Document 6RVNQ1x0NEmbnQ5nJqyawdQqd

FILE NAME:McGraw-Edison (ME) DATE: : DOC#: ME0 DOCUMENT DESCRIPTION: WZZZZ Z United States Patent (19) Johnson et al. 11 Patent Number: 4,948,828 45 Date of Patent: Aug. 14, 1990 (54) ASBESTOS FREE MATERAL FOR GASSING CURRENT LIMITNG FUSES 75 Inventors: Stephen P. Johnson, Olean, N.Y.; Stephen P. Hassler, Muskego, Wis. (73) Assignee: Cooper Industries, Inc., Houston, Tex. (21) Appl. No.: 304,731 22 Filed: Jan. 31, 1989 51 Int, C. ........................... C08K 3/34; C08K 3/22 (52) U.S. C. .................................... 524/437; 524/456; 524/597 58) Field of Search ....................... 200/144 C, 149 A; 174/DIG. 1; 524/437, 456,597 (56) References Cited U.S. PATENT DOCUMENTS 2,596,134 5/1952 Dorst ................................... 524/597 2,917,607 12/1959 Sterling ... ... 524/597 3,242,257 3/1966 Jones et al. ......................... 524/437 Primary Examiner-Lewis T. Jacobs Attorney, Agent, or Firn-David A. Rose 57 ABSTRACT A spider for a gassing current limiting fuse made of an asbestos free material is disclosed. The spider material produces an arc quenching gas and water upon erosion by an arc. The material includes the following propor tions of ingredients: 50-80%. Al2O3.3H2O; 8-22% Wol lastonite (CaSiO3); and 10-25% melamine formalde hyde resin. 9 Claims, 2 Drawing Sheets U.S. Patent Aug. 14, 1990 Sheet 1 of 2 4,948,828 3. C Zast 2 AZZ U.S. Patent Aug. 14, 1990 Sheet 2 of 2 4.948,828 Z 2{4 or era \\\ YYYYCYCO AA AAHAA 4,948,828 1. 2 ASBESTOS FREE MATERAL FOR GASSING CURRENT LIMITING FUSES or finely divided quartz which forms a fulgurate when exposed to an arc and further aids in limiting the cur rent. FIELD OF THE INVENTION The spider in gassing fuses is conventionally formed of an asbestos-containing material. The problems with The invention relates to an asbestos free material for the use of asbestos are well-known. Asbestos fibers and use as the gas-emitting member in a current limiting dust are a significant health hazard, and can cause, gassing fuse. among others, the conditions known as asbestosis and mesothelioma. Asbestos dust can be generated both BACKGROUND OF THE INVENTION 10 during manufacture and during disposal of conventional In a conventional current limiting fuse, a fuse element gassing spiders. Due to worker injury, significant liabil is surrounded by a granular inert material of high di ity for both manufacturers and disposers of asbestos electric strength, such as sand or finely divided quartz. products has become common-place. Accordingly, The fuse element is typically wound onto a support elimination of asbestos from gassing fuses is desirable. core, or spider. When the element is subjected to a 15 Thus, what is needed is a spider material which is current of fault magnitude and vaporizes, arcing of the asbestos free, but which nevertheless functions to current results. The metal and the metal vapors expand quench the arc. into the spaces between the inert material. Contact between the hot arc and the relatively cool granules SUMMARY OF THE INVENTION causes a heat transfer from arc to granules. This dissi 20 The present invention includes a spider material pates the arc energy but causes very little pressure which is asbestos free, and yet is well-suited for use in buildup within the fuse structure. A high resistance current limiting gassing fuses. A gassing fuse is espe results from the vaporization of the fuse element, the cially useful in low fault current applications. The spi removal of metal vapors from the arc path, and the der material is made up of Al2O3.3H2O, CaSiO3 (known rapid cooling of the arc. The current is limited accord 25 as "Wollastonite"), and melamine formaldehyde resin. ingly. The spider material preferably includes the ingredients The resistance increases rapidly. The sand particles in in the following-range of proportions: close proximity to the arc become partial conductors at the high temperature of the arc. However, fused parti cles cool on extinction of the arc and solidify into a 30 50-80% Al2O3.3H2O fulgurate, which is similar to a glass body and is an 8-22% 10-25% Wollastonite; and melamine formaldehyde resin. insulator. In order to insure against surge voltage peaks in ex cess of predetermined limits, the fuse element may have A preferred embodiment has the following propor a variable cross sectional area. It has areas of reduced 35 tions of ingredients: cross sectional area between areas of large cross section. This arrangement can be accomplished by, for example, punching a series of circular perforations in a ribbon 70% Al2O3.3H2O 12% Wollastonite; and fuse. The edges of the perforations form the areas of 18% melamine formaldehyde resin. reduced cross section. These areas of reduced cross 40 section cause progressive insertion of arc resistance into the circuit. In turn, this keeps the rate of current change The spider material of the