US2877320A - Fuse cutout - Google Patents

Description

G. L. HILL FUSE CUTOUT March 10, 1959 2 Sheets-Sheet 1 Filed Aug. 18, 1954 United States Patent FUSE CUTOUT George Leslie Hill, Oakland, Calif.

Application August 18, 1954, Serial No. 450,575

Claims. (Cl. 200-114) My invention relates to fuse cutouts; and more particularly to fuse cutouts of the open, dropout type used in relatively high voltage distribution circuits.

One of the objects of my invention is the provision of a dropout type fuse cutout capable of efliciently interrupting small, low power factor currents without impairment of circuit interruption at high short circuit currents.

Another object of my invention is the provision of an open type cutout in which the various component parts on both terminal ends are shielded from the elements.

Still another object of the invention is the provision of means for more eificiently retaining the fuse cutout operatively interposed in an electrical circuit.

Still another object is the provision of an improved latch and tripping mechanism which requires a relatively small force to retain a relatively large force in the stored energy position of the operating spring.

A still further object is the adaptation of a deionizing and catching chamber on the expulsion end of the expulsion tube to operate efiiciently in cooperation with the other improvements of the device.

The invention possesses other objects and features of value, some of which, with the foregoing, will be apparent from the following description and the drawings.

Referring to the drawings:

Fig. l is a side elevational view of the fuse cutout in operative position. Portions of the device are broken away to disclose the underlying structure.

Fig. 2 is a horizontal sectional view taken in the plane indicated by the line 2-2 of Fig. 1.

Fig. 3 is a vertical sectional view taken in the plane indicated by the line 3-3 of Fig. 2. The view shows the relationship of the parts after the fuse link has ruptured.

Fig. 4 is a fragmentary view partly in vertical section showing a modified construction of the lower end of my fuse cutout.

Fig. 5 is a view in elevation taken in the direction indicated by the arrow 5 in Fig. 4.

Fig. 6 is an elevation of the lower guide ferrule removed from the assembly shown in Figs. 4 and 5.

Broadly considered, the open type dropout fuse cutout of my invention comprises an expulsion tube equipped with upper and lower terminal ends each shielded from the elements, and provided with the conventional fuse link adapted to be interposed in an electrical distribution line. Means are provided on the inside of the expulsion tube for automatically accommodating variations in expulsion pressures, and a deionizing and catching chamber is provided to catch the ruptured and expelled fuse link parts. A trunnion bearing on the lower terminal and carried by an insulator, provides means for supporting the cutout tube in operative position while also providing ice In greater detail then, and referring now to the drawings, my drop-out type fuse cutout assembly comprises the conventional insulator 2 provided with a center bracket 3 for attachment to a cross arm or other support. The bracket is designed so that the insulator is supported at the typical angle with respect to the vertical axis used for dropout cutouts.

Secured to the top and bottom ends of the insulator are clamping rings 4 and 6, providing a mounting for the terminal brackets 7 and 8 respectively. High voltage electrical leads 9 and 12 connect to the terminal brackets 7 and 8 respectively.

' tube when the fuse link ruptures due to an overload or short circuit, the lower end of the expulsion tube is provided with trunnions 21 journaled in the bearing bracket 22, which, in turn is secured to the supporting bracket 8 on the insulator 2.

For ease and economy of construction and assembly of the device, the trunnions are fixed on a cantilever bracket arm 23 integral with the cylindrical expulsion tube guide member 24. The guide member and bracket arm 23 are preferably cast in one integral unit.

The guide member is preferably of such inside diameter as to easily accommodate the coil spring 26 therein, which in the assembly fits around the lower end of the expulsion tube 16 and works between collar rings 27 and 28 shown in Fig. 3.

The collar ring 27 is secured within the upper end of the cylindrical guide member 24 by screws 29, and closely surrounds the expulsion tube which is slidable therethrough.

In Fig. 3 the collar ring 28 is adjustably secured to the tube 16 by set screws 31, and is proportioned to fit slidably within the guide member 24.

Thus, it will be seen by reference to Figs. 1 and 3, that upward movement of the expulsion tube compresses the spring until the parts are in the position shown in Fig. 1. This is the position the parts are in when the cutout is fused and ready to be inserted in the circuit.

