US3519971A - Fuse including improved means responsive to the operation of the fuse - Google Patents

Description

July 7, 1970 F. L. CAMERON FUSE INCLUDING IMPROVED MEANS RESPONSIVE TO THE OPERATION OF THE FUSE Filed March 5, 1969 52A 60 -so I so 52 1s 72 2 Q I00 86B 44A 86A 92 INVENTOR Frank L. Cameron chi; av /4.1L

ATTORNEY United States Patent 3 519,971 FUSE INCLUDING IlVlPROVED MEANS RESPON- SIVE TO THE OPERATION OF THE FUSE Frank L. Cameron, Irwin, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Mar. 3, 1969, Ser. No. 803,655 Int. Cl. H01h 37/46, 85/30 U.S. Cl. 337-241 7 Claims ABSTRACT OF THE DISCLOSURE A fuse comprising an electrically insulating casing having spaced terminal means disposed thereon and electrically conducting means including a fusible element disposed in the casing and electrically connected between said terminal means. An additional fuse wire is disposed in the casing and is connected between said terminal means with means provided adjacent to one end of the casing which responds to the fusion or melting of the fusible element and the fuse wire to change position.

BACKGROUND OF THE INVENTION In certain types of circuit interrupters, such as current limiting fuses, more particularly those which are applied at relatively high voltages, a problem arises in providing a totally enclosed fuse structure with an externally visible means for indicating that the fuse has operated to interrupt an abnormal current. Various fuse constructions have been proposed in the past for providing such an externally visible indication of fuse operation. One general type of fuse construction employs a spring biased member which is normally restrained from movement by one or more fusible elements disposed inside an associated casing such as disclosed in U.S. Pats. 2,306,153; 2,320,494; 2,417,268; 2,435,844; 3,134,874 and 3,179,774. Another type of fuse construction employs a gas evolving material or explosive material which is heated or ignited to apply pressure to or to actuate an indicating member when a fuse operates such as disclosed in U.S. Pats. 2,188,816 and 2,435,844. A disadvantage of these known fuse structures for indicating the operation of the fuse is that they may operate prematurely if the spring fails or if the explosive material where provided ignites accidently for some reason other than the operation of the fuse.

SUMMARY OF THE INVENTION In accordance with the invention, a fuse structure includes an electrically insulating casing with spaced terminal means disposed thereon. An electrically conducting means including a fusible element is disposed in the casing and is electrically connected between the associated terminal means. An end cap or ferrule having an opening therein is mounted at one end of the casing. A generally tubular, electrically insulating housing is mounted at the same end of the casing as the last-mentioned end cap with one end of the insulating housing extending around the opening in the associated end cap. A flexible disc member is disposed to close the opening in the end cap and to normally project axially inwardly from the associated opening. A fuse wire having a relatively higher electrical resistance than the fusible element is also connected between the spaced terminal means with a portion of the fuse wire passing through the insulating housing. The insulating housing is substantially closed at the end of said housing away from the opening in the associated end cap and is substantially filled with a material, such as perlite, whose volume expands to several times its original volume when said fusible element and said fuse wire melt or fuse during the operation of the overall fuse structure and said material is heated to a predetermined temperature to thereby actuate the associated disc member to project axially outwardly with respect to the opening in the end cap. After being heated to the predetermined temperature, the material in the insulating housing remains in the expanded condition independent of temperature to thereby maintain the associated disc member in the outwardly projecting position. Where desired, the fusible element and the fuse wire outside of the associated insulating housing may be surrounded with an arc quenching material.

It is therefore an object of this invention to provide a fuse structure including improved means for indicating or responding to the operation of the fuse structure.

BRIEF DESCRIPTION OF THE DRAWING Other objects of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawing in which the single figure is a view, partly in side elevation and partly in section, of a fuse structure embodying the principal features of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, there is shown a fuse structure 10 which is of the current limiting type, as illustrated, and which is of the general type which is described in greater detail in U.S. Pat. No. 3,134,874 which issued to me on May 26, 1964, and which is assigned to the same assignee as the present application. The fuse structure 10 includes a generally tubular, electrically insulating casing or fuse holder 32 which is formed from an electrically insulating material having suflicient structural strength to withstand the gas pressure which may result during the operation of the fuse structure 10, such as a glass-melamine material. The fuse structure 10 also includes a pair of end caps or ferrules 42 and 44 which are disposed to extend axially over the ends of the casing 32 and which are firmly secured to the ends of the casing 32 by suitable means, such as a bonding material, which cements the end caps 42 and 44 to the casing 32 with the ends of the casing 32 being effectively sealed to said end caps. The end caps 42 and 44 are formed from an electrically conducting material, such as copper, which is silver-plated over the outer surfaces thereof.

