Information
-
Patent Grant
-
6614340
-
Patent Number
6,614,340
-
Date Filed
Monday, February 11, 200222 years ago
-
Date Issued
Tuesday, September 2, 200321 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 337 292
- 337 293
- 337 273
- 337 281
- 337 282
- 337 290
- 337 297
- 337 159
- 337 161
- 337 162
- 337 164
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International Classifications
-
Abstract
A Full-Range fuse element assembly includes an insulative former having opposite first and second ends and electrically conducting connectors coupled to ends of the former. A plurality of fuse elements extend between the first connector and the second connector about the insulative former, and each of the fuse elements include a low current interrupting fuse element portion extending from the first connector and a high current limiting fuse element portion extending from the second connector. An insulative sleeve surrounds each of the low current interrupting fuse element portions, and each sleeve includes an end adjacent a respective one of the high current limiting fuse element portions. Each of the low current interrupting fuse element portions includes a weak spot located proximate the second end of a respective one of the sleeves.
Description
This application claims the benefit of United Kingdom Patent Application Number 0103541.9, filed Feb. 13, 2001.
BACKGROUND OF THE INVENTION
This invention relates generally to fuse element or fuse link assemblies, and, more particularly, to fuse element assemblies for General Purpose or Full-Range fuses.
Fuses are widely used as overcurrent protection devices to prevent costly damage to electrical circuits. Fuse terminals typically form an electrical connection between an electrical power source and an electrical component or a combination of components arranged in an electrical circuit. One or more fusible links or elements, or a fuse element assembly, is connected between the fuse terminals, so that when electrical current through the fuse exceeds a predetermined limit, the fusible elements melt and opens one or more circuit through the fuses to prevent electrical component damage.
General Purpose or Full-Range type high voltage, current-limiting fuses are operable to safely interrupt both relatively high fault currents and relatively low fault currents with equal effectiveness. At least one type of General Purpose or Full-Range type fuses employs a fuse element assembly having two distinct portions. One portion is configured for opening of an electrical circuit under relatively low fault current conditions and a second portion is configured for opening of an electrical circuit under relatively high fault current conditions. The first portion includes a plurality of fuse elements contained in respective insulating sleeves and including a weak spot and/or low melting alloy spot located approximately at the center or midpoint of each of the fuse elements. The second portion includes a plurality of fuse elements fabricated from a high conductivity metal and connected in parallel with one another. The first and second fuse element portions are serially wound onto an insulating former and embedded in a arc-extinguishing material within a fuse body.
Under high fault current conditions, the second portion of the fuse element assembly partially vaporizes, and the arc extinguishing material absorbs energy and attains a high electrical resistance to safely and effectively interrupt current through the fuse. Under low fault current conditions, the first portion of the fuse element assembly interrupts current by melting of a fuse element within one or more of the insulated sleeves. The resultant arc within the sleeves generates ionized gas which is expelled from the open ends of the sleeves.
In elevated voltage and current applications, however, such as for protection of increasingly common 12 kV transformers with ratings as high as 1000 kVA, conventional Full-Range fuses have been found deficient. As current ratings and voltage ratings of Full-Range fuses are increased, the fuse is prone to undesirable internal and external damage from resultant increased energy of ionized gas blasts in operation of the fuse. While reinforcement of the insulating sleeves of the first portion of the fuse element assembly is of some use in producing higher current ratings and voltage ratings of Full-Range fuses, reinforcement of the sleeves tends to complicate assembly and increase manufacturing costs of the fuses without overcoming problematic excessive ionized gas blasts and resultant damage during operation of the fuse.
In addition, while voltage and current ratings of Full-Range fuses may be increased by using fuse elements and fuse constructions of greater cross sectional area and capacity, this increases the physical size of the Full-Range fuse. Especially when a large number of fuses are employed, increasing the size of the fuses is problematic.
