially immediate breakdown between the principal electrodes. The motor action provided by the magnetic means tends to move or spread the resulting are around the surface of the principal electrodes. A resistance is preferably included in series with the starting electrodes so that current therethrough is kept to a minimum, and pitting of the starting electrodes is substantially minimized whereby the predictability of the breakdown voltage thereof is accurately maintained. Thus, the starting gap breaks down at a predictable voltage and immediately causes breakdown of the principal gap insuring adequate protection of the line in spite of wear resulting from subsequent heavy follow currents across the principal gap.

In accordance with another feature of the present invention, a capacitor is preferably disposed in parallel 3 with the starting electrodes for charging up to substantially line voltage. When breakdown occurs across the starting electrodes, the capacitor provides extra current to the arc and thereby establishes a hotter spark for enhanced ionization and more predictable breakdown in the adjacent area at the edge of the principal electrodes.

In accordance with another embodiment of the present invention, an arc discharge is substantially continuously maintained between a pair of starter electrodes disposed in substantially parallel physical and electrical relation with the principal electrodes of the spark-gap device. This continuous arc illuminates and ionizes the region of the gap between the principal electrodes such that the principal electrodes subsequently break down at a more accurately predictable voltage value. Thus, the principal gap will break down at a more predictable value in the case of a fast rise time transient'voltage occurring across the principal electrodes. A fast rise time transient accelerates ions across the principal gap more rapidly than would a slower changing voltage, tending to counteract the tendency towards a lagging breakdown at the principal gap. A spark-gap device is thereby provided which has an impulse ratio of two or less, wherein such impulse ratio is defined as the ratio of impulse breakdown voltage to static breakdown voltage.

The present invention, both as to organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings wehrein like reference characters refer to like elements.

Drawings FIG. 1 is a vertical cross-section of a spark-gap device in accordance with the present invention;

FIG. 2 is a circuit diagram for connecting the FIG. 1 device according to a first mode of operation thereof;

FIG. 3 is a waveform chart comparing spark-gap device breakdown voltage for fast rising transient values and sine Wave values;

FIG. 4 is a diagram of a second circuit for connecting the FIG. 1 device; and

FIG. 5 is a diagram of a third circuit according to the present invention for connecting the FIG. 1 device.

Detailed description Referring to FIGS. 1 and 2, a spark-gap device according to the present invention is housed in a hermetically sealed metal container 10, suitably of circular cross section, and which may contain a particular gas, e.g. argon, under a predetermined pressure, generally less than atmospheric. A suitable pressure for the argon is between two and six inches of mercury. The container is provided with a top closure 12 supported upon a lip member 14 disposed around the top of the container. Machine screws 16 secure closure 12 against lip member 14 with an O-ring seal 17 disposed therebetween to provide hermetic sealing. A polypropylene insulating cap 18 is disposed in a counter-sunk top opening 20 of closure 12 having a ledge 22 supporting cap 18. Stud 24 extends through the top center of cap 18 and is threaded at its upper end to receive support nuts 26 bearing on the top surface of cap 18. At its lower end, stud 24 is threaded and is received within a support member 27 having a cup-shaped extension 28 supporting a large porcelain feedthrough insulator 30, of circular cross section, the latter including a central opening for receiving stud 24. The porcelain insulator 30 also extends through opening 20 in closure 12 and has an upper margin 32 abutting ledge 22. Feedthrough insulator 30 is sealed to closure 12 at this point by mean-s of a thin metal bellows 34 secured to the margin 32 of feedthrough insulator 30 and joined at its outer circumference to the inner edge of opening 20 below ledge 22. The bellows 34 has a curved vertical cross section therebetween to allow for lateral differential expansion between closure 12 and feedthrough insulator 30.

Support member 27 is threaded at its outer diameter to' provide mounting for an upper principal electode 36 of the spark-gap device. This electrode is preferably circular or annular at its lower face having a central aperture region 38. The lower surface 40 of the electrode may also be toroidal, that is, of surface contour generated by the revolution of a curve (the lower cross section indicated at 40), about the axis of stud 24. The outer portion 42 of the electrode, which includes surface 40, threadably receives an inner plate 44 also having inner threads for securing plate 44 to support means 27. The upper principal electrode 36 is thus suspended from stud 24 into container 10 While being insulated therefrom by means of cap 18 and insulator 30.

