CA1186716A - Current-limiting fuse with improved means for interrupting low overcurrents - Google Patents
Current-limiting fuse with improved means for interrupting low overcurrentsInfo
- Publication number
- CA1186716A CA1186716A CA000411665A CA411665A CA1186716A CA 1186716 A CA1186716 A CA 1186716A CA 000411665 A CA000411665 A CA 000411665A CA 411665 A CA411665 A CA 411665A CA 1186716 A CA1186716 A CA 1186716A
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- Prior art keywords
- arc
- insulating member
- fusible element
- location
- overcurrents
- Prior art date
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Abstract
CURRENT-LIMITING FUSE WITH IMPROVED
MEANS OR INTERRUPTING LOW OVERCURRENTS
ABSTRACT OF THE DISCLOSURE
This current-limiting fuse comprises a fusible element having a predetermined location at which an arc will be initiated when prolonged overcurrents of relatively low value have persisted for a predetermined duration. For increasing the arc voltage developed by said arc, an electrical insulating member is disposed about the fusible element in a position where at least a portion of the arc will burn within the insulating member and cause vapors to be evolved from the material of the insulating member. The insulating member is of a material that evolves substantially no vapors or gases at the temperatures reached by the insulating material prior to arc-initiation during prolonged overcurrents of up to one hour in duration. This material is a baked material, a major portion of which is hydrated aluminum silicate including water of hydrogen that is released only at temperatures in excess of those attained by the insulating material during prolonged overcurrents as long as one hour.
MEANS OR INTERRUPTING LOW OVERCURRENTS
ABSTRACT OF THE DISCLOSURE
This current-limiting fuse comprises a fusible element having a predetermined location at which an arc will be initiated when prolonged overcurrents of relatively low value have persisted for a predetermined duration. For increasing the arc voltage developed by said arc, an electrical insulating member is disposed about the fusible element in a position where at least a portion of the arc will burn within the insulating member and cause vapors to be evolved from the material of the insulating member. The insulating member is of a material that evolves substantially no vapors or gases at the temperatures reached by the insulating material prior to arc-initiation during prolonged overcurrents of up to one hour in duration. This material is a baked material, a major portion of which is hydrated aluminum silicate including water of hydrogen that is released only at temperatures in excess of those attained by the insulating material during prolonged overcurrents as long as one hour.
Description
~J ~ 3 6~
-1- llT~04609 CURRENT-LIMITING FUSE WIT~ I~R0~713D
Thi~ in~ention relates ~o an electric fuse oiE
the current-limiting type andO moxe particulArly, ts~ a fllSe of thi~ type which can interrllpt a wide rar~ge o:f abnormal currents but is especi~lly adapted 5 to interxupt relatively low overcurr2n~s..
It is well recognized that a type oiE ~no~mal current that is diificult for a s~urxent~limitirlg fusP to interrupt is a relatively low overcurr r~t thalt persists for a long period of time be:~o:r33 10 mel~ing the fusible element or elemen~s of ~he f use O For example, in a typical curr rlt ~limitting use, an overload current of 1,, 5 to 3 ~imes ithe s t:eady~state ral:ing o the fuse may p~rsist :Eor an hour ox even more before it melts the fll~iible 3.5 elem~n s of the fuse.
To assist in extirlguishing the arc or ar6::s fo~med lapon ~uch melting, i has be~n common to provide, in each regio~ where an arc is .~llticipa~ed structure of gas-evolving material whic:h evolves
-1- llT~04609 CURRENT-LIMITING FUSE WIT~ I~R0~713D
Thi~ in~ention relates ~o an electric fuse oiE
the current-limiting type andO moxe particulArly, ts~ a fllSe of thi~ type which can interrllpt a wide rar~ge o:f abnormal currents but is especi~lly adapted 5 to interxupt relatively low overcurr2n~s..
It is well recognized that a type oiE ~no~mal current that is diificult for a s~urxent~limitirlg fusP to interrupt is a relatively low overcurr r~t thalt persists for a long period of time be:~o:r33 10 mel~ing the fusible element or elemen~s of ~he f use O For example, in a typical curr rlt ~limitting use, an overload current of 1,, 5 to 3 ~imes ithe s t:eady~state ral:ing o the fuse may p~rsist :Eor an hour ox even more before it melts the fll~iible 3.5 elem~n s of the fuse.
To assist in extirlguishing the arc or ar6::s fo~med lapon ~uch melting, i has be~n common to provide, in each regio~ where an arc is .~llticipa~ed structure of gas-evolving material whic:h evolves
2(3 ~n arc-~xtinguishing ga~ when ~xposed tc3 the arc.
Example~ of such fuses ~re di~;clos~d in U~, S .
Pa~ents 3,76~509-Cameron, 37238,333~ozacka~
4,167,723-Wilk~ 3,4~7,971~Mikulecky~ and
Example~ of such fuses ~re di~;clos~d in U~, S .
Pa~ents 3,76~509-Cameron, 37238,333~ozacka~
4,167,723-Wilk~ 3,4~7,971~Mikulecky~ and
3; 562 ,162~Pitha.
1~ s'cudying typlcal sEu~es of ~i~; general type ~ we have o~ served ~hat during a prolollged 5 period ~:~ low s: vercurrent æ uc~h as xeferred to above ~d prif:~r to arc init.iation, the gas etrolvi~ag struc:ture evolves ~substan~ial amo~ts 0:~ ga5i~5 iA response to heating of the fllse lements~ Such ga.~ evolutioll i5 undesirable for 10 at leas t the following reason~:
1. Ths~ total available amount of easily-evolvad gas is limited, and any anLourlt lc1st befor~
a:~c-initiation is not a~ailable for arc-extinction.
Insufficient gas flow at the time of arc~initiatio ï5 could in~rfere with arc-extinction.
2. ~:as evolved be~ore araing may caus~ ex s~essive pressure to dev~lop in th~ fuse.
3O The gas release proc~ss is endothe~:mic so ~hat the desired temperatur@ rise of the fusible 20 elemerlt or elements can be retarded by such gas evolution. This may distort the ~ime-to-melt v.
current curve of the fuse by lncreasing ~he me~Lting time alt low ovPrcurr~3nts.
~ecordingly, an obj~ct of our inventiorl is to pxovide, :Eor a current limiting ~use ~ gas~evolving stxucture which: ~1) is capable of evol~riny he requires~ quantities c~f ga~es for readily extinguish-ing the arc:s produced by fus~-element m~lting after prolonged period~ of low overcurrent~ and ~2) evolves le o.r no signific:ant $~uantities of gas prior to arc~initiakion under such low overcurren~ co~diti~ns.
6~
llT~04609 ~3~-~o~her ob; ect i~ to provid~ yas~evolvirlg s tructure capable of performing as i~ ~e i~s~edi-. a~ely precedialg paragraph ~Eclr prt)tracted ~svercurr~rlts o~ approxilllate~y one hour in durationO
~other objs~c~ i ~o provide gas~d~volving strllcture capable of p~rfo~ing as ~3tate~d in the . first object and alss~ having good electrical ~ SII-lating properties which are maintairl~3d d~spite pro-longed healtins and despite the arcing which ac::com~
panies illterruption.
Ill carryirlg out our invention in one fo:cm J W!e pro~,ride a high-voltage current-limitirly :Eu~e compris-ing a ~usible element and mealls at a predetermined location on the fusible element- for causillg the element to melt at said predetermilled location i~
response to prolonged overcurrents of relatively low value, thereby initiating an arc: at said locatim ; when s~id prolong~d overcurrents have pers.i~ed for a predetermined duratioll. For in~reasing the arc voltage developed by the axc, there i~ provîded gas-evolving means comprising an electric~l insulatillg membex dispc~sed about the f-l~ible e~ ~men~ i~ the region of said location and at a point ~u~ficierlltly close to said locatiorl that at lea~t a p~:rtie3n of the arc burns wit~in said irlsulat:ing me~3ex and causes vapor~ to be evolved from ~e material of the inslllating memberO The insulatirlg member i~ of a mate:rial t~at ~volves substantially no vapors ox gas al: the tlemperatures rE3aGhed by ~a~d in~ulating member pri~r to arc-initiation durirlg proIongesl ov rcurrents of up to s:~ne houx in duration.
