US3188514A - Gas generating electric discharge device - Google Patents

Description

June 8, 1965 J. D. COBINE GAS GENERATING ELECTRIC DISCHARGE DEVICE Filed May 10, 1961 E F/g.

j, 22 U 6 2/ x 7 l I, /3 2 2 1 0 22 22 Pulse Source lnvemar: James D. Cob/he His Aflorney.

United States Patent The present invention relates to electric discharge devices adapted toswitch high voltages and currents with speed and precision, and more particularly to such apparatus in which switching is accomplished by triggering electric breakdown between a pair of fixed electrodes separated by agap in vacuo.

Gap. switching devices are devices normally maintained in an open circuit condition which, when subjected to an appropriate signal, are switched to a closed circuit condition and pass electric current therethrough. Such devicesfare used to great advantage as overload protectors,

lighting arresters and for the precision switching of ex tremely high voltages and currents, as for example, in discharging capacitor banks to obtain a very short pulse of extremely high current.

For these uses, gap discharge devices must be able to withstand high voltages and to break down or fire only when desired. They must be adapted, for many applications, tdfrepeatedly fire, often thousands of times, in response to essentially the same breakdown conditions, with the same firing time. In other applications, as for example, when used as lightning arresters, it is imperative that such gap devices have an extremely short recovery time so as to be ready to function again a short time after firing; i

Most prior art gap discharge devices are charged with a gaseousatmosphere, often at super-atmospheric pressure. Although suitable for many applications, gaseous gap discharge devices usually have long recovery times, due to the necessity of ionized gases therein becoming deionized before full recovery is effected. Additionally, since the hold-oifvoltage of a gap discharge device is dependent upon the dielectric strength of the gas therein, gaseous gaps .areoften quite large when designed for use at high voltages.

Perhaps the greatest disadvantage of scaled gaseous gap discharge devices, however, is. due to the fact that with use, gasis removed or cleaned-up from the device by entrapment with deposited metallic particles which are sputtered from the electrodes of the gap. This cleanup? changes the characteristic of the gap so that it does not perform reproducibly and the device must often be replaced long before actual failure.

Vacuum gap discharge devices have been proposed as a means to overcome many of these disadvantages. In theory, a vacuum gap discharge devicewould be smaller, due to the high dielectric strength of a vacuum; its recovery time would be much shorter; and, since there is no gas to be removed by sputtered metallic particles, a vacuum gap should not change its operating characterisitcs. In

practice, however, prior art vacuum gap discharge devices have not proven to be reliable, either .as to firing voltage, hold-off strength, or recovery time. In prior art vacuum spark gap devices, the operating characteristics seem, to be a function of the devices past history, such as the time lapsed since last firing.

It is a general object of thepresent invention to provide gap discharge devices which overcome one or more of the foregoing disadvantages.

A more specific advantage of the invention is to provide triggered gap discharge devices adapted to reproducibly fire at preselected voltage conditions, and to rapidlyrecover to the prefiring condition.-

Another object of the present invention is. to provide triggered gap discharge devices with reproducibly short firing times.

A further object of the invention is to provide improved gap discharge devices having stable, reproducible holdolf voltages, firing times and recovery times and including dielectric trigger electrodes.

Still another object of the present invention is to provide improved triggered gap discharge devices which are reliable in operation and which may be readily and inexpensively manufactured.

The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself together with further objects and advantages thereof may best be appreciated by referring to the following description taken in connection with the drawing in which:

FIG. 1 is a vertical cross-sectional view of a triggered vacuum gap discharge device constructedin accord with the present invention, and

HG. 2 is an alternative embodiment of theinvention in vertical cross-sectional view.

