US2404999A - Circuit interrupter - Google Patents

Description

y 1946- J: M. WALLACE CIRCUIT INTERRUPTER Filed April 24, 19 10 Inau/af/ofl 2'0 2 WITNESSES: INVENTOR a ;.fam 65 Mh cfl/ace.

Patented July 30, 1946 CIRCUIT INTERRUPTER James M. 'Wallace, Braddock, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 24, 1940, Serial No. 331,337

27 Claims. 1

My invention relates to electric circuit interrupting devices, in general, and more particularly to interrupters capable of automatically, interrupting an electric circuit in response to the passage therethrough of currents above a predetermined value.

Although I will hereinafter disclose my invention as embodied in a high voltage fuse wherein it has particular novel cooperation and utility, it should be understood my invention is also applicable to other types of circuit interrupters and apparatus.

One difficulty with prior high voltage fuses, particularly fuses of low current rating, has been their inability to withstand current surges without operating to open the circuit. Current surges so called, which may be caused by lightning strokes or switching operations, are characterized by a rapid rise in current accompanied by a corresponding voltage rise,and are normally shunted to ground by so-called lightning arrester devices which essentially comprise one or more gaps to ground calibrated so as to flash over at predetermined voltages. Accordingly, it is desirable that fuses and other overload protective devices do not operate on such surges'so that when the surge has been dissipated to ground, the circuit will be uninterrupted. Fuses and other overload protective devices are intended to protect a circuit against rises in current due to overloads or short circuits, such increases in current value are sustained and usually accompanied by a drop in voltage.

Accordingly, it is an object of my invention to provide an improved type of overload protective device which will not operate on surges.

Another object of my invention is to provide a novel type of high voltage fuse which will not be operated by surges.

Another object of my invention is to provide a hi h voltage fuse having means to by-pass surge currents around the fusible portion thereof.

High voltage fuses usually embody a fuse holder or tube having a pair of terminals. and a replaceable fuse link assembly within the fuse tube connected between the terminals.

Another object of my invention is to provide a fuse link unit designed for mounting in a standard fuse holder, which link is constructed so as to be capable of withstanding line surges.

Another object of my invention is to provide a novel arrangement of protective devices for serving high voltage electric circuits or apparatus.

These and other objects of my invention will become more apparent upon consideration of the following specification or one embodiment thereof taken in connection with the attached drawing, in which:

Figure 1 is a longitudinal sectional view through a fuse cartridge embodying my invention with a fuse link unit in the cartridge being shown in elevation;

Fig. 2 is an enlarged longitudinal sectional view through the fuse link unit shown in Fig, 1;

Fig. 3 is a schematic view illustrating the circuit through my novel fuse; and

Fig. 4 is a diagram illustrating one way of using a fuse constructed in accordance with my invention in the protection of an electric circuit or apparatus served thereby.

Voltage and current surges due to lightning striking a transmission line, or due to switching operations are characterized by extremely rapid rises in voltage and current values for an extremely small period of time. The voltage rise may be of the order of from 10 to kilovolts per micro-second with a corresponding current rise. Circuits are protected from such overvoltages by so-called lightning arresters designed to automatically shunt voltages above a predetermined value to ground. The current accompanying these surges, while it may be of a relatively high value, exists for such a small period of time that, in general, no harm is done to the circuit or apparatus served thereby. Consequently, it is desirable that service be uninterrupted following the occurrence of a surge and that none of the fuses blow. With fuses rated above 25 amperes, relatively little difficulty has been experienced by their blowing on surge currents. However, with fuses rated 25 amperes and under, outages frequently occur upon the occurrence of surge currents. and it is with respect to fuses of these ratings that my invention is directed, most particularly, though there are cases where it might be applicable to fuses of higher rating.

In general, my invention contemplates a fuse having a normally non-conductive shunt circuit around the fuse element, which is rendered conductive automatically in response to the passage of surge currents through the device to by-pass these currents around the fuse element and thereby leave the element intact after the surge is dis i ated.