BRIEF SUMMARY OF THE INVENTION
In an exemplary embodiment of the invention, a fuse element assembly for a Full-Range fuse includes an insulative former having opposite first and second ends. A first electrically conducting connector is coupled to the first end of the former and a second electrically conducting connector is coupled to the second end of the former. At least one fuse element extends between the first connector and the second connector about the insulative former. The fuse element includes a low current interrupting fuse element portion extending from the first connector, a high current limiting fuse element portion extending from the second connector, and the low current interrupting fuse element portion and the high current limiting fuse element portion coupled to one another intermediate the first and second connector. An insulative sleeve surrounds the low current interrupting fuse element portion, and each sleeve includes a first end adjacent the first connector and a second end adjacent the high current limiting fuse element portions. The low current interrupting fuse element portion includes a weak spot located adjacent to but within the second end of a respective one of the sleeves. Alternatively, the weak spot is located in a range from 0 to 25% of the length of the sleeve as measured from the second end of the sleeve.
By locating the weak spot of the low current interrupting fuse element at an end of the insulating sleeve opposite the connector from which the low current interrupting fuse elements extend, ionized gas blasts generated in operation of a fuse is directed predominately toward a center of the fuse rather then the ends of the fuse near the end-caps. Therefore, by more efficiently and effectively expelling ionized gas from the insulative sleeve, the fuse element assembly avoids damage to the fuse body and end-caps that has been observed in conventional fuses, and higher voltage and current ratings are facilitated without increasing dimensions of fuse components. Thus, a superior performing Full-Range fuse is provided in a compact, space-saving construction in comparison to known Full-Range fuses.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is sectional schematic of a first embodiment of a Full-Range fuse; and
FIG. 2
is a sectional schematic of a second embodiment of a Full-Range fuse.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1
illustrates a Full-Range fuse
10
including an insulative fuse body
12
, a fuse element assembly
14
within body
12
, electrically conductive end-caps
16
coupled to and enclosing body
12
and electrically connected to fuse element assembly
14
, and an arc quenching material
18
surrounding fuse element assembly
14
within body
12
. Thus, when end-caps
16
are connected to an energized electrical circuit (not shown), a circuit is completed through fuse
10
via fuse element assembly
14
. When current flowing through fuse
10
approaches unacceptable levels, dependent upon characteristics of fuse element assembly
14
and hence the current rating of fuse
10
, fuse element assembly
14
at least partially operates, melts, vaporizes or otherwise opens, as explained more fully below, to limit current flow and interrupt damaging current flow through fuse
10
. Thus, line-side electrical circuits and equipment may be electrically isolated from malfunctioning load-side electrical circuits and equipment to prevent costly damage to the load and line-side circuits and equipment.
In one embodiment, body
12
is fabricated from a known insulative, i.e., non-conductive material, such as ceramic materials, and extends substantially cylindrically between end-caps
16
. It is contemplated, however, that the benefits of the invention may be realized in fuses employing non-cylindrical bodies and fabricated from other materials. In addition, in an exemplary embodiment arc extinguishing medium
18
is granular pure silica sand or powdered quartz that completely surrounds fuse element assembly
14
and substantially eliminates air gaps around fuse element assembly
14
within body
12
. In alternative, embodiments, however, other known arc extinguishing materials and mediums are employed in fuse
10
in lieu of pure silica sand or powdered quartz.
Fuse element assembly
14
includes an insulated former
20
having a first portion
22
and a second portion
24
having a greater relative cross sectional area than first portion
22
. More specifically, in an exemplary embodiment, former
20
is integrally formed and extends substantially cylindrically with a step increase
26
in diameter that delineates former first portion
22
and former second portion
24
into relatively narrow and relatively wide portions, respectively. In alternative embodiments, however, separate narrow and wide portions
22
and
24
are secured to one another in fabrication of former
20
. In addition, it is contemplated that the benefits of the invention may be realized using alternative shapes, i.e., non cylindrical shapes, of former
22
, including but not limited to elliptical cross-sectional shapes, polygonal, ribbed or star cross-sectional shapes. Still further, it will be apparent further below that the invention may be employed on a former
22
having a substantially constant or uniform cross-sectional area, although it is noted that a substantially non-uniform clearance between fuse element assembly
14
and body
12
may result unless body
12
is modified accordingly.
Electrically conductive connectors
28
,
30
are oppositely coupled to former
20
at either end of former
20
, i.e., at respective ends of former first portion
22
and former second portion
24
located away from step diameter increase
26
. Each connector
28
,
30
may include extensions
31
that establish electrical contact with end-caps
16
. Thus, an electrical circuit may be established through fuse elements, explained further below, that are wound about former
20
and electrically coupled to connectors
28
,
30
.
