US3270166A - Fuse having separate telescoping small current and large current arcing chambers - Google Patents

Description

Aug. 30, 1966 R. E. FRINK 3,270,166

FUSE HAVI S RATE TELESCOPING SMA ENT AN A CURRENT ARCING CHAMB Filed Sept. 30. 1963 5 heetsv-sheet l WITNESSES INVENTOR W fay/MM Russell E Frink ATTORNEY R. E. FRINK 3,270,166 ARATE TELESCOPING SMALL CURRENT GE CURRENT ARCING CHAMBERS Aug. 30, 1966 FUSE HAA 5 Sheets-Sheet 2 Filed Sept. 50, 1963 z g MM Aug. 30, 1966 R m 3,270,166

FUSE HAVING SEPARATE TELESCOPING SMALL CURRENT AND LARGE CURRENT ARCING CHAMBERS Filed Sept. 30. 1963 5 SheetsSheer, l5

Fig.5A.

United States Patent 3,270,166 FUSE HAVING SEPARATE TELESCGPING SMALL CURRENT AND LARGE CURRENT ARCING CHAMBERS Russell E. Frink, Forest Hills, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 30, 1963, Ser. No. 312,727 5 Claims. (Cl. 200-120) This invention relates generally to fuse structures, and, more specifically, to fuse structures adaptable to interrupt a relatively wide range of current values.

One object of this invention is to provide a novel type of highvoltage fuse which is relatively simple in construction and economical of manufacture, while being capable of efficiently interrupting relatively large currents.

Another object of the present invention is to provide an improved high-voltage fuse in which the formation of corona during operation of the fuse is minimized to prevent the formation of deleterious acids, which could possibly prevent mechanical actuation of the fuse parts.

Still a further object of the present invention is to provide an improved fuse construction adaptable for selective operation, wherein relatively low-current faults are interrupted within a small-bore fuse chamber, whereas relatively high-current faults are caused to be interrupted within a larger fuse chamber.

Still a further object of the present invention is to provide an improved fuse construction wherein highly efficient operation is achieved over a wide current range by a selective action being obtained in designating in which of two fuse bores interrupting action is achieved.

Still a further object of the present invention is the provision of an improved high-voltage power fuse in which the coaction between the several fuse parts is such as to minimize the formation of corona.

Another object of the present invention is the provision of an improved high-voltage fuse construction utilizing a tubular main arcing rod whereby a better gradient of restored voltage is achieved by the particular configuration of the movable fuse parts.

Still a further object of the present invention is the provision of an improved fuse structure having sufficient exhaust area to accommodate the interruption of high currents, and wherein sufficient diameter and radius of the several parts is utilized to avoid the formation of corona at high voltage.

An ancillary object of the present invention is the provision of an improved high-voltage fuse structure involving a pair of movable interrupting assemblies, one of which is particularly adaptable for high-current interruption, and the other being adaptable for low-current interruption, and wherein a telescopic interrelation between such two interrupting assemblies is provided to minimize the formation of corona during constant highvoltage operation of the fuse structure.

The particular fuse constructions disclosed in the present invention are particularly applicable in utility and industrial high-voltage power systems for protecting power transformers, feeder circuit sectionalizing, distribution transformers, high-voltage capacitors and potential transformers. The voltage range may, for example, range from 7.5 =k-v. to 13-8 kv., and higher, with a continuous current rating of say, for example, /2 ampere to 2100' amperes. Interrupting capacities may range all the way up to 2,000,- 000 kva., and higher.

There are three very distinct problems existing is cirwit-interrupting structures, such as, for example, fuse structure suitable for high-voltage and high-current application. Such problems involve corona at high voltages, the ability to handle high currents, and the ability to in- "ice terrupt low currents. These three problems are interdependent, and as of the present time, no fuse manufacturer has the solution.

The corona problem arises from the relatively small diameter of the arcing rods necessary in conventional designs of the prior art. For example, the formula for determining the corona starting voltage, as arrived by experimental investigation, is given by the following formula:

e =21.1M0r6lnS/r (kv. to neutral) where M0 is the roughness factor and cannot exceed 1.

r is the radius of the conductor in cm.

