US2923849A - Lightning arrestor - Google Patents

Description

Feb. 2, 1960 F. x. REES 2,923,849

LIGHTNING ARRESTOR Filed July 10, 1958 INVENTOR.

F. XREES HlS ATTORNEY United States Patent I 2,923,849 LIGHTNING ARRESTOR Frank x. Rees, Chili, N.Y., assignor to General Railway Signal Company, Rochester, N.Y.

Application July 10, 1958, Serial No. 747,746 17' Claims. (Cl. 313411) of a lightning arrestor which has an air-gap structure inherently having an arc extinguishing characteristic which will minimize the time the lightning arrestor is subjected to the discharge current.

Another object of the present invention is the provision of a lightning arrestor having two metal electrodes forming a major air-gap, one of said metal electrodes having an adjacent auxiliary electrode of semiconductive material forming a minor air-gap with the other metal electrode which is eifective to initially ionize said major airgap at a relatively low critical potential to allow the main disruptive discharge to pass through such major air-gap between said metal electrodes.

Another object of the present invention is the provision of a lightning arrestor structure having a substantial confined internal air space between the metal electrodes to provide adequate internal compression of the air upon a disruptive discharge to tend to move ionized air outwardly from the base of the major air-gapqto assist in the early extinguishing of that disruptive discharge.

Another object of the present invention is the provision of a lightning arrestor which is securely held in its mounting position requiring very little maintenance for an in- .definite period of time.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings, and in part pointed out as the description of the invention progresses.

In describing the invention in detail, reference will be made to the accompanying drawings, in which like reference characters designate corresponding parts throughout the several views, and in which:

Fig. 1 is a side elevational view of the present invention comprising electrodes enclosed in a housing with associated metallic connectors extending to terminal posts of a terminal block;

Fig. 2 is a cross sectional view taken on the line 2-2 of Fig. 1;

Fig. 3 is a cross sectional view taken on lines 3-3 of Figs. 1 and 2;

Fig. 4 is an enlarged view of a portion of the electrodes of Fig. 3;

Fig. 5 is a bottom plan view of Fig. 3 and shows the lightning arrestor connectors held in their housing by metal springs; and

Fig. 6 is a perspective view of one of the metallic conice nectors shown in Fig. 5 and used to electrically connect the electrodes to their respective terminal posts of the arrestor.

In general, the lightning arrestor of the present invention comprises a terminal block 15, a transparent hollow glass housing 12, and the electrodes 21, 22 and 23 which are held in position by the hollow housing 12 and are electrically connected to the terminals 13 and 14 of the terminal block.

The circular metallic electrode 22 (see Fig. 3) has a circular recess 18 for receiving a disc 23 of a suitable semiconductive material such as Carborundum, Everohm, or the like. The material having the trade name Carborundum is essentially a silicon carbide type of material. Everohm is a trade name applied to a semiconductive product particularly adaptable for use in light- "ning arrestors, and comprises powdered graphite or mineral black combined with a finely ground Portland cement binder as fully described in Pat. No. 1,818,l84, dated August 11, 1931. The circular electrode 22 is preferably made of brass and has an axial hole or bore for receiving the stem of insulating material 27 as seen in Fig. 3. This insulating material 27 has an axial bore for receiving the shaft of a bolt 20 and is preferably made of Bakelite type insulating material.

The circular disc 23 of semiconductive material has an outside diameter such as to securely fit into the recess 18 of electrode 22 with a portion protruding therefrom. This disc 23 is an auxiliary electrode so that its tight fit in the recess 18 establishes good electrical connection with the metal electrode 22.

The spacer 19 is in the form of a circular disc with a recess or groove 28 around its periphery. The other metallic electrode 21 is mounted on the stem of insulating material 27 and is provided with an inner circular recess 17 having a diameter less than, the diameter of the circular recess 18 of the circular electrode 22. In other words, the two metal electrodes 21 and 22 are positioned like two cups facing each other separated by a spacer and all having axial bores. The inside of the electrode 21 is smaller so that the inner edge of its rim forms a flat ring 25 adjacent the inner flat surface of the auxiliary electrode 23. This flat ring 25 extends slightly beyond the outside diameter of the auxiliary electrode 23 so as to be directly opposite a flat portion of electrode 22. These fiat portions of electrodes 21 and 22 form what might be termed a major air-gap, from which their sides 24 and 26 slant outwardly or away from each other at an angle of approximately forty degrees to form the sides 24 and 26 of a horn type gap. This horn-shaped air-gap extends circularly around the periphery of these two electrodes 21 and 22. The air-gap between the inner fiat edge 25 of the rim of electrode 21 and the flat inner surface of the auxiliary electrode 23 may be conveniently termed the minor air-gap.

