US3564473A

US3564473A - Surge protector

Info

Publication number: US3564473A
Application number: US684706A
Authority: US
Inventors: Chester J Kawiecki
Original assignee: Joslyn Manufacturing and Supply Co
Current assignee: Joslyn Manufacturing and Supply Co
Priority date: 1967-11-21
Filing date: 1967-11-21
Publication date: 1971-02-16
Anticipated expiration: 1988-02-16

Abstract

A MINIATURE SURGE PROTECTOR INCLUDES A PAIR OF HOLLOW ELECTRODE MEMBERS EXTENDING WITHIN EITHER END OF A CERAMIC CYLINDER, SUCH ELECTRODES BEING BRAZED IN POSITION TO COMPLETE A HERMETIC ENCLOSURE WITHIN THE CERAMIC CYLINDER. THE ELECTRODES ARE PROVIDED WITH END WALLS WHICH FACE ONE ANOTHER WITHIN THE CYLINDER TO DEFINE A GAP, AND WHICH THE HOLLOW PORTION OF EACH ELECTRODE. SUCH MEANS CONTINUATION OF AN ABNORMAL ARC DISCHARGE ACROSS THE GAP. A MEANS FOR MAKING PERMANENT CONTACT BETWEEN THE ELECTRODES, PREFERABLY INCLUDING A FUSIBLE METAL, IS INCLUDED WITHIN THE HOLLOW PORTION OF EACH ELECTRODE. SUCH MEANS IS ADAPTED TO PROTRUDE THROUGH AND MADE SUBSTANTIALLY PERMANENT CONTACT WITH THE OPPOSITE ELECTRODE WHEN THE ELECTRODE END WALLS MELT, WHEREBY TO PROVIDE A FAIL-SAFE FEATURE.

Description

Feb. 16, 1971 c. J. KAwlEcKl SURGE PROZLFIGTORv Fid Nov. 21, 1967 'jv-Fiel n' WAH X lFIGA Mii# CHESTER J. KAwIEcK'l Buc/(Hom, BLOHE, KLAHou/sr a SPAR/MAN ATTORNEYS United States Patent O U.S. Cl. 337-28 19 Claims ABSTRACT OF THE DISCLOSURE A miniature surge protector includes a pair of hollow electrode members extending within either end of a'ceramic cylinder, such electrodes being brazed in position to complete a hermetic enclosure within the ceramic cylinder. The electrodes are provided with end walls which face one another within the cylinder to define a gap, and which are adapted to soften or melt under a prolonged continuation of an abnormal arc discharge across the gap. A means for making permanent contact between the electrodes, preferably including a fusible metal, is included within the hollow portion of each electrode. Such means is adapted to protrude through and make substantially permanent contact with the opposite electrode when the electrode end walls melt, whereby to provide a fail-safe feature.

BACKGROUND OF THE INVENTION Surge protectors or spark gap devices are frequently employed as electrical transient protectors on communications or voltage supply lines for protecting electrical equipment from transient surges. For example, such a device may be employed as a lightning and surge arrester on a telephone line, providing a breakdown path when a lightning surge occurs. The surge can be bypassed to ground via an arc discharge and therefore the surge does not reach and destroy electrical equipment also connected to the line. After the occurrence of an arc discharge, especially an extended discharge, the surge protector frequently will have become damaged to the extent of no longer being operative, or at least not operative at its designed breakdown voltage. Due to the force and heat provided by the arc discharge, the electrodes in the protector may become physically misshapen so that the spacing is not maintained. It is not always possible to detect from the appearance of a surge protector whether it will be operative at the designed breakdown voltage, or even whether a prior discharge has occurred. Moreover, inspection of the surge protectors is not always possible. It is therefore desirable to provide a surge protector with a fail-safe feature such that if a prolonged arc discharge occurs, the protector continues to maintain a short circuited condition thus facilitating its detection and replacement.

While some spark gap devices have been provided with auxiliary external hardware attachments for achieving the fail-safe function, it is desired to provide a miniature surge protector having a self-contained fail-safe feature.

It is also an object of the present invention to provide an improved surge protector which is simple in construction and reliable in operation.

