US2262369A - Expulsion-tube discharge device - Google Patents

Description

Patented Nov. 11, 1941 I r I 2,262,369

EXPULSION-TUBE DISCHARGE DEVICE Alert M. Opsahl, Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 30,1939, Serial No. 297,339 6 Claims. (01, na -30) My invention relates to excess-voltage protector tubes of the gaseous expulsion type, for the protection of line-insulators or apparatusinsulation against excess-voltage surges such as may be caused by lightning.

One of the principal objects of my invention is to devise a practical means for providing a variable-width, protective discharge-path which nected, particularly on lines having extremely small short-circuit currents.

In accordance with my present invention, practical means areprovided for causing the gaseous pressures, which are built up on the slot during either a severe surge-discharge or a severe powerfollow current-flow, to push theslot-walls further automatically varies its widthin accordance with the operating conditions. The discharge-path is made in the form of a long, narrow slot, and

. izing the gas which composes the arc-path, and

hence rendering that gas less conducting or even non-conducting, and at the same time physically aiding in the interruption of the arc by creating a powerful gas-blast which blows the are out of the protector-tube.

Such an excess-voltage protector-tube has two functions to perform. First, it must be capable of discharging the momentarily flowing surgecurrent, which may be of any value ranging over an extremely wide range of values, and lasting for a very small fraction of acycle of a 60-cycle' power-system. After the surgedischarge, the

protector-tube mustbe capable of interrupting the flow of the so-called power-follow current or follow-up current which discharges from the 60- cycle power line through the conducting gases or the arc-path established by the surge-discharge, and this power-follow current may have any one of many different values on different power-systems, ranging from very small currents on long, rural distribution-lines, to extremely heavy currents on important or heavy-duty power-lines of either the transmission or distribution class.

apart so as to avoid rupture of the device, while the narrow initial value of the slot-vvidth enables the device to interrupt the power-follow current on lines in which the short-circuit current is very low. My invention is particularly useful in cases where the same type of tube may sometimes be applied on rural lines, where the lightning-discharge currents are high andof frequent occurrence but the power-follow currents are low, and may at other times be applied on high-capacity power-systems, in connection with which it has heretofore been frequently necessary to add a resistor in series with the excess-voltage protector tubes previously utilized, in order to limit the bursting-effects and the erosion which occurs at the high power-follow currents which are obtained, the resistor being objectionable because it weakens the ability of the tube to protect the line against high surge-voltages.

One of the objects of my invention is to provide means whereby an expulsion-type discharge-tube has the lowest possible ratio of discharge-voltage to interruption-voltage, so that the tube will be capable of flashing over, undersurge-conditions which result in only a small increase over the normal line-voltage. A low flashover voltage, or

lightning-discharge voltage, means a short internal spacing between the electrodes, inside of the tube, as measured through the long, narrow 1 discharge-slot, but when this arcing length, or

In the design of a slot-discharge protective tube,the slot cannot be too narrow, or else the more severe of the lightning-current discharges spacing between electrodes, gets too short, it is much more difficult for thetube to interrupt the power-follow currents at any given voltage, In accordance with my invention, I utilize a slot which is initially of a width corresponding to the narrowest width that would ever be desired, and

I prevent failures due to rupture of the tube by causing the width of the slot to be automatically increased, when occasion demands, said slot 7 automatically returning to its narrower width as soon as the gaseous pressure abates in the tube, so that the maximum power-follow interruptingcharacteristics are always available. I can therefore'build a tube which has a lower ratio of flashover-voltage to line-voltage.

A more specific object of my invention is to provide a discharge-tube having a conically shaped opening at one end, with a conical insulating plug in said opening, the plug being mounted for axial displacement, so as to increase the slot-width between the two conical surfaces, this axial displacement being resisted by a spring.

With the foregoing and other objects in view, my invention consists in the apparatus, combinations, parts, systems and methods hereinafter described and claimed, and illustrated in the accompanying drawing, the single figure of which is a longitudinal sectional view of an exemplary embodiment of an excess-voltage protector-tube made in accordance with my invention.

The particular protective tube which is illustrated in the drawing comprises a tubular insulating member I having an opening which is conically enlarged at one end, as indicated at 2, and a conical insulating plug 3 in said conical opening. At least one of the conical surfaces preferably includes material which is capable of evolving deionizing gases or particles under the s influence of an arc, and in the preferred embodiment of my invention, both the tube I and the plug 3 are made of fiber, which has this property.

The non-conical end of the tube I is closed by a metal cap 4 which carries a centrally mounted metal or other conducting rod 5 which constitutes one of the arc-terminal electrodes of the device, and this is preferably the terminal which is connected to the high-voltage lead 6 which runs to the power-line or electrical apparatus to be protected. The electrode 5 has an inner end, or arc-terminal, which is centrally hollowed, as indicated at I, so as to provide an annular, beveled electrode-end 8 which terminates inside of the tube, adjacent to the small ends of the conical opening 2 and the conical plug 3.