5 is the relative air density and is 1 for standard conditions. S is phase spacing in cm.

Applying this formula to the dimensions commonly used for fuses shows that fuses above '69 kv. having 4 inch diameter arcing rods will operate with continual corona on the rod. The corona oxidizes the nitrogen in the air and these oxides combine with moisture to form nitrous and nitric acids which attach and corrode the internal parts of the fuse. When this condition has progressed far enough, the fuse element may melt, but the arcing rod will not withdraw through the fuse bore and a failure result. Serious field trouble has resulted from this cause. Furthermore, the problem does not yield itself readily to shielding because of restored voltage distribution on interruption.

The second problem concerns the ability to accommodate high currents. The following approximate relations hold. Gas evolution per unit area is proportional to are current. Voltage interrupting capacity is proportional to the length of arc. Exhaust area is proportional to the square of the bore diameter. It follows that:

where:

Q is quantity of gas evolution, i is the current,

d is bore diameter,

1 is length of bore,

and

where Vis the velocity of gas exhaust. However, V" cannot exceed sonic velocity, and l is determined by the required voltage interrupting capacity. It follows that i can be increased until this velocity is approached, and beyond this point the pressure will rise until the tube is ruptured. The other alternate is to increase d to accommodate larger currents.

From the above, it is seen that a larger diameter arcing rod is required to avoid corona, and a large bore is necessary for high currents, but a large bore will not clear low currents since the arc diameter is too small to maintain intimate contact with the gas-evolving material. An experimental fuse with a /8 inch diameter arcing rod cleared top power in a high power laboratory at 44 kv., 66 kv., and 72 kv., but it would not clear 2000 amperes. The low-current problem was solved long ago in the type BA400 fuse, manufactured by the assignee of the instant application, with the use of an auxiliary bore containing a small cable and wire which separate after an appreciable separation of the lower terminal and the arcing rod, as shown in Rawlins U.S. Patent 1,976,634. For low currents, the cable and wire arrangement of the aforesaid patent shunts the current from the main gap, and when they separate, an arc is drawn and interrupted in the small bore. If the current is large, the high are voltage generated in the small bore causes the arc to restrike in the large bore, and interruption takes place in the same manner as if the auxiliary bore were not used. However, tests show that corona on the small diameter cable and wire prevents this arrangement from being used on fuses for the higher voltages. At present, it is desired to produce fuses for voltages through 138 kv., and higher, and with interrupting capacities of 2,000 mva., or more.

Accordingly, it is a further object of the present invention to provide an improved highly efficient fuse structure adaptable for constant service over long periods of time without suffering any disadvantage by virtue of the fact that it is utilized at high voltage, and also wherein regardless of the time element, fast operation is always achieved, in a selective manner, to highly effectively interrupt either low-current faults or high-current faults.

The particular fuse construction of the present invention is particularly suitable for dropout action in a manner as set forth in United States Patent 2,403,121, issued July 2, 1946, to Herbert L. Rawlins and John J. Mikos, and assigned to the assignee of the instant application.

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

FIGURE 1 illustrates, in perspective, a side elevational view of a high-voltage fuse structure embodying the principles of the present invention, and shown in the closed operative position;

FIG. 2 illustrates a longitudinal sectional view taken through the fuse element of FIG. 1 with the fuse end fittings removed;

FIG. 3 illustrates, to an enlarged scale, the internal structure of the fuse device of FIG. 2 to more clearly illustrate the parts, again the fuse elements being shown in their intact condition;

FIGS. 3A and 3B are fragmentary views illustrating respectively low-current operation and high-current operation;

FIG. 4 is a sectional view taken substantially along the line IV-IV of FIG. 3;

FIG. 5 is a vertical sectional view, taken to a somewhat larger scale, of a modified-type of fuse structure embodying the principles of the present invention;

FIG. 5A is a fragmentary view illustrating arc elongation in a fuse structure of the type illustrated in FIG. 5; and

FIGS. 6 and 7 are somewhat diagrammatic views illustrating the improved electrostatic conditions resulting from an application of the features of the present invention.

