Exothermically assisted arc limiting fuses

There is described a fuse comprising a housing and a current carrying strip of metal comprising a fuselink enclosed in the housing, each end of which electrically extends through the housing as an electrical connection. There being at least one first section of the metal strip for severing upon predetermined fault conditions, and at least one second section of the metal strip, distanced from the first section, having the properties of a hinge for pivoting. There further being at least one exothermic source in the proximity of the first section that substantially upon severance of the metal strip at the first section is ignited, and causes at least one segment of the severed metal strip to be propelled about the second section comprising the hinge. There further being an arc chute in proximity to the path of the moving severed edge of the first section such that fault current limiting is obtained.

RELATED APPLICATIONS 
This application claims priority in part to Iversen, "Fast Acting, Arc 
Limiting Fuses", U.S. Provisional Patent Application Ser. No. 60/005,797, 
filed on Oct. 23, 1995. 
BACKGROUND OF THE INVENTION 
1. Field of Invention 
The present invention relates to fuses used, for example, in connection 
with the generation, transmission, distribution and conversion of electric 
power, and in particular, addresses the need for fast acting, arc limiting 
fuses. 
2. Related Art 
In conventional fuses the most general form of fuselink is a strip of 
metal, such as copper or silver, having multiple narrowed segments or 
restricted sections. The higher resistance of the restricted sections, 
that is the smaller cross sections, causes the restricted sections to melt 
first under fault conditions. In conventional fuses, multiple restricted 
sections are employed to cause a sufficiently high voltage drop to be 
developed, after a suitable arcing time which is current dependent, to 
cause the arc to extinguish. To operate at higher voltages, for example, 
above 600V, fuses are long and require larger numbers of restricted 
sections to accommodate the higher voltages. This leads to high inductance 
making them of limited value for use in high frequency switch mode power 
systems, and particularly with power semiconductors. Furthermore, if the 
fault or overcurrent is small, for example, 1.5 to 1, compared to the 
continuous rating of the fuse, only one restriction may melt resulting in 
a long arcing period with potential equipment damage. 
SUMMARY OF THE INVENTION 
There is described a fuse comprising a housing and a current carrying strip 
of metal comprising a fuselink enclosed in the housing, each end of which 
electrically extends through the housing as an electrical connection. 
There being at least one first section of the metal strip for severing 
upon predetermined fault conditions, and at least one second section of 
the metal strip, distanced from the first section, having the properties 
of a hinge for pivoting. There further being at least one exothermic 
source in the proximity of the first section that substantially upon 
severance of the metal strip at the first section is ignited, and causes 
at least one segment of the severed metal strip to be propelled about the 
second section comprising the hinge. There further being an arc chute in 
proximity to the path of the moving severed edge of the first section such 
that fault current limiting is obtained. 
By placing on the fuselink, a suitable exothermic propulsion charge on at 
least one side of the restricted section and preferably in close proximity 
thereto, a capability is provided to rapidly separate the two segments of 
the fuselink from each other upon a fault induced melting of the 
restricted section thereby clearing the fault. Upon arc initiation, a 
suitable fuse located in the restricted section is ignited and quickly 
ignites the exothermic propulsion charge. The exothermic charge acts as a 
propellant to drive each segment of the fuselink away from each other 
thereby creating a suitably large gap between the fuselink segments such 
that the arc cannot be maintained and is extinguished. Thus, the 
dielectric strength of the gap is such that the arc cannot re-strike. To 
further assist in extinguishing the arc and limit the current, the 
exothermic material may have mixed with it or placed near it, material 
that upon heating generates arc quenching gases, such as, 
electro-negative. Suitable materials include, for example, boric acid and 
aliphatic nitrogen and hydrogen producing materials. In addition, arc 
chutes, commonly only used in circuit breakers may be adapted to the 
substantially present invention to provide current limiting action. 
The present invention provides a solution to the non-interrupting band 
which occurs between the rated fuse current and the minimum interruption 
current of conventional fuses. This is the region of low overcurrent, for 
example, 150% of the rated fuse current, where the arc does not clear 
within a specified time, but rather continues to arc with potential for 
fire, and damage and destruction of equipment. The arc clearing times of 
the present invention, whether currents are below the minimum interruption 
current or a heavy short circuit, are substantially the same because arc 
temperatures, which range from about 10,000.degree. K to 15,000.degree. K 
for any current, are more than adequate to ignite the exothermic 
propulsion material and so drive the two fuselink segments apart to clear 
the fault. If an arc is struck, the fault will clear no matter how low the 
current thus making arc clearing times independent of current. Pre-arcing 
characteristics of the present invention are substantially the same as for 
conventional fuses. 
The fuse of the present invention provides for the rapid clearance of a 
fault upon initiation of an arc, the arc clearing time being substantially 
constant and independent of the fault current. 
The fuse of the present invention enables lower minimum currents to be 
cleared and arc clearing times are substantially independent of power 
factor. 
The fuse of the present invention is of inherently low inductance. 
The fuse of the present invention is compact and capable of use at high 
voltages. 
The fuse of the present invention is of low cost construction. 
