US3527874A - Crosslinked polyethylene oil filled high voltage powered cable - Google Patents

Crosslinked polyethylene oil filled high voltage powered cable Download PDF

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US3527874A
US3527874A US667778A US3527874DA US3527874A US 3527874 A US3527874 A US 3527874A US 667778 A US667778 A US 667778A US 3527874D A US3527874D A US 3527874DA US 3527874 A US3527874 A US 3527874A
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oil
cable
crosslinked polyethylene
conductor
high voltage
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US667778A
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Toshiyuki Hayami
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Sumitomo Electric Industries Ltd
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Sumitomo Electric Industries Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B9/00—Power cables
    • H01B9/06—Gas-pressure cables; Oil-pressure cables; Cables for use in conduits under fluid pressure
    • H01B9/0611—Oil-pressure cables

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  • the present invention is directed to the provision of high voltage power cables of excellent electrical properties, preventing the generation of corona at such electrically weak points.
  • This invention is characterized in that the core is provided with a crosslinked polyethylene insulating layer, and the interfaces of the conductor and this insulating layer are maintained filled with silicon oil.
  • a semi-electroconductive layer is provided on the outside of the insulating layer.
  • a second characteristic of the present invention is as follows: Since silicon oil can hardly be absorbed in crosslinked polyethylene insulation, it may fail to give sufficient reinforcement to the weak points caused by voids and foreign bodies in the insulation, even though it can reinforce the weak points on the interfaces of the insulation and the conductor. n the other hand, hydrocarbon insulating oils such as polybutane, etc. are not good for practical use in cables because they cause crosslinked polyethylene to remarkably swell. In view of the above, it is the object of the present invention to obtain cables which are excellent both electrically and mechanically by giving full display to the merits of the two kinds of oil through mixing of a hydrocarbon oil and silicon oil at a certain ratio.
  • the present invention is characterized in that when provision is made for a cable core having a central conductor and an insulating layer, the interfaces of the conductor and the insulating layer are filled with a mixed oil consisting of silicon oil and hydrocarbon oil and a semi-electroconductive layer is provided on the outside of the insulating layer.
  • FIG. 1 is a sectional View of a power cable embodying the embodiments of the present invention.
  • FIG. 2 shows the V-t characteristic curves of the cable of this invention and that of a conventional cable without oil.
  • FIG. 3 shows the V-t characteristic curve of another embodiment of the present invention.
  • FIG. 1 there is shown a hollow conductor 1 having an oil passage in its interior, and a cable insulating layer 2 formed integrally on the conductor by extruding crosslinked polyethylene insulation over the conductor.
  • a semielectroconductive layer 3 is placed on the outside of the cable and is formed by extruding semi-electroconductive polyolefine rendered electroconductive, for example by addition of carbon black.
  • a metallic shielding layer 4 is made by winding copper tape or extruding lead, aluminum or the like over the semi-electroconductive layer 3.
  • An outer anti-corrosion layer of polyvinyl chloride, chloroprene or the like is provided over the shielding layer 4.
  • Silicon oil 6 is provided in the interior of the conductor 1.
  • the method of manufacturing the cable of the present invention may be as follows: An uncrosslinked polyethylene insulating layer 2 containing a crosslinking agent, such as di-a-cumyl peroxide (-D.C.P.), is extruded onto a conductor to cover the same, and crosslinking is caused to take place at a high temperature under high pressure, such as, respectively, 150 C. or higher and 10 atmospheric pressures or more. An outer sheath is then applied over cable cores made in the above-mentioned way, and then silicon oil is poured into one end of the conductor. For pouring the oil into the conductor, it is preferable to first previously evacuate the conductor interior with the object of filling the whole of the cable interior with the silicon oil.
  • the semi-electroconductive layer 3 on the outside may be extruded together with the insulating layer 2 or may be applied after the insulating layer 2 has been crosslinked.