Around the inner periphery of upper principal electrode 36 is preferably disposed an annular permanent magnet 46 having soft iron facings 48. The magnet is suitably poled as indicated with the north pole extending toward the surface 40 of the electrode and is secured between outer portion 42 and plate 44 of the electrode with a fiber washer 49 located between the magnet 46 and plate 44.

A lower principal electrode 50 is supported on a horizontal inner wall 52 of container 10. This principal electrode is also preferably annular in shape and has an upper surface 54 which may also be described as toroidal extending around a central aperture region 38. The toroidal surfaces of

principal electrodes

36 and 50 are similar in cross section and coaxial such that these surfaces are opposed, parallel, and equi-spaced around the electrodes defining a principal gap 56 of substantially constant spacing between

surfaces

40 and 54. Lower principal electrode 50 includes an inner plate 58 having a lower stud extension 60 secured to inner wall 52 with a retaining nut 62. Stud extension 60 is grounded to container 10. Plate 58 is threaded at its outer periphery to secure outer portion 64 of the principal electrode thereto. In a manner similar to that described in connection with upper principal electrode 36, lower principal electrode 50 preferably includes an annular permanent magnet 68 suitably poled as shown, that is with the north pole extending upwardly and the south pole extending downwardly within the toroidal surface of the lower principal electrode. The magnet 68 is also provided with soft iron facings 70 and a fiber washer 72'is positioned between the magnet 68 and plate 58. The

magnets

46 and 68 provide a magnetic flux having components parallel to the opposed surfaces of the principal electrodes.

Outer portions

42 and 64 including

surfaces

40 and 54 are suitably brass or tungsten to render the heavy principal electrodes suitable for withstanding heavy arcing.

The spark-gap device according to the present invention also includes a pair of starter electrodes or trigger

electrodes

74 and 76 having a gap 78 therebetween disposed adjacent to the principal gap 56.

Starter electrodes

74 and 76 are suitably aligned rods formed of molybdenum, tungsten, or the like and are supported in parallel relation to stud 24, locating the gap 78 in a position spaced laterally from the gap 56 but substantially horizontally aligned therewith. Gap 78 is disposed to lie within the longitudinal dimensional limits of the prinicipal gap, that is, substantially directly opposite the principal gap. The lateral spacing between the

starter electrodes

74 and 76 and the

principal electrodes

36 and 50 is preferably at least approximately five times the spacing of gap 78 and suitably less than ten times the same spacing. This spacing is suitable for causing ionization of the gas in gap 56 when an arc is drawn across gap 78. However, the spacing between the gap 7 8i and the gap 56 is such that arcing does not take place between the principal electrodes and the starter electrodes, In a particular embodiment, the spacing between the principal electrodes was 0.150 inch and that between the starting electrodes was 0.030 inch. Thespacing between the principal electrodes in this embodiment is greater than the spacing between principal electrodes in prior art devices wherein such spacing determined the voltage breakdown.

Electrode 74 is supported within ceramic insulating bushing 80 extending through an aperture in closure 12 and supported therewithin 'by means of thin metal bellows '82 extending from closure 12 and secured to bushing 80 to allow for differential expansion between these two members. The elect-rode 74 is threadably received in an inwardly and outwardly threaded stud 84 extending through bushing 80 and provided with nuts 86 supporting the top threaded portion thereof. A metal sleeve 87 is located between the upper portion of stud 84 and ceramic bushing 80. Lower starter electrode 76 is threaded and extends through a wall support 88 and is then secured by means of

nuts

90 and 92 at its lower extremity to inner wall 52, electrode 76 being grounded.

Resistors

94 and 96 respectively connect

studs

24 and 84 to the circuit line 98 to be protected. As further indicated in FIG. 2, a capacitor 100 may be connected between

starter electrodes

74 and 76, respectively, for purposes hereinafter more fully set forth.

As indicated in FIGS. 1 and 2, both the main gap between the principal electrodes and the starting gap between the starting electrodes are suitably coupled between the line 98 and ground. The starting

electrodes

74 and 76 are, however, much more closely spaced than the principal electrodes, for example, on the order of one-fifth the spacing between the principal electrodes so that when a high voltage surge occurs between line 98 and ground, the starting gap 78 will be the first to break down and establish an are. This are ionizes the gas in the immediate area, that is, in the area on at least one side of the gap between the principal electrodes. Moreover, illumination of the principal electrodes by the arc produces photoelect-rons aiding ionization. Immediate arcing then takes place between the principal electrodes and, due to the motor action produced by the magnetic field of

magnets

46 and 68, this are tends to move or spread around the surface of the principal electrodes and minimizes destructive pitting of these electrodes. It is noted that the voltage at which the complete arc conduction to ground is initiated in this embodiment is determined and preset only by the spacing between the

starter electrodes

74 and 76.

