Note: Descriptions are shown in the official language in which they were submitted.
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T~e pxese~t inyent~,on xelates to h;igh Yaltage power fuses
and ~ore paxtiucl~,xl,~ t~ the com~ination o~ current~limiting
deYices ~ith expuls~on ~uses to obtai,n a desirable full range oP
ope~ating characte~istics~
~xpulsion ~uses are well known in the art and are
deslyned to interrupt relativel~ low leyels of current. However,
expulsion fuses are not as suitable for high current interruption
as current-limiting fuses ~or several reasons. For example, the
forces resulting from gas pressure caused by fuse operation
for high current leyels are extremely large, necessitating
expensive housing designs to withstand the forces created by
expulsion fuse operation at high current leyels. In addition, `
expulsion fuses designed to operate at high current levels can ',
produce objectionable noise, hazardous gases and shrapnel during
- 15 operation. Further, for cost and size of package, current~limiting
devices are more suited for high current interruption.
High currents can be limited by a current-limiting `"~
fuse arrangement which operates to limit prospective extremely `
high fault currents to a much lower level~ However, current~
limiting devices are inherently unsuited for interrupting current '
flow at low current levels. ',
It has been previously recognized that current-limitlng ,'~ '
fuses and expulsion type fuses can be connected serially to provide
a greater range of current interruption capabilities. For example, ,
U.S. Patent No. 2,917,605 ~ Fahnoe recognizes that current- '
limiting fuse elements can be associated ~ith expulsion type ~,
fuse elements to proYide a broad spectrum o~ current interruption ,~, ,
cap~bilities. Howe~ex, such prior art combinations haYe resulted ',
in an undesixable lon~ fuse deyice since the current~limiting '~
fuse and the expuls~on fuse have been serially ~oined. This
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increased length ~eclui~es ~ore expensi~e and bulk~ fuse mounting
e~uipment and tends to ~reclude utilizat~on of the conventional
fuse mounting structure.
Therefo~e, it would be a highl~ desirable advance in the
~rt to proYide a Xuse deYice that c~bines the high current-
limit~ng properties o~ a cur~ent-limiting fuse and the low
current interrupting properties of an expulsion fuse in a relatively
short hous~ng so th~t the most efficient operating range of both
deyices can be optimized to provide for efficient interruption
across a greater range of currents.
A fuse deyice in accordance with the present invention -
comprises the utilization of an expulsion fuse means and a current-
limiting means that are joined together so that the internal por~
tions of the current-limiting means can xeceive the operative
portions of the expulsion fuse means thereby reducing the overall
length of the fuse device.
More specifically, a fuse device for interrupting current
flow between two points of an electrical circuit in accordance
with the present invention comprises a hollow first housing formed
of an electrically insulating material having a first end plate
connected to one point of the circuit sealing one end of the
first housing and a second end plate sealing the other end of the
first housingO The second end plate has an aperture opening at
the center thereof through which a hollow thimble is mounted so ~;
that the thi~ble is positioned within the first hollow housing.
fuse element connects the first and second end plates. The
fuse element will fuse when a predetermined current level is
exceeded. A hollow second housing ~ormed of an electrical
insulatlng material is mounted at one end to the second end plate
around the cperture. A second electrical terminal connected to
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another ~oint of the electxical circ~lit is moun-ted on the other
end of the secolld hous~ng~ ~ moY~ble arcing xod is movably mounted
~ithin the second hous~ng and a fusible wiXe connects the arcing
xod and the third end ~late. The fus~ble wire Will fuse when a
second predetermined current level is exceeded. Contact means
5 are provided connecting the second end plate and the arcing rod ;
so that a circuit is completed between the first end plate and
second terminal. Spring means are provided within the second
housing for urgin~ the arcing rod towards the hollow thimble so
that the arcing rod will be rapidly moved into the hollow thimble
within the first housing when the fusible wire fuses.
An insulating material such as quartz sand as is well
known in the art is placed in the first housing to assist in the ~ ;
current-limiting function of the current-limiting portion of the
fuse device~ A hollow annular liner, foxmed of a material capable
of producing an arc-quenching gas when exposed to an electrical
aXc, is positioned in the second housing around the arcing rod.
Thus, the liner facilitates the extinguishment of the art after ` -
the fusible wire fuses.
The fuse element in the first housing may be an essentially
flat ribbon having two opposite flat sides. This fuse element
may be helically wound in an edge-wound configuration so that
the flat sides of the fuse element are essentially perpendicular
to the center line between the first and second end plates.
Suitable mounting brackets may be affixed to the first and third
end plates for mounting the fuse device to electrical circuit
elements.
