CA1107361A - Gas-insulated electrical apparatus utilizing adhesive particle trap - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A gas-insulated transmission line including an outer sheath at low potential, an inner conductor at high potential disposed within the outer sheath, an insulating gas electrically insulating the inner conductor from the outer sheath, and insulators supporting the inner conductor within the outer sheath. Perforated conductive electrodes are spaced from and electrically connected to the outer sheath to produce a low field region, and an adhesive material is disposed within the lowered-field region and extends at least to locations where the electric field has been reduced 50% by the field reducing electrodes.

Description

DY~ ~F ~ _ This invention relate~; ge~erally to gas-lnsulated electrical appara~us and more particularly to a gas-i~sulated transmission line havl~g field reducing mean~ and an ad-hesi~e material disposed within the lowered-field region produced by the field reducing meansO
Gas-insulated transmisslon lines are being used on an ever increasing scale in recent year~ due to the desir-ability o~ ~ncreasing safety, problems in ac~uiring right-of-way for overhead lines, and hlgher power lines re~u~red by growing metropolitan areas and the growing demands for electrical energy~ Compressed gas-insulated transmlssio~
lines ~ypically comprise a hollow sheath, a conductcr withl~
-the sheath, a plurality of solid'~nsl~at~ng spacers whlch support the conductor in the sheath~ and a compressed gas : such as sul~ur hexa~luoride or the 11ke in ths sheath to ~ ' .,, `1--j~
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electri.cally ir-~c;u.l.ate the conductor ~rom the ~h~k'h. Th~
typical assembly has been fa~.~ricate~cl f`rom re~.a~,lv~ly short sections of hol1.ow cyli.ndri.ccll ducts or tubes in which the conductor and lnsulators are inserted. ~rh~ embly .Ls usual.ly completed ln the :fact;ory, and th~ ~ections are welded or otherwl~e secured t;ogethe:r Ln the f:Lel,d to ~orm the transrnlssl.on li.ne. (';as barrier~ are prov.lded ak :Lnter-vals along the len~th of the assembly~ and, a.t7ter evacuat:Lon of the llne, an :l.n~u:Latlng gas -ls forcecl i.nto the sheakh under pressure.
One problem occur~.7lrlg in the ~Ise of gas-ins1llated tran~mlssion llne~ concerns the mo~):l.le conducting or semi-- conductlng particle. These particl~.js~ whLch ma~ enter t,he line during the fabrication of the :I.lne or during lnstalla-tion in the riel.d~ cause problem~ in that, t,hey may lower the .-dielec~ric strength of the insulaking ~as and may lnitia1;e flashover and breakdown of the ~as as they travel between the outer sheath and the lnner conductor. Trump, ln U.S~
Patent No. 3~515~939~ di~closed a mean~ for deactivating and - 20 eliminating the deleterious effects of such conducting :, : particles. In that patent~ Trump describes khe use of electrodes placed inslde the outer sheath to cre~te low field regions which trap ~nd deactivate the parkicleP,~
Whenever a particle enters the low field re~ion, it cannot : acquire enou~h f'orce to propel it out of khe region, and thus is tra~pped in the low f1eld reglon so that it cannot initiate breakdown of the line.
:l ~ However, lk, ha~ been ~oun~ tha~ un~d,er ce~tai~
circumstan~!es, khe ~ie~d re~du¢ln~ means o~ ~ump do not func~on as effectively as may be deælred. For example,

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lt has been ~ourl~ that part;icJes ~,r~pped within t;he 'low field re~ion whlch do not move out o~ thi~, region und~r an AC voltage can be moved out o~ the trap by ~ DC vo~tage.
This can be a problem, not only for '~C transrnlssion line6~
but also for AC transmission llrles. AC g~as--3nsll1ated trans-mission llnes can experience a ~C voltage depending upo~ the transmission system arld the switchlng operatlon of circuit breakers, For ~xample, if a circuit; breaker d:Lsconnects an unloaded transmis6iorl llne, there wil:l be cl DC' trapped char~e remaining on khe li.ne unle~s there are means for dissipatlng the charge.
Another clrcumstance under which the field reduc-ing trap of Trump may not function a~ de:-,ired is lf the transmission line is not horizontal 3 but, instead is slop~
ing, If 'che transmission line is sloping, the particles which had been trapped in the Low ~leld region can be moved by mechanical vibration out of the -low fie]d region, When-ever these particles are outslde the low field region, they can travel between the inner and outer conductors and so initiate breakdown.
A further circumstance when the field reducing means o~ Trump may not be suita'bly effectlve ls when the field reducing means comprise a metal electrode which is .
electrically connected to the interior of the outer sheath.
Typically, this metal electrode has openings or apertures thereto and is spaced apar~ from the outer sheath a diætance so 'chat~ as the par'cicles travel along the line 3 the parti-cles will pass through one of these apertures i~to t,he lo~
eld region between the el~ctrode and the outer .sheat~.
The prob1em in this instance arises because o~ 'che ~ield

