US2523139A - Fuse - Google Patents

Description

P 1950 J. B. OWENS 2,523,139

FUSE

Filed Sept. 28. 1946 fnerf Granu/ar g4 fnsu/of/ny Mafer/a/ WITNESSES: INVENTOR 4 kmesfi. Owens.

Patenteci Sept. 19, 1950 FUSE James B. Owens, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 28, 1946, Serial No. 700,072

9 Claims.

This invention relates to electric circuit interrupters, and more specifically to such interrupters of the fusible type which are adapted to limit the current during circuit interruption.

Electrical apparatus of low current rating when connected to high current circuits is likely to explode or suffer considerable damage in the event of an internal fault. In order to adequately protect such apparatus, it is necessary that the circuit to a faulty device be opened very quickly and the fault current limited. Attempts have been made to group several low current devices such as capacitors in a bank and protect the bank with current-limiting power fuses. These attempts have failed however, since such fuses are unable to limit the current to a low enough value to prevent explosion of a faulty unit before the circuit is opened.

Accordingly, one object of this invention is to provide a novel current limiting fuse adapted for the individual protection of low current apparatus, such as capacitor units or the like.

Another object of this invention is to provide a novel current limiting fuse especially adapted for mounting on and protection of individual capacitor units.

A further object of this invention is to provide a current limiting fuse having novel means providing for visual indication of operation of the fuse to interrupt the circuit.

A more specific object of this invention is to provide in a current limiting fuse having fusible strain means for normally retaining indicating means at a nonindicating position, means providing current limiting action upon fusion of such 7 strain means as well as upon fusion of the main current-carrying fusible means.

A more general object of this invention is to provide a novel current limiting fuse which is small in size and economical to manufacture and is especially constructed for mounting on an individual capacitor unit, and yet is capable of limiting fault currents to a low enough value and of interrupting the circuit soon enough to prevent the building up of dangerous pressures due to internal faults in such unit.

These and other objects of this invention will become more apparent upon consideration of the following detailed description of a preferred embodiment thereof, when taken in connection with the attached drawing, in which:

Figure 1 is a longitudinal section View taken through a fuse embodying this invention with certain of the interior parts shown in elevation; and

iii

Fig. 2 is a transverse section view taken substantially on the line II- II of Fig. l.

The embodiment of the invention shown on the drawing comprises a fuse having a tubular holder 2 of insulating material, such as fiber or a synthetic resin. The lower end of the holder 2 is adapted to be closed by a terminal closure plug 4 which is threaded into the lower end of the holder, and secured as by a pin 6. Terminal plug 4 is provided with a substantially centrally located tapped opening 8, which is adapted to be threaded onto the terminal of a capacitor unit, so that the fuse may be mounted directly on the unit and be directly supported therefrom. The tapped opening 8 in closure plug 4 merges at its inner end into a passage H! of less crosssection area than opening 8, and this passage extends inwardly to be formed in part in a sleeve extension I2 of the closure plug.

A rod 14 of insulating material is adapted to be supported within fuse holder 2, being secured in position by a screw I5 extending through passage [0 of closure plug 4 to be threadedly engaged in a tapped opening in the lower end of rod [4. Preferably, rod I4 is of an insulating material which is capable of evolving an arcextinguishing gas when in proximity to an electric arc, such, for example, as fiber or the like, all for a purpose to be described. Rod I4 is provided with a pair of spiral slots I8 and 20 on the surface thereof, with one slot 18 adapted to receive a fuse wire 24 therein, and the other slot 20 adapted to receive a strain wire 22. Fuse wire 24 is of a low resistance conducting material, such, for example, as silver, Whereas strain wire 22 is of a relatively higher resistance material, such as a copper-nickel alloy. Slots l8 and 20 are spaced apart and extend in generally parallel relation along the length of rod I4 terminating at the opposite ends of the rod. The lower end of fuse wire 24 and strain wire 22 are secured as by soldering or the like. to sleeve l2 on terminal plug 4, so as to be electrically connected therewith.

A closure disc 26 is provided in holder 2 at the upper end of rod M for enclosing the space between the upper end of the rod and terminal plug 4. Closure disc 26 is preferably of an insulating material, such as fiber, and is held in position by a terminal collar 28, which in turn is secured in the fuse holder by a terminal screw 30 extending through an opening 3| in the side of holder 2 and having its inner end threaded into a tapped opening in terminal collar 28. Preferably, terminal screw 30 is secured against rotation in collar 28 as by a pin 29, and has a pair of nuts 32 on the outer end thereof for securing a line conductor thereto.

Mounted in holder 2 above terminal collar 28 is an inverted generally cup-shaped indicator 34 having an outwardl extending flange 3? at the inner end thereof, which is adapted to engage a stop disc 38 to limit outward movement of the indicator. Stop disc 38 may be held in position by any desired means, such, for example, as by the split retainin ring 42, which is received in a groove provided adjacent the upper end of the holder 2. A coil compression spring 32 reacts between terminal collar 28 and flange 3'! of the indicator to bias the indicator outwardly relative to holder 2, but strain wire 22 extends upwardly through an opening in closure disc 26 to have its upper end extend through a central opening 45 in the indicator and be secured thereto as by soldering 44, or the like.