In order to extinguish the arc currents which result during an interrupting operation of the fuse structure 10, the fuse structure 10 includes an arc extinguishing means which is disposed inside the casing 32. The are extinguishing means disposed inside the casing 32 includes a generally tubular rod or spacer member 52 which extends axially inside the casing 32 for a substantial portion of the length of said casing. The spacer member 52 is formed from a suitable electrically insulating material, such as a ceramic material, with the opposite ends of the spacer member 52 being of a reduced cross-section or size as indicated at 52A and 52B. The ends 52A and 52B of the spacer member 52 are adapted to project axially into the central openings provided in the associated terminal members 62 and 64, respectively, and to bear against said terminal members which are disposed adjacent to the opposite ends of the casing 32. The terminal members 62' and 64 are formed from an electrically conducting material, such as copper, and, as illustrated, are formed in the shape of discs which are of sufiicient diameter or size to extend transversely substantially across the interior of the casing 32. The spacer member 52 may be secured to the terminal members 62 and 64 by suitable means, such as a bonding material.

In order to provide an electrically conducting path between the terminal members 62 and 64 and the adjacent end caps 42 and 44, respectively, and to assistant in structurally supporting said terminal members, a plurality of spaced, electrically conducting stud members 82 and 92, respectively, may be disposed between each of said terminal members and the adjacent end cap. More specifically, the conducting studs 82 may be secured to the terminal member 62 by passing the lower ends of the studs 82 through openings provided in the terminal member 62 and then connecting the lower ends of said studs to the terminal members 62 by a mechanical spin-press fit. The ends of the studs 82 may also be brazed or soldered to the terminal member 62. The upper ends of the studs 82 may be similarly secured to the end cap 42 by first passing the upper ends of said studs through openings provided in the end cap 42 and then by means of a mechanical spin-press fit which may then be brazed r soldered.

In order to normally provide an electrically conducting path between the terminal members 62 and 64, one or more fusible elements or links 50 are disposed to extend axially between and to electrically and structurally connect said terminal members as indicated in the drawing. As described in greater detail in US. Pat. No. 3,134,874 previously mentioned, each of the terminal members 62 and 64 may be provided at its outer periphery with a plurality of radially extending angularly spaced slots (not shown) with each said slots being substantially aligned with a corresponding slot in the opposite terminal member. The opposite ends of each fusible element 50 extend or pass through a pair of corresponding aligned slots in the terminal members 62 and 64 and may be bent over at the opposite ends which may then be brazed or soldered to the electrically conducting terminal members 62 and 64.

As illustrated, each fusible element 50 is ribbon-like in shape and is composed of a suitable fusible material, such as silver. Each of the fusible elements 50 includes a plurality of axially spaced points of reduced cross-sectional area which may be formed by V-notching the ribbon material from which the fusible element is formed on both sides at spaced points along its length which result in a series of restricted areas which fuse during an interrupting operation of the fuse structure to provide a series of spaced arcs, the sum of the voltages across said arcs resulting in a relatively high total arc voltage during the operation of the fuse structure 10. By way of example, the silver ribbon fusible element 50 may be one-quarter inch wide by .005 inch thick and provided with V-notches each having an included angle of about 36 at one-quarter inch intervals along its length. It will be understood that the length of each of the fusible elements 50 varies with the voltage of the system in which the fuse structure 10 is to be utilized.

In order to distribute and limit the mechanical stresses on each of the fusible elements 50 which would otherwise result during long periods of service due to changing load conditions to which the fuse structure 10 might be subjected, each of the fusible elements 50 may be prebent at a plurality of axially spaced points along its length which results in a zig-zag configuration as described in greater detail in US. Pat. No. 3,134,874, previously mentioned.

In order to assist in arc extinction during an interrupting operation of the fuse structure 10, the balance of the space inside the casing 32, except for the insulating housing 76 which forms part of the indicating means which will be described hereinafter, may be substantially filled with an arc quenching filler, as indicated at 72, such as a high-purity silica sand with the space inside the spacer member 52 also being substantially filled with the same are quenching filler where desired. Other arc quenching fillers such as calcium carbonate may be combined with silica sand in a particular application, as described in detail in US. Pat. 3,213,242 which issued to me Oct. 19, 1965 and which is assigned to same assignee as the present application.

