US2050277A - Circuit breaker - Google Patents

Description

Aug. 11, 1936. H. J. CRABBS ET AL 2,050,277

CIRCUIT BREAKER Filed Aug. 15, 19:54

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ATTORN Patented Aug. 11, 1936 UNITED STATES PATENT OFFICE CIRCUIT BREAKER Herbert J. Crabbs and Herbert L. Rawlins, Wilkinsburg, Pa., assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 15, 1934, Serial No. 739,892

Claims.v (Cl. 200117) These devices take a multitude of forms, but

perhaps the best known, and certainly the most widely used, is the so-called expulsion fuse. Expulsion fuses fulfill a very definite mission in the 10 electric art, in that they constitute a means whereby protection, against abnormal circuit conditions, may be given to electrical apparatus at a very low cost. Their application is limited only because of the fact that they are inherently one operation device, and must be serviced after each operation.

During the circuit interrupting operation, the heat of the are which is established by the melting of the fusible link causes the evolution of large quantities of gas from the walls of the main fuse tube, and this gas, in venting, flows expulsively through the are, thereby effecting its extinguishment. The device is restored to an operative condition following each operation by replacing 5 the used fusible 'unit with a new one.

One of the most successful commercial forms of expulsion fuse devices comprises a tube, of fiber or other material which is capable of evolving arc extinguishing gas when placed in prox- 30 imity to an electric arc, conducting terminal members mounted at the ends of the tube, and a replaceable fusible unit disposed within the tube for connecting the terminals and for opening the electrical circuit therethrough upon the oo- 35 currence of predetermined overload conditions. One end of the tube isnormally closed and the other end is normally open. Upon the occur- 7 rence of an overload or other abnormal condition the fusible element melts and an arc is estab- 40 llshed within the fuse tube.

In the ordinary operation of these devices, they are called upon to interrupt overloads of widely varying magnitude, and, since the dimensions of the main tube must be sufficiently large to ac- 45 conimodate the largest magnitude are which may be established therein, some difiiculty has been experienced with the prior art devices in the interruption of low-current overloads. This dimculty has arisen because of the fact that the arcs 50 which are produced by low-magnitude overloads are of comparatively small cross sectional area, and thus do not 'cohtacitthe gas evolving walls of the'inain tube sufficiently intimately to produce an adequate amount of arc extinguishing The difficulty of satisfactorily interrupting lowcurrent magnitude arcs is further aggravated, where a simple link-type fusible unit is used because of the fact that only a small portion of the fusible element is melted by the overload, 5 and, since little gas is evolved, the remaining conducting portions of the fusible means are not expelled from the tube so as to draw a long are. The result is that on low current overloads only a short are is drawn and little gas is produced for 10 isfactory than the older devices. Upon the occurrence of large magnitude overloads, the operation is substantially the same as for the unbiased units. The heavy-magnitude overloads cause a 20 substantially instantaneous fusion of the fusible element with a resultant large evolution of gas in the walls of the fuse tube and the combined re sult is to expel the entire fuse means from the tube, thereby securing a long arc which is quickly extinguished by the out-flowing blast of gas. When the device is interrupting low-magnitude overloads, the action of the biasing springs is such as to secure a long arc immediately following the fusion of the fusible element, and the devices are so proportioned that this are is too long to be self-sustained whether or not the gas evolution is very large.

As a further improvement for very low-current operation, an auxiliary tube of insulating material having a cross-sectional area considerably less than that of the main tube is disposed about the fusible element proper. The walls of this tube are relatively weak and are practically immediately ruptured when a large-current-mag-p 40 nitude is drawn, but are capable of aiding very. considerably in the extinction of small-magnitude arcs by the provision of a suitably directed stream of arc extinguishing gas.

Certain difficulties have arisen in the utilization of spring biased fusible elements. Most of these devices have utilized a single tension spring which is stressed when the renewable fuse unit is installed within the main tube of the interrupter. Due to difference in the dimensions of the tubes and in the manner of servicing the devices, the amount of stress on the spring is a variable quantity and the calibration of the fusible element is thus rendered more or less uncertain. It would appear that the solution of this problem liesin when it is intended that that device should be used as refill units for fuse structures nowin existence. Different electrical manufacturers have utilized different sized terminals, tubes, and the like for their expulsion fuses. Practically all ex isting power systems utilize a number of different fuse structures, and to simplify the problem of maintenance and to reduce the cost of the stocks of replacement fuses which must be carried, it is highly desirable that the refill fuse unit be provided with suitable means for allowing the device to be utilized in any of the existing structures.

