CA2008984A1 - Electrical insulation - Google Patents

Abstract

ABSTRACT

An electrical insulation (14, 26, 33, 43, 52) comprises an organic polymer containing a powdered filler and has parts with a thickness of more than 1 mm, which are subjected to a field strength of at least 0.5 kV/mm alternating voltage.
The insulation contains a powdered filler in the form of chromium oxide (Cr2O3), iron oxide (Fe2O3), metal phthalocya-nine, or a mixture of at least two substances of these kinds in such a content that the amount of the powdered filler con-stitutes at least 10% of the total volume of the organic polymer and the powdered filler. The electrical insulation may, inter alia, be arranged as an insulation (14) around con-ductor bundles (17) in coils for electrical machines, as insulation (26) between conductor layers (22) in layer-wound transformers, as insulation (33) around core and windings in instrument transformers, as insulation (43) between conductor (40) and grounded casing (41) in SF6-insulated conductors, and as insulation (52) between conductor (50) and grounded screen (54) in a cable. (Figure 2)

Description

Electrical insulation The present invention relates to an electrical insulation com-prising an organic polymer containing a'powdered filler.
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In relatively thick-walled.insulations for high volt~ge equip- ' ment, such as in the form of many products of moulded, resins, I ,`
5 in the form of resin-impregnated windings of~.for example,mlca' tape, and in the form of many compression-moulded, in~ection-moulded or extruded parts of filler~containing resins, sehsl-tivity to corona (partial discharges,). constitu'tes a serious : problem. In the manufacture of relativ,ely thick-walled insu-10 lations using the methods mentioned, cavities:and pores are easily formed therein, which result in'internal corona when the insulations are subJected to high voltage stresses. The corona gradually breaks down the material,.which may lead to breakdown, The insulations of the kinds mentioned o.ften con-tain powdered and fibrous fillers, such as, for example, alu-minium oxide and chalk, and glass fibre, respectively, .
According to the present. invention, it has been found to be possible to provide insulations of the kind mentioned which .-exhibit a considerably increased reslstance to internaI elec 20 trical partial discharges. According to the:inventlon~ this result is achieved by incorporating lnto.the lnsulatlon a sufficient quantity of at least one'of the substance~ chrom~.um oxide~ iron oxide or a metal.phthalocyanine In powdered form.

A possible explanation of th,e favo.urable results obtained 25 according to the present'invention'maylbe that the corona in cavities and pores "sputter.~q,away" lnsu,lating polymer material from the surfaces of the cavities and pores~.respectively~.and ' that, when using,chr~mium oxide or iron oxide a,s filler, chromium oxide or iron oxide then expoqed in the urfaces of 30 the cavitieq and the pores, respec.tively, because'of their lower resistivity increases the ele'ctrical conductivity localIy in the surface layer of the~cavities and the,pores, ,~ .
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respectively, sufficiently for the extremely concentrated effect of a corona discharge to spread ov~er a larger surface~
hence being effectively reduced Alsof when using metal.
phthalocyanine, it is assumed that a corona discharge will 5 spread over a larger surface. Owing to this process in cavities and pores, surrounding parts of the insulation are protected against the corona.

More particularly, the present invention re}ates to an elec_ trical insulation comprising an organic polymer containing a 10 powdered filler with parts. with a thickness exceeding 1 mm, which are exposed to a field strength of at least 0 5 kV/mm I .
alternating voltage, characterized in that the insulation contains a powdered filler in the form of chromium oxide ~Cr203), iron oxide (Fe203), metal phthalocyanine, or a mix_ 15 ture of at least two substances of these kinds ih such a con-tent that the amount of the powdered filler constitutes atl least 10% of the total volume of the organic polymer and the powdered filler.
' As examples of usable metal phthalo~çyanines may be mentioned I ::
20 phthalocyanines of copper, iron, nllckel, cobalt~ magnesium, aluminium, man~anese, tin, chrqmium, and zinc, separately.or in a mixture. ~Particularly preferred, among o~her things for economical reasons, is copper phthalocyanine, and then parti-cularly ~-copper phthalocyanine, : ' '.
25 The chromlum oxide~ the lron oxide and the metal phthalocyanine, respectively~ preferably have an intrinsic resistivlty of 104-1 o8 ohm m. .~