. In on,e fDrlll s~ the inverltiorl ~ the ~ sulatilag member is of a baked material, a major por1:ion ~sf which is hydrated aluminum silicate iLncludi~g water .. ~
o ,j l . ~ llTRO4609 of hydratisrl that is released only at ~nperatures . in excess o f those attained by said insulating member during prolonged ovex~urren . ~ a5 lorlg a~s one ho~ar~ The material i.~; balced for sevexal hour~
5 at emperatures up to at lea~t the value reachl3d by the irlsulatirlg member duri~g prolonged over s~larrents as long as one hour~
I
i Bri f Desc~on of Drawi ~
For a better understarldi~çl of lthe inventioI, r~fer~nce may be had to the fo11Owing description . tak~n in connection with the drawings J wherein:
Fig~ 1 is a sectional view through a high vo1tage ~urrent-1imiting fuse embodying one form of our invention.
Fig. 2 is ~n enlarged perspective ~iew in simp1ified form of the certain compone~ts contain~d in the fu~e of Fig. 1.
Fig. 3 is a schematic ~howing of a pai.r of fus1b1e elements with gas-evo1vi~g beads located thereon in accordance with one foxm of our inventionO
Detai1ed Descrip ion of ~8~
~ eferxing now to Fig. 1, thare is shown a high-vo1tage current-1imiting fuse comprising a tubu1ar casing 2 of e1ectrica1 insu1ating material elosed at it~ opposite ends by meta1 end cap~ 3 and 4.
Within the casing 2 is an insu1ating coxe 5 on whach ar spira1:Ly wound two fusible e1ements 6 ~nd 6a of ribbon fon~ extending a1Ong the leng~h of th2 core.
Axranged at opposite end~ o~ core 5 in e1ectrica1 contact with the ends of fusible e1~ments 6 a~d 6a ar~ c3nductiv~ t~xmina1 c1amp members 7 and 8 which llTR~4609 5_ electrically connect fusible elenents 6 and 6a to the corlductive end caps 3 anld 4, respectively~ by means of ou~wardly xtending finser~ 11. Filling ~she Gasirlg 2 i~ a pulverulent filler 12 ~ l?referably 5 of quar~z sand~ in whi~h ~he core 5 and ~he fusible elements 6 and ~a are embedded. The depicted coxe, fi.ller 9 and casing stru~tur~ are similar ~o those disclos d in U.S. Pa~ent 3/5627162~Pi~ha issued February 9, 1971 and assi~ned -to the as-si~nee of the present invention.
The illustrated fuse is a circuit pxotecti~e device which acts in a known manner to interrupt ~he curxent therethrough in the event the current should rise to an abnormally high value. If ~he ~bnoxmal current is a fault current, it w.ill rapidly rise t~ward a value tens of times higher -~han normal steady-state current, quickly melting portions of the fusihle el~ments ~ and 6a and produci~g arcs which vaporize the mol en metal and additional metal of ~0 the fusible element~ 6 and 6a. The hot metal vapors resulting from such vapori~ation rapidly ~xpa~d into ~he spaces between the granules of filler material 12~ where they condense and are ~o longex available for ~urrent conduction. This condensing and ~ooling 25 action builds up in the cllrrent pa~h a high arc ~ol age which limits the current ~hrough *he fuse to a small raction of that available in the circuit and also forces the curxent to ~ero bef~re the next natural current zero. Under fault current conditions, aroing i5 initiated at region~ o~ reduced cross-sectio~ i~ the fusible elements 6 and 6a fo~ned by perforatîons 13 in the fusible elements~
If the abnormal current is an overcurrentO rather than a fault: current~ the fusible el~ments do not melk 11~6~
~ -~mmediately but melt only ai.ter the overcurEent has persisted for a predetel~mined period D the dlJratis~n of whic:h is inver~ely relat~d tcl the curlrent magnitu~le. ~or lo~- ïevel o~rercurre~t:s ~
5 ~uch as 1. 5 ta 3 time~ steacly-~tate c:urrent~ the :f usibli3 elemerlts may conduct for an hour or even more bef ore melting . Ts limit this p~riod p :It i~
conventional t:3 provide each Pusi~ble s31ement with one or mc)re overlays capable of producing the 10 so-6al~ed "~q-effe~-t~. In thi~ regard, eas~h over~
lay is of a matf~rial ~ ~uch as tin, which has ~
much lower melting p~int than the silver of the xibbon typ~ fuse elemer~ts. When the ov~rl~
~emperature reaches the melting point o:f the 15 overlay material, the overlay material :~acts me~allurgically with the silver to orm an alloy~
This ;~ y has a relatively high resis i:anc~ ar d a much lower melting point tha~ the silver ~d causes a relativaly :capid meltir~g of the fuslble elem~nt 20 03lce khe overla~ s~arts to melt. Sucll melting pro-dlacl3s a gap in the fusibl~ element across which an arc is initiated. Th~ arc bllrns thP fusi1ble element back to ïengthen the gap and al80 causes gases to be eYolved ~ in a m~nner soon to be described~ These 25 gases play ar~ important role in extinguishing th~
low current arc, a~ will soon be descri~d~
The aboveodescribed overlays ar~ ~how~ on fuse elements ~ and 6a at 15. Each overlay :15 is po~i-tic)ned at ~ region of the f usible elelTle~at which i~
30 of reduced cross~sectio~ as a re~lt o a~ 0ngatsd perforatis~n 16 provided in the fusil:~le el~renl; i~
this regio~O On protracted overcurrerlts 0 ~he ~usible element melts at the overlay g as de~cribed above " and the resulting arc burns back the fusible elemerlt, llTR 04609 forming the above-described gap. Each fusible element is preferably pro~ided with a plurality of regions of restricted cross-section which are provided with overlays of this type where arcs are formed in the above-described manner when the fusible element melts in response to protracted low level overcurrents.
For evolving gases to increase the arc voltage and thus aid in extinguishing such arcs, each of the fusible elements is provided with a plurality of beads 20, respectively located adjacent the regions ~here the above-described arcs are established. Each of these beads is of an electrical insulating material capable of reacting with -the arc to generate the desired gases. A preferred configuration of such a bead is shown and claimed in United States Patent Number ~,339,743, Leach et al issued July 13, 1982 and assigned to the assignee of the present invention.
Referring to our Fi~. 2, each bead comprises a block 20 of electrical insulating material which has a slit 26 in it. The block 20 is preferably assembled onto the ribbon-type fusible element after the fusible element has been wound on the core 5. This is done by slipping the block 20 onto the fusible element from the side of the fusible element, the fusible element entering the slit 26 through the open mouth of the slit at one side of the block.
When the above-described arc burns back along the fusible element, one of its terminals enters the ad~acent bead 20 through the slit 25. As this occurs, the arc ~uickly heats to a h~gh temperature the region ; ~ 60~
of ~h~ bead that is i~ proximity to tlle arc ~ calasing the bead rapidly to evolve the d~!8irl~t9 ~c:~to~tiaguish-ing gas~s, or vapors~ ~hese gases a~d ~e constrict-ing actioll of the walls of l~he sli~ 26 ac~ i:o effect-5 ively extlnguish the arc.
