US2143038A - Fuse - Google Patents

Description

Patented J an. 10, 1939 UNITED STATES PATENT OFFICE FUSE Sidney R. Smith, In, honor, Mass assignor to General Electric Company, a corporation of New York Application May 25, 1937, Serial No. 144,852

SCIaims.

use in relatively high voltage electric circuits in conjunction with apparatus such as capacitors and generators. although not necessarily limited to such use.

Another object of the invention is the provision of an improved fuse which not only is of high current interrupting capacity but which also is capable of interrupting satisfactorily the flow of current over a wide range of power faults including a relatively low current overload.

A further obiect of the invention is the provision of an improved fuse having the characteristics above set forth and which in addition is capable of limiting the magnitude and duration of short-circuit current flow where the available short-circuit current is of an extremely high order.

For certain protective applications, there have been employed in the pest enclosed fuses incormrating only a gas-producing filler material. Such a fuse, of improved design, is disclosed in my copending application Serial No. 144,651, filed May 25, 1937, and assigned to the assignee of the present invention. Fuses of this time, when properly constructed, have been found to meet the requirements of a broad field of protective applications and have been found to operate reliably and satisfactorily over a wide range of power faults from a low cin'rent overload just sumcient to melt the fusible element up to relatively high current overloads. However, special applications arise where there may be encountered also short-circuit currents of an extremely high order and it has been found that the fuses employing solely a gas-producing material do not prove satisfactory for such applications in that they either fail entirely to interrupt the extremely high short-circuit currents or interrupt the current fiow only with attendant undesirable disturbances and possible rupture of the fuse casing. Hence, for such special applications where currents of an extremely high order may be encountered, there have been employed enclosed fuses which incorporate a finely divided inert filling material such as sand, pulverized quartz and the like. Fuses of this latter type are capable of interrupting very satisfactorily short-circuit currents of large magnitude, but it has been found that these fuses do not operate positively or fail entirely to interrupt the current fiow in cases of overloads of a low magnitude unless costly and critical design expedients are employed. Attempts have been made to connect fuses filled with inert material in series with fuses filled with gas-producing material in order to secure the advantages of both types and eliminate the disadvantages of each. However, with such arrangements as heretofore employed, there have been encountered pronounced disadvantages among which are excessive dimensions with re- 10 sultant unwieldiness, inconvenience, and costliness of design.

It is therefore a further and more specific object of the present invention to provide an improved fuse which is of compact and unitary con- 15 struction and which embodies both a gas-producing filler material and an inert filler material in such a manner as to secure in a single fuse device the advantageous characteristics of both types of fuse referred to above.

20 For an understanding of other objects and of that which I believe to be novel and my invention, attention is directed to the following detailed description and the claims appended thereto taken in conjunction with the accompanying drawing 25 in which Fig. 1 illustrates in longitudinal section an exemplary embodiment of my invention and Fig. 2 shows a transverse cross-section taken along line 2-2 of Fig. 1.

The fuse illustrated incorporates an improved 30 multiple tube arrangement and construction such as disclosed in my previously referred to application and which I have found to be particularly well suited to the practice of the present invention, although, as will become apparent from the ensuing description, other multiple tube or multiple compartment arrangements and constructions also may be employed in the carrying out of the invention. By reference to the drawing, it will be seen that the illustrated fuse has 40 an elongated tubular enclosing casing ill within which are disposed three open-ended inner tubes II, II, and il, extending longitudinally of the casing. More than three inner tubes may be employed if desired and the inner tubes as well as the outer casing may be constructed either of fibrous insulating material, as illustrated, or of other suitable insulating material, such as glass.

On the opposite ends of casing iii are mounted terminal caps l4 and i5 respectively which are and I8 respectively by means of which the fuse may be mounted in any commonly employed form of terminal clips (not shown). Openings are provided in the shoulder portions of the terminal caps adjacent the bases of the mounting bosses for venting the interior of the fuse casing, and disks 2| of porous material are placed between the ends of the inner tubes and the terminal caps to prevent escape of filling material from the fuse while providing for the escape of gases through openings 20, as will be discussed more fully hereinafter.