Referring to the drawings, and more particularly to FIG. 1 thereof, the reference numeral 1 generally designates a high-voltage high-power dropout type of fuse structure, the general arrangement of which is set forth in the aforesaid Patent 2,403,121 Rawlins et al. As shown, the fuse structure 1 includes a base 2 formed of sheet metal, and a pair of outwardly-extending insulator supports 3, 4. The upper insulator support 3 serves to support fixedly in position a break jaw 5, the details of which are shown in FIG. 1 of the aforesaid patent.

Supported from the lower insulator support 4 is a hinge jaw 6, which pivotally supports a fuse unit 7, interiorly of which extends fusible elements, more fully described hereinafter. As shown in FIG. 1, the fuse unit 7 serves to electrically bridge the break jaw contact 5 and the hinge jaw contact 6 so that current will pass therebetween by way of terminal pads 8, 9, to which the external circuit L L is connected.

The fuse unit 7 generally comprises a replaceable fuse structure 10, more clearly shown in FIG. 2, and a pair of end fuse fittings 11, 12. The upper end fuse fitting 11 comprises an operating eye, 11a and is, as well-known by those skilled in the art, utilized for effecting opening and closing movement of the fuse unit 7 by means of a conventional hook-stick, not shown.

The lower fuse fitting 12 comprises a hinge lifting eye, 12a which may be employed in conjunction with the aforesaid switch-stick to effect physical removal of the fuse unit 7 from the hinge jaw contact 6 for replacement of the fuse unit 7.

With reference to FIG. 2 of the drawings, it will be noted that the fuse structure 10 comprises a fuse tube 13 of insulating material, such as fiber, synthetic resin or the like, and the opposite ends of the fuse tube 13 are adapted to be closed by end terminal caps, or fuse ferrules 14, 15, as well-known by those skilled in the art. The fuse ferrules 14, 15 may be rolled into indentations 13a of the fuse tube 13, and securely fastened into position by staking pins, so that the end fitting 11, 12 when encircling the ferrules 14, 15 and clamped into position will securely engage the fuse-tube structure Without loosening.

With reference to FIG. 2 of the drawings, it will be observed that, generally, there are three sections to the fuse-tube structure, namely sections A, B and C. The fuse section A indicates the location of the fusible elements 16, which will fuse during operation of the fuse 1. The fuse section B indicates the location of the interrupting arc passages, more fully described hereinafter, involving stacked blocks of gas-evolving material 17, and the fuse section C relates to the biasing-spring section of the fuse structure 10 to bias an arcing rod toward its separated position, as explained more fully hereinafter.

With reference to FIG. 3 of the drawings, it will be noted that a corona tube 18 is soldered, or otherwise securely fastened, to the end of the fuse ferrule 15 and has brazed thereto, for example, a contact block 19. The right-hand end 18a of the corona tube 18, as viewed in FIG. 3 is bent radially inwardly to grade the electrostatic field during fuse rupture, and thereby prevent a concentration of voltage stress resulting from the recovery voltage transient. Additionally, it will be noted that the right-hand end of the corona tube 18:: fixedly secures into place an orifice plug 20 having an orifice opening 21 therethrough. Extending adjacent the opening 21 of the orifice plug 20 is a movable tubular main arcing rod 22 having a cap portion 23 and threadedly secured, as at 24, to an unlatching extension rod 25. As set forth in the aforesaid Rawlins et al. Patent 2,403,121, during fuse operation, the extension rod 25 projects externally of the fuse structure 10 to unlatch a dropout biasing mechanism enclosed in the hood 5a of the upper break jaw contact 5 to effect thereby dropout action of the fuse unit 7.

A tension helical operating spring 26 is provided to bias the main tubular arcing rod 22 toward the right, as viewed in FIGS. 2 and 3, toward a circuit-opening position. During normal operation of the fuse structure 1, the tension spring 26 is extended, and is under tension. Upon rupture of the fuse elements 16, the tension spring 26 will be effective to withdraw the main arcing rod 22 through the annular bore 27 defined by the apertured gasevolving blocks 17 and a relatively stationary inner tubular gas-evolving rod 28. The evolution of gas by the members 17, '28 will be effective to effect an expulsive blast action forcing gas flow longitudinally of the established arc and out through the orifice opening 21 of the orifice plug 20.