Resistors

94 and 96 are disposed between line 98 and the principal electrode and the starting electrode respectively. These resistors have a current limiting function. However, resistor 96 has a resistance much larger than resistor 94. For example, resistor 96 may have a resistance of 250 ohms, while resistor 94 may have a resistance of half an ohm. Due to this difference in resistance, the current in the are between

starter electrodes

74 and 76 will be very much limited in value as compared with the are between the

principal electrodes

36 and 50. Therefore, the closely spaced starting

electrodes

74 and 76 will have less tendency to become pitted and can maintain a reasonably accurate spacing whereby the pretermined value of breakdown voltage therebetween can be maintained.

According to another feature of the present invention, a capacitor mean 100 is suitably disposed between the starting

electrodes

74 and 76 as indicated in FIG. 2. This capacitor should, of course, have a breakdown voltage in excess of that between the starting electrodes. Capacitor 100 tends to charge up to line voltage and therefore toward the value of a high voltage surge. The capacitor has the effect of absorbing some of the line surge and therefore tends to minimize pitting of the starter electrodes. When the starting gap 78 breaks down, the capacitor 100 discharges through the gap 78 providing more current thereto and causing a hotter spark to occur. This hotter spark provides enhanced ionization of the gas in the adjacent region between the principal electrodes aiding prompt breakdown therebet'ween.

As hereinbefore indicated, the breakdown voltage of the embodiment illustrated in FIGS. 1 and 2 is set by the spacing of the starter electrodes which are within hermetically sealed container 10. This voltage is not readily adjustable when the gap 78 is once set. However, an

additional gap, external to container 10, may be provided in series with gap 78 at point 102 as indicated in FIG. 2, if desired, for the purpose of increasing the gap breakdown voltage. Since this gap is external to the container it can be more easily adjusted in its spacing for adjusting the breakdown voltage.

According to another embodiment of the present invention,

starter electrodes

74 and 76 in FIG. 1 are spaced, and the pressure within container 10 is predetermined such that a substantially continuous arc discharge takes place across gap 78 at the value of line voltage normally applied to line 98. In this context, substantially continuous is taken to mean that the arc discharge is substantially continuous in the same sense that the voltage on line 98 is substantially continuous.

Thus, in the case of an alternating current voltage, the arc current will, of course, increase and decrease in response to the AC. voltage variations on line 98 with respect to ground. This arc discharge between the starter electrodes substantially continuously ionizes the gas within container 10 in the region on at least one side of the principal gap 56 and causes illumination thereof. However, in the present device the spacing between the principal electrodes is adjusted such that an immediate arc discharge does not take place been the principal electrodes at the voltage normally applied to line 98 as a result.

Then, at such time as a high voltage subsequently appears on line 98 with respect to ground, the principal gap breaks down and shunts the transient to ground. This breakdown occurs in the present device at a predetermined voltage value, greater than normal line voltage but within a shorter time than would be the case if the region of the principal gap had to be ionized substantially concurrently with the occurrence of such high voltage transient.

By way of example, assume that line 98 is one line of a three-phase, 480 volt system. The normal voltage between line 98 and a grounded neutral point is approximately 277 volts. The starter electrodes 74 and 7 6 are preset, for example, so that discharge therebetween occurs at 270 volts and therefore a substantially continuous arc discharge will take place in gap 78 for ionizing the gas within container 10 in the region of gap 56 and illuminating gap 56. Resistor 9'6 limits the current of the arc discharge across gap 78 to a small value, for example between approximately one-half milliampere and twenty milliamperes, so that excessive current is not drawn from the line and undue electrode erosion does not occur at the ends of

electrodes

74 or 76. A suitable value for resistor 96 according to this embodiment is approximately 150,000 ohms.

A 480 volt three-phase system may have switching surges of 550 volts R.M.S. line to neutral or ground, and it is not desired the principal gap break down until the voltage in excess of that value is reached. In the instance of a device according to the present example, principal gap '56 between

principal electrodes

36 and 50 was preadjusted to break down and estabish an arc discharge at a static breakdown voltage of approximately 750 volts peak. Thus, the principal gap breaks down into an arc discharge when the voltage on the line rises reasonably slowly to 750 volts peak. It is also, of course, desirable for the gap to respond rapidly to fast rise time transients.

