US2880289A - Circuit interrupting means - Google Patents

Description

March 31, 1959 C. VH. BAKER CIRCUIT INTERRUPTING MEANS Filed July 25, 1957 IVENTOR.

United States Patent O CIRCUIT INTERRUPTING MEANS Charles H. Baker, Arlington Heights, Ill., assignor to S&C Electric Company, Chicago, Ill., a corporation of Delaware Application July 2s, 1957, serial No. 674,181

1o Claims. (Cl. 20o-120) This inventio-n relates, generally, to circuit interrupting means and it has particular relation to fuse links. lt constitutes an improvement over the fuse link construction shown in McMahon Patent No. 2,586,171, issued February 19, 1952.

ln the patent above referred to a fuse link construction is disclosed in which an insulating and arc extinguishing sleeve is secured to one of a pair of terminals of the fuse link which are interconnected by fusible means. The sleeve was formed by convolutely wrapping a sheet of paper to form a liner, which was impregnated with an arc extinguishing material, and then surrounding the liner with a convolute Wrapping of pressure sensitive tape. The composite sleeve was adhesively secured to one of the fuse link terminals.

As pointed out in this patent, the fuse link construction was intended for use in expulsion fuse tubes the internal diameter of which ranged upwardly from 5/16. The maximum internal diameter of such fuse tube was about W16". The fuse link construction disclosed in the patent functioned satisfactorily for the interruption of low fault currents and had a maximum interrupting capacity of the order of 200 to 300 amperes. Above this current range, rupture of the fuse link sleeve occurs and then interruption of the current flow depends on the fuse tube without assistance from the sleeve. Thus, that fuse link did not always enable the expulsion fuse tube or cutout to clear satisfactorily when the tube diameter was %6" or larger at currents above 300 amperes and normal frequency recovery voltage corresponding to line circuit voltages of l2 to 13.8 kv.

Since the advent of the fuse link construction of the McMahon patent, the available short circuit current on distribution circuits has become higher and higher. It has therefore become necessary to increase the interrupting capacity of distribution cutouts. This was economically accomplished in many cases by increasing the inside diameter or bore of the cutout fuse tube, thereby reducing the internal pressure developed at these higher short circuit currents and making interrupting possible in a relatively light and inexpensive device.

Because of the increase in inside diameter of expulsion fuse tubes for cutouts and the reduced generation of deionizing gas from the walls of the tube itself by the heat of the arc at all current levels, there has been an increase in the minimum current that can be interrupted satisfactorily` in such a device without the assistance 0f the fuse tube link sleeve. It will be seen that there is a range of fault current somewhat above the 200 to 300` ampere interrupting capacity of the fuse link of the McMahon patent which cannot be interrupted satisfactorily by many expulsion fuse tubes that presently are being employed to meet the liioher interrupting requirement. The reason for this is the greater inside diameter of such fuse tubes. The result has been that there is the likelihood of relatively low current arcs persisting for several cycles or even failure to clear the arc at all when the circuit should have been interrupted promptly. A typical example of ICC such low current interrupting requirements is a secondary fault on a transformer which should be cleared promptly by the cutout connected in series with the primary winding so as to prevent burn out of the windings of the transformer. The transient recovery voltage in such case is relatively more severe than occurs when a primary fault of high current magnitude is interrupted while the generation of deionizing gas without the aid of an efficient link sleeve would be at a low rate.

What is desired is an increase in the interrupting ability and strength of the fuse link to extend its range upwardly in order to permit larger internal diameters of expulsion fuse tubes while at the same time maintaining the same external diameter of the fuse link sleeve so that it still can be employed in existing expulsion fuse tubes having minimum diameters of the order of 5/16 to W16. As pointed out in the McMahon patent, for proper operation, there is a definite relationship between the maximum interrupting ability of the fuse link sleeve and the minimum interrupting ability 0f the expulsion fuse tube. Therefore, the solution to the problem of obtaining higher current interrupting ability in a fuse link sleeve lay not just in making it stronger to prevent bursting at the higher current, but this greater strength had to be obtained with,- out increase in the outside diameter.