The fuse of the present invention provides for limiting of arc currents.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIGS. 1 and 2, shown is fuselink 10 having a least one 
fuselink 10 severance section 17, sometimes referred to as severance 
section, which is caused to melt under fault conditions creating a gap 26 
(FIG. 3) in fuselink 10. Fuselinks 10 are generally strips of metal made 
of, for example, copper, silver or aluminum, alloys thereof or other 
suitable conductor material. Fuselink 10 is enclosed in an electrically 
insulating housing 11, made, for example, of glass, ceramic or plastic, 
with each end of the fuselink 10, protruding through end caps 13 for 
external electrical connections. End caps 13 may be of an electrically 
insulating material, or may be of metal. Fuselink 10 is shown in strip 
form. To cause severance of the fuselink in a predetermined section, 
called severance section 17, of the fuselink under fault conditions, the 
general method is to obtain a high resistivity in the severance section. 
In this manner I.sup.2 R fault induced heating causes severance section 17 
to melt first. Severance section 17 is illustrated as restricted section 
12 which has a cross sectional area less than the main body, width 53 
times thickness 54, of fuselink 10 resulting in a localized high 
electrical resistance. In close proximity to restricted section 12 and 
either fastened to fuselink 10 or an integral part of it, are containment 
wells 16 to hold exothermic material 18. For controlled ignition of 
material 18 a segment of a second exothermic fuse 20 may protrude into 
restricted section 12 such that upon a fault and consequent melting of 
section 12, and before or after striking of an arc between the two 
fuselink segments 22, 24, fuse 20 is ignited and the burning material 
quickly travels to ignite material 18. Alternatively, with exothermic 
material 18 in dose proximity to restricted section 12, material 18 can be 
ignited by the arc upon adequate burn-back of fuselink segments 22, 24. 
The ignition temperature of exothermic materials 18 and 20 may be tailored 
to be above the melting point of restricted section 12 such that the 
ensuing arc ignites materials 18, 20. When employing the Metcalf effect, 
for example, with a strip of tin on the copper or silver fuselink 10, the 
melting point is reduced to about 230.degree. C. Thus, materials 18, 20 
ignition temperature would be set suitably above 230.degree. C. For 
copper, aluminum or silver fuselinks 10, without the Metcalf effect, 
material 18, 20 ignition temperatures at or above the respective melting 
points of 1083.degree. C., 660.degree. C. and 962.degree. C. are 
desirable. With arc temperatures ranging from about 10,000 to 
15,000.degree. K, substantially any ignition temperature for materials 18, 
20 may be accommodated. 
As a further alternative to the use of fuse 20, restricted section 12 may 
be fabricated from a metal or alloy of suitable metals, such as PdAl, or 
other suitable material combination that conducts current and upon an 
overcurrent under fault conditions heats up and ignites in the fashion of 
an exothermic fuse and rapidly burns to then ignite material 18. Thus, 
restricted section 12 serves as both current conductor under normal 
operation and fuse upon a fault. With this construction, the cross section 
will be greater than that of a conventional restricted section 12 because 
of higher electrical resistivity. 
Referring now to FIG. 3, shown are the two segments 22, 24 of fuselink 10 
being propelled 28 apart 26 by burning 30 exothermic material 18. One end 
of segment 22 is fastened to end cap 13 and so well 16 describes a curved 
path, which, in general, is in the general form of an arc. Arc 32 between 
segments 22, 24 is seen as being stretched distance 26 and thus increasing 
in impedance. When spacing 26 between segments 22, 24 reaches a critical 
distance, dependent upon the applied voltage and other factors such as the 
presence of arc quenching gases, the arc is extinguished. At suitably high 
currents and voltages an arc chute may be incorporated. With proper design 
and material selection, arc clearing time in the hundreds of microseconds 
may be obtained. This provides for lower let through energy (I.sup.2 t) 
during the arcing phase with consequent reduced potential for sensitive 
equipment damage. 
With the present invention, the substantially lower let through energies 
(I.sup.2 t) arising from sub-millisecond arcing times result in lower 
pressure build-up compared to conventional fuses. In this manner much of 
the pressure build-up due to the exothermic reactions of materials 18, 20 
can be compensated for, with the end result that internal housing 
pressures may be comparable to conventional fuses. Under conditions of low 
fault currents where conventional fuses have relatively high I.sup.2 t 
energy dissipation due to prolonged arcing, internal housing pressures in 
the present invention may be substantially less. The range of expected 
internal housing pressure variations will be less for the present 
invention than for comparable conventional fuses. 
The thickness 54 of fuselink 10 is generally small for currents up to about 
10A, for example, 0.1-0.4 mm. This coupled with the general softness of 
fuselink 10 material, usually copper, aluminum or silver, makes link 10 
very pliant and easy to flex or curve about thickness 54, that is, around 
axis 52. Fuselink width 53, FIG. 2, which is relatively large, e.g. 5-20 
mm, is substantially unaffected by the flexing or curving movement and 
adds relatively little to exothermic material 18 requirements. In this 
manner, minimal exothermic material 18 is required for propulsion of 
segments 22, 24 with the result that the pressure build-up in housing 11 
is less than the prior art where multiple explosive means are generally 
used to disintegrate, burn or mangle the fuselink at, in general, multiple 
points along its length. The exothermic material is designed for a 
suitable impulse or a controlled burn to act as a propellant. There is 
substantially no change in the width 53 and thickness 54 cross sectional 
geometry, here shown as rectangular, before, during and after a fault. The 
flexing or curving of fuselink 10 during propulsion by exothermic material 
18 is predominantly along its length. This comprises minimal energy 
expenditure and minimal pressure build-up. It is anticipated that less 
exothermic material 18 and resultant energy release will be involved than 
that described in the prior art for explosively activated fuses. 
