US2664518A - Expulsion type lightning arrester - Google Patents

Description

Dec. 29, 1953 T, 1. ELDRIDGE, JR., ETAL 2,654,518

ExPULsIoN TYPE LIGHTNING ARRESTER Filed April 26, 1951 IN V EN TORS TAUSIAS IRVEN ELDRIDGEI'JR WALTER H.YOUNG FREDN G MAC RAE By a. m

HIS ATTORNEY f f f f f f A /0/ f//f/ ..KRMM van. O MRHQ 2 rO n n n f n f n r f n n n f r f n f a n I l IJI I T |v\ ff, /fl/f f/ W//f Patented ec. 29, 1953 UNITED STATES PATENT OFFICE 2,664,518 EXPULSION 'lY'lEl LIGHTNNG ARRESTER Tausias rven Eldridge, Jr., Brookline, and Walter oung, Willow Grove, Pa., and Fred Gr.` MacRae, La Grange, Ill., Service Manufacturing Company,

assignors to Electric Philadelphia,

Pa., a corporation of Pennsylvania. Application April 26, 1951, Serial No. 223,689

7 Claims. l

@or invention is an improved electric protective device or lightning arrester having a housing containing an electrode which, in use, is at line potential; an electrode, which, in use, is normally at ground potential; and an intermediate electrode: the latter being air spaced from the line electrode to form an isolating gap, and spaced from the grounded electrode by a constricted arc slot or slots formed by walls oi a protector tube. Such walls generate the deionizing gases when subjected to the action of an arc and constitute the characteristic element of the arrester for suppressing the flow of follow current to ground after the discharge of a surge due to lightning or transient abnormal voltage.

The stresses to which such devices are subjected in operation usually render. desirable the encirclement of the protector tube with a metal sleeve connected electrically with the grounded electrode and which acts as an electrostatic shield to provide low spark oveI oi the discharge paths through the arc slot between the inter-V mediate electrode and the grounded electrode.

We have found that failures of such arresters occasionally occur after the interruption of a discharge of surge current as a result of flash.- over of dynamic or system current through a shunt air path from the line electrode, around the protector tube to the grounded electrode or the conducting sleeveconnected therewith, Such ilashovers occur despite the fact that such shunt air path is considerably longer than the total of the arcing distances between the isolating gaps and through the arc slot and that dynamic or system current does not arc across either of such arcing distances excepting when the air between the electrodes has been ionized by a discharge of surge current. rlhe dynamic or system current does not iiashover through the shunt air path excepting during a discharge to ground initiated by a surge current or during the cycles immediately following the suppression of a discharge initiated by a surge current.

Discharges of dynamic current to ground' through the characteristic element are satisiactorily suppressed by the deionizing elect and pressure of the gases generated by the action of the arc on the wallsV of the characteristic element. But the ashover through the shunt air path around the characteristic element is not always suppressed, particularly when the shunt ashover occurs immediately after the suppression of the now through the characteristic element at or about a current zero.

We have found that shunt ashovers or re- 2 strikes are particularly likely to occur under circuit conditions which develop high magnitudes of short circuit current, especially at low power factor, and where voltage conditions are such that a relatively high voltage may exist at a time of current zero and upon the suppression of the iow through the characteristic element.

Our observations indicate that sue shunt flashovers or restrikes result from a continued einanation of ions from metallic parts within the housing', and particularly from the electrode at line potential, even after arcing over the isolating gap and through the arc slot of the char acteristicv element has ceased. Such continued emanation of ions appear to result from eit`L thermal or electrostatic conditions during or iollowing the suppression of the arc across the isoflating gap and across the arc slot of the char acteristic element, and when such ions are sufrl ciently concentrated they forni a conducting path between an element or elements at line potential and an element or elements at ground potential, with a resultant ow of dynamic curn rent. to ground and expiosion of the arrester.