Thus, it is a primary object of the present invention to ~
pxovide a fuse deyice combining the relati~e advantages of a ~-
current~limit1ng de~ice and an expulsion fuse so that a wide range
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of curxent interruption perfoxmance can be proYided in a
relatiyel~ short hous~n~
These ~nd othex objects, advantages and ~eatures
shall here~nafter appea~ in the ~ccomp~n~ing dr~wings.
F~GUR~ 1 is a cross-sectional side View of a preferred
embodiment of the present invention.
~IGU~E lA is a cross-sectional vie~ of the embodiment
shown in FIGURE 1 taken substantially along line lA-lA in FIGURE 1.
FIGURE 2 is a cross-sectional side view of an alterna-
10 tive embodiment of the present invention. ;
~ IGURE 2A is a cross-sectional view of the alternative
embodiment shown in FIGURE 2 taken substantially along line
-2A-2A in FIGURE 2.
FIGURE 2B is a cross-sect1onal view taken substantially
along 2B-2B ln F~GURE 2
FIGURE 3 is a cross~sectional side view of another
altexnative embodiment of the present invention.
With reference to FIGURE 1, fuse device 10 comprises
current-limiting portion 11 and expulsion portion 13. Current-
20 limi~ing portion 11 comprises a first cylindrical housing 12 -~
formed of an electrically insulating material having the ends
thereof sealed by first end plate 14 and second end plate 16.
Formed in the center of second end plate 16 is aperture 18
surrounded by flange 20 that is formed perpendicular to the
surface of second end plate 16. Mounted to first end plate 14
is mounting terminal 22 having an opening therein for mounting
fuse device 10 to an appropriate portion of an electrical circuit.
Mounted to second end plate 16 and extending through
aperture 18 is hollow thimble 24 com~ised of insulating material,
~hich extends through first cylindrical housing 12. Hollow
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thimble 24 is ~entagonal in cxoss section and has ~ hollow
circulax inte~io~ poXtion. ~ounted in gXooYes at the corner
apexes of the hollo~ thimble 24 (see FIGURE lA~ are suppcxt
strips 26. Fox~ed on Support stri~s 26 are tongues 28 (see
FIGURE 1) which support a fusible element 30 that is helically
wound around support strips 26. Fusible element 30 is connected
at one end to first end plate 14 and at the other end to second
end plate 16. Fusible ele~ent 30 has formed therein indentations
31 along the edge thexeof to provide initial fusion points and
also to facilitate winding of the element.
Fixst housing 12 is filled with a suitable insulating
material such as ~uartz sand 32 that assists in the current-
limiting function of the current-limiting portion 11 when fusible
element 30 fuses.
Mounted to the flange 20 on second end plate 16 is
second hollow housing 34 formed of an electrical insulating ;
material, Mounted over the opposite end of second hollow housing
34 i5 third end assembly 36 which seals second hollow housing 34.
Third end assembly 36 comprises ferrule 38 partially inserted into
second hollow housing 34 over which is mounted cap 40. Mounted
within ferrule 38 is contact member 48. Also mounted externally
to ferrule 38 is mounting terminal 42.
Positioned within second hollow housing 34 is annular
liner 44 formed o~ a material that will produce an arc quenching ;~
gas when exposed to an elèctrical arc. Annular liner44 has a
hollow interior in which is positioned arcing rod 46. Arcing rod 46
is connected at one end to contact member 48 b~ fusible wires 50
~nd 52. Fusible Wire 52 is made of a nichrome and fusible wire 50
is made of silver. ~ilyex wire 50 is the main current carrying
ele~ent and fuses in xesponse to heatin~ when a predetexmined
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current level is exceeded. Nichrome wire 52 is provided to
~ithstand force~s e~erted upon the a~cin~ rod so that the silver
wire 50 does not h~e ~n~ tensile foxce exerted upon it. Nichrome
wire 52 fuses immed.~ately upon the fusion of silver wire 50.
Connected to the opposite end of arcing rod 46 is con-
tact button 56 and posit~oned immediately adjacent to contact
button 56 is spring insulator 58. Spring cup 60 is mounted
within second houslng 34 and electrically engages flange 20 of
second end plate 16 and also elect.rically engages contact button
10 56 connected to arcing rod 46. ~ spring 62 is mounted within
spring cup 60 and engages spxing insulator 58~ Spring 62 is
compressed in the position shown in FIGURE 1 so that arcing rod
46, contact button 56, and sprin~ insulator 58 are all urged
to~ard the left as shown in FIGURE 1 thereby causing tensile
15 stress to be exerted upon nichrome wire 52.
