JPS6136322B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses a melt-extruded layer of polyolefin resin pellets such as polypropylene, polymethylpentene, and high-density polyethylene as an adhesive, and uses polyolefin laminated paper for electrical insulation, which is made by integrating a plurality of fiber papers as an adhesive, to form at least a portion of the insulating layer. This relates to improving the characteristics of immersed power cables used in Polyolefin laminated paper for electrical insulation has the advantages of low dielectric loss and high electrical breakdown strength, so ultra-high-voltage power cables using it are attracting worldwide attention, and research and development is actively progressing. ing. However, the biggest obstacle in the practical application of this power cable is that the polyolefin layer, which is a film-like material made of high-density polyethylene or polypropylene formed by melt extrusion and is a component of polyolefin laminated paper, is usually used as an insulating oil. The reason for this is that it exhibits a so-called swelling phenomenon and exhibits an increase in thickness in the coexistence with hydrocarbon oils such as mineral oil and alkylbenzene. There are two important problems caused by this increase in thickness: First, due to the increase in the thickness of the polyolefin layer, the flowability of the insulating oil within the insulating layer, which is necessary to compensate for the expansion and contraction of the insulating oil due to temperature changes in the power cable, decreases. be. In conventional kraft paper insulated OF cables, the kraft paper is a porous material, so the insulating oil can penetrate through the kraft paper in the thickness direction, but in polyolefin laminated paper, the film-like polyolefin layer is Because of this, insulating oil cannot penetrate through the thickness of the polyolefin layer, and has no choice but to flow through the voids created by the unevenness of the surface of the kraft paper or the voids between the fibers inside the kraft paper. Even in a state where there is no increase in the insulating oil, the flowability of the insulating oil is essentially poor. Therefore, when polyolefin laminated paper is made into a tape and wound around a conductor, it is necessary to reduce the winding tension or use relatively low-density kraft paper to ensure the above-mentioned distribution. Moreover, if the thickness of the polyolefin layer increases, the kraft paper layer will be compressed and the voids will decrease, which will further reduce the flowability of the insulating oil and eventually make it impossible to secure the necessary flowability of the insulating oil. It is something. The second problem is also caused by the compression of the kraft paper layer. In other words, the compression of kraft paper inevitably increases the surface pressure between adjacent tapes, which makes it difficult for the tapes to slide against each other, and when bending stress is applied during power cable installation, the insulation paper It causes wrinkles in the layers. These phenomena become more pronounced as the rate of increase in the thickness of the polyolefin layer increases and as the ratio of the thickness of the polyolefin layer to the total thickness of the polyolefin laminated paper increases. In other words, the greater the rate of increase in the thickness of the polyolefin layer, the smaller the proportion of the polyolefin layer in the total thickness of the polyolefin laminated paper needs to be. However, from the point of view of the electrical properties of polyolefin laminated paper, the proportion of the polyolefin layer should be larger. Therefore, in order to obtain a power cable with excellent performance, the proportion of increase in the thickness of the polyolefin layer should be minimized. This is very important. Furthermore, another problem with this polyolefin laminated paper is that the low molecular weight components that are naturally present in the polyolefin resin elute into the insulating oil, which increases the viscosity of the insulating oil or precipitates at low temperatures. This impedes the flow of insulating oil within the power cable. As a means for suppressing the swelling and dissolution of polyolefin laminated paper for electrical insulation as described above, for example, in the case of power cables, there is a method such as heat treatment at a temperature below the melting point of the polyolefin resin after winding the paper with tape. The present invention aims to modify the polyolefin resin itself to be melt-extruded in order to avoid the increase in thickness due to swelling of the polyolefin laminated paper itself and the dissolution of the polyolefin layer in insulating oil. Generally, when polyolefin resin is impregnated with hydrocarbon-based insulating oil such as mineral oil or alkylbenzene,
Swelling and dissolution to some extent are unavoidable, resulting in the disadvantages in use as described above. The present inventors devised the swelling, that is, the increase in thickness and dissolution of this polyolefin layer by insulating oil at the stage of manufacturing the laminated paper.