The filler-containin~ polymer preferably has a res~s~ivity in excess of 101 ohm m, 30 The content of powdered filler. in the form of c.hromium oxide, iron oxide, metal phthalo.cyanine, or a mixture of at;least two substances of these kinds, preferably constitutes 10.-40% of the total volume of organic polymer and this powdered filler.

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- ``` 2008984 The particle size of the ~iller mentioned in the preceding paragraph is suitably 0.005-30 ~m and preferably 0 005_5 ~m, A particular advantage o~ chromium ox.ide is that it gives the : film a corona resistance which is not, or only insignificantly, 5 reduced by the influence of external factors, such~as mois_ ture. ' : A particular advantage of the'phthalocyanine is that it gives the insulation a partlcularly low loss factor.
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The organic polymer in the insulation may consist of different ' 10 thermosetting resins and thermoplastic resins of such kinds as : are conventionally used for the manufacture of insulations : using current formlng methods such:as casting~ impregnation, compre3sion moulding~ inJection moulding and extrusion, As examples of polymers wh.ich are particularly wel.l s~ited:for 15 casting~ impregnation and compression moulding may be men- ' tioned curable epoxy resins, unsat.urated polyester~resins, poly-urethane resins, acrylic~resins ahd silicone resins. These curable resins are preferably used without a.solvent in the case of casting and compr~ession moulding and normally dis- I
~: 20 801ved in a solvent in the case of impregnation. As:examples~ ''.
of polymers which are part'1cularly well suited..for inJectionl ~. moulding and'extrusian may b~e mentiQned linear~polymelrs such :~: as polyimide, polycarbonate, polysulf'one~ includli~g polyaryl- , : ~ sulfone and polyethersulfon.e, polyetherlmido~ thermoplastlc 25 polye8ter 8uch a8 polyethyleneglyco~ terepht.halate and poly-~:~ butyleneglycol terephthalate, polyethylene, copolyme~ri~ate ofi' ethy.lene and propylene, o~-of ethylene~ and' propylene wlth diene monomers such as dlcyclopentadlene wlth double llnks remalning from the diene monomer molecules after the polyme~
30 rizatlon, and polyethylene and the mentloned copolymerisate : which~ after forming, are subJected to.cross llnking, ~: ' The organic polymer may co.ntain~.in addition to chromium oxide, iron oxide and/or metal phthalocyanine, fiIlers of conventional . . , . , . . .... , , . - . .

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kind, in the following referred'to as indifferent fillers, such as aluminium oxide, chalk, kaolin, dolomite, talcum, mica powder, quartz. The content of such in.different fillers suitably amounts to 10~50% and preferably to 20-45~ of the 5 total volume of organic polymer and indifferent fillers. In addition, the organic polymer, especially when applying the invention to compression moulding with organic polymer in the form of a thermosetting resin, may contain a fibrous rein-forcing material such as short fibres of glass, polyamide or 10 carbon. The content of such fibrbus reinforcing material, if -.
used, suitably amoun.ts to 1-20%~, preferably to 5-15~ Or the total:volume of organic polymer and fibrous filler.

Especially when applied to in~ection moulding and extrusion ~ith an organic polymer in the form of a linear polymer, t,he organic ~I ~
15 polymer may contain convehtional additives such as plasticlzer1 "
for example dioctylphthalate, peroxide (in case of cros~ linL
~ king), for example ditX-cumyl peroxi'de, activator for~the :~ peroxide,.for example triallylc:y'anura~e, antioxidant, for example polymeri.zed trime.~hyldihydro-q'uinoline, and flame : 20 ~etardent, rOr exa-ple'an'timony trioxide. .