The increase in bursting strength of the fuse link sleeve was not alone the answer to the problem of increased interrupting capacity. In order to realize this ability as the result of greater sleeve strength, it is necessary that the sleeve be retained on the fuse link terminal to which it is attached and to prevent it from being expelled from the cutout tube in the range of currents to be interrupted by the sleeve alone. While the sleeve of the McMahon patent would meet this requirement in the range of current up to 200 amperes, it was found that a reinforced stronger sleeve would not be retained on the terminal at higher current, such as to 800 amperes, which such a reinforced sleeve could interrupt. It was discovered that the innermost layer of paper of the liner for the fuse link sleeve remained firmly attached to the fuse link terminal but that the remainder of the sleeve would be torn from this terminal by delamination between the outer layers of the paper impregnated with arc extinguishing material. This delamination action took place in a range from 400 to 800 amperes. In order to prevent such delamination and expulsion of the sleeve from the cutout tube before it had an opportunity to extinguish the arc it was found that such undesirable action could be prevented by providing a good bond between the layers of the convolutely wound paper at the end immediately surrounding the fuse link terminal. In accordance with this invention this was accomplished by impregnating only that portionv of the paper forming the liner which .was to be coextensive with the fuse link terminal to which it was secured with an adhesive of adequate strength while the paper was being rolled into the tubular configuration. The adhesive impregnant used is of such character that it penetrates the interstices and fibres of the paper and, upon drying of polymerization a substantially solid homogeneous structure was attained. This solid end portion of the completed and reinforced fuse link sleeve then is attached to the terminal by a suitable adhesive. When such a construction is employed delamination and loss of the fusev link sleeve does not occur within the interrupting range ofv sleeve of a fuse link without increasing its outside diameter; to provide a construction that can resist endwise forces between the sleeve and the terminal of the fuse link to which it is attached on blowing of the fusible means connected to the terminal in the range of currents to be interrupted in the sleeve; and to limit the applicaion of adhesive for that purpose to the line or of the sleeve and its convolute layers for bonding them together and securing the sleeve to the fuse link terminal substantially only to that portion that is coextensive with the fuse'link terminal in order to avoid interference with the impregnation of the balance of the liner with arc extinguishing material and subsequent liberation of water from the arc extinguishing material when the liner is subjected to the heat of an arc incident to the opening of a circuit on the occurrence of a fault therein.

Other objects of this invention will, in part, be obvious and in part appear hereinafter.

This invention is disclosed in the embodiment thereof shown in the accompanying drawing and it comprises the features of construction, combination of elements and arrangement of parts that will be exemplified in the construction hereinafter set forth and the scope of the application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of this invention reference can be had to the following detailed description, taken together with the accompanying drawing, in which:

Figure 1 is a plan View of a paper sheet that is rolled convolutely in order to form the liner for a fuse link sleeve;

Figure 2 is a plan view of a wrapper which is convolutely wound around the liner in completing the formation of the fuse link sleeve; and

Figure 3 is a longitudinal sectional View of a fuse link employing the fuse link sleeve of the present invention.

Referring now to Figure 3 of the drawing, it will be observed that the reference character 10 designates, generally, a fuse link which is typical of the fuse links to which the present invention can be applied. The fuse link 10 includes relatively infusible terminals 11 and 12 which are interconnected by fusible means that comprises a strain wire 13 and a fusible element 14. In some fuse links only the strain element 13 is employed, the fusible element 14 being dispensed with. The upper end 15 of the terminal 11 is threaded for receiving a removable button head 16 with which a washer 17 cooperates to adapt the fuse link 10 for mounting in fuse tubes of varying diameters and to facilitate connection to one terminal of the fuse tube. A stranded exible conductor 18 extends from the other terminal 12 for a length sufficient to extend out of the other end of the expulsion fuse tube for connection to a second line terminal.

Surrounding the fusible means comprising the strain wire 13 and fusible element 14, secured to the terminal 11 and extending over the terminal 12 is an insulating and arc extinguishing sleeve that is indicated, generally, at 21 in which are embodied the improvements of the present invention. It will be noted that the upper end of the sleeve 21 abuts a radial flange 22 forming a part of the terminal 11 and that it is secured to a sleeve attaching portion 23 intermediate the ends of the terminal 11 by an adhesive 24 which may be the adhesive disclosed in the McMahon patent on the adhesive referred to hereinafter.