In order to provide an indication of the operation of the fuse structure 10 which is visible externally of the fuse structure 10, the indicating means 20 is disposed adjacent to the lower end of the casing 32 as shown in the drawing. The indicating means 20 comprises a generally tubular, electrically insulating housing 76 which may be formed from the same electrically insulating material previously mentioned in connection with the casing 32. The upper end of the housing 76 as viewed in the drawing includes a portion of reduced cross section which projects axially into the same opening as the lower end of the spacer member 52 and with the shoulder thus formed bearing against the terminal member 64 as shown in the drawing. The housing 76 extends axially away from the terminal member 64 with the lower end of the housing 76 hearing against the end cap 44 and extending around an opening 44A provided in the end cap 44. The opening 44A in the end cap 44 is closed by a metallic disc member 86 which is disposed inside the lower end of the housing 76 as shown in the drawing and includes a flange portion 86A at its outer periphery which bears against a turned in portion of the end cap 44 around the opening 44A. The disc member 86 also includes a flexible central portion or diaphragm portion, as indicated at 86B, which normally projects axially inwardly from the opening 44A and away from the lower end of the casing 32 or the lower end of the end cap 44. It is to be noted that the disc member 86 is relatively thin and is formed from a suitable metallic material such as copper. In other words, the central portion of the disc member 86 is normally concave in form as shown in solid lines in the drawing.

In order to actuate the operation of the indicating means 20 as will be explained hereinafter, an auxiliary fuse wire is electrically and structurally connected between the terminal members 62 and 64 as shown in the drawing with at least a portion of the fuse wire 60 passing through the insulating housing 76 through an opening 76A provided at the upper end of the housing 76. The fuse wire 60 is formed from a fusible material such as a nickelchromium alloy having a relatively high electrical resistance compared with the electrical resistance of the fusible elements 50. The balance of the opening 76A through which the fuse wire 60 passes into the housing 76 is substantially closed off by a plug member 74 which is also formed from electrically insulating material and which assists in retaining the fuse wire 60 in its proper operating position, as shown in the drawing. The portion of the fuse wire 60 which is disposed inside the housing 76 is preferably coiled for one or more turns as indicated at 60A to increase the effective length of the fuse wire 60 which is disposed inside the housing 76. The upper end of the fuse wire 60 may be secured to the terminal member 62 or to the conducting stud '82 by suitable means, such as wrapping one or more turns of the fuse wire 60 around the con ducting stud 82 while the lower end of the fuse wire 60 may be retained or clamped in engagement with the lower terminal member 64 as shown in the drawing between the terminal member 64 and the upper end of the insulating housing 76.

In order to actuate the movement or deformation of the disc member 86 from the normally axially inwardly projecting position shown in the drawing in solid lines to an outwardly projecting position, as indicated in phantom at '86 in the drawing, upon the operation of the fuse structure 10, the insulating housing 76 is substantially filled with a material as indicated at 100 in granular or powder form whose volume increases at least several times its original volume when the material 100 is heated to a predetermined temperature and remains in the expanded state after the temperature is increased to the predetermined temperature independent of the temperature of the material 100, such as the material perlite. Perlite is a naturally occurring siliceous volcanic glassy rock which usually contains to silicon dioxide (SiO 10 to 20% aluminum oxide (A1 0 2 to 5% water (H 0), and smaller amounts of soda, potash and J lime. When perlite is heated to a suitable point or temperature in its softening range, perlite expands to form a light fluffy material having a volume of the order of or about four to twenty times its original volume.

In the operation of the fuse structure 10, it is to be noted that normally the fuse wire 60 carries a negligible amount of current due to the relatively high electrical resistance of the fuse wire =60 compared with each of the fusible elements 50. Upon the occurrence of a predeter mined overload condition, the electrical current through the main fusible element 50 will cause each of the fusible elements 50 to fuse or melt and the electrical current which is normally carried by one or more of the fusible elements 50 will then temporarily transfer to the fuse wire 60 which is electrically connected in parallel with each of the fusible element 50 between the terminal members 62 and 64. The electrical current which is transferred to the fuse wire 60 will produce significant heating of the fuse wire 60 due to the relatively high electrical resistance of the fuse wire 60. The fuse wire 60 will then melt and vaporize and the electrical current which is momentarily carried by the fuse wire 60 will be returned to the main fusible elements 50 where the electrical current will be finally interrupted as described in detail in US. Pat. No. 3,134,874 previously mentioned. During the time interval that the electrical current is carried by the fuse wire 60 during an interrupting operation of the fuse structure 10, electrical energy transferred to the fuse wire 60 will be proportional to the product (exixt) of the instantaneous voltage (e) across the are which develops between the melted ends of the fuse wire 60 times the instantaneous current (i) times the time (t) during which the fuse wire 60 carries the electrical current during an interrupting operation. The energy which is developed in the confined volume or space of the housing 76 will be suflicient to heat a significant portion of the perlite or a similar material contained therein to the predetermined temperature at which the material 100 expands to at least several times its original volume to thereby actuate the disc member 86 from the inwardly projecting concave position shown in solid lines in the drawing to the convex position indicated in phantom at 86 in the drawing.