present invention is used to relatively low. As a result, this tends to limit the induc support a fuse element, and when contacted by an arc, tive surge voltage which may occur when a current generates an arc quenching gas as well as water. It can limiting fuse operates, which otherwise might damage 45 be used for all the same purposes as a conventional circuit insulation. asbestos-containing arcquenching material, but does not A gassing current limiting fuse is an improvement suffer from the health-related problems associated with over that described above. In such a gassing fuse, the asbestos use. spider which supports the main fuse element, or at least Other objects and advantages of the invention will the portions of the spider which contact the main fuse 50 appear from the following description. element, are made of a material which generates an arc BRIEF DESCRIPTION OF THE DRAWINGS quenching gas when contacted and eroded by the heat from an arc. Such materials include, for example, For a detailed description of a preferred embodiment molded thermosetting compositions which include a of the invention, reference will now be made to the water insoluble binder and an anti-tracking substance 55 accompanying drawings wherein: such as hydrates or oxides of aluminum and magnesium. FIG. 1 is a side view, partially in cross section, of a The material can also include various fillers, for exam current limiting fuse utilizing the spider material of the ple, mica, glass, fiber, asbestos or silicon. One suitable present invention; material comprises about 75 percent aluminum hydrate FIG. 2 is a side view of a spider subassembly of the filler, 20 percent polyester resin, and 5 percent glass current limiting fuse shown in FIG. 1; fiber. See U.S. Pat. No. 3,294,936 at col. 3, lines 43 et FIG. 3 is a perspective view of one end of the spider Seq, subassembly shown in FIG. 2; The gas which is generated upon erosion by the arc FIG. 4 is a view of one end of the fuse shown in FIG. cools the decaying fuse element and fulgurate, and also 1; and provides a high resistance to further current flow. In 65 FIG. 5 is a longitudinal cross sectional view of an this manner high current flow which could damage the other current limiting fuse in which the spider material circuit is, impeded, and heat is dissipated. As in a con of the present invention can be advantageously em ventional fuse, the fuse element is surrounded by sand ployed. 4,948,828 3 4. DESCRIPTION OF THE PREFERRED preferred shape for the spider 10, suitable for use in a EMBODIMENTS gassing fuse, is shown in the accompanying drawings and described above. Referring initially to FIG. 1, there is shown one en The embodiment of spider 10 shown in FIGS. 1 to 4 bodiment of a gassing current limiting fuse 21 having is suitable for use with the preferred gassing, current included therein a spider 10 made of the asbestos free limiting fuse 21 of the present invention. Conducting material of the present invention. Fuse 21 includes a end caps 68, 70 at opposite ends of fuse 21 include ele main fuse element 20 wrapped around the spider 10 and ment terminations 22 having tabs 74 and 76. Tabs 76 are housed within a fuse tube 82. Conducting end caps 68, affixed to raised shoulders 18 at end of spider 10 by 70 are fitted over the ends of tube 82 to encapsulate fuse O extending over the shoulders 18 and surrounding them element 20 and spider 10 therewithin. Studs 83, 85 are affixed to each end cap 68, 70 respectively for conduct on two sides. This arrangement fastens element 22 ing current through the fuse 21. firmly to each end of spider 10. Tabs 74 on element 22 Referring now to FIGS. 2 and 3, the spider 10 has mate with a recessed portion in the end wall of each of the end caps 68, 70. This arrangement provides a resil four radially protruding fins 14. Each fin 14a, 14b, 14c and 14d includes a series of alternating depressions 16a, 15 ient mounting of spider 10 within the fuse tube 82 of 16b, 16c and 16d (the latter not shown), respectively, fuse 21. which extend longitudinally on each fin 14. Each pair of In fuse 21, main fuse element 20 is spirally wound successive depressions 16 forms a series of raised shoul around raised shoulders 18, and each end of element 20 ders 18 on each fin. 20 is connected to a termination element 22 (as shown in Depressions 16 are staggered along the spider 10. As FIG.3). Fuse element 20 includes two spots 90,92 made best seen in FIG.3, depression 16a on fin 14a is elevated of a low melting temperature alloy such as tin-lead from depression 16b on fin 14b, which in turnis elevated solder. Fuse 10 is connected with a circuit through from depression 16c on fin 14c, such elevations being studs 83 and 85. Current flows from the stud 85 to the measured from the central axis of the fuse 21. The de 25 conducting end caps 68, through tabs 74 and to element pressions 16 and raised shoulders 18 define