Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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
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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
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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
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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
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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.
I~F r~3~ rs~o~ ~ ~
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
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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
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~'~ 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
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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
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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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