As examples of high voltage eguipment, which may advantageously be provided with an electrical insuIation according to the ~ .
pre~sent invention~ the following.may be mentioned.
, _ As main insulation in form-wound colls for ele¢trical machlnes for an operating voltage of at lea9t 2 kV. The lnsulatlon ~: i9 then arranged around a bundle Or a plurallty Or lengths, arranged side by side,~f'conductors of rectangular cro.ss sectlon for insulation Or the bundle against slots ln a sta-tor or rotor in the machine. I

30 - As insulation between conductor layers in th.e winding of a layer-wound transformer or reactor for an operating voltalge of at least 5 kV. . I

- As an insulation cast around st 1east part~.or the~core and "

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at least one of the windings in an instrument transformer for an operating voltage of at least 2 kV. .;~
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- As a solid insulation between a conductor for an operating .voltage of at least 6 kV along part of the~extension of the `~
5 conductor and a grounded casing surrounding the conductor, ~:
which casing is'filled with SF6 and'which, together with the solid insulation, insulates the conductor from the casing.

As insulation'ibetween a conductor and a grounded.screen in : a cable for an operating voltage of~.at least 2 kV. :;

:~ 10 The invention will be explained in greater detail, by way of ~ `
examples, with reference to the accompanying schematic drawing, ~-., ~
wherein l ~
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Figure 1 shows a side view of a coil for an electrical machine !' with a main insulation according to thelpresent inven-:
~. ~-. , ~ 15 . tion, ''~h~ Figure 2 shows the same coil in cross section, Figure 3 shows a longltudinal se:ction through a~wind.ing for a layer-wound trans~former with an insulation according to the present invention, 20 Figure 4 shows part of a c.ross section A-A through the win.ding in Flgure 3 Figure 5 shows an instru~en~ transformer with a surrounding .. cast ingula:tion according to the.present invention, : partly ln front view, partly.in cross sectlon~ .

; 25 Flgure 6 shows a cross section of part of a conductor, insula-ted wi.th SF6 and with a solld lnsulator in the form , ~ '~
an insulation according to the present invention, "

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Z0~85~84 Figure 7 shows a cross section of a high voltage cable with an insulation according to the present invention.

The coil according to Figure 1 has straigh-t parts 10 and 11 intended to be placed in the stator slots of a high voltage 5 machine, and bent end parts 12 and 13; extending outside the slots of the machine. It is provided with a main insulation 14 according to the present invention The coil has terminals designated 15 and 16. ~ I
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The coil according to Figure 1, as will be clear fromlFigure 10 2, has a bundle 17 of several.'individual conductors 18 arranged ..
- side by side, each conductor being provided with a conductor i insulation 19. The slots Or the machine are design:ated 20. 1 :
The bundle 17 may then consist of several turns of one single conductor. It may al80 consist of several separate insulated 15 conductors, usually called strands, which at their ends are electrically connected to each other, usually parallel-connected... The conductor insulation 19 may conslst of only one enamel layer of such a type.as..is n.ormall.y used for..
'~. enamelling winding wire~ such as a coating of.. epoxj resin, 20 terephthalic acid alkyd ? po.lyester imide, polyimide, polyamide ~ imide, polyurethane, polysulfone,lsilicone, polyamide or a .':; polymer based on polyhydantoin~ The conductor insulation may also consist Or a wrapplng of glas$~yarn which 19 l~pregnated ~ with such an enamel and which i~ then cured, Furthor, the '~ 25 conductor in8ulatlon may consi~.t of a thln m~ca ta~pe~ wound ~r , folded around the conductor~l or a.thin.tape.in the form a.f a ~- film Or a linear:polymer such a8~ polyimide, polylcarbonate~
polysulfone including poly~ylsulrone an'd polyethePsulfone, polyetherimide~ polyamide~ polyamidelmide, or polyethylene- ~
30 glycol terephthalate, In the materia~ used as conductor . ;' insulation~ to counteract,the occurrence of co~ona damage, ; there may be incorporated powdered chromium oxide ~Cr203), iron oxide ~Fe203),: metal phthalocyianine, prefer.'ably..copper : phthalocyanine, or a mixture of at least.two substances of 35 these kinds in such.an amount that'the content of this pow-dcred flller constitutes at least 10~, prefer..ably 10-40~ of :. : . ........... . . ....... .. .. - .-. -. ~ . ~ . .