During the protr~cted perioà when ~e ~usible elemPnt~ 6 and 6a ar~3 carrying low l~vel oveEc::urreAts, the temperatur~ of the fusible element~ in the r2gions of the beads can rise to relatively high 1~l3vel~ rh~
extent of t:his ternperature rise is 1 ed by the presence of the "M-effect" overlays and d~pend$ upon the material of these overlays. ~ith an overlay o~
tin, we estimate that the fusible element in the region of a bead 20 rises to about 35DC before m~lting of the fusible element at the ovexlay occ~s.
As pointed out in the i.ntroductory port:io~ of this ~pecification, temperatures i~ thi~ ranse maintained for substantial durations are capable of causing typically used gas-evolving ma~erial~ to ~volve substantial quantities of gases. ~his is undesirable for at least ~h8 thr~e re~ons set ~orth in th~ introductory portion t and e~pecially becau~e it can materlally reduce the quantity o ga~e~ that are available for arc-extinction when the arc i~
25 i~itiated~
An ob~ec~ of our invention i~ to limit to insigniflca~t qua~tities the volume o~ ga~ evolved prior to arc-initiation by protracted low level~ of overcurrent requiring up to approximately one hour for fuse me.Ltins. In one e~bodiment of our invention, we are ~ble .~ achi~ve this object by fonming our ~eads 20 fr~m a completely inorganic material that ~11 is primarily o hydrated aluminum ~ilicate in the ~L8~i~16 ~3 so~
~g :Eorm of kaolirl clay and (2) i~ cured by 1ba:ki:n~T it (a~ for a substantial periodl 21t a ternperature lev 1 ~xceeding the teloperatur~s that it w.ill ~be 2XpC)Sed to prior . o ~:c initiation durillg ~uch S protracted overcurrents, bult. tb) at a tem;peratur~
lev~l sufficien~ly low for the kaolin clay ~o r~tain most of its water of hydratiorl. In one ~nhodiment, where protracted overcurrents of a~ lc~ng as ~pproxi-~akely on~ hour are exp~cted b~for~ arc-ini~ia~ioxl, 1 n we rely upsn a ba~sing operatio~ that corltirlues for at least: approximately one hour at the above-d~?scribed temp~rat;are level. In addition, the temperature during the ~aking operation is raised to ~his level progressively over the course of seve.ral hours.
In on~ specific embodiment of ~he inven~ion, we form ~he bead 20 by starting wi~h a d~y powder comprising the following components by weight p~rcent ~loxida kaolin clay ~12Si207 2 ~2)~ 66.7 Mill~d Zircon (Zr2SiO4) ~ 22.3 Boxon Phosphate (BPO4~ 11.0 These components are thoroughly blended in a mixer to form the powder. T~ ~his powdex i$ added a liquid binder in a ratio of 4 parts by weight liquid binder to 15 parts by weight p~wdarD The li~uid binder is made from the following components by weight percent:
A 50~ solution of monoaluminum phosphate ~A1~2PO4)3)---40%
Watex ~ $0%
The liquid binder and the dry powder are ~horoughly mixed usi~g a morta~ and pestle. The mixed material is then screened through a 12 mesh screen.
llT~Q4609 The resul~ rag material i~ then a~olded in steel dies Df a sui~able shape to :~orm ~e bloc:ks 20, Glycerine is pr~ferably used a a mold xF~leaseD
The mcalding pxe~suxe is about 6~01D psio The molded bl~clcs are then removed from he dies and ~ub jec~ed to the fs:llowing cure~e ~cleO
; a. Air dry at ~m ambient :for 1 hour bo Raise t~nperature to 60~C a~ 40~C per hour~
c. Hold a-t 60C for 1 hour"
d. Raise temperature to 360~C a~ 90~C pPr hourD
e~ ~lold at 360$:: for 1 hour~, f~ Cool to room temperature iLn î 1/2 t:o 2 hours.
The resulting compo~ition is a pximarily lcaolin clay material that is converlted by the b~k.ing operating 15 into a hard, rigid solid! but, significani;ly, a ~olid which i~ st.ill not vitrified.
Despite the lbalcirlg operatio~ ~ the kaol:Ln ~lay ~omponent oiE i:his material has retained over 90 percent by weight of its water of hydratiorl. I t is ollly wh~n ~0 $emperatures in the ran~e of 4SS - 600C are reached ~hat a :Large portion of thi~ wat~r of ~dration of the kaolin clay is released, more ~pecifically abc)llt 77%.
A9 pe~in~e~l out above, we texminat~ the balcirlg operation when the temperature is well below this range and there--25 fQre do not r~lease lthi~ major portion of t~e water o:Ehydra~io~ The ~aked material cDntains a very low pe.rcenta~g~ of ~he liquid bi~der th~lt was u~;~d in[ com-polmding it ~ince thi~ liquid, ~rhich is pr:imar:Lly wa er~
haL~ been 3mostly ~vaporated by the baking operation, 30 ~OyO ~ the se~ral houx~ in progressivel~ buildi2lg up to 360Ge ancl i::he one hour at 360C. Although sc~me of thi~ water O b~fvre the bakin~ operaltion ~ apE~ea:rs as water of hydration ~Eor the boron phosphate ~ almost all of this wa~!r of hydration is released by the l:~ak:Lng lïT~4609 op@ratiorl~ More specifically ~ ~out 90P~ oP bsron phosphate I s water of hydlration is released at temp ~rakures below 260~C.
~he xircon additive is an es~ntially inert 5 filler and does not chemically combirle with the water that i~ ~ased for hondi~g; and thus there :Ls no signif-icallt water vapc)r evolved ~Erom the zircon duri3lg the period when the fusible el~merlt is beirlg heated by overcurrerlts O
lD The monoalumimam phosphate ~hat is u5ed in ithe binder acts as a ceramic cement ~or holding the kaolin clay together and gives it increased mechan~cal s~ab.ili~yO Most of the water contained in the mono-alum.inlIm phosphate is raleased by ~he bak.ing operation lS and is thus not present to create wat~r Yapor during the overcurrent heating period.
~ uses using beads of the above describ2d material h~e shown exceptional ability to interrupt low valu~s of ovexsurrent. Extensive tests have shown that, despite the persistence of low overcurren for one hour or even lon~er before an axc is ini~iaked, ~u~f i-cient quantities of water vapor are retained by the bead material until it is exposed to ~he c~rc to en~ble the fuse to ~ffectively achie~e such interruptio~.
~5 The presence of the boron phosphate component appear~
to aid in ~uch i.nterruption ~i~ce its dec~mposition products have a high electron af~inity~ thereby eon-~ributing to ~n increas~d rate of dielectric recove~y a~ter a curr~nt zero. Alth~ugh our inv2ntion in it8 preexr~d form use~ boro~ pho~phate a~ a ccmponent of ~.he bead mal~erial, the invention in its b~oade.r aspects con~emplates using for the ~ead a material primarily o~ ~aolin clay compounded substa~tially as above de~-cribed but without the ~oro}l phosphate.
~ 6û9 f' -12-: It has heretofore be~n proposed to make the . core portioal c>f th~ fuse c~f a material which evolves arc-extin~uishing gase~ when ~ os~d to an are: 80 as to ~ssis t i~ low overcurrent int:srruption~ ,. A cora mad of our gas-~volvi~g material ~, if o ~e rather intric:ate cros~-sectional ciDnfiguratie:~n s~own~ ha~
a tende~ y ~o develop cracks during the baking oper~
atiorl or during its assembly or u~e in ~e fusa~ D an~
such crarks constitute di~les::tricall3! w~ah; rQ~ions 10 that can detract from tl e insulating properties of the c:ore. We are able to utilize our gas~evolvirlg mat:erial without encounterirlg dielectric probl~ms associated with such cracks by employing such material, not in the core, but rather in beads (20~ that are : 15 relatively small arld o~ low mass compared to the core.
