US2281029A

US2281029A - Fuse link

Info

Publication number: US2281029A
Application number: US320903A
Authority: US
Inventors: Ralph H Earle
Original assignee: Line Material Co
Current assignee: Line Material Co
Priority date: 1940-02-26
Filing date: 1940-02-26
Publication date: 1942-04-28
Anticipated expiration: 1959-04-28

Description

R. H. EARLE pril 28, 1942.

FUSE LINK Filed Feb. 26, 1940 INSULATION INVENTOR.

ATTORNEY.

Patented Apr. 28, 1942 r FUSE LINK Ralph nl Earle, wauwatosa. wis., animar to Llnc Materia l Company, Milwaukee, Wis.. a ycoa'potation of ADelaware Application February ze, 1940, serial No. 320,903

(c1. zoo- 135) 17 Claims.

This invention relates to improvements in fuse links.

It is desirable to provide for a pretensioned I fractional amperage fuse llnkadapted for use in electrical distribution systems, a fusible section that will rupture ons. small fault current in a relatively short period of time, which will not blow unnecessarily on lightning surges and which is strong `mechanically. These requirements prevent the use of the type of fusible section, such as illustrated in the pending application of Alwin G. Steinmayer and Chester W. Brown, Serial No. 199,335, filed April l, 1938, for Pretensioned fuse link, heretofore in common use, because it has been impractical to make fusible sections of this type\suilic iently small to render them operable on fractional ampere currents, and at the same time strong enough mechanically to withstand the constant mechanical strain commonly occuring in apparatus of this type. In other words, if the diameter of the strain wire is sufilciently small to function properly on a small fault current, it will be too weak mechanically to withstand the mechanical strain andconsequently rupture unnecessarily.

Therefore, it is an object toprovide a fuse link having a strain section including a meltable portion, a major part of which is not subjected to the direct flow of current but is subjected to the influence of heat generated by the ilow of current through the link, thereby permitting the strain section to rupture upon the occurrence of a predetermined current and thereby introduce a gap in the circuit.

Another object of this invention is to provide in a fuselinkcomprising a conducting member, a strain section insulated from the conducting member and including a meltable joint in combination with an electrically conductive heat-generating portion which bridges the insulated end of the strain section and subjects the joint to heat sufficient to permit rupture thereof upon the occurrence of a predetermined current flow through the link.

Also, another object is to provide in a fuse link, a heat-destructible mechanical Joint in combination with an electrically-conductive heat-producing means which is out of mechanical contact with one part of the joint, thereby permitting free separation of one part of the joint from the heatproducing'means upon the occurrence of a predetermined fiow of current through the link.

It is also an object of this invention to provide for a pretensioned fuse link having a fusible section comprising current-conducting portions electrically and mechanically joined by a lowmelting point alloy, a heater winding of resistance wire adapted to melt the alloy and allow separation of the electrically-conductive portions upon the occurrence of a predetermined current. r Still another object is to provide for a pretensioned fuse link having a fusible section comprising current-conducting strain wires electrically and mechanically joined by a low-melting point alloy, a heater winding of wire having a greater current-carrying capacity than the strain wires, whereby the strain wires will melt on a heavy short circuit before the soldered joint has parted, thereby introducing a gap in the circuit.

A further object is to provide for a pretensioned fuse link having a fusible section comprising current-conducting strain wires electrically and mechanically joined by a low-melting point alloy, a heater winding of wire having a greater current-carrying capacity than the strain wires, whereby the strain wires will melt on a heavy short circuit before the heater winding itself has been rendered inoperable.

A further object is to provide for a fuse link a pair of fusible sections, one of which includes a heat-responsive means and an electrically-conductive heater winding in series relationship with the other of the fusible sections, whereby the heater winding acts to melt the heat-responsive means upon the occurrence of a moderate overload, whereas upon the occurrence of a heavy short circuit the other of the fusible sections is rupturedI either section operating to introduce a gap in the circuit.

A further object is to provide for a fuse link a pair of fusible sections, one of which includes a heat-responsive means; an insulating element and an electrically-conductive heater winding bridging the insulating element and being in series relationship with the other of the fusible sections, the heater winding acting under moderate overload to melt the heat-responsive means, whereas upon the occurrence of a heavy short circuit the other of the fusible sections is .rup-

tured, either section operating to introduce a gap in the circuit.