In PEG. 1, a triggered vacuum gap device includes an evacuable envelope, represented generally as 1, including an insulating cylindrical side Wall member 2 and apertured metallic disc-shaped end wall members 3 and 4 spaced at opposing ends of cylindrical member 2 and hermetically sealed thereto by suitable annular flange members. A first electrode 5 and a second electrode 6 are suspended Within envelope 1' in spaced-apart relation to define a breakdown gap 7. Second electrode 6 is suspended upon electrode support member 8 which is -passed through the aperture in end wall member 3 and hermeti cally sealed thereto by means of annular flange 9. Support member 8 terminates in a threaded stud 10 for connection to an electrical circuit. Elect-rode 5 passes through the aperture in end Wall 4 and is hermetically sealed thereto by means of annular flanges 11 and 12. Electrode 5 is a hollow cylindrical member with a nearly close-d end having an aperture 13 therein. The interior hollow portion of electrode 5 is shaped with a recessed region .14 at the upper portion thereof upon which rests a C-shaped dielectric trigger electrodemember 15. Trigger electrode 15 is electrically connected to the electrode upon which it rests on one side thereof andto a trigger electrode leadld which passes out through a flanged end cap member 1'7 Whichis hermetically sealed to the exterior portion of electrode member 5 by glass-to-metal seals 18 and an annular flange member 19. A threaded stud 2i? is integrally connected with the protruding end of electrode 5 for connection to the electrical circuit to be switched or protected. A cylindrical metallic shield member 2 1 is interspaced between breakdown gap 7 and the walls of cylindrical sidewall member Zto protect the latter I from becoming covered with metal evolved from electrodes 5 and 6 when an electric arc is established there-. betweenso as to maintain the insulating characteristics of cylindrical member 2. Shield 21 is supported in place by springs 22 whichride upon beads 23 upon the interior surface of wall 2. Cylindrical side wall member 2 is hermetically sealed to end Wall members 3 and 4 by suitable annular flange 24. v

Electrode 5 and electr'ode6 are preferably constructed of gas-free copper containing less than 10- parts by weight of all non-condensable gases or non-condensable mately. amperes. or greater currents must not cause latented June 8, 1965 I aisasia the pressure within the volume, a few cycles after arcing, to rise beyond the initial value, even when this value is 10* mm. of mercury or less. Other metals than copper, if similarly free of gases,.may be used when appropriate. The other metallic constituents within the device may be constructed of stainless steel since they are not directly subjected to the high current are and are not potential sources of gas contamination.

Insulating side wall member 2 is conveniently constructed of Pyrex or Vycor glass or a suitable ceramic. If glass is utilized, the flange members used to make hermetic seals thereto may be constructed of a fernico. If, on the other hand, ceramics such as forsterite ceramics or such ceramics as American Lava T164 or Coors V200, are used, then the metallic parts sealed thereto should be a metal which can be used to form a good ceramic-to-metal seal, as for example, titanium. Dielectric trigger electrode is constructed of a material having an exceedingly high dielectric constant, as for example, barium titanate. The dielectric chosen should be such that when a voltage pulse of short duration is impressed thereupon, substantially the entire voltage is impressed upon the C-gap thereof so as to cause the establishment of an arc thereacross. The edges of the C-gapf immediately adjacent thereto are coated with a thin film of a gas-absorbent material such as carbon or titanium and the coating is heavily impregnated with an ionizable gas, as for example, hydrogen.

In operation of the device in accord with the present invention, the high voltage to be switched or, if the device is to be utilized as a lightning arrester, the circuit to be protected, is connected between the primary electrode studs and a source of pulsed signal voltage is connected between the first electrode stud and the trigger electrode lead 16. When a voltage pulse as low as 100 volts and of 5-10 microseconds duration, for example, is applied to the trigger electrode, substantially all this voltage is impressed across the gap thereof anda breakdown is initiated. This breakdown heats the edges of the dielectric adjacent to the C-gap s-umciently to cause the evolution of gases therefrom. By virtue of the construction of the C-gap, these gases must necessarily be propagated upwardly through the aperture 13 in the cathode electrode and into the breakdown gap 7. The presence of ionized particles within breakdown gap 7 causes breakdown of the main gap between first electrode 5 and second electrode 6 and the subsequent passage of high currents therebetween.

