US2750471A - Electric fuse - Google Patents

Description

J. R. M BRlDE June 12, 1956 ELECTRIC FUSE Filed Dec. 25, 1953 FICiZ FIG. i

INVENTOR JOSEPH R. M BRIDE ATTORNEY United States Patent ELECTRIC FUSE Toseph R. McBride, Hampton, Ga., assignor to Southern States Equipment Corporation, a corporation of Georgia Application December 23, 1953, Serial No. 399,945

8 Claims. (Cl. 200-420) This invention relates to electric fuses and more particularly to an improved fuse link for use in electric fuses and cutouts.

In electric fuses and cutouts of a given current interrupting rating, it is usually possible to effect prompt interruption of fault or overload currents by expulsion action where the magnitude of current is substantially in excess of the minimum current required to rupture the fusible element. This condition is well understood and is due to the fact that the quantity of gas emitted by the walls of the fuse tube and the resulting expulsion action are functions of the magnitude of the current being interrupted.

When the current magnitude is but slightly in excess of the current required to rupture the fusible element, the quantity of gas emitted by the walls of the fuse enclosure is small and the resulting expulsion action may be of such a character as to fail to extinguish the are drawn within the fuse enclosure.

It is well-known that high pressure in the region of an arc aids materially in its extinguishment. It is also wellknown that an arc is more easily extinguished if it is rapidly stretched. Furthermore, if the ionized and other products of arcing are quickly scavenged from the in terrupter, it is unlikely that the arc will reestablish itself.

An object of this invention is to provide an improved fuse link for electric fuses and cutouts which is particularly adapted to interrupt currents which are but slightly in excess of the current required to rupture the fusible element of the fuse link.

Another object of this invention is the provision of an electric fuse or cutout which is adapted for increasing the pressure in the region of the are, which is arranged quickly to elongate the arc, and which promptly scavenges the interrupter of the ionized and. other products of arcing.

The invention in one form as applied to a fuse. link having a fusible element mounted in an enclosing structure of material which evolves a gas in the presence of an arc comprises a first sealing member mounted on a conductor which is connected with the fusible element and which extends out of the enclosing structure to form one terminal for the fusible element, and a second sealing member mounted on the enclosing structure in spaced relation to the first sealing member. When the fusible element is ruptured the gas evolved raises the pressure in the region of the arc and drives the first sealing member into engagement with the second sealing member thereby to isolate the are from atmosphere. As the pressure builds up further, a point is reached at which the second sealing member is severed from the enclosing structure thereby to allow the sealing members to be blown out of the enclosure and to effect a prompt and thorough scavenging of the enclosing structure. Also, the terminal, on which the first sealing member is mounted, is blown out of the enclosure under high pressure effecting a rapid stretching of the are.

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For a better understanding of the invention reference may be had to the following description taken in conjunction with the accompanying drawing in which Figure 1 is a side view of an electric cutout and in which Figure 2 is an enlarged cross-sectional view of a portion of the fuse tube and parts associated therewith which comprise the interrupting element shown in Figure 1.

With reference to Figure l, the numeral 1 designates a metallic arm which at its left-hand extremity is arranged for mounting on a pole crossarm or other suitable supporting structure (not shown) and which at its righthand extremity is secured to the upper insulator 2 and to the lower insulator 3. Afiixed to the upper end of insulator 2 as by the bolt 4 is the terminal bracket 5 which is provided with a longitudinally split bolt 6, the tines of which are disposed within a pair of openings in terminal bracket 5. Bolt 6 constitutes a means for securing a conductor of the associated circuit to the cutout. Bracket 5 at its upper extremity is provided with an opening 7 for receiving a looped portion of the circuit conductor (not shown) which is secured to terminal 5 by bolt 6. Terminal 5 is provided with a downwardly extending portion 8 to which is aifixed by suitable means a metallic brush 9 and a contact element 10. As is well understood in the art brush 9 could be made of a plurality of laminations of conducting material arranged to bias the contact element 10 toward the right. Pivotally mounted at 11 to bracket 5 is the terminal hood 12 which protects the contact elements from the adverse effects of precipitation. Formed within the hood 12 is a latching surface 12A the purpose of which will be described later.