Because of their size and low mass the i:)eads c:an readily be formed and balced as above descril;ed without developillg any detrimental c:raoks~
3~ecaus~ we do ns:~t rely upon the core ~5~ for 20 ~as evolutiorl~ it can be made Ol' an inexperlsive, low-mass s::onstrUC~iQn. For example, it c:an be made of twc~ plat~s oiE mica ~ disposed at right angles to each other. Ea h of the~e plal:es i~ provided with a . entrally located slot ~not ~hown~ extending along 25 ha:Lf i~s length and permittixlg the plates to b mated ts:)gether at ri~ht angles to each s:~therO The det2~
of l;his ~use coxe form no part s:~f the pre~ent invesltion and are therefore not ~pecifically illustxated or described.
In one embodiment, the fuse o~E this application is ~o const:xucted that the beads on a given ~usible eïement not only assist in l2xt:inguishis~g the ars:s initi~ted along lthat particular fusible elemellt during low overcurxent intexruptions I ~ut al50 assis t în ~ .
llTR04609 ~: ~13-extinguishins the arcs init.iated alollg ~ ~ad~ acent : el~Qent during such interruptic)n. More speci:~c:ally d re:Eerri~ o the ~;chematic ~showing oP ~ 3, ~th;E~
beads 20 on ~he first fusib:Le element 6 ~:re loc~ated 5 ~ot only adjac:ent its OWll a'Lloy-forming overlay~ 15 but ~lso adjace3lt the alloy~ forr~in5~ ov~rïay~ on the ad; acenlt fu~ible element 6a, As a r~sult ~ when ar a~rc i~ :Lrlitiat~d at the overlay on the adjac:ent element 6a in response to melting under low over;
10 current c:onditions, an external surface of ~e b ad 2û on element 6 is located i~ proximi~ to this arc, and the arc is able to react with the mat:2ri2l1 of the external surf ace to evolve the des.ired aro~
extinguishing gases ts~ aid i.n arc ext~nctiorl.
The material o: bead 2a, beirlg c~npletely inorganic, is not susceptible to tracki~g a~; a re~ult of arcing or other forms of electrical dis-charge. As a result, i~s surfaces ma:intain their diel~c~ric strength and do not ~orm dielectrically ~0 wealc paths between the usible elements or acxos~
~y gaps forrned in the fusible ~lemer~ts ~s a xesult of :u~ operation.
As poi:nted out above ~, the monoalumirlum phosphate bindex and the zircon ~Eiller ~npart mechanical strength and stability ~co the bead matexial, This help~ l~e bead 20 withs~and without disinteg.rat:Lng or breaking up the c:ombinatioll Df pre~sures and high temperatures that it is exposed . o ~d r high current interrupti ng Col dltis:~ns .
~l~hough, ideally ,, we bake the beads at a temper-ature in exc:ess of that which will be reached by ~e beads ,during any lnw overcurrent conilitions that the :use will 'be exposed to, our invention in its ~roader ______ 7~
llTP~04609 aspects cs:)ntemplates bakirlg at temperatllres at least a~ high as that reached by t:he bead~ du.ria~g pxolonged ovexcurrents as long as one ~hour. Th2 m~im~ b~king ~emperature i~ kep~ ~3uffic:iently low that th~ hydrated 5 aluminum silicate, or kaolirl c:lay~ will re~ain mv~t o:~ its water of hydration de~spite the baking operatio Although we prefer ~hat each bead 20 be slightly spaced from the locatîon whe:re the as~ociated low overGurrent arc will be initiated, a~ Llu~trated in khe drawiIlgs ~ our invention in its broader aspects con~emplates locati~g the bead around ~he arc=initiation location so tha~ the arc is initiated within th~ bead.
In ~his arrangement, as well as khat illustratedJ ~he alloy-forming overlay 15 limits the temperature rise o~ ~he bead pxior to arc-initiation under low over-eurrent conditions to a level sufficienkly low to :Limit to insignificant quantiti~s the vol~me o gases evolved prior to such arc-initiation.
Although we prefer to use alloy-forming means 20 such as ~hown at 15 iEor initiating ars:~ing ~u~der low overc:urrent conditions ~ our invention ira it:5 br~ader aspects contemplates the use of other converltiorlal means, such as an overlay of explosive material ~ for initiating arcing at the elongated perfc~ratis~n 16 in 25 response ~c the persistence of a low overcurxent ~or a predetermined prolonged perivdO
While we have shown only two locations OII each ribbon where ~rci~g i~ initia~ed in xe~p~nse ~o low o~excuErent~, it i~ to be understood that few~r or more ~uch lDcations ~an b~ pro~ided, as is xe~uired for sa~isfactory interruption. A gas evolvincJ bead, such a~ ~0 D i~ preferably provided at each ~uch location.
~ ~8~
11~E~0~6û~
-~5 I~ is nolted that in the above descrlptioIl, , the terms ~gase~" and ~'vaps~r~ re used inte;rcharlge-}` ~ly is~ referrin~ to thç~ product~; eYolved fr~m the bead mate~eial.
~ 5 While we have ~hown and de~cribed pa:rtlcular r embc)dilllent5 of our inven~ion, it wiL31 b¢ e:bviou~ to those skiïled in ~he art that various c~anges ~d modificatiorls may be made without d~paxSing frsm our inventioFI in its bro2lder aspeelts; and we ~ there~ore, 10 intend her~in to c:over all suc:h changes and mosli~Eications as ~all within lthe t:rue spirilt and ~cope of s:jur in-Sren1:ion ~
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i, h v ,S~' .~
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1~ s'cudying typlcal sEu~es of ~i~; general type ~ we have o~ served ~hat during a prolollged 5 period ~:~ low s: vercurrent æ uc~h as xeferred to above ~d prif:~r to arc init.iation, the gas etrolvi~ag struc:ture evolves ~substan~ial amo~ts 0:~ ga5i~5 iA response to heating of the fllse lements~ Such ga.~ evolutioll i5 undesirable for 10 at leas t the following reason~:
1. Ths~ total available amount of easily-evolvad gas is limited, and any anLourlt lc1st befor~
a:~c-initiation is not a~ailable for arc-extinction.
Insufficient gas flow at the time of arc~initiatio ï5 could in~rfere with arc-extinction.
2. ~:as evolved be~ore araing may caus~ ex s~essive pressure to dev~lop in th~ fuse.
3O The gas release proc~ss is endothe~:mic so ~hat the desired temperatur@ rise of the fusible 20 elemerlt or elements can be retarded by such gas evolution. This may distort the ~ime-to-melt v.
current curve of the fuse by lncreasing ~he me~Lting time alt low ovPrcurr~3nts.
~ecordingly, an obj~ct of our inventiorl is to pxovide, :Eor a current limiting ~use ~ gas~evolving stxucture which: ~1) is capable of evol~riny he requires~ quantities c~f ga~es for readily extinguish-ing the arc:s produced by fus~-element m~lting after prolonged period~ of low overcurrent~ and ~2) evolves le o.r no signific:ant $~uantities of gas prior to arc~initiakion under such low overcurren~ co~diti~ns.
6~
llT~04609 ~3~-~o~her ob; ect i~ to provid~ yas~evolvirlg s tructure capable of performing as i~ ~e i~s~edi-. a~ely precedialg paragraph ~Eclr prt)tracted ~svercurr~rlts o~ approxilllate~y one hour in durationO
~other objs~c~ i ~o provide gas~d~volving strllcture capable of p~rfo~ing as ~3tate~d in the . first object and alss~ having good electrical ~ SII-lating properties which are maintairl~3d d~spite pro-longed healtins and despite the arcing which ac::com~
panies illterruption.