Secured to the lower end of the expulsion tube as by threads 32, is a ferrule 33 provided with an annular flange 34 and a cylindrical threaded extension 36 adapted to engage the threads 37 of a catching and deionizing chamber 38. A notch 39, formed in the flange 34 and threaded extension, provides for the passage therethrough of the outer portion of the pigtail or flexible conductor. The end of the flexible conductor is looped around the threaded stud 41, fixed on the pivotally mounted latch plate 42. A terminal thumb nut 43 is shown in Figs. 1 and 3 to insure positive contact and anchoring of the pigtail. It should be noted that before the pigtail is anchored to the latch plate, at the terminal the pigtail is passed over the bifurcated end 44- of the latch plate.

for pivotal movement of the cutout expulsion tube when I the fuse link ruptures due to an overloaded circuit. Means are provided on the lower end of the expulsion tube for retaining the fuse cutout operatively engaged in the circuit, and for quickly separating the upper terminal end from the line terminal when the fuse link ruptures.

The latch plate, shown best in Figs. 1 and 3, is pivotally mounted on the guide member by means of the pin 46 journaled in bearing tabs 47. Spaced below the pivot point-and extending laterally from the latch plate in cantilever fashion is a latch stud 48. When the'cutout is in loaded condition, as shown in Fig. 1, the latch stud extends through the aperture 49 in the guide member, and the proportions of the parts are such that the latch' stud underlies the collar ring 28, which has been moved upwardly to a point determined by the 3 length of the fully loaded spring. When the parts are in this position, that is, with the latch underlying the collar ring 28 and the spring fully loaded, the pigtail is pulled taut and anchored under terminal thumb nut 43.

Thus, it will be apparent that downward pressure on the expulsion tube exerted by the spring results in a rotary movement being applied to the latch plate, tending to rotate it counter-clockwise to the position shown in Fig. 3. counteracting this rotary movement and tending to hold the latch and latch stud engaged, is the tension in the pigtail being applied at the bifurcated end 44 of the latch plate. As a result, the horizontal force exerted on the end of the latch plate is only a small percentage of the downward force exerted by the spring. Hence, when the fuse link ruptures, tension in the pigtail immediately drops to zero and the overwhelming pressure exerted by the spring throws the latch stud out of engagement and the parts instantly assume the position shown in Fig. 3. It will be readily apparent that the strain imposed on the fuse link is very small as substantially all of the force exerted by the spring is sustained by the pin 46.

When an overload or short circuit occurs and the fuse link ruptures, the resultant arc and combustion of the fuse link parts generates an exceedingly high pressure within the expulsion tube. Since the cap 17 closes off the upper end of the expulsion tube, the pressure must be relieved downwardly. Since it is desirable that the fuse link parts be expelled from the tube, the pressure generated is utilized for that purpose. The deionizing and catching chamber 38 catches these molten and hot parts, while providing for the cooling and subsequent escape of the gases.

Tests and field experience have shown that typical expulsion cutouts without the deionizing and catching chambers will usually expel the fuse link and flexible conductor with a sufficiently high velocity to pull it loose from the terminal thumb nut 43 at the bottom of the cutout when a heavy short circuit occurs. If the link is allowed to fall to the ground in a rural area during the dry season it constitutes a fire hazard and may start a disastrous grass and forest fire or it may hit a person or automobile if in an industrial area.

A light fault current may expel the fuse link and pigtail from the tube but on cutouts without the deionizing and catching chamber it will be dangling from the bottom terminal. If another fuse on the same transformer bank or capacitor bank remains intact the dangling fuse link and conductor will be energized from this other source. A dangling fuse link and conductor is not readily visible, particularly on dark or stormy nights (when a large percentage of fuse blowings occur) and it constitutes a hazard to the man who must climb the pole to replace the blown fuse. Therefore the adaptation of the deionizing and catching chamber to the dropout cutout is a distinct improvement on this type of device.

