US2365595A - Spark gap device - Google Patents

Description

De. 19, 1944. w. G. ROMAN 2,365,595

SPARK GAP DEVICE Original Filed Jan. 26. 1939 WITNESSES: ,7

51, WQWW ATTORNEY INVENTOR Waite/ 6T Par/7027.

Patented bec. 19, 1944 SPARK GAP DEVICE Walter G. Roman, Forest Hills, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Original application January 26, 1939, No. 252,928. Divided and this application March 4, 1942, Serial No. 433,352

6 Claims.

My invention relates in general to spark gap devices, and more particularly to a spark gap having a low and consistent breakdown voltage and a low impulse ratio, which is particularly suitable for use in lightning arresters or other over-voltage discharge devices.

This application is a division'of my prior copending application Serial No. 252,928, flled January 26, 1939, now Patent No. 2,279,249, issued April 7, 1942, and assigned to Westinghouse Electric & Manufacturing Company.

to a conductor when thevoltage applied to itexceeds a predetermined value. Thus, when a high voltage such as a lightning surge is applied to the arrester, the valve element permits the flow of large surge currents to ground, but after the surge has passed and the voltage drops to approximately the normal linevoltage, it reduces the current to a very small value which can readily interrupted by the series gap.

The series spark gap used in such arresters performs three functions. Under normal conditions, it insulates the arrester from the line and prevents the flow of leakage current through the arrester. when a lightning or other high voltage surge occurs, however, the gap breaks down and connects the arrester to the line, thus permitting the flow of surge current to ground. After the surge has disappeared, the gap performs its third function of interrupting the relatively small power follow or leakage current caused by the normal line voltage. It will be evident, therefore, that in order to secure the sreatest degree of protection, the gap should have a relatively high 60-cycle or normal frequency breakdown voltage in order to prevent operation under low voltage disturbances, and should have a relatively low surge breakdown voltage to insure rapid operation when a high voltage surge occurs. The ratio of the surge or impulse breakthe voltage to the normal frequency breakdown it is obviously desirable that this ratio should be as close to unity as possible.

As usually constructed, series spark gap devices for lightning arresters consist of generally disk-shaped electrodes of brass, or other suitable metal, separated by an annular spacer, usually either of procelain or of a resistance material if it is desired to control the voltage distribution across the individual units of a multiple gap structure. A suflicient number of such gaps is used in series to obtain the desired voltage rating. It has been found in practice, however, that spark gaps constructed in this manner have relatively high and inconsistent surge breakdown voltages, giving impulse'ratios ranging from about 1.5 to as high as 2.0. These high breakdown voltages under surge-conditions are due to a time lag after the voltage has risen above the static breakdown voltage before the gap actually breaks down, and this time lag may vary in diiferent tests of the same gap, giving inconsistent results and making it diilicult to predict the behavior of the sap under given conditions. It will be apparent, therefore, that in order to obtain low and consistent surge breakdowns, it is necessary to reduce this time lag to a minimum.

The object of the present invention is to provide a spark gap device having a low and consistent surge breakdown voltage and a low impulse ratio.

More specifically, the object of the invention is to provide a spark gap device in which the time a voltage is called the impulse ratio ofthe 8 D, and I5 lag of breakdown is materially reduced by causing ionization of the air in the gap, which is very eil'ective in initiating breakdown with a minimum time lag. I have found that this result may be 'accomplished by causing high voltage gradients to occur in local regions of the gap adjacent the contactsbetween the insulating spacer and an electrode. The high voltage stresses in these regions cause electrical discharges, which may be similar to corona, and these discharges are very eiiective in causing ionization of the air, and may also cause the emission of a radiation into the gap which is also eiiective in ionizing the air as well as in producing free electrons in the gap. The ions and electrons thus formed are very effe'ctive in initiating rapid breakdown-of the gap and causing it to occur with a minimum time lag.

These high voltage gradients in local regions of the, gap may be produced in various ways, and can oonveniently be caused by d the gap in such a manner that the electric field between the electrodes is distorted so that high local concentrations of voltage stress exist. This distortion of the field may be produced by reducing the area of contact between one of the electrodes and the spacer to a very small area, or by introducing conducting elements into the gap which cause local distortion adjacent the electrode, or

in any other suitable manner.