Referring now to FIG. 4, shown are the final resting positions of fuselink 
10 segments 22, 24, now spaced apart distance 34. Distance 34 may be 
selected such that failure of one of propulsion material 18 to ignite 
still provides sufficient spacing, that is, half of 34, such that adequate 
voltage isolation is obtained and the arc 32 is extinguished and does to 
re-ignite. Segments 22 and 24 have the flat faces 36, 38 of cold strip 
metal facing each other thereby minimizing the electric field strengths, 
there being no hot, sharp edges 40, 42 opposing each other. Also, the 
leading edges 40, 42 of melted restricted section 12 are shown facing away 
from each other and spaced 44 apart, which is further apart than faces 36, 
38 with consequent lower electric fields between 40, 42. 
The geometry and travel path of segment 22 has been designed to cause tip 
40 to wedge itself against the inside surface 46 of envelope or housing 
11. This further serves to quench the hot tip 40 to further insure arc 
extinction in addition to the effect the mechanical action of forcing tip 
40 against surface 46 has on extinguishing the arc. In addition, a layer 
of material 48 that produces arc quenching gas may be deposited on surface 
46 such that when hot tip 40 strikes surface 46 coated with material 48, 
arc quenching gases are produced accompanied by an increased cooling rate 
of hot tip 40. To improve the locking action of tip 40 onto surface 46, a 
predetermined surface geometry such as corrugations 50 may be employed. 
This is also useful in environments of high shock and vibration. When 
corrugations 50 are extended the length of housing 11, improved electrical 
insulation is obtained. Corrugations 50 may also be on the external 
surface of housing 11. 
As an alternative, segment 24 is shown as having been simply driven into an 
arc shape with tip 42 not contacting surface 46. In case of high internal 
pressures being developed from the burning of material 18, relief valve 
52, which may be a disc of silicon rubber, and which may be equipped with 
a pressure responsive relief hole, may be installed. 
Referring now to FIG. 5, shown are containment wells 16 in fuselink 10 
having arc extinguishing material 18 incorporated into wells 16. First 
well 16 shows material 48 in the bottom whereas second well 16 has 
material 48 at the top. First well 16 produces arc extinguishing gases 
after material 18 has burned a specified time whereas second well 16 
produces arc extinguishing gases substantially immediately upon ignition 
of material 18. Alternatively, materials 18 and 48 may be mixed for 
continuous production of arc extinguishing gases. This may be further 
refined by varying the ratio of mix of materials 18 and 48 with depth to 
obtain a varied and predetermined arc quenching gas production during the 
burning period of material 18. 
Referring now to FIGS. 6 and 7, shown is fuselink geometry that permits 
segments 22, 24 to describe predetermined paths when propelled by material 
18. -Segments 22, 24 of fuselink 10 have edges 56 bent up, or 
geometrically distorted, for a predetermined length 58 resulting in rigid 
construction thereby ensuring that the axis of rotation 52 is along 
section 21 on segments 22, 24. Section 21 acts as a hinge for segments 22, 
24 to bend or pivot about. The production of fuselink 10 with wells 16 and 
bent edges 56 may all be done in a single stamping operation. 
Alternatively, flat fuse links 10, with arbitrary planar geometries may be 
made by chemical milling with wells 16 and bent edges 54 stamped in a 
secondary operation. In general, the cross sectional area of fuselink 10 
preferably remains substantially constant to maintain constant resistance 
except for the restricted section 12. All embodiments of the present 
invention may incorporate the structures illustrated in FIGS. 6 and 7. 
Referring now to FIG. 8, shown is an alternative geometry for fuselink 10. 
Fuselink 10 is shown in a generally "S" shaped configuration with the 
restricted section 12 approximately in the middle. Sections 62, 64 of 
segments 22, 24 serve the dual purpose of expansion relief, thereby 
minimizing thermal fatigue and to provide the maximum economy of space in 
that when segments 22 and 24 are propelled by exothermic material 18, 
substantially the full height 66 of housing 11 may be used thereby 
obtaining maximum final spacing, that is, higher voltage isolation, 
between segments 22, 24 after fault clearance. Wells 16 are shown on 
opposing surfaces of fuselink 10 in order to propel segment 22 in 
direction 28, and to propel segment 24 in opposing direction 28A, both of 
which provide for maximum final spacing between segments 22 and 24. This 
provides for a very compact structure and is suitable for use with 
semiconductors or high voltage applications. 
Another embodiment of the present invention is shown in FIGS. 9, 10 and 11 
and is particularly suited for use in applications where heat dissipated 
in fuselink 10 must be efficiently removed. Referring now to FIG. 9, 
insulating housing 11 incorporates at least one dielectric surface that 
has moderate to high thermal conductivity, here shown as plate 72 fastened 
to dielectric housing 11. For moderate thermal conductivity Al.sub.2 
O.sub.3 may, for example, be used as plate 72. For high thermal 
conductivity BeO, SiC or AlN ceramics may, for example, be used. Housing 
11 may be completely made of the above ceramics or other suitable 
dielectric material. 