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distortion caused by the metal el~ctrode. Unler,s khe elec~
trode is pre~ent throughout the ent:lre dista.nce of t;he transm~sslon llne~ it will have an eclge~ ~lnf3~ the field ad~acent ko this edg~e wil.l be hlgher than it La wikhln the lnterlor part of the electrode. The distorklon o~ the ~leld at this edge ir, gradual, wlth the si.æe of the ~ield reduc~
tion beinK gradllal].y recluced as one moves aW;ly ~rom khe ed~e of the trap. The.refore, there are areas adlacent to the edge of the trap when the field .l; reduced, buk not reduced as much as desLrab:Le to dea.ctivate the conduct:lng partlcles.
However, as the partlcles travel back and forth bet;ween the inner and outer conductors and al.ong the llne 3 these parti-cles may he temporar~l.ly deactivated wLkh:Ln thLs ~lightly lowered ~leld reglorl, whlch region may not have a low enou~h field to deactlvate the parkicle if~ for examp].e, surge : vo].kages occur on the Lnner conduckor and thereby l.ncrease the entire electrical fleld. In thls irlskance~ the kempor~
~ ar.ily trapped conducting particles can l.eave khe low fi.eld .; ~ region and thereby inikiate flasho~er and breakdown.
SUMM Y. OF' THE INvENrI-N
In accordance with this lnvention, lt has been :! .
found that a more c~esirable gas-insu].ated transmission line is provided whlch ~omprises an outer sheath at low poken tial, an lnner conductor of hlgh potential with respect to the outer sheakh disposed wikhin the sheath~ and an lnsulat~
ing gas disposed withln the outer sheath for electrically lnsulatlng the inner conductor ~rom khe outer sheakh. The .

inrler conductor a~d ~he æuter sheakh ~or~ there~etwee~ an e~ectr.~c ~i.e1d, and ~e~ns a-re i.ncl~ded for ~.nsulatably supporting~the inner conductor within the outer sheath.
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Means for reducing -the electric field adjacent the ou-ter sheath pro(luce a lowered~field region, and an adhesive ma-terial is disposed wi-thin the lowered-field region. The adhesive material extends at least to locations wherein the elec-tric field is reduced 50% by the ~ield reducing means.
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Reference is made to -the description of the pre-ferred embodiment 9 illustrated in the accompanying drawings, in ~hich:
Figure 1 is an eleva-tional sectional view of a gas-insulated transmission line utilizing the teachings of this invention;
Figure 2 is a sectional view ~aken along the line II-II of Figure 1, Figure 3 on the same sheet as Figures 8 and 9 is an enlargement of the edge of the field reducing means utilized in Figure l;
Figure 4 illustrates a modification of the field reducing means of Fij~ure l;
Figure 5 is a sectional ~iew taken along the llne V-V of Figure 4, Flgure 6 lllustrates a modification of the field reducing means of Figure 4;
Figure 7 is a sectional view taken along the line VII-VII of F.igure 6;
Fij~ure 8 is a further modi~ication of the view illustrated~:in Figure l; and ; Fil~ure 9 is a detailed view of the ed~e of a ~ield reducing me~ls illustrated in Figure 8.
3Q DESCRI] ~ ~ ~ ~
Fi~re 1 illustrate~ a gas-insula~ed transmission '~' . :