The stem of insulating material 27 extends through the axial bores of the electrodes 21, 22, 23 and the spacer 19 with a small portion extending out of the electrodes 21 and 22 on both ends of the stem when assembled. An axial bore is provided in the stem of insulating material for receiving the shaft of a bolt 20. The extended portions of the stem of insulating material receive the cut-out portions 32 of the metal connectors 10 and 11 which are held tightly in their positions by a bolt 20 provided with a nut at one end. The assembled unit is held in the glass housing 12 by the recesses 29 in the lower portion of the housing 12 which cooperate with the resilient mounting springs 36 to form an integral whole which is mounted on the terminals 13 and 14.

Electrical connection is made between the metallic electrodes 21 and 22, and the terminals 13 and 14 through the metallic connectors 10 and 11, one of which is shown in perspective in Fig. 6. Each of these metaIIiccOnnectors is provided with a base portion having at one end a cut-out portion 35 and at'the other end a diagonally attached adjacentthereof bymeans of metal rivets 37. The cut-out portion 35 at the end of the tail portionprovides an opening for receiving the terminal. bolt and against which a lock nut can be tightened. An arm 33 adjacent the flanged portion 34 is bent at an angle from the base andv has a'cut-out portion 32 at its-other endfor receiving the stem of insulating material 27. The'two metallic connectors and 11 are identical in form except for two portions of metal in the CUteOllt portion 32 for the nut of bolt 'ltland are reversibly positioned when assembled sowthatthere is a tail portion extending outwardly in opposite directions as shown in Fig. 1. In-this way, the electrode 21'is connected through'connector -11 to the terminal 14; whereas, the electrode 22 and the auxiliary electrode 23 are connected through connector 10. tothe terminal 13.

With the parts in the positions as above described, a space 38 is provided between the diagonally flanged portions 34 as can best be-seen in Fig. '5. This space 38 allows any condensation formed on the inner walls of the glass housing 12 to be evaporated or to drop out at the bottom'of the housing. This space also serves for the movement of air which may take placeas a result of dis- .ruptive discharges between the electrodes.

One of the purposes of the presentinvention is to pro- :vide an arrestorwhich will be suitable for use with various communication facilities where the breakdownof the protecting arrestor-should be in-the'order of'GOO-volts. To provide such an arrestor of the air-gap type means ..rupte.d when the major portion of the discharge wave flanged -.portion-34-:-with.a resilient;mounting=2spring 36 1 air causes the discharge to move outwardly where the of one metallicconnector-which are 'cut at their sides and bent at theirba ses so as to be. substantially perpendicular 'tothe upper part ofthearmii? to form a locking feature that the breakdown gap mustbe in the order of'five' 'thousandths of an inch. 'Such'a small air-gap isobviously subject to the collection of particles that might well provide a short'betw'een thetwo electrodes.

Thepresentinvention proposes to avoid the difliculty 'of a small air gap by actually providing an'airgap'iirthe order of twenty thousandths of an inch'between the metal electrodes and then have a minor air-gap between the auxiliary electrode and the other metal *electrodewhich minor air-gap is inthe orderof five thousandths of an inch. With this structure any particles that collectinthe minorair-gap do not provide a short'be'tween the electrodes because at the potentials normally usedto operate the communication facilities the auxiliary'electrode is'a relatively high resistance'in the order of megohms.

Although there may be'several explanations as to the operation ofthe electrical phenomena involved in' the present invention, .it is believed that one explanation should be. given' to. more clearly .point out what are believed to be theadva'ntageous characteristics ofits struc ture.