A still further object is to provide in a fuse link having a destructible mechanical Joint including a heat-conducting portion and an electrical conductor connected by a low-melting point alloy, a current-conducting heater coil adjacent the heat-conducting portion, the hea r coil operating to generate sumcient heat at a'rfietermined current value to melt the alloy and ereby Dermit the joint. when placed under tension, to be ruptured. Y

Still another object is to provide for liquid fuses a fuse link having a strain section comprising a pair of cooperating sleeves joined by` a low-melting point alloy and a heater winding of high resistance wire disposed within at least one of the sleeves for conducting an electric current and adapted to generate heat at a predetermined current value sufilcient to melt the alloy and permit separation of the sleeves when placed under tension, thereby interrupting a circuit through the link.

Also an object is to provide in fuse links, a mechanical joint including a heat-responsive means in combination with a heater coil which is electrically associated in series relationship with the joint and relatively positioned thereto, whereby heat from the coil upon apredetermined current flow through the link will destroy the means and permit separation of the joint when placed under tension, therebyl interrupting the circuit through the link.

In the drawing:

Fig. 1 is a view in side elevation, partly in section, showing a spring-tensioned fuse link embodying one form of this invention.

Fig. 1A is an enlarged view of the intermediate portion of the fuse link shown in Fig. 1. A

Fig. 2 is a view in side elevation, partly in section, illustrating a modification of this invention.

Fig. 3 is a sectional enlarged view taken on the line 3-3 of Fig. 2.

Fig. 4 is a fragmentary sectional view taken on the line 4-4 of Fig. 3. y

Fig. 5 is a View in side elevation of a liquid fuse showing a further embodiment of this invention, parts of the structure being broken away.

The fuse link shown in Fig. 1 comprises a contact button I, a rigid terminal 2 formed of tubular stock to provide a flattened portion 3 having a notch at 4 adjacent its upper end and a threaded tubular portion at 5 adjacent its lower end. When the terminal is thus formed, shoulders 6 are provided intermediate the ilattened and threaded portion of the terminal 2 by the flattening of the portion 3.

An insulating tube I made of fibre or any similar electrically non-conductive material is threadedly mounted on the threaded portion 5 and supports a strain section 8 at its lower end in non-conducting relationship with the rigid terminal 2.

' its upper end by a tubular insulator 25 surroundterminal 2, coiled at 2| about the reduced portion II on the tube 9 and secured at its lower end to the portion II at 22. The resistance wire 20 has a greater current-carrying capacity than the strain wire I2 for reasons hereinafter described. Interposed between the coil 2| and the tubular portion II is a mica sheet 23 or similar heat-resisting insulating material for holding the coil out of direct contact with the portion II. As will be seen from the drawing, the upper portion of the resistance wire 20 passes downwardly through the tube 'I and to the exterior of the tube 9 through the aperture I3 and is held in insulated relation therewith by means of an insulating sleeve 20A. Mounted upon the conductor I5 is a coil spring 2 4 which is spaced therefrom at ing the strain wire I2 and anchored thereon by means of the reduced convolutions 26. The lower end of the spring 24 is provided with a ferrule 21 threaded thereon for engagement with the lower end of an insulating tube 28 which surrounds the spring 24, strain section 8, and tube l. The upper end of the tube 28 is provided with a collar or washer 29 which engages the shoulders 6 on the terminal 2. l y

The insulating fuse tube 28 is mounted upon the fuse link Vbefore the terminal 2 is flattened and threadedly engaged with the member I. The spring 24 is expanded as the ferrule 21 is forced downwardly by the lower end of the tube 28. The top of the tube 28 is positioned (during the assembly operation not shown) a short distance below the top of the memberI in order to expose enough of the member to permit it to be rmly held Yas the terminal 2 is threaded into place and flattened as heretofore described. After the The' strain section 8, more clearly shown in Fig. 1A, comprises a metal tube 9 threaded at III for engagement with the member I and having a' reduced portion II extending downwardly a short distance from the threaded portion III, a strain wire I2 extending into the portion II to a point below the aperture I3 in the portion II, and a low-melting point heat-responsive alloy I4 which secures the wire I2 to the portion II. It may beg'noted that the heat-responsive alloy I4 may, fr example, comprise a mixture of bismuth and 40% tin. v

The strain Wire I2 extends into a rigid tubular conductor I5 and is secured therein by means of an indent I6 in the conductor I5. The conductor I5 is secured to a flexible leader I'I by means of a deformed ferrule I9.