Fuselink 10 has, for example, restricted section 12 generally centered in 
housing 11. Fuselink 10 is shown as entering a first end cap 13 
approximately in the center and then bending approximately 90.degree. or 
other suitable angle and being directed toward plate 72. In proximity to 
plate 72, link 10 is bent about 90.degree. or other suitable angle on a 
suitable radius to then lie substantially parallel to plate 72. Upon 
reaching the vicinity of the opposing second end cap 13, link 10 again 
goes through two successive 90.degree. or other suitable angle bends to 
exit out approximately centered from the second end cap 13 as shown. As in 
FIG. 8, sections 62, 64 of link 10 serve as expansion joints and permit 
use of the full height of housing 11 for segments 22, 24 travel during 
fault clearance. Plate 72 may be prepared with a small recess 79 to ensure 
that restricted section 12 operates properly and is not inappropriately 
cooled by plate 72. Plate 72, housing 11 and end caps 13 may be joined and 
sealed with suitable adhesives or other means. FIGS. 1 to 4 could employ 
similar joining means. 
Referring now to FIG. 11, shown is plate 72 having plastic side rails 74 
molded on to it. Rails 74 may have periodically spaced holding means 76 
incorporated during the molding operation. Holding means 76 may be 
suitably formed beryllium copper strips 76 applying suitable force 78 to 
hold link 10 against plate 72 to ensure proper heat transfer. Strips 76 
also serve to dampen vibration perpendicular to the surface of plate 72. 
The force 78 exerted by strips 76 on link 10 is overcome by the propulsion 
force 30 (FIG. 3) of exothermic material 18 upon a fault condition 
whereupon normal fault clearing operation, as previously described, 
ensues. Strips 76 may be oriented or twisted in such manner that they 
readily and with minimum resistance disengage from link 10 as it is 
propelled from plate 72 under fault conditions. To further enhance heat 
transfer, a suitable heat transfer medium such as thermal grease 77 may be 
employed to join link 10 and plate 72 opposing surfaces. In general, 
thermal grease is kept away from material 18 and restricted section 12. 
Referring again to FIG. 10, shown are multiple strips 76 for holding link 
10 against plate 72 for predetermined heat transfer. Thermal cycling of 
link 10 causes it to expand and contract. With plate 72 as a heat sink the 
expansion of link 10 is kept to a minimum because of minimal temperature 
excursions. Referring again to FIG. 9, what expansion of link 10 there is, 
is taken up by sections 62, 64 with minimal stress to link 10. Strips 76 
also serve to ensure that adequate thermal contact between link 10 and 
plate 72 is maintained during shock, vibration, expansion and contraction. 
Referring again to FIG. 11, since strip 76 pressure 78 is substantially 
orthogonal to link 10 expansion, link 10 is free to expand and contract 
with no adverse interaction. If heat sink compound 77 is used between link 
10 and plate 72, force 78 from strip 76 helps maintain intimate contact 
during thermal cycling. 
Referring again to FIG. 9, exposed exothermic material 18 is shown in close 
proximity to and facing plate 72. This enclosing of material 18 provides 
greater efficiency in propulsion of segments 22, 24. The surfaces of plate 
72 opposing material 18 may be coated with a material, such as boric acid, 
which will generate arc extinguishing gases when heated by the burning 
material 18. For low voltage applications, for example, to about 2000 V, 
the external surface of plate 72 may be attached to a suitable heat sink, 
e.g. a chassis. For high voltage use, the fuse may be enclosed in a 
container with a suitable dielectric heat exchange fluid, such as 
transformer oil, that can cool plate 72 by convective or forced flow heat 
transfer. 
Referring now to FIG. 12, shown is plate 72, which in addition to ceramic, 
may also be a suitable high temperature plastic or other insulating 
material, prepared with cavities 79. Exothermic material 18 containment 
wells 16 have a reversed geometry of wells 16 shown in FIG. 9. The opening 
of well 16 in FIG. 9 is substantially co-planar with the plane of fuselink 
10, whereas well 16 in FIG. 17 has the opening below the plane of fuselink 
10. Referring again to FIG. 12, wells 16 are preferably a close fit into 
cavities 79 with just sufficient clearance to be ejected without 
interference upon ignition of exothermic material 18. Cavities 79 serve to 
confine the propulsion gases generated by exothermic material 18 thereby 
generating and maintaining higher gas pressures until wells 16 of link 
segments 22, 24 are propelled clear of cavities 79. Much like a bullet 
being propelled down a barrel, more efficient use of exothermic material 
18 is obtained as compared, for example, to FIGS. 9-11. Fault response in 
FIG. 12 is shown with cutting charge 80, as in FIGS. 13, 14 with charge 80 
then igniting propulsion material 18 by suitable fuse means, such as fuse 
20 in FIG. 1. All embodiments of the present invention may incorporate the 
design concepts of FIGS. 9, 10, 11 and 12. 