The invention will be more fully understood from the following detailed description of certain preferred embodiments, taken in connection with the accompanying drawing in which:

Figure 1 is a vertical sectional view of a lighthing arrester spark gap device, with the associated apparatus shown diagrammatically;

Fig. 2 is a perspective view of the lower electrode of the gap of Fig. 1;

Fig. 3 is a perspective view showing a modified form of lower electrode;

Fig. 4 is a vertical sectional view of a double spark gap, illustrating another embodiment of the invention;

Fig. 5 is a plan view of the gap of Fig. 4 with the upper electrode omitted; and

Fig. 6 is a fragmentary perspective view showing the method of assembly of the gap of Fig. 4.

The spark gap device shown in Fig. 1 consists of an upper electrode 5 and a lower electrode 2, separated by an annular spacer member 3 of porcelain, or other suitable insulating material. The electrodes may be made of brass or other suitable metal and are generally disk-shaped Since it is usually desirable to have the thickness of the spacer substantially greater than the actual gap space, the upper electrode 1 is shown as being dished or shaped so that its central portion approaches the lower electrode more closely than the periphery to form an annular gap space indicated-at i. The upper electrode i is connected to a transmission line conductor 5, or other electrical device to be protected, and the lower electrode 2 is connected to a lightning arrester valve element 6, which is connected to ground as indicated at I. In an actual construction, of course, a sufiicient number of gaps would be used in series to obtain the desired voltage rating.

In order to cause high concentrations of voltage stress adjacent the points of contact between the lower electrode and the spacer, the area of contact between these elements is made very small. As shown in Figs. 1 and 2, this is accomplished by providing a plurality of projections on the upper surface of the electrode to space it a small distance from the spacer and which have a very small area of contact with the spacer. These projections may be conveniently provided by securing short lengths of wire 8 to the upper surface of the electrode by soldering, or other suitable means, as shown in Fig. 2. Projections may also be provided on the electrode by forming it with an annular ridge 9, as shown in Fig. 3, or by forming it with projecting portions of any suitable configuration which will space it a small distance from the spacer 3 and have a very small area of contact therewith.

The efiect of this construction is to cause a.

impulse ratios as low as 1.00 to 1.05 have been obtained with gaps of this type. It will be evident that these projections might be provided on the upper electrode if desired, although the eifect would probably not be as great, since the ionization of the air would occur at points farther removed from the actual gap space. The embodiment of the invention shown in Figs. 1 to 3 is claimed in the above-mentioned parent application.

Another embodiment of the invention is shown in Figs. 4 and 5. A double gap device is shown in these figures, although it will be understood that the arrangement shown may be used equally well with a single gap. The gap device consists of an upper electrode iii, an intermediate electrode or gap plate ii, separated from the electrode ID by an annular spacer i2, and a lower electrode i3, separated from the electrode II by an annular spacer M. The spacers are made of porcelain or other insulating material, while the electrodes are preferably made of brass, and the upper and lower electrodes are dished in the usual manner to permit the outer peripheries to be spaced apart a greater distance than the actual gap space. In this embodiment of the invention, the high local voltage gradients are produced by introducing a. conducting element into the gap space for the purpose of distorting the electric field between the electrodes. For this purpose, spring members l5 are placed in the gap on each side, in contact with the intermediate electrode and with the inner surfaces of the spacing members. The springmembers i6 may be made of brass, phosphor bronze or other suitable metal and, as more clearly shown in Fig. 6, are generally H-shaped. A slot 18 is formed in the electrode I l on each side for the reception of the springs. In assembling the gap, the springs are inserted in the slots of the electrode H as shown in Fig. 6, and the spacer members l2 and M are then placed in position, causing the springs to assume the position shown in Fig. 5 with their outer ends tightly in contact with the inner surfaces of the spacers.

When a voltage is applied across the gap, the presence of these springs will cause the electric held to be badly distorted in the regions around the points of contact between the springs and the spacer which are adjacent to the intermediate electrode ii. This distortion causes high voltage gradients to exist in these regions, which results in ionization of the air in the gap in the manner described above, and this ionization is very effective in causing breakdown of the gap to occur with a minimum time lag.

