JPS6137726B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to an improvement in electrical insulating paper for oil-immersed insulation, which can be used for oil-immersed insulated power cables and the like to improve their properties. Conventionally, for example, in oil-immersed insulated power cables,
It is well known that it is effective to use insulating paper, which is a combination of insulating kraft paper and plastic with small ε and tanδ, in order to reduce the dielectric loss of oil-immersed insulators. Various types of paper have been proposed, including kraft paper mixed with short fibers of the plastic during papermaking, and laminates of kraft paper and plastic film. The inventors also found that poly-4-methylpentene was used as the plastic for the above-mentioned composite insulating paper due to its ε and tanδ values as well as its heat resistance.
1 is the most promising, and various studies have been conducted and it has been confirmed that it has excellent properties. By the way, an insulating paper made by laminating the poly-4-methylpentene-1 film and kraft paper was impregnated with dodecylbenzene, which is a hydrocarbon-based synthetic insulating oil that is commonly used as an insulating oil. Obtain an aluminum sheathed OF cable, and
When we conducted a bending test with a cable 20 times the diameter back and forth twice, contrary to expectations, bending wrinkles appeared in the oil-immersed insulator layer, which would not be observed when using kraft paper alone. It was found that the voltage resistance characteristics of the cable were significantly reduced due to this. As a result of various studies on the causes of these bending wrinkles, we found that
The above poly-4-methylpentene-1 is swollen by the impregnated dodecylbenzene to a thickness of about 10
%, and when the insulating paper is wound into several layers, the thickness increases, and the mutual pressing force between the insulating paper layers increases, causing slippage of the mutual surfaces when bent. It was found that this resulted in the formation of the above-mentioned bending wrinkles, which was the cause of the above-mentioned deterioration of the withstand voltage characteristics. As a result of intensive studies to solve the drawbacks of composite electrical insulating paper made by laminating poly-4-methylpentene-1 and kraft paper, the inventors have developed the above-mentioned poly-4-methylpentene-1. They found that this problem could be significantly suppressed if the density was less than 0.833, and completed this invention. That is, this invention provides poly-4 having a density of less than 0.833.
-Methylpentene-1 This is an electrical insulating paper for oil-immersed insulation, characterized by laminating kraft paper on one or both sides of the film. In the present invention, the aforementioned poly-4-methylpentene-1 film having a density of less than 0.833 exhibits extremely small swelling due to insulating oil, and as a result, wrinkles and the like due to the aforementioned increase in thickness hardly occur. This is considered to be the reason for solving the shortcomings. Poly-4-methylpentene in this invention
The film used in No. 1 has a density of less than 0.833. If the density is less than 0.833, the above-mentioned swelling rate in the insulating oil can be suppressed to about 5% or less in the thickness direction, and the occurrence of the above-mentioned bending wrinkles can be appropriately prevented. As mentioned above, the swelling rate reaches about 10%, and the above-mentioned drawbacks are unavoidable. The insulating paper according to the present invention, as shown in FIGS. 1 and 2, is obtained by laminating kraft paper 2 on one or both sides of a poly-4-methylpentene-1 film 1 having a density of less than 0.833. As the kraft paper 2, commonly used materials can be used without any limitation. As mentioned above, ε of poly-4-methylpentene-1
and tan δ are significantly smaller than those of kraft paper, so in order to reduce the dielectric loss as an insulating layer, it is a good idea to increase the proportion of the former. However, poly-4-methylpentene-1 has a high swelling property in insulating oil, and care must be taken to avoid the other drawbacks mentioned above due to this. The poly-4-methylpentene-1 film having a density of less than 0.833 is preferably obtained by extrusion molding, but the density may change depending on, for example, the film cooling conditions during extrusion molding or annealing of the formed film. It is desirable to select appropriate manufacturing conditions. The present invention is particularly suitable for use in insulating paper for oil-immersed insulated cables, etc., but may also be used in other equipment, and as insulating oil, general-purpose dodecylbenzene,
Can be applied to polybdenum, mineral oil, etc. As described above, the present invention uses a poly-4-methylpentene-1 film having a density of less than 0.833 in a composite insulating paper in which kraft paper is laminated on one or both sides of a poly-4-methylpentene-1 film. By doing so, as is clear from the examples below, it is possible to significantly reduce the deterioration of the electrical characteristics of, for example, oil-immersed insulated cables.
Its industrial value is very large. The present invention will be specifically explained below with reference to Examples. Examples 1 to 4, Comparative Examples 1 to 2 Poly-4-methylpentene-1 resins of various densities were made into films (50μ thick or 90μ thick) using an extruder.
Kraft paper (30μ or 50μ thick) was applied to both sides of the molten film and heated and pressed to obtain a laminated insulating paper with a thickness of 150μ. The kraft paper was peeled off from each laminated paper, and the density of the poly-4-methylpentene-1 film was determined using a density gradient tube and is shown in the following table. Each insulating paper was dried for 24 hours at 100℃ and 0.1mmHg, and impregnated with dodecylbenzene at 85℃.
Measure tanδ and show the results in the same table, and further increase the temperature to 100℃.
The rate of increase in thickness after holding for 240 hours is calculated and displayed below. Next, a suitable semiconducting layer was placed on a 1 x 2000 mm ² copper conductor, and each insulating paper was wrapped around this to a thickness of 15 mm to make a cable with the same external semiconducting layer and aluminum sheathing. The cables were vacuum dried at 100° C. and 0.1 mmHg for 120 hours, and then impregnated with dodecylbenzene to obtain OF cables of Examples 1 to 4 and Comparative Examples 1 to 2. For each OF cable obtained, the presence or absence of wrinkles and the impulse breakage value were determined after two reciprocating bending tests at a diameter 20 times the outer diameter of the aluminum jacket, and the results are shown in the same table.

[Table] As is clear from the results in the above table, poly-4-methylpentene-1 with a density of less than 0.833 has a lower thickness in insulating oil than a comparative example with a density higher than this. The increase rate of
Furthermore, the impulse breakdown value also remained at a constant level. It was also clear that even if the content ratio of poly-4-methylpentene-1 in the insulating paper was increased, the above-mentioned effects did not decrease, and that ε and tan δ were further reduced, and dielectric loss could be reduced.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of insulating paper according to one embodiment of the present invention, respectively. 1...Poly-4-methylpentene-1, 2...Kraft paper.

Claims (1)

[Claims] 1 Poly-4-methylpentene-1 film is laminated with kraft paper on one or both sides, and the poly-4-methylpentene-1 film has a density
Electrical insulating paper for oil-immersed insulation, characterized in that it is less than 0.833.