The sleeve 21 is provided with a liner 25 that is formed by convolutely rolling a sheet 26, Figure 1, of alpha cellulose paper to form a tube. In accordance with this invention a layer of adhesive 27 is applied along one end of the sheet 26, as shown in Figure l, for a limited extent which is substantially coextensive with the length of the sleeve attaching portion 23 of the terminal 11. The'adhesive 27, like the adhesive 24, can be an acetate adhesive, as disclosed in the McMahon patent, or it can be a'water base emulsion of a synthetic resin which is of the rubber complex type. Whatever adhesive is used, it should be one which will completely penetrate and im-` pregnate the portion of the sheet 26 to which it is applied so that, when itis convolutely wound to provide the liner 25, a homogeneous mass is provided which, in effect, is a solid in which the paper forms merely a ller. On blowing of the fusible means of a fuse link having the sleeve formed and attached as just described, a blast of arc extinguishing vapor and gas is generated by the ensuing arc. There is a relative endwise force applied to the sleeve 21 and terminal 11. Since there is no likelihood of delamination of the liner 25' where it is secured to the sleeve attaching portion 23 of the terminal 11, the sleeve 21 remains in place and holds the liner 25 where the arc extinguishing material impregnated therein is available for arc extinguishing purposes until the arc is completely extinguished. Even though it were possible to impregnate the sheet 26 of paper with some arc extinguishing material before winding it to form the liner 25, the application of a strong adhesive over the entire surface of the sheet 26 and between the layers of the same when it is convolutely wound would interfere with the liberation of arc extinguishing gas from all but the innermost convolution. If such a construction, as just described, is not employed, the innermost convolution of the liner 25 remains attached to the attaching portion 23 of he terminal 11 while the immediately surrounding portion becomes detached and the principal portion of the sleeve 21 is expelled from the cutout tube before the arc is extinguished.

By applying the adhesive 27 only to a limited portion of the sheet 26 and subsequently impregnating the balance of the sheet 26 with an arc extinguishing material, such as magnesium borate, boric acid, etc., there is no interference with the evolution of arc extinguishing vapors or gases from the convolute layers of the liner 25l when it is subjected to the heat of the arc.

In order to withstand the greater bursting pressure within the liner 25 incident to the use of the fuse link 10 in larger diameter expulsion fuse tubes than heretofore and interruption of currents below the values that can be interrupted by the fuse tube itself, a wrapper 28 is convolutely applied which has a higher strength than does the cellulose acetate wrapper for the sleeve shown in the McMahon patent. As illustrated in Figure 2 of the drawing a sheet 29 of pressure sensitive tape is employed which preferably is a polyester resin film made from ethylene glycol and terephthalic acid that is sold in the' can be used to reinforce the liner 25, such as the sheath of iiber that is shown in U. S. Patent No. 2,253,720 or the phenolic condensation product layer shown in U.S. Patent No. 2,324,044.

Since certain changes can be made in the foregoing construction and different embodiments of the invention can be made without departing from the spirit and scope thereof, it is intended that all matter shown in the ac-` companying drawing and described hereinbefore shall be interpreted as illustrative and not in a limiting sense.

What is claimed as new is:

l. In a sleeve for attachment at one end to a terminal I of a fuse link, a liner of convolutely wound paper having a portion at said one end coextensive with the portion of the terminal to which it is secured substantially completely impregnated with adhesive material having relatively high bonding strength and formed into a non-laminar section, the remaining portion of said liner being impregnated with arc extinguishing material different from said adhesive material and having substantially less mechanical strength than said portion at said one end.

2. A sleeve for attachment at one end to a terminal of a fuse link comprising, in combination, a liner of convolutely wound paper having a portion at said one end coextensive with the portion of the terminal to which 1t is secured substantially completely impregnated with adhesive material and formed into a non-laminar section having relatively poor arc extinguishing characteristics, the remaining portion of said liner being impregnated with arc extinguishing material and providing said remaining portion with relatively good arc extinguishing characteristics, and a wrapper overlying said liner and reinforcing the same.

3. A sleeve for attachment at one end to a terminal of a fuse link comprising in combination, a liner of convolutely wound paper having a portion at said one end coextensive with the portion of the terminal to which it is secured substantially lcompletely impregnated with adhesive material having relatively high bonding strength and formed into a non-laminar section, the remaining portion of said liner being impregnated with arc extinguishing material containing a substantial amount of water of crystallization, and a Wrapper convolutely wound on said liner and reinforcing the same.

4. A sleeve for attachment at one end to a terminal of a fuse link comprising, in combination, a liner of convolutely wound paper having a portion at said one end coextensive with the portion of the terminal to which it is secured substantially completely impregnated with adhesive material and formed into a non-laminar section of relatively high mechanical strength, the remaining portion of said liner being impregnated with arc extinguishing material and having relatively low mechanical strength, and a wrapper convolutely wound on said liner and reinforcing the same, said Wrapper being formed of polyester resin tilm pressure sensitive tape.