A plurality of low current interrupting fuse elements
32
are wound about former first portion
22
and extend longitudinally from connector
28
toward former step increase
26
in a helical fashion. Each low current interrupting fuse element
32
is fabricated from a relatively low-melting point alloy or metal such as tin, or alternatively, for example, from a silver or copper element having an M effect overlay (low melting alloy spot)
34
or M spot thereon and located intermediate connector
28
and former step diameter increase
26
.
More specifically, in an exemplary embodiment, each low current interrupting fuse element
32
is at least partially coated with an overlay
34
of a conductive metal that is different from a composition of fuse element
32
. In one illustrative embodiment, for example, fuse elements
32
are fabricated from copper or silver and overlay
34
is fabricated from tin. As tin has a lower melting temperature than copper or silver, overlay
34
is heated to a melting temperature in an overcurrent condition before copper fuse element
32
. The melted overly then reacts with copper or silver fuse element
32
and forms a tin-copper alloy that has a lower melting temperature than either metal by itself. As such, an operating temperature of fuse element
32
is lowered in an overcurrent condition, and each fuse element
32
is prevented from reaching the higher melting point of silver or copper. Thus, conductive characteristics and advantages of copper or silver are utilized while avoiding undesirable operating temperatures. In alternative embodiments, other conductive materials may be used to fabricate fuse elements
32
and overlay
34
, including but not limited to copper and silver alloys and tin alloys, respectively, to achieve similar benefits. In further alternative embodiments, overlay
34
is fabricated from antimony or indium.
Overlay
34
is applied to respective fuse elements
32
using known techniques, including for example, gas flame and soldering techniques. Alternatively, other methods, including but not limited to electrolytic plating baths, thin film deposition techniques, and vapor deposition processes may be employed. Using these techniques, in various embodiments overlay
34
is applied to some or all of fuse elements
32
. For example, in one embodiment, only a central portion of a fuse element
32
includes overlay
34
, while in another embodiment, an entire surface area of a fuse element
32
includes overlay
34
. In a further embodiment, overlay
34
is applied on one side only of a fuse element
32
, while in a different embodiment, both sides of a fuse element
32
include M effect overlay
34
.
Each low current interrupting fuse element
32
further includes a narrowed portion, or weak spot
36
, of reduced cross sectional area in which fuse element
32
is designed to melt, open, or otherwise break an electrical connection through fuse
10
. Because of the reduced cross-sectional area of weak spot
36
relative to a remainder of fuse element
32
, weak spot
36
is heated to a higher temperature as current flows therethrough than through a remainder of fuse element
32
, and hence reaches the melting point of fuse element
32
before the remainder of fuse element
32
. Thus, fuse element
32
predictably opens in the area of weak spot
36
before other portions of fuse element
32
. It will be appreciated by those in the art that weak spots
36
could alternatively be formed according to other known methods and techniques known in the art, such as, for example, forming holes in fuse elements
32
rather than narrowed regions.
Each low current interrupting fuse element
32
is further encased in a flexible thermally insulative sleeve
38
of slightly greater dimension than a width of each fuse element
32
. Insulative sleeves
38
are fabricated from materials capable of withstanding high temperatures when fuse
10
is operated and also has a sufficient electrical resistance for insulative purposes. In an exemplary embodiment, sleeves
38
are fabricated from silicon rubber. In alternative embodiments, other known materials are used in lieu of silicone rubber for fabricating sleeves
38
. In further embodiments, inserts (not shown) of, for example, silicon grease, are positioned in respective ends of open sleeves
38
adjacent connector
28
and former step diameter increase
26
to prevent arc extinguishing medium
18
from entering sleeves
38
, yet while allowing ionized gas to escape sleeves
38
as fuse
10
is operated.