It will be noted that the fusible elements 16 are attached at one end to the extremity 22a of the main arcing rod 22, whereas the other, or left-hand ends of the fusible elements 16, as viewed in FIG. 3, are secured to a contact block 22 secured, for instance, by a plurality of bolts 30, to the contact block 19 and also to the fuse tube 13 itself.

The contact block 29 is provided with an end portion 29a, which is drilled and tapped to threadedly receive the threaded end 28a of the relatively stationary tubular gasevolving rod 28. Moreover, a conducting fuse cable 31 is electrically connected, as by a bolt 32, to the contact block 29 and hence through the corona tube 18 to the end fuse ferrule 15.

Making contacting engagement for a several inches of axial length of the fuse cable 31 is a relatively smalldiameter fuse wire 34, which is attached to the cap portion 23 of the main tubular arcing rod 22.

Encompassing the helical operating spring 26 is a metallic tube spring shunt 35, which provides a friction stop 36 to prevent rebound of the arcing rod 22 following opening movement of the same by the tension spring 26. The left-hand end of the contact shunting tube 35 is slotted as at 35a, to form thereby a plurality of inwardlybent contact fingers, which bear against the top portion 23 of the arcing rod 22 to enable current flow therebetween.

In order to bias the contact fingers 35a radially in- Wardly against the top of the arcing rod 23, a tension garter spring 38 is utilized. To prevent the establishment of corona from the sharp corners of the contact fingers 35, preferably a corona shield 39 is used, which coacts with the tube 35 to perform an electrostatic shielding function.

Fuse operation The operation of the fuse unit 7 will now be described. Fusible elements '16 rnelt in response to overcurrent, and the operating spring 26 is effective to move the main arcing tube 22 toward the right, as viewed in FIGS. 2 and 3, at a high rate of speed. For the first few inches of travel, wire 34 is in contact with the cable 31, and if the current is low, they will carry it for an instant until their ends separate and draw an arc 50 in the bore 40 provided by the opening through the gas-evolving rod 28. By this time, the main arcing tube 22 has moved far enough to withstand considerable voltage, and the arc is interrupted within the small fuse bore, or fuse chamber 40. FIG. 3A illustrates arc establishment and the relative position of the several parts during such low-current interruption.

However, if the fuse operates on a heavy current, such as a high-current fault current, the fuse cable 31 and the fuse wire 34 will fuse completely almost simultaneously with the fusible elements 16, and before the main fuse tube 22 has inoved an appreciable distance. The higharc voltage in the relatively small fuse bore 40 causes the arc to strike from the end 22a to the contact block 29 and to be interrupted within the annular space between the aperture blocks 17 and the inner gas-evolving tube 28, as shown more clearly in FIG. 3B.

FIG. 5 illustrates a modified type of construction in which the inner gas-evolving tubular rod 128 has a spiral groove 128a cut, or otherwise formed, on the external surface thereof. The purpose of this groove 128a is to cause the arc to spiral around the rod and thus increase its length as shown in FIG. 5A.

It will be readily apparent to those skilled in the art that certain advantageous results are achieved by the aforesaid described fuse construction. Specifically, there is provided sufficient diameter in radius of the several conducting parts to avoid the formation of corona at high voltage. There is also provided suificient exhaust area to accommodate the high currents. The auxiliary bore 40 for low-current interruption is completely shielded against corona by being telescoped within the outer main tubular fuse rod 22, as shown. Additionally, there is provided a better gradient of restored voltage due to the size of the moving elements, as described in more detail hereinafter.

There is a higher ratio of surface to volume of arcing space resulting in higher evolution of gas and better performance. To illustrate this point more specifically, an annular space between a 1% diameter bore .and a /1 diameter rod has a volume of .55 cubic inch per linear inch of bore, and a surface exposed to arcing of 5.89 square inches per linear inch. The ratio is 10.7. The volume is equivalent to a 27/32 diameter cylindrical bore, which has a surface of 2.65 square inches per linear inch, or a ratio of 4.8.

