CA1189159A - Mineral insulated electric cables - Google Patents
Mineral insulated electric cablesInfo
- Publication number
- CA1189159A CA1189159A CA000409991A CA409991A CA1189159A CA 1189159 A CA1189159 A CA 1189159A CA 000409991 A CA000409991 A CA 000409991A CA 409991 A CA409991 A CA 409991A CA 1189159 A CA1189159 A CA 1189159A
- Authority
- CA
- Canada
- Prior art keywords
- powdered
- sheath
- tube
- filling
- insulated electric
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 229910052500 inorganic mineral Inorganic materials 0.000 title claims abstract description 10
- 239000011707 mineral Substances 0.000 title claims abstract description 10
- -1 polysiloxane Polymers 0.000 claims abstract description 15
- 229920001296 polysiloxane Polymers 0.000 claims abstract description 15
- 125000002496 methyl group Chemical group [H]C([H])([H])* 0.000 claims abstract description 14
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 claims abstract description 9
- 239000000395 magnesium oxide Substances 0.000 claims abstract description 8
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 claims abstract description 7
- 230000035515 penetration Effects 0.000 claims abstract description 7
- 239000011810 insulating material Substances 0.000 claims abstract description 5
- 239000000843 powder Substances 0.000 claims description 28
- 239000004020 conductor Substances 0.000 claims description 21
- 229910052751 metal Inorganic materials 0.000 claims description 5
- 239000002184 metal Substances 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 claims description 4
- 238000003466 welding Methods 0.000 claims description 4
- 238000005452 bending Methods 0.000 claims 1
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 6
- 238000000034 method Methods 0.000 description 5
- 238000000137 annealing Methods 0.000 description 3
- 229910052786 argon Inorganic materials 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 238000010791 quenching Methods 0.000 description 3
- 230000000171 quenching effect Effects 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 238000005299 abrasion Methods 0.000 description 2
- 230000015556 catabolic process Effects 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 239000012809 cooling fluid Substances 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 230000001627 detrimental effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- WTEVQBCEXWBHNA-YFHOEESVSA-N neral Chemical compound CC(C)=CCC\C(C)=C/C=O WTEVQBCEXWBHNA-YFHOEESVSA-N 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- WWYNJERNGUHSAO-XUDSTZEESA-N (+)-Norgestrel Chemical compound O=C1CC[C@@H]2[C@H]3CC[C@](CC)([C@](CC4)(O)C#C)[C@@H]4[C@@H]3CCC2=C1 WWYNJERNGUHSAO-XUDSTZEESA-N 0.000 description 1
- 241000465531 Annea Species 0.000 description 1
- WTEVQBCEXWBHNA-UHFFFAOYSA-N Citral Natural products CC(C)=CCCC(C)=CC=O WTEVQBCEXWBHNA-UHFFFAOYSA-N 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- 229920001213 Polysorbate 20 Polymers 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- WTEVQBCEXWBHNA-JXMROGBWSA-N citral A Natural products CC(C)=CCC\C(C)=C\C=O WTEVQBCEXWBHNA-JXMROGBWSA-N 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000007717 exclusion Effects 0.000 description 1
- 238000005429 filling process Methods 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000000314 lubricant Substances 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- MYWUZJCMWCOHBA-VIFPVBQESA-N methamphetamine Chemical compound CN[C@@H](C)CC1=CC=CC=C1 MYWUZJCMWCOHBA-VIFPVBQESA-N 0.000 description 1
- 238000005192 partition Methods 0.000 description 1
- 239000000256 polyoxyethylene sorbitan monolaurate Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
- H01B7/28—Protection against damage caused by moisture, corrosion, chemical attack or weather
- H01B7/282—Preventing penetration of fluid, e.g. water or humidity, into conductor or cable
- H01B7/285—Preventing penetration of fluid, e.g. water or humidity, into conductor or cable by completely or partially filling interstices in the cable
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A30/00—Adapting or protecting infrastructure or their operation
- Y02A30/14—Extreme weather resilient electric power supply systems, e.g. strengthening power lines or underground power cables
Landscapes
- Insulated Conductors (AREA)
- Manufacturing Of Electric Cables (AREA)
- Processes Specially Adapted For Manufacturing Cables (AREA)
- Resistance Heating (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
In a mineral insulated electric cable there is dispersed within the powdered magnesium oxide insulating material a propor-tion of methyl polysiloxane sufficient to reduce moisture penetration.