The principal object of our invention, therefore, is to provide an improved, universally applicable replacement fuse structure which shall be suitable for use in all existing types of expulsion fuse devices, and which shall be superior in its operating characteristics to the previously known devices.

Another object of our invention is to provide an improved fuse unit for expulsion fuses or simi- 'lar devices which shall be provided with two spring biased fusible element wherein the biasing force exerted by the spring on the fusible section is accurately adjusted to a fixed value during the manufacture of the fuse, in order to secure the maximum possible accuracy of calibration of the device.

A second further object of our invention is to provide a spring biased fusible element which shall utilize a compression spring for supplying a tensioning force to the fusible section of the element.

A still further object of our invention is to provide an improved terminal means for use with electric fuses generally, our improved means to permit a single fuse refill unit to be used with structures having fuse engaging means of differing dimensions, our improved terminal means to utilize no loose parts which might become lost and to be so arranged that a good electrical connection is assured at all times. I

These and other objects of our invention will be made more apparent from the following description of a preferred embodiment of our invention. Referring to the drawing:

Figure 1 is a sectional view, partially in elevation, of an expulsion fuse utilizing a refill unit which includes the principal features of our invention.

Fig. 2 is an enlarged sectional view, partially in elevation, of the refill unit forming a part of the fuse structure shown in Fig. 1.

Fig. 3 is a fragmentary elevation view showing the fusible sections of the refill unit illustrated in Fig. 2.

Fig. 4 is a developed plan view of the upper terminal of the refill unit shown in the other figures of the drawing.

Fig. 5 is an enlarged sectional view on the line V-V of Fig. 2.

- Fig. 6 is a fragmentary perspective view of the upper terminal portion of the refill element shown in Figs. 1 and 2, and

Fig. 7 is a developed plan view of a modified upper terminal member suitable for use with the refill unit illustrated in the other figures of the drawing.

The expulsion fuse structure which is shown in Fig. 1 includes a main tube ll of fiber or other suitable insulating material, which is threaded at its unit it in contact with the upper contact member 5. The refill unit itself is positioned within the main fuse tube l and is provided with a flexible conductor is for engaging the screw connection [15 which forms a part of the lower ferrule 3 in order to complete the electrical circuit through the device. The lower end of the fuse tube l is normally open in order to allow a free out-flow of the gas which is evolved from the walls of the main tube. during the circuit interrupting operation.

In order to obtain the greatest possible extension ofthe'operating range of the fuse, the refill unit is provided with two serially connected fusible elements, each of which will be described in some detail later. One of these elements is adapted to fuse substantially instantaneously upon the occurrence of heavy overloads or other similar circuit disturbances, and the other element is adapted to fuse after a time delay upon the occurrence of prolonged moderate overloads. This arrangement, while giving adequate protection to the connectedequipment, serves to minimize undesirable and annoying discontinuities in the flow of power throughthe system.

The upper terminal portion ll of the refill element 9, as is shown particularly in Figs. 2 and 4, comprises a fiat sheet of conducting material which is cut so as to form a plurality of cooperating circular sections l1, l8, l9 and 2|, which may be bent one over the other so as to define button or cap-type terminals of at least two different dimensions. The method of bendin this terminal portion H is shown particularly in Fig. 6, wherein the several elements have been bent to form the largest possible button or cap-type terminal for the refill element. If a cap portion having a smaller diameter is desired, the larger of the cooperating sections ll of the upper terminal member I I is bent back and forth a few times so as to cause it to be broken away from the remaining sections, thus leavinga. cap having the diameter of the section Hi. If it is desired to use the device in a device must be capable of accommodating itself to other structures.

By forming the entire terminal portion II from a single sheet of conducting material, all loose parts are eliminated, and one serious 0bjection to some of the prior art devices isovercome. Also, this arrangement assures a good electrical connection between the refill terminal and the refill itself, thus preventing high resistance contacts and their accompanying dangers.

The lower end of the shank portion 23 of the upper terminal member II is somewhat narrower than the main body of that portion and is adapted to extend into suitable slots 29 pro vided in the upper end of an auxiliary fuse tube 21 which forms apart of the refill unit. The lower edges 3| of the body portion 23 serve as shoulders for engaging the ends of the slots 29. 1

Two holes 33 are punched in the reduced section of the body portion 23 for allowing the pasing the manufacture of the refill unit to any desired value, for producing a tensioning force upon both of the fusible elements of the refill unit.