In the case of prior art devices, however, a fast rise transient having a rise time of say 10 kilovolts per microsecond might typically reach a voltage in excess of 3,000 volts before breakdown would occur, for example when a gap was set for 750 volts static breakdown. In the instance of the present device, on the other hand, where starter gap '78 provides continuous illumination and ionization of the principal gap, the principal gap breaks down into an arc discharge at less than 1500 volts on a voltage ramp of 10 kilovolts per microsecond. The impulse ratio for the principal gap thus is less than two, wherein impulse ratio is defined as the impulse breakdown voltage divided by the static breakdown voltage. This impulse ratio is substantially less than heretofore attained.

In the case of the present device, a fast rise time transient accelerates ions, already present in the principal gap, more rapidly than would a slower changing voltage, thereby tending to counteract the usual tendency towards a lagging breakdown in the principal gap. It is possible to obtain breakdown at a lower voltage in the case of a fast rising spike applied across the principal gap than in the case of a sine wave having a peak voltage of the same value. FIG. 3, for example, illustrates a sine wave of voltage 104, having a maximum or peak positive value, at 106 which would not cause gap breakdown. A voltage transient, 10 8, has a rise time appreciably faster than sine wave 104, and would reach twice the maximum value of the sine wave at 110. However, since the transient 108 accelerates ions already present in the principal gap more rapidly than sine wave 104, the principal gap can break down when the transient is applied and by the time voltage level 106 is reached. It is therefore possible to obtain an impulse ratio approaching one, resulting in line protection as adequate in the case of a very fast rise time high voltage transient as in the case of a slower rise time voltage.

FIG. 4 illustrates a circuit employed according to the second embodiment of the present invention wherein starter gap 78 substantially continuously supports an arc discharge at the normal voltage of line 98. In this circuit, resistor 96' in series with gap 78' is shunted with a neon lamp 112 in series with resistor 114. The current of the discharge in gap 78 drops a voltage across resistor 96' sufiicient for exciting the neon lamp 112. This lamp will normally be illuminated, indicating that the spark gap device has not lost its pressurization or has not otherwise become inoperative.

The arc discharge across principal gap 56 will ordinarily conclude at the first power current zero of the A.C. wave from the power source after the occurrence of a high voltage surge. However, in some instances, design considerations may dictate a particular gap spacing of gap 56 and a particular choice of ionizable gas and pressure such that automatic extinguishing of the principal gap does not occur. In such case, the circuit of FIG. 5 may be employed wherein a relay or switch (preferably vacuum type) 116 includes normally-closed contacts 118 connected in series between line Q8 and resistor 94'. Again gap 78' substantially continuously fires so that the region of gap 56 is substantially continuously ionized. Upon the occurrence of high voltage transient, gap 56 fires to shunt such transient as well as the resulting power-follow current to ground, with resistor 94 limiting this current to a particular maximum value. Magnetic means employed with the gap,

e.g. magnets

46 and 68 of the FIG. 1 device tend to extinguish this current, by motor action, at the first current zero of the alternating current wave after discharge. However, if the arc in the gap 56 is not then extinguished, the current through resistor 94 will drop a voltage causing coil 120 of vacuum relay 116 to open contacts 118, thereby extinguishing the arc. Coil 120 is suitably constructed so that it will not operate contacts 118 on the first half: cycle of the alternating current wave after breakdown. However, the coil will operate after a somewhat longer time, for example after one and one-half cycles of the A.C. wave, and will open contacts 118 at such time.

Since contacts 118 interrupt the circuit to gap 56, the arc thereacross will be extinguished.

Under normal circumstances, the high voltage transient will no longer be present when the normally-closed contacts 118 close again, and therefore the spark gap device will be restored to normal condition. However, under unusual circumstances, a high voltage condition may still be present on the line, or gap 56 may have become shorted, such that relay 116 will pump or operate intermittently. For this reason, it is desirable that relay 116 be constructed to latch open after one or more operations. This relay may then be manually reset to re-close contacts 118.

