JPH047046B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an ultra-high voltage, low-loss oil-immersed power cable, and more particularly to an ultra-high-voltage oil-immersed plastic insulated power cable with extremely excellent oil-immersed properties and electrical properties. As the demand for electricity increases, the need for long-distance, large-capacity power transmission is increasing. In this case, OF cables with an insulating layer made of kraft paper/insulating oil have traditionally been used as the essential large-capacity underground power transmission line. However, the power transmission capacity of these OF cables is limited by the dielectric properties of the insulating material, and in the case of kraft paper, which has a large dielectric loss, the capacitance limit value is low. Ultra-high voltage power transmission is economically advantageous by finding physicochemically stable low-loss materials with excellent withstand voltage performance. Plastics are a group of materials that have lower dielectric loss than kraft paper, but among them polyolefin is a general-purpose plastic that is superior in terms of cost and physical properties. However, when these polyolefins coexist with low-loss alkylbenzene-based insulating oils, the polyolefins undergo swelling and low molecular weight components dissolve, impairing their insulating function. For these reasons, all-plastic insulated OF cables have not yet been put into practical use. As a result of intensive research into the material composition of plastic cable insulation, the inventors formed a layer around the conductor by alternately wrapping a uniaxially stretched film mainly made of polyolefin and a polar plastic film, and coated this with electrical insulating oil. It was discovered that an ultra-high voltage OF cable with excellent electrical properties could be obtained by impregnating it with oil and making it into an oil-immersed plastic insulated power cable. In the oil-immersed plastic insulated power cable of the present invention, the film mainly composed of polyolefin is uniaxially stretched, so the crystallinity of the film is increased and the thickness swelling rate due to insulating oil is suppressed to a low level. Young's modulus is increased.
Therefore, the shape stability of the insulating layer in the oil is ensured, and the interlayer sliding of the insulating film occurs smoothly against mechanical bending deformation of the cable, causing wrinkles in the laminated film that can cause dielectric breakdown. , buckling phenomenon, disordered winding, etc. are prevented. Furthermore, the polar plastic film, which is alternately wound with a uniaxially stretched film mainly made of polyolefin, has a solubility that is far different from that of insulating oil.
Parameter value and has a high Young's modulus equal to or higher than that of uniaxially stretched film,
Swelling due to the insulating oil does not occur and it is possible to resist the swelling pressure of the adjacent uniaxially stretched film due to the insulating oil. As a result, the polyolefin film is prevented from falling into the gap between the film gaps.
The radial compressive Young's modulus of the cable can be kept small, resulting in an excellent oil-immersed plastic insulated cable. Note that unlike non-polar plastics such as polyolefin, polar plastics with large dielectric loss generate heat when placed in an alternating current field, but by arranging polar and non-polar plastics in alternating windings, the entire laminated portion is heated. There is no practical problem because the heat generating portion can be dispersed over the area, thereby increasing the cooling effect. FIG. 1 is a conceptual diagram regarding the formation of an insulator layer according to the present invention. A uniaxially stretched polyolefin film and a polar plastic film are alternately wound around a portion of the central conductor 1, and an oil-immersed insulator layer 2 is formed with gap gaps serving as oil passages provided in each film layer. There is. An aluminum sheath 3 and an anti-corrosion plastic sheath 4 are successively provided on the outside. The uniaxially oriented polyolefin film referred to in the present invention has a thickness within the range of 80 to 300μ and a thickness swelling rate of 5% or less in dodecylbenzene oil at 100℃, and its materials include high density polyethylene, low density polyethylene, isotactyl polyethylene, etc. Target polypropylene, polybutene, poly-4-methylpentene-1, or a mixture of two or more of these components. Among these, isotactic polypropylene, which has an insoluble content of 95% or more in boiling heptane, is particularly preferred and often used. Furthermore, in order to suppress swelling in insulating oil, it is advantageous to use polypropylene of high MI grade with excellent crystallinity, preferably MI>15. In this case, a composition in which 10 parts by weight or less of a low dielectric loss resin component such as a fluorine resin or an aromatic resin is mixed with 100 parts by weight of polypropylene is particularly effective.
Among these, a film in which fine fibers are uniformly dispersed, which is obtained by dispersing and mixing unfired polytetrafluoroethylene dispersion into polypropylene powder and melting and kneading the mixture after drying, is most effective. A uniaxially stretched film made of a polyolefin film or a composition consisting mainly of polyolefin and polytetrafluoroethylene uniformly dispersed therein has a Young's modulus of 25,000 Kg/cm ² or more, which is sufficient to fully demonstrate its function as an insulating film. It is possible. Polar plastics as used in the present invention include polyether sulfon, polysulfon, polycarbonate, polyethylene terephthalate, polyphenylene oxide, fluoropolyolefin polymers, or copolymers thereof, such as tetrafluoroethylene resin, tetrafluoroethylene - Hexafluoropropylene copolymer resins, trifluorochlorinated ethylene resins, perfluoroalkoxy resins, etc. are included. Films made of these materials can be produced using extrusion or cutting methods (especially for fluoropolyolefin polymers).
In some cases, these films may be uniaxially or biaxially stretched. The film thickness should be between 80μ and 300μ. Furthermore, the polar plastics referred to here have a Solubility Parameter of commonly used insulating oil.
However, most of the substances, except for polytetrafluoroethylene, usually show values of 8 or more. The electrical properties of the polarized plastic of the present invention are superior to those of conventional cable insulating paper, with a dielectric constant of 3.5 or less and a tan δ value of 2.2× when measured at 25°C and 600Hz. 10 ^-3 or less or the ε tan δ value is 0.495 or less.
These polar plastics have very little swelling in insulating oil. As this evaluation method, 100℃,
A thickness increase in dodecylbenzene is considered; for the polar plastics used here, this increase remains below 3%. Note that the surfaces of both types of films used in the present invention may be embossed. In this case, a passage for the insulating oil is ensured, and the compressive Young's modulus in the radial direction can be expected to be lowered, which is advantageous since buckling can be prevented. In the present invention, the volume ratio of the two types of films greatly affects the properties of the resulting insulating layer. Since the dielectric loss of polar plastic films is greater than that of polyolefins in most cases, it is necessary to keep the proportion of this material small. The volume fraction of this material used in the present invention is 50% or less, preferably 40% or less to 20% or more, which is effective in terms of characteristics. If the above conditions are exceeded and a polar plastic film is used, although the dimensional stability in oil and heat resistance are significantly improved, the dielectric loss of the entire insulating layer increases and the expected effect cannot be obtained. The insulating oil used in the present invention is Solubility
It is an organic liquid with a parameter close to the value of polyolefin, that is, 8.4, and has a high withstand voltage. Specifically, it is an alkylbenzene-based dodecylbenzene oil, polybutene oil, etc. used as an insulating oil for OF cables. be. Since the cable produced by the method of the present invention has all the insulating layers made of plastic, compared to the conventionally used kraft paper type cable, manufacturing problems such as moisture removal can be avoided and it is cost-effective. It is. Next, the present invention will be explained by giving examples. Examples 1-2 Isotactic polypropylene (MFR=
25), 2 parts by weight of polytetrafluoroethylene dispersion was uniformly blended, and after drying, the polypropylene was kneaded while melting, and the above-mentioned,
Polytetrafluoroethylene was uniformly dispersed. Thereafter, a T-die sheet with a thickness of 0.8 m/m was obtained using a single screw extruder. This was stretched in the uniaxial direction using a roll stretching device at 145 to 150°C to obtain a stretched film having a width of 30 m/m, a thickness of 110 μm, and a tensile Young's modulus of 35000 Kg/cm ² . This was then passed through an embossing roll kept at 50°C to obtain an embossed film with a finished thickness of 154μ. To make a prototype model cable, we next made polyether sulfonate (PES) film (thickness 100μ),
The above-mentioned polyolefin embossed film was wound alternately around the conductor to form a cable insulating layer, and after covering the outside with an aluminum corrugated sheath with an outer diameter of 60 mm, in a vacuum maintained at 10 ^-2 mmHg,
Impregnated with alkylbenzene-based insulating oil. Thereafter, a 60KV class model cable was made by covering the aluminum sheath with a polyethylene jacket. In addition, a model cable using FEP (fluorinated ethylene propylene copolymer) film (thickness: 110 μm) as a material other than the polyether sulfon was also created by a method similar to the above process (Example 2). In order to evaluate the characteristics of the prototype model cable, first, the cable diameter is
A 20x vent test was conducted, and then the AC breakdown value and cables were disassembled and visually inspected for the presence or absence of disordered film winding of the insulator layer. For comparison, a model cable with an insulating structure made solely of the polypropylene uniaxially stretched film used in the examples was made, and the same characteristic tests were conducted. The results obtained above are shown in Tables 1 and 2.