The resistance of .the member 45 is so proportioned that the heating produced by the prolonged flow therethrough of a predetermined current is capable of effecting the melting of the low melting point solder which serves to connect that member with the upper fusible element 31 and the terminal portion 41. When this occurs the biasing action of the spring 5| effects the opening of the electrical circuit through the refill unit at that point. The accurate tensioning 0f the fusible elements which is made possible by the utilization of a compression spring which is adjusted at the factory, assures accurate calibration and accurate maintaining of the calibration of both of the fusible elements.

sage of two rivets 35 which are adapted to electrically and mechanically connect the upper terminal 39 of the instantaneousfusible element 31 thereto. This fusible element 31 comprises a fiat strip of conducting material which, in addition to the enlarged terminal portion 39 for engaging the lower end of the upper terminal member, is provided with a portion 4| of reduced cross-sectional area, which is adapted to fuse substantially instantaneously upon the passage therethrough of predetermined magnitude currents, and a lower portion 43 which is adapted to be soldered by a low melting point solder to a flat.conducting member 45 of substantially the same cross sectional dimensions as the lower portion of the fusible element itself.

The member 45 is formed of a resistance material such as German silver or the like, and is soldered at its lower end, likewise by a low melting point solder, to a terminal strip 41, the lower end of which, in turn, is soldered by a high melting point solder to the upper end of the flexible conductor 3. The member 45 and the two associated soldered joints comprise the second fusible element.

The auxiliary fuse tube 21 is of suflicient length to enclose the-fusible portion 4| of the upper fusible element 31 and the two soldered connections'of the member 45 positioned beneath that element. At its lower end, the auxiliary fuse tube 21 is provided with a hollow cylindrical member 49, which may be of metal, for positioning the upper end of the compression spring 5|, the upper end of this spring being adapted to abut against the lower end of the auxiliary fuse tube 21 when the device is in the normal operative position. The lower end of the compression spring 5| engages a suitable funnel shaped member 53 which is rigidly soldered to the flexible conductor, in the position shown in Fig. 2, during the assembling of the device.

As mentioned previously, the shoulders 3| which form a part of the upper terminal member engage the lower ends of the slots 29 cut in the auxiliary fuse tube 21, and serve to-trans mit the reaction force of the compression spring 5| to the upper end of the upper fusible'portion 4| of the refill element. The biasing force of the 7 Upon the occurrence of a very heavy overload in the controlled circuit, the upper fusible element is melted at the portion 4|, substantially instantaneously, and the compression spring 5| is then free to move all of the conducting portions of the refill unit disposed beneath'the upper fusible portion out of the auxiliary fuse tube 21. The are drawing operation, following the occurrence of very heavy overload takes place, however, at extremely high speed, and simultaneously with the separation of the terminal portions 39 and 43 of the upper fusible element, which is effected by the biasing spring 5|, there is a large evolution of the gas from the auxiliary fuse tube 21 which may effect a rupture of the tube accompanied by an expanding of the are into the main fuse tube If the are energy is very large, the rate of gas evolution soon becomes sufficient to effect a very rapid expelling of the auxiliary fuse tube 29, the

spring 5|, and the flexible conducting member l3 from the lower open end of the main tube with the result that a long arc is established therewithin. This are contacts the walls of the tube and evolves a very considerable quantity of arc extinguishing gas which gas in venting flows expulsively through the open lower end of the fuse tube, thereby effecting the extinguishment of the arc.

Upon the occurrence of ,a low magnitude overload, the resistance member 45 begins to heat, and if the overload persists for a sufficient period of time the heating causes the low melting point solder to be melted. Simultaneously with the melting of this solder the compression spring 5| moves the flexible lead l3 and the .terminal strip 41 aflixed thereto in the direction of the lower,

fusing of either fusible element usualy produces sufficient reaction forces to cause the spring, the

flexible lead |3, and the terminal 41 aflixed thereto to be moved entirely out of the main fuse tube Even if this is not done, however, there is a sufficient separation of the current-carrying parts to assure a rapid extinction of low magnitude arcs.

The cross-sectional dimensions of the fusible elements are such that they may be moved into the central opening within the spring-5| when the spring expands during the operation of the device. This assures that there will be no jamming or failure of the device to operate. The presence of the auxiliary fuse tube during the interruption of low magnitude overloads is of particular value in assuring that the arc shall be subjected to an adequate blast of arc extinguishing gas.