It is another object of the present invention to provide an improved miniaturized surge protector of economical construction incorporating integral fail-safe features.

The invention, both as to organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings wherein like reference characters refer to like elements.

3,564,473 Patented Feb. 16, 1971 DRAWINGS FIG. l is a side view of a surge protector according to the present invention as supported in a holder;

FIG. 2 is an enlarged longitudinal cross section of the surge protector according to the present invention;

FIG. 3 is a broken-away and enlarged view of the FIG. 1 surge protector illustrating the fail-safe operation thereof;

FIG. 4 is a longitudinal cross sectional view of a modified surge protector according to the present invention;

FIG, 5 is a transverse cross sectional view of the FIG. l surge protector further illustrating alternative location of a radioactive material provided therefor;

FIG. 6 is a side view of a surge protector according to the present invention provided with a deposit of radioactive material in its outer wall; and

FIG. 7 is a side view partially broken away in cross section of an alternative embodiment of a surge protector according to the present invention.

DETAILED DESCRIPTION Referring to the drawings, and particularly FIGS. 1 through 3, a miniature surge protector according to the present invention includes a cylindrical spacer tube 10 preferably taking the form a ceramic tube approximately 5X1@ inch in diameter by approximately W16 inch in length. This tube is most clearly shown in FIG. 2, wherein the surge protector according to the present invention is illustrated in greatly enlarged cross section. In assembling the surge protector according to the present invention, the ends of the ceramic spacer tube 10 are suitably metallized as indictaed 12 and 14, and brazing

washers

16 and 18, which may be formed of copper or an alloy of copper and silver, are located on the metallized ends. Then, thinwalled

hollow electrodes

20 and 22, preferably formed of Kovar, are inserted into either end of ceramic tube 10, each of these electrodes having annular radial flange 24 for making contact with brazing

washers

16 and 18. The

electrodes

20 and 22 are substantially cylindrical toward their inner aligned ends at 26 and 28, and are ared outwardly and rearwardly towards the aforementioned flanges 24.

To secure the

electrodes

20 and 22 within spacer tube 10, the assembly of these components, with brazing

washers

16 and 18 in place, is suitably raised in temperature to braze the assembly, with the interior of the envelope being evacuated. The tube 10 may sometimes be provided with a deposit 32 of getter material active to absorb undesired gases within envelope 30. Deposit 32 may be flashed with conventional electronic equipment (not shown).

Electrodes

20 and 22 include end portions having

respective end walls

34 and 36 which face one another and dene a gap 38 therebetween. The electrode end walls are suitably slightly cup-shaped or concave where they face one another for the reception of a deposit 40 of a material such as cesium chloride.

According to an important feature of the present invention, the usrge protection device is provided with means for establishing a substantially permanent contact between electrodes after an extended larc discharge occurs therebetween, including means for applying pressure on the electrode end walls at a time appropriate for establishing such connection. In the embodiment of FIGS 1 through 3, such means for establishing a substantially permanent metal contact comprises a fusible metal 42 contained within each hollow electrode. Thus, fusible metal suitably substantially lls the interior of each electrode, back of

end walls

34 and 36, and may comprise a solder or fusible alloy, Ifor instance an alloy including lead and tin. This solder has a lower melting point than I 3 the

end walls

34 and 36 of

electrodes

20 and 22. Within fuisible metal 42 and inside an end wall there may be provided a radioactive spot 44 acting as a prompter. This radioactive material, e.g. radium, provides ionization before arc discharge, aiding in the formation of a discharge at a stabilized breakdown voltage.

The surge protector is suitably supported and connected in the circuit to be protected employing a `holder generally indicated at 46 and including

spring clips

48 and 50 joined at insulated base 52 as illustrated in FIG. l.

Spring clips 48 adn 50 terminate in

caps

54 and 56, shown in cross section in FIG. l, employed for engaging the end flanges 24 at the ends of the surge protector. The

spring clips

48 and 50 are adapted to urge the caps against 'flanges 24 to make good contact therebetween, but the caps are suitably somewhat loose fitting so as to allow the passage of gases, and specifically, atmospheric pressure, to the rear of electrodes and 22.