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the total volume of this powdered filler and organic polymer contained in the conductor insulation, such as in the form of the mentioned enamel or ~he mentioned linear polymer~ In an exempli~ied concrete case the conductor insulation consists of 5 a wrapping of glass yarn impregnated with an epoxy resin to which chromium oxide (Cr203) has been added, whlch epoxy resin has thereafter been cured. The epoxy resin may consist of a polyamide-modified epoxy resin (such as AF_42 from Minnesota Mining and Manufacturing Compary) The conductor 10 insulation may have a thickness of 100 ~m and contain 20 per cent by volume chromium oxide with.a grain size of less than 5 ~m. Instead of incorporating the mentioned f.iller chromium oxide~ iron oxide or methal phthalocyanine into the polymer in the conductor insulation, the filler can be i~corporated 15 only in a protectiY~e layer protecting against corona damage applied on the surface of the enamel layer or on the outwardly-facing surface of that tape in the form of polymer film which~
is folded or wound around the conductor, the.same co.nteht of the f-iller..being used in the protectiv,e layer as has been sta-20 ted above for the filler in the organic polymer of the conduc- I
tor insulation. It is then suitable to use in the protective layer an organic polymer of the same kind.as exemplified above as material in an enamel layer and whi.ch has been stated to be used normally for enamelling winding wire.. As a concrete 25 example of a conductor insulation with a prote~ive layer may be mentioned a film of polyimide ~e..g ~apton~ fr~m Du Pont), wound around the conductor, with a thickness of~75 ~m, which film is provided on the outwardly facing side ~ith a protective layer of polyamide imide with a thickness of 25 Jum and con_ taining 25 per cent by vQlume chromium oxide (Cr203?.

Around the conductor bundle, a micaceous main insulation 14 is arranged~ It is built up by winding with, for example half an overlap, of an insulating tape, for example having a width of.
25 mm and consisting of an 0.09 thick self-supporting layer of 35 small mica flakes, overlapping each other, fixed to an 0 04 mm thick woven glass fibre tape with an 0.006 mm thick pol.yethylene glycol terephthalate film. When being fixed ~the film partialiy . -.

2008984 .

melts and accumulates at contact surfaces between mica tape and glass fibre threads. Such an insulating tape is desc.ri- -bed in Swed.ish Patent 200 820. When the bundl.e has been provided with a wrapping of, for example, twenty layers of the ~:
mica tape, located one layer aboye the other, the winding is .
first evacuated at a pressure of 0.1 mm Hg and at a tempera-ture of 40C, whereupon an impregnating resin containing copper phthalocyanine with a grain size of below 0.1 pm is I
supplied at the pressure mentioned for impregnation of the wrapping. When all resin has.been supplied.~ the pressure ls increased to, for example, 10 ~icm2,. ~he resin may cons~lst of 100 parts by weight of an epoxy resin, whi:ch is:manufac-tured in a manner known per~se from epichlorhydrin and 4.4'-dioxydiphenyl dimethylmethane and which ~has an epoxy equiva-lent of 192~ and 100 part5 ~y weight of a curing agent con-. I ..
~ sisting of a mixture of 75 parts by weight hexahydro.phthalic acid anhydride and ,25 parts by weight.tetrahydrophthalic acidanhydride. The volume:of copper phthalocyanine in the resin amounts to 30~ o.f the total volume of copper phthalocyanine and resin. Upon the impregnation, resin with copper phthalo-cy~anine penetrates into spaces between. the mica layers and ~:; into the mica layers themselves, In order for,.the re~in.not to penetrate out of the insulation during the subse.qent curing operation, the impregnated conductor bundle wi.th the mica .tape wrapping may be surrounded by a sealing tape of polytetra~luoro ethylene or the like. The coil ls then placed.in.la mouldlng `~ tool far curing the resinous materla.l, The curlnoe is perfor--med at a temperature of about 160C for a period o.~ 1b hours. ;.
In the finlshed cQll~ mlca cons.titutes 27%~.resln 45~, copper :.
phthalocyanine 20~ and ~lass ~ibre.8~ of the total volume of the main insulation.