The modified upper terminal member 6 l l which is illustrated in Fig. 7 is essentially similar to the previously described member 8 l. Similar to that member, it comprises a flat sheet of conducting material which is cut so as to define a. plurality of cooperating circular sections ill, M8, M9, arc and Hill, which may be bent one over the other so asto define a button or cap-type terminal of at least two different dimensions. The chief diiierences between the two members reside in the provision of two shank portions 023 in the modified structure and in the arrangement of the circular sections.

From the foregoing it will be seen that we have provided an improved refill unit for use with expulsion fuses or similar devices which possess numerous advantages over the devices previously known to the art. Our improved reiill unit is provided with a novel terminal means for permitting it to be used with devices whose physical dimensions vary over a considerable range. Moreover, it includes two serially connected fuelble elements each of which is capable of fusing upon the occurrence of differing predetermined conditions, and a single compression spring for submitting those elements to a substantially constant tensionlng force at all times. Further, we have shown how the features of our improved refill unit may be embodied into a device which utilizes an auxiliary fuse tube for aiding in the extinction of low magnitude overloads.

While in accordance with the patent statutes, we have disclosed the foregoing details of a preferred embodiment of our invention, it is to be understood that many of thesedetails are merely illustrative, and that variations in their precise form may be possible and necessary in many applications. It is our desire, therefore, that the language of the accompanying claims shall be accorded the broadest reasonable construction, and that our invention shall be limited only by what is expressly stated therein and by the prior art.

We claim the following as our invention:

1. A replacement fuse means, comprising a fusible element, terminal means for said element, and a compression spring, which is stressed during the manufacture of said means, for subjecting said fusible element to a substantially constant tension stress at all times, one of said terminal means comprising a liat sheet of metal which is cut so as to provide a plurality of cooperating. sections which may be bent so as to form button terminals of at least two difierent sizes.

2. A replacement fuse unit comprising a fusible element, terminal means electrically and mechan= ically connected to either end or said element, one of said terminal members comprising a fiat sheet of conducting material which is cut so as to form a body portion having shoulder members formed integral therewith and a plurality of cooperating sections which may be bent so as to form button terminals of at least two different sizes, an auxiliary fuse tube disposed so as to enclose said fusible element, and a normally stressed compression spring for subjecting said fusible element to a substantially constant tension stress at I all times, one end or said stressed spring being mechanically connected to the other of said ter minal members, and the other end of said spring abutting against one end of said tube, the other end of said tube engaging said shoulder portions in order to transmit the reaction force of said spring to said first mentioned terminal member.

3. A terminal means for a fusible element comprising a flat sheet of metal which is cut so as to form a plurality of cooperating sections which may be bent so as to form terminals of at least two diiierent dimensions.

4. A terminal member for an electric fuse com-- prising a hat sheet of conducting material having cuts therein forming a plurality of cooperating circular sections which may be selectively bent so as to form circular terminal members or at least two different diameters.

5. A terminal member for an electric fuse comprising a flat sheet of conducting material having a shank portion and a plurality of cooperating sections which may be bent so as to form button terminals of at least two different dimensions, the axis or" said shank portion being substantially perpendicular to the plane of said button terminal means.

6. A terminal member for an electric fuse comprising a fiat sheet of conducting material having a body portion of less width than length and a plurality of cooperating circular sections which may be selectively bent so as to form circular, button type terminals of at least two different diameters, the longitudinal axis of said body portion being substantially perpendicular to the plane of said button terminal means.

7. A terminal means for a fusible element comprising a plurality of integrally formed, cooperating portions which define a button head of predetermined transverse dimensions, and means whereby at least one of said portions may be readily broken away to effect a change in the transverse dimensions of said button head.

8. A terminal means for an electric fuse comprising a shank, a plurality of integrally formed, cooperating portions which define a button head of predetermined transverse dimensions at one end of said shank, and means whereby at least one of said cooperating portions may be readily broken away to effect a reduction in the transverse dimensions of said button head.

9. A terminal member for an electric fuse comprising a fiat sheet of metal, cut so as to. form a plurality of integral cooperating sections which may be bent to form a button head of predetermined transverse dimensions, and means whereby at least one of said sections may be readily broken away from said sheet to efiect a change in the transverse dimensions of said button head.

10. A terminal member for an electric fuse comprising a fiat sheet of metal, cut so as to define a plurality of integral portions which 00- operate to form a shank and a' button head of preetermined transverse dimensions amxed to said shank, the longitudinal axis of said shank being substantially perpendicular to the plane of said i button head, and means whereby at least one of 5 said portions may be broken away from said sheet to reduce the transverse dimensions of said button head.

' HERBERT J. CRABBS.

HERBERT'L, RAWLINS.

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