US1852104A - Electric fuse - Google Patents

Description

`April 5., 1932- A. J. BwlE 1,852,104

ELECTRIGl FUSE Filed D90. 29, 1923 INVEN TOR.

improvements in electrical fuses.

Patented Apr.. 5, 1932 AUGUSTUS JESSE BOWIE, F SAN FRANCISCO, CALIFOBJL1A.

ELECTRIC FUSE Applicationnld December 29, 1923. Serial No. 683,496.

It is the object of this invention to provide The principles herein will apply broadly to any class (if fuse, but more particularly to high tension uses.

The particular application is to fuses of the expulsion type wherein the circuit is interrupted by the expulsion' of the gases or arc from the container in which the circuit is interrupted. l'

The fuses in high tension work are generally made in tubular form, either illed or with a non-arcing compound,lor left open, the power developed by the heat of the fuse when the circuit is interrupted generating sufcient blow out action to extinguish the arc. The pressures generated are often great under' severe short circuits requiring tubes of considerable mechanical strength to withstand the impact and yet rendering material, such as glass'orporcelain, inadvisable for this duty, since the heat generated is sufficient tp crack such tubes for fuses of large capacity.

To obtain the best results, the fuse tube is hence made of material of suiiicient strength to withstand both'the blow out and the temporary heat caused by the ruptureof the circuit. Materials suitable for tubes of this type, will under some circumstances be Adefective in surface leakage after long exposure to the Weather. To overcome this difficulty box type housings are sometimes provided for fuses of moderate voltages, but for high voltages this is impracticable.

One feature of my invention includes the provision of a double tube of material comrising an inner casing, capable ofwithstanding shock and an exterior casing of preferably a vitreous material like glass or porcelain integral with' the fuse structure. In otherwords, an interior and' exterior tube substantially concentric, constltuting a single fuse element having suitable terminals thereon for engaging the clips.` f

The filled fuse is'much` superior in blow ont action to the open fuse, since the scouring ei'ect of theiille'r is of great importance in extinguishing the arc. On the other hand, a filled fuse has a radically different thermal condition from the unfilled, the heatvbeing carried away much more quickly than with the unfilled type, and when fuses are of a larger size limiting problems occur in the heating ofthe fuse element causingundne heating of the casing. It is one of the objects of this invention to overcome such limitations and to allow the use of fuses of a capacity which would otherwise be prohibitive, and also of materials which could otherwise not be employed. By further extension of the principles of this invention, fuses of any desired capacity may be employed successively. i

The interruption of high tension circuits is greatly limited by the capacity of the fuse element. For example, fuses of moderate size work successfully, whereas fuses of larger size, owing to the heat of the fuse element under continuousload will often fail, and

it is one of the objects of this invention to overcome theseinherent difficulties.

Among the general types of fusible elementsare included the lead, zinc tin alloy type of fuse commonly used which melts at a comparatively low temperature, fuses of zinc which melt at a much higher temperature, and fuses of,l aluminum which melts at a still higher temperature. Except for small capacities, the latter two types are impracticable, if the fuse elelnentis run for any period of time near the blowing point, as the continuous temperature would result in the destruction of the envelope, unless made of porcelain or glass. By means of my invention this ditliculty is also overcome.

Figure l shows a longitudinal cross section of a fuse with an inner casing enclos- -ing the fuse wire and a concentric outer casing adaptedto withstand weather conditions.

Figure 2 shows an end view of the same.

F igurev 3 shows a longitudinal, section of a fuse with a chamber in the center which may be used for forming an arc.

Figure 4 shows an end View oi the salne.

Figure 5 shows apartial longitudinal section of a modiied fuse of the type shown in Figure 3.

Figure 6 shows an end view of same.

lFigure 7 shows a longitudinal section of a fuse with ka central -chamber filled with powder `or similar material for increasing the blow out action.

Figure 8 shows an end view of the same `in section.

Figure 9 shows a-longitudinal section of the preferred type of construction of the central fuse chamber shown in Figure 3.

Figure 10 shows an end view of the same.

holder mounted securely on ferrule 2, and

6, is a corresponding holder mounted so that it will slip under pressure on the ferrule 2 on the other` end.

As shown in Figs. 1, 3, 5 and'G, the circumferential edges of the caps 3 are sealed by frictional contact a ainst the inside surfaces of the ferrules, t ereby normally preventing the escape of gases or air at points between thel caps and ferrules.

Holders 5, 6, have rigidl connected therein a weatherproof cylin rical casing 7 The interior space within casing 1 and the space between ,theY casings 1 and 7, are preferably filled with powdered filler of the granularl type, marked respectively 12 and 23. The function of the filler around the fuse has previously been described, namel to -provide a better blow out of the arc, an also to insulate the sides of the container, not

only from the heat of blowout, but from the normal heating of the fuse.