Notably, and unlike conventional Full-Range fuses, weak spot
36
of each low current interrupting fuse element
32
is located proximally to step diameter increase
26
of fuse assembly former
14
, or toward a center of fuse
10
. In other words, in one embodiment weak spots
36
of low current interrupting fuse elements
32
are located, to the extent possible, as far away from connector
18
and end-cap
16
as is practicable but still within respective sleeves
38
. As fuse elements
32
open near weak spots
36
, an electrical arc is generated across the break in weak spot
36
within sleeves
38
. The resultant blast of ionized gas is expelled from sleeve
38
predominately through the closer end of sleeve
38
located opposite from connector
28
and toward a center of fuse
10
, i.e., proximal to former step diameter increase
26
in the illustrated embodiment. Therefore, only a small portion of ionized gas travels through sleeves
38
to their ends adjacent connector
28
, and excessive exhaust pressure generated in sleeves
38
is primarily, and harmlessly, dissipated in arc extinguishing medium
18
surrounding fuse element assembly
14
away from connector
28
and end-cap
16
, or adjacent former step diameter increase
26
in the illustrated embodiment. Only a small portion of exhaust pressure travels longitudinally through sleeves
38
and exits sleeves
38
adjacent connector
28
and end-cap
16
. Thus, unlike known Full-Range fuses, increased energy of ionized gas blasts from elements
32
operating at higher currents, i.e., up to 100 A, and high voltages, i.e., 12 kV to 38 kV may be safely and effectively dissipated without rupturing fuse body
12
near end-cap
16
adjacent connector
28
and without damaging or displacing end-cap
16
.
It is contemplated that the benefits of the invention could be attained in alternative embodiments by locating weak spot
36
of each low current interrupting fuse element
32
in a range of positions toward a center of fuse
10
and away from a central region of respective low current interrupting fuse elements
32
. More specifically, some or all of the above-described advantages accrue to fuse elements
32
having weak spots
36
located up to about 25% of the total length of a sleeve
38
as measured from the end of the sleeve opposite connector
28
, i.e., the end of a sleeve
38
located closest to the center of fuse
10
.
In the illustrated embodiment, a reinforcing medium
40
is employed over insulating sleeves
38
to prevent damage to sleeves
38
from exhaust pressure in sleeves
38
when fuse
10
operates. In one embodiment, reinforcing medium is glass-fiber tape, although in alternative embodiments other known reinforcing media known in the art is employed to accomplish similar objectives. It is appreciated, however, that positioning weak spots
36
of each low current interrupting fuse element
32
away from connector
38
and toward a center of fuse
10
may obviate the need for reinforcing media
40
in certain fuse ratings by more efficiently dissipating exhaust pressure in sleeves
38
away from connector
28
and end-cap
16
where fuse
10
is less susceptible to damage, thereby simplifying manufacturing of fuse
10
and reducing manufacturing costs.
A plurality of high current limiting current fuse elements
44
are wound around former second portion
24
and are electrically coupled to connector
30
on an end of former
20
opposite connector
28
. Each high current limiting fuse element
44
is fabricated from a relatively high-melting point material, such as silver or copper, and extends in a helical fashion from connector
30
toward step diameter increase
26
of fuse element assembly former
22
. Each high current limiting fuse element is connected in parallel via connector
30
and includes a plurality of weak spots
46
or narrowed regions of reduced cross sectional area located at spaced intervals between connector
30
and low current interrupting fuse elements
32
. It will be appreciated by those in the art that weak spots
46
could alternatively be formed according to other methods and techniques known in the art, such as, for example, forming holes in fuse elements
44
rather than narrowed regions.
Each high current limiting fuse element
44
is coupled to a respective one of low current interrupting fuse elements
32
to form a plurality of continuously extending fuse elements that are partly high current limiting fuse elements
24
and partly low current interrupting fuse elements
32
. The continuously extending fuse elements are wound about former
22
in a helical fashion and are connected in parallel with one another between connectors
28
,
30
.
In an alternative embodiment, low current interrupting fuse elements
32
and high current limiting fuse elements
44
are connected to an interconnector member (not shown) disposed between low current interrupting fuse elements
32
and high current limiting fuse elements
24
in the vicinity of former step diameter increase
26
. As such, different numbers of low current interrupting fuse elements
32
relative to high current limiting fuse elements
44
may be employed to vary voltage and current ratings of fuse
10
. As will be appreciated by those in the art, actual voltage and current ratings of fuse
10
may be further manipulated by altering dimensional characteristics of low current interrupting fuse elements
32
and high current limiting fuse elements
44
.