Ill carryirlg out our invention in one fo:cm J W!e pro~,ride a high-voltage current-limitirly :Eu~e compris-ing a ~usible element and mealls at a predetermined location on the fusible element- for causillg the element to melt at said predetermilled location i~
response to prolonged overcurrents of relatively low value, thereby initiating an arc: at said locatim ; when s~id prolong~d overcurrents have pers.i~ed for a predetermined duratioll. For in~reasing the arc voltage developed by the axc, there i~ provîded gas-evolving means comprising an electric~l insulatillg membex dispc~sed about the f-l~ible e~ ~men~ i~ the region of said location and at a point ~u~ficierlltly close to said locatiorl that at lea~t a p~:rtie3n of the arc burns wit~in said irlsulat:ing me~3ex and causes vapor~ to be evolved from ~e material of the inslllating memberO The insulatirlg member i~ of a mate:rial t~at ~volves substantially no vapors ox gas al: the tlemperatures rE3aGhed by ~a~d in~ulating member pri~r to arc-initiation durirlg proIongesl ov rcurrents of up to s:~ne houx in duration.
. In on,e fDrlll s~ the inverltiorl ~ the ~ sulatilag member is of a baked material, a major por1:ion ~sf which is hydrated aluminum silicate iLncludi~g water .. ~
o ,j l . ~ llTRO4609 of hydratisrl that is released only at ~nperatures . in excess o f those attained by said insulating member during prolonged ovex~urren . ~ a5 lorlg a~s one ho~ar~ The material i.~; balced for sevexal hour~
5 at emperatures up to at lea~t the value reachl3d by the irlsulatirlg member duri~g prolonged over s~larrents as long as one hour~
I
i Bri f Desc~on of Drawi ~
For a better understarldi~çl of lthe inventioI, r~fer~nce may be had to the fo11Owing description . tak~n in connection with the drawings J wherein:
Fig~ 1 is a sectional view through a high vo1tage ~urrent-1imiting fuse embodying one form of our invention.
Fig. 2 is ~n enlarged perspective ~iew in simp1ified form of the certain compone~ts contain~d in the fu~e of Fig. 1.
Fig. 3 is a schematic ~howing of a pai.r of fus1b1e elements with gas-evo1vi~g beads located thereon in accordance with one foxm of our inventionO
Detai1ed Descrip ion of ~8~
~ eferxing now to Fig. 1, thare is shown a high-vo1tage current-1imiting fuse comprising a tubu1ar casing 2 of e1ectrica1 insu1ating material elosed at it~ opposite ends by meta1 end cap~ 3 and 4.
Within the casing 2 is an insu1ating coxe 5 on whach ar spira1:Ly wound two fusible e1ements 6 ~nd 6a of ribbon fon~ extending a1Ong the leng~h of th2 core.
Axranged at opposite end~ o~ core 5 in e1ectrica1 contact with the ends of fusible e1~ments 6 a~d 6a ar~ c3nductiv~ t~xmina1 c1amp members 7 and 8 which llTR~4609 5_ electrically connect fusible elenents 6 and 6a to the corlductive end caps 3 anld 4, respectively~ by means of ou~wardly xtending finser~ 11. Filling ~she Gasirlg 2 i~ a pulverulent filler 12 ~ l?referably 5 of quar~z sand~ in whi~h ~he core 5 and ~he fusible elements 6 and ~a are embedded. The depicted coxe, fi.ller 9 and casing stru~tur~ are similar ~o those disclos d in U.S. Pa~ent 3/5627162~Pi~ha issued February 9, 1971 and assi~ned -to the as-si~nee of the present invention.
The illustrated fuse is a circuit pxotecti~e device which acts in a known manner to interrupt ~he curxent therethrough in the event the current should rise to an abnormally high value. If ~he ~bnoxmal current is a fault current, it w.ill rapidly rise t~ward a value tens of times higher -~han normal steady-state current, quickly melting portions of the fusihle el~ments ~ and 6a and produci~g arcs which vaporize the mol en metal and additional metal of ~0 the fusible element~ 6 and 6a. The hot metal vapors resulting from such vapori~ation rapidly ~xpa~d into ~he spaces between the granules of filler material 12~ where they condense and are ~o longex available for ~urrent conduction. This condensing and ~ooling 25 action builds up in the cllrrent pa~h a high arc ~ol age which limits the current ~hrough *he fuse to a small raction of that available in the circuit and also forces the curxent to ~ero bef~re the next natural current zero. Under fault current conditions, aroing i5 initiated at region~ o~ reduced cross-sectio~ i~ the fusible elements 6 and 6a fo~ned by perforatîons 13 in the fusible elements~
If the abnormal current is an overcurrentO rather than a fault: current~ the fusible el~ments do not melk 11~6~
~ -~mmediately but melt only ai.ter the overcurEent has persisted for a predetel~mined period D the dlJratis~n of whic:h is inver~ely relat~d tcl the curlrent magnitu~le. ~or lo~- ïevel o~rercurre~t:s ~
5 ~uch as 1. 5 ta 3 time~ steacly-~tate c:urrent~ the :f usibli3 elemerlts may conduct for an hour or even more bef ore melting . Ts limit this p~riod p :It i~
conventional t:3 provide each Pusi~ble s31ement with one or mc)re overlays capable of producing the 10 so-6al~ed "~q-effe~-t~. In thi~ regard, eas~h over~
lay is of a matf~rial ~ ~uch as tin, which has ~
much lower melting p~int than the silver of the xibbon typ~ fuse elemer~ts. When the ov~rl~
~emperature reaches the melting point o:f the 15 overlay material, the overlay material :~acts me~allurgically with the silver to orm an alloy~
This ;~ y has a relatively high resis i:anc~ ar d a much lower melting point tha~ the silver ~d causes a relativaly :capid meltir~g of the fuslble elem~nt 20 03lce khe overla~ s~arts to melt. Sucll melting pro-dlacl3s a gap in the fusibl~ element across which an arc is initiated. Th~ arc bllrns thP fusi1ble element back to ïengthen the gap and al80 causes gases to be eYolved ~ in a m~nner soon to be described~ These 25 gases play ar~ important role in extinguishing th~
low current arc, a~ will soon be descri~d~
The aboveodescribed overlays ar~ ~how~ on fuse elements ~ and 6a at 15. Each overlay :15 is po~i-tic)ned at ~ region of the f usible elelTle~at which i~
30 of reduced cross~sectio~ as a re~lt o a~ 0ngatsd perforatis~n 16 provided in the fusil:~le el~renl; i~
this regio~O On protracted overcurrerlts 0 ~he ~usible element melts at the overlay g as de~cribed above " and the resulting arc burns back the fusible elemerlt, llTR 04609 forming the above-described gap. Each fusible element is preferably pro~ided with a plurality of regions of restricted cross-section which are provided with overlays of this type where arcs are formed in the above-described manner when the fusible element melts in response to protracted low level overcurrents.
For evolving gases to increase the arc voltage and thus aid in extinguishing such arcs, each of the fusible elements is provided with a plurality of beads 20, respectively located adjacent the regions ~here the above-described arcs are established. Each of these beads is of an electrical insulating material capable of reacting with -the arc to generate the desired gases. A preferred configuration of such a bead is shown and claimed in United States Patent Number ~,339,743, Leach et al issued July 13, 1982 and assigned to the assignee of the present invention.
Referring to our Fi~. 2, each bead comprises a block 20 of electrical insulating material which has a slit 26 in it. The block 20 is preferably assembled onto the ribbon-type fusible element after the fusible element has been wound on the core 5. This is done by slipping the block 20 onto the fusible element from the side of the fusible element, the fusible element entering the slit 26 through the open mouth of the slit at one side of the block.