The solid insulating material in the main insulatlon may be .: lmpregnated with the impregnating res.in either after the lnsu-~ }ating material ln the ~orm of a wrapplng has been.appl.led around the conductor bundle~ as rec:ent}y described~.or before . the solid insulating material is applied around the conduc-tor bundle to form a wrapplng. In the forme~ case the pow-' ,~
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dered filler is supplied to the impregnating resin prlor to the impregnation. In the latter case the fil.ler can be sup-plied before or after the impregnation. When supplying it af~er the impregnation, the filler may, for exampl.e, be applied as a su.face layer on the impregnated insulati.ng material before~
it is formed into a wrappihg around the conductor bundle.
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Thus, in the manufacture of a .coil according to Figures 1 and 2, the copper phthalocyanine and.the impregnating resin~ when applylng the latter method, may:ble su~pplied to the mica.tape before the winding of the tape around the conducto~ bundle t7,~
either by impr~egnating the tape with ~he resin.contalning : copper phthalocyanine or by impregnating the tape with onlr l -: : the impregnating resiin and coating the surface of.the im_ pregnated tape with copper.phthalocyalnine. The impregnating resin may then conslst of 100 parts, by weight of epoxynovolalk : : "DEN 438" (Dow Chemical ¢o.-) and 3 parts by weight of the boron trifluoride complex "HZ 935 J50"~.(Ciba Geigy AG). The amount.of..copper phthalocyanine may constitu.te 20~ of the total volume of resin and copper pht:halocyanlne. The tape is wound around the conductor bundle 17~ with half an overlap into thirty layers located one above the~other to form.the main insiulation 14. The coil is then placed in a moulding tool for curing the resin at a temperaturé Or 160C for a period of 8 I hours. This causes the tiller, together with the resin~ to penetrate into and ~ill up all the spaces ln the lnsulation 14. In the fInished coll~ mlca constltutes 27~ resin 52 copper phthalocyanlne 13~ and glass fibre 8~ o~.the total volume o~ the main insulatlon.

Instead of using an insulating tape wlth mica ln the.two cases ~: 30 exemplified above~ it is posslble to use an insulatlng tape wlthout ~ica~ such as a woven glas.s fibre tape. When usiing an 0.2 mm thlck woven glass flbre tape lnstead of ~lca.tape in the above two.exempllfied cases,; blut otherwlse uslng. the same procedure, resin will constitute 70%, copper.phthalo-cyanIne 23~ and glass fibre 7~ of the total vo}ume of.the main insulation. . ., .. ~