Fuse
10
operates as follows. During low overcurrent conditions, e.g., less than six times the current ratings of fuse element assembly
14
, high current limiting fuse elements
44
are cooled by arc extinguishing medium
18
and low current interrupting fuse elements
32
open at M spots
34
within sleeves
38
. Low pressure ionized gas from resultant arcs is expelled from sleeves
38
at either end of sleeve
38
without damaging fuse body
12
or end cap
16
adjacent connector
28
.
At higher current conditions just before the point where high current limiting elements
44
take over the duty of fault interruption, fuse elements
32
open at weak spots
36
within sleeves
38
due to temperature effects from thermally insulating sleeves
38
before M effect spots
34
have sufficient time to operate and interrupt current through fuse elements
32
. The resultant arc when fuse elements
32
open at weak spots
36
is extinguished in sleeves
38
by the above-described expulsion process of ionized gas in sleeves
38
. As gas is predominately dissipated harmlessly into arc quenching medium
18
toward the center of fuse
10
and away from connector
28
and end-cap
16
, damaging effects of high exhaust pressure near connector
28
is avoided. With proper dimensioning of weak spots
36
, it can be ensured that operation of fuse elements
32
occurs at weak spots
36
before opening of fuse element
32
in the vicinity of M spots
38
at predetermined current levels that approach current values sufficient to operate high current limiting fuse elements
44
.
At even higher values of overload current, opening of fuse elements
32
at weak spot
36
and opening of fuse elements
44
at weak spots
46
occurs substantially simultaneously. Consequently, arc energy is dissipated in each of the single weak spots
36
of fuse elements
32
. However, at such higher current, an even greater gas blast may be generated within sleeves
38
. Thus, positioning of weak spot
36
of respective low current interrupting elements
32
closer to center of fuse and in the vicinity of former step diameter increase
26
if of greater significance to direct damaging gas blasts away from connector
28
at the end of fuse
10
.
A fuse
10
is therefore provided that controls ionized gas blasts in sleeves
38
at a full range of fault currents, including takeover current values wherein current interrupting duty is transferred from low current interrupting fuse elements
32
to high current limiting fuse elements
44
. Therefore, fuse
10
is capable of performing at higher voltage and current ratings than known Full-Range fuses. A much wider range of applications is therefore available for using fuse
10
due to controlled ionized gas blast in sleeves
38
. For example, a Full-Range fuse
10
having a voltage rating of 10 kV and a current rating of 100 A may be used to protect a transformer of 1000 kVA or greater. Similarly, Full-Range fuses
10
having voltage ratings as high as 38 kV may be constructed.
In addition, by locating weak spots
36
of low current interrupting fuse elements
32
at an end of insulating sleeves
38
opposite connector
28
and therefore directing ionized gas blasts predominately toward a center of fuse
10
rather then the ends of fuse
10
, fuse
10
is capable of attaining higher voltage and current ratings without increasing dimensions of fuse components. Thus, a superior performing Full-Range fuse
10
is provided in a compact, space-saving construction in comparison to known Full-Range fuses.
FIG. 2
is a sectional schematic of a second embodiment of a Full-Range fuse
60
wherein common features with fuse
10
(shown in FIG.
1
and described above) are indicated with like reference characters. Comparing fuse
10
and fuse
60
, it may be seen that fuse
60
includes an M spot
62
located proximally to weak spot
36
of each low current interrupting fuse element
32
, as opposed to M spot
34
(shown in
FIG. 1
) located in a central portion of each fuse element
32
. Therefore, in addition to the benefits described above when fuse elements
32
open at weak spots
36
, ionized gas generated from operation of fuse elements
32
at M spots
34
also is harmlessly dissipated into arc extinguishing medium through sleeves
38
toward the center of fuse
60
. Fuse
60
otherwise operates substantially as described above with respect to fuse
10
, and the benefits described above in relation to
FIG. 1
are also attained. Positioning of M spot
34
either in a center of respective sleeves
38
(as shown in
FIG. 1
) or proximal to weak spots
36
(as shown in
FIG. 2
) is dictated by thermal parameters of specific materials of the fuse components.