`Mounted on the reduced portion II of the tube 9, is a predetermined length of -high resistance wire 20 which is secured at its upper end to the member 2 is flattened and the tube 28 is released,

the spring 24 urges the tube into abutting relay 30 of the wire I2 from the tube 9 normally held i therein by the alloy I 4.

Normally the fuse link operates to conduct an electric current by means of the terminal 2, the heater coil 2|, the lower end of the tube 9 and alloy I4, the strain wire I2 and the conductors I 5 and I'I. Heat generated by the heater coil is directly proportional to the resistance of the wire 20 and the square of the current flowing therethrough. Therefore, it may be seen that the amount of heat. produced by means of the heater coil conducting a predetermined amount of current, is regulated by the length, size and kind of wire used.

Under normal load currents which the link is` designed to conduct, the heat generated by the* has been ruptured by a heavy short circuit, its ruptured ends'are drawn apart by means of the spring 24. thereby introducing a gap in the circuit.

Figs. 2, 3, and 4 show a modification of the fusible section, previously described, including a terminal 3| flattened at 32 to hold a strain wire 33 therein and to form shoulders 34 'against which a collar 35 is anchored.

The lap joint fusible section 36, more clearly shown in Fig. 4 and as more fully disclosed in the pending application hereinbefore referred to, comprises a foil-like metal strip 31 having each end arcuately bent toward each other at 31A and provided with apertures \,36 through eachA of which the strain wire 33 extends. A strain wire 33 bent doubleis inserted through the lower aperture 33 so that its upper ends 46 extend through the upper aperture 36. The strain wires are held against separation from each other by a low-melting point alloy 4l lying between the arcuately-bent ends 31A of the metal strip 31.

A strain wire v42 extending upwardly from the conductor l is tensioned and anchored in the manner described heretofore with reference to Fig. 1 and is connected to and insulated from the lower end of the strain wire 33 by means of an insulating block 43 which is provided at each end with apertures 44 receiving therein the

respective strain wires

33 and 42 as indicated. It may be noted that the block 43 connects the fusible section 36 in non-conducting relation to the conductor 42. A heater coil 45 comprising a predetermined length of high resistance wire 20A, provided with a covering of insulating material such as enamel 45A, is connected at the upper end of the metal strip 31 by any convenient means as solder 46 and extends downwardly around the alloy and metal strip in a series of spaced apart convolutions 41 each being insulated from the other and from the strip and alloy by the enamel 45A or similar material not readily carbonized by heat. The lower convolution extends down wardly into a length of wire 46 which is secured to the strain wire 42 at 43A below the insulating block 43. It may be noted that the resistance wire 26A and the strain wire42 have a greater current-carrying capacity than the strain wire 33 for reasons hereinafter apparent.

The fuse tube 28 is mounted over the fusible section 36 and in relation to the spring -24 in the manner heretofore described in reference to Fig. 1.

The link shown in Fig. 2 functions electrically in the manner heretofore described with reference to Fig. l, the current being conducted through the link by the terminal 3l, the strain wire 33, the heater coil `45, the strain wire 42 and the conductor I5. Under normal operating conditions the heat generated by the heater coll 45 is not sumcient to melt the alloy 4i.- When a moderate overload current occurs, the heater coil 45 generates heat sumcient to melt the alloy 4l and thereby allow the entire lower portion of the link to be withdrawn from the strain wire 33 and interrupt the flow of current through the circuit to which the link is connected. When a heavy short circuit occurs, the lesser currentcarrying capacity strain wire 33 melts before the greater current-carrying capacity strain wire 42 has melted or the heater coil 45 has allowed section 36 to function. Under ruptured conditions, the spring 24 operates to introduce a gap in the circuit in a manner described in reference io Fig. 1.

