US2392703A - High voltage fuse - Google Patents

Description

Jan. 8, 1946. o. R. SCHURIG HIGH VOLTAGE FUSE Filed March 11, 1943 3 Flu/5M5 l5 ELEMENT Inventor: Otto R. Schurig, y W 5! Y H if M |I|..k l 41] V V u H m i is Attor' neg.

Patented Jan. 1946 HIGH VOLTAGE FUSE Otto R. Schnrig, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application March 11, 1943, Serial No. 478,785

2 Claims.

My invention relates to high voltage fuses, and more particularly, to high voltage fuses of the current limiting type.

The current limiting fuse functions by dissipation of'the fusible element throughout a fusible section of considerable length, as distinguished from dissipation only at a point of reduced cross section, upon subjection of the fuse to excess currents of large magnitude. If the diameter of the fuse wires is increased for applications where transient high currents must be passed without damage to the fusible elements, then of course, the magnitude of the current at which melting of the fusible element occurs is greatly increased. To afford protection under sustained overload current conditions whichjwould otherwise not be sufficient to cause substantially instant fusing of the fusible element and yet permit the passage without damage to the fusible elements of transient overloads, other means must be provided.

It is an object of my invention to provide a new and improved current limiting fuse.

It is another object of my invention to provide a new and improved current limiting fuse which may be constructed for use at higher current ranges than was heretofore thought possible and which furthermore will give complete protection on sustained overcurrents which would otherwise be insufficient to cause fusing of the fusible element.

Further objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of my invention reference may be had to the accompanying drawing inwhich Fig. 1 is a view partly in section of a current limiting fuse embodying my invention; Fig. 2 is an enlarged view of a portion of the fusible element of the fuse of Fig. 1; Fig. 3 is a perspective view of a portion of Fig. 2 to illustrate a modification of my invention; Fig. 4 is a view similar to Fig. 3 illustrating still another modification of my invention; and Fig. 5 is a sectional view of a portion of a modification of the fuse of Fig. 1 to which my invention is applied.

Referring now to the drawing, I have disclosed a tubular enclosing casing I 0 which is constructed of glass, porcelain, or other suitable insulating material. Metallic terminal ferrules II are secured respectively on thebpposite ends of the casing by means of any suitable form of seal not shown. If the casing I0 is glass, 9. suitable glassto-metal seal will be provided. Within casing l0 there is suitably mounted anelongated'insulating support or core l2, composed of a high heatresisting ceramic or other suitable material. Core 12, which extends longitudinally in casing III, is

of generally star-shaped construction in that it has a plurality of longitudinally exte ding fins,

though the illustrated core 12 has four such fins, a core having more than four fins may be employed depending upon the rating and size of the particular fuse.

Core I2 serves to support a circuit interrupting element or conductor, generally indicated at It which in accordance with my invention comprises a plurality of serially arranged portions. The major portion of the conductor ll comprises one or more parallel arranged fusible wires, or elements l5, which are constructed of a material such as silver and which are adapted to dissipate throughout a fusible section of considerable length as distinguished from dissipation only at a point of reduced cross section upon subjection of the conductor H to excess current of large magnitude. It should be understood, however, that the above statement does not require instant dissipation throughout the entire length of wires it, but such wires may be constructed in accordance with the teachings of United States Letters Patent 2,157,907Lohausen, granted May 9, 1939, and assigned to the same assignee as the present application.

Although we have shown two parallel wires, or fusible members IS in Fig. 1, it should be understood that more than two such wires may be employed, or only a single such wire as indicated in Fig. 5 may be employed depending upon the current rating of the fuse. The reason for using one or more fusible wires such as I5, is that it has been found that most effective current limiting action is produced when conductors of very thin cross section are employed. Hence where the current rating demands a relatively large cross section, it is desirable to divide this total cross section into a number of parallel conductors having a thin cross section such as a plurality of fine silver or zinc wires.

L In order to obtain operation of the fuse of .Fig. 1, on currents which will not cause melting of the fusible wires i5, I provide one or more thermal storage bodies such as are indicated at It which may be formed of copper or the like. As is best indicated in Fig. 2, the wires l 5 maybe inserted in recesses or cavities I! each of which is filled with a fusible conducting material such as is indicated at I8, preferably comprising a low melting point solder of some sort, such as lead or tin, or alloys thereof. Although in Figs. 1 and 2 two thermal storage bodies It have been indicated, it should be understood that only one of these thermal storage bodies may be used if desired. Upon moderate overload currents, the wires l5 will begin to heat up and part of this heat will be dissipated or absorbed by thermal storage body It. When this heat is suflicient to melt the fusible material It, an arc will be initiated be ween wires l5 and body it, and interruption of the circuit will occur after a time lag depending upon the magnitude of the overcurrent.

In Order to improve the operation, I preferably provide a resistor portion is interconnecting thermal storage body it as indicated in Figs. 1 and 2. This resistor portion acts as a heater to control the time current characteristic of the fuse link on moderate overload currents. As illustrated in Fig. 2 the resistor or heater section is may be fastened to thermal storage body II by crimping, as generally indicated at 20. It should be understood, however, that if desired, resistor section is may be fastened to thermal storage body IS in the same manner that fuse wires I! are fastened thereto.

