US2343224A - Electric circuit-interrupting device - Google Patents

Description

IFeb. 29, 1944. A H. PQWELL ELECTRIC CIRCUIT-INTERRUPTING DEVICE Inventor Filed June 16, 1942 Zig/ f//f/ f//f //////////////f/ Patented Feb. 29, 1944 ELECTRIC CiaCmT-INTEaRIJPrmG DEVICE Alric H. Powell, Yeadon, Pa., asslgnor to General Electric Company, a corporation of New York Application June 16, 1942, Serial No. 447,200

12 Claims.

My invention relates to improvements in electric circuit-interrupting devices, such as fuses, for protecting high-voltage electric circuits.

High voltage fuses which consist in the main of a fusible element in the form cf one or more conductors of suitable metal, such as silver or zinc, embedded in a granular inert or refractory arc-extinguishing material of high dielectric strength, such as sand or relatively nely divided quartz are well known. In many of the commercial high-voltage fuses, the fusible conductor or conductors are wound on a suitable supporting core of high temperature resistant ceramic material. To these parts are added an enclosing housing and terminals for the fusible conductor or conductors. The construction and process of assembly of fuses of this type was greatly simplifled by the invention disclosed and claimed in the copending joint application of George R. Serfling and Carl L. Schuck, Serial No. 410,382, led September 11, 1941, now Patent 2,387,937. The present application is an improvement on the abovementioned copending application.

Power fuses of the type referred to above, usually called fuses of the enclosed type, are capable of interrupting currents of large magnitude without noise, discharge of liquid or solid particles or production of gases which must be either discharged to atmosphere or dissipated in a highpressure chamber. Difficulties have beenvencountered in such fuses in providing suitable indicating means to indicate operation thereof. One satisfactory indicating means which has been used successfully is disclosed and claimed in United States Letters Patent 2,188,816, granted January 30, 1940, upon an application of W. K. Rankin, and assigned to the same assignee as the present application. On fault currents of low magnitude which cause rupture of the fusible element it is possible in fuses embodying the indicator of the above-mentioned Rankin patent, that this current is not sufficient to cause operation of the indicating device.

Accordingly, it is an object of my invention to provide a new and improved indicator for circuitinterrupting devices such as fuses.

It is another object of my invention to provide a new and improved indicator for high voltage fuses which may be subjected to jarring or rough handling without deleterious effects.

It is another object of my invention to provide a new and improved fuse device which is simple and inexpensive to manufacture, rugged in con-- struction, and very emcient in operation.

Further objects and advantages of my invention For a better understanding of my invention, reference may be had to the accompanying drawing in which Fig. 1 is a sectional view of an exemplary form of high-voltage fuse constructed in accordance with my invention showing the indicating device in the normal non-indicating position, Fig. 2 is a sectional view of the end cap of the fuse embodying my invention showing the indicator in the position assumed upon rupture of the fusible element, Fig. 3 is a sectional view taken on line 3-3 of Fig. l, Fig. 4 is a perspective View of the ceramic gap included in the fuse device of Fig. 1, Fig. 5 is an enlarged view partly in section cf the ceramic bead or thermal chamber associated with the fuse device of Fig. 1, and Fig. 6 is a perspective view of a portion of the ceramic bead of Fig. 5.

Although it will be evident that certain parts of the present invention may be practiced to advantage with diierent types and forms of electric fuses, the invention lends itself most advantageously to practice with the enclosed type of fuse such as is disclosed and claimed in the abovementioned Rankin patent or in United States Letters Patent 2,157,907, grantedV May 9, 1939. upon an application of K. A. Lohausen, and assigned to the same assignee as the present application, wherein the fusible conductor is shown as being enclosed in a tubular casing of suitable insulating material and surrounded by or embedded in a pulverulent or sandy arc-quenching material.