The upper end of fuse wire 24 extends through another opening in closure disc 26 and is secured to terminal collar 28 in any desired manner, for example, as by soldering or the like. It is now apparent that fuse wire 24 is in series in the circuit through the device shown, being connected to terminal collar 23 and terminal screw 3t at its upper end and being connected to terminal plug 4 at its lower end.

The particular structure described above, wherein strain wire 22 and fuse wire 24 are located in slots l8 and 20, is especially designed so that when these wires are melted, the resulting arc will be so confined and acted upon as to create a high enough arc voltage that the :1.

current flow at that time will be limited to a value less than the particular fault is capable of causing, and in order to interrupt the circuit before any appreciable damage to the protected capacitor is accomplished this structure also is especially arranged to interrupt the circuit at the first current zero. It is essential that the current be limited in a small fraction of a half cycle in order to prevent serious damage, and for this purpose it will be noted that the slots i and 26 are made to be of substantially the same size as fuse wire 24. Since an are formed within these slots would tend to blow out of the slots, a plurality of spaced washers 46 are provided along the length of rod M to retain correspondingly spaced portions of the arc within the slots. The washers 46 are of an insulating material, such as fiber or the like. When an arc is struck in slot l3 or 2D, the arc voltage will immediately rise at a rapid rate due to restriction of the arc cross section in the narrow confines of the arc passage, and it will be extinguished at the first current zero by the arcextinguishing action of the slot itself. The gases evolved from the material comprising the slot walls will be directed by the slot transversely through the arc and will then ass into the finely divided inert insulating material 48 occupying the space between rod 14 and the inner walls of holder 2. This transverse blast of gas effectively de-ionizes the arc path because it acts to sweep all metal vapor and other ionized particles in the arc path into the material 43 where it is dispersed and/or condensed in separated insulated relation. As stated above, the width of slots i8 and is made as small as possible being limited only by the diameter of fuse wire 2%, and the depth of the slots is preferably greater than the slot width, being on the order of about twice the slot width.

While the lower end of strain wire 22 is connected to terminal plug 4, the upper end thereof being connected to indicator 2% which in turn is electrically connected with terminal collar 28 by the turns of coil spring 42, means that this element is connected in parallel with fuse wire 24 between terminals 4 and 30. However, since strain wire 22 is of a relatively high resistance material which may also have a greater mechanical strength than fuse wire 24, it is smaller in cross-section and normally carries only a very small current. Accordingly, when a fault occurs, fuse wire 24 melts first, and the voltage appearing across strain wire 22 causes a current to flow in it to fuse the strain wire. While the arc will usually persist in the slot occupied by fuse wire 24 when strain wire 22 is melted, and be finally interrupted in slot [8, it is obvious that by providing strain wire 22 in a similar slot 22, if the arc should transfer to the path occupied by the strain wire, it will be extinguished, and the current will be limited in the same manner described above.

When strain wire 22 melts, indicator 34 is no longer held at the inner position shown in Fig. l, and spring 42 is free to move it outwardly rela tive to holder 2 until its flange 37 engages stop disc 38, at which position it will be readily visible to indicate blowing of the fuse.

It is apparent from the foregoing that the fuse structure described above provides for current limitation and fast interruption of the circuit in a fuse especially designed for mounting on and the protection of capacitor units and the like. Moreover, this fuse further includes a means for givin a clear visible indication of the blowing of the fuse without interfering in any way with the efficiency of the fuse to either limit the current or rapidly interrupt the circuit. This last feature is very important where capacitors are being protected, because they are usually grouped in banks containing a great many capacitor units, and it will be appreciated that it is very difficult to determine which units are faulty unless a dependable fuse indication is incorporated in each fuse.

Having described a preferred embodiment of this invention in accordance with the patent statutes, it is desired that this invention be not limited to this particular embodiment inasmuch as it will be apparent, particularly to persons skilled in this art, that many modifications and changes may be made in this particular structure without departing from the broad spirit and scope of the invention. Accordingly, it is desired that the invention be interpreted as broadly as possible and that it be limited only as required by the prior art.

I claim as my invention:

1. In a. fuse, a tubular fuse holder of insulating material having spaced terminals thereon, solid means of insulating material positioned in said holder and extending longitudinally thereof, a plurality of continuous generally parallel narrow spiral passages formed as grooves in the outer surface of said solid means, a fuse wire in one of said passages connected between said terminals, a relatively high resistance strain wire in another of said passages also connected between said terminals, and indicating means movably mounted on said holder and being biased for movement relatively to the holder but normally being restrained by said strain means.

2. In a fuse, a tubular fuse holder of insulating material having spaced terminals thereon,

solid means of insulating material positioned in said holder spaced from the inner walls of said holder and extending longitudinally thereof, a plurality of continuous generally parallel nar row passages in the form of grooves in the outer surface of said solid means and extending along the length thereof, a fuse wire in one of said passages connected between said terminals, a relatively high resistance strain wire in another of said passages also connected between said terminals, and indicating means movably mounted on said holder and being biased for movement relatively to the holder but normally being restrained by said strain means.