The present invention was developed after intensive research into ways to reduce this problem. The present invention involves immersing polyolefin resin pellets in a liquid solvent, eluting internal easily soluble components into the solvent, removing the liquid solvent adhering to the pellet surface, and then melt-extruding the pellets. The present invention provides a method for manufacturing an oil-immersed insulated power cable in which an electrically insulating polyolefin laminated paper, which is formed by compositely integrating a plurality of fiber papers using the same as an adhesive, is wound around at least a portion of an insulating layer. That is, polyolefin resin pellets are immersed in a liquid solvent such as insulating oil, and components that are easily dissolved into the solvent, such as low molecular weight components, present in the pellets are eluted into the solvent from inside the pellets. After the operation is completed, the surface of the pellet taken out from the solvent is washed to remove solvent residue on the surface, and then fed to a lamination process, that is, melt extrusion. When resin pellets for melt extrusion are immersed in a solvent in this manner, easily soluble components are eluted and removed from the pellets as described above, and the internal structure of the pellets is swollen by the solvent and some of the solvent is removed. is retained inside the pellet. FIG. 1 is an example of a cross-sectional view of a power cable manufactured by the manufacturing method of the present invention, in which a polyolefin laminated paper is wrapped in a tape form as an insulating layer over a conductor 2 having an oil passage 1 over all or at least a portion thereof. Metal sheath 4 protected by anti-corrosion layer 5
is provided to prevent moisture absorption and oxidation of the insulating layer and to prevent oil leakage. FIG. 2 shows a schematic cross section of a polyolefin laminated paper for electrical insulation produced by the manufacturing method of the present invention, and shows a state in which fiber papers 21 and 21' are compositely integrated using a polyolefin resin film 22 as an adhesive. . The polyolefin laminated paper produced using the polyolefin resin pellets subjected to the above treatment has the following characteristics. 1. Since components that easily dissolve in insulating oil have been removed in advance, the polyolefin layer is less likely to dissolve in insulating oil when used as an insulating layer for power cables. 2 In addition, in the above case, the increase in thickness due to swelling of the polyolefin layer is small. 3. Generally, as the low molecular weight components of polyolefin are dissolved, secondary impurities such as catalyst residues and oxidation stabilizers that are harmful to dielectric properties are removed, so the dielectric loss tangent can be reduced. A known method similar to the present invention is a method of kneading insulating oil into polyolefin resin. This kneading method involves adding insulating oil before turning the polyolefin resin into pellets, or
This method heats the pellets, adds insulating oil, and then mechanically kneads the insulating oil. That is, since the insulating oil is contained in the pellets, the polyolefin laminated paper using the pellets in such a state is less likely to swell in the insulating oil, and therefore the increase in thickness due to swelling can be suppressed. It is something. However, this method does not discharge easily soluble components to the outside, so the above-mentioned features of the polyolefin-in laminated paper according to the present invention
The effects of 3 and 3 cannot be expected and are not desirable. The present invention will be explained in more detail below with reference to Examples. Example 1 General-purpose polypropylene resin (pellet form) A
After vacuum drying at a temperature of 80° C. or 100° C. for 4 hours, an excess of hard type alkylbenzene was added, and the mixture was allowed to stand for one round while maintaining the temperature and vacuum. Then, take out the polypropylene resin,
Washed with methanol and dried. Polypropylene resin C for melt extrusion (80℃ immersion) or
C′ (100℃ immersion). Next, unoil-immersed resin A
A polypropylene resin B for melt extrusion was prepared by mixing the above-mentioned oil-impregnated resin C at a weight ratio of 1:1. While melting and extruding these A, B, C and C' resins, we used them as an adhesive to make insulating paper for capacitors.
Thickness 125μ made by bonding two 43μm sheets together
Three types of electrically insulating polypropylene laminated paper of m150μm and 200μm were created and heated to 100°C.
The polypropylene layer was immersed in hard type alkylbenzene to measure various properties including the rate of increase in thickness due to swelling of the polypropylene layer by the oil. The results are shown in Table 1.