Referring to Fig. 1 of the drawing, I have shown a fuse generally indicated by the number I which includes an outer insulating fuse tube 2 which may be made of any desired insulating material, such, for example, as fiber, porcelain, synthetic resin or the like, but a material such as fiber which gives off gas when acted upon by the arc is preferable for at least the inner surface of the tube. An upper fuse terminal ferrule 4 is threadedly engaged with the upper end of the fuse tube 2 and a lower ferrule sleeve or collar 6 is suitably secured adjacent to the lower end of the fuse tube 2. A fuse link unit 8 is supported within the tube 2, with the terminal head lil thereof seated on the outer end of the terminal ferrule 4 and secured to the ferrule 4 by an end cap l2 threadedly engaged with the ferrule 4. The fuse link unit has a lower terminal 44 from which extends a flexible conductor tail is outwardly of the lower end of the fuse tube 2 to be secured to the terminal sleeve 6 as by the thumb screw l8.

The structure of the fuse link unit 8 is more particularly shown in Fig. 2 wherein I have shown the link as including an insulating tube 20, which is frictionally maintained in position on an upper terminal strap 24 which is fixed to the terminal head ill, by an insulating spacing bushing 22. The tube 26 and bushing 22 may be of any desired insulating material, preferably of fiber, or some other insulating material which is frangible in response to blowing of the fuse link on relatively high currents on the order of short-circuit currents. The upper terminal strap 24 is provided with an inner aperture 28, through which extends a conductor 26 to be secured to the terminal strap in any desired manner, such, for example, as by soldering or the like. The conductor 26 is wound about a small insulating tube 62 of fiber or the like, in a plurality of turns 36 to form an inductance for a purpose to be hereinafter referred to. The conductor 26 is suitably insulated by an enameled or cotton covering to insulate the turns 36. An iron core 34 which may comprise a short length of iron wire or the like, is preferably provided within the insulating tube 62. The lower end of the conductor 26 extends from the bottom coil of the inductance and is secured to a short length of fusible Wire 36 which may be of any desired fusible material, such, for example, as a lead alloy or silver. The fuse wire 36 is secured to the conductor 26, for example, as by soldering or the like, and in a like manner is secured to the lower terminal strap M of the fuse link unit. A relatively high resistance strain wire 38 having a higher tensile strength than the fuse wire 36 is connected in parallel with wire 36, between the lower end of the conductor 26 and the fuse link terminal strap I4, to relieve the strain on the fuse wire 36. The train wire 38 extends through an aperture 40 in the fuse link terminal strap !4, to be secured thereto as by soldering or the like. For the purpose of relieving the strain on the coils 36 of the conductor 26, an insulating strain member 42 connects the portions of the conductor 26 extending from the end coils 30 of the inductance. The strain element 42 is preferably of some insulating material such, for example, as cotton cord or preferably, and as shown, may comprise a fiber strip apertured at its ends to receive portions of the conductor 26.

A tubular electrode 44 of suitable conducting material, such as brass, copper, or the like, is telescoped over the fuse link insulating tube 26 and has one end thereof secured to the terminal head it! of the fuse link in any desired manner, for example, as by soldering. A second tubular electrode 46 provided with a closed end 48 suitably apertured for the reception of the lower fuse link terminal strap I4, is provided over the lower end of the fuse link insulating tube 20 and has its closed end 48 secured to the fuse terminal strap I4, for example, as by soldering or the like. A coil compression spring 50 has one end seated against the closed bottom of the electrode 46 and the other end bearing against the lower end of the fuse link insulating tube 26 to normally urge the lower fuse link terminal l4 and electrode 46 outwardly with respect to the fuse tube 26.