The conical-opening end of the tube I, which is usually the lower end, is engaged by a vented metal capping-piece Ill which is of open tubular construction and which has an inner, annular seat or flange II, which constitutes the second conducting electrode of the device, said second conducting electrode being disposed adjacent to the large ends of the aforesaid said conical opening-portion 2 and conical plug 3, as indicated at II. The end of the cap-member I0 is vented, or open to the atmosphere, and this end of the capmember I0 is also arranged to integrally support a central cup-member I3 which is united to the tubular part of the cap-member by means of a plurality of webs or spider-arms I l. The large end of the conical plug 3 has a reduced extension I5 which extends into the top of the cup I3, and the cup I3 is fitted with a strong compressionspring IG which bears up against the bottom of the plug-extension I5 and yieldingly presses the plug in an exial direction tending to force it into the conical opening 2.

In accordance with my invention, I preferably provide spacing-means for causing at least portions of the two conical surfaces to be separated by an initial or minimum separation or slotwidth of at least one sixty-fourth of an inch, or of anywhere from one sixty-fourth of an inch to one twenty-fourth of an inch, depending upon the design-conditions. In the illustrated form of my invention, this spacing-means takes two forms, either or both of which can be omitted, andv either of which can be changed so as to have other formations. One of the means for preventing the plug 3 from being pressed too far into the conical opening 2, by the axially directed spring I6, is a suitable abutment on the inner terminal of the upper, electrode 5, for the small end of the plug 3. In the illustrated embodiment, this abutment takes the form of a plurality of small lugs II carried by the walls of the central hollow I of the electrode 5. Another means for preventing the plug 3 from being pushed too far into the conical opening 2 may take the form of longitudinally extending ribs, or preferably short, discontinuous projections I8, carried either by the plug 3 or the walls of the conical opening 2, so as to properly align the plug 3 within the opening 2 01 to limit the minimum possible slot-width between the two conical surfaces. Some adjustment of the minimum slot-width between the two conical surfaces may be obtained by axially ad justing the upper electrode 5, as by means of a threaded connection I9 between said electrode and the closed cap-end 4.

In certain cases, I may also provide a special venting-means for the normally closed electrode 5, and in the illustrated form of the invention, this special venting-means takes the form of a long, narrow, centrally disposed opening 2|, extending through the rod-like electrode 5, from the inner, arc-terminal depression I to a second hole or cup-like depression 22 which is provided at the outer end of th electrode-rod 5, the junction between the small central hole 2I and the bottom of the cup-like depression 22 being normally closed by a spring-pressed relief-valve 23. With this construction, the plug-like electrode 5 is normally closed or unvented, but in case the internal gaseous pressure should become very excessive, threatening to exceed the rupturing strength of the insulating tube I, this pressure can be automatically relieved by the opening of the valve 23, thus avoiding a failure of the protective tube.

The bottom, or permanently vented, electrodemember Ill-II will, in general, be the low-voltage electrode of the device, as indicated by the ground-connection 24.

In operation, the high-voltage terminal-lead 6 is connected to the line or apparatus which is to be protected by my device. In case a surge of any sort should cause a momentary rise in the voltage which is applied to the terminal-lead 6, a very slight increase in this voltage, over and above the normal or rated value, will suihce to cause an internal discharge within the tube, in the long, narrow slot between the two conical openings, said discharge passing from one electrode-tip 8 to the other electrode-tip I I, through said slot. It is necessary that this discharge shall be an internal discharge, in the long, narrow slot provided therefor, rather than an external discharge between the two end cap-pieces 4 and II], respectively, across the external discharge-space which is indicated at 25, because the long, narrow internal slot between the two conical surfaces, and the gas evolving wall-material of said slot, both combine to provide good arc-interrupting characteristics so as to interrupt the resulting power-follow current, which would not be the case in the event of an external discharge across the outside space 25. It is necessary, therefore, for one or both of the arc-terminal electrodes to extend part way into the tube I, for a sufficient total distance, so that the length and fiashover-voltage of the internal arcing-space between the electrode-tips 8 and II, shall be small enough so that the discharge always takes place interiorly, rather than externally across the outer gap 25.

