US1807228A - Electric fuse - Google Patents

Description

J. H. STARR ELECTRIC FUSE May 26, 1931.

Filed Aug. 19, 1929 A TTORNE Y.

Patented May 2s, 193i l UNITED s'nif'rf-Es PATENT om-ics JAMES H. STARR.,y F OAK PARK, ILLINOIS, ASSIGNOR T0 ELECTRICAL ENGINEERS `.EQUIPM ENT .COMPAN Y, A CORPORATION 0F ILLINOIS ELECTRIC FUSE Application Yfiled Angust 19, 1929. Serial No. 386,791.

The present invenion' relates to electric fuses of .the type wherein the electric terminals' of the fuses are forcibly separated.

Sometimes in a fuse of this kind a quenchingy liquid contained in the fuse casing is 'pro-v vjected violently against the resulting arc to 'extinguish it. Sometimes the quenching liquid is-omitted. My invention may .,be. em-

bodied in either form. lo There are many kinds of electrical apparatus which require to be protected 'against short circuits, sudden eXtra heavy overloads .and prolonged and lessy severe` overloads. Transformers should be thus protected and are mentioned here by way of illustration. There have beenefforts to meet these operating conditions by the use of circuit breakn ers and like expensive equipment. In many cases their cost has prevented any protective equipment of the kind being used? ne object of the present invention is to devise an electric fuse thatwill perform all these functions. Such a fuse will render the vcost of the initial installation much more economical and will afford protection equal to that required of the more expensive control devices.

I believe I am the first to provide a fuse for the purpose stated. Y

3g In brief the new structure possesses main circuit terminals and connections, a main fuse strip, and auxiliary branch circuit contacts and connections for actuating the fuse under the prolonged less severe overloads.

Among the featuresvof the invention is a novel fuse strip mounting by ,which a knife edge severs thestrip when the fuse is operated on a prolonged overload. To bring this about the strip is mounted so as normally to have some slack in its length which permits relatively free movement ofthe separating terminals for some distance before the strip becomes taut. This brings the strip over the knife edgewith considerable force which consummates its rupture. l

There is also a novel arrangement of thread-like supports for the movable termi-y nal. When these are broken then the spring is free to jerk the terminals apart and with this movement the fuse strip is ruptured.

The crossed wires, constituting these thread-like supports, 'provide for novel circuits through the fuse. In the embodiment illustrated,fthe main fuse is paralleled by a current path through the supporting wires while the path for the auxiliary circuit is independent of, or possibly, in some cases, in series with the fuse strip.

The structure has the usual cartridge form but the end caps which serve to connect the 6o fuse with the circuit clips or other contacts on the support must share this function with l a third contacting surface in the form of an intermediate ring about the cas-ing. The latter is connected by alieXible electric conduc- G5 tor to a third terminal on the plunger or movable terminal and forms part of the auxiliary control circuit.

For a full understanding of these and other features of my invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, which description and drawing, taken together, disclose the preferred embodiment of the invention. For statements of the scope of the invention attention is directed to the appended claims.

In said drawings, Fig. l is a central longitudinal section of a fuse structure-constructed and arranged in accordance with the present 8o invention, parts being shown in elevation;

Fig. 2 is a transverse section of the same,

parts within the fuse at the fuse strip end being shown inelevation, the plane of section being indicated by the line Q-Q of Fig. :35 l; Fig. 3 is an end elevation of a cap at the opposite end of the fuse; Fig. 4 is a plan view of the plunger or movable fuse terminal; Fig. 5. is a longitudinal section of said plunger, the plane of section being indicated by the line 5-5 of Fig. 4 Fig. 6 is a longitudinal section of the'fuse strip end of the fuse structure. parts' being shown in elevation, the plane of section being indicated b v the line 6 6 of Fig. 2; Fig. 7 is a perspective view of one of 95 the knife edged supports of the main fuse strip; and Fig. 8 is an electrical diagram illustrating the fuse in association with a transformer which it protects. Throughout these views like characters refer to like parts,

`Referring said drawings in detail, A

designates a clip-engaging terminal which also forms one end of the fuse structure, B a similar clip-engaging terminal at the other end of the fuse, C glass tubing for completing the cartridge-like casing, D` the movable fuse terminal within the casing, E the main fuse strip, F a thread-like support for the terminal D, G a tension spring by which the freed terminal D is drawn away from the member B `whichconstitutes the other fuse terminal of the structure, H an intermediate clip-engaging terminal by which the auxiliary circuit of the fuse is closed, and J the quenching liquid contained in the casing and operative when the fuse is blown to quench the arc formed between .the movable terminal D and the fixed-terminal B.