- Fusible element 30 is designed so that when a pre-
determined current flowing through fusible element 30 is
exc~eded, fusible element 30 will fuse initially at indentations
31 on the edge of fusible element 30. If a severe and high
20 magnitude fault occurs in the circuit being protected by the fuse
device 10, fusible element 30 will almost instantaneously fuse
and vaporize the silver material from which fuse element 30 is ,`:
fabricated. Fusible element 30 thus acts in such a way as to
effectively insert a high resistance between the two end plates -~
25 thereby limi.ting the current to a fraction of the potential fault ;
current that would otherwise flow.
~ilver wixe 50 and nichrome wire 52 are d~si~ned to
ef~ectivel~ operate to intexrupt curXent rlow at much lower current
leyels than the cuxrent-limiting portion 11 of fuse deyice 10.
The current-limiting portion 11 of fuse device 10
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operates mo~st effectiyel~ to inte~xupt high c~rrent levels,
whereas e~pulsion fuse poxtion 13 of ~use dey~ce lO operates
most effectivel~ to intexrupt lowex current leYels.
After silYer wire 50 and nichrome wire 52 fuse, spring -~
62 moVes areing rod 46 through the opening in linex 44 until the
end of arcing rod 46 has moved all the way into thimble 24. When
silvex wire 50 and nlehrome wire 52 fuse, an arc forms between
~reing rod 46 and eontact member 48. However, as areing rod
46 moves rapidl~ through liner 44 and the are is "stretehed",
the are eomes in contaet with annular liner 44 Whieh is formed
o~ a material which emits an arc-quenehing gas when exposed to an
eleetrieal arc. Thus, the rapid combination of the movement of ~
areing rod 46 and the emission of are-quenching gas from liner i :
- 44 tends to extinguish the arc thereby interrupting current flow. ;
~ne uni~ue feature of the present invention is the
eombination of a current-limiting fuse portion and an expulsion
t~pe fuse portion so that the moving parts of the expulsion type ;
fuse, namely arcing rod 46, contact button 56 and spring insulator
58 move into a space within the current~limiting portion of the
~use, i.e., thimble 24. It would ordinarily be expected that it
would be impractical to permit metallic components to enter into
or along the length of the current-limiting portion of a fuse
device because this might limit the voltage withstand capabilities
of the eurrent-limiting portion of the fuse device.
However, it has been discoyered that this unique
eombination does not affeet the voltage withstand eapabilities of
the eurrent-limiting portion of the fuse deyice. For example,
at overlo~d or low ~ault curxent levels, only the expulsion fuse
portion, i.e. ! onl~ s~ilYer wire 50 and nichrome wixe 52 fuses
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and fusible element 30 remalns intact. In this instanee, no
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Yolta,ge ~p~eaxs ac~ss ~l,rst a,~d seco~d end Rla~es 14 and 15 and
the pXesence o~ the ~rc~ng ~od 46 ! con~act blltton 56r and spring
~nsula,tor 58 ~th~n th,im~le 24 has a limited, i~nconse~uential
e~ect upon the vo~ta~e wi,thstand capabillties o~ the current-
limiting portion of the ~use device 10.
,~t lntermediate current levels, where the current is
high enou~h to melt the fusible element 30 as well as silver
wire 50 ~nd nichrome wixe 52, the movement of the fuse components ~; ,
into thimble 24 still produces no detrimental effect because
either the expulsion fuse portion of the fuse device 10 is suffi-
cient to interrupt current flow without assistance from the
current-limiting portion, or at currents of this level, the ''
maximum arc voltage produced by the current-limiting section
is relatively low, tending to be inversely proportional to the
excursion of the fuse arcing rod at the time crest voltage occurs.
Thus, the withst~nd capabilities of the current-limiting portion
enclosed in housing 12 are not affected, and the thimble is thus '~ ~;
not subjected to severe dielectric stress. '~-~
At high fault currents, interruption is substantially
brought about by the current-limiting section. The current is
rapidly forced to a low level when fusible element 30 fuses,
and is thus interrupted before a significant motion of fuse arcing ,~
xod 46 occurs. Thus, during the portion of time that maximum
voltage exists between first and second end plates 14 and 16, the
metallic fuse components, i.e., arcing rod 46 and contact button '~
56, do not extend far enough into thimble 24 so as to reduce the
voltage withstand capabillty and cause dielectric failure of the
thimble wall between the element 30 and the metallic use parts.