A fusible conducting element 22, which may comprise either a single conductor or a plurality of conductors connected in series to form a continuous element, is threaded back and forth successively through the inner tubes ll, l2, and E3. The opposite ends of the fusible conductor have portions which are bent out around the edges of the disks 2| respectively at the opposite ends of the casing, as indicated at 23, and'the extreme ends of the conductor are then brought out through vent openings 20 in the opposite terminal caps and fastened in any suitable manner, as for example by soldering, to the outside surfaces of the terminal caps, as indicated at 24. Thus the fusible conducting element is electrically connected between the two terminal caps.

As will be seen from the drawing, the conductor passes from tube II to tube I2 through openings located in the walls of these two tubes at substantial distances from the ends of the tubes which are adjacent terminal cap I, while the conductor passes from tube l2 to tube l3 through openings 25 located in the side walls of these latter two tubes at substantial distances from the ends of the tubes which are adjacent terminal cap I5. Thus, as more fully pointed out in my copending application previously referred to, it is rendered impossible for short-circuiting arcs to strike, upon fuse operation, between courses of the conductor lying in different ones of the tubes or between any portion of the conductor and the terminal caps H and IS with resultant short-circuiting or loss of efiect of a portion of the conductor.

In the practice of the present invention, tubes II and I2 are filled with finely divided inert arcquenching material A, such as sand, pulverized quartz, or the like, while tube I3 is filled with a gas-producing arc-quenching material B such as a calcium or boric acid compound. In order to insure proper venting of tube I3, which is filled with the gas-producing material, there are provided vent openings 21 in the walls of that portion of tube l3 which is not traversed by the fusible conductor. Also, with the gas-producing material in tube' l3, it is necessary to locate the openings 26 at a certain minimum distance from the ends of tube l3 adjacent terminal cap E5 in order to insure that gases discharged out the end of this tube will not cause short-circuiting arc-over between terminal cap l5 and the portion of the conductor which passes through openings 26. On the other hand, due to the fact that practically no gases will be discharged from the ends of tubes l l and I2, which are filled with inert material, the openings 25 through which the conductor passes intermediate tubes II and I2 may be located at a lesser distance, as illustrated, from the ends of the tubes adjacent terminal cap l4 without danger of short-circuiting arc-over between terminal cap l4 and the portion of the conductor passing through openings 25. Thus, it ts possible to utilize, with safety, a greater portion of the length of tubes H and i2.

The fuse is provided with an indicator of the type disclosed in the copending application of R. S. Bennett, Serial No. 144,660, filed May 25, 1937 and assigned to the assignee of the present invention, although other forms of indicating arrangements may be employed if desired. The illustrated indicator consists mainly of a spring operated plunger 30 disposed within cylindrical mounting boss I] on terminal cap l4 and arranged to be held normally retracted in a non-indicating position by means of a strain wire 3| which extends in substantially parallel relation with the portion of the fusible conductor which is embedded in the gas-producing material in tube l3. Plunger 30 is arranged to be operated outwardly through an opening 32 in the end of mounting boss I! by means of a spring 33 which acts between disk 2| and a shoulder 34 carried by the plunger. Any bright color may be applied to the plunger to make it more readily observable when it projects through opening 32 beyond the end of mounting boss II. The outer end of strain wire 3| is fastened in an opening 35 in the base of the plunger while the inner end of the strain wire extends through the same opening 26 in tube l3 through which the fusible conductor extends and is anchored directly to tube l3 by passing the end of the wire through a pair of openings 36 in tube l3 and tieing the same. Thus, the fusible conduc tor itself is entirely relieved of any strain such as would be imposed by spring 33 if the inner end of the strain wire were anchored directly to the conductor. However, due to the arrangement described, the strain wire is in such contiguity to the conductor that, upon rupture of the conductor due to current overload, electrical connection of the strain wire in the circuit is effected either through contact of the strain wire with a remaining end of the fusible conductor or by means of an arc drawn between the strain wire and the remaining end of the ruptured conductor. The outer end of the strain wire is electrically connected with terminal cap H by means of spring 33 or in any other suitable manner. In order to insure rupturing of the section of the fusible conductor which extends through tube l3, provision is made for a so-called hot spot at some point in this section. This may be accomplished by a reduction in cross-section of the conductor, as by means of a small hole positioned as indicated at 31 in the drawing.