Referring now to the drawing, I have illustrated an electric fuse device which has a housing structure or casing l0 of open-ended tubular form constructed of suitable insulating material, such as glass or fiber. A suitable fuse link or fusible element generally indicated at ll is suitably mounted in tubular casing vl 0 and, in accordance with the teachings of the above-mentioned copending vjoint application of Seriiing and Schuck, the central core. which has usually been required for centering the fuse link or fusible element Il in the prior-art construction during the process of filling the tubular casing with inert granular arc extinguishing material l2.has been dispensed with. However, in order that the fuse device may have a reasonable length, the fusible element I I follows a devious course within casing l0 such as a helical path which may readily be obtained by winding the fusible element Il on a mandrel or the like. The fuse link Il may, if desired, embody the construction of the abovementioned Lohausen patent so as to include a Central section of reduced cross section, thereby providing more satisfactory operation. Although the particular size of cross section of the fuse wire and the material from which it is madey form no part of the present invention, I have found that silver operates very satisfactorily.

In order to simplify the assembly of the fuse device embodying my construction, the ends ot the fusible conductor II are each provided with a contact I3 of suitable conducting material having a portion I3' looped back upon itself to permit welding or soldering of .the fusible element, within the looped back portion. Since the contacts I3 are of relatively small construction and may be inserted in tubular housing III, the welding operation of the fusible element Il and the contacts I3 may be performed before any assembly operation in housing l of the fuse device takes place. The contacts I3 also include a portion I3" bent at right angles to the main body of the contact which is adapted to nt along the outer wall of the housing or casing I8 and to be electrically connectedwith suitable terminals to be described hereinafter.

In order to close the ends of tubular housing I0, I provide suitable end caps or closure members I4 which are saucer shaped. As shown in the drawing. these end caps are provided with an interlocking means illustrated as an oifset shoulder I4', and they are adapted to be held in sealed relationship with tubular casing or housing I0 by metallic ferrules I5 which are molded or die cast around the end of tubular casing I0 so as to envelop the offset shoulder I4' of end cap I4 while permitting the maior portion of the end cap to remain exposed. 'I'he metallic ferrules I5, are, of course. electrically connected with the contacts I3 and. consequently, provide the upper and lower terminals of the fuse device. Although, I have specifically shown this interlocking means as comprising an oiIset shoulder I4', it should be understood that such interlocking means might `equally well consist of pin pricks, corrugations,

knurling, or grooves of some sort. Furthermore, the inherent irregularities of the end caps I4 might be depended upon for obtaining the desired mechanical grip. Accordingly, any suitable end cap for obtaining the desired mechanical interlock may be employed in a manner disclosed and claimed in the above-mentioned copending joint application of Seriiing and Schuck.

Since the maior portion of the end caps I4 remain exposed after the molding or die cast operation, suitable indicia may be provided on this surface ot the end caps to set forth the fuse size or any other pertinent information.

In order that the end caps I4 may nt properly on the ends of tubular housing I8 in spite of the contacts I3, I provide suitable spacer plates I8 for each end of tubular housing I Il, best shown in Fig. 3, which are of the same thickness as contact I3 and are arranged to fit closely adjacent thereto to prevent, during the molding or die casting operation, the molded or die cast metal from flowing into the nely divided arc-extinguishing material I2 contained in housing Iii. As shown in Fig. 3, the spacer plates I3 are generally annular in construction and are provided with a discontinuous section or cutout portion I1 within which contact members I3 are adapted -to be positioned. Spacer plates I8 are also provided with a fingerlike extension I8' serving as an anchoring point for a suitable indicator wire to be described hereinafter. The spacer plates are formed of conducting material and serve to position the end caps so that they set level on the ends of housing I0.

It is desirable to provide means which indicate whether the fuse device embodying my invention has operated to interrupt the circuit and. to this end, I provide a suitable target or indicating means. generally indicated at i 8 in Figs. 1 and 2. This indicating means is suitably supported from one o! the end caps, such as the lower end cap I4, which is identical with the upper end cap except for the provision of -a suitable opening I8 5 into wnicnls fitted an insert zo which may be spun over or fastened to the edges of the opening Il by any other suitable means to provide an inwardly projecting boss which, preferably, supports a tubular target or indicator housing 2| constructed of glass or other suitable insulating material. Preferably, housing 2i, which really is an extension of the boss comprising insert 2li, is cemented as at 22 to lower end cap I4. A suitable indicator or plunger 23 is slidably mounted in the boss comprising insert 20. Indicator 23 is provided with an enlarged portion 23' and a suitable compression spring means 24 bearing against enlarged portion 23' and insert 20 constantly biases plunger or indicator 23 to the indicating position shown in Fig. 2.