In assembling the fuse link shown in Fig. 2, the upper terminal strap 24 may be first assembled to the conductor 26, inductance, fusible wire 26, and lower terminal strap l4 with its connected tail portion l6, Then, the bushing 22 and insulating tube 26 may be slipped over the tail portion IE to the position shown in Fig. 2, after which, or prior to which, the upper electrode 44 may be secured to the terminal head It]. Subsequently, the lower electrode 46 with spring 50 seated therein, may be slipped over the tail portion lb of the fuse link and moved to the position shown in Fig. 2, while stressing coil spring 56, whereupon the lower terminal strap 14 may be soldered to the closed end 48 of the electrode 46.

It will be noted that the connections comprising the conductor 26, strain elements 42 and 38,

v and fusibl wire 36, between the terminal straps 24 and M of the fuse link, determine the separation of the electrodes 44 and 46 under the influence of the coil compression spring 56. The gap between the electrodes 44 and 46 should be made as small as possible, and is preferably on the order of A", but a gap as small as 5" has been found to be entirely practical.

In operation the fuse described above operates on normal continuing overloads and short circuits in the same manner as a conventional fuse. In other words, upon the occurrence of such overloads, thefuse wire 36 melts, and almost immediately thereafter the strain wire 36 is also melted, whereupon the coil compression spring 56 operates to move the lower fuse link terminal strap I4 and the electrode 46 associated therewith outwardly with respect to the fuse tube 26, to thereby elongate and extinguish the are formed. In the event the fuse blows on extreme ly heavy currents such as short-circuit currents, the insulating fuse tube 26 is designed to burst to permit expansion of the gases into the relatively larger chamber formed by the fuse tube '2 in the same manner described andclaimed in the. patent to J. Sandin No. 1,944,762, issued January 23, 19/34, to the assignee of this application.

Obviously, movement of the lower tubular electrode 46 outwardly with respect to the insulating fuse link tube 26 will permit the tube to burst in the event pressure within the tube exceeds a predetermined value.

Now upon the occurrence of surge currents in the line to which the fuse is connected, the rapid change in current value will cause a corresponding increase in voltage across the inductance coils 30, and cause a flashover of the gap between the tubular electrodes 44 and 46. This is due to the fact that the voltage across the inductance increases directly with respect to the rate of change of current and, consequently, with the extremely rapid rate of change occurring under surge conditions, it can be seen that the voltage across the inductance will correspondingly increase to at least a high enough value to fiashover the gap between the electrodes 44 and 46. The induct ance and gap between the electrodes are proportioned so that the gap will be flashed over before the surge current reaches a value sufficient to fuse the fuse wire 36, and is preferably designed to flashover in response to a current rise at the rate of 50 amperes per micro-second or greater. Obviously, when the gap between the electrodes 44 and 46 breaks down, the surge current will be by-passed through the electrodes from the terminal head l6 to the tail I6 of the fuse link, around the fusible element 36, to thereby prevent its fusion. When the surge disturbance has passed, the voltage across the inductance drops to its normal low value which is less than the voltage across the gap defined by the tubular electrodes 44 and 46 so that the gap again becomes non-conducting and the fusible element 36 again carries the normal load current.

The electrical circuit through my novel fuse construction is shown diagrammatically in Fig. 3, wherein it clearly appears that the coils 36 of the inductance are in series with the fuse wire 36, and that the electrodes 44 and 46 are connected in shunt or parallel relation, with respect to this series arrangement.

It is believed obvious from the foregoing that I have provided relatively simple yet efficient means for preventing the blowing of a fuse link upon the occurrence of surge currents in its associated line conductors, -by providing means in series with the link for causing the flashover of a shunt gap in response to the occurrence of such currents. It should also be apparent that I have provided a replaceable fuse link unit which isadapted for mounting in standard fuse holders, and which link unit includes means for bypassing surge currents around the fusible portion of the link. It should also be noted that my novel fuse link is of the pretensioned type, so that upon blowing of the fuse at least one of the fuse link terminals is moved away from the other terminal. The spring which is employed for separating the fuse link terminals when the fuse blows also cooperates with one electrode of the parallel gap, for maintaining the same in predetemined spaced. relation with respect to the other electrode of the gap. It should also be noted that the gap electrodes 44 and 46 are preferably constructed as shown in Fig. 2 to fit loosely over the fuse link tube 26 to facilitate their assembly, and movement of the fuse link terminal strap l4 away from the terminal strap 24 when the fuse blows on normal overloads.