More specifically, when the critical potential gradient exists" between the metalelectrode 2'1 andthe auxiliary electrode 23, an initial limited discharge takes place. Thus, the air is ionized in the minor air-gap. The=flow of the current of such limited discharge'along the surfaces of the semiconductive material of the auxiliary electrode 23 also adds toithe ionization of the air at the base of the major air-gap. In this way, the aireatthe base of the major air-gap is sufficiently ionized .to allow a disruptive discharge of current-to pass through the major air gap. It is alsonoted that the mass ofthe metal electrodes 21 and-.22.;is: relatively large so as to provide heat distributing and dissipating surfaces to avoid the melting-of. the electrodes in the :presence of relatively heayyidischarges. Also, since the surfaces 241and'26 slane outwardly, Y there :is a: tendency for the discharge to travel outwardly-sand. thus .become more quickly inter horn-shaped gap between the metal electrodes is constantly enlarging and'thus assists in the early extinguishing of such disruptive discharge after the major peak of the discharge wave has passed. In other words, the discharge moves away from what has been termed the major air-gap into what has been-termed as the horn-shaped air=gap. As can be seen from Fig. 4, there is considerable mass of metal in the electrodes 21 and 224a'djacent this horn-shaped air-gap, which'mass of metal serves as heat sinks. Although the manufacture of theseelectrodes and their assembly may be performed fairly; accurately, thedischarge will be initiated at thosepoints around the minor air-gap 'ofthe electrodes which --are 'closesttogether, and the disruptive discharge will occur at corresponding'points in the major air-gap. But the heat of course will be rapidly conducted by the mass-of metalto allparts of'the electrodes. This avoids the con- I 'centration of sufficient heat at any onepoint'to cause the melting of the electrode.

it should also be noted that the fiat portion 25 'ofth'e rim of the electrode 21 extends sufficiently below the outer periphery of the auxiliary'electrode 23 as to provide a very uniform minor air-gap in spite of slight irregularities at the edge of the auxiliary electrode 23*which irregularities arehard to avoid due to its granuiar 'composition.

In the above description and in the drawings,' theelectrodes 21, 22 and 23 are shown as being circular in form. Such form has been particularly selected'because of the feasibility of providing tools for manufacturing such a form; but it is to be understood that the electrodes-could be of any other suitable configuration such as square, rectangular, triangular, or the like.

Having described one form of a lighting arrestor as embodying the present invention, it is-desired-tobe understood that this particular form is selectedto facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and, it 18 to be further understood that various modifications, adaptations and alterations may be applied '--to specific form shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention.

What I'clairn-is:

1. A lightning arrestor comprising, in combination, a

metal electrode having a circular recess in one 'faceand a fiat edge'on the periphery of said recess'from which thegadjoining 'surface of said electrode slants'outwardly, an auxiliary electrode of relatively 'high'resistance semiconductive material of such a shape to-enable said recess to receive'said auxiliary electrode'with aportion protruding from said recess, asecon'd metal electrode having a circular recess in one facewith the-periphery ofxsaid recess havirigafiat edge from which the surface of said second electrode slants outwardly, an insulating spacer-provided to place the outer edge of said auxiliary electrode in close proximity to the said flatedge 'provided on said second "metal, electrode, and mechanical connecting means to hold the assembled said parts in a protective housing. V 2'.A lightning arrestor comprising, in combination, a metal electrode in the form of a circulardisc having *a througmaxiaL bore, a circular recess in one face, and a flat edge on the periphery of said recess from which the adjoining surface of said electrode slants outwardly at an angle of twenty degrees, an auxiliary electrode of relatively high resistance material having a through axial bore, which said recess of said metal electrode is provided to receive said auxiliary electrode; a second metal electrode in the form of a circular disc having a circular recess of less diameter than said recess of first said metal electrode, a fiat edge on the periphery of said circular recess which said fiat edge is adjacent the outside edge of said auxiliary electrode when said parts are assembled, a through axial bore and the free edge adjoining said fiat edge slanting outwardly at an angle of twenty degrees; an insulating spacer in the form of a circular disc with a recess around the periphery of said disc; and mechanical connecting means for holding said assembled parts together in a protective housing.

3. A lightning arrestor comprising, in combination, an auxiliary electrode of relatively high resistance semiconductive material, a metal electrode having a circular recess in one face with a diameter substantially equal to the external diameter of said auxiliary electrode of semiconductive material, said metal electrode receiving said auxiliary electrode of semiconductive material with a portion of said auxiliary electrode protruding therefrom, a second metal electrode spaced so as to form a hornshaped air-gap with said metal electrode, said second metal electrode having a circular recess of an internal diameter less than said recess of first said electrode with the outer periphery of said circular recess having a flat edge, means for positioning said electrodes on an axis passing through the central portion of the bases thereof with said fiat edge of the said second electrode presented toward the first said electrode and the said fiat edge thereof substantially in the plane of the outside periphery of said auxiliary electrode of semiconductive material,

said auxiliary electrode forming a minor air-gap with said second metal electrode, said minor air-gap being of a shorter dimension than the base of said horn-shaped air-gap, said auxiliary electrode being of such a high resistance in the order of megohms thereby allowing an initial limited discharge to take place in the minor airgap when the critical potential gradient exists between the second said electrode and the said auxiliary electrode thereby ioninzing the air in the minor air-gap and at the base of the said horn-shaped air-gap allowing the disruptive discharge of current to pass through the said horn-shaped air-gap, said horn-shaped air-gap having a capacity to quickly interrupt the disruptive discharge of current when the major portion of the discharge wave has passed.

