Patent Application
20140266561
The present invention relates generally to the field of electrical protection devices, more particularly to an electric current interruption device, and even more particularly to a medium voltage current-limiting fuse.
Medium voltage (MV) current-limiting fuses are widely used in the electrical utility and switchgear manufacturing industries for voltages typically in the range of 1 kV to 72.5 kV. The main function of such fuses is to protect electrical apparatus (e.g., distribution transformers, motors, and capacitor banks) against over currents. In some fuse applications, it is desirable to trigger (i.e., open) the fuse when an event external to the fuse occurs.
The present invention provides a medium voltage electric fuse that is operable to open if subjected to excessive short circuit conditions and that can be caused to open in response to an electrical signal that is triggered by an external event.
In accordance with a preferred embodiment of the present invention, there is provided an electric fuse, comprised of a tubular casing formed of an electric insulating material. A first conductive ferrule is attached to a first end of the casing the first conductive ferrule having an opening therethrough. A second conductive ferrule is attached to a second end of the casing. A first fusible element within the casing is electrically connected to the second conductive ferrule. A disconnect section is electrically connected in series to the first fusible element and the first conductive ferrule. The disconnect section is comprised of a first stationary contact electrically connected to the first conductive ferrule and a second stationary contact electrically connected to the first fusible element. A movable contact is movable from a first position electrically connecting the first and second stationary contacts to form a conductive path through the disconnect section to a second position electrically separating the first and second stationary contacts from each other and terminating the conductive path through the disconnect section. The movable contact is biased toward the second position. A retaining element holds the movable contact in the first position. The retaining element is operable to release the movable contact from the first position when activated by an electrical (actuation) signal from an external source.
In accordance with another aspect of the present invention, there is provided an electric fuse, comprised of a tubular casing formed of an electric insulating material. A first conductive ferrule is attached to a first end of the casing, the first conductive ferrule having an opening therethrough. A second conductive ferrule is attached to a second end of the casing. A first conductive path is defined between the first ferrule and the second ferrule. The first conductive path is comprised of a disconnect section in series with a first fusible element having a first current carrying capacity. The disconnect section is comprised of spaced-apart contact elements, a movable contact element, and a retaining element maintaining the movable contact in electrical contact with the spaced-apart contacts. A biasing element biases the movable contact element to a second position destroying the first conductive path. A second conductive path defined between the first ferrule and the second ferrule. The second conductive path is comprised of a second fusible element in series with the first fusible element. The second fusible element has a second current carrying capacity less than the first current carrying capacity.
An advantage of the present invention is the provision of a MV current-limiting fuse that responds rapidly to interrupt the electrical current in the event of high current faults.
Another advantage of the present invention is an electric fuse that operates as a conventional fuse when subject to excessive short circuit conditions, and can also be caused to open by an electrical signal applied to the fuse by an external source.
Another advantage of the present invention is the provision of a controllable MV current-limiting fuse.
Another advantage of the present invention is the provision of a MV current-limiting, controllable fuse as described above, that responds rapidly to interrupt the electrical current in response to an external condition, such as, by way of example and not limitation, an arc flash, overvoltage, light level, temperature, pressure, or the like.
Another advantage of the present invention is to provide a time delay fuse as described above that is operable to actuate an external device such as an electrical switch.
Another advantage of the present invention is to provide a time delay fuse as described above having a fusible element that is not influenced by a biasing device.
Another advantage of the present invention is MV fuse as described above that contains an arc-quenching material that does not interfere with a mechanical disconnect section.
Still another advantage of the present invention is the provision of a MV current-limiting controllable fuse that is responsive to an external condition, such as an arc flash, an overvoltage condition, a temperature level, a pressure level, etc.
These and other advantages will become apparent from the following description of a preferred embodiment taken together with the accompanying drawings and the appended claims.
The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail in the specification and illustrated in the accompanying drawings which form a part hereof, and wherein:
Referring now to the drawings wherein the showings are for the purpose of illustrating preferred embodiments of the invention only, and not for the purpose of limiting same,
A first end ferrule 22 is provided for attachment onto one end of fuse casing 12 and a second end ferrule 24 is provided for attachment onto the other end of fuse casing 12. First end ferrule 22 includes an opening 26 therethrough that communicates with cavity 14. Ferrules 22, 24 are formed from an electrically conductive metal such as bronze, copper or alloys thereof.
Attached to ferrule 22 is a connector 32, and attached to ferrule 24 is a connector 34. Connectors 32, 34 are preferably identical. Therefore, only ferrule 32 will be described in detail, it being understood that such description also applies to ferrule 34. Connector 32, best seen in
Contained within cavity 14 of fuse casing 12 is a fuse assembly 50. Fuse assembly 50 is comprised of a disconnect section 60 and a high-current fuse section 260.
Disconnect section 60 is basically comprised of two, spaced-apart stationary contacts 70, 80 and a movable contact 150. First stationary contact 70 (best seen in
Second stationary contact 80 is also a cylindrical block having an opening 82 formed therethrough. A cylindrical wall 84 extends from one side of second stationary contact 80. Wall 84 and opening 82 are symmetrical about an axis through second stationary contact 80. Spaced-apart slots are formed in wall 84. The slots are aligned along lines radiating from the central axis of opening 82 through second stationary contact 80.