Fig. 5 illustrates a well-known type of liquid fuse 49 which comprises an insulating tube 56 of glass or other suitable material provided with a lower contact 5I and an upper contact 52. The upper contact 52 is provided with shoulders 53 against which a bridge member 54 is supported. A conducting member 55 which operates as a fusible section under predetermined conditions of short circuit is attached to the bridge in any suitable way, as by means of a bolt 56.

The fuse link designated generally by the numeral 51 comprises a metal sleeve 58 spun inwardly at. 59 to form a support against which an insulating disk 60 is anchored. The lower end of the conducting member 55 extends through the apertures 6| in the disk and isheld therein by the loopedend 62. The lower portion of the sleeve 56 encircles the upper portion of a cup-like conducting member 63 spaced therefrom by a narrow margin, the sleeve and member being held in rigid relation to each other by a lowmelting point alloy 64 disposed within the margin as shown. It may be noted that the insulating disk 60 holds the fuse link 51 in non-conducting relation to the conducting member 55.

A heater coil 65 comprising a series of convolu tions mounted upon an insulator rod 66, made preferably of a ceramic material and further identified by the word Insulation, is disposed within the cup member 63 and secured therein by an electrically non-conductive cernentitious material 61` The coil is formed of a predetermined length of high resistance wire, preferably of the kind described in reference to Fig. l. The upper end of the coil is joined to the loop 62 by any convenient means as by solder 66 and the lower end extends through the aperture 69 in the bot tom of the cup 63 where it is electrically secured in any suitable manner, not shown. A heatin sulating material, such as cork, in the form of a sleeve 'I0 is tightly mounted upon the sleeve 56 and extends downwardly for positive engagement with the lower portion of the cup 63, thereby protecting the fuse link against the cooling action of the surrounding medium and preventing the dissipation of heat away from the solder joint, which heat may be generated by the heater coil. It may be noted that the conducting member 55 is of a lesser current-carrying capacity than the heater coil 65 for reasons hereinafter' explained.

Integrally secured to the bottom or" the cup 63 is a downwardly extending arm il to which a connector or clip 12 is detachably secured by means of a bolt 13 and which in turn is firmly attached at its lower end 14 to the upper end of a helical spring 15 and to a fiexible conducting cable or leader 16.

The liquid fuse operates electrically to conduct a current under normal conditions by means of the contact 52, the bridge 54, the conductor 55. the heater coil 65, the arm 'i l, the clip l2 and 'the conductor 16, and the heat generated by the coil 65 is insuiiicient to melt the alloy 64. When a moderate overload current exists in the circuit to which the fuse may be connected, sufficient heat is generated by the coil 65 and dissipated through the material 61 and sides of the cup 63 to melt the alloy 64, thereby allowing the spring 15 to withdraw the cup and heater coil from the sleeve 56 and break the mechanically weak electrical joint on the loop 62. Under conditions of heavy short circuit the lesser current-carrying capacity member 55 operates as a fusible section and melts permitting the spring 15 to draw the fuse link 51 away from the ruptured member 55, thereby introducing a gap in the circuit.

It may be noted here that substantially all of the heat generated by the yheater coil I5 is ,conducted through the cementitious material 81 and the cup 83 radially outwardly toward theV alloy 64 and held Within this area by theinsulating medium 10, thereby preventing unnecessary loss of heat to the surrounding area and delay inthe melting of the alloy I4 and interruption of current flow through the various conducting portions.

From the foregoing description, it may be noted that the objects of this invention have been accomplished by providing al fractional amperage fuse link having a fusible section vvcomprising a pair' of cooperating portions heldin rigid relationship to each other by a relatively low-melting point alloy and by providing a heat-producing,

current-conducting means which operatesl at a.

predetermined value of current to allow separa# tion of the cooperating portions by melting the 1. A fuse link comprising a pair of conductors,V

an insulator connected to one of said conductors,

a strain section connected to said insulator andk including a meltable alloy, a strain wire mechanically and electrically connected tothe other of said conductors and with said strain section by said meltable alloy, and an electrically-conductive heater portion adjacent said section and connected electrically with said conductors, said strain wire being released from said strain sec-A tion when said alloy is melted by heat transmitted from said conductive heater upon the occurrence of a predetermined current iiow through said link.