In protective service of the type for which the present fuse is particularly designed, it is desirable, as pointed out hereinbefore, that the fuse be capable of interrupting satisfactorily the current flow over a wide range of power faults from one involving only a small current overload just suflicient to cause fusion of the fusible conductor up to a short-circuit which may involve a current flow of an extremely large magnitude. With a fuse constructed in accordance with the present invention, upon occurrence of a short circuit resulting in a current fiow of large magnitude, substantially the whole length of the fusible conductor heats rapidly and volatilizes, while the portion of the conductor embedded iii the inert material in tubes II and I2 operates to interrupt the current fiow. From tests made upon fuses employing inert filler material, it appears that the action of the inert material filled portion of the fuse of the present invention is as follows: Upon volatilization of the conductor and the establishment of an are along the path formerly occupied thereby, the heat of the arc causes fusion of the immediately surrounding body of inert filler which, as previously pointed out, comprises sand, pulverized quartz, or the like, resulting in the formation of a cylindrical core of fused material which is partially conducting. The current fiow immediately transfers from the arc path to this partially conducting core which causes a dying-out of the arc and a resultant lessening of the heat produced thereby. Due to the proximity of the surrounding filler material, the core cools very rapidly and as it does so, its resistance increases rapidly to a value such that the core again becomes an insulator upon solidification. This effectively interrupts the current flow. Also, at ,the instant volatilization of the fusible conductor occurs, the metallic vapors caused by volatilization of the conductor are dispersed through the inert filler and condense on the particles thereof toward the outer region of the fused core in such a manner as to be substantially non-conducting. These actions take place in an extremely short time so that the current does not attain a value more than a fraction of that corresponding to the short-circuit impedance of the circuit. The portion of the fusible conductor embedded in the gas-producing filler does only a portion, if any, of the circuit interruption at such high currents and due to the rapidity with which the inert material filled portion of the fuse operates, the gasproducing material filled portion of the fuse shows little gassing or distress of any kind.

Thus, it will be seen that the inert material filled portion of the fuse operates in an extremely satisfactory manner to interrupt a current flow of large magnitude. However, as previously indicated, fuses filled with inert material may not operate sufficiently positively or may fail entirely to interrupt the current flow upon low current overload. With a fuse constructed in accordance with the present invention, the portion of the fuse filled with gas-producing material operates to interrupt the current flow upon low current overload. Upon occurrence of such a low current overload, at least that section of the conductor lying within tube ll fuses and volatilizes with the formation of an are along the path formerly occupied thereby. The resultant fuse particles, as well as the heat and gases, are dissipated through and to some extent absorbed by the immediately surrounding filler material while the heat of the arc at the same time causes large amounts of gas to be driven off from the filler, resulting in an extreme turbulence which exerts a rapid cooling and disintegrating action on the arc, tending to extinguish the arc and interrupt the current flow. Moreover, as described more fully in my copending application previously referred to, there is created a forced movement of gases axially of the tube It and toward its open ends. The portions of these gases which are not completely absorbed by the filler material within tube I3 are discharged outwardly through the ends of this tube and also through the openings 21 in the side walls thereof and finally pass through the porous disks 2| and vent openings at the ends of the casing. This forced axial movement of the gases also contributes materially to the interruption of the arc and the current flow. Thus, the gas-producing material filled portion of the fuse of the present invention opcrates in a satisfactory manner tointerrupt a current overload of low magnitude which could not be interrupted satisfactorily by that pertion of the fuse which is filled with inert material. Also, the operation of the gas-producing filler portion of the fuse upon relatively low current overload is not attended by gassing or distress to an undesirable degree.

Upon the occurrence of fault currents in the range intermediate the relatively low overload currents and the extremely high short-circuit currents previously referred to, the two portions of the fuse function in the manners peculiar to their types of filler as previously described and share to a greater or less degree the interrupting duty so that the fuse of the present invention operates satisfactorily to interrupt the current fiow over an extremely wide range of power faults.

As previously pointed out, the section of the fusible conductor in tube It, which is embedded in the gas-producing material, fuses upon either high or low current overload. As a result, a portion of the current flow is transferred to strain wire 3|, either due to contact of the strain wire with a remaining end of the ruptured conductor or due to arc-over between the strain wire and such remaining end of the conductor, with the result that the strain wire is burned in two and releases the spring operated plunger 30. This plunger thereupon moves outwardly through the opening in the end of mounting boss H to give a readily observable indication of fuse operation.