As before noted, the structure may be built up for use without the liquid J. In such case the tubing C'is preferably made of bakelite or some similar material. However, the structure will be described herein as made for use Wittig the 'liquid J and the tube C willbe a glass tu The cap A is snugly fitted against the adjacent end of the tube C, and the parts are cemented together with a suitable cementi# tions material, suchas litharge, or are leaded together-with-a metallic'alloy. The opposite end of theztube C is similarly attached to the terminal B. Parallel surfaces 10, 10 on opposite s'i'des of the cap A are kadapted to fit against the spring clips 12 when the fuse is incirc'uitQ Similar surfaces 11, 11 on opposite sides of the terminal B perform a similar function with reference'to the spring clips 13. k

I The interior of the cap A is provided with an annular projection 14 which is threadedfor thev reception of a terminal member 15. Thej latter is provided with lugs 16 for the reception' of one or more turns at one end of the coiled tension s ring G. The other end of the coiled' spring lis likewise connected to the skirt of the movable terminal D by means of similar lugs 16 similarly engaging end turns' ofthe `spring G. The member 15, being -electrically and' mechanically connected' Y to the terminal A, is in turn electrically connected toa yterminal 17 at Aone end of a pluralityA of flexible insulated conductors 18.`

i flhe'terminal17'closely fits within the bore of the member land is firmly heldinplace v' by any suitable means, as a set screw 19. The

other'end ofthe conductors '18 is vprovided with a similar terminal 20 which likewise snugly fits 'within the ,bo're 'of-the plunger D terminal D.

-an'd .is ,he-ld iii-place by any suitable means,.

such as a set screw 21. Thus the c'ap terminal A is' electrically united through the member' 15 and the conductors 18 tothe movable fuse The fuse "terminal D, besides having' the inner skirt 22, has an outer flaringfiange 23 :which has a diameter approximately 'equal' the support F. 'When so positioned and at' rest, the contained fluid extends to a point in the neighborhood of, or slightly above the fuse link E. Whenv Ithe supportin'gmgembers give way and the plunger D is drawn down by the'spring G, then the flange 23, by closely engaging with the walls of the tube C, insures a flow of the liquid J through 2 the openings '25, 26, and 27 formed in the inclined flange 23. By this means the liquid is projected in forceful streams against any arc which may be vformed by reason' of the rupture of the strip E.` Normally the outer end -of the terminal B is closed by-an end` 'which is `flanged at its periphery plate 27a so" as to fit snugly within 'the bore 'of the terminal at its outer end. The plate is secured to the terminal at its periphery'by jewelers cement or the like. Besides being weakly secured in place it is itself quite thin. Consequently when the fuse blows, the plate 27a may be readily dislodged, thereby leaving the top of the terminal .open 'for the escape of gases and products ofcombustion under pressure.

"The vcross wire structure F constitutes the main support for the plunger D and it is by means of this structure that the plunger is held adjacent to thegfuse terminal B against the tension exerted by the springG which at this time is stretched and exerts a strongpull upon the member D. The cross wire structure includes a fine strain wire 28 which is secured at its opposite ends to the. 1

terminal by any suitable means, such as screws 29 and 30, which, be it noted, also secure the knife edge members 31 and 32 respectivelyto the same terminal. A second strainwire 33 passes over thestrain wire 28 andkisfsecured at its lower ends to the' plunger fuse terminal D.' This wire may' also be secured in various ways. It is shown as connected at one end to the terminal D by the screw 34' and yat the other end by the screw 35 to the insulating block' 36 mounted in an opening in the side of the terminal D. A short tube 37 of conducting/.material encloses thewire 28 and serves as a wearing.