The space between the tubes 1 and 7, contains filler, 23 to convey the heat generat-` ed by the fuse, directly to the air. outside, which would not be the case were an air space left between the -two tubes. Owing to the difference of ex ansion of tubes land 7, which are made of ifferent materials, the joint between 6 and 2, is a slip type which will prevent undue temperature stresses. This ]oint, however, is tight under atmospheric conditions and excludesdirt and mois. ture.

preferably non-absorbtive of-water and a good insulator such as bakelite, whereas the casing-7, is of material like porcelain-or glass, providing a permanent surface, not affected by weather conditions.

While, as heretofore mentioned, box type housings have been provided in which the y t smallest The material of' casingi, is strong, and

fuses are housed for voltages of moderate value, the construction herein is novel, in that the housings and fuses are combined in the single element giving a combination of the high breakage strength, freedom from instantaneous heat and good exterior surface leakage conditions.

In Figure 3, 8 is a cylindrical arcing chamber provided with end plugs 9, 9, which` preferably fit snugly in same and yet allow ready expulsion under pressure within the chamber. 10, 10, arel electrical'connections, preferably soldered to the fuse element 4, which is of relatively short length. l1, 1l, are the joints between connections l0, 10 and fuse 4, and may be made of solder or other material; the connections 10, 10, are soldered directly to the end caps 3, 3, from which contact is madel to the metallic ferrules 2, l2, adapted to be inserted in suitable clips. The chamber 8, is preferably left unfilled for fuses of large capacity, and the balance of ythe tube is preferably filled with the granular filler, .12, 12. -Around chamber 8, is the filler 13, made of different material from` filler 12, 12. l v

There are two points .to be ,considered in fuse design,`first the'condition obtaining under'heavy loads not sufficient to blow the fuse, wherein the fuse element will necessarily heat, partl of it approaching the melting point of the material, and second, the condition affectin the blowing of the fuse.

n large fuses the amount of heat which i maybe generated in the fuse element is so great that a fuse tube of large and often impractical 'size must be provided to carry off safely the heat of the fuse without danger of-.destruction of the tube. This is articularly the case with the filled tube or high voltages where the heat mustl be disposed of thru the walls of the tube and cannot be taken thru the end ferrules, owing to the length of the fuse tube. To overcome this vwould be liable to damage the adjacent tnbe, `unless s ecial precautions are taken.

- The rst requirement then of a fuse, without resortin to an excessive -amount of metal which wou d be objectionable, is .that the generate fuse 4, should be protected from damaging the walls of the -tube 1.' It is desirable to dissipate thru the walls ofthe tube as vrapidossible amount of heat should beA in 10, 10, and that the heat in ly as possible, the heat from connections `10,'

10. This I accomplish by the use of a granular filler 12, of high thermal conductivity, at

the same time around the central portion of the fuse, I use a filler 13, of low thermal conductivity, preventing the heat from fuse 4, affecting the walls of the tube andl forcing the heat generated therein to dissipate itself fuse element 4, or else the granular filler 13, l may be made of the same material as the balance of the filler 12, the thermal insulation of element 4, being' obtained thru the chamber 8. In either event the invention in this phase lies in the provision of different thermal insulation between the fuse element 4, and the tube 1, than obtains between the connections 10, 10, and the tube 1.

The connections 10, 10, may be of the same material as thepfuse 4, a larger section giving the increased conductivity, but it is preferable to make them of a different material and this is a novelfeature in fuse construction. y Connections 10, 10, may be of such nature as would be consumed by the current, in the event of a very high current, but the preferable form of operation is the expulsion thereof from the ends of the tube. When the fuse 4, blows heat will be generated in the center therefrom, and when this is broken it y will volatilize the material therein and cause l suficient pressure to expel the caps 3, 3, and

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connections 10, 10, :from opposite ends of the tube, the expulsion extinguishing the arc and opening the circuit, sincethe end caps 3,'3, are designed for such purpose, namely, to provide both a safety valve and to allow a suiiicient pressure to extinguish the are when the f .use operates.