  • the conductor be a hollow conductor.
  • a decision as to whether a hollow conductor or an ordinary conductor should be used should be made after considering the cable size, length, etc.
  • the essential requirement is that silicon oil be present at all times between the conductor and the insulation.
  • the oil pressure regulating device As to the oil pressure regulating device, a suitable one may be selected after considering the installation condition of the cable, the quantity of the oil, etc. In some cases no such device is necessary.
  • FIG. 2 shows a comparison between the V-t characteristic curve of the cable of the present invention and that of a crosslinked polyethylene cable without oil filling.
  • the specimens are crosslinked polyethylene cable, 100 mm. with an insulation thickness of a 3 mm.
  • Curve A is for the cable of the present invention and the curve B for the cable without oil filling.
  • the degree of swelling of the crosslinked polyethylene, the insulation layer 2 for the cables of the present invention was measured by immersing it in silicon oil having a viscosity of 10 centistokes heated to weather temperature, C., C., C. and C. According to the results, the degree of swelling was 0.2% or less even in the case where the oil was heated to 150 C. (The limit for weight ratio measurement is 0.2% or more.)
  • tan 8 stands for the dielectric tangent and p the specific volume resistivity.
  • the cables will have a longer life for high voltage use. Furthermore, as silicon oil is used, the insulation is not swollen due to the oil even at a high temperature, so that thermally stable cables may be obtained in the case of the present invention. Also, as silicon oil has almost the same dielectric characteristics as crosslinked polyethylene, the dielectric properties of the insulation are not impaired by the introduction of the oil. Thus it is possible to obtain cables having good dielectric properties of dielectric constant (e), dielectric tangent (tan 6), etc. The cables have also a great advantage of a very large current carrying capacity, the product of dielectric constant and dielectric tangent being 1/ 10-1/ 30 times that of oil-filled paper cables. It
  • Crosslinked polyethylene above 300 hours: 10 of 10 specimens free 1polyethylene subjected to crossfrom cracking.
  • the cable made according to the present invention has excellent dielectric characteristics and has a good stability, it being possible to take a higher design stress than in the case of the plastic cables heretofore in use. It is therefore possible to apply the invention to high voltage power cables of 275 kv. or 500 kv. class.
  • Another embodimentof the present invention involves the filling of the cable conductor with a mixed oil of silicon oil and a hydrocarbon oil instead of silicon oil used in the first embodiment.
  • the degree of swelling of FIG. 3 shows a comparison of the V-t characteristic of crosslinked polyethylene, 3 mm. thickness and mm.
  • Curve A is for the cable according to the present invention filled with silicon oil with 5% hydrocarbon oil
  • curve B for the cable filled with silicon oil only
  • curve C is for the cable without any oil filling. From the results shown in FIG. 3, it can be seen that the cable according to the present invention having curve A is superior toB and C with respect to the Vt characteristic.
  • the cables of the present invention have better electrical properties because reinforcement can be provided not only in connection with electrically weak points on the interface between the conductor and the insulation but also in connection with electrically weak points caused by bubbles and foreign bodies which are liable to take place in the insulation by providing a mixture of silicon oil and hydrocarbon oil to continually maintain on the conductor side of a crosslinked polyethylene cable formed in one body by an extruder.
  • the quantity of a hydrocarbon oil added to silicon oil is preferably between 1% and 30%, inclusive.
  • a conductor having improved dielectric properties, a conductor, a crosslinked polyethylene insulating layer extruded on said conductor, said cable characterized by an insulation oil mixture of silicon oil with a hydrocarbon oil content in the range of 1 to 30 percent supplied interior of said insulating layer to maintain said oil mixture in continuous attendance at the interface between said conductor and the inner surface of said insulating layer to prevent the generation of corona.
  • the high voltage cable of claim 1 characterized by a semi-electroconductive layer extruded over said insu lating layer.
  • the high voltage cable of claim 1 characterized in that said conductor is stranded and has a hollow interior to receive said insulation oil mixture.