In accordance with our invention, we preclude the formation of a conducting path of con centrated ions, in the space surrounding the characteristic element, between any conducting element at line potential and any conducting element at ground potential. The interruption of any such path of concentrated ions may be effected in various ways, as, for instance, sy venting, cooling and obstructing such ions and completely shielding therefrom by insulation all element and the insulating wall of the housing. however, the ionized gases are subdivided and deionized by the interposition oi fibrous strands between the region of the isolating air gap and any conducting element conM nested with the ground terminal, and the deionized gases are then discharged from 'the hous ing through avent. Such brous strands are preferably ot vitreous material matted or inten iaced together to form a porous resilient fabric or bat containing a multitude of restricted tortuous paths in which the ionized gases may diiiuse and in which they are cooled and deionized before cont cting any grounded member and before their discharge from the arrester housing.

The vitreous bres are preferably matted together in layers to .form a bat which may be wrapped around the outer wall of the protector tube so as to cover and insulate all grounded conducting parts and ll the space between the protector tube and the arrester housing with a compressible resilient mass permitting any requisite slight expansion of the protector tube during a heavy discharge.

The principles of our invention, and the best mode in which we have contemplated applying such principles will further appear from the following description and the accompanying drawings illustrating a preferred embodiment of our invention.

In the drawings, Fig. 1 is a tional view of an illustrative form of lightning arrester or protective device embodying our invention; Fig. 2 is a detached, fragmentary perspective view of the characteristic element for suppressing a normal follow current arc and preventing formation of a shunt arc around the characteristic element; Fig. 3 is a transverse sectional view taken on the line 3-3 of Fig. 1; Fig. i is a plan View of a fragmentary section of the porous, fibrous bat preferably used to trap, interrupt and deionize gases otherwise tending to facilitate the formation of a shunt arc around the characteristic element; and Fig. 5 is an enlarged, partly broken away, perspective View of the cylindrical conductor shown at the bottom of Fig. 2.

The lightning arrester shown in the drawings as an embodiment of our invention, comprises an external housing composed of a hollow, cylindrical, wet-process porcelain body I and a porcelain plug 2 glazed into the top oi' the body. The bottom of the housing is countersunk to form a seat 3 for the flanged edge t of a conducting cup 5 which may be provided with a hollow depending terminal boss for the attachment of a ground l. The cup 5 is secured against the seat 3 by a plastic seal 8 and non-plastic cement Si.

longitudinal sec-l A characteristic element or a protector tube Y is operatively associated with the ground terminal and includes a cylindrical shell Iii having its end threaded into the threaded cup 5. The shell IG is encircled, exteriorly, by a steel, seamless, reinforcing sleeve or shield I l which may be staked to the cup 5 and is therethrough connected to the ground. The sleeve I! projects along the shell I0 part way to the top I2 of an intermediate electrode extending downward within, and sealing the top of the tube I0.

In accordance with our invention, the space between the inner wall of the body I and the outer walls of the conducting sleeve Il and most of the length of the non-conducting hard iibre shell Iii is filled by a porous, non-hygroscopic, non-absorbent, compressible, fibrous fabric I3 which is lapped around the sleeve and shell above the hanged edge li of the cup 5 and effectively traps ionized gases and prevents their passage toward the grounded members 5 and II.

The fabric i3 preferably comprises a bat composed of loosely matter layers of resin-impregnated glass fibers, known commercially as Aerocor, and forming a multitude of restricted, tortuous pores or passages which trap and retard the movements of ionized gases while they are cooled and deionized by contact to the glass rlbres. The porosity and compressibility of the bat I3 permits slight expansion of the shell I under the pressures built up therein and allow for expansion of such gases as may be formed wi thin the housing.

The lapped bat may be prevented from unwrapping by the adhesive tapes I3'.

A cylindrical conductor Iii is seated and grounded on the cup 5 within the shell and has a peripheral wall l containing the countersink i5 at the upper end thereof and diametral slots i? which communicate, through an aperture Iii in the bottom of the electrode, with a discharge passage 2@ through the terminal boss t.

A hard fibre tube 2S is mounted on the ignite edge of an annular electrode 22 seated in the countersink it of the ring lf2- and is centered thereby in spaced relation to the inner wall of the shell Iii.

A rubber gasket is seated on top of the tube 2l and supports the anged top 2e of the element 25 of the intermediate electrode. A hard nbre core 225 is suspended by a screw 3i from the meinber 2d concentrically within the tube 2i and slightly spaced from the inner wall thereof.

The tubes i6 and 2l and the core 25, or some of these parts, are formed of hard ibre or horn libre or contain boric acid or other suitable gas generating substances activated by arcs between the respective electrode members fait and it and the grounded electrode 22.

