US3522571A - Electric fuse-link,particularly for outdoor use - Google Patents

Description

Aug. 4, 1970 F. c. E. TAPLIN EFAL 3,522,571

I ELECTRIC FUSE-LINK, PARTICULARLY FOR OUTDOOR USE Filed Jan. 30, 1969 1 2 Sheets-Sheet 1 M/VENTDRS Fmcns cYku. 6470M TAPLIA/ Tum Rmmu Am! I Arms/Viv:

ELECTRIC FUSE-LINK, PARTICULARLY FOR OUTDOOR USE Filed Jan. 30, 1969 g- 19.70 F. c. E. TAPLIN ET AL 2 Sheets-Sheet 2 7 am WM 1 ABSTRACT OF THE DISCLOSURE A fuse-link in an insulative. fuse body, said link being securedwbetween twoterminals enclosed in a first insulative tube, said first insulative tube being secured. to a first terminal, a second insulative tube is secured to a second terminal said second tube being fitted slidably over said first tube, whereby said second tube slips oif said first tube-when said fuse-link melts.

This invention relates to fuses for use in medium and high-voltage systems, and more particularly to fuse-links for the electro-conductive connection of units of electric equipment g(.transformers,: circuit-breakers or the like) with a power transmission line or with each other via another conductor of electricity.

Such fuses are normally made of a short length of a readily fusible, electrically conductive metal wire materialv designed tomelt when passed by a current of a predetermined intensity over a given-usually 'briefperi0d of time. Particularly foruse in the open air, the fuse is frequently arranged vertically, or substantially vertically, between two terminals or: conductors which form part of the fuse-linkand havecross-sections which considerably :exceed that of the fuse itself, the fuse being secured to theterminals in any suitable manner to ensure the flow of current under normal conditions. a

In someqknown constructions thefuse is surrounded by atubeofinsulating material, which is attachedto one ofrthe terminals,,the,tube being spaced from the fuse. The .-insu,lating tube limits the spread of fuse particles when the fuse, melts which often occurs-explosively. Moreover, it limits the spread of the arc and may also contribute to the cooling of these particlesbut, as a rule not toan adequate extent.- a l 1 i In expulsion fuses such as are used in the open, the tube .is mounted as a rule on a terminal arranged at a higher level, its openend surrounding the lower terminal, and, meansare often provided either in close association withflth e fuse, or externally, thereof, to secure a rapid separation of the terminals after the melting of the fuse for the purpose of increasing the length of the arc. The are causes arapid rise of the temperature of the air or gas contained in'the tube which, consequently expands towards the open tube end and assists the expulsion from the tube of the movable terminal attached to the lower conductor. With the air or gas, and the terminals, however, also the molten fuse metalis expelled, at least partly in the form of liquid particles which may be extremely hot'or incandescent. Y

If the current is grossly excessive, the fuse metal may be completely evaporated, but under most conditions incandescent metal particles are produced which may reach the ground in that condition and may, therefore, cause ignition of combustible material on the ground and thereby give rise to bushfires, grass fires and other fire damage,

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particularly in dry weather or under unfavourable conditions.

The object of the present invention is to provide a fuselink construction suitable for use in high and mediumhigh voltage systems and more particularly for use in the open air, or otherwise under conditions involving fire danger, the fuse-link being constructed and designed to exclude, or at least very considerably reduce, the likelihood of expulsion therefrom of incandescent fuse material which could reach the ground in a dangerously hot condition.

. According to the invention this is achieved by providing means which cause the expulsion of the fuse material to berestrained and/or delayed, and any molten fuse material to be deflected away from combustible material.

In the fuse-link according to the invention the fuse wire secured between two terminals in the system to be protected, is enclosed within a tube or sleeve-hereinafter called the first tube-of highly heat-resistant, electrically non-conductive material secured to one of said terminals, with no or only little space between the fuse proper and the inner wall of said tube, the fuse-link in cluding at least one further tube or sleeve of highly heatresistant, electrically non-conductive material-hereinafter called the second tube-which is secured to the second terminal and, being a sliding fit on said first tube,

- is slidably displaceable along the latter, the second terminal being connected to a flexible conductor for attachment to an appliance, apparatus or the like to be protected by the fuse-link from overload. The second tube or sleeve which surrounds the first tube over a substantial part of the length of the latter, thus can slip olf the first tube when the fuse melts, and then drop down from the fuse-link by gravity and/ or spring action, or otherwise.