2. A fuse link comprising a pair of conducting portions, a destructible section holding one of said portions in position relative to the other, a heater element connected electrically with said portions,

and an insulating member disposed between saidl portions and adapted to allow complete current iiow through said heater element, said element acting when an overload current is established therethrough to produce suicient heat to destroy said section and interrupt the now of current through said link.

3. A fuse link comprising a pair of conducting portions, a mechanical connection between said portions connected to one of said portions in electrically non-conducting relationship thereto, a meltable alloy securing the other of said portions to said connection, and a predetermined length of resistance wire connected electrically with said portions and having a greater part of its length disposed in close proximity to the alloy, said wire acting to-produce suiiicient heat to melt said other of said alloy and allow separation of said other of said portions and said connection, thereby introducing a gap in a circuit including the' link. A

4. A fuse link comprising a pair of conducting portions, a mechanical connection between said portions connected to one of said portions in electrically non-conducting relationship thereto, a heat-responsive alloy securing the other of said portions to said connection, and a predetermined length of resistance wire connected electrically with said portions and having a greater part of its length electrically insulated from and disposed in close proximity to the alloy, said wire portions, an insulating l .upon one of said portions `and held` under tenf bridginlitheow of current around-,said alloyy and acting to produce sumcient Vheat te melt said al-. Y

loy andI allow separation of said lothero! said portions and said connection, .thereby introducing a gap in a circuit including the link. e

5. Aiuse'link comprising apair of conducting tube, a 'spring mounted sion by said tube, a holding'means connecting said 'portions in electrically non-conducting relation, a meltable"alloyv securing one 'of said 'pori vtions to said means andan electrically-conductive heater section surrounding .said holding means and connected electrically with said portions,`f"said heater section acting' to generate sumcient heat to-melt said'alloy and allow separation of `one of said portions from saidfalloy when `a vpredetermined currentl occurs in said link.

6; Atensioned fuse link comprising a terminal member, anV insulating sleeve secured to said te'rminal member, a heat-conductive portion secured to said sleeve vin electrically non-conducting relation to said terminal member, a strain wire se-r cured to said conductive portionA bymeans of a meltable alloy, a conductor mechanically connected to said strain wire,4` and a predetermined length of resistance wire having a greater part of its length mountedon said heat-conductive portion and electrically connecting said strain wire with said terminal, said resistance wire acting `as an electrical conductor and a heat-producing agent, whereby sufficient heat is produced to melt said alloy when a predetermined value of current is established in said link, thereby allowing separation of said strain wire from said portion and interrupting the flow of current therethrough.

'7. A tensioned fuse link comprising a terminal member, a first strain wire secured .to said terminal member, a holding means secured to said wire by means of a predetermined melting point alloy, a second strain wire securedin insulated relation to said holding means, a conductor mechanically connected to said second strain wire, and a' predetermined length of elec-- a meltable alloy carried by said metal strip, said conducting portions held in iixed relation to each other by said meltable alloy, an electrically-conductive heater portion surrounding said metal strip and electrically connecting said conductive portion, a spring carried by one of said conductive portions, an insulating element disposed between said portions and adapted to permit c'urrent now through said heater portion only, and a tube surrounding said section and lholding said spring under tension, whereby upon melting of said meltable alloy, a gap is introduced in a circuit including the link.

9. A fuse link comprising a pair of conducting portions, a strain section connecting said portions and including a meltable alloy, a strain wire mechanically connected to one of said conducting portions and held in electrical relation with said strain section by said meltable alloy, an electrically-conductive heater portion surrounding said section and electrically connecting said conductive portions, said strain wire having a lesser current-carrying capacity than said heater portion thereby providing a fusible section for said link when said link is subjected to heavy current flow.

10. A fuse link comprising a pair of conducting portions, a destructible section connecting said portions and including a meltable alloy, a strain wire mechanically connected to one of said conducting portions and held in electrical relation with said strain section by said meltable alloy, an electrically-conductive heater portion surrounding said section and electrically connecting said conductive portions, said strain wire having a lesser current-carrying capacity than said heater portion thereby providing a fusible section for said link when said link is subjected to heavy current flow.