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,: , , ' . . ' Although many epoxy resins as well as unsaturated polyester resins suited for impregnation of form-wound coils are known, some additional examples of such resins will be mentioned.
Thus, there may be used, for example, a polyester resin consis-5 ting of 60 parts by weight of a reaction pril~uct of 3 molesmaleic acid anhydride, 1 mole adipic acid and 4 4 moles ethy-lene glycol with an acid value of 30, and of 40 part~ by weight diallylphthalate and containing 0~75% benzoyl peroxide and a polyester resin consisting of 70 parts by~weight of a reac-10 tion produce of 1 mole fumaric acid, 1 mole phthalic acid and2.2 moles propylene glycol with an acid value of 25, and of 30 parts by weight monostyrene and containing 0.5% benzoyl per~o-xide, as well as an epoxy resin consis$ing of 100 parts by weight "Epon 828" (Shell Chemical Co~) and 65 parts hexa-15 hydrophthalic acid anhydride~ an epoxy resin consisting of 85parts by weight "Araldit F", 100 parts by wei~ht 'lCuring Agent 905" ~both from Ciba Geigy AG, Switzerland) and 15 parts by weight phenylglycidyl ether orlan epoxy resin consisting of 100 parts ~by weight ''Dow 331" ~Dow Chemical Co ) and 65 parts by weight tetrahydrophthalic acid anhydride Figures 3 and 4 show a winding which is a high voltage winding for a layer-wound transformer. In these figuresl 21 des~gnates a spacer between the conductors 22 in the form of copper wire.
The conductors are wound close to each other, in the axial 25 direction, in layers 23. The spacers which keep the conductors at the intended distance from each other in the radial direc-tion may consist of elongated impregnable elements 24, for example glass fibre roving, which form between themlchannels 25~ Alternativelyl the e~ents 24 may consist of a voidless 30 line or rod Or a linear polymer such as polyamide. The win~
ding is impregnated with and cast int~o a filler-containing resin 26 so as to fill up all the voids in the winding inclu-ding the impregnable elements 24 when using such elements As impregnating resin there is used a solventfree resin such 35 as an epoxy resin, an unsaturated polyester resin, or a poly-urethane resin The resin, for example an epoxy resin consis-ting of 100 parts by weight of a resin of bis~henol type .
1 1 , , (e.g. Araldit F from Ciba AG~, 100 par~s by wei'ght curing agent of anhydride type (e.g. HY 905 from Ciba. AG) andll part by weight amine accelerator (e.g. DY 061 from Ciba.AC), con-tains copper phthalocyanine with a grain size of less than 0.1 5~um and quartz powder with a grain size of less than 500 pm so !
that the content of copper phthal:ycyanine constitutes i5% of the total volume of copper phthalocyanine and epoxy.resin and the content of quartz powder 20% of the total volume of quarts powder and epoxy resin. In an analogous manner, a winding for 10 a transforme.r, which in a known manner is built up of tape, usually aluminium tape, instead of threads 22 may be impregna_ ted and surrounded with a cast resin. In the same way as has been described for the manufacture of form_wound coils for elec-trical machines,.it is also possibIe to use an insulaking tape, 15 for example a glass fibre tape,` preimpregnated with. the filler_ containing resin~ which tape is impregnated with the epoxy resin I
~ust mentioned and containing copp.er phthalocyanine and quartz ':
: powder to make an insulation 26 (Fig. 4) of the mentioned ki~d for a layer-wound transforme'r, wheth.er the condu~ct.ors,in each.
20 layer consist of a plurality of turns,'arranged si'de-by-sid.e, , of a wire-formed conductor or.of a tape-'formed conductor~
having the corresponding éxtent. Layers of conductors? for example tapes of aluminium of app~oxf~ately the same wi.dth as the length of the wlndinglin. the axia.lld.irec.ti~n, and an.
25 intermediate insulation are then wound alternately an.top of each other until the intended geometry of the wlnding haQ been attained~ whereafter the resln in the lnsulatlon 18 cured.

Flgure 5 shows an lnstrument transformer ln the form of a vol-tage transformer wlth an ir6n core 28, a primary windlng 29, 30 termlnals for the prlmary wlndlng 30, a secon.dary winding 31, terminals for the secondary winding 32, an insulat.ion 33, an outer easing 34, a clampln~ fra~e 35, a ground connection~ 36 and covering lids 37 and 38. The insula.tlon 33 ls cast around the central part of the core and around the.prlmary and .secon-35 dary windings. The insulation 33 may conslst of a materialof the same kind as that used in the insulation 26 in the transformer accordlng to Figures 3 and 4. In an instrument 't~ , I

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~ I 2008984 transformer in the form of a current transformer, a core in its entirety and only the secondary winding may be cast into an insuIation of the stated kind, whereas the primary winding is located outside.