line utilizi.ng the teachings of thls i.nvent,ion. A.l~hou~/;h the description 1~ made wlth regard to a gas-.ln~uls,te~
transmission line~ it 1B to be understood that the lnventlon is likewise applicable to gas-lnsu:Lated circuit, brea~.ers or any gas-lnsulated eleckrical apparatus wherein moblle con-ducting or semlconducting particles cou.d lnl~lat,e br~3akflowr7, of the apparatus and it i9 desirable ~;o trap and deactlvat~
these particles. 'I'he gaa-lnsulated transmiC3~10n llne com prises an el.ongated tubular outer sheath 10 which typlcally is made o~ alumlnum and is at low or grouncl electrlcal potential. Disposed withirl the outer sheath 10 ls an elon-gated inner conductor 12 which is at hl~3h potential with respect to the outer shea.th 10, ar7d typLcally may carry currents at voltages such as 345 KV. ElectrlGally insulat-ing the inner connector 1.2 rrom the outer sheath 10 1~ an lnsulatln~ gas lLI~ typ~cal of wh:l.Gh ls sulfur hexa~luorlde.
Insulatably supportln~ the lnrler conductor 12 wlthln thQ
outer shea~h 10 is an insulating spacer 15~ and for trapplng conducting or semiconducting partlcles ls a field reducirlg 20 mean~ 18 lllustrated as the apertured ring 20. The ring 20 is spaced apart f'r~m the outer sheath 10, and .~orms a lowered-fleld reglon 22 therebetween. The rlng 20 and the .
~'~ outer sheath 10 are at the same electrlc potentialg and are electrically cormeGted by means such as the lear contact 24 illustrated, irl Fi~ure 2. Disposed wlthin the lowered~field reglon 22 ls an adhesive material 26 ~or mechanically trapplng any conductlng or semlconducking particles which majy be present wlt~ln the transmisslorl line. ~6 illu~trat~ ?
t~e adh~eslve ~akerial ~6 i8 disposeq on a s~et member 2,~
which may be o~ plastic or metal. The sheet member 28, and ; -6~
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the adhe~:Lve rnater:l.al 2~ thereon ext~rlds outw~rdly ~rom ~he lowered-field re~.r:lon 22 to at least t:hose l.ocati~ns wh~rein the electr:Lc field has beell reduced by 50~ hy ~h~ ~leld reduc:Lng means 18 over what the electric fleLd would have been in the absence of khe ~ield reducing means It3 ~lgure 3 illustrates a cletailed view of the edge o-f' the ed~e of the ring 20, and wi.ll illustratl the desirabili~y of so-ext,ending the adhesive materl.al 26.
As can be seen ~rom Figllre 3~ ~he rLng 20 hllS a plurality of apertures 30 therein which lead into the lowerecl-field region 22 between the ring 20 and the outer sheath 10. Also lllustra~ecl i.n Fi~uY-e 3 ar~ equipotentl~l lines 32, 3l~, 36, 38, and. 40. These equipotentia]. llnes illustrate the distortlon of the electric fleld by the ring 20 and how the ring 20 produces a lowered~ield region 2~ to deacti.vate the particles. Llne.s 32, 31~, and 36 are nearest to the high pokential inner conductor 12, and are nok di~--torted by the rlng 20. However, lines 38 and 40 are dis~
; posed ad~acent to the ring 20, and as the field cannot penetrate through the ring 20, the lines are dlstorted and moved away from the ring ~0. (~lthou~h this description i~
made utllizing equipotential llnes, it is to be understood that the e:Lectric field is at right angles to the equi-potential lines illu~trated, and is distorted coxrespond-lngly The equipotential lines are utilized to more clearly illustrate how the distortlon o~ khe electrlc ~ield occur~.) As can be seen~ the equipotential line 40 is moved outwardly from the outer sheakh 10 in the vicinity of khe ring 20j and ~; creates the lowerea-rield re~lon 22 between the rin~ 20 and 30 the outer sheath 10. Parkicles 112 tra~el b~ck and forkh ~ ~ .