For high current operation, a further embodiment of the present invention 
is shown in FIGS. 13, 14, and 15. To operate at high currents, for 
example, the thousand ampere range, much larger fuselink 10 cross sections 
are required to maintain reasonable fuselink temperatures due to I.sup.2 R 
losses during normal operation. At these high currents, restricted section 
12 construction is generally no longer practical. 
In FIGS. 13-15 the fuselink 10 cross section area is preferably 
substantially constant along its length. To provide a rupture in the 
fuselink at severance section 17 and between the exothermic charges 18, a 
cutting charge 80 is provided, as used in, for example, explosive bolt 
cutters. A fault sensing circuit 82 determines a fault condition and 
commands a trigger circuit 84 to send current down the wire 86 to detonate 
the cutting charge 80 which then cuts 91 the fuselink 10 in two, and then 
with a suitable time delay method 88, ignites 89 the propulsion material 
18 to drive the fuselink segments 22, 24 apart as in FIGS. 1 to 4. 
Alternatively, instead of separate charge 18 ignition means 88, part of 
the cutting charge gases 91 may be suitably diverted to ignite propulsion 
charge 18. The chemistry of the ideal cutting explosive 80 is such that 
the gases 91 emitted are arc 32 cooling and de-ionizing. Since arc 32 
temperatures range from 10,000 to 15,000.degree. K, almost any gas source 
will be cooler. In this manner, even as an arc 32 is struck between the 
severed fuselink segments 22, 24 current limiting de-ionizing gases are 
present to limit the arcing current compared to an arc in air. As the fuse 
segments 22, 24 are propelled apart, the de-ionizing gases from the 
propulsion charges 18 pick up where the cutting charge 80 gases 91 left 
off and continue the current limiting function coupled with the arc chute 
90 effects. In general, the arc 32 will remain locked on the hot tips 92 
of fuselink segments 22, 24 as long as any other potential path does not 
have a lower impedance. If necessary, for example, the fuselink behind the 
containment wells 16, which run relatively cool, may be coated with an 
insulator 94, for example, high temperature (&gt;500.degree.) silicon rubber 
or plastics, or saureisen cement to insure that the arc 32 does not 
propagate along segments 22, 24. 
Referring again to FIG. 14, at high currents, typically several hundred to 
several thousand amperes, the thickness 54 of fuselink 10 may range, for 
example, from one to ten millimeters. At increasing fuselink 10 
thicknesses 54, fuselink 10 rigidity increases which requires an increase 
in exothermic material 18 to propel fuse segments 22, 24 about the axis 52 
of rotation. 
A flexible section 21 of fuselink 10 acting as a hinge may be provided in 
the proximity of pivot point 52. It may, for example, comprise a plurality 
of thin laminations 23 of metal such as copper or aluminum, bonded 25 
metallurgically, such as by brazing, at each end to fuse segments 22, 24. 
In general, the cross section of flexible section 21 is comparable to that 
of fuselink 10 so as to provide substantially the same electrical 
resistivity. Laminations 23 would have width 53, and, for example, at a 
thickness of 0.5 mm each, then ten laminations 23 would be required to 
equal a 5 mm thickness of fuselink 10. To further enhance flexibility of 
section 21, a small gap 27, for example, 0.1 mm may be provided between 
adjacent lamination 23. This can minimize friction and interference 
between adjacent laminations 23 during bending and rotation about axis 52. 
Each lamination has a slightly different radius of curvature about pivot 
axis 52. In general, the stiffness of fuselink 10 when made thick, such as 
5 mm, for high current use is such that bending up the edges 56 as 
described in FIGS. 6,7 is not necessary to provide rigidity to confine 
bending to axis 52. 
To provide further control of the curved path traversed by arcing tips 92 
of fuselink segments 22, 24, that is, to ensure that tips 92 remain in 
predetermined proximity to arc chute plates 96 during movement 28, 
restricting means, such as bar 43 is placed in proximity of flexible 
section 21 to constrain any undesirable movement of fuselink segments 22, 
24. Bar 43 may be attached, for example, to housing 11 or base plate 72. 
Referring again to FIG. 15, to enhance high current fault clearing 
characteristics, the fuse has incorporated an arc chute 90. The arc chute 
90 may combine the beneficial attributes of both the insulated plate arc 
chute and the cold cathode arc chute used in power circuit breakers and 
may, for example, have well-known "U" or "H" geometries. The arc chute 90, 
made of an insulating material such as ceramic or plastic, has the surface 
closest to the arc path prepared with cold cathode plates 96. The cold 
cathode plates 96 may be designed in a manner similar to that for circuit 
breakers and may, for example have well-known "U" or "H" geometries, or 
may be short strips of metal as illustrated. The surface 98 of the arc 
chute 90 in the vicinity of the cold cathode plates 96 may be coated, 
impregnated or composed of material that in the presence of arc 32 
generates arc cooling and/or deionizing gases or vapors. 
In general, plates 96 may protrude from the surface of arc chute 90 
sufficiently so as to shield or mask the insulating surface 98 of arc 
chute 90 between plates 96 from the line of sight deposition of vaporized 
metal from fuselink 10. Because a fuse is a one time device and need not 
endure numerous fault cycles as required of circuit breakers and other 
switchgear, the design and cost parameters for the arc chute and cold 
cathode plates are much less stringent than would be for circuit breakers. 