In order to maintain plunger or indicator 23 in the nonindicating position shown in Fig. l, the upper end of tubular indicator housing 2| is closed by a suitable insulating member 25, preferably constructed of ceramic material, best shown in Figs. 2 and 4, having a projection or ear 25 and a plurality of openings 28 and 21 therein. A suitable tension spring 28 has one end thereof fastened to plunger 23 as indicated at 29 While the other end thereof is fastened to strain wire 30, which, in turn, passes through opening 28 in ceramic member 25 and is twisted around projection or ear 25'. Tension spring 28 is stressed as shown in Fig. 1 so that plunger 23 is held in a floating condition with a. substantially constant force applied to strain wire 30, whereupon jarring or rough handling of the fuse device will not harm or cause rupture of strain wire 30. It will be obvious that the compression spring 24 must be a weaker spring than tension spring means 28. Also tension spring 28 will tend to hold indicator housing 2l in position around insert 28 even without the cementing shown at 22. With the iioating construction of plunger 23 described above, a much weaker strain wire 30 may be used without danger of stretching or rupturing to permit the indicator or plunger 23 to move to the indicating position shown in Fig. 2. I have discovered that, without the use of spring 28, strain wire 30 must be able to withstand ten or more times the force of spring means 28, to prevent movement of the plunger 23 out of its non-indicating position merely due to normal handling of the fuse device.

In order that the ngerlike extension I5' of the lower spacer plate I8 does not interfere with the indicator generally illustrated at I8 when the lower end cap I4 is placed on housing I0, this iingerlike extension Ii' is preferably bent out of the way as indicated in Fig. 1.

It is desirable to obtain operation of indicator I8 in response to rupture of the fuse link or fusible element II and, to this end, I provide an indicator wire 3| having the upper end thereof attached or anchored to the ngerlike extension I8' of upper spacer plate I 6, as best shown in Fig. 3, so as to be electrically connected with the upper ferrule or terminal I5. The other end of indicator wire 3I is passed through the opening 21 in ceramic member 25 and fastened in any suitable manner as by twisting back around itself or the like to hold it in place. In view of the space between openings 28 and -2`l in ceramic member 25, a suitable dielectric means equivalent to -an arc gap is provided between strain wire 30 and indicator wire 3| so that normally no current flows through strain wire 30. Upon rupture of the fusible element due to excess current, a potential is established across the ceramic gap between the lower end of indicator wire 3| and the upper end of strain wire 30 rwhich potential produces arcing across the gap with consequent rupture of strain wire 30 either by melting due to current owing therethrough or by the direct heat of the arc, which will cause rupture even at very low currents.

In order to cause proper operation of the fuse device described above on long continued overload conditions, it is desirable to provide one or more thermal chambers such as is generally indicated at 33 in Figs. 1 and 5. Thermal chambers have been used heretofore which usually comprise means for localizing heating such as a sealed chamber surrounding a portion of the fuse link and formed of a. poor conductor of heat which tends to concentrate the heat and cause melting of the fusible element at that portion of the fuse link. Thermal chamber 33 preferably comprises a tubular member 34 and co-operating end closure members 35 which latter are best shown in Fig. 6. The end closure members 35 are preferably .provided with a relatively small opening 36 through which the fusible element II may extend so that the space within tubular member 34, which is preferably filled with air, is kept tightly sealed, whereby the heat applied to fusible element I I within thermal chamber 33 is more dependent upon the current flowing therethrough than it would be if surrounded by the granular material I2. In order properly to support the thermal chamber 33 on fusible element II, the members 35 of closure chamber 33 are each `provided with a projection 35 around which the conductor or fusible element is looped in the nature of a half hitch, thereby providing a very satisfactory assembly ofthe fuse link and thermal chamber without requiring any special cement or other means as was the case heretofore.

