US3253106A - Indicating fuse constructions - Google Patents

Description

y 24, 1966 H. R. HOLSINGER 3, ,106

INDICATING FUSE CONSTRUCTIONS Filed May 2, 1962 2 Sheets-Sheet l Fig.|.

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y 1966 H. R. HOLSINGER INDICATING FUSE CONSTRUCTIONS 2 Sheets-Sheet 2 Filed May 2, 1962 Fig. I I.

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INVENTOR Howurd R. Holsinger BY WW1. 6M2

ATTORNEY lllllll'lll United States Patent 3,253,106 INDICATING FUSE CONSTRUCTIONS Howard R. Holsinger, Bloomington, Ind., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed May 2, 1962, Ser. No. 191,951 4 Claims. (Cl. 200121) This invention relates generally to indicating fuse constructions and, more particularly, to indicating fuse constructions wherein an indicating assembly is desired for externally indicating operation of the fuse in response to overload or fault conditions.

A general object of the present invention is to provide an improved indicating fuse construction of highlyefiicient operation, composed of few parts and yet providing an improved external indication of operation of the fuse under overload or fault conditions.

A more specific object of the present invention is the provision of an indicating-type fuse having relatively few parts, and associating an indicating-rod assembly with one of the terminals of the fuse, so as to give an external readily-visible indication of fuse operation.

A further object of the present invention is the provision of a fuse, particularly adapted for capacitor-unit installations, wherein an insulating fuse-indicator rod is employed, the fuse construction being very suitable for confinement within an enclosed cubicle construction without the hazard of any flashover occurring between the grounded cabinet and the indicator assembly to the live terminals of the fuse during fuse operation.

Still a further objectof the present invention is the provision of an improved method for assembling 'a fuseindicator device with a fuse for eliminating as far as possible soldered connections, and providing instead crimping operations, or threaded connections,.for good contact transfer and adequate securement of the several parts.

Still a further object of the present invention is the provision of an improved indicator assembly for a fuse having a fuse-indicating rod which protrudes axially through a fuse terminal to an external length sufficient for readilyvisible external indication.

Yet a further object of the present invention is the provision of an improved fuse construction wherein a biasing spring adapted for fuse-terminal withdrawal is also effective as a biasing means for an indicating-rod assembly.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:

FIGURE 1 is an end section view, partially in section, of an enclosed protected capacitor installation indicating internal stacking of capacitor units with individual protective fuse elements closely situated to the cabinet wall;

FIG. 2 is an enlarged axial sectional view taken through the improved indicating fuse construction of the present invention, with the fuse elements shown in their intact condition;

FIG. 3 is a fragmentary sectional view, similar to that of FIG. 2, but indicating the position of the several parts following blowing, or operation of the fuse elements;

FIGS. 4 and 5 illustrate, respectively, end and side elevational views of the deformed connector element of the present invention;

FIGS. 6 and 7 illustrate, respectively, side elevational and end elevational views of the push-on-type speed nut utilized in an assembly operation of the present invention;

FIGS. 8 and 9 illustrate, respectively, side elevational and end elevational views of the perforated condenser 'ice chamber utilized in the fuse construction of the present invention;

FIGS. 10-12 illustrate, respectively, detailed views of the improved terminal-stud construction of the present invention;

FIGS. 13 and 14 illustrate, respectively, side elevational and end elevational views of the metallic crimp washer used in an assembly operation;

FIGS. 15 and 16 illustrate, respectively, side elevational and end elevational views of the metallic connector sleeve utilized in the indicator assembly of the present invention; and,

FIG. 17 is afragmentary side elevational view indicating installation of the fuse construction of the present invention on the terminal of a capacitor unit.

Although the improved fuse construction of the pres ent invention may be utilized in a wide variety of applications, merely for the purpose of describing the present invention, and not by way of limitation, the fuse construction is illustrated as applied to an individual capacitor unit. As well known by those skilled in the art, the primary purpose of fusing individual capacitor units is to remove a faulted capacitor from service before the capacitor case ruptures and damages adjacent units. The removal of the faulted capacitor unit must take place before the main protective device can operate and interrupt service to the remaining capacitor units, which are unaffected. Another purpose is to protect the unaffected capacitor units from the high transient current associated with the failure of a capacitor unit in the same capacitor bank.