5 Figure 6 shows a high vol.tage conduc~tor~which may be used, intër alia, in a connecting line betwee~ a ~ransformer and static convertor valve units in a static.co,nvertor st.ation in a plantl for power transmission bylmeans of high. voltage.direct:current.
The device of Figure 6 comprises a conductor 40 and.a grouhded ~ :
10 casing 41 in the form of a tube whiGh.surrounds.the.conductor.
In the shown part of the conn.ecting. line, two.casing tubes 41a and 41b make contact:with each o.ther at end surfaces. Along the main portion of its extension, the conductor is insulated ..
from the casing by pressurized~SF6 arranged in the space 42, ~ 15 and along part of lts extension by a soli.d insulator~43 . .
arranged between the conductor and the casing, or by several such insulators. The insulator is sealingly fixed to the casing by a ring 44 and supports~the conductor via a central hole 45.

20 The solid insulator may,.for example, be man.ufactur.ed from a .; resin conslsting of 100 parts by weight of an ep.oxy.resln. olf bisphenol A-type and containing 5,15-5.5 moles epoxy groups p~er ~:~ kilogram ~e,g. CY 205 from Ciba Geigy, Swltzerland)., 80 *arts.
by weight methyltetrahydrophthallc aci.d anhydride a.nd.1 part 25 by weight benzyldimethyl amine~ to which have been added copper phtha}ocyanlne Wlth a graln.8ize~0flle88 thanl0.1 ~um an.d aluminium oxide powder with a grain size of 0_1.40 ~um an~ a.mean .
grain slze of 1~5 ~um~.~so t~h~6 the content oÇ.co;pper.phtyalocya-~ . nlne constitutes 30% of the tot.al,vo.lume of e.poxy.resln and ;~ 30 copper phthalocyanine and the.co:nten.t of alumlnium oxi.de. l OX
of the total volume of epoxy r.eslr. and aluminlum ~xide, Curing of the resin may be carried out by gelling at 150C for 45 minutes.

Instead of epoxy resin, an acrylic resin may~ inter alia, be 35 used which is manufactured from 100 parts by weigh~ decyl-h . l I
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2 0 ~8 g 84 methacrylate, 5 parts 1-4 butane.diol dimethacrylate and l part benzoyl peroxide, whi.ch can be cured.at 50C ~or 3.hours, or an unsaturated polyester resin cons.~sting of a r.eaction pro_ I
duct of 1 mole isophthalic acid, 0.5 mole adlpic.acid, 0.5 mole 5 maleic acid, and 2.2 mole prop~lene glycol,~ t.o which.have been added 30 per cent by weigh~t s~yrene and .1 per.~ent ~y.weight benzoyl peroxide. The res~n can be~cured'at 130C ~or 3 hoyrs.
The manufacture of the solid~insu~ator may take place by cas-ting or compression mould1ng.

10 Figure 7 ~hows a high voltage cable. In this the conduc~tor 50 is surrounded in conventional manner ~y, respectively', an inner semiconducting layer 51, an extrud~ed ins.ulation.52, an outer semiconducting layer.53, a screen 54 of metal whilch ls.nor-mally grounded, and a sheath 55.of poly;mer material, for 15 example PVC.