In constructing or assembling the fuse device of Fig. 1, the fusible element II, contacts |3, and thermal chamber 33 are rst assembled. Also indicator Il and indicator wire 3| are assembled with lower end cap I4. Thereafter, the fuse link II and associated contacts I3 and spacer plates I6 are assembled on tubular housing III. The lower end cap Il, indicator I3, and indicator wire v3| are then assembled and the upper end of the indicator wire 3| is attached to the flngerlike extension I6 of upper spacer plate I6. The housing I is then filled with sand or other inert granular arc-extinguishing material through the opening in the upper spacer plate I6 in a manner described in the copending joint application of Serfling and Schuck, after which the upper end cap I4 is placed on housing III. Upper end cap I4 may, if desired, be provided with suitable indicia or the like giving information regarding the fuse size, etc. Thereafter the molding or die casting operation is performed to produce ferrules or terminals I which envelop the interlocking means specifically illustrated as offset shoulders I4' of end caps I4 so as to hold them in sealed relationship with respect to housing I0 as well as to form good electrical contact with the ends of contact I3, and consequently, with fusible conductor I I. Any suitable indicia appearing on the end cap I4 will remain visible after the die casting or molding operation since as shown in Fig. 1

the major portion of each end cap I4 is exposed, and the die cast metal merely grips the interlocking means illustrated as the offset shoulder 'I'he operation of the fuse device embodying my invention will be obvious from the detailed description given above. By virtue of the ceramic' gap between indicator wire 3| and strain wire 3l, no current will now through indicator wire 3| under normal conditions of the fuse device and strain wire 30 will hold plunger or indicator 23 across the ceramic gap between strain wire 3l A and indicator wire 3| which will cause the gap to arc over and the strain wire to rupture either by the heat of the arc or the heat produced by the current flowing therethrough, whereupon plunger 23 is released and permitted to move to the indicating position shown in Fig. 2.

From the foregoing, it will be seen that I have provided a new and improved fuse construction including an indicator which is satisfactory under al1 conditions and will not be affected by jarring or rough handling. Furthermore, the fuse device while being of simple and rugged construction greatly simplifies the manufacturing processes with consequent cost reduction and provides a very satisfactory fuse in every respect.

Although I have elected to describe and illustrate herein a preferred embodiment of my invention as employed in a fuse device as well as the process of construction thereof, it is contemplated that other applications of my invention to fuses or like electrical devices other than the particular form illustrated will suggest themselves to those skilled in the'art. It is intended that such other applications or modifications as do not depart from the true spirit and Ascope of my invention will be covered by the appended claims.

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

1. In an electric circuit-interrupting device, the combination with an enclosing casing and a fusible element therein, an indicator for indicating operation of said circuit interrupting device, means for maintaining said indicator out of its indicating position, and means including a spring for preventing high impact forces due to jarring or other rough handling of said device from adversely affecting said last mentioned means.

2. In a fuse device, an insulating housing, a fusible conductor in said housing, terminals carried by said housing and electrically connected to said conductor, and means for giving an indication of fuse operation comprising an element biased to an indicating position, means including a spring for preventing high impact forces due to jarring or other rough handling of said device from adversely affecting said element by causing it to move to the indicating position, and means for causing said last-mentioned means to release said element upon operation of said device.

3. In a fuse device, a casing having spaced apart terminals, a fusible conductor of greater iength than the distance between said terminals. means supporting said conductor within said casing with the conductor extending by a devious course between said terminals, means electrically connecting the terminals respectively with the opposite ends of said conductor, an indicating element movably supported at one end of said casing, means for biasing said indicating element to the indicating position, and means arranged to oppose said last-mentioned means while said fusible conductor is in the unruptured condition, said last two mentioned means being so constructed and arranged as to maintain said indicating element in a floating condition so `iarring or rough handling will not cause it to move to the indicating position.

4. In a fuse device, a tubular casing, a pair of terminals associated with said casing, a. fusible element disposed within said casing and connected between said terminals, an end cap for said casing including a boss thereon, a plunger slidable in said boss and biased to move outwardly to an indicating position, and means including a spring and strain wire for maintaining said plunger normally retracted in a nonindicating position and arranged to release said plunger upon fuse operation, said spring being so constructed and arranged with respect to said plunger biased to move to an indicating position as to maintain said plunger in a floating position during the unblown condition of said fuse device so that impact forces will not adversely affect said last mentioned means.