In a mineral insulated electric cable there is dispersed within the powdered magnesium oxide insulating material a propor-tion of methyl polysiloxane sufficient to reduce moisture penetration.
Description
-2~
Thi~ invention relates to mineral insulated electric c~bles, that is to say cables of the t~pe co~prising cne or more electIical conductor ~ires enclosed l3ithin a tubular metal s~e~th, co~only of 5 co~per, ~nd insl1la~ed from the sheath by a ~illing of com7~cted po~dered in;ulating material.
It will be unders-tood th~t the term "~neral in~ulated electric cables" is to be understood to include~ in addition to wirin~ cables for the 10 conduckion of electric curIent; Ior general pulpoC,es~
Gables of the construction described above and employed for othex purposes, for example heating cables and thermocouple cables~ ~he invention also includes within its scope the manufacture of such cables.
'The powdered insulating material which is most co~monly used is magnesium oxlde either fused or calcined or as sea-washed magnesia~ and although magnes um oxide has a high electrical breakdown strength when dry the presence of even a small amount 20 of moisture can reduce this significantly~
Consequently the ingress of moisturè is a major problem, particularly in the case of high voltage cables~ and it is therefore recommended that the ends of lengths of cable in store be provided 25 with temporary seals to reduce moisture penetration.
Nevertheless prior to forming a termination in a length of stored cable required for use it is invaria~ly necessary to cut off an appreciable length~ in some cases as much as eighteen inches, from the ends o~ the ~ cable in order to ensure that any aamp powder, which would effect the insulating properties of the cable, is remo~ed. ~his is clearl~ wasteful. Moreover the formed termination needs to provide an effective seal to preven~ any subsequent moisture penetration in 35 useO
AccoIdi~gg therefore 7 to the present inven-tion a mineIal insulated electric cable has ~J~
dispersed within the powdered insulating material between 0.1 and 5.0% by weight of powdered methyl polysiloxane which i5 suffici~nt -to reduce moisture penetration. I'hus a cable having a filling comprising powdered magnesium oxide incorporating only 1% by weight of methyl polysiloxane does not exhibit any significant degree of moisture penetration, even after many weeks storage, without the need for any separate end seals.
~ccordingly a cable in accordance with -the invention can be stored without temporaxy end seals, and when required to be used the end does not require to be cut back further than is necessary to physically form the required terminations, as there is no damp powder which needs to be removed.
Moreover not only does the incorporation of methyl polysiloxane within the filling have no detrimen-tal effect on the electrical insulating properties of the filling, it has in fact, been found to improve the electrical breakdown strength of the filling, particularly at high voltages, due, it is believed, to the exclusion of free moisture throughout the length of the cable.
Preferably the methyl polysiloxane powder has a grain size of be-tween 20 and 200 microns, and lies mainly in the range 30 to 70 microns.
When the me-thyl polysiloxane is incorporated in the filling materia] care should be taken that the temperature of the filling material does not rise above 65C as it is being introduced into the sheath, as it becomes tacky or ~iquid at higher temperatures, which could adversely affec-t the filling process. Where the sheath is conti~.uously formed from a ductile rletal ~tri~ ~cy ~endin the ~tlip into tubular ~o-r~, an~ weldil-~ t`ne ed-es to-etrier, wh.ils-t si~ 21tan~ol~sly introdl~cir!- the fi]lin-~~aterial ~Ind the conduct;or ~ e or -~:ires into tne s~^ce-tfl tlibe ~o formed, lleans t~ l accordin-~ly need to be ~rovided for cooli-.~ the sheeth tube imnedi.Gtely afte~ the ~eld to r vent an undue a-~lount o~ heat beinc~ -tra~s~e~red from -the sheath tube to the filling ma.teri.al as the latter is bein~r fed in.to the tube. Following the introduction of the conductor or conductors and the filling material the diameter of the shea-th tube will usually be reduced by passing it through a series of reduction rollers or dies and annealin~ furnaces in kno~
manner~
~ Conveniently the powder filling is .introduced into 1.5 the sheath tube through a delivery tube having its outlet downstream of the weld, and in such case means ma~ also be provided for cooling the delivery tube, particularly in the re~ion of the weld, and possibly also the conductor wire or wires before the introduction of the latter into the sheath tube.