If the surge-current which is discharged by the device is small, the surge-current flow will not develop suflicient gaseous pressures to move the plug 3 in a radial direction against the-opposition of its compression-spring I6. After the discharge of the current, which constitutes the surge, if the power-follow current is also small, it too Will develop only a small gaseous pressure in the arcing path, so that the plug 3 will still remain unmoved in an axial direction, and hence the slot-width of the discharge-path between the two conical surfaces will remain at itsminimum set value, so asto produce a maximum currentinterrupting ability as a result of the blast of un-ionized gases or particles which are emitted by the Walls of the conical surfaces as a result of their being subjected to the intimate play of the power-follow arc thereagainst. The tube is thus enabled to interrupt the feeble arcs which are produced by the lowest range of power-follow currents or short-circuit currents of the protected line or apparatus, these small power-follow arcs being usually among those which are the most difiicult for the tube to interrupt, because of the relatively small amount of gas-evolution which is evoked by such weak arcs.

If, however, the tube should be applied on a line or apparatus in which the power-follow currents are very severe, such that the currentinterrupting limits of the tube are determined by the blasting-resisting strength of the tube, then the gaseous evolution is so strong as to develop a high gaseous pressure in the arcing path between the two conical surfaces, and this gaseous pressure will develop an axial component which moves the plug 3 man axial direction out of the conical opening 2,and against the yielding force exerted by the axially applied compressionspring I6. It will be noted that the small angle or inclination of the conical walls results in the arc because of their greater separation. The

tube is thus protected against bursting, and this same solution is available also, in the event of extremely high-current surge-discharges.

As a further protection against bursting, the

pressure-relief valve 23 of the upper electrode can be provided and adjusted to become unseated in the presence of abnormal pressure-conditions, so as to vent the top end as well as the bottom end of the tube, in order to avoid a bursting or rupture of the tube.

The inner, arc-terminal depression 1 in the rod-like electrode 5 also serves as a gas-expansion chamber in which gas may flow or accumulate, until it builds up a pressure equal to the gaseous pressure in the narrow slot between the two conical surfaces, thus also relieving the severity of the gaseous-pressure conditions in the long, narrow slot.

In the event of an extremely severe surgecurrent on a protected power-line which has only a very small short-circuit current-value for producing a power-follow current in the dischargetube, the plug 3 may move radially outwardly with respect to the conical opening 2 during the heavy-current surge-discharge, after which the gaseous pressure within the tube will be reduced, because of the small power-follow current, so that=the compression-spring l6 will returnthe plug 3*to its initial positiomthus reducing the slot-width to the point where the tube can interrupt the weak power-follow current.

7 'While I have illustrated and described my invention in a single exemplary form of embodimen't, I wish it to be understood that said exemplary form' is only by way of il1ustration,fiand not intended to be by way of limitation to this one precise form. I desire, therefore, that the appendedclaims'shall be accorded the broadest construction consistent with their language and the prior art.

I claim as my invention:

1. An excess-voltage protective device of the expulsion-tube type, comprising a tubular insulating structure having an opening which is conically enlarged at one end, a conical insulataxially into said conical opening, at least one of the conical surfaces including material capable of evolving deionizing gases or particles under the influence of an arc, the internal fiashovervoltage of the protective device being less than ing opening a portion of which is conically shaped, a conical insulating plug, means for mounting said plug so that it has some capability of longitudinal movement with respect to said tubular insulating structure and including means for yieldably pressing said conical plug axially into said conical opening, at least one of the conical surfaces including material capable of evolving delonizing gases or particles under the influence of an arc, and a plurality of permanently separated and electrically insulated arcterminal electrodes so disposed, with at least one of said electrodes extending partway into the tubular insulating structure, so that any electrical flashover between said electrodes always results in a long, narrow discharge between said plug and said conical opening.

4. An excess-voltage protective device of the expulsion-tube type, comprising a tubular insulating structure having a. longitudinally extendingopening a portion of which is conically shaped, a conical insulating plug, means for mounting said plug so that it has some capability of longitudinal movement with respect to said tubular insulating structure and including means for yieldably pressing said conical plug axially into said conical opening and means for limiting the extent to whch said plug is axially thrust into said conical opening so as to provide a long, narrow, slot-like separation of at least one sixtyfourth of an inch between said plug and said conical opening at least one-of the conical surfaces including material capable of evolving deionizing gases or particles under the influence of an arc, and a plurality of permanently separated and electrically insulated arc-terminal electrodes so disposedgwithat least one of said electrodes extending partway into the tubular insulating tructure, so/that any electrical'flashoverbetween said electrodes always results in a long, vnarrow discharge through said slot-like 10 acterized by means for so enclosing and venting the device that'an-electrical discharge resultsin a gaseous blast flowing through the conical opening from the smaller to the larger end thereof.

6. The invention as defined in claim 4, characterized by means for so enclosing and venting the device that an electricaldischarge results in a gaseous blast flowing through the conical opening from the smaller to the larger end thereof.

ALERT M. 'OPSAHL.

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