5. A replaceable fuse link comprising, in combination, a pair of terminals interconnected by fusible means, one of said terminals having a sleeve attaching portion intermediate its ends, and an arc extinguishing sleeve surrounding said fusible means, said sleeve being adhesively secured to said sleeve attaching portion of said one terminal and extending over the other terminal, that portion of said sleeve immediately surrounding said fusible means being formed by a convolutely wound paper sheet impregnated with an arc extinguishing material and having adhesive along one end coextensive substantially only with said sleeve attaching portion of said one terminal and unitarily securing the juxtaposed portions of the convolutions to hold them in place on said sleeve attaching portion when the sleeve is subjected to an endwise force relative to said one terminal on blowing of said fusible means, that portion of said sleeve coextensive with said sleeve attaching portion of said terminal containing substantially none of said arc extinguishing material and having relatively high mechanical strength and that portion of said sleeve carrying said arc extinguishing material being relatively weak mechanically.

6. A replaceable fuse link comprising, in combination, a pair of terminals interconnected by fusible means, one of said terminals having a sleeve attaching portion intermediate its ends, and an arc extinguishing sleeve surrounding said fusible means, said sleeve being adhesively secured to said sleeve attaching portion of said one terminal and extending over the other terminal, that portion of said sleeve immediately surrounding said fusible means being formed by a convolutely wound paper sheet impregnated with an arc extinguishing material and being relatively weak mechanically and having adhesive along one end coextensive substantially only with said sleeve attaching portions of the convolutions which are substantially free of said arc extinguishing material and are relatively strong mechanically to hold them in place on said sleeve attaching portion when the sleeve is subjected to an endwise force relative to said one terminal on blowing of said fusible means, and a Wrapper overlying said liner and reinforcing the same.

7. A replaceable fuse link comprising, in combination, a pair of terminals interconnected by fusible means, one of said terminals having a sleeve attaching portion inter mediate its ends, and an arc extinguishing sleeve surrounding said fusible means, said sleeve being adhesively secured to said sleeve attaching portion of said one terminal and extending over the other terminal, that portio-n of said sleeve immediately surrounding said fusible means being formed by a convolutely wound paper sheet impregnated with an arc extinguishing material containing a substantial amount of water of crystallization and having adhesive along one end coextensive substantially only with said sleeve attaching portion of said one terminal and unitarily securing the juxtaposed portions of the convolutions which are substantially free of said arc extinguishing material to hold them in place on said sleeve attaching portion when the sleeve is subjected to an endwise force relative to said one terminal on blowing of said fusible means, and a wrapper convolutely wound on said liner and reinforcing the same.

8. A replaceable fuse link comprising, in combination, a pair of terminals interconnected by fusible means, one of said terminals having a sleeve attaching portion intermediate its ends, and an arc extinguishing sleeve surrounding said fusible means, said sleeve being adhesively secured to said sleeve attaching portion of said one terminal and extending over the other terminal, that portion of said sleeve immediately surrounding said fusible means being formed by a convolutely wound paper sheet impregnated with an arc extinguishing ma terial containing a substantial amount of water of crystallization and being relatively weak mechanically and having adhesive along one end coextensive substantially only with said sleeve attaching portion of said one terminal and unitarily securing the juxtaposed portions of the convolutions which are substantially free of said arc extinguishing material and are relatively strong mechanically to hold them in place on said sleeve attaching portion when the sleeve is subjected to an endwise force relative to said one terminal on blowing of said fusible means, and a wrapper convolutely wound on said liner and reinforcing the same, said wrapper being formed of polyester resin lm pressure sensitive tape.

9. Method of making a liner for a fuse link which comprises: applying an adhesive along substantially the entire width at one end of a sheet of paper capable of absorbing the same, rolling the sheet convolutely to form a tube, and impregnating the portion of the tube exclusive of the portion carrying the adhesive with an arc extinguishing material.

10. Method of making a sleeve for a fuse link which comprises: applying an adhesive along substantially the entire width at one end of a sheet of paper capable of absorbing the same, rolling the sheet convolutely to form a tube, impregnating the portion of the tube exclusive of the portion carrying the adhesive with an arc extinguishing material, and convolutely winding a relatively high strength wrapper around said tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,328,825 McMahon Sept. 7, 1943 2,586,171 McMahon Feb. 19, 1952 2,740,016 Hughes Mar. 27, 1956

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