3. In a fuse, a tubular fuse holder of insulating material, spaced terminal means on said holder one of which is adjacent to but spaced inwardly from one end thereof, indicating means movably mounted in said one end of said holder outwardly of said one terminal means and biased to move from a position wherein a major portion thereof is within said holder to a position wherein a substantial portion thereof projects from said one end of the holder, and fusible strain means in said holder connected between said terminals and directly engaging said indicatin means for normally maintaining the latter at its inner position.

4, In a fuse, a tubular fuse holder of insulating material, spaced terminal means on said holder one of which is adjacent to but spaced inwardly from one end thereof and extends through the side wall of said holder, indicating means movably mounted in said one end of said holder outwardly of said one terminal and biased to move from a position wherein a major portion thereof is within said holder to a position wherein a substantial portion thereof projects from said one end of the holder, and fusible strain means in said holder connected between said terminals and directly engaging said indicating means for normally maintaining the latter at its inner position.

5. In a fuse, a tubular fuse holder of insulating material, spaced terminal means on said holder one of which is adjacent to but spaced inwardly from one end thereof and extends through the side wall of said holder, indicating means movably mounted in said one end of said holder outwardly of said one terminal and biased to move from a position wherein a major portion thereof is within said holder to a position wherein a substantial portion thereof projects from said one end of the holder, fusible means in said holder directly connected between said terminals, relatively high resistance fusible strain means directly connecting the other of said terminals and said indicating means, and said indicating means being at least in part of an electrical conducting material which is in conductive relation with-said one terminal.

6. In a fuse, a tubular holder of insulating material, a terminal closure at one end of said holder, terminal means secured in said holder at a point adjacent to but spaced from the other end thereof and having a terminal portion extending through a side opening in said holder to the exterior thereof, closure means for said other end of said holder located within said holder adjacent said terminal means, indicating means movably mounted in said other end of said holder outwardly of said terminal means and biased to move from a position wherein a major portion thereof is within said holder to a position wherein a substantial portion thereof projects from said other end of the holder, fusible means and are controlling means in said holder between said closures, and said fusible means being connected between said terminals and including a strain portion extending through said closure means for normally holding said indicating means at its inner position. I

'7. In a fuse, a tubular holder of insulating material, a terminal closure atoneend of said holder, terminal means secured in said holder at a point adjacent tobut spaced from the other end thereof and having a terminal portion extending through a side opening in said holder to the exterior thereof, closure means for said other end of said holder located within said holder adjacent said terminal means, indicating means movably mounted in said other end of said holder outwardly of said terminal means and biased to move from a position wherein a major portion thereof is within said holder to a position wherein a substantial portion thereof projects from said other end of the holder, fusible means and are controlling means in said holder between said closures, said fusible means comprising a low resistance fusible element and a relatively high resistance fusible strain element supported in spaced insulated relation in said holder and being connected in parallel circuit relation between said terminals, and said strain element extending through said closure means for normally holding said indicating means at its inner position.

8. In a fuse, a tubular fuse holder of insulating material having spaced terminals thereon, solid means of insulating material positioned in said holder spaced from the inner walls of said holder and extending longitudinally thereof, a plurality of generally parallel narrow passages in the form of continuous grooves in the outer surface of said solid means and extending along the length thereof, at least inner walls of said passages being of a material capable of evolving an arcextinguishing gas when in proximity to an electric arc, means of an inert finely divided insulating material in the space between said solid means and holder, a fuse wire in one of said passages connected between said terminals, a relatively high resistance strain wire in another of said passages also connected between said terminals, and indicating means movably mounted on said holder and being biased for movement relatively to the holder but normally being restrained by said strain means.

9. In a fuse, a tubular fuse holder of insulating material having spaced terminals thereon, solid means of insulating material positioned in said holder spaced from the inner walls of said holder and extending longitudinally thereof, a plurality of generally parallel narrow passages in the form of continuous grooves in the outer surface of said solid means and extending along the length thereof, at least inner walls of said passages being of a material capable of evolving an arcextinguishing gas when in proximity to an electric arc, means of an inert finely divided insulating material in the space between said solid means and holder, spaced barriers alon the open sides of said passages but covering only a minor portion thereof for preventing the escape of correspondingly spaced portions of an arc therefrom, a fuse wire in one of said passages connected between said terminals, a relatively high resistance strain wire in another of said passages also connected between said terminals, and indicating means movably mounted on said holder and being biased for movement relatively to the holder but normally being restrained by said strain means.

JAMES B. OWENS.

REFERENCES CITED The following references are of record in the file of this patent:

Number 8 UNITED STATES PATENTS Name Date Slepian et a1 Sept. 26, 1933 Slepian et a1. Nov. 28, 1933 Rawlins et a1. Feb. 9, 1937 Smith, Jr. Jan. 10, 1939 Thommen et a1. Jan. 28, 1941 Rawlins et a1. Jan. 19, 1943

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