Capacitor equipment usually consists of a number of individual capacitor units connected in parallel to make up the total capacity required for a given installation. In most installations, the complete equipment is protected by a circuit breaker or power fuses. The current rating is determined by the normal current rating of the equipment plus an ample margin to allow for increased current due to operation above rated voltage, manufacturing tolerances, presence of harmonics, and transient currents during switching operations.

Usually, individual capacitor units are liberally designed to withstand the requirements of normal service; nevertheless, a capacitor unit may fail if operated under abnormal conditions. Should this occur, no protection can be expected from the circuit breaker or power fuses, because of the high ratio of total bank current to the small current that can be drawn by a faulty capacitor unit. As a result, individual capacitor unit fuses are recommended for use on all power capacitor installations to provide maximum protection, preserve continuity of service and provide identification of a faulted capacitor unit.

Referring to FIG. 1 of the drawings, it will be observed that a capacitor bank compartment 1 encloses a plurality of stacked capacitor units 2 in a plurality of banks 3. Individual capacitor fuses 4 are secured to one of the terminals 6 of the capacitor units 2 for protection against fault conditions. It will be observed that the indicating assembly 7 of the capacitor fuse 4 is situated relatively closely to the wall 8 of the compartment 1. As a result, there is the danger of flashover conditions occurring between the capacitor fuse 4 and the grounded compartment wall 8 if the fuse is not properly constructed.

In previous individual capacitor fuses, operation of the fuse element was indicated by the position of a coiled flipper spring attached to a flexible cable at the lower end of the fuse assembly. Such a flipper indicating spring, at the time of fuse operation, moves several inches, carrying with it a portion of the flexible fuse cable. When the capacitor, to which the fuse is connected, is mounted inside a cubicle, or compartment (as is usually the case). special care must be exercised to allow suflicient electrical clearance between the lower end of the fuse, the indicator parts, and the sides, or 'walls of the cubicle compartment 1. This often requires extra space inside the cubicle, which was undesirable. In addition, previous individualtype capacitor fuses were suitable only for bus mounting, there being no means of attachment of the lower end of the fuse assembly to the terminal bushing of the capacitor unit.

The improved indicating fuse construction of the present invention comprises generally the addition of a condenser chamber, together with an indicator-rod assembly extending through the condensing chamber and also through the terminal stud. Electrical connection is preferably made to the terminal stud, which may also be used to support the fuse itself. As a result, the fuse may be mounted directly onto a capacitor bushing by means of a simple fiat mounting strap. Moreover, the fuse may also be mounted upon a capacitor bus for other installations. The utilization of a condensing chamber permits the fuse to be used more closely adjacent other live parts, because the expelled gases, generated during fuse operation, are cooled and deionized by the condenser chamber.

FIG. 2 shows more clearly the improved fuse construction of the present invention. As shown, the fuse 4 is of the current-limiting type for limiting the fault current passing through the fuse 4. More specifically, the fuse unit 4 isencased by a tubular fuse holder 9 made of insulating material, such as fiber, or synthetic resin and by a terminal cap 11 and condenser chamber 12 associated with opposite ends of the fuse tube 9.

The current-limiting section 13 includes a supporting or interrupting rod 14 of suitable insulating material, such as fiber, or the like. Preferably, the insulating rod 14 is helically grooved, as at 16, for the accommodation of a plurality of parallel-disposed current-limiting fuse wires 17, preferably of silver Wire. Reference may be had to United States Patent 2,605,371, issued July 29, 1952, to Harold H. Fahnoe, and assigned to the assignee of the instant application for a detailed description of the function and operation of the current-limiting section 13. As shown, fiber washers 18 are slipped over the helicallygrooved insulating rod 14 to prevent flashover, and to increase the arc voltage during a current-limiting operation. In addition, a suitable filler, such as quartz sand 19, is disposed interiorly of the fuse tube 9 for condensation of the fused metallic particles caused during fuse operation.

In addition to the provision of a current-limiting section 13, there is also provided a boric-acid interrupting section 21 comprising a plurality of apertured boric-acid blocks 22, through which extends a fusible element 23 comprising a fuse wire 24 and a strain wire 26. The fuse wire 24 and the strain wire 26 are suitably secured by means of a hole 27 bored transversely through a rod end portion 28, to which the plurality of silver fuse Wires 17 are conductively secured, as by solder.