a continuous termination 22. Main fuse element 20 is connected with helical path for the main fuse element 20. element termination 22. The same arrangement of ele The asbestos free spider material for the spider 10 ments is present at the opposite end of fuse 21. includes the ingredients Al2O3.3H2O, Wollastonite Referring again to FIG. 2, fuse 21 also includes an (CaSiO3), and melamine formaldehyde resin. This mate 30 auxiliary fuse element which has two wires 46 spirally rial is suitable for any application in which a conven wound around the depressions 16 of spider 10. The ends tional gassing fuse material can be employed. of wire 46 are connected to respective air gap elec To make the spider material of the invention, the trodes 40. Between fuse element 20 and air gap elec foregoing ingredients are mixed and a small amount of trodes 40 is an air gap of predetermined size. One side of acetic acid (less than 1%) is added, with blending. 35 the auxiliary fuse element wires 46 is connected to con Thereafter, this mixture is packed into a mold having a ducting end cap 68, through wire 50 and vent indicator desired shape. Later, it is removed from the mold, and wire 62. then air dried. Air drying for a period of 24 hours is Referring now to FIG. 3, fuse 21 includes a wire preferred. The mold and the mixture are then heated, assembly 48. Assembly 48 has a wire 50 which is preferably to between 200-300' F., and most prefera threaded through a passage 56 extending from the axial bly to 240 F., and dried. The dried mixture will now center of one end of spider 10 to a point on the periph have the desired shape. ery of spider 10, and secured to an eyelet 52 of element The proportions of the ingredients in the final dry termination 22. Wire 50 is then spirally wound around mixture can range as follows: spider 10 in the helical path defined by the depressions 45 16, and electrically connected to the electrode 40 which S0-80% Al2O3.3H2O; is nearest to opening 58 and eyelet 52. 8-2.2% Wollastonite; and Referring now to FIG. 4, at this same end of fuse 21 10-25% melamine formaldehyde resin. is a vent indicator wire assembly. A vent wire 62 of high resistance material, for example tungsten or nichrome, A preferred embodiment of the spider material has the SO is connected to an eyelet which is in the center of the following proportions of ingredients in the final mix end of fuse 21. This eyeletis connected with eyelet 52 of ture: the auxiliary wire assembly 48. Wire 62 extends through passage 66 in the conducting end cap 68, and to the 70% Al2O3.3H2O; 12% Wollastonite; and 1892, melamine formaldehyde resin. outside of fuse 21. Wire 62 is soldered to a point 63 on 55 the outside of the conducting end cap 68. Fuse tube 82 is filled with sand or finely divided quartz. Optionally, an elastomeric gasket can be fitted An alternate preferred embodiment of the spider mate on the ends of tube 82, and end caps 68 and 70 can be fitted over the gasket. The end caps and gaskets can be rial has the following proportions of ingredients in the 60 sealed with epoxy to provide an air and water-tight seal. final mixture: Optionally, second end caps (not shown) can be fitted over conducting end caps 68 and 70. The second end 65% Al2O3.3H2O; caps compress the gasket (if present) and produce a 15% Wolastonite; and water-tight seal between the ends of the second end 20% melamine formaldehyde resin. 65 caps and tube 82. The manner of assembling fuse 10 and its respective The shape of the mold, and thus of the spider 10, can parts is explained in more detail in U.S. Pat. No. vary depending on the intended use for the material. A 4,150,353, incorporated herein by reference. 5 4,948,828 6 In operation, a fault current will open the fuse ele main element 138. The current passes through main fuse ment 20 at two spots 90 and 92, which are preferably element 138 to element 117, which is connected to the made of a low melting temperature alloy such as tin circuit. lead solder. The voltage of the arc across the open Although the spider material of the invention has section of the main fuse element 20 will also develop the been described as useful with fuse embodiments 21 and air gap between the other end of auxiliary fuse wires 46 110, it can also be used with virtually any other type of and the main element 20. The arc voltage will increase gassing fuse. In addition, the spider material can be used as the length of the arc increases, eventually causing the anywhere that arc-tracking resistance is needed. These air gap at the unconnected end of auxiliary fuse wires 46 uses include utilization in high voltage devices as substi to force current flow to the auxiliary indicator circuit, 10 tute, or a cover over, materials which can track an arc. which consists of wires 46 and vent indicator wire 62. Because the spider material evolves gas and water in Current flow through the high resistance wire 62 