The change in position of the disc member 86 from the normal concave position shown in the drawing to the convex position of said disc member in which the disc member projects axially outwardly from the opening 44A in the end cap 44 will provide a visible indication that the fuse structure has operated to interrupt an overload current. The change in position of the disc member 86 may also be employed to actuate the operation of associated electrical equipment such as the dropout operation of a fuse cutout or the tripping operation of an associated circuit breaker. It is important to note that the material 100 after expanding to a relatively larger volume which is at least several times its original volume remains in its expanded condition independent of the subsequent cooling of the fuse wire 60 and a decrease in the temperature inside the housing 76 to maintain the disc member 86 in the outwardly projecting position indicated in' phantom 86' in the drawing.

It is to be understood that the teachings of the applicants invention may be applied to a fuse structure in which the disc member 86 is modified to be a bimetallic disc member which is formed from suitable materials, such as copper and nickel, and which when heated is actuated to change positions with a snap action. In such a modified construction, the heating of the material 100 would serve to actuate the snap action of the bimetallic disc member and the expanded volume of the material 100 would serve to maintain such a bimetallic disc member in the position to which the bimetallic member would be actuated by the heating of the material 100.

It is also to be understood that the teachings of the applicants invention may be applied to a fuse construction in which the fuse wire which actuates the operation of the indicating means 20 may be the only fusible element in such a modified fuse structure rather than having additional fusible elements such as the fusible elements 50 which are electrically connected in parallel with the fuse wire 60 as disclosed.

The apparatus embodying the teachings of this invention has several advantages. For example, an improved indicating means is disclosed for a fuse structure which will not be subject to premature or false operation due to either the failure of a biasing spring or due to the premature igniting of an explosive material. In addition, an improved indicating means for a fuse structure as disclosed readily lends itself to a totally enclosed or hermetically sealed fuse construction with the disc member as disclosed serving to maintain the overall fuse structure in a totally enclosed condition both before and after the disc member is actuated by an interrupting operation of the overall fuse structure. Finally, it is important to note that a filler material such as perlite serves in the applicants construction to both actuate the operation of an indicating means and to maintain the indicating means in the final operating position to which the disc member 86 is actuated independently of heating or temperature conditions following the operation of the indicating means.

Since numerous changes may be made in the abovedescribed apparatus and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all the matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A fuse comprising a tubular electrically insulating casing, terminal means disposed adjacent to each end of the casing, electrically conducting means including a fusible element in the casing connected between said terminal means, an end cap having an opening therein disposed at one end of said casing, a tubular insulating housing mounted at said one end of said casing with one end of said housing extending around said opening, a flexible disc member disposed to close said opening and to normally project axially inwardly from said end of said casing, a fuse wire of relatively higher resistance than said fusible element connected between said terminals and having a portion passing through said housing, and means substantially filling said housing whose volume expands at least several times its original volume when said fusible element and said fuse wire fuse and said means is heated to a predetermined temperature, said means remaining in an expanded condition independent of temperature after being heated to said predetermined temperature to thereby actuate said disc member during the expansion of said means to project outwardly from said opening and to maintain said disc member in the outwardly projecting position.-

2. The combination as claimed in claim 1 wherein the last-mentioned means is predominantly perlite material.

3. The combination as claimed in claim 1 wherein said fusible element and the portion of said fuse wire outside said housing are surrounded by are quenching material.

4. The combination as claimed in claim 1 wherein a second end cap is disposed at the other end of said casing to substantially close off said other end of said casing.

5. The combination as claimed in claim 1 wherein the end of said insulating housing away from the opening in said end cap is substantially closed.

6. The combination as claimed in claim 1 wherein said disc member includes an outer flange portion and a central diaphragm portion which normally projects axially inwardly from said opening in said end cap.

7. The combination as claimed in claim 2 wherein said fusible element and the portion of said fuse wire outside said housing are surrounded by an arc quenching material.

(References on following page) References Cited UNITED STATES PATENTS Lindell 337-241 X Reynolds 337320 X Fahnoe 337243 Cameron 337-159 8 2,694,415 11/1954 Dillon 92-101 3,390,365 6/1968 Lindberg 337--320 X H. B. GILSON, Primary Examiner US. Cl. X.R. 337244, 320

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