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Description

United. States Patent 3,527,874 CROSSLINKED POLYETHYLENE OIL FILLED HIGH VOLTAGE POWERED CABLE Toshiyuki Hayami, Osaka, Japan, assignor to Sumltomo Electric Industries, Ltd., Osaka, Japan, a company of Ja an F Filed Sept. 14, 1967, Ser. No. 667,778 Claims priority, application Japan, Sept. 27, 1966, 41/90,009, 41/90,010 Int. Cl. H0111 7/34, 9/36 U.S. Cl. 174-24 3 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to an improvement in crosslinked polyethylene high voltage cables.
With crosslinked polyethylene high voltage power cable cores manufactured by the extrusion process, it is not possible to completely eliminate gaps and injuries on the interface between the conductor and the insulation, or small voids formed in the insulation, or foreign bodies which find their way into the cable, etc., so that there may develop electrically weak points where the corona effect takes place upon application of a high voltage to the cable and, as a result, causes insulation breakdown.
The present invention is directed to the provision of high voltage power cables of excellent electrical properties, preventing the generation of corona at such electrically weak points.
This invention is characterized in that the core is provided with a crosslinked polyethylene insulating layer, and the interfaces of the conductor and this insulating layer are maintained filled with silicon oil. A semi-electroconductive layer is provided on the outside of the insulating layer.
A second characteristic of the present invention is as follows: Since silicon oil can hardly be absorbed in crosslinked polyethylene insulation, it may fail to give sufficient reinforcement to the weak points caused by voids and foreign bodies in the insulation, even though it can reinforce the weak points on the interfaces of the insulation and the conductor. n the other hand, hydrocarbon insulating oils such as polybutane, etc. are not good for practical use in cables because they cause crosslinked polyethylene to remarkably swell. In view of the above, it is the object of the present invention to obtain cables which are excellent both electrically and mechanically by giving full display to the merits of the two kinds of oil through mixing of a hydrocarbon oil and silicon oil at a certain ratio.
That is to say, the present invention is characterized in that when provision is made for a cable core having a central conductor and an insulating layer, the interfaces of the conductor and the insulating layer are filled with a mixed oil consisting of silicon oil and hydrocarbon oil and a semi-electroconductive layer is provided on the outside of the insulating layer.
Other objects and advantages appear hereinafter in the following description and claims.
The accompanying drawings show, for the purpose of exemplification without limiting the invention or the Patented Sept. 8, 1970 "ice claims thereto, certain practical embodiments illustrating the principles of this invention wherein:
FIG. 1 is a sectional View of a power cable embodying the embodiments of the present invention.
FIG. 2 shows the V-t characteristic curves of the cable of this invention and that of a conventional cable without oil.
FIG. 3 shows the V-t characteristic curve of another embodiment of the present invention.
In FIG. 1, there is shown a hollow conductor 1 having an oil passage in its interior, and a cable insulating layer 2 formed integrally on the conductor by extruding crosslinked polyethylene insulation over the conductor. A semielectroconductive layer 3 is placed on the outside of the cable and is formed by extruding semi-electroconductive polyolefine rendered electroconductive, for example by addition of carbon black. A metallic shielding layer 4 is made by winding copper tape or extruding lead, aluminum or the like over the semi-electroconductive layer 3. An outer anti-corrosion layer of polyvinyl chloride, chloroprene or the like is provided over the shielding layer 4. Silicon oil 6 is provided in the interior of the conductor 1.
The method of manufacturing the cable of the present invention may be as follows: An uncrosslinked polyethylene insulating layer 2 containing a crosslinking agent, such as di-a-cumyl peroxide (-D.C.P.), is extruded onto a conductor to cover the same, and crosslinking is caused to take place at a high temperature under high pressure, such as, respectively, 150 C. or higher and 10 atmospheric pressures or more. An outer sheath is then applied over cable cores made in the above-mentioned way, and then silicon oil is poured into one end of the conductor. For pouring the oil into the conductor, it is preferable to first previously evacuate the conductor interior with the object of filling the whole of the cable interior with the silicon oil. The semi-electroconductive layer 3 on the outside may be extruded together with the insulating layer 2 or may be applied after the insulating layer 2 has been crosslinked.
It is not always necessary that the conductor be a hollow conductor. A decision as to whether a hollow conductor or an ordinary conductor should be used should be made after considering the cable size, length, etc. The essential requirement is that silicon oil be present at all times between the conductor and the insulation.
As to the oil pressure regulating device, a suitable one may be selected after considering the installation condition of the cable, the quantity of the oil, etc. In some cases no such device is necessary.
FIG. 2 shows a comparison between the V-t characteristic curve of the cable of the present invention and that of a crosslinked polyethylene cable without oil filling. The specimens are crosslinked polyethylene cable, 100 mm. with an insulation thickness of a 3 mm., Curve A is for the cable of the present invention and the curve B for the cable without oil filling.
The degree of swelling of the crosslinked polyethylene, the insulation layer 2 for the cables of the present invention, was measured by immersing it in silicon oil having a viscosity of 10 centistokes heated to weather temperature, C., C., C. and C. According to the results, the degree of swelling was 0.2% or less even in the case where the oil was heated to 150 C. (The limit for weight ratio measurement is 0.2% or more.)