Atfixed to the lower extremity of insulator 3 by the bolt 13 is the lower terminal bracket 14. Formed within bracket 14 is a slot 15 for receiving one tine of a longitudinally split terminal bolt 16 which is for the purpose of aflixing a circuit conductor (not shown) to the terminal bracket 14. Terminal bracket 14 is provided with a pair of longitudinally disposed structures 14A between which is mounted by screw 17 a terminal brush 18 to the upper right-hand extremity of which is attached the contact element 19. Each of the horizontally disposed structures 14A is provided with a jaw portion 20 in which is disposed a trunnion 21. Trunnions 21 are formed integrally with terminal element 22 which is pivoted at 23 to the collar 24 which in turn is aflixed to fuse tube 25 by means of the screw 26. Terminal ele ment 2-2 is also provided with a contacting surface 22A which is engageable with the contact element 19.

Mounted within the fuse tube 25 is a fusible element comprising the conducting elements 27 and 28 which are joined together by solder which is schematically represented at 29 in Figure 2. Secured to the lower end of conducting element 23 by any suitable means is a conductor 30 which in Figure 1 is shown extending out of the lower extremity of the fuse tube 25. Conductor 30 is electrically connected to the terminal element 22 by suitable means such as a clamping screw (not shown).

From the above description it will be understood that terminal element 22 is retained in the position shown in Figure 1 by means of conducting means in the form of the conductor 30 and parts associated therewith. Furthermore, it will be understood that contact brush i8 is constructed so as to bias the contact element 19 into firm contact making engagement with the contacting portion 22A of terminal element 22.

Secured to the upper extremity of the conducting element 27 is a conductor 31 which in Figure 1 is shown secured by means of the clamping screw 32 to the terminal element 33. Terminal element 33 is provided at its left-hand extremity with contacting portion 33A against which the contact element 10 is biased by means of the brush 9. Terminal element 33 is pivotally mounted by the pin 34 to a metallic link 35 which in turn is connected by pin 35 to the collar 37 mounted by means of the screw 38 to the fuse tube 25. Thus it will be understood that the conductor 31 and parts associated there with serve to maintain the parts associated with terminal element 33 in the positions represented in Figure l. The structure just described which forms the upper terminal assembly of the cutout is more fully described and claimed in U. S. Patent No. 2,172,143 granted September 5, 1939 upon an application of George N. {cannon and assigned to the assignee of this invention.

Upon the occurrence of a fault or overload condition the fusible element comprising elements 27-29 is ruptured and the terminal element 22 rotates about trunnions 21 in a clockwise direction. This motion of terminal element 22 allows the pivot 23 to move in a clockwise direction about the trunnions 21 thereby to move the fuse tube downwardly. Simultaneously, the contacting portion 33A is released from the latch 12A formed within the hood 12 thereby to allow the fuse tube 25 and the collar 37 together with the parts associated therewith to swing in a clockwise direction about the trunnions 2i. Simultaneously, the terminal element 33 is free to disengage the upper end of the fuse tube 25, all as explained more fully in the above mentioned Patent No. 2,172.14

The internal construction details of the fuse tube 25 and parts associated therewith can be best seen from Figure 2. Tube 25 is of conventional construction and is provided with an inner lining element 39 formed of fiber or other suitable insulating material.

The fuse link as constructed in accordance with this invention and as shown in Figure 2 comprises a tubular element 40 of insulating material in which the conducting elements 27, 28 and solder connection 29 are disposed. The upper extremity of tubular element it) is closed by closure element 41 which is securely affixed to the conductor 31 as by crimping or other suitable means and which is also securely atfixed within the tubular element 40 by cement or other suitable means.