Second stationary contact 80 is spaced from first stationary contact 70 by a tubular insulator 92. Insulator 92 is a cylindrical tube having a first end that is dimensioned to be connected onto first stationary contact 70. A second end of insulator 92 is dimensioned to receive second stationary contact 80. In this respect, first and second stationary contacts 70, 80 are spaced apart from each other and are positioned to be symmetrical about the axis of insulator 92. Fastener elements 94, in the form of plastic pins, having heads 96 secure tubular insulator 92 to first and second stationary contacts 70, 80. In the embodiment shown, insulator 92 is formed from a glass-melamine material.
First and second contact members 70, 80 are dimensioned such that, when mounted to insulator 92, opening 82 in second stationary contact 80 is co-axially aligned with cylindrical opening 72 formed in first stationary contact 70. As illustrated in the drawings, first and second stationary contacts 70, 80, together with tubular insulator 92, define an enclosed chamber 98.
As indicated above, end surface 70a of first stationary contact 70 abuts one side of bottom wall 36 of connector 32. As best seen in
An insulating block 112 is dimensioned to be positioned against bottom wall 36 of connector 32 on the opposite side to first stationary contact 70. In the embodiment shown, insulating block 112 is cylindrical in shape, and has a cylindrical bore 114 extending into one side thereof. Bore 114 is coaxially aligned with openings 72, 82 in first and second stationary contacts 70, 80. Bore 114 is dimensioned to correspond in diameter to opening 72 in first stationary contact 70.
A tubular insert 122 (best seen in
A like insert 122 with fingers 124 is disposed in opening 82 of second stationary contact 80. As will be appreciated, because openings 72, 82 in first and second stationary contacts 70, 80 are coaxially aligned, openings through inserts 122 are also coaxially aligned.
A shutter assembly 132, best seen in
Shutter 136 is a plate-like member having a generally rectangular body 136a with outward extending arms 136b formed at one end thereof. Rectangular body 136a of shutter 136 is dimensioned to be disposed within narrow section 138a of slot 138 in frame 134. Arms 136b of shutter 136 are dimensioned to be received within wider portion 138b of slot 138 in frame 134. Shutter 136 includes an opening 146 near one end thereof. In the embodiment shown, opening 146 is circular and is disposed near the end of shutter 136 where arms 136b extend therefrom. Opening 146 is dimensioned to allow movable contact 150 to pass therethrough. Frame 134 has a similar opening 148 centrally located therein.
Frame 134 includes a plurality of mounting holes 149 dimensioned to receive conventional fasteners (not shown) that extend through frame 134 into first stationary contact 70. Frame 134 is mounted to first stationary contact 70 with shutter 136 disposed therebetween. When shutter 136 is disposed within slot 138 of frame 134, biasing elements 144, i.e., the compression springs within parallel channels 142 act against outward extending arms 136b of shutter 136 to bias shutter 136 to one edge of frame 134. Shutter 136 is movable against biasing elements 144 to a position where opening 146 in shutter 136 aligns with opening 148 in frame 134, as shown in
Referring now to
In the embodiment shown, movable contact 150 is formed of a first section and a second section. The first section is preferably formed of a conductive material, such as, copper or brass or an alloy thereof. In the embodiment shown, the second section is comprised of an elongated shoulder screw having a threaded portion. The portion of the elongated shoulder screw is received within a threaded bore in the end of the contact section of movable contact 150.
Both first section 150A and second section 150B have the same outer diameter. Movable contact 150 has a uniform outer diameter over the major length thereof. The free end of first section 150A of movable contact 150 includes an axially aligned bore 162 dimensioned to receive a set pin 172. Bore 162 in the end of first section 150A of movable contact 150 defines a cylindrical, outer wall 164. Set pin 172 includes an annular groove 174, best seen in
The free end of section 150B of movable contact 150 defines an enlarged portion defining an annular surface. It is contemplated that movable contact 150 could also be formed of a single, elongated cylindrical rod of copper or a copper alloy and have a washer (not shown) maintained by an e-ring or cotter pin at one end thereof.
A biasing element 182 is operable to bias movable contact 150 in a first direction. In the embodiment shown, biasing element 182 is a helical spring that surrounds extending portion 152 of movable contact 150 and exerts an axial biasing force thereon. One end of the helical spring abuts insert 122 in second stationary contact 80, and another end of the helical spring abuts the annular surface defined by head 156 of the shoulder screw that forms second section 150B of movable contact 150.