It has been found through experience with this type of cutout that expulsion tubes having an internal diameter of the order of about /2" or 25 are very etficient in expulsion of fuse link parts when high short circuiting currents are involved. However, when low currents at low power factors, such as in highly inductive circuits and in circuits having capacitors as the load, are involved, the expulsion tubes of large inside diameter have proved to be inefficient, with a resultant prolongation of the arcing interval, resulting in failure of the device to interrupt the circuit in some cases.

I have discovered that the solution of this problem lies in control over the time-pressure ratios at the instant of interruption and shortly thereafter. Thus, in a large inside diameter expulsion tube, interruption of a high short circuiting current results in the generated pressure rising to a peak very rapidly in point of time, and then tapering 01f gradually as the relatively large inside diameter allows the gases to escape. If an expulsion tube having a relatively small inside diameter, say about or A or less is used with the same current, the rapid build-up of pressure and the relatively restricted escape path results in a pressure that will burst the expulsion tube.

On the other hand, small low power factor currents do not generate sufiiciently high pressures, and the large inside diameter of the tubes allows escape of the gas at a relatively low velocity, in some cases the pressure and velocity combination not being sufficient to expel the fuse link parts. Thus, the industry has resorted to different size cutouts and designs to handle the variations in circuit conditions and overloads.

To obviate this problem, the cutout of my invention is provided with an expulsion tube which will operate safely and efficiently in either circumstance. As shown in Figs. 1 and 4, the inside surface of the tube 16 is formed with a wide and relatively deep spiral groove 51 in the nature of a thread extending the length of the tube.

In high short circuit current interruption, the spiral groove provides the necessary volume for safe expansion and escape of the gases under high pressure conditions before the fuse link parts are expelled entirely from the tube. This portion of the gases escaping spirally down the groove, are cooled as they go, due to the increased length of travel. The rest of the gases are expelled straight down at considerable velocity due to the restricted passage and operate to expel the fuse link parts from the tube.

In small low power factor currents, while the pressure generated is not as great, the relatively restricted escape passages acts to maintain a high escape velocity in the gases, thus completely expelling all fuse link parts.

In Figs. 4, 5 and 6 I have shown a modified form of the lower part of the cutout, especially the ferrule 33, and a modified means for anchoring the end of the pigtail.

The guide ferrule 33 in these figures differs from that shown in Figs. 1 and 3 only in that the upper end has been extended and is provided at its top with a groove 52 to receive a snap ring 53. This form eliminates the collar 28 on the tube 16. The tube 16 is guided in the guide member 24 by the aperture 54 therein and the ring 56. This base ring 56 is slideable within the guide member 24 and provides a base against which the lower end of the spring 26 may abut. The snap ring 53 has sufficient clearance between its outside diameter and the inside diameter of guide member 24 to be expanded and then snap into the groove 52. The snap ring acts as a stop for the ferrule 33 as it slides through the aperture 54 in guide member 24. If desired the base ring 56 may be eliminated and the spring allowed to abut against the end of the ferrule or directly on the snap ring. In this case the ring 27 may act as the guide for the tube 16.

There is sometimes a tendency for the expulsion tube and ferrule to rotate within the guide member 24. To prevent rotary movement of the parts, a small inwardly projecting lug 57 on the lower end of the guide member 24 is adapted to project into the vertical groove 58 formed in the periphery of the ferrule 33.

The modified anchoring means for the pigtail includes a shorter stud 41 provided with a nut 59 retaining a spring clip 61 of suitable material such as beryllium copper on the latch plate. Crowding the end of the pigtail between the clip 61 and the plate 42 allows the resilience of the clip to act as a clamp and retain the pigtail in a securely anchored condition at the terminal.

One of the objects of my present invention is to provide a cutout of the drop-out type in which means are provided to protect the upper and lower terminals from the ele ments, particularly salt air spray, sleet and ice formation and highly contaminated industrial atmosphere.

To this end I provide a hood 63 fixed securely to the upper terminal bracket 7 by means of the bolt 64. A re silient contact plate 66, preferably of beryllium copper po sitioned within the hood serves to electrically and mechanically connect the terminal bracket 7 and the capped upper end of the expulsion tube to hold it in closed position. The hood is preferably formed with a top 67 and sides 68 which flare out slightly at the bottom; and the extreme outer ends 69 of the sides project beyond the top and are flared out to permit easy entrance of the cap 17 therebetween when the tube is inserted in the circuit by means of the ring 71.