During arcing, each plate 96 provides a cathode and anode voltage drop, 
typically greater than 20V for each restriction, for current limiting. In 
addition to the above, the chute 90 provides arc lengthening properties. 
Furthermore, the arc cooling and arc de-ionizing gases generated from 
material in the path of the arising arcs from the chute surface further 
serve to limit current, that is, reduces let-through energy (I.sup.2 t). 
For profuse generation of arc cooling and/or arc de-ionizing gases, vents 
may be provided. In FIG. 15 shown are, for example, two vents 52, one 
adjacent each end cap 13. Since generation of arc cooling/de-ionizing 
gases are generally in the middle of the fuse, pressure waves are directed 
towards both ends of the fuse body 11 and will tend to predominately drive 
out air, and with continued generation of gases the air residue becomes 
small leaving behind gases better suited to withstand restrikes. The vents 
may be of silicone rubber with outwardly moving flaps which are glued or 
molded in place such that a predetermined internal fuse pressure ruptures 
the adhesive seal and vents gas. Upon approaching equilibrium pressure, 
the elastic flap closes sealing in the remaining gases which are 
predominately those generated for arc de-ionization and cooling. An ideal 
gas is SF.sub.6 which may be absorbed in suitable porous media and 
released by the heat of the arc. Both the exothermic propellant and 
cutting charge may employ sf.sub.6 as the de-ionizing gas. 
When used with restricted section fuselinks, such as semiconductor fuses 
shown in FIGS. 1-11, the arc chute 90 requires no special protection. 
However, when used with high current fuselinks which employ a cutting 
charge 80 to cut the fuselink 10 in half, then the tip 99 of the arc chute 
90 opposing the cutting charge 80 is subject to residual hot cutting gases 
91. This may be put to good use by composing the tip 99 of the arc chute 
of a material that upon decomposing under the residual hot gases 91 of the 
cutting charge 80 generates arc cooling and/or de-ionizing gases at 
essentially time zero. This further reduces let-through energy (I.sup.2 
t). In addition, as shown in FIG. 15, the propulsion charge gases 30 are 
directed at least partially toward the arc 32 on the arc chute 90 serving 
to further disrupt the arc 32 in a manner similar to air blast circuit 
breakers. This may be augmented with the addition of deionizing gases in 
propulsion gas stream 30. 
Referring now to FIG. 16, shown is a face on view of arc chute 90 having 
cold cathode plates 96. The two staggered columns 108, 109 of plates 96 
serve to effectively increase the arc 32 length and increase the number of 
plates 96 for a given arc chute 90 geometry while maintaining spacing 104, 
106 between plates such that adequate electrical insulation is provided 
between adjacent plates 96. Though two columns 108, 109 of plates 96 are 
shown, more may be employed. 
Again referring to FIG. 16, the spacing 104 between adjacent plates 96 in 
column 108 is greater than the spacing 106 between adjacent plates 96 of 
columns 108 and 109. Spacing 104 is sufficiently greater than spacing 106 
such that when arc 32 strikes across spacing 106 there is no tendency for 
the arc 32 to redirect its path across spacing 104. The impedance of path 
104 between plates 96 is greater than the impedance of path 106 which 
ensures that the arc 32 follows a zig-zag path as it progresses up the 
plates 96 of columns 108, 109. The long arc 32 zig-zag path and the 
increased number of plates 96 serves to further increase the arc voltage 
drop thereby improving current limiting and an associated reduction in 
damaging let through energy (I.sup.2 t). When employing multiple columns 
of plates 96, combinations of suitable plate 96 geometries and arc 32 
current interactions, similar to that employed in power circuit breakers, 
may be obtained such that the arc 32 rapidly shifts among the plates 96. 
This ensures that the arc 32 does not dwell long enough on one plate to 
cause overheating. This is particularly useful at high fault currents. The 
design of arc chutes, for example, of the cold cathode plate and insulated 
plate types are well-known in art and may, for example, be found in 
"Circuit Interruption" and cited references, edited by T. E. Browne, 
Marcel Dekker, NY, N.Y., 1984, herein referred to as Browne. The arc chute 
90 design, or other geometries, such as those described or cited in 
Browne, may be employed in all embodiments of the present invention. 
A further embodiment of the present invention is to employ the fuselink 10 
as a component of the exothermic reaction. For example, the combination of 
palladium and aluminum when heated to about 660.degree. C. react 
exothermically reaching temperatures in excess of about 2800.degree. C. 
Other combinations of metal, for example, boron and carbon mixtures with 
titanium and zirconium, may be employed. 
Referring now to FIG. 17, fuselink 10 may be made of aluminum. Containment 
wells 16 have a thin layer of palladium 110 shown affixed intimately to 
the inside walls of wells 16. A strip of palladium 110 may extend from 
containment wells 16 to the restricted section 12 to act as a fuse. To 
provide a source of gas to assist in propulsion, suitable material 112 
that decomposes to provide gaseous products at the Pd--Al reaction 
temperatures of about 2800.degree. C. may be employed and so assist in 
propelling the fuselink segments 22, 24 apart. To minimize the amount of 
Pd 110 and gas producing material 112 needed for propulsion, closure of 
well 16 by various means 114, such as a plug of high temperature silicon 
rubber or a layer of cured saureisen cement, may be employed. This serves 
to allow a pressure build-up and discharge or rupture of the closure means 
114. The reaction, in accordance with Newton's laws, serves to more 
efficiently drive fuselink segments 22, 24 apart. The silicon plug 114, or 
other means, may also serve to seal the Pd 110 and gas forming material 
102 from the environment. In general, the thickness of aluminum fuselink 
10 preferably exceeds the Pd 110 reaction depth to ensure that a hole does 
not appear in well 16, and that propulsion of fuselink segments 22, 24 is 
not affected. 