~ith reference to FIGU~E 2, an alternative embodiment
of the present inYention is illustrated. Fuse device 210 comprises
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current-limltin~ po~tiQn 211 and ex~ulsion portion 213. Current- ;
li~iting portion 2ll com~riseS ~irst c~lindrical housin~ 212
sealed at one end b~ first end plate 214 and sealed at the other
end o~ second end plate 216~ Second end pla,te 216 has formed `~
therein aperture 218 ~round which is formed flange 220. A
mountin~ terminal 222 is mounted to first end plate 214 for
mounting the fuse device to appropriate portions of an electrical
circuit.
Positioned within first cylindrical housing 212 is
hollow thimble 224. Hollow thimble 224 has a pentagonal cross
section and supported at grooves at each corner of the pentagonal
cross section and supported at grooves at each corner of the
pentagonal hollow thimble 224 are support strips 226 ~see FIGURE 2A).
~ongues 228 are formed on support strips 226 tsee ~IGURE 2) and
support a fusible element 230. Fusible element 230 has indenta-
tions 231 formed around the edge thereof to facilitate hexagonal
windiny of the fusible element 230, and also to provide a reduced
area for initial ~usion of fusible element 230. First cylindrical
housing 212 is filled with a suitable insulating material such
as quartz sand 232 that assists in the current-limiting function
of the current limiting portion 211. Mounted to flange 220 around
aperture 218 is second hollow housing 234. Partially inserted
into the other end of second hollow housing 234 is third end
assembly 236 comprising cylindrical portion 238, sealing plate
25 240 and mounting terminal 242.
Positioned within second hollow housing 234 is hollow
annular liner 244 which is formed of ~ mate~ial that produces
an arc~uenching yas when exposed to an electrical ~rc. Positioned
~thin the hollow portion of annular portion 244 is arcing rod 246~ -~
A contact member 248 ~see FIGURES 2 and 2B) is electrically-
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connected to fl~n~e 22Q o~ sec~nd end pl~te 216. Axcing rod
246 is connec!ted to contact membe~ 248 by silyer wire 250 and
nichxome wire 252. ~ilverwire 25Q and nichxome wire 252 are ,'.
designed to fuse in response to heating when a predetermined
curXent leyel is exceeded~ ~
A ca,ble 256 is connected between arcing rod 246 and
cylindrical portion 238 of third end assembly 236 so that a
positive electrical connection is maintained between between the
arcing rod 246 and the third end ~ssembly 236~ A spring 258 is ~.
connected to arcing rod 246 and to sealing plate 240. Spring
258 is stretched so that it tends to ur~e arcing rod 246 towards :
the right as viewed in FIGURE 2. However, as long as nichrome ~,' ''
wire 252 remains intact, arcing rod 246 is reta,ined in the ~,
position illustrated in ~IGURE 2.
Thimble 224 forms an exhaust control chamber that may
be filled with any suitable condensing media such as alumina
particles 260 which act as a muffler to condense hot arc gases
when silver wire 250 and nichrome wire 252 are fused during the
operation of expulsion portion 213. ~ perforated cap 262 retains '
alumina particles 260 within hollow thimble 224, but allows the
entry of arc gases during the operation of expulsion portion 213.
The ~IGURE 2 embodiment operates in substantially the '`,i`~:'
same manner as the FIGURE 1 embodiment except that the arcing
xod mo~es away from the current-limiting portion 211 during '~
25 operation of the expulsion portion 213. Thus, there is no '
movement of metallic ~embers into the current~limiting portion
211 during operation of the fuse deYice 210. The muffler portion '~,
comprising alumina pa~ticles 260 ls positioned within the
cur~ent-limitin~ portion 211 to facilitate the condensation of
hot arc gases thereby permit~ing operation of the expulsion
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~ortion 213 ~lthout discharge of hot gases to the ambient
atmosphere~
F2GUXE 3 illustxates a third embodiment of -the present
invention~ In this e~bodiment ~use device 310 comprises two
current-limiting portions 312 and 314 connected to opposite
ends o~ an expulsion portion 316. It can be readily observed ~`
~ithout detailed explanation that the FIGURE 3 embodiment comprises
a combination of the FIGURE 1 and FIGURE 2 embodiments so that ~:
the arcing rod 320 moves into thimble 322 in current-limiting
portion 312 and the arc ~ases are condensed in muffler 324 in
current-limiting portion 314 upon operation of expulsion portion :
316. The FIGURE 3 embodiment provides increased current inter-
xupting capabilities at high current levels since the separate : :
current-limiting portions 312 and 314 need to only be capable of
providing one-half the total interrupting capabilit~ of the
fuse device 310 at high current levels. ~ ;
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