As best seen in
Referring now to
Movable contact 150 is maintained in the first position (best seen in
In the embodiment shown, retaining element 192 is a length of metal wire that extends through hole 176 in set pin 172 in the end of movable contact 150. One end of the wire is positioned to be connected to one of nails 194 embedded in insulating block 112, and the other end of the wire is positioned to be connected to the other nail 194 in insulating block 112. More specifically, in the embodiment shown, retaining element 192 is an elongated length of metal wire that is bent at its mid-section to form two side-by-side lengthwise sections of wire having a loop at one end. The looped end of the wire is attached to insulating set pin 212 that is fastened to insulating block 112. The two side-by-side sections of the wire extend from set pin 212 through an opening 196A in insulating block 112, through hole 176 in set pin 172 in moving contact 150 and then through an opening 196B in insulating block 112, as best seen in
It is contemplated that a single wire extending through set pin 172 in movable contact 150 may be used to retain moving contact 150. By providing two smaller wires dimensioned in relation to biasing force exerted on moving contact 150, better performance can be obtained, as shall be described below.
Referring now to
First fusible element 262 is comprised of one or more flat conducting members 274. Conducting members 274 preferably take the form of flat ribbons (rather than wires) to increase the surface dimensions. Conducting members 274 are wound around support 264 in a helical arrangement to increase the length of conducting members 274. Conducting members 274 of the illustrated embodiment include perforations (and/or notches) formed therein that reduce the cross-section of each member 274 and establish the current carrying capacity thereof. Conducting members 274 are preferably formed of silver, copper or copper alloys. The number and size of conducting members 274 determine the ampere rating of fuse 10. The present invention finds particular application for fuses rated from 0 to 100 Amps, but could also be used in fuses rated up to 600 Amps.
One end of first fusible element 262 is electrically connected to a conductive strap 276 that in turn is welded or soldered onto second stationary contact 80. The other end of first fusible element 262 is electrically connected to a conductive strap 278 that is welded or soldered onto connector 34 that in turn is electrically connected to second end ferrule 24.
A second fusible element 282, best seen in
An arc quenching material (not shown) is disposed within cavity 14 of fuse casing 12 and surrounds disconnect section 60 and fuse section 260. In a preferred embodiment, the arc quenching material is comprised of silica quartz sand. As illustrated in the drawings, the configuration of disconnect section 60 is such that the arc quenching material is prevented from penetrating into chamber 98 defined by insulator 92. Still further, the arc quenching material does not enter into passageway 268 defined by tubular body 264a of support 264.
An electric fuse 10, as described above, defines two conductive paths. A first conductive path between first end ferrule 22 and second end ferrule 24 is comprised of disconnect section 60 in series with first fusible element 262. In this respect, first end ferrule 22 is in electrical contact with connector 32, which in turn, is in electrical contact with first stationary contact 70. Through movable contact 150, first stationary contact 70 is in electrical contact with second stationary contact 80 that, in turn, is connected to first fusible element 262. First fusible element 262 in turn is electrically connected to connector 34 that is electrically connected to second end ferrule 24.
A second conductive path defined between first end ferrule 22 and second end ferrule 24 is comprised of second fusible element 282 in series with first fusible element 262. In this respect, one end of second fusible element 282 is electrically connected to connector 32 and first end ferrule 22. The other end of second fusible element 282 is connected to one end of first fusible element 262. The other end of first fusible element 262 is connected to connector 34 that is connected to second end ferrule 24. In the foregoing configuration, second fusible element 282 is basically arranged in parallel to disconnect section 60.
It is contemplated that fuse 10 will be used as part of a fuse system 300, schematically illustrated in
Sensing device 320 is operable to detect an external condition or event, such as an arc flash, an overvoltage condition, a temperature level, a pressure level, etc. In response to detection of the external condition, controller 310 is programmed to command fuse 10 to open by supplying a “trigger signal” (i.e., a pulse of electrical energy) to retaining element 192 via leads 202A, 202B. In this respect, controller 310 causes energy source to apply sufficient electrical energy to retaining element 192 to heat the same to a temperature at which retaining element 192 melts. While fuse controller 310 in
In the illustrated embodiment, controller 310 responds to sensing device 320 (e.g., a light sensor or dedicated arc flash detection equipment) detecting an external condition or event (e.g., an arc flash) by closing switch 312, and thereby applying a rapid pulse of electrical energy from energy source 314 (e.g., 1000 uF capacitor charged to 50V) to retaining element 192.
Referring now to the operation of fuse 10, under a conventional short circuit condition, when current in excess of approximately 20 times the nominal rated current of the fuse 10 passes through fuse 10 longer than 3-4 milliseconds, first fusible element 262 ionizes and forms and interrupts arc. (At higher currents, first fusible element 262 ionizes even sooner.) The interrupt arc is quenched within fuse casing 12 by the arc-quenching material. As a result, current flowing through first fusible element 262, and in turn fuse 10, is thus terminated.
Fuse 10 may also be operated by a signal from fuse system 300 that is connected by leads 202A, 202B to disconnect section 60. The normal operating configuration of disconnect section 60 is illustrated in
The present invention thus provides a medium-voltage fuse 10 that provides standard, conventional over-current protection to a fuse circuit but, at the same time, is responsive to commands from an external sensing circuit 300 to open fuse 10 when an event outside fuse 10 occurs.
The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purposes of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.