The extinguishing of the arc depends upon the rapidity of action, and hence for this reason it Ais desirable to make the connections v10. 10, as light as possible. Also it is desirable to make theni as high a conductor of heat as possible, in order to dissipate the normal heat from the fuse element 4.' For, this reason I preferably'made connections 10, 10, of copper, which is made especially iiexible, since copper isa' very high conductor of both electricity and heat. e

The construction in Figures 1 and 3, shows the fuse soldered to the end caps 3, 3. However, this is not necessary since any other means of connection may be given, as shown in Figure 5, wherein the fuses are fastened to contact cap 14 preferably thru strip 15, made of low melting material. Where lead or zinc type of fuse is used, in larger capaci/- ties in a filled chamber, there is a tendency for the fuse to vremain as a column of liquid and to conduct current in this condition, vhence generating an undue amount of heat. This diiculty I overcome thru the arcing chamber -8, which being unfilled also allows the arc generating heat with extreme rapidity causes instantaneous action. y

It is desirable to have a limited amount of air in the arcing chamber to aid in the blow out of the fuse ends. In the construction in Figure 3, the arcing chamber 8, may be made of strong, preferably fireproof rigid material such as ebony asbestos which will prevent the extreme instantaneous pressure coming on 'the tube 1, which may be of porcelain, and which will also insulate this tube from the extreme heat generated. In this event the construction in Figure 3, is in effect a modification of the principle shown in Fig ure 1, namely, a combination of two tubes,

the inner tubehowever, not extending the full length.

In the construction shown in Figure 5, advantage is taken of the fact that the lead type of fuse and the connection 15 if made of similar material and of approximately the same area will melt atthe same time from short circuits. The result of this will be that under normal conditions the heat from connection 15, will be carried away by connections 10, 10, and ferrules 2, 2, but in event of a short circuit, the connections 15, and fuse 4, would melt at approximately the same time, 15 remaining as a liquid, whereas 4vwould open the circuit `and generate an arc, allowing the ready expulsion of connections 10, 10,' without the blowing out of contact cap 14.

The principle of operation of fuses by means of a direct arcing chamber is of value, in the prompt action of the fuse. The gas generated f'or' the expulsion is derived from the volatilization of the fuse link 4. A Where the other material therein is insuiicient to give the desired action, it may be reinforced by theuse ofbuttons 11, 11, of solder or corresponding material of sufficient size to generate the desired amount of gas. The advantages are obvious in that it is preferable to volatilize material which melts at a low temperature rather-than one which melts at a higher temperature, such` as are connections 10,10, which are preferably made of copper.

To increase the blow out action of the fuse,

consisting, for example, of gunpowder, which will safely stand the temperatures of low uit melting fuses, but will be ignited by blowing c of the fuse and will generate suiiicient gas to expel the end caps and connections.

Where fuses of large capacity are employed, the resulting pressure from blowing the fuse within chamber 3, is liable to be very high, due to the great heat suddenly generated. To overcome this diiiiculty Figures 9 and 10 show the preferred type of construction wherein the casing 8, is of insulating material such as mica,- which., will stand high momentary temperatures. This is reinforced by aY casing 22, of high strength material 10 pressure.

ling no indication that the circuit has been opened. The use in a fuse tube of powder or corresponding material readily Volatilized on blowing of the fuse which will act with certainty and blow` out thel end caps, thus 2 serves the doubly useful purpose of providing this understanding and does not means .fuse

a definite indication ata glance that the fuse has blown,` as well as extinguishing there-y sultiiig arc.

The term fuse, as is commonly applied to 25 apparatus of this nature constitutes an integral fuse element comprising the fuse link,

holder for same and suitable terminals therefor, and in the claims, the term is used with 3 links alone.

In the construction of the fuse element the material used in link 4, may be extended toVv the end cap connections, the conductors 10, 10, being reinforced by either a larger section ofthe same'material or by the addition .of a reinforcing piece of another material4 connected thereto and running from the ends of 4, to or nearly to the end caps or corresponding connection 3. An excellent type of reinforcement consists of plating the end connections 10, of the main fuse by such material as copper,to provide the necessary reinforcing.

w, Figurey 11 shows lthe fuse element only,

with plating 23 on the connection 10.

Figure 12 shows an alternative type of reinforcement, 10 consisting of two branches for each half, affording alarge radiating surface for the heat: When the fuse blows,

0 especially if of the zinc tin type, if the end cap does not blow oi instantly the connection of the branches will melt and carry current, Y which will automatically follow one of the branches, which it will promptly melt oil and 5 blow.

If desired, wires 10, 10 may be made stili, causing the blow out in the center to give direct pressure thereto on the end caps.

The filled fuse has van advantage over the unfilled in that the entrained air is very much less requiring a correspondingly smallwmerxamount of heated vapor to cause proper expulsion'.VV A limited quantity of air in casw ing is of advantage in forming the nec- GJ essary blow out pressure reserve capacity for putting out the arc. A very suddenly applied pressure in the central part of the tube, as in Fig. 3, particularl with the fuse tube lilled with a granular ler, is apt to blow up the tube before it has time to expel the end caps 3. If conductors 10-10 are rigid, the internal pressure acting thereon will be transmitted by direct compression thereon to the end caps, which will be mechanically expelled without damaging the tube.