When the above-described arc burns back along the fusible element, one of its terminals enters the ad~acent bead 20 through the slit 25. As this occurs, the arc ~uickly heats to a h~gh temperature the region ; ~ 60~
of ~h~ bead that is i~ proximity to tlle arc ~ calasing the bead rapidly to evolve the d~!8irl~t9 ~c:~to~tiaguish-ing gas~s, or vapors~ ~hese gases a~d ~e constrict-ing actioll of the walls of l~he sli~ 26 ac~ i:o effect-5 ively extlnguish the arc.
During the protr~cted perioà when ~e ~usible elemPnt~ 6 and 6a ar~3 carrying low l~vel oveEc::urreAts, the temperatur~ of the fusible element~ in the r2gions of the beads can rise to relatively high 1~l3vel~ rh~
extent of t:his ternperature rise is 1 ed by the presence of the "M-effect" overlays and d~pend$ upon the material of these overlays. ~ith an overlay o~
tin, we estimate that the fusible element in the region of a bead 20 rises to about 35DC before m~lting of the fusible element at the ovexlay occ~s.
As pointed out in the i.ntroductory port:io~ of this ~pecification, temperatures i~ thi~ ranse maintained for substantial durations are capable of causing typically used gas-evolving ma~erial~ to ~volve substantial quantities of gases. ~his is undesirable for at least ~h8 thr~e re~ons set ~orth in th~ introductory portion t and e~pecially becau~e it can materlally reduce the quantity o ga~e~ that are available for arc-extinction when the arc i~
25 i~itiated~
An ob~ec~ of our invention i~ to limit to insigniflca~t qua~tities the volume o~ ga~ evolved prior to arc-initiation by protracted low level~ of overcurrent requiring up to approximately one hour for fuse me.Ltins. In one e~bodiment of our invention, we are ~ble .~ achi~ve this object by fonming our ~eads 20 fr~m a completely inorganic material that ~11 is primarily o hydrated aluminum ~ilicate in the ~L8~i~16 ~3 so~
~g :Eorm of kaolirl clay and (2) i~ cured by 1ba:ki:n~T it (a~ for a substantial periodl 21t a ternperature lev 1 ~xceeding the teloperatur~s that it w.ill ~be 2XpC)Sed to prior . o ~:c initiation durillg ~uch S protracted overcurrents, bult. tb) at a tem;peratur~
lev~l sufficien~ly low for the kaolin clay ~o r~tain most of its water of hydratiorl. In one ~nhodiment, where protracted overcurrents of a~ lc~ng as ~pproxi-~akely on~ hour are exp~cted b~for~ arc-ini~ia~ioxl, 1 n we rely upsn a ba~sing operatio~ that corltirlues for at least: approximately one hour at the above-d~?scribed temp~rat;are level. In addition, the temperature during the ~aking operation is raised to ~his level progressively over the course of seve.ral hours.
In on~ specific embodiment of ~he inven~ion, we form ~he bead 20 by starting wi~h a d~y powder comprising the following components by weight p~rcent ~loxida kaolin clay ~12Si207 2 ~2)~ 66.7 Mill~d Zircon (Zr2SiO4) ~ 22.3 Boxon Phosphate (BPO4~ 11.0 These components are thoroughly blended in a mixer to form the powder. T~ ~his powdex i$ added a liquid binder in a ratio of 4 parts by weight liquid binder to 15 parts by weight p~wdarD The li~uid binder is made from the following components by weight percent:
A 50~ solution of monoaluminum phosphate ~A1~2PO4)3)---40%
Watex ~ $0%
The liquid binder and the dry powder are ~horoughly mixed usi~g a morta~ and pestle. The mixed material is then screened through a 12 mesh screen.
llT~Q4609 The resul~ rag material i~ then a~olded in steel dies Df a sui~able shape to :~orm ~e bloc:ks 20, Glycerine is pr~ferably used a a mold xF~leaseD
The mcalding pxe~suxe is about 6~01D psio The molded bl~clcs are then removed from he dies and ~ub jec~ed to the fs:llowing cure~e ~cleO
; a. Air dry at ~m ambient :for 1 hour bo Raise t~nperature to 60~C a~ 40~C per hour~
c. Hold a-t 60C for 1 hour"
d. Raise temperature to 360~C a~ 90~C pPr hourD
e~ ~lold at 360$:: for 1 hour~, f~ Cool to room temperature iLn î 1/2 t:o 2 hours.
The resulting compo~ition is a pximarily lcaolin clay material that is converlted by the b~k.ing operating 15 into a hard, rigid solid! but, significani;ly, a ~olid which i~ st.ill not vitrified.
Despite the lbalcirlg operatio~ ~ the kaol:Ln ~lay ~omponent oiE i:his material has retained over 90 percent by weight of its water of hydratiorl. I t is ollly wh~n ~0 $emperatures in the ran~e of 4SS - 600C are reached ~hat a :Large portion of thi~ wat~r of ~dration of the kaolin clay is released, more ~pecifically abc)llt 77%.
A9 pe~in~e~l out above, we texminat~ the balcirlg operation when the temperature is well below this range and there--25 fQre do not r~lease lthi~ major portion of t~e water o:Ehydra~io~ The ~aked material cDntains a very low pe.rcenta~g~ of ~he liquid bi~der th~lt was u~;~d in[ com-polmding it ~ince thi~ liquid, ~rhich is pr:imar:Lly wa er~
haL~ been 3mostly ~vaporated by the baking operation, 30 ~OyO ~ the se~ral houx~ in progressivel~ buildi2lg up to 360Ge ancl i::he one hour at 360C. Although sc~me of thi~ water O b~fvre the bakin~ operaltion ~ apE~ea:rs as water of hydration ~Eor the boron phosphate ~ almost all of this wa~!r of hydration is released by the l:~ak:Lng lïT~4609 op@ratiorl~ More specifically ~ ~out 90P~ oP bsron phosphate I s water of hydlration is released at temp ~rakures below 260~C.
~he xircon additive is an es~ntially inert 5 filler and does not chemically combirle with the water that i~ ~ased for hondi~g; and thus there :Ls no signif-icallt water vapc)r evolved ~Erom the zircon duri3lg the period when the fusible el~merlt is beirlg heated by overcurrerlts O
lD The monoalumimam phosphate ~hat is u5ed in ithe binder acts as a ceramic cement ~or holding the kaolin clay together and gives it increased mechan~cal s~ab.ili~yO Most of the water contained in the mono-alum.inlIm phosphate is raleased by ~he bak.ing operation lS and is thus not present to create wat~r Yapor during the overcurrent heating period.
~ uses using beads of the above describ2d material h~e shown exceptional ability to interrupt low valu~s of ovexsurrent. Extensive tests have shown that, despite the persistence of low overcurren for one hour or even lon~er before an axc is ini~iaked, ~u~f i-cient quantities of water vapor are retained by the bead material until it is exposed to ~he c~rc to en~ble the fuse to ~ffectively achie~e such interruptio~.
~5 The presence of the boron phosphate component appear~
to aid in ~uch i.nterruption ~i~ce its dec~mposition products have a high electron af~inity~ thereby eon-~ributing to ~n increas~d rate of dielectric recove~y a~ter a curr~nt zero. Alth~ugh our inv2ntion in it8 preexr~d form use~ boro~ pho~phate a~ a ccmponent of ~.he bead mal~erial, the invention in its b~oade.r aspects con~emplates using for the ~ead a material primarily o~ ~aolin clay compounded substa~tially as above de~-cribed but without the ~oro}l phosphate.