The conductor H, including the portions l5, l8 and i9, is serially wound on core l2 and the interior of easing I is filled with a granular inert arc-quenching material 2! such as fused quartz, or sand. By using a star-shaped core l2 as indicated in Fig. 1 the conductor l4 touches the core only at spaced points so that the maximum length thereof is exposed to the inert granular filler material indicated at 2|. spirally winding the interrupting element on core l2 permits the installation of an element of relatively great length in a casing ill of practical dimensions.

Instead of providing recesses i! in thermal storage body IS, the fuse wires I! may be fastened thereto merely by a bead of solder such as indicated at 22 in Fig. 3, thereby providing separation of the wires l5 from the thermal storage mass it. Also, if desired, the heater or resistor l9 may be fastened to thermal storage mass l6 by a bead 23 of low melting point solder.

Under certain conditions, it may not be necessary to use a low melting point solder and both the wires I5 and the heater or resistor portion is can be fastened to thermal storage body l6 as by crimping, indicated at 20 in Fig. 4.

In Fig. 5 I have shown my invention as applied to a current limiting fuse of the type disclosed in the copending joint application of George R. Serfilng and Carl L. schuck, Serial No. 410,382, filed September 11, 1941, now Patent 2,337,937, and assigned to the same assignee as the present application. In current limiting fuses of the type disclosed and claimed in that copending application, no supporting core for the conductor is provided. As illustrated in Fig.5, this fuse comprises a casing 24 filled with an inert granular arc-extinguishing material 25. A fusible element generally indicated at 26 comprises a major portion of relatively fine zinc or silver wire 21 which is serially arranged with thermal storage bodies 28 interconnected by a heater or resistor section 29.

In the constructions described above the joints between wires l5 or resistor portion is and thermal storage body ii are designed to fuse at a substantially lower temperature than the wires 15. Upon applying an overload current to the fuse illustrated in Fig. 1 which current is in the neighborhood of two or three times the rated current of the current limiting fuse, each of the fuse wires l5 adjacent to the joint with the thermal storage body (8 raises the temperature of the joint, the mass of the member l6 providing the desired time lag in the heating of the joint. When the melting temperature of the fusible portions l8 of Fig. 2, or 22 or 23 of Fig. 3 is reached, separation of portions of conductor l4 occurs, initiating the interruption of the current flowing therethrough. Only a single thermal storage body IS without heater section I 9 may be employed, but by arranging the thermal storage bodies in pairs separated-by a short length of heater wire or resistor wire, the time lag characteristic may be further increased. In the arrangement disclosed in Fig. 1 the fusible joints are heated in part by the fuse wiresand in part by the resistance wire which joins the two heat storage bodies.

when short circuit currents are applied to the fuse embodying my invention, that is, currents in excess of the magnitudes ordinarily encountered in overloads or transient inrush currents, the fuse wires i5 dissipate substantially instantly to produce a high current limiting action.

While I have disclosed certain particular embodiments of my invention, it will be apparent to those skilled in the art that my invention is not limited to the particular constructions shown, but that changes and modifications can be made without departing from the spirit and scope of my invention, and I therefore aim in the appended claims to cover all such changes and modifications.

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

1. In a high voltage fuse of the current limiting type, a casing, a pair of terminals one associated with each end of said casing, an inert granular arc-extinguishing material in said casing, and a conductor embedded in said arc-extinguishing material interconnecting said terminals comprising three serially connected portions including a first portion adapted to dissipate throughout a fusible section of considerable length as distinguished from dissipation only at a point of reduced cross section upon subjection of said conductor to excess current of large magnitude, a non-fusible thermal storage body of substantial mass connected to said first portion and a third portion connected to said body by means of low melting point solder including a short rod of resistance material for heating said solder and melting the same to interrupt the circuit upon moderate overcurrents which would not cause melting of said first portion, said serially connected portions being arranged so that current flowing through said high voltage fuse also flows through said solder.

2. In a high voltage fuse of the current limiting type, a casing, a pair of terminals one associated with each end of said owing, a star-shaped insulating support mounted in said casing, an inert granular arc-extinguishing material surrounding said support and a conductor spirally wound on said support interconnecting said terminals comprising a plurality of serially connected portions including a first portion adaptedto dissipate throughout a fusible section of considerable length as distinguished from dissipation only at a point of reduced cross section upon subjection of said conductor to excess current of large magnitude, a pair of separated thermal storage bodies of substantial mass at least one of which is connected to said first portion, a third portion connected between said bodies, and means comprising a low melting point solder for uniting at least some of said portions, said third portion including a short length of resistance material for heating said solder and melting the same to interrupt the circuit upon moderate overcurrents which would not cause melting of said first portion, said serially connected portions being arranged so that current flowing through said high voltage fuse also flows through said solder.

O'I'IQ R. SCHURIG.

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