In a preferred embodiment of the invention the second tube or sleeve is a sliding fit, and is thus slidably displaceable, within a third tube secured to the first mentioned terminal, the length of said third tube being such that the second tube is still in part accommodated therein after having been displaced past the first tube. In that case, s12 1cm s12 oqn; tsrg our urqtrm popuedxo sJnodeA snoesafi hot or glowing metal particles entering the space surrounded by the third tube are not immediately discharged to the ambient atmosphere after the second tube has been detached from the first tube, but are first made to enter I the space between the first and third tubes in a direction towards the first terminal, and are allowed to escape into the atmosphere only after the second tube has been detached from the third tube, whereby the escape of the gases and vapours as well as of any liquefied metal from i the fuse-link into the atmosphere is still further delayed so that the danger of ignition of combustible material such as dry leaves, twigs, etc. lying on the ground is practically eliminated.

If so desired an additional tube of heat-resistant material may be accommodated within the abovementioned form of liquid particles, is very small. It is assumed that the very high pressure developed within the tube or sleeve which closely surrounds the fuse material, effects the elimination and rapid suppression of the arc produced therein when the fused material is vapourised. The very high temperature within that innermost tube under such conditions material. The metal vapour which eventually escapes into the atmosphere is cooled so effectively that its contents cannot cause any fire danger. Any glowing or incandescent fuse particles leaving the open end of the first tube or sleeve at an early stage are expelled and are made to impinge upon the inner wall of said second tube on which they are cooled so that they are not likely to be dangerously hot when they flow out from that tube after it is detached from the fuse-link.

For very high voltages, e.g. of 10,000 v. or more, the duration of the arc may be too long for effecting a sufiiciently rapid cooling of the vapours and it is in this case that the provision of a third outer tube is of particular advantage, as the third tube will cause a further delay in the discharge of the gas, metal vapour or vapours and of liquid particles, if any, into the surrounding atmosphere.

In order to more particularly describe the invention, reference is made to the accompanying drawings wherein:

FIGS. 1 to 3 are views showing, by way of example only, the general arrangement of a disconnecting switch, in four successive phases of its operation, in which the fuse-link according to the invention may be used, the switch being shown as connected between a power transmission !line and a consumer unit, e.g. a transformer.

FIG. 4 shows diagrammatically in longitudinal section an embodiment of the fuse-link according to the invention suitable for higher voltages, e.g. voltages of 10,000 v. or more.

FIG. 5 shows, likewise diagrammatically and in longitudinal section, another embodiment of the fuse-link suitable for medium and lower voltages.

The disconnecting switch shown in FIGS. 1 to 3 comprises a tubular bridge made of insulating material for attachment between two resilient electro-conductive elements 11 and 12 which are secured to the opposite ends of an insulator 13. The element 11 is provided with a terminal 14 suitable for attachment to a conductor 15 and by suitable clamping means 16, e.g. to a power transmission line 17. Similarly, the resilient element 12 is provided with a terminal 18 suitable for attachment by a conductor 19 to a terminal of an electrical apparatus or unit, e.g. a transformer 20, circuit-breaker or the like. The insulator 13 of the connecting switch may be fastened, for instance, to a part 21 of a mast or tower of a transmission line by means of a bracket structure 22 and a loop or ring 23.

The arrangement of the bridge 10 is either vertical or substantially vertical as shown, the lower end of the bridge being secured to the lower end 24 of the insulator 13 for instance by a detachable hinge structure 25 which includes a bell-crank lever 26 on a hinge-pin 27. A fuse conductor 28 is attached to the lever 26 and extends into the tubular bridge 10 to the required extent.

The upper end portion 29' of the bridge is provided with a knob 30 which normally engages a recess 31 provided at the free end of the resilient element 11, the knob 30 being detachable, e.g. manually with the aid of a properly insulated rod and hook (not shown) when the latter is made to engage in a ring 32 which forms a part of the upper bridge end portion 29 and pull is exerted on the ring by an operator.

The disconnecting switch illustrated in FIGS. 1 to 3 represents only a specific embodiment of a device which can be fitted with a fuse-link according to this invention, the fuse-link being accommodated in the tubular bridge 10 of the switch. In this case the break of the switch can also be effected by an overload in the connection or phase between the transmission line 17 and the unit, e.g. a transformer 20 fed from the line 17, due to the action of the fuse-link which serves for protecting the apparatus or a phase of the latter.