saddle Vfor the wir e33. It will be seen that the wire 28 is -electrically in cont-act with Athe terminal B at all times. One end of the wire 33 is likewise electrically connected at all times to the terminal D, but the other" end of the w-ire 33 is electrically connected to the screw 35 which is insulated from the member D` by the block 36. The tube 37 is merely usedfor the purpose of protecting readily through the ot-her.

the wires and preventing the one cutting too This tube also serves as a conductor of electricity between the two wires. The wires 28 and 33 are preferably line steel wires having high tensile strength. Although this is preferable it will be understood that'other like materials may be used in place of steel without departing from the spirit of my invention. T he m'ain fuse E extends between the fuse terminals B and D in two branches. This construction is employed with the intent that' when the ylink E is being cut by the knife edges 41 substantially equal forces Vare applied to the moving terminal D as a single unbalanced force would tend to cause the terminal D to4 assume a. position not in alignment with the glass tube C with consequent reduction in the speed of operation. Although this is preferable it will be understoody that a single fuse link equivalent to one-halt of link E as shown may be employed without departing from the spirit of my invention. The two branch connection is brought aboutby connecting the center of the strip E mechanically andelectrically to the top of the plunger D. This may be done by any suitable'means, as a screwr39, the latter passing through an opening in the strip and being screwed into a threaded open# ing 40 in the top of the plunger D. The ends of the strip E are electrically and, mechanically fastened to the protruding ends of the supporting members 31 and 32. As clearly shown, the free end of each of the members 31 and 32 is provided with an upturned'knijfe edge 41 over which the strip E extends and adjacent to which it is electrically and mechanically connected by any suitable means, as a screw 42. Adjacent to the knife edges 41 the strip E is bent upward to provide loops on either side of the screw 39 and in this way 'slack is provided which allows the terminal D to have considerable freedom of movement, in case either of the wires 28 or 3-3 is broken, before pulling out the slack inthe strip E and mak# ing the latter taut. When this taut condition is established, the knife edges 41 cut the strip and so break the circuit which would normally iiow between the terminals B and D through the strip E.

The auxiliary circuit' extends from the screw 35, mounted in the insulating block 36 in the terminal D, through an insulated wire 43 extendingto the clip-engaging terminal H. The wire 43 is provided at the end adjacent to the plunger with the terminal 44 through which the screw 35 passes. The block 3G is preferably held iir'mly within the termi nal D by a transverse screw 45 and the end of the wire 43 adjacent to the terminal H is connected to theinner end of a pin 46 which extends through an opening in the tube C and isA secured at its outer end to the terminal H by any suitable means, such as solder. 'In order to properly seal the opening through which the pin 46 passes, a suitable sealing material, such as litharge or a metallic alloy, should be employed.

When the parts are put together in the manner described, the fuse is ready for insertion into the clips 12, 13 porting structure, the terminal A being between clips 12, the terminal H between clips 47 and the terminal B between clips 13. The clips 12 and 13 constitute the terminals of the main circuit and the clip 47 is included in the auxiliary circuit. yAs clearly shown, the clip 12 is connected by wire 60 to one end of the primary winding 49 of the transformer T; the other end of the said winding being connected by conductor 50 with supply wire 51. The other supply wire 52 is connected by conductor 53 with clip contacts 13. The secand 47 of the supondary winding 54 of the transformer is inductively related to the primary winding 49. lVithin the transformer is a thermostat 55. This is set to close the auxiliary circuit whenever the transformer overheats. l @ne terminal of the thermostat is connected by conductor 56 to the clip 47 and the other terminal57 is connected to the winding 49 at a point which will give the necessary potential for the auxiliary circuit. As shown in the diagram, Fig. 8, the fuse is withdrawn from theclips. This was done merely to make the diagram a little clearer.

`With the'circuit arrangement of .F ig. 8 and the fuse in circuit, it will be seen that current will normally flow over a path between the supply wires which maybe tracedA from supply wire 51 through conductor 50, primary transformer winding 49, clips 12,

terminal A, strands 18, movable terminal D,

fuse strip E, contact B, clips 13 and conductor 53 to the return wire 52 of the supply circuit. Tt will be noted that the current passing between terminals B and D will pass through the fuse strip Tt will also be seen that there is a path for current between these same two terminals B and D through wire 33, Wear saddle 37 and wire 28. 1n case of a short'circuit, there will be a low of current through the circuit just traced. The

fuse strip E, and immediately thereafter one or both of the wires 28 or 33, will be heated to a point of rupture. As a result, the terminalD will be jerked quickly toward the cap A by the spring G. Any arc that was formed between the terminals B and D, will be quenched by the flow of thepliquid J through the openings 25, 26 and 27 in the flange 23 of the terminal D.