The concentric cylindrical arc slots formed between the spaced members i l, l2 and 25 are preferably of unequal lengths: the inner slet being of smaller cross-sectional area and being the shorter. This tends to divert impulses of steep wave fronts to the outer and longer arc slot and to divert heavy currents of slower rising steepness to the inner, shorter arc slot. The concentricity'of the walls forming the concentric arc Vslots results in gas generating areas which are large relatively to the lengths of the slots of the arrester. The diffusion of the arc or arcs over a large area minimizes the charring or pitting of the gas generating surfaces, and is of particular value in preventing self destruction under discharges involving current magnitudes of very high order because of the multiple paths principle.

The constricted slots and gas generating walls form effective means within the shell i@ for suppressing an arc formed by the discharge of a surge and the iiow of follow current thereaiter.

The member 25 of the intermediate electrode is conductively connected with the member i2 thereof by a conducting tube 32 which is telescoped over the boss 33 of the member 26 and over the boss 35 of the member l2 within the tube it. There is no communication permitting the movement of gas from within the tube I@ to the space between this tube and the interior of the housing I or vice versa.

A conducting plug 36, seated in the member I2, and an electrode Si, carried by the end closure 2, form an isolating gap 38 normally isolating the arc suppressing elements of the arrester from line but providing a path to ground for impulse surges due to lightning or other transient abnormal voltages.

The electrode Si has a threaded shank Se which passes through an aperture in the closure f- 2 and the joint between the shank and closure is sealed by the washers dal, i2 which are squeezed by the head of the electrode 3l and line terminal i3 when the line terminal is screwed onto the shank.

A wire clamp .lie may be provided for gripping the line conductor inserted into the aperture t.

rEhe space between the interior oi' the housing I and the protector tube ie is ventilated through Ventilating apertures il through the ange Il and the cement 8 and 9.

The arrester 'may be mounted-'in 'any suitable.'v position adjacent toa circuit to be protected .by-- a metal bracket iii! encircling the housing I intermediate the ends of the reinforcing sleeve Il;

bracket to being spaced from the line terminal of the arrester the corrugated area of surface of the housing l to avoid external na hovers.

When a surge of lightning or other transient igh potential electric disturbance reaches the section of the line with which the line terminal is connected, it is discharged across the isolating gap i, through the member Hl, conductor 'w electrodes and 24, thi'ough one or both of the arc slots, electrode cup 5 and ground terminal e to ground. The arcs through thel arc slots cuiiclrly generates large volumes of deionizing ga which extinguishes the arc maintained -by fellow current, generally at or before the nest cero point of the cycle of the alternating current. The generated gas is expelled from the arc slots through the slots Il and passages is and Zii, away from the ground conductor l.

Air in the upper or line end of the housing, ionized by electrical and thermal conditions acc ing and immediately following the operation. of the arrester, is dilused through the ion trap formed by the long and tortuous paths of the bat it before contacting any grounded conducting element. The air in such paths, is normally of lof-.v ionic content and of high electrical resistivity. Movement of ionized air from the interior of the line and of the housing to any other area is delayed; as it diuses through the it is mixed with the un-ionized air therein and its ion concentration is reduced, and further deionization is effected by processes of cooling and recombination. The nal result of these three actions is that as equalization of air p-ressures within the housing proceeds, deionized non-conductive air replaces relatively highly ionized conductive air that otherwise would flow along the path between the line and ground elements and to the vent lll. There is thus no tendency for external flashovers between the members or 3l and the grounded shield l i and complete cut olf by the arrester is maintained after the suppression of the follow current arc through the arc slot.

While the loosely matted, porous bat of glass fibres constitutes the best mode in which we have contemplated applying the principle of our invention of interposing an effective barrier to any path of concentrated ions from an element at line potential to any element at ground potential, our invention is not necessarily limited to such speciiic embodiment as a barrier may be formed by completely covering all exposed surfaces of grounded elements within the space between the tubes l and il with insulation, or by housing all ion emanating elements within a line metallic screen acting on the Davy lamp principle to cool and deionize the ionized gases before they have traveled far from the ion emanating elements, or by venting ionized gases adjacent to the ion emanating elements and interposing a non-conducting diaphragm between all ion emanating elements and all grounded conducting elements which have exposed surfaces in the space between the tubes i and il. Such modifications are, however, deemed by us less desirable for general use than the glass fibre bat hereinbefore described.