It is well-known that certain materials in the presence of an electric are are capable of emitting gases which are of value in effecting the prompt extinguishment of the arc. Such a substance is fiber which may be the material of which tube 40 is made. load condition develops, the soldered connection 29 melts to establish an arc in close proximity to the tube 48 thereby to initiate the rapid emission of arc quenching gas which aids in interrupting the arc in known manner.

In accordance with this invention the gas evolved by the tube at is confined temporarily so that the pressure in the region of the arc is rapidly increased to aid in extinguishing the arc. Also in accordance with this invention the arc thereafter is rapidly stretched in the region of high pressure and the ionized and other products of arcing are scavenged from the region of the are so as to effect extinguishment and to prevent reestablishment or restriking of the arc.

As is shown in Figure 2 a sealing member 42 in the form of a sleeve or collar is mounted on the conductor 30 and a sealing member 43 in the form of a sleeve is mounted within tube 49 at the lower extremity thereof. Scaling member 42 is secured to conductor 30 by crimping, soldering or other suitable means while sealing member 43 is secured within tube 4-0 by cement or other suitable frangible means, or if desired member 43 could comprise an integral part of tube 40. Thus when an arc is drawn between conducting elements 27 and 28 due to the melting of soldered joint 29 gas is given off by tube 40 and the pressure built up within tube 40 drives con-- ductor 3t), conducting element 28 and sealing member 42 downwardly to cause sealing member 42 to engage sealing member 43 thereby to form a seal for the lower end of tube 40. As the pressure continues to rise a. point will be reached at which sleeve 43 is forced down- Thus when a fault or overi wardly out of tube 40 along with sealing member 42 conductor 30 and conducting element 28. Thus it will be understood that the increased pressure within tube 40 due to the scaling effect of members 42 and 43 aids in interrupting the arc, and that the expulsion of members 42, 43, 30 and 28 stretches the arc and effects a scavenging of the region within tube 40 thereby to hinder the reestablishment or restriking of the are.

It will be understood that this invention is particularly useful for interrupting arcs the current magnitude of which is but slightly in excess of the current for which the fuse link is designed to rupture. While the invention is especially useful for low current arcs, a fuse link constructed in accordance with the invention is capable of effecting prompt extinguishment of high current arcs and of hindering restriking thereof.

Although the invention as described above utilizes a tube 46 which is capable of emitting arc extinguishing gas, it will be understood that gas emitting material such as boric acid powder could be disposed in the region of the are for this purpose.

While I have shown and described a particular embodiment of the invention, it will be understood that i do not wish to be limited thereto and intend in the anpended claims to cover all changes and modifications as fall with in the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. Sealing means for one end of a fuse tube in which a fusible element is mounted comprising a conductor connected with said fusible element and extending out of one end of said tube to form a terminal for said fusible element, a first sealing member mounted on said conductor, and a second sealing member releasably mounted on said tube and normally disposed in spaced relation to said first sealing member, said first sealing member being movable into engagement with said second sealing member to form therewith a seal for said one end of said tube in coordination with the establishment of an arc therein by said fusible element, said second sealing member being releasable from said tube in co ordination with the establishment in said tube of a predetermined pressure condition.

2. Sealing means for one end of a fuse tube in which a fusible element is mounted comprising a conductor connected with said fusible element and extending out of one end of said tube to form a terminal for said fusible element, a first sealing member mounted on said conductor, and a second sealing member mounted on said tube and engageable with said first sealing member to form therewith a seal for said one end of said tube in coordination with the establishment of an are therein by said fusible element, at least one of said sealing members being mounted by frangible means which is ruptured in response to the establishment of predetermined con ditions within said tube.

3. Sealing means for one end of a fuse tube in which a fusible element is mounted comprising an elongated conductor electrically connected with said fusible element and forming a terminal therefor, a first sealing member mounted on said conductor, and a second sealing member mounted on said tube, said second sealing member being normally spaced from said first sealing member and being engageable therewith to establish a seal for said one end of said tube in coordination with the drawing of an are within said tube, at least one of said sealing members being mounted by means which is releasable in coordination with the establishment of predetermined conditions within said tube.