Conveniently a guide tube for the, or one of the 9 conductor wires extends adjacent to the path of t~avel of the meeting edges of the bent metal strip, and at the welding position the guide tube is formed with an aperture, so that some of the heat from the weld is transferred to the conductor and is ca.rried away ~rom the powder delivery tube by the moving conductor.
~ he use of methyl polysiloxane has the unexpected advantage, however, that its conversion to liouid on being heated, during subseauent reducing and annealin~ processes, causes it to act as a lubrican.t, and this results in a pro-~ nounced reduction in the degree of abrasion of the conductor ; wire or wires and of the inner surface of the ~heath.
Conseguently the pronounced adherence of the fillin~
powder to the conductor wire or wires, as is commonly e~peri-enced with mineral insulated electric cables as manufac-tured hitherto, i9 virtually avoided, and any loose powder on the surfaces of the wire or wires or on -the inner surface o-E the sheath tube can be removed withou-t difficulty when forming a terminationO
One mineral insulated electric cable and the manufacture thereof will now be described by way of example with :reference -to Figuxes 1 to 4 of the accompanying schematic drawinys, in which E'igure 1 represents a -transverse section through the cable, Figure 2 illustrates diagrammatically a sectional elevation of part of one form of apparatus for use in maufacturing the cable, and Figures 3 and 4 represent on an enlarged scale an elevation and a plan section of a portion of the apparatus illustrated in Figure 2.
Referring first to Figure 1 the cable comprises an outer sheath 1 formed from a copper strip bent into tubular form and argon arc welded along the abutting edges. The sheath contains a plurality of conductor wires 2 (in this case two) separated from each other and from the sheath 1 by powdered magnesium oxide
Thi~ invention relates to mineral insulated electric c~bles, that is to say cables of the t~pe co~prising cne or more electIical conductor ~ires enclosed l3ithin a tubular metal s~e~th, co~only of 5 co~per, ~nd insl1la~ed from the sheath by a ~illing of com7~cted po~dered in;ulating material.
It will be unders-tood th~t the term "~neral in~ulated electric cables" is to be understood to include~ in addition to wirin~ cables for the 10 conduckion of electric curIent; Ior general pulpoC,es~
Gables of the construction described above and employed for othex purposes, for example heating cables and thermocouple cables~ ~he invention also includes within its scope the manufacture of such cables.
'The powdered insulating material which is most co~monly used is magnesium oxlde either fused or calcined or as sea-washed magnesia~ and although magnes um oxide has a high electrical breakdown strength when dry the presence of even a small amount 20 of moisture can reduce this significantly~
Consequently the ingress of moisturè is a major problem, particularly in the case of high voltage cables~ and it is therefore recommended that the ends of lengths of cable in store be provided 25 with temporary seals to reduce moisture penetration.
Nevertheless prior to forming a termination in a length of stored cable required for use it is invaria~ly necessary to cut off an appreciable length~ in some cases as much as eighteen inches, from the ends o~ the ~ cable in order to ensure that any aamp powder, which would effect the insulating properties of the cable, is remo~ed. ~his is clearl~ wasteful. Moreover the formed termination needs to provide an effective seal to preven~ any subsequent moisture penetration in 35 useO
AccoIdi~gg therefore 7 to the present inven-tion a mineIal insulated electric cable has ~J~
dispersed within the powdered insulating material between 0.1 and 5.0% by weight of powdered methyl polysiloxane which i5 suffici~nt -to reduce moisture penetration. I'hus a cable having a filling comprising powdered magnesium oxide incorporating only 1% by weight of methyl polysiloxane does not exhibit any significant degree of moisture penetration, even after many weeks storage, without the need for any separate end seals.
~ccordingly a cable in accordance with -the invention can be stored without temporaxy end seals, and when required to be used the end does not require to be cut back further than is necessary to physically form the required terminations, as there is no damp powder which needs to be removed.
Moreover not only does the incorporation of methyl polysiloxane within the filling have no detrimen-tal effect on the electrical insulating properties of the filling, it has in fact, been found to improve the electrical breakdown strength of the filling, particularly at high voltages, due, it is believed, to the exclusion of free moisture throughout the length of the cable.
Preferably the methyl polysiloxane powder has a grain size of be-tween 20 and 200 microns, and lies mainly in the range 30 to 70 microns.