As illustrated in FIG. 2, the lower ends of the strain link 26 and main fuse element 29 are soldered to a crimped portion 30 of a fuse connector 31, the particular configuration of which is more clearly shown in FIGS. 4 and of the drawings.

As shown in FIG. 2, an indicator compression spring 33, which is of coiled spring construction, is placed over the fuse connector 31, and is compressed by a crimp washer 34, the latter being shown more clearly in FIGS. 13 and 14 of the drawings. A speed nut 36, more clearly shown in FIGS. 6 and 7 of the drawings, is frictionally pressed on over the tubular portion 31a of the fuse connector 31 to temporarily frictionally maintain the indicator spring 33 in compression.

At this point in the assembly operation a connector sleeve 38 is slipped over the connector 31; and flexible leads 41 and insulating indicator rod 42 are inserted a short distance, such as or /2 inch for example, into the open tubular end 31b of connector 31. The rod 42 is centered in the several strands of flexible leads 41. A first crimping step takes place by means of pressing the connector sleeve 38, shown in FIGS. 15 and 16, over the tubular portion 31a of the fuse connector 31 to deform the same to an oval configuration. Such a oval deformation maintains the crimp washer and the push-on-type speed nut 36 into a fixed permanent position as contrasted to the previous temporary position of the speed nut 36), so that the lower end of the indicating spring 33 is fixedly determined into a proper permanent position, as shown in FIG. 2. The upper end of sleeve 38 and end 31a of connector 31 are crimped simultaneously the operation also securing the leads 41 fixedly into position.

A second crimping operation is subsequently performed between the lower end of the connector sleeve 38 and the flexible leads 41 and the insulating indicator rod 42. The second crimping operation thereby ensures a fixed securement of the insulating indicator rod 42 together with the flexible leads 41 into a proper position and importantly provides additional contact between leads 41 and connector sleeve 38, and hence to connector 31. The lower ends of the flexible leads 41 have terminal lugs 43 secured thereto, which terminal lugs are fastened by mounting screws 44 to a terminal stud 46, the particular configuration of which is more clearly shown in FIGS. l012 of the drawings.

With reference to FIGS. 10-12 of the drawings, it will be observed that a transversely-extending hole 47 is provided, and tapped, to accommodate the mounting screws 44. Additionally, an axial bore 48, through the terminal 46, is provided for the accommodation of the insulating indicator rod 42. Finally, the terminal stud 46 has a shoulder portion 49 adapted for insertion through a substantially square hole 51 of the tubular condenser chamber 52, the configuration of which is more clearly shown in FIGS. 8 and 9 of the drawings. As a result, the terminal stud 46 will not turn within the hole 51 of condenser cap 52 upon rotation of a clamping, or jam nut 53. Preferably, a lock washer 54 and an oversized metallic washer 56 are additionally employed under the nut 53.

As shown in FIG. 17, by the addition of a capacitor mounting strap 57, the fuse 4 may be fixedly secured to the terminal 58 of a capacitor unit 2.

During the existence of fault conditions associated with the capacitor unit 2, the fuse 4 will function to provide a current-limiting action, 'as provided by the currentlirniting section 13. Additionally, the fusible element 23 will blow to release the indicator spring 33, which additionally functions as a fuse-terminal retraction spring. The indicator rod 42 will be ejected to a readily-visible external position, as indicated in FIG. 3 of the drawings.