~ 6û9 f' -12-: It has heretofore be~n proposed to make the . core portioal c>f th~ fuse c~f a material which evolves arc-extin~uishing gase~ when ~ os~d to an are: 80 as to ~ssis t i~ low overcurrent int:srruption~ ,. A cora mad of our gas-~volvi~g material ~, if o ~e rather intric:ate cros~-sectional ciDnfiguratie:~n s~own~ ha~
a tende~ y ~o develop cracks during the baking oper~
atiorl or during its assembly or u~e in ~e fusa~ D an~
such crarks constitute di~les::tricall3! w~ah; rQ~ions 10 that can detract from tl e insulating properties of the c:ore. We are able to utilize our gas~evolvirlg mat:erial without encounterirlg dielectric probl~ms associated with such cracks by employing such material, not in the core, but rather in beads (20~ that are : 15 relatively small arld o~ low mass compared to the core.
Because of their size and low mass the i:)eads c:an readily be formed and balced as above descril;ed without developillg any detrimental c:raoks~
3~ecaus~ we do ns:~t rely upon the core ~5~ for 20 ~as evolutiorl~ it can be made Ol' an inexperlsive, low-mass s::onstrUC~iQn. For example, it c:an be made of twc~ plat~s oiE mica ~ disposed at right angles to each other. Ea h of the~e plal:es i~ provided with a . entrally located slot ~not ~hown~ extending along 25 ha:Lf i~s length and permittixlg the plates to b mated ts:)gether at ri~ht angles to each s:~therO The det2~
of l;his ~use coxe form no part s:~f the pre~ent invesltion and are therefore not ~pecifically illustxated or described.
In one embodiment, the fuse o~E this application is ~o const:xucted that the beads on a given ~usible eïement not only assist in l2xt:inguishis~g the ars:s initi~ted along lthat particular fusible elemellt during low overcurxent intexruptions I ~ut al50 assis t în ~ .
llTR04609 ~: ~13-extinguishins the arcs init.iated alollg ~ ~ad~ acent : el~Qent during such interruptic)n. More speci:~c:ally d re:Eerri~ o the ~;chematic ~showing oP ~ 3, ~th;E~
beads 20 on ~he first fusib:Le element 6 ~:re loc~ated 5 ~ot only adjac:ent its OWll a'Lloy-forming overlay~ 15 but ~lso adjace3lt the alloy~ forr~in5~ ov~rïay~ on the ad; acenlt fu~ible element 6a, As a r~sult ~ when ar a~rc i~ :Lrlitiat~d at the overlay on the adjac:ent element 6a in response to melting under low over;
10 current c:onditions, an external surface of ~e b ad 2û on element 6 is located i~ proximi~ to this arc, and the arc is able to react with the mat:2ri2l1 of the external surf ace to evolve the des.ired aro~
extinguishing gases ts~ aid i.n arc ext~nctiorl.
The material o: bead 2a, beirlg c~npletely inorganic, is not susceptible to tracki~g a~; a re~ult of arcing or other forms of electrical dis-charge. As a result, i~s surfaces ma:intain their diel~c~ric strength and do not ~orm dielectrically ~0 wealc paths between the usible elements or acxos~
~y gaps forrned in the fusible ~lemer~ts ~s a xesult of :u~ operation.
As poi:nted out above ~, the monoalumirlum phosphate bindex and the zircon ~Eiller ~npart mechanical strength and stability ~co the bead matexial, This help~ l~e bead 20 withs~and without disinteg.rat:Lng or breaking up the c:ombinatioll Df pre~sures and high temperatures that it is exposed . o ~d r high current interrupti ng Col dltis:~ns .
~l~hough, ideally ,, we bake the beads at a temper-ature in exc:ess of that which will be reached by ~e beads ,during any lnw overcurrent conilitions that the :use will 'be exposed to, our invention in its ~roader ______ 7~
llTP~04609 aspects cs:)ntemplates bakirlg at temperatllres at least a~ high as that reached by t:he bead~ du.ria~g pxolonged ovexcurrents as long as one ~hour. Th2 m~im~ b~king ~emperature i~ kep~ ~3uffic:iently low that th~ hydrated 5 aluminum silicate, or kaolirl c:lay~ will re~ain mv~t o:~ its water of hydration de~spite the baking operatio Although we prefer ~hat each bead 20 be slightly spaced from the locatîon whe:re the as~ociated low overGurrent arc will be initiated, a~ Llu~trated in khe drawiIlgs ~ our invention in its broader aspects con~emplates locati~g the bead around ~he arc=initiation location so tha~ the arc is initiated within th~ bead.
In ~his arrangement, as well as khat illustratedJ ~he alloy-forming overlay 15 limits the temperature rise o~ ~he bead pxior to arc-initiation under low over-eurrent conditions to a level sufficienkly low to :Limit to insignificant quantiti~s the vol~me o gases evolved prior to such arc-initiation.
Although we prefer to use alloy-forming means 20 such as ~hown at 15 iEor initiating ars:~ing ~u~der low overc:urrent conditions ~ our invention ira it:5 br~ader aspects contemplates the use of other converltiorlal means, such as an overlay of explosive material ~ for initiating arcing at the elongated perfc~ratis~n 16 in 25 response ~c the persistence of a low overcurxent ~or a predetermined prolonged perivdO
While we have shown only two locations OII each ribbon where ~rci~g i~ initia~ed in xe~p~nse ~o low o~excuErent~, it i~ to be understood that few~r or more ~uch lDcations ~an b~ pro~ided, as is xe~uired for sa~isfactory interruption. A gas evolvincJ bead, such a~ ~0 D i~ preferably provided at each ~uch location.
~ ~8~
11~E~0~6û~
-~5 I~ is nolted that in the above descrlptioIl, , the terms ~gase~" and ~'vaps~r~ re used inte;rcharlge-}` ~ly is~ referrin~ to thç~ product~; eYolved fr~m the bead mate~eial.
~ 5 While we have ~hown and de~cribed pa:rtlcular r embc)dilllent5 of our inven~ion, it wiL31 b¢ e:bviou~ to those skiïled in ~he art that various c~anges ~d modificatiorls may be made without d~paxSing frsm our inventioFI in its bro2lder aspeelts; and we ~ there~ore, 10 intend her~in to c:over all suc:h changes and mosli~Eications as ~all within lthe t:rue spirilt and ~cope of s:jur in-Sren1:ion ~
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Claims (11)
1. A high-voltage current-limiting fuse comprising (a) a generally tubular electrically insulating casing, terminal means disposed adjacent each of the opposite ends of the casing, and a pulverulent arc-quenching filler within said casing, (b) a ribbon-type fusible element disposed within said filler and electrically inter-connecting said terminal means, (c) means at a predetermined location on said fusible element for causing said fusible element to melt at said predetermined location in response to prolonged overcurrents of relatively low value, thereby initiating an arc at said location when said prolonged overcurrents have persisted for a predetermined duration, (d) gas-evolving means for increasing the arc voltage developed by said arc comprising an electrical insulating member disposed about said fuse element in the region of said predetermined location and at a point sufficiently close to said predetermined location that at least a portion of said arc burns within said insulating member and causes vapors to be evolved from the material of said insulating member, (e) said insulating member being of a material that evolves substantially no vapors or gases at the temperatures reached by said member prior to arc-initiation during prolonged overcurrents of up to one hour in duration.
2. The fuse of claim 1 in which said electrical insulating member is spaced a short distance from said predetermined location and said arc, following initiation at said location, burns along said fuse element into said insulating memeber.