When the me-thyl polysiloxane is incorporated in the filling materia] care should be taken that the temperature of the filling material does not rise above 65C as it is being introduced into the sheath, as it becomes tacky or ~iquid at higher temperatures, which could adversely affec-t the filling process. Where the sheath is conti~.uously formed from a ductile rletal ~tri~ ~cy ~endin the ~tlip into tubular ~o-r~, an~ weldil-~ t`ne ed-es to-etrier, wh.ils-t si~ 21tan~ol~sly introdl~cir!- the fi]lin-~~aterial ~Ind the conduct;or ~ e or -~:ires into tne s~^ce-tfl tlibe ~o formed, lleans t~ l accordin-~ly need to be ~rovided for cooli-.~ the sheeth tube imnedi.Gtely afte~ the ~eld to r vent an undue a-~lount o~ heat beinc~ -tra~s~e~red from -the sheath tube to the filling ma.teri.al as the latter is bein~r fed in.to the tube. Following the introduction of the conductor or conductors and the filling material the diameter of the shea-th tube will usually be reduced by passing it through a series of reduction rollers or dies and annealin~ furnaces in kno~
manner~
~ Conveniently the powder filling is .introduced into 1.5 the sheath tube through a delivery tube having its outlet downstream of the weld, and in such case means ma~ also be provided for cooling the delivery tube, particularly in the re~ion of the weld, and possibly also the conductor wire or wires before the introduction of the latter into the sheath tube.
Conveniently a guide tube for the, or one of the 9 conductor wires extends adjacent to the path of t~avel of the meeting edges of the bent metal strip, and at the welding position the guide tube is formed with an aperture, so that some of the heat from the weld is transferred to the conductor and is ca.rried away ~rom the powder delivery tube by the moving conductor.
~ he use of methyl polysiloxane has the unexpected advantage, however, that its conversion to liouid on being heated, during subseauent reducing and annealin~ processes, causes it to act as a lubrican.t, and this results in a pro-~ nounced reduction in the degree of abrasion of the conductor ; wire or wires and of the inner surface of the ~heath.
Conseguently the pronounced adherence of the fillin~
powder to the conductor wire or wires, as is commonly e~peri-enced with mineral insulated electric cables as manufac-tured hitherto, i9 virtually avoided, and any loose powder on the surfaces of the wire or wires or on -the inner surface o-E the sheath tube can be removed withou-t difficulty when forming a terminationO
One mineral insulated electric cable and the manufacture thereof will now be described by way of example with :reference -to Figuxes 1 to 4 of the accompanying schematic drawinys, in which E'igure 1 represents a -transverse section through the cable, Figure 2 illustrates diagrammatically a sectional elevation of part of one form of apparatus for use in maufacturing the cable, and Figures 3 and 4 represent on an enlarged scale an elevation and a plan section of a portion of the apparatus illustrated in Figure 2.
Referring first to Figure 1 the cable comprises an outer sheath 1 formed from a copper strip bent into tubular form and argon arc welded along the abutting edges. The sheath contains a plurality of conductor wires 2 (in this case two) separated from each other and from the sheath 1 by powdered magnesium oxide
3, the powder being compacted around the conductors, following the introduction of the powder and conductors into the formed sheath, by a series of reduction stages, each followed by an annealing and quenching stage in known manner. In accordance with the invention the magnesium oxide powder contains, dispersed within it, approximately 1% by weight of powdered methyl polysiloxane having a grain si~e of between thirty and seventy microns. The methyl polysiloxane even in this small proportion has been found to impart a '.
.
hydrophobi.c qua~.ity to the filling which resists the penetration of moisture, and prevents any significant deterioration of the insulating properties of the filling adjacent severed ends of the cable for long periods without the need to provide additional seals, either during storage or when forming subsequent termina-tions.
Consequently when forming a termination it is not necessary to cut back the end of the cable furthe:r than is necessa:ry to physically form the termination.
The cable may be manufactured by a process generally similar to that described in Uni-ted Kingdom Patent No. 2,0111,260, and as illustrated i.n part in ~igures 2 to Ll.