4. A metal electrode in the form of a circular disc having a circular recess and a free outer edge in one face of said electrode, said free outer edge having a flat edge on the periphery of said circular recess, said free outer edge adjoining said flat edge slanted outwardly, a through axial bore, and said electrode requiring external support.

5. A lighting arrestor comprising two metal electrodes each having the surface of one side laterally formed outward with respect to its periphery and the surface of the opposite side, said two electrodes being spaced apart so as to form a horn between the laterally formed sides with the closest surfaces of the two electrodes adjacent the throat of said horn being effective to provide a minor air-gap for allowing a discharge to be initiated, while the laterally formed sides of the two electrodes from said closest surfaces to the mouth of said horn are effective to extinguish the are caused by the discharge.

6. A lightning arrestor according to claim 5, wherein an auxiliary electrode of relatively high resistance semiconductive material is included with and connected to one of said electrodes adjacent the throat of said horn, whereby the minor air-gap is formed between the periphery of said auxiliary electrode and the closest surface of the other electrode for allowing a discharge to be initiated.

7. A lightning arrestor according to claim 6, wherein the surface of said other electrode adjacent the periphery of said auxiliary electrode is normal to the periphery of said other electrode, whereby the minor air-gap is formed between the periphery of said auxiliary electrode and said surface for allowing a discharge to be initiated.

8. A lightning arrestor comprising, at least two electrically conductive electrodes having respective opposing faces closely spaced in part to form a major air gap and also diverging in part to provide an air gap of increasing size as compared to said major air gap, and auxiliary electrode of semi-conductive material being electrically connected to one of said conductive electrodes and partially bridging said major air gap to thereby form a minor air gap with the other of said conductive electrodes, whereby an arc discharge initiated in said minor air gap is quickly transferred to said major air gap and is extinguished in said air gap of increasing size and whereby a short circuit across said minor air gap produces only a high resistance connection through said auxiliary electrode between said two conductive electrodes.

9. The lightning arrestor as defined in claim 8 wherein said minor air gap has a length corresponding substantially to the air gap breakdown length for the amplitude of voltage at and above which said arrestor is desired to provide a discharge path through said auxiliary electrode between said two conductive electrodes.

10. The lightning arrestor defined in claim 8 wherein said respective opposing faces are parallel plane surfaces over that part forming said major air gap.

11. The lightning arrestor according to claim 8 wherein the diverging portions of said opposing faces are linear.

12. The lightning arrestor according to claim 8 wherein said electrically conductive electrodes are both cupshaped and said respective opposing faces are the respective lips thereof.

13. The lightning arrestor according to claim 12 wherein said cup-shaped electrodes are circular.

14. The lightning arrestor according to claim 12 wherein said auxiliary electrode closely fits within the cavity of one of said cup-shaped electrodes and protrudes at least at its outer edge slightly above the lip of said one cupshaped electrode to thereby partly bridge said major air gap betwen said one electrode and the other of said conductive electrodes.

15. The lightning arrestor according to claim 14 wherein the innermost edge of the lip of said other electrode lies within the outermost edge of said auxiliary electrode.

16. The lightning arrestor defined in claim 14 wherein an insulating member fits within the cavity of said other cup-shaped electrode and abuts against said auxiliary electrodes to thereby space said facing lips of said two cup-shaped electrodes, said insulating member having its periphery spaced from the inner surface of the cavity of said other electrode wherefore said insulating member and said cavity together define an annular air space wherein the air is compressed upon the occurrence of an arc discharge between said opposing faces to thereby aid in forcing said are out along said air gap of increasing size.

17. A lightning arrestor comprising, at least two electrically conductive electrodes having respective surfaces opposing each other, said opposing surfaces being sufficiently closely spaced in part to form an arc discharge air gap from one electrode to the other, said opposing surfaces diverging outwardly from the region of said arc discharge air gap to thereby form an outwardly flaring horn between said opposing surfaces with said horn having its throat substantially at said arc discharge air gap, whereby an arc initiated across said are discharge air gap is extinguished as it travels along the outwardly flaring sides of said horn.

Reid Aug. 5, 1919 Everett May 28, 1929

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