3. A high-voltage current limiting fuse comprising:
(a) a generally tubular electrically insulating casing, terminal means disposed adjacent each of the opposite ends of the casing, and a pulverulent arc-quenching filler within said casing, and a pulverulent arc-quenching filler within said casing, (b) a ribbon-type fusible element disposed within said filler and electrically interconnecting said terminal means, (c) means at a predetermined location on said fusible element for causing said fusible element to melt at said predetermined location in response to prolonged overcurrents of relatively low value, thereby initiating an arc at said location when said prolonged overcurrents have persisted for a predetermined duration, (d) gas-evolving means for increasing the arc voltage developed by said arc comprising an electrical insulating member disposed about said fusible element in the region of said predetermined location and at a point sufficiently close to said predetermined location that at least a portion of said arc burns within said insulating member and causes vapors to be evolved from the material of said insulating member, (e) said insulating member being primarily of a baked material, a major portion of which is hydrated aluminum silicate including water of hydration that is released only at temperatures in excess of those attained by said insulating member during prolonged overcurrents as long as one hour, (f) said material being baked for several hours at temperatures up to at least the value reached by said insulating member during prolonged overcurrents as long as one hour.
(a) a generally tubular electrically insulating casing, terminal means disposed adjacent each of the opposite ends of the casing, and a pulverulent arc-quenching filler within said casing, and a pulverulent arc-quenching filler within said casing, (b) a ribbon-type fusible element disposed within said filler and electrically interconnecting said terminal means, (c) means at a predetermined location on said fusible element for causing said fusible element to melt at said predetermined location in response to prolonged overcurrents of relatively low value, thereby initiating an arc at said location when said prolonged overcurrents have persisted for a predetermined duration, (d) gas-evolving means for increasing the arc voltage developed by said arc comprising an electrical insulating member disposed about said fusible element in the region of said predetermined location and at a point sufficiently close to said predetermined location that at least a portion of said arc burns within said insulating member and causes vapors to be evolved from the material of said insulating member, (e) said insulating member being primarily of a baked material, a major portion of which is hydrated aluminum silicate including water of hydration that is released only at temperatures in excess of those attained by said insulating member during prolonged overcurrents as long as one hour, (f) said material being baked for several hours at temperatures up to at least the value reached by said insulating member during prolonged overcurrents as long as one hour.
4. The fuse of claim 3 in which said baked material is the reaction product of a mixture of ingredients comprising said hydrated aluminum silicate in the form of kaolin clay, boron phosphate, and an aqueous binder baked for several hours at temperatures gradually raised to around 350°C and thereafter maintained at between 350°C and 400°C.
5. The fuse of claim 4 in which said mixture contains a minor percentage of inorganic filler.
6. The fuse of claim 4 in which said mixture contains a minor percentage of zircon.
7. The fuse of claim 3 in which the maximum baking temperature is kept sufficiently low that said hydrated aluminum silicate will retain most of its water of hydration despite the baking operation.
8. The fuse of claim 3 in which:
(a) additional means is provided on said fusible element at a predetermined location spaced from said first location for causing said fusible element to melt at a second location in response to prolonged overcurrents of relatively low value, thereby initiating a second low overcurrent are at said second location, (b) second gas-evolving means for increasing the are voltage developed by said second are comprising a second electrical insulating member disposed about said fusible element in the region of said second location and at a point sufficiently close to said second location that at least a portion of said second arc burns within said second insulating member and causes vapors to be evolved from the material of said second insulating member, (c) said second insulating member being primarily of a baked material conforming to that defined in (e) and (f) of claim 3.
(a) additional means is provided on said fusible element at a predetermined location spaced from said first location for causing said fusible element to melt at a second location in response to prolonged overcurrents of relatively low value, thereby initiating a second low overcurrent are at said second location, (b) second gas-evolving means for increasing the are voltage developed by said second are comprising a second electrical insulating member disposed about said fusible element in the region of said second location and at a point sufficiently close to said second location that at least a portion of said second arc burns within said second insulating member and causes vapors to be evolved from the material of said second insulating member, (c) said second insulating member being primarily of a baked material conforming to that defined in (e) and (f) of claim 3.
9. A fuse as in claim 3 further comprising:
(a) a core of electrical insulating material about which said first fusible element is wound, (b) a second fusible element electrically in parallel with said first fusible element and wound about said core in close side-by-side relation with said first fusible element, (c) means at a predetermined location on said second fusible element for causing said second fusible element to melt at said second predetermined location in response to prolonged overcurrents of relatively low value, thereby initiating a second arc at said second location when said prolonged overcurrents have persisted for a predetermined duration, (d) said electrical insulating member on said first fusible element being located close to said second location so that said second arc contacts said electrical insulating member and evolves arc-extinguishing gas therefrom.
(a) a core of electrical insulating material about which said first fusible element is wound, (b) a second fusible element electrically in parallel with said first fusible element and wound about said core in close side-by-side relation with said first fusible element, (c) means at a predetermined location on said second fusible element for causing said second fusible element to melt at said second predetermined location in response to prolonged overcurrents of relatively low value, thereby initiating a second arc at said second location when said prolonged overcurrents have persisted for a predetermined duration, (d) said electrical insulating member on said first fusible element being located close to said second location so that said second arc contacts said electrical insulating member and evolves arc-extinguishing gas therefrom.
10. A fuse as in claim 3 further comprising:
(a) a second fusible element electrically in parallel with said first fusible element and disposed in close side by-side relation with said first fusible element, (b) means at a predetermined location on said second fusible element for causing said second fusible element to melt at said second predetermined location in response to prolonged overcurrents of relatively low value, thereby initiating a second arc at said second location when said prolonged overcurrents have persisted for a predetermined duration, (c) said electircal insulating member at said first fusible element being located close enough to said second location so that said second arc contacts said electrical insulating member and evolves arc-extinguishing gas therefrom.
(a) a second fusible element electrically in parallel with said first fusible element and disposed in close side by-side relation with said first fusible element, (b) means at a predetermined location on said second fusible element for causing said second fusible element to melt at said second predetermined location in response to prolonged overcurrents of relatively low value, thereby initiating a second arc at said second location when said prolonged overcurrents have persisted for a predetermined duration, (c) said electircal insulating member at said first fusible element being located close enough to said second location so that said second arc contacts said electrical insulating member and evolves arc-extinguishing gas therefrom.
11. The fuse of claim 3 in which said electrical insulating member is spaced a short distance from said predetermined location and said arc, following initiation at said location, burns along said fuse element in-to said insulating member.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000411665A CA1186716A (en) | 1982-09-17 | 1982-09-17 | Current-limiting fuse with improved means for interrupting low overcurrents |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000411665A CA1186716A (en) | 1982-09-17 | 1982-09-17 | Current-limiting fuse with improved means for interrupting low overcurrents |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1186716A true CA1186716A (en) | 1985-05-07 |
Family
ID=4123611
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000411665A Expired CA1186716A (en) | 1982-09-17 | 1982-09-17 | Current-limiting fuse with improved means for interrupting low overcurrents |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1186716A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2016133574A3 (en) * | 2014-12-02 | 2016-10-20 | Cooper Technologies Company | Power fuse and fabrication methods with enhanced arc mitigation and thermal management |
-
1982
- 1982-09-17 CA CA000411665A patent/CA1186716A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2016133574A3 (en) * | 2014-12-02 | 2016-10-20 | Cooper Technologies Company | Power fuse and fabrication methods with enhanced arc mitigation and thermal management |
| CN107004547A (en) * | 2014-12-02 | 2017-08-01 | 库珀技术公司 | Alleviate the power fuse and manufacture method with heat management with enhanced electric arc |
| US10446357B2 (en) | 2014-12-02 | 2019-10-15 | Eaton Intelligent Power Limited | Power fuse and fabrication methods with enhanced arc mitigation and thermal management |
| US10650998B2 (en) | 2014-12-02 | 2020-05-12 | Eaton Intelligent Power Limited | Power fuse and fabrication methods with enhanced arc mitigation and thermal management |
| CN107004547B (en) * | 2014-12-02 | 2020-09-15 | 伊顿智能动力有限公司 | Power fuse with enhanced arc mitigation and thermal management and method of manufacture |
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| MKEC | Expiry (correction) | ||
| MKEX | Expiry |