In Fig. 4 I have shown one way in which my novel fuse may be connected in relation to other protective apparatus for protecting a secondary circuit and apparatus connected thereto. Referring to Fig. 4, 52 denotes a line conductor to which my novel fuse l is connected as by conductor 54. The other terminal of the fuse is connected to a conductor 56 which in turn leads to one terminal of the primary of a transformer 62, and also to one electrode of a lightning arrester 58. The other terminal of the primary winding of the transformer and lightning arrester, are connected to ground as by the conductor 66. The transformer 62 is shown merely for purposes of illustration, and it will be readily appreciated that the particular type of apparatu served is immaterial.

This arrangement with respect to apparatus or circuit protected thereby, differs from the usual arrangement in that the fuse I is connected ahead of the arrester, so that a failure of the arrester will not interrupt the service to the apparatus or circuit protected.

of fuse and lightning arrester This arrangement is especially useful with my novel fuse construction, inasmuch as the fuse will not be blown on surge currents, and hence may be connected ahead of the arrester'since it need not be protected thereby. This arrangement also has the advantage of positioning the arrester closer to the apparatus or circuit it is intended to protect, so that better protection and continuity of service are possible with this arrangement utilizing a fuse constructed in accord ance with my invention.

Having described preferred embodiments of my invention in accordance with the patent statutes, I desire that my invention be interpreted as broadly as possible, in asmuch as it will be obvious, particularly to persons skilled in the art, that many changes and modifications may be made in the particular embodiments illustrated with-' out departing from the broad spirit and scope of my invention. Therefore, I desire that the following claims be interpreted as broadly as possible and that they be limited only by the prior art and by what is expressly stated therein.

I claim as my invention:

1. In a fuse, a fuse tube having a pair of contacts, a replaceable fuse link unit in said fuse tube having terminals connected to said contacts, respectively, said fuse link unit including an insulating tube of a size to be spaced from the inner walls of said fuse tube, a circuit between said ter-' minals including a gap positioned in the space between said tubes, 2. parallel circuit between said terminals including fusible means in said insulating tube, and means responsive to surge currents for rendering said gap circuit conducting,

2. In a fuse, a fuse tube having a pair of contacts, a replaceable fuse link unit in said fuse tube and having terminals connected to said contacts, respectively, said fuse link unit including an insulating tube of a size to be spaced from the inner Wall of said fuse tube, spaced conductive members mounted on the outside of said insulating tube and connected to said terminals, respectively, a parallel circuit between said terminals including fusible means in said insulating tube, and means responsive to surge currents for rendering the gap between said conducting member conductive.

3. A fuse link unit having a pair of terminals, fusible means and wound inductive means connecting said terminals, means normall urging said terminals apart, and means for relieving the strain on said fusible means and the turns of said inductive means.

4. A fuse link unit including an insulating tube having terminals projecting from opposite ends thereof, fusible means and an inductance coil in said tube and connecting said terminals, resilient means acting between said tube and one of said terminals for normally urging said one terminal outwardly of said tube, and means for relieving the strain on said fusible means and the turns of said inductance coil.

5. A fuse link unit including an insulating tube having terminals projecting from opposite ends thereof, conductors mounted on the outer side of said tube extending over the major portion of the length of said tube, the inner ends of said conductors being spaced to provide a small air gap, and the outer ends of said conductors connected to said terminals respectively, means including fusible means in said tube connecting said'terminals for normally preventing the separation of said conductors, and resilient means reacting between one end of said tube and one ofsaid ter-.

minals for moving said terminal out of said tube when said fusible means blows, and for normally maintaining said conductors in predetermined spaced relation.

6. In a device of the type described, spaced concentric tubes of insulation material, spaced tubul'arel'ectrodes inthe space between said tubes, and terminals adjacent the ends of the outer one of said tub-es connected to said electrodes, respectively.