The guide member 24 and latch mechanism is protected by a hood or housing 72, having a top 73, a bottom 74, and side walls 77. The top is preferably bifurcated to accommodate the expulsion tube, and the sides are provided with the circular sections 77 adapted to enclose and resiliently grip the sides of the guide member 24. It will thus be seen that sleet, ice and contamination are efifectively prevented from fouling the operating mechanism, thereby reducing the likelihood of the cutout not operating properly when an overload occurs. It is to be understood that I do not limit myself to the embodiments shown and described, but may embody my invention in various forms within the scope of the appended claims.

I claim:

1. In a fuse cutout of the drop-out type, an expulsion tube, a fuse link within the tube, terminals on the cutout, a guide member pivotally mounted on one of said terminals, said guide member apertured to slidably receive said tube, a collar ring fixed on the expulsion tube and slideable wholly within said guide member between upper and lower limits, a coil spring interposed between said collar ring and the guide member, and latch means on the guide member adapted to engage said collar ring at its upper limit within the guide member to lock the spring in compressed condition.

2. In a fuse cutout of the drop-out type employing an expulsion tube having a fuse link and flexible conductor therein for interposition between terminals of said cutout, a guide member pivotally mounted on one of said terminals and slidably enclosing a lower portion of the expulsion tube, a collar ring fixed on the expulsion tube and slideable therewith wholly within said guide member between upper and lower limits, a coil spring surrounding the tube within the guide member and engaging the collar ring and compressible thereby when the collar ring is at its upper limit within the guide member, a latch pivotally mounted on the guide mmeber and adapted to lock the spring in compressed condition, and means including said flexible conductor for retaining the cutout in latched condition.

3. In an expulsion fuse cutout assembly of the drop-out type, the combination comprising an expulsion tube having at least one open end, a fuse link in the tube for insertion in an electric circuit, and a spiral groove within and extending the length of said expulsion tube for accommodating variations in pressure therein.

4. In a fuse cutout of the drop-out type, an expulsion tube having a fuse link therein for interposition between terminals of said cutout; a guide member pivotally mounted on one of said terminals, a collar ring adjustably secured on the expulsion tube and slideable therewith wholly within said guide member between upper and lower limits therein, a coil spring interposed between said collar ring and the guide member to impart a downward force on the expulsion tube when the collar ring is at its upper limit within the guide member and the spring is compressed, latch means pivoted on the guide member and projecting thereinto to releasably lock the collar ring at said upper limit, and a hood resiliently mounted on the guide member to shield said latch and component parts from the elements in all positions of the cutout.

5. In combination, a dropout fuse cutout comprising upper and lower terminals mounted on an insulator, a bearing for a trunnion on the lower terminal, an expulsion fuse tube between the terminals, an apertured hollow cylindrical guide member enclosing the lower end of the tube and having a trunnion, said tube passing longitudinally through said guide member, a fuse link within the expulsion tube, a collar on the tube, a spring positioned for exerting a downward force on the tube, a tripping mechanism held in restraint by the fuse link, said mechanism including a lever arm pivoted on the guide member and in its restrained position lying substantially parallel to the longitudinal axis of the tube, and a latch on the lever arm positioned to project into said aperture in the guide member and extending under the collar on the tube.

References Cited in the file of this patent UNITED STATES PATENTS Re. 20,420 Mangan June 22, 1937 2,151,159 Schultz Mar. 21, 1939 2,223,975 Traver Dec. 3, 1940 2,253,719 McMahon Aug. 26, 1941 2,291,646 Ramsey Aug. 4, 1942 2,291,647 Ramsey Aug. 4, 1942 2,309,013 Rawlins et al. Jan. 19, 1943 2,334,134 Steinmayer Nov. 9, 1943 2,462,212 Mosley Feb. 22, 1949 2,466,486 Schultz Apr. 5, 1949 2,483,577 Fahnoe Oct. 4, 1949 2,626,332 Earle et al J an. 20, 1953 2,658,977 Hoye Nov. 10, 1953 FOREIGN PATENTS 319,749 Great Britain Dec. 29, 1930

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