It will be seen that in both embodiments of the invention means are provided for causing a high concentration of voltage stress in local regions of the gap adjacent the points of contact between an electrode and the spacer member. In both cases, these high stresses cause electrical discharges in the nature of corona which cause ionization of the gas and which may also cause the emission of a radiation which causes further ionization and the production of free electrons in the gap. The effect of this ionization is in greatly facilitate breakdown of the gap and to cause it to occur with a minimum time lag, thus giving low and consistent breakdown voltages. It will be apparent that the high voltage gradients necessaryfor causing this effect can be produced in other ways than by the specific arrangements illustrated, and any other suitable means for causing distortion of the field in the gap to produce high local voltage gradients may he used without departing from the spirit of the invention. 1

It will be seen, therefore, that a spark gap device has been provided which is of relatively simple construction but which has very desirable characteristics in that it has a low and consistent surge breakdown voltage and a low impulse ratio. It is to be understood that although certain specific embodiments of the invention have been illustrated and described, it is not limited to the particular arrangements shown, but that in its broadest aspects it includes all equivalent embodiments and modifications which come within the scope of the appended claims,

I claim as my invention:

1. A double spark gap device comprising a plane intermediate electrode, an upper electrode, a first annular insulating spacer member disposed between the intermediate electrode and the upper electrode to space them apart, a lower electrode, a second annular insulating spacer member disposed between the intermediate electrode and the lower electrode to space them apart, and a conducting member carried by said intermediate electrode, said conductin member having a portion in contact with the inside cylindrical surface of the first spacer member and having another portion in contact with the inside cylindrical surface of the second spacer member.

2. A double spark gap device comprising a plane intermediate electrode, an upper electrode, a first annular insulating spacer member disposed between the intermediate electrode and the upper electrode to space them apart, said upper electrode having a portion extending part way through the spacer member toward the intermediate electrode to form a spark gap between the electrodes at a distance from the spacer, a lower electrode, a second annular insulating spacer member disposed between the intermediate electrode and the lower electrode to space them apart, said lower electrode having a portion extending part way through the spacer member toward the intermediate electrode to form a spark gap between the electrodes at a distance from the spacer, and a conducting member carried by said intermediate electrode, said. conducting member having a portion in contact with the inside cylindrical surface of the first spacer member and having another portion in contact with the inside cylindrical surface of the second spacer member.

3. A spark gap device comprising a pair of generally disc-shaped electrodes, an annular spacer member disposed between said electrodes to space them apart, at least one of said electrodes having a central portion extending part way through said spacer toward the other electrode to form a spark gap between the electrodes at a distance from the spacer, and a conducting member engaging the internal cylindrical surface of the annular spacer member opposite said spark gap and spaced therefrom, said conducting-member being in electrical contact with one of said electrodes 4. A spark gap device comprising a pair of generally disc-shaped electrodes, an annular spacer member disposed between said electrodes to space them apart, at least one of said electrodes having a portion extending part way through said spacer toward the other electrode to form a spark gap between the electrodes, and a metal spring member associated with one of said electrodes and in electrical contact therewith, said spring member bearing tightly against the internal cylindrical surface of the annular spacer member opposite said spark gap.

5. A spark gap device comprising a pair of generally disc-shaped electrodes,-an annular spacer member disposed between said electrodes to space them apart, at least one of said electrodes having a portion extending part way through said spacer toward the other electrode to form a spark gap between the electrodes, and a metal spring member supported on one of said electrodes, said spring member having a portion bearing tightly against the internal cylindrical surface of the annular spacer opposite said spark gap.

6. A spark gap device comprising a pair of generally disc-shaped electrodes, an annular spacer member disposed between said electrodes to space them apart, at leasa one of said electrodes having a portion extendin part way through said spacer toward the other electrode to form a spark gap between the electrodes, one of said electrodes having a slot therein, and a metal spring member supported in said slot, said spring member having a portion bearing tightly against the internal cylindrical surface of the annular spacer.

WALTER G. ROMAN.

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