7. A fuse link unit including an insulating tube havin terminals projecting from opposite ends thereof, one of said terminals having a portion engaging on end of said tube for limiting inward movement thereof, conductors on the outer side of said tube connected to said terminals, respectively, said other terminal and its associated conductor being slidably mounted with respect to said tube, resilient means engaging said tube and other terminal for biasing said other terminal outwardl of said tube, and fusible and strain means in said tube connecting said terminals and being of a length to maintain said conductors in predetermined spaced relation.

8. In a circuit interrupter, spaced concentric tubes of insulation material, spaced tubular electrodes in the space between said tubes, terminals adjacent the ends of the outer one of said tubes connected to said electrode respectively, and a serial arrangement connected between said terminals, said serial arrangement includin fusible means and means responsive to surges in the circuit to cause the gap between said electrodes to break down.

9. A fuse link unit including an insulating tube, a terminal unit at each end of said tube, said terminal units including, respectively, electrodes mounted on the exterior of said tube in predetermined spaced relation, and a serial arrangement of fusible means and means responsive to surges in the circuit, for causing the space between said electrodes to break down, said serial arrangement connecting said terminal units and located interiorly of said tube.

10. A fuse link unit including an insulating tube, a terminal unit at each end of said tube, said terminal units including, respectively, tubular electrodes mounted on the exterior of said tube in predetermined spaced relation, and a serial arrangement of fusible means and means responsive to surges in the circuit for causing the space between said electrodes to break down, said serial arrangement connecting said terminal units and located interiorly of said tube.

11. In a device of the type described, an outer tube of insulating material, an inner insulating member in said tube spaced from inner walls of said tube to form an annular arcing space, spaced tubular electrodes in said arcing space, and terminals adjacent the ends of said tube connected to said electrodes, respectively,

12-. In a device of the type described, an outer tube of insulating material, an inner insulating member in said tube spaced from inner walls of said tube to form an annular arcing space, wall portions of said arcing space being of a material capableof evolving an arc extinguishinggas' when in proximity to an electric arc, spaced tubular electrodes in said arcing space, and terminals adjacent the ends of said tube connected to said electrodes, respectively.

13. A fuse device comprising in combination a cylindrical tube of insulating material, conducting members extending longitudinally of said tube in concentric relation therewith and provided said other conducting member other terminal of with spaced surfaces forming an arc gap, a fusible element mounted Within said tube in spaced axial relation with respect to said gap, a terminal member electrically connected with one terminal of said gap and. one terminal of said fusible element, and means operative upon rupture of said fusible element for expelling said terminal from said '1' to said conducting members, a terminal element closing one end of said tube and conductively connected with one of said conducting members and one-end of said fusible element and a second terminal element conductively connected with and the other end of said fusible element.

15. A fuse device comprising in combination a supporting tube of insulating material, conducting members arranged Within said tube and hava ing axially spaced surfaces cooperating to define arc gap, a fusible element mounted Within said tube in axially spaced relation with respect to said conducting members, an inductive winding, means conductively connecting one end of said winding with one of the conducting members of said are gap, means conductively connecting the other end of said winding with one terminal of said fusible element, means conductively connecting the other conducting member and the said fusible element, and terminal means of said device electrically connected with each of said conducting members,

16. A fuse device comprising in combination a cylindrical tube of insulating material, conducting members extending longitudinally of said tube in concentric relation therewith and provided with spaced surfaces forming an arc gap, a fusible element mounted within said tube in spaced relation with respect to said ga a terminal member electrically connected with one terminal of said gap and one terminal of said fusible element, and

means operative upon rupture of said fusibleelement for expelling said terminal from said tube.

17. A fuse device comprising in combination a supporting tube of insulating material, conducting members arranged within said tube and having axially spaced surfaces cooperating to define an arc gap, a fusible element mounted within said tube in spaced relation with respect to said gap, a terminal element closing one end of said tube and conductively connected with one of said conducting members and one end of said fusible element and a second terminal element conductively connected with said other conducting member and the other end of said fusible element.