The surge protector according to the present invention is connected to the line to be protected, or between a line and ground, by means of spring clips 48 and 60. When a predetermined voltage level is reached across the surge protector, e.g. as a result of high voltage transient on the line, the gap 38 breaks down into an arc discharge, thereby shorting out the high voltage transient and protecting equipment on the line. As hereinbefore described, the occurrence of such a discharge, especially for an extended period, is apt to alter the operating characteristics of the surge protector, for example, by altering the spacing of gap 38. However, according to the present invention, the hollow interiors of

electrodes

20 and 22 are provided with a quantity of fusible metal 42. During normal operation of the protector, this lfusible metal is, of course, a solid and provides an integral solid interior for the electrodes as well as aiding in heat transfer by providing additional mass. Also, the fusible material within the electrodes tends to seal any tiny pinholes in the electrodes which may have gone undetected during the manufacture thereof.

However, an arc discharge for an extended period of time, for example carrying long duration fault currents, will tend to soften

end walls

34 and 36 as well as fusible metal 42. The outside atmospheric pressure being greater than the pressure inside envelope will, through fusible metal 42, tend to urge the

end walls

34 and 36 toward one another for making contact. For this purpose a sufcent area of these adjacent end walls may be provided such as to permit central distortion of each end wall toward the opposite electrode. Alternatively, one or more of the end walls suitably melts as a result of the heat of the discharge, exposing the fusible metal 42 which also melts, and this fusible metal flows through the ruptured end wall or walls under the influence of atmospheric pressure from the rear of the electrode. A contact of fusible metal is then formed as indicated at 58 in FIG. 3. Such further Ifusible material may be forced within the envelope 30 by atmospheric pressure as may be required to provide a substantially permanent short circuit across the gap, and such metal, and the short circuit, remain at the conclusion of the arc discharge. The device according to the present invention thus provides a built-in -fail-safe feature providing a 'solid connection at the end vnumerals refer to like elements. This embodimnt has approximately the same overall dimensions as the FIG. l device. In this embodiment a pair of metal contact members 60 and 62. bear upon relatively at

end Walls

34 and 36 of

electrodes

20 and 22. These contact members are rod shaped having tapered ends where they contact the aforementioned end walls and are provided With enlarged heads 64 and (66 on the opposite ends thereof, these heads being engaged by

end caps

54 and 56. The contact members 60 and 62 are normally secured in the position be means of fusible metal 42 so that, even though

spring clips

48 and 50 urge the contact members against

thin end walls

34, and 36, the contact members are ineffective at this time to distort the end walls. However, as the result of currents of an extended arc discharge,

end walls

34 and 36 soften, and likewise, the fusible metal 42 softens allowing the spring-biased contact members 60 and 62 to urge

end walls

34 and 36 toward one another, The end walls have facing areas permitting central distortion thereof under the force of contact members 60 and 62. Therefore, the end walls will be forced together in contacting relation and the end walls will fuse together where they contact. Alternatively, the end walls may melt whereby one or both of the contact members `6() and 62 themselves provide the permanent shorted connection. Fusible material 42 will also ilow into the gap enhancing the connection and again holding the contact members in place.

VAlthough the presence of fusible metal 42 is highly desirable in the embodiment of FIG. 4, for example for initially holding the contact members in place and aiding the formation of a permanent connection, it will be seen that its presence is not entirely necessary inasmuch as the contact members themselves can provides the means for establishing a permanent contact between the electrodes subsequent to an extended arc discharge.

The material of contact members 60 and 62 should, of course, be conductive, and should desirably have a higher melting point than the electrodes so as to make connection even though the electrodes melt. It should also be noted that distance A in FIG. 4 plus the distance B desirably exceeds the space of gap 38 whereby a permanent contact may be made between the forward ends of contact members 60 and 62 before

heads

64 and 66 reach flanges 24 of the electrodes.

FIGS. 5 and 6 illustrate further alternative forms of the present invention wherein a radioactive spot 32 or strip 32" is disposed on the outside of cylinder 10 rather than within the electrodes as indicated at 32 in FIG. 2. This radioactive prompter material can be applied after manufacture of the device, and is suitably covered over with molten solder or lead 68 whereby such deposit is not easily uncovered.

