US2903538A - Electric fuse - Google Patents

Description

Sept. 8, 1959 o. RICHARDSON ELECTRIC FUSE Filed June 4, 1957 FIG.

INVENTOR ATTORNEY FIG. 2 OLAN R/CHARDSO United States Patent i ELECTRIC FUSE Olan Richardson, Hampton, Ga., assignor to Southern States Equipment Corporation, a corporation of Georgia Application June 4, 1957, Serial No. 663,479

'4 Claims. (Cl. 200127) This invention relates to electric fuses and more particularly to fuses which are especially adapted to interrupt a wide range of fault currents.

In electric cutouts having a fuse tube in which a fusible element is mounted, it is common practice to provide means for closing one end of the fuse tube for fault currents of a low order of magnitude and which is arranged so as to yield upon the occurrence of fault currents of a high order of magnitude thereby to open both ends of the tube and release the high pressures generated therein due to the formation of high current arcs. The are explusion action for low current arcs is thus rendered effective due to the single vented effect and for high current arcs the device operates as a double vented cutout thereby to facilitate the quick release of high pressures built up within the tube and to aid in the prompt interruption of such high current arcs.

A principal object of my invention is to provide an improved cutout having yieldable means for promptly relieving high pressures built up within the cutout fuse tube during high current faults and which effectively closes one end of the tube during low current faults thereby to accommodate a wide range of fault currents.

. Another object of this invention is the provision of pressure responsive means for use on cutouts which performs with inverse time characteristics when lnterruptlng unusually large currents.

ing flange-like means on the tubular element for normally holding the disc in its normal position, the disc being released from its normal position upon the establishment of a high current are within the fuse tube to relieve the pressure thus developed.

For a better understanding of the invention reference may be had to the following detailed description taken in conjunction with the accompanying drawings in which Fig. 1 is a side view of an electric cutout to which the invention is applicable; Fig. 2 is an enlarged view in cross-section of the upper end of the fuse tube shown in Fig. 1 with the parts occupying their normal positions; and in which Fig. 3 is a view similar to Fig. 2 except that the parts in Fig. 3 are shown during interruption of a high current arc.

With reference to Fig. '1 thenumeral l designates a metallic arm the left end of which normally is mounted on suitable supporting structure such as a pole crossarm, not shown, and which at its right end supports a pair of coaxially arranged insulating elements 2 and 3. Mounted atop the insulator 2 is a terminal generally designated by the numeral 4 and which is affixed to insulator 2 by bolt 5. Terminal 4 comprises a connector portion 6 which is arranged to be electrically connected with a circuit conductor forming a part of the electric circuit which is in series with the cutout of Fig. l. Disposed atop the terminal 4 is an eyelet 7 in which a Patented Sept. 8, 19 59 switch stick may be inserted for handling the cutout as desired during installation or maintenance operations. Also affixed to and constituting a part of terminal 4 is a contact 8 on which is mounted a yieldable contact finger 9. Pivotally mounted to the contact 8 is a sleet hood 10 which is held in place by a pin 11.

Atfixed to the lower extremity of insulator 3 is a terminal generally designated at 12. Terminal 12 constitutes suitable means generally indicated at 13 for forming an electric connection with a conductor which forms a part of the circuit with which the cutout is connected in series. The terminal element 12 also comprises a pair of outstanding brackets 14 in each of which a jaw 15 is formed. Mounted intermediate the two arms 14 is a contact finger 16. Both contact fingers 9 and 16 are yieldable and are biased toward the right to engage the fuse tube assembly next to be described.

The fuse tube assembly generally designated by the numeral 17 comprises a fuse tube 18 atop which is mounted a metallic terminal element 19 by suitable means such as a pin 20 which extends angularly through the terminal element 19 and the body of the fuse tube 18 to secure these parts in position. Since the left-hand extremity of the terminal 19 engages a latch inside the sleet hood 10 to hold the parts in position, it is necessary in order manually to release the upper end of the fuse assembly 17 to lift the sleet hood 10 by rotating it counterclockwise about its pivot 11. For this purpose an operating arm 21 is pivotally mounted at 22 to the terminal 19 and is provided at its right-hand extremity with an eyelet 23. Thus with a switch stick inserted in the eyelet 23, the operating arm 21 is rotated clockwise about its pivot 22 to lift the sleet hood 10 upwardly thereby to unlatch the left-hand end of the terminal 19 and to allow the parts of assembly 17 to swing down to open circuit position in known manner.

Mounted at the bottom of fuse tube 18 is a collar 24 by means of a pin 25 which is similar to pin 20 above described. Collar 24 is also provided with pivot 26 which serves as a mounting for the conducting element 27. Conducting element 27 is provided with a pair of trunnions 28 which are mounted within the jaws 15 of the brackets 14. Conducting element 27 is held in its normal position shown in Fig. 1 by means of the condoctor 29 one end of which connects with the fusible element mounted within the fuse tube 18 and the other end of which is afiixed by a suitable clamping screw (not shown) to the conducting element 27. It will be understood that conducting element 27 is provided with a contact surface 30 which is engageable with the finger contact 16 to establish a current path therebetween. Furthermore, it will be understood that the portion 31 of terminal 19 constitutes a contact surface which cooperates with finger contact 9 to establish a current path therebetween.