Further adaptation of circuit breaker arc control methods as, for example, 
described in Browne, include substitution or combination cold cathode 
metal plates 96 with insulated plates 96, such as ceramic. The arc 32 may 
be driven into the space between plates 96 by J.times.B forces where it is 
cooled and confined thereby increasing the arc voltage, for example, to 
400V. Methods to obtain the desired force on arc 32 are well-known in the 
art and include, for example, the use of one or more loops of the current 
carrying lead wire, as described in Browne. Slot motors may also be 
employed. Under short circuit conditions, currents in the tens of 
thousands of amperes may flow, about ten to hundreds of times the rated 
current. Proper orientation and geometry of the magnetic fields arising 
from these high currents produce the J.times.B forces to force the arc 32 
into plates 96, or to otherwise direct and control it beneficially for 
rapid fault clearance and lower let-through energy (I.sup.2 t). 
Alternatively, permanent magnets, preferably non-conducting may be 
embedded in arc chute 90 to provide the desired magnetic field. 
Referring now to FIG. 18, shown is dielectric housing 11 with base 72, 
which may be a plate, with recess 79 containing at least one but 
preferably two wells 16 to hold exothermic material 18. Base 72 may be a 
ceramic which has recess 79 formed during manufacture. Alternatively, base 
72 may be a suitable plastic into which structure 73, which may be of 
suitable heat resistant material such as metal or ceramic, is molded 
during manufacture to provide recess 79. 
Fuselink 10 is provided with severance section 17, such as restricted 
section 12 such that upon a fault condition, restricted section 12 melts 
and arc 32 is struck between fuselink segments 22, 24. Arc 32 than ignites 
fuse 20 in recess 79 which in turn ignites exothermic material 18. The hot 
gases from exothermic material 18, which are confined in wells 16, 
provides an upward thrust to propel 28 fuselink segments away from each 
other. In general, there is a small spacing between restricted section 12 
and fuse 20. Fuse 20 ignition of exothermic material 18 is in principle 
similar to that described in FIGS. 1 to 4. Alternatively, severance 
section 17 may employ the cutting charge 80 construction of FIGS. 13-15 in 
FIGS. 18, 19 and 20. 
Referring now to FIG. 19, shown is dielectric housing 11 with base 72 which 
may be a ceramic with recess 79 or it may be a plastic with a metal, 
ceramic or other high temperature material pre-form 81 inserted into base 
72 in which is placed cutting charge 80. Cutting charge 80 is constructed 
and functions in substantially the same manner as described in FIGS. 13, 
14. Fuselink 10 construction, including electrical circuitry 82, 84, 86 is 
substantiality the same as described in FIGS. 13, 14. Upon a fault 
condition and detonation of cutting charge 80 and cutting 91 of fuselink 
10, fuselink segments 22, 24 are propelled 28 away from each other. In 
this embodiment, cutting charge 80 is designed to both cut 91 fuselink 10 
and propel 28 fuselink segments 22, 24 away from each other. 
Alternatively, separate propulsion for each of segments 22, 24 may be 
provided by exothermic material 18 embedded in plate 72 in a manner 
similar to FIG. 18. 
Referring now to FIG. 20, shown are fuselink segments 22, 24 being 
propelled 28 around axis 52 after ignition of material 18 in FIG. 18. The 
bending of fuselink segments 22, 24 takes place in flexible sections 21. 
During the movement 28 of segments 22, 24 about axis 52, arc 32 engages 
plates 96 of arc chute 90 in substantially the same manner as described in 
FIGS. 15. 
In the various described embodiments of the present invention, fuselink 10 
is described as being divided into two propelled segments 22, 24. Various 
alternative configurations are possible, such as a single moving segment 
or more than two moving segments 22, 24, as might be used at high 
voltages, such as distribution voltages up to 69 kV. Alternatively, with 
suitably means to provide current sharing between segment pairs 22, 24, a 
wide 53 fuselink 10 may be slotted into multiple parallel segments 22, 24 
with arc chute 90 extending width 53. Corresponding independent plate 96 
sets for each segment pair may be provided to substantially isolate 
adjacent arcs 32 in adjacent arc chutes 90. Suitable arc 32 sweeping means 
may also be incorporated. 
Referring now to FIG. 21, shown is fuselink 10 divided into multiple 
seriesed segments 22, 24, here shown as two, for high voltage 
applications, each segment pair having independent severance sections 17, 
such as restricted section 12 of FIG. 1 or severance section 17 of FIGS. 
13, 14 with cutting means 80. Fuselink 10 is attached 100 to base 72 
intermediate between segment pairs 22, 24. 