In such a process the cable sheath 1 is formed in a continuous manner from a thoroughly degreased copper strip la, by means of a tube forming machine (not shown) which bends the downwardly fed strip into tubular form, and an argon arc welding head 4 which welds the abutting edges of the strip. The formed sheath tube 1 is fed vertically downwards to a reduction machine, which reduces the diameter of the tube and compacts the filling powder 3 around the conductor wires 2. The reduced cube is then fed through an annea]ing f`urnace, and then through a water quenching tank in which the cable is turned in a catenary curve to continue travelling horizontally through further reduction machines, annealing furnaces and quenching tanks. The reduction machines and associated equipment have, however~ been omitte~ from the drawing for simplicity.
The conductor wires 2, which are also thoroughly 5~
degreasedg are continuously fed into the sheath tube 1 as it is being formed through a pair of guide tubes 5, 6 rigidly located in desired positions within a powder delivery tube 7 through w:hich the filling powder, consi.sting of magnesium oxide with the methyl po]ysiloxane additive dispersed within it are introduced i.nto the sheath tube 1. The powder filling is introduced into the delivery tube 7 from a hopper 8 kept replenished from a vibratory co-nveyor supplied, in turn, from a powder reservoir.
The lower ends of the powder delivery tube 7 and of the guide tubes 5, 6 terminate below the weld position so that the filling powder is effectively introduced into the formed and already welded tube, and is thereby prevented from contaminating the weld. Surrounding the sheath 1, just below the wel.d position and above the lower end of the powder delivery tube 7, is a jacket 9 through which a cooling fluid, for example water, is passed to reduce the amount of heat which is transmitted to the powder filling by the sheath. In addition the wall of the powder delivery tube 7 adjacent the weld position is formed with a slot 10 as is the adjacent guide tube 5. The slots 10 and 11 in the delivery tube 7 and guide tube 5 respectively are in alignment, and their surrounding edges are soldered together to pre-vent escape of the powdered filling at that position. The one of the conductor wires 2 which is within the guide tube 5 is thus exposed to the weld, and accordingly acts as a heat sink to carry away heat from the weld region, as described in more detail in United Kingdom Patent No. 2,0~1,260.
Gooling is necessary when forming a cable by the process i9 described as it is essential to maintain the temperature of the powder filling below 65C until it leaves the delivery tube 7~
because above this temperature the methyl polysiloxane becomes tacky and eventually liquefies as i.ts temperature is further increased, and this could interfere with the delivery of the powder or even clog the outlet from the delivery tube complete].y.
-7a-"~
--8~
For thi.s reason the filling powder is preferably ~aintained at a .suitably low temperature;
for e~ample less than 50C9 prior to being introduced into the delivery tube 7, and in addition the condllctor 5 wires 2 ~re also cooled, for exl~ple by ~rgon at low te.nperature~ before their introduction into the respective guide tubes 5, 60 The powder delivery tube 7 nlay~ if necessary~ also be provided, as shol~rn~ with spaced double walls 12, 13 the space between which is 10 separated~ by longitudinal partitions 1~ into two flow paths 15, 16 communicating at the lower end of the tube 7. In operation a cooling fluid, possibly water or freon or possibl~ argon at a suitably low ternperature is passed down one flow path~ e.g. 15 and returns vi.a 15 the other flow path 16.
~ fter delivery into the formed sheath tube 7~
heating of the powder filling will not give rise to any difficulties, and it has~ in fact, been found that the uefaction of the methyl polysiloxane during the 20 subsequent reduction and annealing stages has a beneficial~ rather than a detrimental, effect. It is : believed that the liquid meth~l polysiloxane, which reverts again to its solid state on cooling below 65C~
acts as a lubricant which prevents abrasion of the 25 surfaces of the conductor wires 2 and the internal surface of the sheath tube 1 duri~g the reduction stages, as inspection of a completed cable sho~Js that these surfaces remain smooth, and adhesion of the powder to the surfaces~ as is commonly experienced with 30 mineral insulated electric cables formed by conventional processes, is virtually absent~ thus facilitating the formatio~ of subse~uent terminationsO
.
hydrophobi.c qua~.ity to the filling which resists the penetration of moisture, and prevents any significant deterioration of the insulating properties of the filling adjacent severed ends of the cable for long periods without the need to provide additional seals, either during storage or when forming subsequent termina-tions.
Consequently when forming a termination it is not necessary to cut back the end of the cable furthe:r than is necessa:ry to physically form the termination.