5. An electric circuit-interrupter comprising an insulating casing, terminal means arranged on one end of said casing, a fusible circuit-interrupting element arranged in said casing and connected a-t one end to said terminal means, an indicator device mounted on an end of said casing and movable outwardly with respect thereto, ac-

tuating means for said indicator device including a rst spring, means including a second spring for restraining said indicator device in an inoperative condition, said first and second springs providing a floating arrangement of said indicator device so that jarring and rough handling will not cause said device to move to the indicating position, and means responsive to an excess current flow through said fusible element for effecting release of said indicator device.

6. An electric circuit-interrupting device comprising an insulating casing, terminal means are ranged on one end of said casing, a fusible circuit-interrupting element arranged in said casing and connected at one end to said terminal means, an indicator device mounted on an end of said casing and movable outwardly with respect thereto, actuating means comprising a first spring for said indicator device, and means including a second spring for restraining said indicator device comprising a strain wire and serially arranged dielectric means connected in parallel with said fusible element, said dielectric means normally preventing current from flowing through said strain wire until rupture of said fusible element whereupon an arc is produced across said dielectric means for severing said strain wire even under low fault current conditions to permit said indicator to move to said indicating position, said rst and second springs providing an arrangement to maintain said indicator device in a floating inoperative condition so that jarring and rough handling will not cause said indicator device to move to the indicating position.

7. An electric circuit-interrupting device comprising an insulating casing. terminal means arranged on one end of said casing, a fusible circuit-interrupting element arranged in said casing and connected at one end to said terminal means.

an indicator device mounted on an end of said casing and movable outwardly -with respect thereto, a housing for said indicator device, actuating means for said indicator device, and means for restraining said indicator device in a nonindicating position comprising a strain wire and serially arranged dielectric means connected in parallel with said fusible element, said dielectric means being mounted to close one end of said housing and normally preventing current from flowing through said strain wire until rupture of said fusible element whereupon an arc is produced across said dielectric means for severing said strain wire by melting due to the heat of said arc under low fault current conditions to permit said indicator device to move to its indieating Position.

B. In a fuse device, a casing having spacedapart terminals, a fusible element interconnecting said terminals, an indicating element movably SuppOrted at one end of said casing, means for biasing said indicating element to an indicating position, and means for restraining said indicating element in a nonindicating position comprising a strain wire and serially arranged dielectric means connected in parallel with said fusible element, a housing for said indicating element mounted at said one end of said casing, said dielectric means forming a closure for one end of said housing and normally preventing current from flowing through said strain wire until rupture of said fusible element whereupon an arc is produced across said dielectric means for severing said strain wire and permitting said indicating element to move to said indicating position.

9. In a fuse device, a casing having spacedapart terminals, a fusible element interconnecting said terminals, a thermal chamber enclosing a portion of said fusible element for localizing the heating of said fusible element, and means for supporting said thermal chamber on said fusible element comprising a projection on said thermal chamber around which said fusible element is looped.

10. In a fuse device, a casing having spacedapart terminals, a fusible element interconnecting said terminals, a thermal chamber enclosing a portion of said fusible element for localizing the heating of said fusible element, and means for supporting said thermal chamber on said fusible element comprising a projection at each end of said thermal chamber around which said fusible element is looped.

11. In a fuse device of the current-limiting type a casing having spaced-apart terminals, a fusible element interconnecting said terminals, a ller of arc-quenching material in said casing surrounding said fusible element, a thermal chamber enclosing a portion of said fusible element for localizing the heating of said fusible element, and means for supporting said thermal chamber on said fusible element comprising a projection at each end of said thermal chamber around which said fusible element is looped.

12. In an enclosed fuse comprising a casing having a filler of arc-quenching material, a pair of spaced terminals on said casing, a fusible element embedded in said filler interconnecting said terminals, a thermal chamber enclosing a portion of said fusible element for localizing the heating of said fusible element, and means for supporting said thermal chamber on said fusible element comprising a projection at each end of said thermal chamber around which said fusible element is looped.

ALRIC H. POWELL.

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