18. A fuse device comprising in combination a supporting tube of insulating material, conducting members arranged within said tube and having axially spaced surfaces cooperating to define" an arc gap, a fusible element mounted within said tube in spaced relation with respect to said gap, an inductive winding, means conductively connecting one end of said winding with one of the conducting'members of-said arc gap, means conductively connecting the other end of said Winding with one terminal of said fusible element, means conductively connecting the other conducting member and the other terminal of said fusible element, and terminal means of said de- 9 vice electrically connected with each of said conducting members.

19. In a fuse, spaced conducting means forming an arc gap therebetween, a series arrangement of a fusible element and inductive means, means electrically connecting said series arrangement across said are gap, one of said first two mentioned means being annular in form and having the other received therein, and means of insulating material positioned between said first two mentioned means.

20. In a fuse, a tubular member of insulating material, spaced conducting means forming an arc gap therebetween, a series arrangement of a fusible element and inductive means, means electrically connecting said series arrangement across said arc gap, one of said first two mentioned means being annular in form and having the other and said tubular member received therein, and the other of said first two mentioned means positioned in said tubular member.

21. In a fuse, spaced conducting means forming an arc gap therebetween, a series arrangement of a fusible element and inductive means, means electrically connecting said series arrangement across said arc gap, one of said first two mentioned means being annular in form and having the other received therein, a tubular member of insulating material in said annular means and itself containing said other of said first two mentioned means, and means of insulating material positioned about said annular means.

'22. In a fuse, tubular means of insulating material, spaced conducting means forming an arc gap therebetween, a series arrangement of a fusible element and inductive means, means electrically connecting said series arrangement across said are gap, one of said first two mentioned means being annular in form for receiving the other, and said inductive means mounted in and substantially coaxially of said tubular means.

23. In a fuse, tubular means of insulating material, spaced terminals supported in insulated relation by said tubular means, inductive means in said tubular means, a fusible element connected to one of said terminals, means connecting said inductive means between said fusible element and the other of said terminals, spaced electrodes forming an arc gap therebetween, and said electrodes electrically connected with said terminals, respectively.

24. In a fuse, tubular means of insulating material, spaced terminals supported in insulated relation by said tubular means, inductive means in said tubular means, a fusible element in said tubular means and connected to one of said terminals, means connecting said inductive means between said fusible element and the other of said terminals, spaced electrodes forming an arc gap therebetween with said gap also located in said tubular means, and said electrodes electrically connected with said terminals, respectively.

25. A fuse device comprising in combination a cylindrical tube of insulating material, conducting members extending longitudinally of said tube in concentric relation therewith and provided with spaced end surfaces forming an arc gap, a fusible element mounted within said tube in spaced relation with respect to said gap in the direction of the axis of said tube, a terminal member electrically connected with one terminal of said gap and one terminal of said fusible element, and means operative upon rupture of said fusible element for expelling said terminal from said tube.

26. A fuse device comprising in combination a supporting tube of insulating material, conducting members arranged within said tube and having surfaces spaced in the direction of the axis of said tube cooperating to define an arc gap, a fusible element mounted within said tube in spaced relation with respect to said conducting members in the direction of the axis of said tube, a terminal element closing one end of said tube and conductively connected with one of said conducting members and one end of said fusible element and a second terminal element conductively connected with said other conducting member and the other end of said fusible element.

27. A fuse device comprising in combination a supporting tube of insulating material, conducting members arranged within said tube and having surfaces spaced in the direction of the axis of said tube cooperating to define an arc gap, a fusible element mounted within said tube in spaced relation with respect to said conducting members in the direction of the axis of said tube, an inductive winding, means conductively connecting one end of said winding with one of the conducting members of said are gap, means conductively connecting the other end of said winding with one terminal of said fusible element, means conductively connecting the other conducting member and the other terminal of said fusible element, and terminal means of said device electrically connected with each of said conducting members.

JAMES M. WALLACE.

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