The cable may be manufactured by a process generally similar to that described in Uni-ted Kingdom Patent No. 2,0111,260, and as illustrated i.n part in ~igures 2 to Ll.
In such a process the cable sheath 1 is formed in a continuous manner from a thoroughly degreased copper strip la, by means of a tube forming machine (not shown) which bends the downwardly fed strip into tubular form, and an argon arc welding head 4 which welds the abutting edges of the strip. The formed sheath tube 1 is fed vertically downwards to a reduction machine, which reduces the diameter of the tube and compacts the filling powder 3 around the conductor wires 2. The reduced cube is then fed through an annea]ing f`urnace, and then through a water quenching tank in which the cable is turned in a catenary curve to continue travelling horizontally through further reduction machines, annealing furnaces and quenching tanks. The reduction machines and associated equipment have, however~ been omitte~ from the drawing for simplicity.
The conductor wires 2, which are also thoroughly 5~
degreasedg are continuously fed into the sheath tube 1 as it is being formed through a pair of guide tubes 5, 6 rigidly located in desired positions within a powder delivery tube 7 through w:hich the filling powder, consi.sting of magnesium oxide with the methyl po]ysiloxane additive dispersed within it are introduced i.nto the sheath tube 1. The powder filling is introduced into the delivery tube 7 from a hopper 8 kept replenished from a vibratory co-nveyor supplied, in turn, from a powder reservoir.
The lower ends of the powder delivery tube 7 and of the guide tubes 5, 6 terminate below the weld position so that the filling powder is effectively introduced into the formed and already welded tube, and is thereby prevented from contaminating the weld. Surrounding the sheath 1, just below the wel.d position and above the lower end of the powder delivery tube 7, is a jacket 9 through which a cooling fluid, for example water, is passed to reduce the amount of heat which is transmitted to the powder filling by the sheath. In addition the wall of the powder delivery tube 7 adjacent the weld position is formed with a slot 10 as is the adjacent guide tube 5. The slots 10 and 11 in the delivery tube 7 and guide tube 5 respectively are in alignment, and their surrounding edges are soldered together to pre-vent escape of the powdered filling at that position. The one of the conductor wires 2 which is within the guide tube 5 is thus exposed to the weld, and accordingly acts as a heat sink to carry away heat from the weld region, as described in more detail in United Kingdom Patent No. 2,0~1,260.
Gooling is necessary when forming a cable by the process i9 described as it is essential to maintain the temperature of the powder filling below 65C until it leaves the delivery tube 7~
because above this temperature the methyl polysiloxane becomes tacky and eventually liquefies as i.ts temperature is further increased, and this could interfere with the delivery of the powder or even clog the outlet from the delivery tube complete].y.
-7a-"~
--8~
For thi.s reason the filling powder is preferably ~aintained at a .suitably low temperature;
for e~ample less than 50C9 prior to being introduced into the delivery tube 7, and in addition the condllctor 5 wires 2 ~re also cooled, for exl~ple by ~rgon at low te.nperature~ before their introduction into the respective guide tubes 5, 60 The powder delivery tube 7 nlay~ if necessary~ also be provided, as shol~rn~ with spaced double walls 12, 13 the space between which is 10 separated~ by longitudinal partitions 1~ into two flow paths 15, 16 communicating at the lower end of the tube 7. In operation a cooling fluid, possibly water or freon or possibl~ argon at a suitably low ternperature is passed down one flow path~ e.g. 15 and returns vi.a 15 the other flow path 16.
~ fter delivery into the formed sheath tube 7~
heating of the powder filling will not give rise to any difficulties, and it has~ in fact, been found that the uefaction of the methyl polysiloxane during the 20 subsequent reduction and annealing stages has a beneficial~ rather than a detrimental, effect. It is : believed that the liquid meth~l polysiloxane, which reverts again to its solid state on cooling below 65C~
acts as a lubricant which prevents abrasion of the 25 surfaces of the conductor wires 2 and the internal surface of the sheath tube 1 duri~g the reduction stages, as inspection of a completed cable sho~Js that these surfaces remain smooth, and adhesion of the powder to the surfaces~ as is commonly experienced with 30 mineral insulated electric cables formed by conventional processes, is virtually absent~ thus facilitating the formatio~ of subse~uent terminationsO
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A mineral insulated electric cable comprising at least one electrical conductor wire enclosed within a tubular metal sheath and insulated from the sheath by a filling of compacted powdered insulating material consisting of powdered magnesium oxide, and having dispersed within the powdered insulating material, between 0.1 and 5.0% by weight of powdered methyl polysiloxane which is sufficient to reduce moisture penetration.