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between ~he inner connector 1~ and th~ out~r ~h~ath ~0 in a manner described in the a~or0mentior~ed q'rump Patent until they eventually paE~s throu~ on~ of ~he apert,ur~s 30 and become trapped and cleactivated in the lowered~field reglon 22. Generally, the fleld wl,thin the lowered-fleld region 22 is reduced by 90% from what it otherwise would have been had not the field reduclng means 1~ been incorporated into the tra,nsmisslon line.
Figure 3 also lllustrates one of th~ circumstances in which the prior art particle trapp:l.ng means may be less e~fective than as des,ired. The particle 44 has been cau~ht in the loweredvfiel.d region ad~acent the ed~e 46 of the ring 20, but where the particle ll4 has been trapped the field strength at this point is greater than the fleld strength within the lowered-field region 22 ~etween the ring 20 and the outer sheath 10~ The fi.eld stren~th at this location ls ~ hlgher because the field reducing means 18 do not extend outwardly this far, and the distortion caused by the pres-ence of the ring 20 is gradually reduced as the longitudinal distance from the edge 46 of the ring 20 increases.
It has been found that the particles ~4 wlll generally not become entrapped where the field reducing ~.
~: means 18 has only reduced the field less than 10%, and that the particles 44 will generally become trapped where the field reducing means 18 has reduced khe electrlc field 50%.
, Howe~er, even in those locatlons where the field has been reduced 50~ it is still possible that the particles may be lifted out o~ the lowered-field region ad~acent the edge 46 , of the rin~ 20 upon the occurrence o~ a DC charge of the line7 or upon the occurrence of surge volkages along the : -8-~37~
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lnner conduct;or ].2. Theref'ore, to .insure thc~t the partic].es 42, 4LI remain in the lowered f`ielcl re~:lon 22~ an adhesive materlal 26 is :lnserted within t;he lowered-f:leld reglon ~2.
The adhesive materJ.al 2~ mechanically catches anfl traps the conductlng or semiconcttlctinlg partlcles l~2, 114. ~h~ aclh~slve material 26 can, as ilJ.ustrated ir, F:lgure 1~ be ct.lspo.~ed upon a sheet member 28, or, as illustrat;ed :l.n F.l~ure 3, be disposed directl.y on the outer sheath 10. The adheslve materlal 26 shoul.d extend from the l.ower~(.t~f,.eld reçrio~ ~2 at the least to a polilt; wherein t;he electric ~leld intenslty has been reduced by 50~ by the .~:Leld reducln~ means ~8.
Pre~erably~ to lnsure that all partlcles whiah may become deactivated wlthLn the lowering of' the fieJ.d caused by the -rln~ 20 are caught~ the adhesive maker:Lal 26 can extend outwardly to where the e,.ectric field ha~ been reduced only 10% by the fie]d reducin~ mean~ 18 over what the f~eld would 7~e in the absence o~ the fi.eld reducln~ means 18. The adhesi~e material 26 can~ for example~ be polybutene or the coating descrlbed ln IJ.S~ Patent No. 3,911, 937 to Sletten and Cookson, ~~hus, 7~1th the particle~ 42~ 44 caught wlthln the ;~adhesive mater:I.al 26 wlthin the reglon whereln the eleckric field has been reduced, the partlcles 423 44 are permanentl~
deaotivated and wlll not lnltlate flashover or breakdown even in the event of DC voltages, vlbrak~on of the line~ or sur~e volt;ages. Addltionally, b~ so trapplng the partlcle3 42~ 44 in a lowered-~eld reglon 227 the partlcles 42~ 44 wlll not glow or cause corona as may occur 1~ the adh~ e mat;e.rlal 2~ were dis~s~?d on th~e ~uter shea~h 10 and not 1 a lowered--~leld region.
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Referr.l.ng now to ~l~ures ll and 5, thereln i.1 ~hown a modificatlon of the ~ielcl reducing m~ans 18 i.l.l.u~trated ln Figure l. In Figures 4 and 5~ the ~ield reducin.~r means 18 comprise an electrode 50 which is welclecl or otherwlse se-cured to the interior 52 of the outer ~heath 10 ~o as to be electrically connected thereto. Thus~ the elect;rode 50 ls at the same low or ground potential as t~le ouke~ sheath lO.
The electrode 50 may have apertures 5LI therel.n whlch ~aclli-tate the ~low of partlc:Les to wlthin the lowered~fi.eld region 56 between the electrode 50 and the outer sheakh lO.
As shown in Figures 4 and 5~ not only is the el.ectr-ic field .; distorted at the edges 58~ 60 of the electrode 50 ln the longitudinal directi.on, but the elec~rlcal field ls also distorted in the circumferential direction. In Figure 5 : equipotential line 62 ls shown as being dlstorted in the circumferentlal di.rection by the electrode 50 which does not extend circumferentially about the inner conductor 12 adJa-cent the outer sheath 10. Thus not only is the adhesive ~: material 26 disposed in the lowered-fi.eld reglon in the longitudinal directlon outwardly from the electrode 50~ but is al.so disposed circum~erentially about khe electrode 50 on the outer sheakh lO. As be~ore 7 it is desirable that such ;~ : adhesive material 26 extend at least to those locations ;~ wherein the electric field has 4een reduced 50% by the ; : ~: electrode 50.
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Ihls fleld distortton in the circum~erential .~ direction caused by the electrode 50 can also ~e u~ilized to .~ ~ modi~y khe design o~ the ~ie~d reducin~ means 18. A~