In case of a heavy overload upon the transformer, the circuit just described will be ruptured in the same way.

0n the othery hand, if there is a slight overload, but one which continues a long time, in-

jury to the transformer Winding might reice 9 nal44, w1re- 33, mam termmal D, conductor thermostat contacts, 57, 55, wire 56, clips 47 contact ring-H, post 46, conductor 43, termistrands 18, fuse cap A, clips 12, and wire 60 to the upper terminal of the transformer winding 49. The current circulating in this local circuit will immediately heat the infcluded wire 33 to the point-of rupture and terminal D will thereupon be released. It

will then promptly respond to the pull of the spring G and draw the strip E sharply against the knife edges 41. -The strip E will thus be severed and the cir-cuit opened. In the meantimethe liquid .l rushing against the parts above the terminal D will promptly quench any arc that might be formed between the terminals. y

Where no liquid J is used, the throw of the lower terminal D is relied upon to break the circuit by a separation sucient to prevent undue arcing.

lt will be understood that in carrying out p my invention many alterations and changes may be made in the details of the structure illustrated and describedwithout departing from the spirit and scope of my invention. l therefore do not wish to be limited to the exact details disclosed but aim to cover by the terms of the appended claims all those alterations and modifications which rightly come within the spirit and scope of my invention.-

What/I claim as new and desire to secure by a patent ofthe United States is:

1. A device ofthe class described comprising relatively movable electric terminals, a knife edge, a fusestripelectrically joining said terminals and passing with accumulated slack over saidknife edge, and means for forcibly drawing upon said fuse strip to take up its slack and bring it sharply against said knife edge to sever said strip.

2. A device of the classl described comprising a relatively xed electric terminal, a relatively movable electric terminal, a knife edge carried by said fixed terminal, a fuse strip electrically uniting said terminals` and passing with accumulated slack over said knife edge, and means for moving said movable terminal away from said fixed terminal to take up the slack in said fuse l strip and draw it sharply against said knife edge to disrupt said strip.

3. A device of the class described comprising an annular terminal having .a central opening therein, supports secured to said terminal and having at their inner 'ends knife edges spaced apart insaid opening, a fuse 'strip secured to said supports and passing over said knife edges and the space between said knife edges in said opening, the bridging portion of said strip' between said knife edges being slack so as to allow considerable movement at its center before becoming taut, a movable terminal secured to said Istrip in said opening, spring means fordrawing said movable terminal away from said annular terminal-in the direction of the axis ofsaid opening to draw said strip taut against the knife edges of said supports to serve in disrupting said strip. l

4. A device of the class described comprising relatively movable electric terminals, a knife edge, a fuse strip electrically connecting said terminals and movable into engagement with said knife edge to be severed thereby, means for separating said terminals with enough force to sever said strip on said knife edge, and means operative under normal elec-- trical conditions to hold said terminals against separation and under other electrical conditions to free said terminals for separation.

5. A device of the class described comprising relatively movable electric terminals, a knife edge, a fuse strip electrically connecting said terminals and movable into engagement with said knife edge -to be severed thereby, a tension spring for separatingsaid terminals, said spring being normally under tension, mechanical means for holding said terminals innormal position with said spring under tension, and electrical connections with said mechanical means responsive to current therein to break the hold of said mechanical means' to thereby free said terminals for separation.

6. A device of the class described compris- ,in-g relatively movable electric terminals, a

knife edge, a normally slack fuse strip electrically connecting said terminals and posi-y tioned to engage said edge and to be severed thereby when drawn taut, a tension sprmg normally under tension and operative to separate said terminals when freed, a metal linkv for mechanically holding said terminals with said fuse strip slack, and connections for said link to supply current thereto to disrupt said linkto thereby free said tension' springto separate said terminals and sever said fuse strip.