4. Sealing means for one end of a fuse tube in which a fusible element is mounted comprising an elongated conductor electrically connected with said fusible element and forming a terminal therefor, a first sealing member mounted on said conductor, said conductor and said first sealing member being movable axially within said tube in response to the drawing of an are by said fusible element, and a second sealing member mounted on said tube by frangible mounting means, said second sealing member being normally spaced from said first sealing member and being engageable therewith to establish a seal for said one end of said tube, said frangible mounting means being severable in response to the establishment of predetermined conditions within said tube to cause said sealing members to be expelled therefrom thereby to form an exhaust passage to atmosphere from within said tube.

5. An electric fuse comprising a tube of insulating material, a fusible element disposed within said tube, means securing one end of said fusible element in position adjacent one end of said tube and forming a closure for said one end of said tube, conducting means electrically connected with the other end of said fusible element and extending out of the other end of said tube, means responsive to the drawing of an arc within said tube for evolving an arc extinguishing gas, a first sealing member mounted on said conducting means and slidable within said tube, a second sealing member mounted on said tube in cooperative relation to said first sealing mem ber, said sealing members being elfective to prevent the free escape of pressure from within said tube and at least one of said sealing members being mounted by releasable means responsive to a predetermined pressure condition in said tube to establish an exhaust passage to atmosphere.

6. An electric fuse comprising a tube of insulating material, a fusible element disposed within said tube, means securing one end of said fusible element in position adjacent one end of said tube and forming a closure for said one end of said tube, conducting means electrically connected with the other end of said fusible element and extending out of the other end of said tube, means responsive to the establishment of an are within said tube for increasing the pressure therein, a first sealing member mounted on said conducting means and slidable Within said tube, a second sealing member mounted within said tube and yieldably secured therein, said sealing members being engageable in response to the rupture of said fusible element after predetermined sliding movement of said first sealing member to prevent the free escape of pressure from within said tube, said second sealing member being movable out of said tube in respouse to the establishment of a predetermined pressure Within said tube.

7. Sealing means for one end of a fuse tube in which a fusible element is mounted comprising a first sealing member slidable within said tube and having a normal position therein in which said member is restrained by said fusible element, and a second sealing member releasably mounted on said tube and normally in spaced relation to said first sealing member, said first sealing member being movable into engagement with said second sealing member upon the rupture of said fusible element thereby to form a seal for said one end of said tube and said second sealing member being releasable from said tube in response to pressure within said tube above a predetermined value.

8. Sealing means for one end of a fuse tube in which a fusible element is mounted comprising means responsive to the establishment of an electric are within said tube for emitting arc extinguishing fluid, a first sealing member slidable within said tube and having a normal position therein in which said member is restrained by said fusible element, and a second sealing member mounted on said tube and normally in spaced relation to said first sealing member, said first sealing member being movable into engagement with said second sealing member upon the rupture of said fusible element thereby to form a seal for said one end of said tube for preventing the escape therefrom of pressure fluid at pressures below a predetermined value, at least one of said sealing members being yieldable in response to pressure within said tube above a predetermined value to establish an exhaust passage to atmosphere.

References (Iited in the file of this patent UNITED STATES PATENTS 805,288 Haskins Nov. 21, 1905 1,829,604 Natalis Oct. 27, 1931 1,987,057 Earle Jan. 8, 1935 2,043,024 Williams June 2, 1936 2,067,577 Mosley et al Jan. 12, 1937 2,111,745 Boothe Mar. 22, 1938 2,338,946 Kesselring Jan. 11, 1944 2,545,596 Amundson et al Mar. 20, 1951 FOREIGN PATENTS 325,285 Great Britain Feb. 17, 1930

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