Finally, there is a wider range of equivalent performance because the arc will be restricted when its diameter becomes equal to the clearance between the blocks 17 and the inner rod 28 (128), but it can expand to completely fill the annular space 27 provided therebetween.

I have discovered that the diameter of the movable tubular arcing rod 22 should not be less than /2 inch in diameter. If this criterion is followed, deleterious effects resulting from corona formation will not occur even at the higher voltages at which the fuse structure may be operated in service.

The following is an explanation of the increased ability of the fuse 1 of this invention to withstand a higher restored voltage than prior-art fuses. In prior-art fuses it was necessary to use a small diameter fuse bore to provide low-current interrupting ability, which consequently necessitated a small-diameter arcing rod. In the new fuse 1 of this invention, this is no longer necessary. When two conductors, spaced apart, have a potential difference between them, the voltage gradient at the surface of the conductors varies inversely with the size of the conductors. An accurate field map of the fuses would be difficult because of the close proximity of insulating materials, and because of the 3 dimensional configuration. However, the principle is illustrated in FIGS. 6 and 7 of the drawings. Suppose an arcing rod 51 has a number of flux lines i// terminating on its surface. Now suppose that the rod 51 is replaced by a larger rod 52 shown in FIG. 7 and that the same number of flux lines terminate on its surface. It will be observed that the flux lines terminating on the surface of rod 51 are spaced much more closely together than they are when they terminate on rod 52. This means that the gradient next to the surface at rod 51 is higher than at the surface of rod 52 with the same potential existing. The result is that a breakdown will be initiated between electrodes of the size illustrated in FIG. 6 at a lower voltage than would occur if the diameter of the electrodes were increased as shown in FIG. 7. It will therefore, be apparent that because of the diameter of the tubular arcing rod 22, the same functions, in effect, as an electrostatic shield in the current-carrying, or intact condition of the fuse structure, shown in FIGS. 2 and 3 of the drawlngs. I

From the foregoing description of the invention it will be apparent that there is provided an improved fuse structure 1 particularly adaptable for high-voltage operation and effective to minimize the formation of corona by employing relatively large-diameter conducting parts. Additionally, the telescopic arrangement between the two movable arcing assemblies 22, 31, 34 shields the inner assembly 31, 34 by the outer one and enables the adaptation of such an auxiliary fuse wire construction 31, 34 to the higher volt-ages.

Although there has been illustrated and described specific structures, it is to be clearly understood that the same were 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. In combination, an elongated insulating fuse tube having a pair of spaced terminals disposed adjacent opposite ends thereof, interrupting means disposed interiorly of said fuse tube including means forming a stationary annular gas-evolving fuse bore, conducting means disposed within the fuse tube electrically interconnecting said terminals and including a movable tubular arcing rod having an arcing portion at one end thereof, means biasing said movable tubular arcing rod along the annular gas-evolving fuse bore, means holding the arcing rod in its intact connecting position including fusible means connecting the arcing end of the arcing rod to one of said spaced fuse terminals, a stationary tubular filler rod extending within the movable tubular arcing rod,

means securing the last-named rod in position so that relative movement of said rods will occur, and separable low-current conducting means disposed interiorly of the stationary filler rod and arranged to separate subsequent to initial opening movement of the tubular arcing rod.

2. A fuse structure including an elongated insulating fuse tube having a pair of spaced terminals disposed at opposite ends thereof, one of the spaced terminals including a contact block having an axially extending threaded bore therein, relatively high-current interrupting means extending between said terminals including means defining an annular fuse bore and a movable tubular arcing rod movable therein, means electrically connecting one end of the movable tubular arcing rod to one of the spaced fuse terminals, fusible means electrically connecting the other end of the movable tubular arcing rod to the other spaced fuse terminal, relatively lowcurrent interrupting means extending between said spaced fuse terminals including separable low-current conducting means and disposed interiorly of the movable tubular arcing rod, the separable low-current conducting means including a stationary tubular filler rod extending within the movable tubular arcing rod, the filler rod having a threaded end in threaded engagement in the threaded bore in the contact block, whereby fusion of said fusible means will effect separation of said separable low-current conducting means subsequent to opening movement of the tubular arcing rod.