What I claim is:

1. Afuse comprising a fuse link, terminal connections for same, an inner imperforate casing composed of material of high strength, iii combination with an outerimperforate casing composed of material of high resistance to surface leakage, and granular filling material betweensaid inner and outer casings.

2. A fuse comprising a fuse link, terminal connections for said fuse, an inner imperferate casing composed of material of high strength, in combination with an outer imperfoi'a-te casing comprising avitreous material, and granular filling material between said inner and outer casings. 1

3. A fuse comprising a casing normally closed-to the atmosphere, terminal connec- Lions for said fuse,'a fuse link within said.

casing, conductors within said casing connecting said' fuse link and said terminal connections, thermal insul-ating means between said fuse link and said casing, said conductors and said thermal iinsulating means being adapted to be ejected from said casing upon the blowing of said fuse.

4. A fuse comprising a casing normally vclosed to the atmosphere, terminal connections for said fuse, a fuse link within said casing, electrical connections between said fuse link and said terminal connections, said electrical connections being ada ted to'be ejected from said casing on the lowing of said fuse, a filling material of relatively low thermal conductivity between said electrical connections and said casing, in combination with thermalinsulating means between said fuse link and said casing of higher thermal insulation than that ouf said filling material.

5. A fuse comprising a casing normally closed to the atmosphere, terminal connections for said fuse, a fuse link within said casing, rigid electrical connections between said fuse link and said terminal connections, and vent means for opening said casing to the atmosphere thru pressure generated by the blowing of said fuse and transmitted directly by said rigid electricalconnections to said vent means, thereby opening said fuse to the.y atmosphere.

6. Afuse comprising an outer casing nor-` mally closed to the atn'iospliere, terminal connections for said fuse, a fusel link, insulating fillingr material for saidcasing, an inner casing surrounding said fuse link, and means for'v excluding therefrom said filling material, in

.combination with means operated `by the blowing of said fuse for opening said casing l to the atmosphere.

7. A. fuse lcomprising an outer casing nor- A mally closed to the atmosphere,terminal co'nnections for-.said fuse, a fuse link,lan innercasing surrounding said lfuse link, electrical '20 inner casing surrounding said fuse link and excluding therefrom said filling material, in combination with end members for closing said inner casing and means actuated by the blowing of said fuse for ejecting said end 25 members and also for opening said outer casing'to the atmos here.-

9. A fuse comprising an outer casin nor.- mally closed to the atmosphere, termina connections'for said fuse, a fuse link within said casing, electrical connections between said fuse link and said terminal connections,

an inner casing surrounding said fuse link, llingginsulating material surrounding said electrical connections, means for excluding said filling material from said inner casing, and means actuated by the blowing of said fuse for ejecting said electrical connections from said outer casing. v

10.' A fuse comprising a fuse link, terminal 40 connections for same,l an' inner casing of arc resistingv material, in combination kwith an outer imperforate casing of material of high resistance to` surface leakage, and filling insulating material between said inner and out- '45 er casings adapted to transmit the normal heat of the fuse to the atmosphere. i

11'. A fuseomprising a fuse link, a tubular casing enclosingsaid fuse link, terminal connections fpr said fuse link, end ca s onv e0 the ends of said tubular casing, said en caps being adapted to normally seal the ends of the casing to maintain a certain gas pressure ated in the tube upon the blowin of the fuse link, and conductors within sai` casing between the said fuse link and the caps,`the said conductors being adapted to .be ejected from the casing by the pressure generated upon the blowing of the fuse link.

13. A fuse comprising a fuse link, a tubular casing enclosing said fuse link, terminal connections for said fuse link, imperforate caps in the `ends of the casing, the said caps being normally maintained in the ends of t e casing by their frictional engagement with the walls of the casing, and adapted to normally seal the ends of the tube, the said caps also being adapted to be ejected from the tube by a pressure generated in the said tube by the blowing of the fuse link, and conductors Within the casing connecting the caps with the fuse link, the said conductors being adapted to be ejected from the tube by the pressure ejecting the caps.

AIn testimony whereof I aix my signature. AUGUsTUs JESSE noWiE.

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within the casing, andiconductors in the cas- .l

A ing between the fuse link and thecaps, which 55 said conductors are adapted to be ejected from l the casing-1825011'. tliel blowin of the fuse link.

12. .A comprising a use link, a tubuconnections for'said fuse link, imperforate eo caps for sealing the ends of the tubular casingythe saidcaps'being frictionally sealed n, lar casing enclosin .said fuse link, terminal I agaiiisttheendspj the casing so as to normally revent air from passin throu h the endso the casing saidcaps eing a apte Y. t' 'es to-beblown fromntli e tube by pressure gene vIso

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