7. A device of the class described comprising a fixed electrical terminal, a relatively 4 movable electrical terminal, a tension spring to separate said terminals, looped wires mechanically connecting said terminals to holdl them against the separating action of said tension spring, an electrical connection to said wires whereby excessive current will rupture at least one of them to free said tension spring to separate said terminals, and other electrical connections whereby current Y 1n normally spaced relation, means for forcibly separating said terminals when one of said loops is broken, a fusible element calibrated to rupture at a specified current and providing a preferred path for current between said terminals, and electrical connections to one of said loops whereby current may be supplied to produce a break therein by fusion which will free said separating means for action regardless of the condition of said fusible element.v

9. A device of the class described ,comprising relatively movable main terminals,v

looped wires for mechanically holding said main terminals in spaced relation, means for forcibly separating said main terminals when one of said wires breaks, a third terminal, one of said wires being electrically connected only to one of said main terminals and the other of said wires being electrically i connected at one point to the other of said main terminals and at another point to said third terminal, and external contacts for engaging termina-l clips on a support, said external contacts being connected respectively to said other main terminal and to said third terminal thus providing a portion of a local protecting circuit through the fuse.

li0. A device of the' class described comprising a fixed terminal, a cooperating movable terminal, a third terminal` mechanically xed upon and electrically insulated from said movable terminal, a wire loop having its ends secured to said fixed terminal, a second wireloop passing through said first loop and having one end electrically and mechanically connected to said movable contact and its other end mechanically and electrically connected to said third terminal and thereby mechanically connected to said movable terminal, said loo-ps holding said fixed and movable terminals in spaced relation,-and means for forcibly separating said fixed and movable terminals when a break occurs in one of said loops.

l1. A device of the class described comprising an annular terminal having a central opening therein, a movable terminal in line with the axis of said opening, awire loop having its ends secured to said annular terminal and spanning said opening, a second wire loo passing through said first loop and having its ends secured to said movable terminal, said loops mechanically holding said terminals in normally spaced relation, a

spring acting on said movable terminal and tending to draw it away from said annular terminal, and electrical connections to said loops whereby electric current may be passed through portions of said loops to produce a break therein by fusion which will allow said spring to separate said terminals.

l2. A device of the class described comprising an annular terminal having a central opening therein, a second terminal movable in line with the axis of said opening, a third terminal mechanically secured to and electrically insulated from said movable terminal, a first wire loop having its ends secured mechanically and electrically to said annular terminal and spanning said opening, a second wire loop passing through said rst loop and having its ends secured mechanically and electrically to said second and third terminals respectively, said loops holding said annular and second relation, and means for forcibly drawing said movable terminal from said annular terminal when a break occurs in one of said loops.

13.4 A device of the class described comprising a fixed electrical terminal, a rela-tively movable electrical terminal, a tension spring to separate said terminals, looped wires mechanically connecting said terminals to hold them against the separating action of said tension spring, electrical connections to said wires whereby electric current may be utilized to rupture them by fusion to free said tension spring to separate said terminals, a normally slack fuse strip electrically connecting said fixed and movable terminals, and severing means for rupturing said strip when stretched tight by said tension spring.

14. A device of the class described comprising relatively movable terminals, a wire loop having its ends secured to one of said terminals, a second wire loop passing through said first loop and having its ends secured to the other of said terminals, said loops mechanically holding said terminals in i normally spaced relation, means for separating said terminals when one of said loops breaks, electrical connections to said loops whereby current may be directed through portions of said loops to produce a break therein which will free said separating terminals in spaced forcibly means for action, a normally slack fuse strip trically connected only to one of said termi-f;

nals and the other of said wires being electrically connected at one point to the other of said terminals, lan electrical connection to y prising a fixed terminal, a cooperating mov able terminal, a third terminal mechanically fixed upon electrically insulated from said movable terminal, a Iwire loop having its ends secured to said fixed terminal, a second wire loop passing through said first loop and having one end electrically and mechanically connected to said movable contact and its' other end mechanicallyand electrically connected to said third terminal and thereby me- 1 chanically connected to said movable terminal, said loops holding said fixed and movable terminals in spaced relation, means for forcibly separating said fixed and movable terminals when a break occurs in one of said loops, a normally slack fuse strip electrically connecting said fixed and movable terminals, and means for severing said strip when stretched by said separating means.