3. An elongated fuse-tube structure having a cylindrical gas-evolving lining and having separate high-current interrupting means and low-current interrupting means, the combination therewith of a contact block near one end of the fuse tube, the contact block having an axially extending threaded bore therein, the high-current interrupting means including a movable tubular arcing rod biased at one end to an open-circuit position and mechanically held at the other end by fusible means, the lowcurrent interrupting means including a stationary tubular filler rod having a threaded end in threaded engagement in the threaded bore in the contact block and longitudinally-separable overlapping fusible elements disposed interiorly of the tubular filler rod and separable only after opening movement of the movable tubular arcing rod, whereby low-current are drawal will occur between the separated fusible elements of the low-current interrupting means after previous movements of the movable tubular arcing rod.

4. A fuse structure including an elongated fuse tube having terminal means adjacent opposite ends thereof and a gasevolving inner surface and a longitudinallyextending tubular filler rod co-acting therewith to define an annular fuse bore, a movable tubular arcing rod movable along said annular fuse bore and mechanically held adjacent one end thereof by fusible means, said fusible means being connected to one of said terminal means, biasing means biasing the movable tubular arcing rod toward the other terminal means, a low-current interrupting means disposed interiorly of said tubular filler rod and including longitudinally-overlapping fusible elements separable only after movement of the movable tubular arcing rod, means electrically connecting said low-current interrupting means llIl electrical parallel with the tubular arcing rod and said first-mentioned fusible means between the two terminal means, said electrical connecting means including a contact block adjacent said one terminal means and supporting the tubular filler rod in fixed position, whereby initially fuse operation occurs by fusion of said fusible means, and high or low-current interruption is selectively achieved in either said annular fuse bore or within the bore of the tubular filler rod.

5. A fuse according to claim 1 in which the separable low-current conducting means is additionally characterized as including a wire and cable in normal electrical contact and slidable with respect to each other.

References Cited by the Examiner UNITED STATES PATENTS 2,183,751 12/1939 McMahon et al. 200-117 2,247,702 7/ 1941 Ramsey 2001 17 2,253,719 8/1941 McMahon 200-120 2,567,768 9/1951 Fahnoe 200-120 2,917,605 12/1959 Fahnoe 200120 BERNARD A. GILHEANY, Primary Examiner.

Claims (1)

1. IN COMBINATION, AN ELONGATED INSULATING FUSE TUBE HAVING A PAIR OF SPACED TERMINALS DISPOSED ADJACENT OPPOSITE ENDS THEREOF, INTERRUPTING MEANS DISPOSED INTERIORLY OF SAID FUSE TUBE INCLUDING MEANS FORMING A STATIONARY ANNULAR GAS-EVOLVING FUSE BORE, CONDUCTING MEANS DISPOSED WITHIN THE FUSE TUBE ELECTRICALLY INTERCONNECTING SAID TERMINALS AND INCLUDING A MOVABLE TUBULAR ARCING ROD HAVING AN ARCING PORTION AT ONE END THEREOF, MEANS BIASING SAID MOVABLE TUBULAR ARCING ROD ALONG THE ANNULAR GAS-EVOLVING FUSE BORE, MEANS HOLDING THE ARCING ROD IN ITS INTACT CONNECTING POSITION INCLUDING FUSIBLE MEANS CONNECTING THE ARCING END OF THE ARCING ROD AT ONE OF SAID SPACED FUSE TERMINALS, A STATIONARY TUBULAR FILLER ROD EXTENDING WITHIN THE MOVABLE TUBULAR ARCING ROD, MEANS SECURING THE LAST-NAMED ROD IN POSITION SO THAT RELATIVE MOVEMENT OF SAID RODS WILL OCCUR, SAID SEPARABLE LOW-CURRENT CONDUCTING MEANS DISPOSED INTERIORLY OF THE STATIONARY FILLER ROD AND ARRANGED TO SEPARATE SUBSEQUENT TO INITIAL OPENING MOVEMENT OF THE TUBULAR ARCING ROD.

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