[Table] As shown in Table 1, when the resin to be melt-extruded is impregnated with hard type alkylbenzene, C is compared to the conventional non-impregnated type A.
The increase in thickness and amount of dissolution due to swelling caused by insulating oil can be reduced by more than half, and tan δ is also reduced. Further, other electrical properties and physical properties are not significantly deteriorated. Even in B, which is a mixture of A and C, the rate of increase in thickness, amount of dissolution, and tan δ are reduced, and the effect is seen. In this example, the polyolefin-in laminated paper manufactured by the manufacturing method of the present invention has less swelling and dissolution in insulating oil, which has been considered a drawback in the past.
Dielectric properties are also improved. Note that polyethylene and polymethylpentene are also polyolefins similar to polypropylene, so they exhibit almost the same tendency. If xylene is used as a solvent, it can be extracted to the same extent as alkylbenzene at a temperature 20 to 30°C lower than that of alkylbenzene. In this case, the surface can be removed immediately by simply drying it, but the xylene inside is also easily removed, so long-term storage is not possible. In the lamination process, when melt-extruding pellets containing the solvent according to the present invention, there is a risk that the solvent will oxidize due to the high temperature at that time and the dielectric properties will deteriorate. It is desirable to extrude and laminate with a reduced amount. In addition, during extrusion, a large amount of solvent vapor is generated, so it was found through prototype research that measures to exhaust the vapor are important. That is, the generated steam condenses and condenses on surrounding equipment, becomes oil droplets, incorporates impurities, and adheres to the insulating paper. Therefore, forced exhaust that does not create oil droplets is desirable. After the immersion treatment, the solvent adhering to the surface of the pellets taken out from the solvent acts to reduce the friction between the pellets when the screw in the die rotates during the melt lamination process, and prevents the pellets from being fed to the melting zone. It is desirable to remove it. As a method of removal, as shown in the examples, the pellets may be washed with a solvent such as methanol at room temperature, or the pellets taken out may be vacuum dried at high temperature. The liquid solvent used in advance for swelling and dissolution treatment may be any solvent as long as it removes the easily soluble portion of the polyolefin resin, but it is suitable for use in electrical equipment such as power cables in which the laminated paper is used. Most preferably, it is a hydrocarbon-based insulating oil such as diallylalkane, alkylnaphthalene, or polybutene. In addition, it is desirable that the temperature during dipping be higher as it will allow the specified treatment to be carried out in a shorter time, but if the temperature exceeds 120℃, the resin may deteriorate.
It is desirable to keep the temperature below, and the most suitable temperature is about 80° to 100°C, which is the operating temperature of electric kale. This method of manufacturing oil-immersed insulated power cables is constructed using laminated paper using soaked pellets, so problems of swelling and dissolution are eliminated, and the polyolefin ratio (=thickness of the polyolefin film) is reduced. /Total thickness of laminated paper) can be increased. For example, the εtanδ of kraft paper and polyolefin, which are the constituent elements of laminated paper, is 3.4×0.002=6.8×10 ^-3 , respectively.
Polyolefin has a much smaller value of about 2.2 x 0.0002 = 4.4 x 10 ^-4 . Therefore, if the polyolefin ratio is increased, a power cable with a small ε tan δ can be easily obtained, and its practical effect is great.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a power cable manufactured by the manufacturing method of the present invention, and FIG. 2 is a schematic cross-sectional view of an electrically insulating polyolefin laminated paper used in the power cable manufactured by the manufacturing method of the present invention. 1...Oil passage, 2...Conductor, 3...Insulating layer, 4
...Metal sheath, 5...Corrosion-resistant layer, 21, 21'...
...Fiber paper, 22...Polyolefin resin film.

Claims (1)

[Claims] 1. Polyolefin resin pellets are immersed in a liquid solvent, the easily soluble components inside are eluted into the solvent, the liquid solvent adhering to the surface of the pellet is removed, and then the pellet is melt-extruded. A method for manufacturing an oil-immersed insulated power cable, comprising winding at least a part of an insulating layer with polyolefin laminated paper for electrical insulation, which is made by integrating a plurality of fiber papers as an adhesive.