While I have shown and described preferred embodiments of my invention, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from my invention in its broader aspects. I therefore intend the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

I claim:

1. A spark-gap device suitable for providing accurate transient protection to a line above predetermined voltage levels, said device comprising:

a pair of principal eletcrodes adapted for connection between said line and ground, at least one of said principal electrodes having an annular surface in opposed relation to the other principal electrode defining a gap therebetween, and

a pair of starter electrodes also adapted for coupling between said line and ground, said starter electrodes defining a starting gap therebetween which is disposed adjacent the outer edge of the gap between said principal electrodes in sufficient proximity thereto to provide illumination and ionization in the gap between the principal electrodes at a time when arcing is caused to occur between staid starter electrodes, but laterally spaced from the gap between said principal electrodes by a sufiicient distance to prevent discharge between said principal electrodes and said starter electrodes,

the starting gap between said starter electrodes being substantially shorter than the gap between said principal electrodes.

2. The spark-gap device according to claim 1 further including magnetic means providing a magnetic field in the gap between said principal electrodes for causing movement of the are initiated therebetween when started by means of said starter electrodes.

3. The spark-gap device according to claim 1 further including a cur-rent limiting resistor means connected in series with said starter electrodes, said limiting resistor means having a value for limiting the current to the starter electrodes to a small fraction of the current to the principal electrodes.

said principal electrodes is normally illuminated and ion ized at said voltage levels normally applied to said line.

6. A spark-gap device suitable for providing accurate transient protection to a line above predetermined voltage levels, said device comprising:

a pair of principal electrodes adapted for connection between said line and ground, each of said principal electrodes having surfaces of similar toroids aligned in coaxial relation wherein said toroidal surfaces are equally spaced from one another in opposed relation defining a gap therebetween, and

a pair of starter electrodes adapted for coupling between said line and ground, said starter electrodes being disposed in parallel physical relation to said principal electrodes adjacent the outer edge of said toroidal surfaces but laterally spaced from the gap between said principal electrodes by a suflicient distance to prevent discharge between said principal electrodes and said starter electrodes, and in sufiicient proximity to provide illumination and ionization in the gap :between the principal electrodes at least in the area of the gap between said principal electrodes which is adjacent said starter electrodes as arcing is caused to occur between said starter electrodes,

said starter electrodes defining a starting gap therebetween which is substantially shorter than the gap between said principal electrodes.

7. The spark-gap device according to claim 6 wherein said starter electrodes each comprise aligned rods disposed in a direction parallel to the coaxial direction of said principal electrodes,with the gap therebetween positioned adjacent the gap between said principal electrodes, said starter gap falling in an area immediately adjacent the gap between the principal electrodes and having a length defined within the longitudinal extent of the gap between the principal electrodes.

8. The spark-gap device according to claim 6 wherein said starter electrodes are spaced beside said annular principal electrodes at a distance from the outer edge of the annular principal electrodes which is between approximately five times and ten times the spacing between said starter electrodes.

9. A spark-gap device according to claim 6 wherein the spacing between said starter electrodes is such that the voltage normally applied to said line establishes a substantially continuous arc discharge between said starter electrodes so that the region of the gap between said principal electrodes is normally illuminated and ionized.

10. The spark-gap device according to claim 6 further including a current limiting resistor means connected in series with starter electrodes.

11. The spark-gap device according to claim 6 having capacitor means coupled across said starter electrodes for developing a charge therebetweenand providing additional current for the are between said starter electrodes.

12. The spark-gap device according to claim 6 further including magnetic means providing a magnetic field in the gap between said principal electrodes for causing movement of the are initiated therebetween when started by means of said starter electrodes.

13. The spark-gap device according to claim 6 further including magnetic means providing a magnetic field in the gap between said principal electrodes for causing movement of the arc initiated therebetween when started by means of said starter electrodes, wherein said magnetic means comprises annular permanent magnets disposed within the toroidal surfaces of said principal electrodes for causing a magnetic field having components substantially parallel to the surfaces of said principal electrodes in the gap therebetween.

14. The spark-gap device according to claim 6 further including an additional spark-gap in series with said starter electrodes for setting the discharge voltage of said starting gap.