By way of recapitulation, the assembly operations are performed by first lowering the current-limiting fuse section 13, together with the fusible element 23 and attached connector sleeve 30, through the bore 59 of the fuse tube 9, so that the terminal cap 11 may be crimped into an annular recess 60 provided thereon. A square centering washer 61 is employed to center the currentlimiting interrupter rod 14. The fuse tube 9 is preferably inverted so that the cap 11 is positioned downwardly, at which time a suitable filler, such as quartz sand 19, is poured downwardly into the fuse tube 9 past the square positioning washer 6-1. The tube 9 may be vibrated to settle and compact the sand. When the fuse tube 9 has been properly filled with the quartz sand 19 to the requisite amount, a closure washer 62 of round configuration is pushed over a tapered portion 63 of the fuse rod 14. Subsequently, the boric-acid blocks 22 are placed, or stacked into position together with a metallic apertured spring-seat washer 6 5, which provides a metallic seat for one end of the indicator spring 33. The spring 33, crimp washer 34, and frictionally-engaging speed-nut 36 are pushed over connector 31. The speednut 36 temporarily holds the lower end of the spring 33 in positiomas viewed in FIG. 2. Then, connector sleeve 38 is slipped loosely over connector 31. The flexible leads 41, together with indicator rod 42, are inserted into the open tubular end 31b of the fuse connector 31; and the aforesaid first crimping operation is performed. Subsequently, the second crimping operation is additionally performed to provide thereby additional secure attachment of the leads 41 with the connector sleeve 38 with good current-carrying qualities. This assures additional contact between leads 41 and sleeve 38 and hence to connector 31. The terminal lugs 43, secured to the flexible leads 41, are secured by the mounting screws 44 into the transversely-tapped bores 47 of the terminal 46. Finally, a rolled-up copper screen 68 is inserted into the condensing chamber 52 for the condensation of the evolved gases during fuse operation and the condenser closure '52 is slipped over the reduced end 46a of the terminal stud 46, and the crimping operation performed to crimp sleeve portions 70 into annular recesses 71 for secure attachment. As shown in FIGS. 8 and 9, the condenser chamber 52 has venting apertures 67 associated therewith for expulsion of the generated gases. As a final operation, the jam nut 53 is tightened over the lock washer 5'4 and oversize washer 56 to fixedly force the enlarged portion 46b of the terminal stud 46 against the inside surface 73 of the end 74 of condenser chamber 5-2.

From the foregoing description of the invention it will be apparent that there is provided an improved indicating fuse construction particularly adapted for the individual protection of capacitor units in capacitor installations, but not exclusively limited to this use. The invention has particular applicability for enclosed constructions, as pointed out hereinbefore, by the use of the insulating indicator rod 42, the indicating position of which does not reduce the fiashover distance D (FIG. 1) between the fuse unit 4 and the wall 8 of the cubicle compartment 1.

The novel indicating fuse construction of the present invention has an additional advantage inasmuch as the expelled gases, generated during fuse operation, are cooled and deionized prior to ejection through the venting holes 67 of condenser chamber 52 to the atmosphere.

As pointed out hereinbefore, during the crimping operations, there is avoided the presence of soldered joints; and preferably all connections are attached by crimping and threading operations. Thus, there is a minimum of risk that a soldering operation on the indicator will damage any portion of the fusible element 23, which cannot normally be seen after the fuse has been completely assembled, since it is completely enclosed.

Although the invention has been described as particularly relating to an individual capacitor-unit indicating fuse device, nevertheless it will be apparent to those skilled in the art that certain features of the invention are applicable, as indicating devices, to other types of fuse constructions for different applications other than the capacitor application herein described merely by way of illustration of one possible use of the invention.

Although there has been illustrated and described a specific structure, it is to be clearly understood that the same was merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the invention.

I claim as my invention:

1. The combination in an indicating-type fuse of a tubular fuse holder having at least an axial portion thereof composed of insulating material, a first fuse terminal secured to one end of the fuse holder, a second fuse terminal secured to the other end of the fuse holder, a currentlimiting fuse section connected to said first fuse terminal, an axial bore-type interrupting section having gas-evolving wall portions intermediate the current limiting fuse section and the second fuse terminal, a fuse element in the interrupting section, a retracting spring for biasing said fuse element to a separated condition, a fuse connector for the fuse element electrically connecting the fuse element to the second fuse terminal and having a tubular portion, and an indicating rod fixedly secured within said tubular portion, the second fuse terminal having an axial bore therethrough, the indicating rod being positioned within said axial bore of the second fuse terminal and slidable therein to an indicating position in response to force applied thereto from the retracting spring when the fuse element blows.

2. The combination in an indicating-type fuse of a tubular fuse holder having at least an axial portion thereof composed of insulating material, a first fuse terminal secured to one end of the fuse holder, a second fuse terminal secured to the other end of the fuse holder, a current-limiting fuse section connected to said first fuse terminal, an axial bore-type interrupting section having gasevolving wall portions intermediate the current limiting fuse section and the second-fuse terminal, a fuse element in the interrupting section, a retracting spring for biasing said fuse element to a separated condition, a fuse connector for the fuse element electrically connecting the fuse element to the second fuse terminal and having a tubular portion, means defining a spring seat secured to said fuse connector, said spring having one end thereof abutting against said spring seat, and an indicating rod fixedly secured within said tubular portion, the second fuse terminal having an axial bore therethrough, the indicating rod being positioned within said axial bore of the second fuse terminal and slidable therein to an indicating position in response to force applied thereto from the retracting spring when the fuse element blows.