11. A disconnect device for electric circuits, said device including a tubular member having an aperture extending through the side and adjacent one end thereof, a meltable alloy in said member, a conductor wire held by said meltable alloy, and a second wire extending into said member and outwardly through said aperture and then coiled about the outer periphery of said member.

12. A fuse link comprising a pair of spaced contacts, a heat destructible section connecting said contacts and including a pair of tubular portions received in telescopic relation to each other, a meltable alloy normally holding said portions in fixed relation to each other, and an electrically-conductive heater unit carried by one of said tubular portions and electrically connecting said contacts, said alloy being fused by said heater unit upon occurrence of an overload in said link.

13. A fuse link comprising a pair of conducting portions, a destructible section connecting said portions, said section including a tubular portion open at one end, a sleeve received in telescopic relation with said tubular portion, a meltable alloy normally holding said sleeve in iixed relation to said tubular portion, and an electrically conductive heater unit carried in said tubular portion and electrically connecting said conducting portions, said alloy being fused by said heater unit upon occurrence of an overload in said link.

14. A fuse linkcom'prising a pair of conductlng portions, a strain section connecting said contacts, said strain section including a tubular portion open at one end, a sleeve received in telescopic relation with said tubular portion, an

insulating element secured to one of said conducting portions and said sleeve, a meltable alloy holding said sleeve in fixed relation to said tubular portion, and an electrically-conductive heater unit carried in said tubular portion and electrically-connecting said conducting portions, said alloy being fused by said heater unit upon occurance of an overload in said link.

15. A fuse link comprising a pair of conducting portions, a strain section connecting said contacts, said strain section including a tubular portion open at one end, a sleeve received in telescopic relation with said tubular portion, an insulating element secured to one of said conducting portions and said sleeve, a meltable alloy holding said sleeve in iixed relation to said tubular portion, an insulating element surrounding said sleeve, and an electrically-conductive heater unit carried in said tubular portion and electrically-connecting said conducting portions, said alloy being fused by said heater unit upon occurrence of an overload in said link.

16. A fuse link comprising a rigid metal cony tact, an insulating tube having one end threaded on one end of said contact, a metal tube threaded on the end of said insulating tube remote from said contact and having an aperture adjacent the end of said insulating tube, a strain wire extending into said metal tube and secured therein by means of a low melting alloy to normally prevent withdrawal of the wire therefrom, a conductor secured to said wire remote from said metal tube, and an insulated conducting wire in said insulating tube electrically connected to said metal contact and extending through the aperture in said metal tube andy being coiled about said metal tube, said insulated conducting wire being electrically connected with said strain wire at a poin't remote from said insulating tube, whereby said metal tube is electrically non-conducting and subjected to heat generated in the coiled portion of said insulated conducting wire.

17. A fuse link comprising a terminal contact including a conducting portion, an insulating member supported by said conducting portion, a tubular element supported by and in spaced relation to said insulating member, a conductor releasibly secured to said tubular element by means of a low melting alloy, and a heater element concentrically positioned relative to said tubular element adjacent said alloy, said heater element including a coiled insulated conducting wire electrically connected with said conducting portion and with said conductor at a point remote from said insulating member.

RALPH H. EARLE.

Certificate of Correction Patent N o. 2,281,029 April 28, 1942 RALPH H. EARLE It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Page 4, first column, line 62, strike out the Words "other of said; and that the said Letters Patent should be read With this correction therein that the same may conform to the record of the case in the Patent Office. Signed and sealed this 10th day of January, A. D. 1950.

[WAL] THOMAS F. MURPHY,

Assistant Uommssz'oner of Patents.

Certificate of Correction Paf-,ent No. 2,281,029 April 28, 1942 RALPH H. EARLE It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Page 4, rst column, line 62, strike out the Words other of said and that the said Letters Patent should be read With this correction therein that the same may conform to the record of the ease in the Patent Office. Signed and sealed this 10th day of January, A. D. 1950.

[IML] THOMAS F. MURPHY,

Assistant Uommsstoner of Patents.