A further embodiment of the present invention is illustrated in FIG. 7 wherein like reference numerals also refer to like elements. Here, the ceramic cylinder is divided into sections IllA and 10B with an annular electrode 70 inserted therebetween. The annular electrode 70 is secured to the ceramic material in the same manner as hereinbefore described with respect to

electrodes

20 and 22, that is, the ceramic is metallized and the electrode is secured thereto by means of brazing washers.

Annular electrode 70 in FIG. 7 is similarly hollow and lled with fusible metal 72 such as solder, communicating to the atmosphere at its outer periphery whereby breakdown and melting of the electrode 70' will cause solder therefrom to flow into the gap and provide a permanent fail-safe short circuit. In this connection it should be noted that an arc breakdown may occur between

end electrodes

20 and 22 or between one of such electrodes and electrodes 70, or between all three.

Annular electrode 70 is desirably closely spaced to

electrodes

20 and 22 and has an axis substantially coincident with the direction of alignment of

electrodes

20 and 22. The end walls of

electrodes

20 and 22 in the FIG. 7 embodiment are suitably rounded to provide annular gaps between such electrodes and electrode 70, as well as a longitudinal gap between

electrodes

20 and 22. Electrode 70 is ordinarily connected t0 ground in a circuit wherein spring clips 48 and 50 are connected to either side of a line to be protected. For the purpose of groundlng electrode 70, a connector 74 may be joined to the outer periphery of electrode 70 in a manner such that atmospheric pressure is not prevented from reaching the fusible metal 72 therewithin.

While particular dimensions and materials have been mentioned with respect to the construction of the present invention, it is understood that the invention is not restricted thereto. For example, the surge protector electrodes may be formed of some other conductive metal which does not have an excessively high melting or softening point. Furthermore, surge protectors accordlng to the present invention are frequently advantageously orlented with their longitudinal axis disposed vertically rather than horizontally as illustrated herein. Then, in the case of devices employing fusible material for making a faxlsafe contact, such contact will be aided by the force of gravity upon the fusible material in addition to the pressure of the atmosphere. Also, other connectors or holders may be employed, or soldered connections can be made to the various electrodes of the device.

While I have shown and described preferred embodiments of my invention, it will be apparent to those skilled in the art that many other changes and modifications may be made without departing from my invention in rts broader aspects. I therefore intend the appended claims to cover all such changes and modiiications as fall within the true spirit and scope of my invention.

I claim:

1. A surge protector comprising:

a pair of aligned conductive electrodes at least one of which is adapted for connection to a line to be protected, said electrodes having adjacent opposed portions deining a gap therebetween adapted to break down and support an arc discharge as the voltage between said electrodes reaches a predetermined level,

the said portion of at least a first such electrode having a wall adjacent said gap, said Wall having a melting point adapting said wall at least to soften as a result of heat caused by an extended arc discharge across said gap,

and means for establishing substantially a permanent metallic contact between said electrodes, which contact is maintained after said arc discharge, including means on the opposite side ofthe wall of said irst electrode from said lgap for applying pressure in the direction of said wall of said iirst electrode.

2. The apparatus according to claim 1 wherein said means for applying pressure in the direction of the wall of said first electrode includes a spring-biased contact member bearing upon the said wall of said rst electrode in the direction of the opposite electrode.

3. The apparatus according to claim 2 wherein said contact member is secured to the wall of said first electrode by a fusible metal.

4. The apparatus according to claim 1 wherein means enclose the region between at least opposed portions of said electrodes and wherein the pressure within the last mentioned means is less than atmospheric pressure,

said means for applying pressure comprising a fusible metal contained adjacent said wall of said first electrode being urged toward said wall by higher outside pressure.

5. The apparatus according to claim 4 wherein said fusible metal has a lower melting point than said wall of said first electrode.

6. The apparatus according to claim 1 wherein said wall has an area adjacent the opposite electrode permitting central distortion of said wall toward the opposite electrode.