As long as a voltage difference exists between electrode 5 and electrode 6, the arc is sustained. Upon the disappearance of a potential difference between these electrodes, however, the arc is extinguished and the conduction carriers therein, which consist entirely of electrons and ionized'metallic atoms evolved from the electrodes by the action of the arc, diffuse to shield 21, and other walls and adjacent members within the envelope 1, are cooled and deionized. With the disappearance of conduction carriers and the restoration of the high vacuum within breakdown gap 7, the dielectric strength of the gap increases very rapidly, within a few microseconds, and the device is ready to function again.

In FIG. 2 of the drawing, there is illustrated, in vertical cross-sectional view, a vacuum gap discharge device constructed in accord with another embodiment of the invention. The device of FIG. 2 includes an envelope represented generally as and including a generally cylindrical side wall member 31 having a base portion 32 terminating in a pinch Y33 and a pair of disc-shaped end wall members 34- and 35 hermetically sealed to insulating side wall member 31. A pair of primary electrodes 36 are disposed within envelope 30 in spaced-apart relation to define a breakdown gap 37. The electrode members are supported upon electrode support members 38 and 39, which are passed through and hermeticaly sealed by appropriate annular flange members to end wall members 34 and 35 respectively. Electrode 36 and breakdown gap 37 are surrounded by a cylindrical ferruled shield member 40 utilized to prevent metallic particles evolved from the electrodes from diffusing to insulating cylindrical side wall member 31 to destroy the insulating characteristic thereof. A (I-shaped dielectric trigger electrode 41 is supported upon a pair of trigger electrode support and lead'members 42 and 43 which are passed through pinch 33 in base portion 32 of side wall member 31. The open portion 44 of electrode 41 defining the trigger gap is aligned with an aperture 45 in shield member 40 to permit the injection of a burst of conduction carriers into the vicinity of breakdown gap 37 when trigger electrode 41 is suitably pulsed. The edges of trigger electrode 41 adjacent trigger gap 44 are coated with carbon, titanium or another gas-absorbing substance and impregnated with an ionizable gas, as for example, hydrogen.

In operation, the device of FIG. 2 functions much the same as the device of FIG. 1. The voltage to be switched is connected between studs 46 and 47 on electrode support members 38 and 39 respectively, and a source of pulsed voltage is connected between dielectric trigger electrode support and lead members 42 and 43. When it is desired to fire the device and render the gap conducting, a pulse of, for example, 5-10 microseconds of signal voltage, which may range from -3000 volts, depending up on the magnitude of the voltage to be switched, is supplied thereto. a breakdown is initiated across trigger gap 44. This results in the evolution of i onizable gas from the adjacent portions of dielectric trigger electrode 41 and, by virtue of the C-shaped configuration thereof, the injection of a burst of ionizable gas into breakdown gap 37 to render the gap conducting.

While the invention has been set forth herein with re-. spect to certain specific embodiments thereof many modifications and changes will readily occur to those skilled in the art. Accordingly, by the appended claims I intend to cover all such modifications and changes as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric discharge device adapted to change from a non-conducting state to a conducting state in response to a pulsed signal and comprising: an hermetically sealed envelope evacuated to a pressure of 10 mm. of mercury or less; a pair of primary electrodes located within said envelope and spaced apart from each other to define a breakdown gap therebetween; means for connecting said electrodes between terminals of a voltage to be switched; a trigger electrode comprising a body of high dielectric constant having a gap therein and adapted to sustain a trigger discharge across said gap when a voltage is supplied thereto; and means for supplying pulsed voltage signals to said trigger electrode to render said breakdown gap conducting.

2. An electnic discharge device adapted to change from a non-conducting state to a conducting state in response to a pulsed signal and comprising: an hermetically sealed envelope evacuated to a pressure of 10-5 mm. of mercury or less; a pair of primary electrodes located within said gap and spaced apart from each other to define a breakdown gapv therebet-ween; means for connecting said electrodes between terminals of a voltage to be switched; a trigger electrodecomprising a body of high dielectric constant having a gap therein; the dielectric constant of said body being sufficiently high so that when a voltage is applied to portions of said body on opposite sides of said gap substantially all of said voltage is developed across said gap to cause the initiation of a trigger discharge thereacross; and means for supplying pulsed voltage signals to said trigger electrode to render said breakdown gap conducting.