2. A mineral insulated electric cable according to Claim 1 wherein the methyl polysiloxane powder has a grain size of between 20 and 200 microns, and lies mainly in the range 30 to 70 microns.
3. The manufacture of a mineral insulated electric cable according to Claim 1 in which the sheath is formed continuously from a ductile metal strip by bending the strip into tubular form and welding the edges together, whilst simultaneously introducing the conductor wire or wires and a filling comprising powdered magnesium oxide with a proportion of powdered methyl polysiloxane dispersed within it, into the sheath so formed, wherein the powdered filling is introduced into the sheath tube through a delivery tube having its outlet downstream of the weld, and wherein the delivery tube and sheath tube are cooled in the region of and immediately following the weld respectively to maintain the powdered filling within the delivery tube at a temperature of not more than 65°C.
4. The manufacture of a mineral insulated electric cable according to Claim 3 wherein a guide tube for the, or one of the, conductor wires extends adjacent to the path of travel of the meeting edges of the bent metal strip, and at the welding position the guide tube is formed with an aperture, so that some of the heat from the weld is transferred to the conductor and is carried away from the powder delivery tube by the moving conductor.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8128518 | 1981-09-21 | ||
| GB8128518 | 1981-09-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1189159A true CA1189159A (en) | 1985-06-18 |
Family
ID=10524652
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000409991A Expired CA1189159A (en) | 1981-09-21 | 1982-08-24 | Mineral insulated electric cables |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS5861506A (en) |
| AU (1) | AU553229B2 (en) |
| CA (1) | CA1189159A (en) |
| DE (1) | DE3234766A1 (en) |
| FR (1) | FR2513428A1 (en) |
| IT (1) | IT1155932B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4491822A (en) * | 1981-11-02 | 1985-01-01 | Xco International, Inc. | Heat sensitive cable |
| CN108630349B (en) * | 2018-04-26 | 2019-11-05 | 东阳市天齐知识产权运营有限公司 | Composite radiating cable |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2514578B2 (en) * | 1975-04-03 | 1978-09-07 | Fa. Fritz Eichenauer, 6744 Kandel | Refractory, granular investment material for electric heating coils |
| JPS54135397A (en) * | 1978-04-12 | 1979-10-20 | Arita Kosei | Preparation of insulating powder for heating unit |
| US4269639A (en) * | 1979-02-08 | 1981-05-26 | Lewis Robert J | Manufacture of mineral insulated cables |
| JPS5641606A (en) * | 1979-09-10 | 1981-04-18 | Okazaki Mfg Co Ltd | Miicable and production thereof |
| JPS588806B2 (en) * | 1979-11-19 | 1983-02-17 | 佐野 茂樹 | Method and device for covering the entire surface of the ridges with a film at the same time as forming the ridges |
| JPS588806U (en) * | 1981-07-10 | 1983-01-20 | 日立電線株式会社 | heat resistant wire |
-
1982
- 1982-08-24 CA CA000409991A patent/CA1189159A/en not_active Expired
- 1982-08-25 AU AU87581/82A patent/AU553229B2/en not_active Ceased
- 1982-09-20 DE DE19823234766 patent/DE3234766A1/en active Granted
- 1982-09-20 FR FR8215815A patent/FR2513428A1/en active Granted
- 1982-09-20 IT IT68113/82A patent/IT1155932B/en active
- 1982-09-21 JP JP57163275A patent/JPS5861506A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| AU8758182A (en) | 1983-03-31 |
| DE3234766A1 (en) | 1983-03-31 |
| IT1155932B (en) | 1987-01-28 |
| FR2513428A1 (en) | 1983-03-25 |
| DE3234766C2 (en) | 1992-02-13 |
| JPS5861506A (en) | 1983-04-12 |
| JPH0328766B2 (en) | 1991-04-22 |
| AU553229B2 (en) | 1986-07-10 |
| FR2513428B3 (en) | 1984-08-24 |
| IT8268113A0 (en) | 1982-09-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEC | Expiry (correction) | ||
| MKEX | Expiry |