FIG. 4 shows an embodiment of a fuse-link suitable, for instance, for a voltage of 10,000 to 12,000 v. or

V 4 I 3 more within the bridge 10*. The fuse-link comprises two tubular electro- conductive contact elements 36 and 37 in mutual alignment. The contact element is a tight fit in a blind bore 38 formed centrally in a terminal 39 which may be the upper terminal of the fuse-link accommodated within the upper part 29 of the bridge 10. The tubular contact element 37 which is arranged at a distance from the element 36, is rigidly fitted into an end portion of a ferrule 40, the opposite (lower) end portion of which clampingly retains the dropout conductor 28 which in FIGS. 1 to 3 is illustrated in different positions relative to the bridge 10.

A first insulation tube 42 of highly heat-resistant and non-inflammable material such as polytetrafiuorethylene (e.g. that sold under the registered trademark Teflon) or horn fibre, is rigidly secured to the contact element 36, and to the terminal 39. A thin high-tensile wire 43, e.g. a steel wire, is anchored to the elements 36 and 37. At least one fuse wire 44 of a required current carrying capacity is secured together with the steel wire 43 at two distant points between the tubular contact elements 36 and 37. The fuse wire 44 extends parallel to the steel wire 43 which in this embodiment acts mainly as a mechanical reinforcement within a hollow space 45 which, if so desired, may be bounded or restricted by a narrower insulating tube 46 disposed between the ends 47 and 48 of the tubular contacts 36, 37 which face one another within the insulating tube 42. The fixation of both the fuse wire or wires 44 and the steel wire 43 is effected by squeezing the wires together within the tubular contact elements, e.g. at 49.

A second insulating tube 50, which is likewise highly heat-resistant and non-inflammable, consisting for instance also of Teflon, is rigidly secured to the ferrule 40 by a collar or bandage 51. y

The second tube 50 which in the normal operational condition of the fuse-link extends over at least a part of the length of the first tube 42,- is slidably displaceable on the latter so that, if by an overload the fuse wire or wires 44 and, consequently, also the steel wire 43 are caused to melt and/or to be vapourised, the air or gas and metal vapours, if any, contained in the space 45 expand rapidly and the second tube 50 is displaced along the first tube until it is completely detached therefrom.

A still further or third insulating tube 52 of the same or of a similar heat-resistant and non-inflammable material is secured to the terminal 39. In the operative condition of the fuse-link this third tube extends over the full length of the first tube 42 and also over most of the length of the second tube 50 so that the latter, which is slidably displaceable within the third tube 52, is practically completely encased therein. There is an annular space 53 between the first tube 42 and the third tube 52 in which the second tube 50 is slidingly accommodated.

If after the melting of the fuse wire or wires 44 and the steel wire 43 the second tube 50 has overshot the (lower) end 54 of the first tube 42, the spaces 45 and 53 are interconnected so that expanding gases and vapours have the tendency now to continue their expansion into the space 53, the direction of their flow to be partly reversed, and the ejection of atomised and/ or liquid fuse particles to be slightly delayed until in the course of the further displacement of the second tube caused by the expansion of the gas the tube 50 is entirely expelled from the open (lower) end 55 of the third tube 52. An insulating ring 56 fitted in the space 53 between the insulating tubes 42 and 52 close to the terminal 39, prevents contact between the latter and the hot metal vapours of the arc.

During the total period of expulsion the hot metal particles pass the initially cool inner walls of the first, second and third tubes 42, 50 and 52 so that they are themselves subjected to a strong cooling action which is continued during the final drop of the metal particles to the ground through the air. Consequently, such liquid or solid metal particles as finally reach combustible material, e.g. on the ground are no longer likely to have an incendiary effect on such material.

The modified form of fuse-link illustrated in FIG. in which the same reference numerals denote the same parts, differs from that described with reference to FIG. 4 only by the omission of the third tube. In this embodiment also the flow of the expanding gas and/ or vapour is deflected and at least momentarily reversed after the second tube 50 has passed the open (lower) end 54 of the first tube 42. The escape of hot metal particles and vapour from the hollow space 45 and/ or from the innermost tube 46 in the direction of the original expansion is therefore delayed, and cooling of this hot material intensified.