The extruded insulation 52 may, for example, be.o~ polyethylene, a copolymerisate of.ethylene and.propylene.or of ethy.lene and : propylene with a diene monomer, in non-cross-lin.ked or cross-~linked form. As a concrete example may be mentioned .a cross-.
20 linked insulation manufact.ured from'l00 parts by weight.LD
polyethylene wlth a melting lndex Or 0.2-20~, 2 pantQ by weight di-~-cumyl peroxide, 0.2 parts~ by weight polymerized~.tri~ethyl dihydroquinoline tantioxidant) and .copper phthalocya.nlne.with a grain size of.les~ than 0.1 ~m in"such.an amount that ithe 25 copper phthalocyanine constltutes 1.0%.of.the.total volume. of polymer and copper phthalocyanine~ The extruslon may..ta~e place at 120C and the cro98 llnklng at.215C.
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In the exampl.es gl.ven the copper ph.thalocyanlne may.be repla.Ged ' completely or partlally by"other metal phthalacyanin,els such i~s 30 nickel~ cobalt or ~ron phthalloc~anlne, a~ well as by,chnomlum oxlde (Cr2o3~ and lron oxide (Fe203) ~r.mixtures ~r at.least two of all the substances mentioned abov'e.
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Claims (13)

1. An electrical insulation (14, 26, 33, 43, 52) comprising an organic polymer containing a powdered filler with parts with a thickness of more than 1 mm, which are subjected to a field strength of at least 0.5 kV/ mm alternating voltage, c h a r a c t e r i z e d in that the insulation contains a powdered filler in the form of chromium oxide (Cr2O3), iron oxide (Fe2O3), metal phthalocyanine or a mixture of at least two substances of these kinds in such a content that the amount of the powderd filler constitutes at least 10% of the total volume of the organic polymer and this powdered filler.

2. An electrical insulation according to claim 1 or 2, c h a r a c t e r i z e d in that the metal phthalocyanine consists of copper phthalocyanine.

3. An electrical insulation according to claim 1 or 2, c h a r a c t e r i z e d in that the powdered filler in the insulation has an intrinsic resistivity of 104-108 ohm m.

4. An electrical insulation according to any of claims 1-3, c h a r a c t e r i z e d in that the filler-containing poly-mer has a resistivity in excess of 1010 ohm m.

5. An electrical insulation according to any of claims 1-4 c h a r a c t e r i z e d in that the content of powdered filler in the form of chromium oxide, iron oxide, metal phthalo-cyanine or a mixture of at least two substances of these kinds constitutes 10-40% of the total volume of organic polymer and this powdered filler.

6. An electrical insulation of a kind described in any of the preceding claim, c h a r a c t e r i z e d in that it (14) is arranged around a bundle (17) of a plurality of lenghts, arranged side-by-side, of conductor of rectangular cross section for insulating the bundle against a slot (20) in a stator or rotor in an electrical machine, in which the bundle with the surrounding insulation is arranged.

7. An electrical insulation of a kind described in any of claims 1-5, c h a r a c t e r i z e d in that it (26) is arranged between conductor layers (22) in a layer-wound transformer or reactor.

8. An electrical insulation of a kind described in any of claims 1-5, c h a r a c t e r i z e d in that it (33) is arranged in the form of a cast polymer cast around at least part of the core (28) and at least one of the windings (29, 31) in an instrument transformer.

9. An electrical insulation of a kind described in any of claims 1-5, c h a r a c t e r i z e d in that it (43) is arranged between a conductor (40) along part of the extension of the conductor and a grounded casing (41), surrounding the conductor, which is filled with SF6 which together with the insulation insulates the conductor from the casing.

10. An electrical insulation of a kind described in any of claims 1-5, c h a r a c t e r i z e d in that it (52) is arranged between a conductor (50) and a grounded screen (54) in a cable.

11. An electrical insulation according to any of claims 1-9, c h a r a c t e r i z e d in that the organic polymer consists of a thermosetting resin transferred into cured state.

12. An electrical insulation according to any of claims 1-5 and 10, c h a r a c t e r i z e d in that the organic polymer constitutes a linear polymer.

13. An electrical insulation according to claim 12, c h a r a c t e r i z e d in that the linear polymer is cross linked.