3. In combination, an indicating fuse including a fuse- -cap terminal secured to one end of a tubular insulating fuse holder, a tubular apertured metallic condensing chamber secured to the other end of the fuse holder, means defining a current-limiting section, a tubular gas-evolving axial-bore-type interrupting section having rupturable fuse means therein, a condensing chamber section, a deformed tubular fuse connector, said rupturable fuse means being secured to the deformed end of the fuse connector, an indicating insulating rod, at least one fuse cable secured to the undeformed end of the tubular connector, a terminal stud having an axial bore therethrough secured to said condensing chamber and having said indicating rod extending through the axial bore thereof, and means conductively securing the other end of said fuse cable to the interior end of the terminal stud.

4. In combination, an indicating fuse including a fusecap terminal secured to one end of a tubular insulating fuse holder, a tubular apertured metallic condensing chamber secured to the other end of the fuse holder, means defining a current-limiting section, a tubular gas-evolving axial-bore-type interrupting section having fusible fuse means therein, a condensing chamber section, a deformed tubular fuse connector, said fusible fuse means secured to the deformed end of the fuse connector, an indicating insulating rod and at least one fuse cable secured to the undeformed end of the tubular connector, a terminal stud having an axial bore therethrough secured to said condensing chamber and having said indicating rod extendin axially through the axial bore thereof, and an indicator spring encircling said deformed tubular fuse connector and biasing the same to an indicating condition of the fuse wherein said indicator rod is ejected along said terminal stud bore.

(References 011 following page) 7 8 References Cited by the Examiner 2,435,472 2/ 1948 Shuck 200-120 A NT 2,483,577 10/1949 Fahnoe 20012O UNITED STAT ES P TE S 2,493,434 1/1950' Yonkers 29-155.5 P61161161 et a1. X 2 567 768, 9 1951 Fahnoe 20O 120 2/1937 saudlcoeur 5 2,813,952 11/1957 Baker et a1. 200-120 X 7/ 1939 Lemmml 200-117 2,872,549 2/1959 Lindell 200 121 UNITED STATES PATENTS 2,918,551 12/1959 KOZfiCkfl 200-121 9/1942 Williams 200-120 BERNARD A. GILHEANY, Primary Examiner. 12/1946 Brown 29--155.5

6/1947 Strang et a1. 200-121 10 LAWRENCE A. WRIGHT, Assistant Examiner.

Claims (1)

1. THE COMBINATION IN AN INDICATING-TYPE FUSE OF A TUBULAR FUSE HOLDER HAVING AT LEAST AN AXIAL PORTION THEREOF COMPOSED OF INSULATING MATERIAL, A FIRST FUSE TERMINAL SECURED TO ONE END OF THE FUSE HOLDER, A SECOND FUSE TERMINAL SECURED TO THE OTHER END OF THE FUSE HOLDERM A CURRENTLIMITING FUSE SECTION CONNECTED TO SAID FIRST FUSE TERMINAL, AN AXIAL BORE-TYPE INTERRUPTING SECTION HAVING GAS-EVOLVING WALL PORTIONS INTERMEDIATE THE CURRENT LIMITING FUSE SECTION AND THE SECOND FUSE TERMINAL, A FUSE ELEMENT IN THE INTERRUPTING SECTION, A RETRACTING SPRING FOR BIASING SAID FUSE ELEMENT TO A SEPARATE CONDITION, A FUSE CONNECTOR FOR THE FUSE ELEMENT ELECTRICALLY CONNECTING THE FUSE ELEMENT TO THE SECOND FUSE TERMINAL AND HAVING A TUBULAR PORTION, AND AN INDICATING ROD FIXEDLY SECURED WITHIN SAID TUBULAR PORTION, THE SECOND FUSE TERMINAL HAVING AND AXIAL BORE THERETHROUGH, THE INDICATING ROD BEING POSITIONED WITHIN SAID AXIAL BORE OF THE SECOND FUSE TERMINAL AND SLIDABLE THEREIN TO AND INDICATING POSITION IN RESPONSE TO FORCE APPLIED THERETO FROM THE RETRACTING SPRING WHEN THE FUSE ELEMENT BLOWS.

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