Referring now to FIG. 22, shown is fuselink 10 constructed of strips of 
thin laminated metal, for example, copper, silver or aluminum. Fuselink 10 
comprises, as here illustrated, thin strips 23 A,B and C with intermediate 
thin strips 102 A,B interposed. Strips 23, may, for example, have a 
thickness of 1 mm and strips 102 may, for example, have a thickness of 0.1 
mm, and therefore comprise a small percentage of the thickness 54 of 
fuselink 10. Strips 23 may extend the full length of fuselink 10. Strips 
102 extend to flexible section 21 from both directions and terminate 
yielding spacing 27 between adjacent strips 23. Spacing 27 between strips 
23 serve to substantially eliminate binding and interference between 
adjacent strips 23 as fuselink segments 22, 24 pivots about pivot point 52 
on radius 104. Each successive strip, from 23A to 23C bend on successively 
larger radii and thus want to slip relative to each other. When strips 23 
are clamped stationary with respect to each other, strips 23 sections in 
the flexible section bend into the spacing 27 between strips 23 upon 
pivoting about pivot axis 52. In this manner, minimal energy is required 
to cause fuselink segment 22 to pivot about axis 52. 
Block 43 serves to capture and position fuselink 10 at each end adjacent 
relief sections 62, 64 and is fixedly mounted to base 72 or housing 11. It 
is provided with a curved surface of radius 104 centered at the pivot axis 
52 for segments 22, 24 to bend about. In this manner, precise control may 
be obtained over the path traversed by tips 92 of segments 22, 24. Block 
43 acts as a stationary hinge about which sections 21 of segments 22, 24 
rotate in a precise manner, similar to the manner that the door edge 
opposing the hinge rotates. This maintains control over the spacing 106 
between tips 92 of segments 22, 24 and arc chute plates 96 over the path 
of travel of tips 92. This maintains substantially uniform arcing 
characteristics. Brace 108, on the opposing side of sections 62, 64 from 
block 43 may be provided to further restrict movement of sections 62, 64. 
Referring again to FIG. 22, one or both surfaces of strips 23 may be coated 
with an insulating layer 120, for example, parylene or Teflon. Parylene is 
a conformal coating that is pinhole free, has a dielectric strength of 
7,000V for a thickness of 0.025 mm (0.001") and has a low coefficient, 
0.25, of static and dynamic friction. In this manner fuselink 10 is 
composed of multiple paralleled conductors made up of strips 23 which may 
be commonly connected electrically at each end. At high frequency 
operation, currents are substantially on the surface of the conductor 23 
and so thick conductors are inefficiently used. The most efficient 
individual thickness of multiple thin strips 23 is twice the skin current 
depth thus providing minimum inductance and I.sup.2 R losses at high 
frequency operation for a given thickness 54 of fuselink 10. 
Referring now to FIGS. 23 and 24, shown is laminated fuselink 10 of FIG. 22 
now configured only with strips 23 A, B, C, D. Strips 23 A,B,C,D are 
substantially continuous for the entire length of fuselink 10. To provide 
for the relative movement of strips 23 A, B, C, D each with a different 
radius of curvature, as segments 22,24 pivot about axis 52, they are 
permitted to slip relative to each other, illustrated as distances 114, 
116, 118 as shown at tip 92 of segment 22. At least one surface of 
opposing of strips 23 may be dialectically coated with, for example, 
parylene, for lower high frequency current losses as described in FIG. 22. 
The low coefficient of friction of parylene facilitates the relative 
sliding movement of adjacent strips 23. Since strips 23 A,B,C,D are 
mechanically independent, segment 22 may be girdled with strap 110 which 
confines segments 23 A,B,C,D but permits the desired relative sliding, 
shown as 114, 116, 118, of strips 23 A,B,C,D with minimal friction. Shield 
112 may be employed to provide line-of-sight interception of fuselink 10 
material evaporated by cutting charge 80. Strap 110 and shield 112 may be 
inexpensively fabricated from a stamped and bent sheet metal piece. In 
general, the time constants of arc clearance, a few milliseconds, are 
short enough that the molten metal at tips 92 of segments 22, 24 do not 
harden to inhibit relative strip 23 sliding during segment 22 movement. 
Again referring to FIGS. 23 and 24, to maintain predetermined rigidity of 
multiple superimposed strips 23 of segments 22, 24, the edges of top strip 
23A and bottom strip 23D are bent up or rolled over 56 for distance 58, or 
otherwise geometrically formed to permit predetermined bending 
characteristics of link segments 22, 24 about hinges 21. That is, the 
pivoting or bending of segments 22, 24 is substantially restricted to 
hinge section 21. 
For improved high frequency performance thin strips 23 have N-1 sides 
coated with an insulator 120, such as parylene, where N is the number of 
strips 23. For example, the surface of 23A opposing surface 23B is coated, 
the surface of 23B opposing surface 23C is coated and the surface of 23C 
opposing 23D is coated. Strip 23D is not coated. Thus, all adjacent strips 
23 are insulated from each other while the outer surfaces of strips 23A 
and 23D are uncoated for electrical connections, such as soldering. 
Although the invention has been described in conjunction with the appended 
drawings, those skilled in the art will appreciate that the scope of the 
invention is not so limited. Various modifications in the selection and 
arrangement of the various components discussed herein may be made without 
departing from the spirit of the invention as set forth in the appended 
claims.