15. A spark-gap device suitable for providing transient protection to a line above predetermined voltage levels, said spark-gap device comprising:

a pair of principal electrodes adapted for coupling between said line and ground, said principal electrodes having opposed parallel surfaces defining a gap therebetween,

a pair of starter electrodes also suitable for coupling between said line and ground which are disposed adjacent the outer edge of said principal electrodes in spaced relation from said principal electrodes, said starter electrodes defining a gap therebetween spaced adjacent the outer edge of the gap between said principal electrodes, and

capacitor means coupled across said starter electrodes adapted to be charged by the voltage across said starter electrodes for contributing current to the illumination and ionization between said starter electrodes and the adjacent gap area of said principal electrodes when the voltage across said starter electrodes is sufiicient to provide an arc discharge between said starter electrodes.

16. The spark-gap device according to claim 15 further including resistor means in series with staid starter electrodes.

17. A spark-gap device suitable for providing accurate transient protection to a line at voltages above the voltage level normally supplied to said line, said device comprising:

a pair of principal electrodes adapated for coupling between a conductor of said line and ground, said principal electrodes including spaced opposed surfaces defining a principal gap therebetween.

and a pair of spaced starter electrodes coupled between said line and ground which are disposed adjacent said principal gap, said starter electrodes including spaced opposed surfaces defining a starter gap therebetween, said gap having a spacing substantially less than the spacing between said principal electrodes for normally establishing an arc discharge between said electrodes at the voltage normally applied to said line, while said principal electrodes are spaced apart at a greater distance such that no arc discharge normally occurs therebetween at the said voltage normally applied to said line,

said discharge between said starter electrodes illuminating and ionizing the region of said principal gap enabling said principal gap to break down more quickly upon the occurrence of a fast rise time transient surge of high voltage on said line.

18. The spark-gap device according to claim 17 including an enclosure for said spark-gap device Within which said principal electrodes and said starter electrodes are located, the pressure within said enclosure being maintained at less than atmospheric pressure, said enclosure including an ionizable gas.

19. A spark-gap device suitable for providing accurate transient protection to a line above predetermined voltage levels, said device comprising:

an enclosure for said spark-gap device containing an ionizable gas,

a pair of principal electrodes located in said enclosure at least one if which is adapted for connection to a conductor of said line, said electrodes respectively having spaced opposed surfaces defining a principal gap therebetween,

and a means for providing a substantially continuous arc discharge within said enclosure in proximity to said principal gap for illuminating and ionizing the region of said principal gap so that said principal gap more quickly breaks down into an arc discharge when a voltage above a predetermined voltage level occurs across said principal electrodes.

20. The spark-gap device according to claim 19 wherein said means for providing a substantially continuous arc discharge comprises a pair of starter electrodes having spaced opposed surfaces defining a starter gap therebetween, said starter electrodes being located adjacent said principal electrodes so that said starter gap is adjacent said principal gap,

and means for coupling said starter electrodes to a voltage for energizing said arc discharge therebetween.

21. The spark-gap device according to claim 17 includ- 3,448,337 11 12 ing a resistor in series with said starter electrodes for References Cited limiting the current of the normal arc discharge break- UNITED STATES PATENTS down between said starter electrodes.

22. The apparatus according to claim 17 including 3. 2,508,954 5/1950 Latoul' et 3 55 X resistor in series with said starter electrodes, and n indi- 5 3,141,111 7/ 1964 G p e 315l81 cating means connected to said resistor for detecting the 3,320,478 5/1967 Harlflsoll 13155 X flow of current to said starter electrodes. 3,328,632 6/1967 RObIIlSOIl 313307 X 23. The apparatus according to claim 17 further in- JAMB W. LAWRENCE, Primary Examiner. eluding switching means having normally closed contacts 0 R CAMPBELL Assistant Examiner in series with said principal electrodes, which contacts are 1 adapted to open after a predetermined time period of arc discharge breakdown between said principal electrodes. 313-161, 198; 315135, 245, 275, 340, 355; 3l7-62 P0405) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3,448,337 Dated June 3, 1969 Inventor(s) Chester J. Kawiecki It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 30, "wehrein" should read -wherein-- Column 5, line 64, "mean" should read -means.

Column 6, line 59, after "of" insert --say--; Column 6, line 64, "estabish" should read --establish-- Column 8, line 25, "eletcrodes" should read --electrodes--; Column 8, line 37, "staid" should read Said-.

Column 9, line 43, after "with", insert '--said-- Column 10, line 14, "staid" should read -said--; Column 10, line 20, "adapated" should read adapted--.

SlGnED AND SEALED MAR 1 01970 Attest:

Edward M. Fletcher, Ir. WILLIAM E. SCIHUYLER, JR.

testing Officer Commissioner of Patents