It will be seen from the foregoing discussion that the present invention provides a simple and inexpensive fuse capable of easy assembly, which combines in a compact, unitary structure both a gas-producing arc-quenching material and an inert arc-quenching material so that efficient and reliable interruption of both low overload currents and short-circuit currents of an extremely large magnitude is insured. A further advantage of the construction described is that the inert filler and the gas-producing filler, though embodied in a single fuse requiring a minimum of space for installation, are physically separated so that no detrimental interaction may occur between the two different types of material, either before fuse operation or during fuse operation. Moreover, the fuse construction of the present invention permits sufficient length of fusible conductor in each of the filler materials to obtain the required voltage gradient and proper fuse operation upon, both low and high current overload without resorting to excessive dimensions or unwieldy and costly design expedients.

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

1. In a fuse device, an enclosing casing, conducting means in said casing including a fusible section, terminals for said conducting means, a body of relatively finely divided inert arc-quenching material embedding a substantial length of said fusible section located in one portion of said casing, a body of material capable of giving off arc-quenching medium upon subjection thereof to the heat of an are disposed in contiguity with another portion of said fusible section located in another portion of said casing, and means physically separating said bodies of material.

2. In a fuse device, an enclosing casing, means defining a plurality of separate compartments within said casing, conducting means having a fusible section in each of said compartments, terminals for said conducting means, a body of material capable of giving off arc-quenching medium upon subjection thereof to the heat of an arc, disposed in contiguity with the fusible section located in one of said compartments, and a body of relatively finely divided inert arc-quenching material embedding a substantial length of the fusible section located in another of said compa-rtments.

3. In a fuse device, an enclosing casing, means defining a plurality of separate compartments within said casing, conducting means having a fusible section in each of said compartments, terminals for said conducting means, a body of material capable of giving off arc-quenching medium upon subjection thereof to the heat of an arc, disposed in contiguity with the fusible section located in one of said compartments, and a body of sand embedding a substantial length of the fusible section located in another of said compartments.

4. In a fuse device, an enclosing casing, means defining a plurality of separate compartments within said casing, conducting means having a fusible section in each of said compartments, terminals for said conducting means, a body of material capable of giving ofi arc-quenching medium upon subjection thereof to the heat of an arc, disposed in contiguity with the fusible section located in one of said compartments, and a body of relatively finely divided quartz embedding a substantial length of the fusible section located in another of said compartments. 1

5. In a fuse device, an enclosing casing, means defining a plurality of separate compartments within said casing, conducting means having a fusible section extending in each of said conipartments, terminals for said conducting means, a bodyof relatively finely divided inert arcquenching material embedding a substantial length of fusible section in one of said compartments, means in contiguity with a fusible section located in another of said compartments capable of giving off arc-quenching gas upon subjection thereof to the heat of an arc, and vent means for the relief of gases from said last mentioned compartment.

6. In a fuse device, a casing, terminals carried thereby, means providing a plurality of compartaisaoee ments within said casing, a fusible conductor connected between said terminals and extending successively through said compartments, a body of gas-producing arc-quenching material embedding the portion of the conductor lying in at least one of said compartments, a body of relatively finely divided inert arc-quenching material embedding the portion of the conductor lying in other of said compartments, and means providing for the venting of gases from the compartment occupied by said gas-producing material.

7. In a fuse device, an elongated tubular casing having terminals at opposite ends thereof, a plurality of tubes disposed longitudinally and in parallel relationship within the casing, a fusible conductor connected between said terminals and extending successively through said tubes, gas-producing arc-quenching material disposed in contiguity with the portion of the fusible conductor extending through at least one of said tubes, said last mentioned tube having openings for the venting of gases therefrom, relatively finely divided inert arc-quenching material embedding the portion of said conductor extending through other of the tubes, and means providing openings at the ends of said casing for the venting of gases therefrom.

8. In a fuse device, an enclosing casing, a conductor in saidcasing having an elongated fusible section, terminals for said conductor, a body of relatively finely divided inert arc-quenching material embedding a substantial portion of the length of said fusible section, means in contiguity with another substantial portion of the length of said fusible section capable of giving off arcquenching medium uponsubjection thereof to the heat of an arc, means for insuring rupture of said last mentioned portion of said fusible section upon subjection thereof to excess current of relatively low magnitude, indicating means, and means for efiecting operation of said indicating means including an auxiliary conductor arranged so as to shunt only said last mentioned portion of the fusible section upon fuse operation.

, SIDNEY R. SMITH, JR.

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