lus~rated in Figu~es~6 ~nd 79 tpe ~ield re~ing mean~ 18 : 30 can comprise a solid metal rod or bar 70 which is disposed :
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at the bottom o~ the outer sheath 10. Thl~ rod 70 dlstor'c~
the electric ~leld in khe circum~erent:5.al direction7 as illustrated by the equipotential llrle 72~ and al~o dl~torts the field in the longitudinal dlrection at the edge 74, 76 thereo~. As there ls no spaced-apark re~ion b~tween the rod 70 and the outer ~heath 10, particles preæent may be caught in the lowered-fleld region 78 on either s:lde o~ the ~olid rod 70 in the clrcum~erential direction, and this lowere~-~ield region 78 ~hould have disposed therein the adhe~ive material 26 to mechanlcally capture and deactivate the conductlng partlcles. As hereto~ore described, the trappin~
of the~e particles ~n the lowered~leld region 78 by tho adhe~i~e material 26 prevents the oscurrence o~ a low or ; corona e~ect even 1~ the particles are radially dlspo3ed.
.~ Figures 8 and 9 illu3trate how the provl~lon o~
having the adheslve material 26 wlthln the lowered-~eld region 22 can be retrofitted to existing in3tallatlons. As shown, the adheslve materlal 26 ls disposed upon two sheet~
80~ 82. ~he sheet.s 82, ~or example, havs a radial nub 84 incorporated khereln~ and khis radlal nub 84 extend~ ~or a distance substantlally equal to the di~tance between the ring 20 and the outer sheath 10. The sheets 82~ 80 are then inserted into the lowered-~leld region 22 between the ring 20 and the outer sheakh 10 until such kime as the nub 84 contact~ the ring 20. This can occur ~rom either longi- :
tudinal direction of khe ring 20~ and thu~ khe adhesive material 26 is dlsposed within the lowered-~ield r~gion 22 in e~istlnK installa~io~ nd -~111 thu~ inG~ease the ~fe¢~ive~ s ~ ~he ~i~ld ~ c~n~ mean~ 1~ to trap an~
deactivate conducting part~cles. As be~ore, the sheek~ ~0, ~ .
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82 should extend outwardly beyond the edge Ll6 of the rin~ 20 to a distance where the f'ield has been reduced at least 50%.
Thus~ lt can be seen that khls lnvention provide~
a means for trapping and deactlvating conductlng or ceml-conductlng particles ln gas--lnsulated electrical apparatus even in the presence o~ DC vo].tages or surge voltages.

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Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A gas-insulated transmission line comprising:
an outer sheath at low potential;
an inner conductor at high potential with respect to said outer sheath disposed within said outer sheath, said inner conductor and said outer sheath forming an electrical field therebetween;
an insulating gas disposed within said outer sheath and electrically insulating said inner conductor from said outer sheath;
means for insulatably supporting said inner conductor within said outer sheath;
means for reducing said electric field adjacent said outer sheath to produce a lowered-field region for the entrapment of particles therein; and an adhesive material disposed within said lowered-field region and extending at least to locations when said electric field is reduced 50% by said field reducing means, said adhesive material extending only to those locations wherein said electric field is reduced by said field reducing means.

2. The gas-insulated transmission line according to claim 1 wherein said field reducing means comprises an electrode electrically connected to said outer sheath, said electrode, at some portion thereof, being spaced apart from said outer sheath.

3. The gas-insulated transmission line according to claim 2 wherein said electrode is apertured.

4. The gas-insulated transmission line according to claim 1 wherein said field reducing means comprises a solid rod disposed on said outer sheath.

5. The gas-insulated transmission line according to claim 1 wherein said adhesive material is disposed on a sheet member, such sheet member being disposed within said lowered-field region.

6. The gas-insulated transmission line according to claim 1 including a plurality of inner conductors dis-posed within said outer sheath and spaced apart from each other, said supporting means supporting said plurality of inner conductors.

7. The gas-insulated transmission line according to claim 1 wherein said adhesive material is polybutene.

8. The gas-insulated transmission line according to claim 1 wherein said field reducing means comprises an apertured ring electrically connected to said outer sheath, said ring at a portion thereof being spaced-apart from said outer sheath, said ring and said outer sheath forming a lowered-field region therebetween;
said adhesive material is disposed on a sheet member positioned intermediate said ring and said outer sheath and extending outwardly therefrom; and said sheet member is secured to said ring.

9. The gas-insulated transmission line according to claim 1 wherein said outer sheath is at ground potential;
and said insulating gas comprises sulfur hexafluoride.

10. Gas-insulated electrical apparatus comprising:
an outer housing at low potential;
an inner member at high potential with respect to said outer housing disposed within said outer housing, said inner member and said outer housing forming an electric field therebetween;
an insulating gas disposed within said outer housing and electrically insulating said inner member from said outer housing;
means for reducing said electric field adjacent said outer housing to produce a lowered-field region for the entrapment of particles therein; and an adhesive material disposed within said lowered-field region and extending at least to locations wherein said electric field is reduced 50% by said field reducing means, said adhesive material extending only to those loca-tions wherein said electric field is reduced by said field reducing means.