【table】

[Table] Examples 3 to 4 High-density polyethylene (MI=7, mp. 137°C) was molded into a 1.0 mm thick sheet using a 75 mm diameter uniaxial screw type extruder equipped with a T-die.
This was done using a roll stretching device with a surface temperature of 151℃.
It was uniaxially stretched 8.5 times. Obtained thickness 102μ
Slit the stretched film to a width of 30m/m and heat it at 60℃.
It was finished with an embossing roll heated to 150 µm (apparent thickness: 158μ), and wound into a pad so that it could be set in a cable paper winding machine. To prototype a model cable, we used a polycarbonate (PC) film (thickness 100μ), the high-density polyethylene film (Example 3), the FEP film used in Example 2, and the high-density polyethylene film (Example 4). They were arranged around the conductor in an alternating manner to form an insulating layer. Each of the two types of cable cores obtained in this way has an outer diameter of 60 mm.
A 60 KV class model cable was made by covering the cable with an aluminum corrugated sheath of 1.0 mm in diameter, impregnating it with alkylbenzene-based insulating oil in a vacuum, and then covering the aluminum sheath with a polyethylene jacket. In order to evaluate the characteristics of the prototype model cable, the cable was placed in a thermostat at 100℃ for 50 minutes.
After leaving the cable for some time, the cable was dismantled and observed whether or not the upper layer tape surface had fallen into the gap between the insulating tapes. In addition, in order to measure the oil flow resistance of the insulator layer, a sample of 20 layers of PTFE tape (width 12 mm) wrapped in a cable shape with 50/50 registration was used to measure the oil flow resistance from one end of both terminal seals to the cable core. The amount of oil flowing out due to pressurization with a nitrogen cylinder was measured using a measuring cylinder.

【table】 [Brief explanation of drawings]

The drawing is an explanatory cross-sectional view for explaining the structure of the insulator in the oil-immersed plastic insulated power cable of the present invention. 1...Conductor, 2...Oil-immersed insulator layer, 3...Aluminum covering,
4...Anti-corrosion sheath.

Claims (1)

[Claims] 1. In an oil-immersed plastic insulated power cable in which an oil-immersed plastic insulating layer is provided on a conductor, the oil-immersed plastic insulating layer is formed by alternately winding a uniaxially stretched film mainly composed of polyolefin and a polar plastic film. , an oil-immersed plastic insulated power cable characterized by being impregnated with electrical insulating oil.