3. The electric discharge device of claim 2 wherein said trigger electrode body is formed of barium titanate. 4. An electric discharge device adapted to change from Upon application of this pulsed voltage,

'a non-conducting state to a conducting state in response to a pulsed signal and comprising: an hermetically sealed envelope evacuated to a pressure of 10* mm. of mercury or less; a pair of primary electrodes located within said envelope and spaced apart from each other to define a breakdown gap therebetween; means for connecting said electrodes between terminals of a voltage to be switched; a trigger electrode comprising a body of high dielectric constant having a substantially C-shaped configuration and defining a trigger gap, the edges of said body adjacent said gap being coated with a material having good gas-absorbing characteristics; means for supplying a pulsed voltage signal to said trigger electrode to cause a trigger discharge to be initiated across said trigger gap, resulting in the evolution of ionizable gas from the coating upon said body and the injection of ionized particles into said breakdown gap to render said gap conducting.

5. The electric discharge device of claim 4 wherein said coating of gas absorbing material is charged with hydrogen gas.

6. An electric discharge device adapted to change from a non-conducting state to a conducting state in response to a pulsed signal and comprising: an hermetically sealed envelope evacuated to a pressure of 10 mm. of mercury or less; an apentured first electrode and second electrode located within said envelope and spaced apart from each other to define a breakdown gap therebetween; means for connecting said electrodes between terminals of a voltage to be switched; a trigger electrode comprising a C shaped body of high dielectric constant having a gap therein and adapted to sustain a trigger discharge across said gap when a voltage is supplied thereto, said trigger electrode being located so as to propel ionized conduction carriers through the aperture in said first electrode and into said breakdown gap; and means for supplying pulsed voltage signals to said trigger electrode to render said breakdown gap conducting.

7. An electric discharge device adapted to change from a non-conducting state to a conducting state in response to a pulsed signal and comprising: an hermetically sealed envelope evacuated to a pressure of 10 mm. of mercury or less; a pair of primary electrodes located within said envelope and spaced apart from each other to define a breakdown gap therebetween, means for connecting said electrodes between terminals of a voltage to be switched; a trigger electrode comprising a C-shaped body of high dielectric strength having a gap therein and adapted to sustain a trigger discharge across said gap when the voltage is supplied thereto, said trigger electrode being laterally disposed adjacent said breakdown gap; and means for supplying pulsed voltage signals to said trigger electrode to render said breakdown gap conducting.

No references cited.

GEORGE N. WESTBY, Primary Examiner. JOHN W. HUCKERT, Examiner.

Claims (1)

1. AN ELECTRIC DISCHARGE DEVICE ADAPTED TO CHANGE FROM A NON-CONDUCTING STATE TO A CONDUCTING STATE IN RESPONSE TO A PULSED SIGNAL AND COMPRISING: AN HERMETICALLY SEALED ENVELOPE EVACUATED TO A PRESSURE OF 10-5 MM. OF MERCURY OR LESS; A PAIR OF PRIMARY ELECTRODES LOCATED WITHIN SAID ENVELOPE AND SPACED APART FROM EACH OTHER TO DEFINE A BREAKDOWN GAP THEREBETWEEN; MEANS FOR CONNECTING SAID ELECTRODES BETWEEN TERMINALS OF A VOLTAGE TO BE SWITCHED; A TRIGGER ELECTRODE COMPRISING A BODY OF HIGH DIELECTRIC CONSTANT HAVING A GAP THEREIN AND ADAPTED TO SUSTAIN A TRIGGER DISCHARGE ACROSS SAID GAP WHEN A VOLTAGE IS SUPPLIED THERETO; AND MEANS FOR SUPPLYING PULSED VOLTAGE SIGNALS TO SAID TRIGGER ELECTRODE TO RENDER SAID BREAKDOWN GAP CONDUCTING.

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