" 17. A device of the class described com-I prising an annular terminal having a central opening therein, a second terminal movable in line with the axis of said opening, a wire loop having its ends secured to said 'annular terminal and spanning said opening, a second wire loop passing through said first loop and having 'its ends mechanically secured to said second terminal, said loops mechanically holding said terminals in normally spaced relation, a spring acting on said second terminal and tending to draw'it'away from said Vannular terminal, electrical connections to said loops whereby current mayv be directed through portions of' said loops to produce a break therein which will allow said spring to separate said terminals, a normally slack fuse strip electrically connecting said annular and second terminals, and means for severing said strip when stretched by said spring. p

18. A device of the class described comprising an annular terminal having a central opening therein,la second terminal movable in line with thel axis of said opening, a third terminal mechanically secured to and electrically insulated from said second terminal, a firstx wire loop having its ends secured mechanically and electrically to said annular terminal and spanning said opening, a second wire loop passing through said first loop and having its ends secured mechanically and electrically to said second and third terminals respectively, said loops holding said annular and second terminals in spaced rela# tion, means for forcibly drawing said second terminal from said annular terminal when a break occurs in one of said loops, a normally slack fuse strip electrically connecting said annular and movable terminals, and meansv for severing said strip when stretched by said drawing means.

19. A device f the class described comprising a fixed terminal, a relativelymoyable o terminal, a spring to'separate said terminals, l

a fuse strip electrically connecting said terminals, looped wires mechanically connecting said terminals to hold them against the separating action of said Spring, and an auxiliary terminal mounted upon and insulated from said movable terminal, said looped wires providing a path for current 'between said fixed and movable terminals in parallel to that providing by said fuse strip, and said wires also providing a path for currentbetween said movable and auxiliary terminals.

20. A device of the class described, an enclosing casing, a fixed fuse terminal, a cooperating movable fuse terminal in saidcasing, said fixed terminal being at one end of said casing, a cap at the other end of said casing,

-a terminal ringsecured to said casing inter-` mediate of its length, said fixed terminal, cap and ring being adapted for connection to spaced terminals on a support, a coiled spring in said casing connecting said cap to said movable terminal, a third terminal secured to and insulated from said movable tery minal, a flexible conductor connecting said cap and movable terminal, an auxiliary flexible conductor connecting said ring and third A terminal, both lof' said flexible conductors lying wholly within said casing, a fuse strip electrically connecting saidI fixed and movable-terminals, and looped wires mechani-l cally and electrically connecting said fixed,

a movable and third terminals, said wires ro strain wire electrically in circuit between said terminals and mechanically operative to hold said terminals against the separating action of said spring, an electrical fuse connection in shunt to said strain wire vpath for current whereby excessive current will blow said fuse and' then rupture said wire to freev said tension spring to separate said terminals, s

and other-electrical connections whereby current may be introduced to said wire to rupture the same, to cause a separation of said terminals independently of the action of said fuse connection.

22. A device of the class. described comprising relatively movable terminals, means including a strain wire electrically in circuit between said terminals and mechanically operative 'to hold said terminals in normally spaced relation, means for forcibly separating said terminals when said strain wire is broken, a fusible element-electrically interposed between said terminals and calibrated to' rupture at a specified current, said fusible element providing a preferred path alternative to said strain wire path for current be-- tween said terminals, and electrical connections to introduce current to said strain wire to produce avbreak therein by fusion which will free said supporting means for'action rel gardless of the condition of said fusible element.

23. A device of the class described comprising relatively movable electric terminals,

means for forcibly separating said terminals, a fuse link and a strain wire providing parallel paths for current between said terminals, said fuse link being calibrated to rupture at a specified current and normally in- CERTIFICATE/0F coRRECTIoN.

Patent No. 1,807,228.'

JAMES H. "STARR,

It is hereby certified that error'appears inthe printed specification of they above numbered patent requiring correction as follows: Page 6, line 8, claim 16, 'after the word "upon" insert the Word and; and that the said Letters Patent should be read with this correction therein that record of the case-Ain the Patent Office. Y

ASigned and sealed this 14th day ofiJuly, A. D.- 1931'.

the same may conform tov the (Seal) s c'tingpCommissioner of Patents. n

" y Granted Maize, 1931, m

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