As is best shown in Fig. 2 a hollow tubular element 32 is threadedly secured atop the terminal element 19. Furthermore, from Fig. 2 it is apparent that disc 33 is held in place by the flange-like means 34 formed integrally with the hollow tubular conducting element 32. Fusible element 35 mounted within fuse tube 18 is provided with a button head 36 which engages the upper end of the terminal element 19 to establish electric contact therebetween. Contact pressure between the button head 36 and the terminal element 19 is provided by the tension in fusible element 35 and also by the force exerted on the top of the button head by the disc 33. Thus the deformable element or disc 33 constitutes an alternative or shunt path for current flowing between the button head 36 and the terminal element 19, the magnitude of current flowing through this shunt path being a function of the current in an are established within the tube 18 upon rupture of fuse link 35.

Thus for currents of a low order of magnitude which are sufficiently large to melt the fuse link 35, an arc is drawn within the fuse tube 1 8 and is extinguished by explusion action through the lower end of the fuse tube, the cutout performing as a single vented device. During such an operation the button head 36 is held in secure engagement with the upper end of terminal 19 by the disc 33 and even though the current may be relatively small sufiicient gas is generated within the tube to perform an efiicient arc interrupting operation.

If, however, the current magnitude is very large the gas developed within the fuse tube 18 and the current flowing in the arc will be substantial and such pressure and current will result in the deformation of the deformable element 33 or of the flange-like means 34 or both and will result in the blowing of the button head 36 together with the disc 33 outwardly as indicated best in Fig. 3. By suitable choice of material for disc 33 and by making the diameter thereof sufiiciently greater than the diameter of the button head 36 and in proper relation to the flange 34, I find that excellent results are achieved. Preferably the diameter of the inner edge of the flange-like means should be somewhat greater than the diameter of the button head plus twice the thickness of the disc. An explanation of these excellentresults lies in the possibility that high current arcs establish an initial pressure which tends to move the lower edge of the button head out of engagement from the terminal 19 thereby to cause at least a part of the large current to be shunted through the disc 33, flange 34, and the hollow tubular element 32 to the terminal element 19. Such high current tends to heat and thereby to soften the disc 33 and the flange-like means 34 and in this manner may expedite the blowing of the disc 33. Thus it would appear that this arrangement affords an inverse time characteristic which relieves the pressure more quickly for very large currents than for currents of more moderate magnitude.

Of course it will be understood that melting of the fusible element, no matter what the current magnitude, releases the conducting element 27 from its normal position relative to the other parts and thereby allows element 27 to rotate clockwise about trunnions 28 in known manner. Such rotation causes pivot 26 to inscribe an are about the trunnions 28 as a center. Thus the lower end of tube 18 is moved downwardly and somewhat toward the right initially thereby to lower the upper end of tube 18 and associated parts. When the left-hand end of terminal element 19 is moved downwardly a suificient distance to clear the latch within the sleet hood 10, the entire assembly 17 swings in a clockwise direction about the trunnions 28 to occupy a lowermost position and thus affords a visible indication of the fact that the circuit is open.

While I have shown and described a particular embodiment of the invention, I do not wish to be limited thereto and intend in the appended claims to cover all such changes and modifications which fall within the true spirit and scope of the invention.

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

1. An electric fuse comprising a fuse tube, a terminal element of conducting material mounted on one end of said fuse tube and having a passage therein, a hollow tubular element mounted on said terminal element and forming a continuation of said passage, a closure element normally closing said tubular element, and flangelike means on the outer end of said tubular element for normally holding said closure element in its normal position, said closure element and said flange-like means being deformed upon the establishment of a high current are within said tube so as to release said closure element from its normal position without rupturing said closure element or said flange-like means.

2. An electric fuse comprising a' fuse tube, a terminal element of conducting material mounted on one end of said fuse tube and having a passage therein, a hollow tubular element mounted on said terminal element and forming a continuation of said passage, a closure element normally closing said tubular element, and flange-like means on the outer end of said tubular element for normally holding said closure element in its normal position, said closure element being deformed and released from said tubular element upon the establishment of a high current are within said tube without being ruptured.

3. An electric fuse comprising a fuse tube, a terminal element of conducting material mounted on one end of said fuse tube and having a passage therein, a hollow tubular element mounted on said terminal element and forming a continuation of said passage, a closure eleelement normally closing said tubular element, and flangelike means on the outer end of said tubular element for normally holding said closure element in its normal position, said flange-like means being yieldable so as to release said closure element from its normal position upon the establishment of a high current are within said tube without being ruptured.

4. Replaceable closure means for mounting on a terminal element of a fuse tube comprising a hollow tubular element having an internally threaded portion at one end and an integral internal flange-like portion at the other end, the internal diameter of said threaded portion being less than the internal diameter of said flange-like means and said threaded portion extending from said one end toward said other end to a point immediately adjacent said flange-like portion, and a semi-rigid closure element normally disposed in abutting relation with the end of said threaded portion adjacent said other end of said tubular .element and normally closing said other end of said hollow tubular element and being of a thickness generally comparable to the thickness of said flange-like portion, said closure element being normally held in its normal position by said flange-like means.

References Cited in the file of this patent UNITED STATES PATENTS 1,294,621 Conrad Feb. 18, 1919 1,635,049 McGee July 5, 1927 2,074,538 Conrad Mar. 23, 1937 2,135,164 Brock NOV. 1, 1938 2,459,691 Earle et al. Jan. 18, 1949 2,583,440 Oxley et al. Jan. 22, 1952 2,846,544 Wood Aug. 5, 1958 FOREIGN PATENTS 54,804 Netherlands May 16, 1943

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