It was also found that the electrical properties (e tan 6 p) of crosslinked polyethylene immersed in silicon oil for one month remained entirely unchanged as compared with the same properties before immersion. In the above formula e stands for the dielectric constant,
tan 8 stands for the dielectric tangent and p the specific volume resistivity.
crosslinked polyethylene immersed in various oils is shown in Table II below.
TAB LE II Hydrocarbon oil (polybutane. Silicon oil Silicon oil insulatm g 011 for I containing 3% containing oil-filled cables) Sihcon oil hydrocarbon oil hydrocarbon oil Degree of swelling at 80 0.... 2-3 times Almost no swell- 3 10 }ng)(0.2% or ess The construction according to the present invention being as described above, silicon oil fills up thin layer gaps which may be present due to poor adhesion between conductor and insulation, scars which may exist on the conductor, etc., so that corona effect does not take place in interface between the conductor and the insulating layer. Cables having good properties with respect to high voltage applications are thus obtained, and it is possible to make the design stress higher than in the case of plastic cables without oil. The cables will have a longer life for high voltage use. Furthermore, as silicon oil is used, the insulation is not swollen due to the oil even at a high temperature, so that thermally stable cables may be obtained in the case of the present invention. Also, as silicon oil has almost the same dielectric characteristics as crosslinked polyethylene, the dielectric properties of the insulation are not impaired by the introduction of the oil. Thus it is possible to obtain cables having good dielectric properties of dielectric constant (e), dielectric tangent (tan 6), etc. The cables have also a great advantage of a very large current carrying capacity, the product of dielectric constant and dielectric tangent being 1/ 10-1/ 30 times that of oil-filled paper cables. It
is well known that crosslinked polyethylene having netted molecular structure as a result of molecular cross-linking has a greater resistance to heat than polyethylene. In the case of oil-filled cables like that of the present invention, the property to resist environmental stress cracking (E.S.C.) due to ambient medium is a problem. However, there is no need for concern in this connection because crosslinked polyethylene is far superior to polyethylene in this respect. As a result it enhances the dependability of the cables.
The Table I below shows the result of tests to compare the E.S.C. of polyethylene and crosslinked polyethylene.
mens cracked. Crosslinked polyethylene (above 300 hours: 10 of 10 specimens free 1polyethylene subjected to crossfrom cracking.
lllfilng.
The tests were made by immersing in silicon oil of 50 C. the specimens of polyethylene and crosslinked polyethylene which had been bent to a certain shape and measuring the time that passed before the specimens cracked. From the test results shown in the above Table I, it can be seen that crosslinked polyethylene has excellent resistance to E.S.C.
As described above, the cable made according to the present invention has excellent dielectric characteristics and has a good stability, it being possible to take a higher design stress than in the case of the plastic cables heretofore in use. It is therefore possible to apply the invention to high voltage power cables of 275 kv. or 500 kv. class.
Another embodimentof the present invention involves the filling of the cable conductor with a mixed oil of silicon oil and a hydrocarbon oil instead of silicon oil used in the first embodiment. The degree of swelling of FIG. 3 shows a comparison of the V-t characteristic of crosslinked polyethylene, 3 mm. thickness and mm. Curve A is for the cable according to the present invention filled with silicon oil with 5% hydrocarbon oil, curve B for the cable filled with silicon oil only, and curve C is for the cable without any oil filling. From the results shown in FIG. 3, it can be seen that the cable according to the present invention having curve A is superior toB and C with respect to the Vt characteristic.
As previously explained, the cables of the present invention have better electrical properties because reinforcement can be provided not only in connection with electrically weak points on the interface between the conductor and the insulation but also in connection with electrically weak points caused by bubbles and foreign bodies which are liable to take place in the insulation by providing a mixture of silicon oil and hydrocarbon oil to continually maintain on the conductor side of a crosslinked polyethylene cable formed in one body by an extruder.
. The quantity of a hydrocarbon oil added to silicon oil is preferably between 1% and 30%, inclusive.
I claim:
1. In a high voltage cable having improved dielectric properties, a conductor, a crosslinked polyethylene insulating layer extruded on said conductor, said cable characterized by an insulation oil mixture of silicon oil with a hydrocarbon oil content in the range of 1 to 30 percent supplied interior of said insulating layer to maintain said oil mixture in continuous attendance at the interface between said conductor and the inner surface of said insulating layer to prevent the generation of corona.
2. The high voltage cable of claim 1 characterized by a semi-electroconductive layer extruded over said insu lating layer.
3. The high voltage cable of claim 1 characterized in that said conductor is stranded and has a hollow interior to receive said insulation oil mixture.
References Cited UNITED STATES PATENTS 3,077,510 2/1963 Olds 174-25 3,244,800 4/1966 McLaughlin et al. 174-110 3,329,764 7/1967 Tanges 17474 3,297,819 1/1967 Wetmore 174l27 3,078,333 2/1963 Kang 174-26 X 2,377,689 6/1945 Hyde l7425 X FOREIGN PATENTS 697,963 11/1964 Canada.
940,269" 10/ 1963 Great Britain.
958,418 5/ 1964 Great Britain.
OTHER REFERENCES Insulating Materials For Design and Engineering Practice, John Wiley & Sons, Inc., 1962, pp. 241-243.
LARAMIE E. ASKIN, Primary Examiner A. T. GRIMLEY, Assistant Examiner US Cl. X.R. 174-15, 102,
US667778A 1966-09-27 1967-09-14 Crosslinked polyethylene oil filled high voltage powered cable Expired - Lifetime US3527874A (en)