It is contemplated that the benefits of the invention could be achieved at lower fuse ratings using a single low current interrupting element
32
and a single high current limiting member
44
. In addition, in alternative embodiments, low current interrupting elements
32
may employ more than weak spot
36
located toward a center of fuse
10
and away from a central region of fuse elements
32
. Still further, in alternative embodiments, fuses are electrically connected to end-caps
16
without being helically wound about former
20
, such as for example, by employing substantially linear fuse elements between end-caps
16
, with or without former
20
.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
Claims
- 1. A fuse element assembly for a Full-Range fuse, said fuse element assembly comprising:an insulative former comprising opposite first and second ends; a first electrically conducting connector coupled to said former first end; a second electrically conducting connector coupled to said former second end; at least one fuse element extending between said first connector and said second connector about said insulative former, said at least one fuse element comprising a low current interrupting fuse element portion extending from said first connector, a high current limiting fuse element portion extending from said second connector, and said low current interrupting fuse element portion and said high current limiting fuse element portion coupled to one another intermediate said first and second connector; and an insulative sleeve surrounding said low current interrupting fuse element portion, said sleeve having a first end adjacent said first connector and a second end adjacent said high current limiting fuse element portion, said low current interrupting fuse element portion comprising a weak spot located adjacent said second end of said sleeve.
- 2. A fuse element assembly in accordance with claim 1, said former comprising a first portion having a first cross-sectional area and a second portion having a second cross sectional area, said second cross sectional area greater than said first cross sectional area.
- 3. A fuse element assembly in accordance with claim 2, said former further comprising a step increase in cross sectional area between said former first portion and said former second portion.
- 4. A fuse element assembly in accordance with claim 3 wherein said at least one fuse element extends helically about said former.
- 5. A fuse element assembly in accordance with claim 1 comprising a plurality of fuse elements, said plurality of fuse elements are connected in parallel.
- 6. A fuse element assembly in accordance with claim 1 wherein said low current interrupting fuse element portion further comprises an M effect overlay.
- 7. A fuse element assembly in accordance with claim 6 wherein said M effect overlay is located adjacent said weak spot of each low current interrupting fuse element portion.
- 8. A fuse element assembly for a Full-Range fuse, said fuse element assembly comprising:an insulative former comprising opposite first and second ends; a first electrically conducting connector coupled to said former first end; a second electrically conducting connector coupled to said former second end; a plurality of low current interrupting fuse elements extending from said first connector toward said second connector; each of said low current interrupting fuse elements comprising a weak spot therein; a plurality of said high current limiting fuse elements extending from said second connector toward said first connector, each of said high current limiting fuse element portions comprising a plurality of weak spots, said low current interrupting fuse element portions and said high current limiting fuse element portions coupled to one another intermediate said first and second connectors; and a plurality of insulative sleeves each surrounding one of said low current interrupting fuse element portions, said sleeves each having a first end adjacent said first connector and a second end opposite said first end, said second end of each sleeve located proximally to a respective said weak spot of a respective one of said low current interrupting fuse elements.
- 9. A fuse element assembly in accordance with claim 8 wherein each of said low current interrupting fuse elements are connected in parallel.
- 10. A fuse element assembly in accordance with claim 9 wherein each of said low current interrupting fuse elements extends helically about said former.
- 11. A fuse element assembly in accordance with claim 8 wherein said former comprises a first portion, a second portion, and a step increase intermediate said first portion and said second portion, said second end of said sleeve positioned adjacent said step increase.
- 12. A fuse element assembly in accordance with claim 8 wherein each of said low current interrupting fuse elements comprises an M effect overlay.
- 13. A fuse element assembly in accordance with claim 12 wherein said M effect overlay is located adjacent said weak spot on each of said low current interrupting fuse elements.
Priority Claims (1)
Number |
Date |
Country |
Kind |
0103541 |
Feb 2001 |
GB |
|
US Referenced Citations (5)
Foreign Referenced Citations (3)
Number |
Date |
Country |
2126808 |
Mar 1984 |
GB |
2184301 |
Jun 1987 |
GB |
216852 |
May 1997 |
HU |