Having described our invention, we claim:

- l. A lightning arrester comprising an insulating housing; 'a line terminal assembly including an electrode in said housing and at line potential when in use; an intermediate assembly including a fiber tube within and spaced from the interior periphery of said housing and also including an electrode co-acting with the first named electrode to form an isolating gap; a ground terminal assembly including an electrode complementary to and spaced from said second named electrode and also including a grounded conductor in the space between said ber tube and the interior periphery of said housing and reenforcing said tube; said second named electrode projecting into said tube such distance that the sum of the dash-over distances across said isolating gap and between said second and third named electrodes is less than the flash-over distance through said space from said nrst named electrode to the nearest part of the ground terminal assembly, and said housing having an aperture venting said space without passage through said tube o' ions emanating from said gap electrodes; and a barrier to the formation of any ion path connecting either of said gap electrodes with said ground terminal assembly through said space.

2. A lightning arrester comprising an insulating housing; a line terminal assembly including a gap electrode in said housing; an intermediate assembly including a tube within and spaced from said housing and having an electrode in operative relation to said electrode first named; a ground terminal assembly having an electrode in operative relation to said intermediate assembly and a grounded conducting sleeve encircling said tube in the space between said tube and housing; and a barrier to the formation of an ion path through said space between said sleeve and gap electrodes and comprising a porous, insulating fibrous filler.

3. A lightning arrester comprising a housing having a line terminal and a ground terminal, an intermediate assembly including a protector tube operatively associated with said ground terminal and having walls forming a restricted arc slot and electrodes positioned to permit arcing through said slot, electrodes forming an isolating air gap between said protector tube and said line terminal, and strands interposed between said isolating air gap and said ground terminal and co-acting to sub-divide and deionize gases ionized by an arc across said isolating gap and by emanations from the electrodes thereof.

4. A lightning arrester comprising a housing having a line terminal and a ground terminal, an intermediate assembly including a protector tube operatively associated with said ground terminal and having walls forming a restricted arc slot and electrodes positioned to permit arcing through said slot, a metallic sleeve encircling said protector tube and electrically connected with said ground terminal, electrodes forming an isolating air gap between said protector tube and line terminal, a porous fabric interposed between said isolating air gap and said sleeve and subdividing and deionizing gases ionized by an arc across isolating air gap and by einanations from the electrodes thereof.

5. A lightning arrester comprising a housing having a line terminal and a ground terminal and containing a vent, an intermediate assembly including a protector tube operatively associated with said ground terminal and comprising walls forming restricted arc slot and electrodes posiasesora,

tioned to permit arcing through said slot, electrodes forming an isolating air gap ybetween said protector tube and said line terminal, and a porous fabric interposed between said isolating air gap and said vent and sub-dividing and deionizing gases ionized by an are across said isolating gap and by ernanations from the electrodes thereof and ilowing toward said vent.

6. A lightning arrester comprising a housing having a line terminal and a ground terminal, an

vintermediate assembly including a protector tube operatively associated with said ground terminal and having Walls forming a restricted are slot and electrodes positioned to permit arcing through said slot, electrodes forming an isolating air gap between said protector tube and said line terminal, and. a hat of vitreous bres surrounding said protector tube and deionizing gases ionized by an arc across said isolating gap and by emanations from the electrodes thereof.

7. A lightning arrester comprising an insulating housing containing an electrode member which, in use, is normally at line potential; conducting members, including a second electrode, which, in use, are normally at ground potential; a third electrode intermediate said electrodes and having a portion forming, with the first electrode member, an isolating gap; an arc suppressive element operatively associated with said second electrode and with a portion o1 said third eleotrode and spaced from the interior of said housing; and a barrier to the formation of a conn centrated ion path around said element from any member at line ypotential to any member at ground potential.

TAUSIAS IRVEN ELDRIDGE, JR.

WALTER H. YOUNG.

FRED G. MacRAE.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 20 2,284,478 Roleson May 26, 1942 2,289,389 Stroup July 14, 1942 2,545,993 Dyer Mar. 20, 1951

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