7. The apparatus according to claim 1 wherein said wall has an area adjacent the opposite electrode permitting central distortion of said wall toward the opposite electrode,

said apparatus further including an elongated spring biased contact member bearing on the central portion of said wall,

and a quantity of fusible metal contained adjacent said wall of said iirst electrode, said fusible metal normally holding said contact member in position.

8. A surge protector comprising:

a pair of aligned conductive electrodes adapted for connection to a line to be protected and having conductive end portions for supporting an arc discharge,

insulating spacer means positioning said electrode end portions in facing relation with respect to one another so that end faces thereof deline an arc discharge gap therebetween,

at least one of said electrodes having an internal cavity at least within such electrodes end portion defining an end wall between said cavity and the said face of said one electrode,

said end wall having a melting temperature adapting the same to melt as a result of the heat caused by a predetermined arc discharge between said electrodes,

and a quantity of fusible metal contained within said cavity for flowing towards said gap aud completing a metallic circuit between said electrodes, said metallic circuit remaining at the conclusion of said arc discharge.

9. The apparatus according to claim 8 wherein said fusible metal has a lower melting point than the said end wall of said electrode.

10. The apparatus according to claim 9 wherein said fusible metal comprises a solder.

11. The apparatus according to claim 8 wherein said spacer means comprises a substantially cylindrical enclosure between said electrodes within which said end portions extend, and within which less than atmospheric pressure is normally maintained, said cavity and said fusible metal within said cavity being exposed to a higher pressure outside said enclosure such that said higher pressure urges said fusible metal into said gap upon the melting of said end wall to produce rupture of said end Wall.

12. The apparatus according to claim 8 wherein both of said electrodes are provided with an internal cavity deiining an end wall at the end portion of each electrode, and a quantity of fusible material contained within each such cavity wherein said fusible metal has a lower melting point than said end walls.

13. The apparatus according to claim 12 wherein each of said electrodes'is thin-walled and substantially hollow, extending rearwardly from said gap so as to contain a substantial quantity of said fusible metal within the cavity thereof.

14. The apparatus according to claim 1 further including an annular electrode adjacent and spaced from the gap between said pair of aligned electrodes, said annular electrode having an axis substantially coincident with the direction of the alignment of said pair of electrodes.

15. The surge protector according to claim 12 wherein the end walls of each of said electrodes is cup shaped to provide a substantially concave face opposite the other electrode.

16. The apparatus according to claim 12 having radioactive material disposed upon said spacer means.

'17. The apparatus according to claim 8 wherein said spacer means is formed of ceramic material having a substantially higher melting point than said electrodes and said fusible material.

18. A surge protector comprising:

a pair of aligned conductive electrodes adapted for connection to the conductors of a line to be protected,

each of said electrodes comprising a hollow cylindrical member having a closed end wall forming the end of such cylinder, the opposite end of the cylinder being open and ared outwardly to provide an annular ange,

a ceramic spacer cylinder sealed between the anges of said electrodes for positioning said electrodes with c 19. The apparatus according to claim 18 further includtheir end walls in facing relation internally of said ,ing a quantity of radioactive material disposed on the cylinder to vprovide an arcv discharge gap therebeoutside of said ceramic cylinder.

tween, said ceramic spacer cylinder forming with said electrodes an enclosure wherein a pressure less than References Cited atmospheric is maintained, 0 FOREIGN PATENTS and aquantity of fusible metal contained Within each hollow cylindrical rrember, said fusible metal hav- 974817 2/1951 France 31761 ing a melting point ess than that of the electrodes, a predetermined arc discharge between the end walls BERNARD A' C HLHEANY. Primary Examiner of said electrodes being effective to melt the end walls lo R COHRS, Assistant EXamllleI' ,of said electrodes and allow said fusible metal to ow between said electrodes to complete a metallic cir- U-S- C1XR- cuit between said electrodes. 317-61; 337-404 (SEAL) Attest:

Patent No.

Inventorfs) line line line line line line UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Dated Feb. 16, 1971 CHESTER J. KAWIECKI It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

"electrodes 70" should be electrode 7( and subst Signed and sealed this 10th day of August 1 971 EDWARD M.FLETCHER,JR. Attestng Officer WILLIAM E. SCHUYLER, JR. Commissioner' of Patents FORM PO-105O (HJ-69)