will cause wire 62 to vaporize, providing indication that the response to an arc, it will quench an arc in any of these fuse has operated. Upon vaporization of wire 62, cur situations. rent flow returns to the main fuse element 20. An exami 15 It should be understood that the terms and embodi nation of wire 62 on the outside of second end cap 78 ments described above are exemplary only and not limiting, and that the scope of protection is limited only can be used to indicate whether fuse 21 is operating properly, or has operated. by the claims which follow, and includes all equivalents Referring now to FIG. 5, there is shown an alternate of the subject matter of the claims. fuse embodiment for use with the spider material of the 20 What is claimed: s present invention. A tubular casing 112 for a current 1. An improved material for a spider of a gassing fuse, limiting fuse 110 is constructed of suitable insulating consisting essentially of the ingredients in substantially material such as glass fiber, or glass fiber impregnated the following ranges of proportions: with epoxy resin. A metallic end piece 11R may be secured on the right end of casing 112 by means of any 25 suitable seal such as epoxy cement, and a metallic end 50-80% 8.22% Al2O3.3H2O; Wollastonite (CaSiO3); and piece 11L may have external threads engaging internal 10-25% melamine formaldehyde resin. threads near the left end of casing 112 to affix end piece 11L to casing 112. A metallic hinge assembly 114 may be secured to the opposite end piece 11R. The end piece 30 2. The material of claim 1 wherein the proportions of 11L has a portion 115 with an axial bore 116. A tubular ingredients are as follows: metallic member 117 extends into axial bore 116 with a force fit and is rigidly secured to end piece 1.1L by pins 70% Al2O3.3H2O; 118 extending radially through tubular member 117 and 12% Wollastonite; and portion 115 of end piece 11L. Terminal member 117 is 35 18% Inelanine formaldehyde resin. adapted to fit within a stationary contact jaw (not shown) of an electrical switch, and an insulating mem 3. The material of claim 1 wherein the proportion of ber 119 may be secured in the end of tubular member by ingredients is as follows: suitable means such as epoxy cement. An arc extin guishing sleeve 120 slidably fitting over casing 112 may have an inner tubular portion 121 of insulating material 65% Al2O3.3H2O; telescoped over terminal member 117 and may cover 15% Wollastonite; and terminal member 117 by a helical spring 122 com 20% melamine formaldehyde resin. pressed between end piece 1.1L and the end portion 124 of arc extinguishing member 120 for the purpose of 45 4. A process for preparing an arc-quenching material, interrupting any stray arc. comprising: Metallic end plates 125 are disposed against the inter preparing a mixture consisting essentially of the fol nal surface of end pieces 1.1L and 11R and are secured lowing ingredients in the following proportions: thereto. Each end piece 125 has a plurality of radially extending tabs 127 adjacent its outer periphery which 50 may form terminals to which conductors may be con nected. An elongated insulating spider 128 is axially mounted within casing 112. The ends of spider 128 ar 50-80% 8-2.2% 10-25% Al2O3.3H2O, wollastonite, melamine formaldehyde resin; affixed to end pieces 11R and 11L. s Spider 128 is of generally star-shaped cross section (as 55 adding water to the mixture and stirring to form a described above) with radially extending fins 132. Each putty; fin 132 has a plurality of depressions 133 and raised shoulders 134 as described above. The depressions 133 of peripherally successive fins 132 are progressively molding the putty into a shape desired; heating the putty; and staggered to form support means of helical configura drying the putty, tion for a helically wound circuit interrupting fuse ele ment 138 interconnecting the end pieces 1.1L and 11R. The remainder of the features of fuse 110 are substan 5. The process of claim 4 wherein the water added is tially the same as those described above for fuse 21, and substantially in the amount of 7% of the mixture. as set forth in U.S. Pat. No. 3,294,936. Fuse 110 is con 65 6. The process of claim 4 wherein the putty is heated nected to a circuit through an eyelet 126 in metallic to about 240 F., and is air dried for 24 hours. hinge assembly 114. Assembly 114 is connected with 7. The process of claim 4 wherein the mixture consists collar 11R, and from there to wire elements 141 and essentially of the following proportion of ingredients: 4,948,828 70% Al2O3 3H2O:- 12% wollastonite; and 18% melamine formaldehyde resin. 15% wollastonite;yand 20% nelanine formaldehyde resin. 5 9. A product produced by the process as in one of 8. The process of claim 4 wherein the mixture consists claims 4 through 8. essentially of the following proportion of ingredients: 10 15 20 25 30 35 45 50 55 65