The fuse-link described with reference to FIG. 5 although not as effective as that described in the first place, is nevertheless suitable for use in systems employing medium or lower voltages, i.e. voltages below 10,000 v.

The fuse-link according to the invention is capable of still further modification within the scope and ambit of the appended claims.

Thus, for instance, it is possible to use a fourth outer tube, or sleeve, in which the third tube is displaceable, if it is necessary to obtain a further deflection or change of direction in the flow of the expanding gas and/or metal vapour.

In the embodiment shown and described it was assumed that the expanding gas and the hot metal particles tend to be expelled in a downward direction, e.g. toward the ground. It should be understood, however, that the device can also be arranged differently in space, if so required.

In the fuse-links described above, a high-tensile wire, e.g. a steel wire, is used for the purpose of mechanically reinforcing the fusible system. The invention however, is also applicable to fuse-links which do not employ such a reinforcing wire. Moreover, it is within the scope of invention to use a high-tensile wire or wires alone as the fusible material.

It should finally be noted that the values of voltages stated in the foregoing are only approximate values, as the capability of the fuse-link according to the invention of handling voltages of a given magnitude does not depend exclusively on the number of mutually displaceable insulating tubes, but also on other factors which include the lengths and other dimensions of these tubes, of the fuse wire or wires and/or the arrangement of the fuse-link relative to the ground and/or to other parts of a system.

What we claim is:

1. A fuse-link connected between two terminals in an electric system to be protected against overload, said fuse-link comprising at least one fuse wire enclosed within a tube or sleeve of highly heat-resistant and electrically non-conductive material-hereinafter called the first tubethe first tube being secured to one of said terminals with little, if any, space between the fuse wire and the inner wall of said first tube, and at least one further tube or sleeve of highly heat-resistant electrically non-conductive material-hereinafter called the second tube-said second tube being secured to the second of the two terminals and being slidably displaceable along the first tube, said second terminal being connected to a flexible conductor for attachment to a unit to be protected.

2. A fuse-link as claimed in claim 1 wherein said second tube isslidably displaceable within a still further tube or sleeve of highly heat-resistant and electrically non-conductive material-hereinafter called the third tubethe said third tube being secured to the first-mentioned terminal concentrically to the first tube with such clearance between the first and third tubes that the second tube can be freely displaced relative to the first and third tubes when the fuse wire is broken, the length of the third tube being such that it projects beyond the free end of said first tube so that it accommodates at least a part of the length of said second terminal when the fuse-link is in its operative condition.

3. A fuse-link as claimed in claim 1, wherein the second tube is a sliding fit on the first tube.

4. A fuse-link as claimed in claim 2, wherein the second tube is a sliding fit on the first tube and a sliding fit within the third tube.

5. A fuse-link as claimed in claim 1, wherein the fuse wire is held in position within the first tube by two mutually spaced tubular contact elements, one of said contact elements being connected with said first-mentioned terminal and secured to the said first tube, whereas the other contact element is conductively connected and rig idly secured to said second terminal and is displaceable within said first tube together with said second terminal.

6. A fuse-link as claimed in claim 5, wherein the fuse wire is, or the fuse wires are secured to the said tubular contact elements by clamping same into the end portions of said contact elements which face one another within the first tube.

7. A fuse-link as claimed in claim 5, wherein the said fuse Wire is, or the fuse wires are clamped into the end portions of said tubular contact elements which face one another within the first tube, together with a high tensile wire adapted to act as a mechanical reinforcement for said fuse wire or fuse wires.

8. A fuse-link as claimed in claim 5 wherein the said fuse wire is constituted by a steel or other high tensile wire.

9. A fuse-link as claimed in claim 1, wherein the said fuse wire is, or the said fuse wires are encased within a further insulating tube accommodated within the said first tube between the said tubular contact elements.

10. A fuse-link as claimed in claim 2, wherein a ringlike body of insulating material is accommodated within the clearance between the said first and third tubes close to said first-mentioned terminal, said ring-like body preventing the establishment of electric contact between the said terminal and hot metal vapours of an are within said clearance, in the event of an overload.

References Cited UNITED STATES PATENTS 2,749,408 6/1956 Billings 337-248X 3,374,329 3/1968 Bronikowski 337203 X HIRAM B. GILSON, Primary Examiner US. Cl. X.R. 337

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