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4092488A (en) * 1975-10-24 1978-05-30 Sumitomo Electric Industries, Ltd. Connection or terminal portions for cross-linked polyethylene cables
US4483808A (en) * 1982-02-18 1984-11-20 At&T Technologies, Inc. Methods of making a compositely insulated conductor having a layer of irradiation cross-linked polymeric material
US4845309A (en) * 1987-04-23 1989-07-04 Dow Corning Corporation Silicone water block for electrical cables
US4961961A (en) * 1987-04-23 1990-10-09 Dow Corning Corporation Silicone water block for electrical cable
US4978694A (en) * 1987-04-23 1990-12-18 Dow Corning Corporation Silicone water block for electrical cables
US5200234A (en) * 1991-12-16 1993-04-06 Dow Corning Corporation Method for restoring underground electrical cable
US20100314022A1 (en) * 2008-02-20 2010-12-16 Abb Research Ltd. Method for providing an insulated electric high voltage dc cable or a high voltage dc termination or joint
US20110005805A1 (en) * 2009-07-08 2011-01-13 Hitachi Cable, Ltd. Cable

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0101768B1 (en) * 1982-08-25 1986-08-20 Cable Technology Laboratories, Inc. Extension of cable life

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2377689A (en) * 1943-05-17 1945-06-05 Corning Glass Works Dielectric composition
US3077510A (en) * 1959-06-02 1963-02-12 Anaconda Wire & Cable Co High voltage power cable
US3078333A (en) * 1963-02-19 High voltage power cable
GB940269A (en) * 1959-02-20 1963-10-30 Gen Electric Improvements relating to electric cables
GB958418A (en) * 1961-12-20 1964-05-21 Ass Elect Ind Improvements relating to electric cables
CA697963A (en) * 1964-11-17 Anaconda Wire And Cable Company High voltage electrical apparatus
US3244800A (en) * 1960-06-23 1966-04-05 Amp Inc Corona-free high voltage cable
US3297819A (en) * 1964-08-10 1967-01-10 Raychem Corp Heat unstable covering
US3329764A (en) * 1965-05-17 1967-07-04 Jr John H Tanges Conductive plastic cable shield

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3078333A (en) * 1963-02-19 High voltage power cable
CA697963A (en) * 1964-11-17 Anaconda Wire And Cable Company High voltage electrical apparatus
US2377689A (en) * 1943-05-17 1945-06-05 Corning Glass Works Dielectric composition
GB940269A (en) * 1959-02-20 1963-10-30 Gen Electric Improvements relating to electric cables
US3077510A (en) * 1959-06-02 1963-02-12 Anaconda Wire & Cable Co High voltage power cable
US3244800A (en) * 1960-06-23 1966-04-05 Amp Inc Corona-free high voltage cable
GB958418A (en) * 1961-12-20 1964-05-21 Ass Elect Ind Improvements relating to electric cables
US3297819A (en) * 1964-08-10 1967-01-10 Raychem Corp Heat unstable covering
US3329764A (en) * 1965-05-17 1967-07-04 Jr John H Tanges Conductive plastic cable shield

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4092488A (en) * 1975-10-24 1978-05-30 Sumitomo Electric Industries, Ltd. Connection or terminal portions for cross-linked polyethylene cables
US4483808A (en) * 1982-02-18 1984-11-20 At&T Technologies, Inc. Methods of making a compositely insulated conductor having a layer of irradiation cross-linked polymeric material
US4845309A (en) * 1987-04-23 1989-07-04 Dow Corning Corporation Silicone water block for electrical cables
US4961961A (en) * 1987-04-23 1990-10-09 Dow Corning Corporation Silicone water block for electrical cable
US4978694A (en) * 1987-04-23 1990-12-18 Dow Corning Corporation Silicone water block for electrical cables
US5200234A (en) * 1991-12-16 1993-04-06 Dow Corning Corporation Method for restoring underground electrical cable
US20100314022A1 (en) * 2008-02-20 2010-12-16 Abb Research Ltd. Method for providing an insulated electric high voltage dc cable or a high voltage dc termination or joint
US8398803B2 (en) * 2008-02-20 2013-03-19 Abb Research Ltd. Method for providing an insulated electric high voltage DC cable or a high voltage DC termination or joint
US20110005805A1 (en) * 2009-07-08 2011-01-13 Hitachi Cable, Ltd. Cable

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