JPS6115536B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sheet-like insulator and a power cable using the same, and is particularly directed to an OF cable. OF cables have traditionally been constructed by winding cellulose-based insulating paper (hereinafter referred to as insulating paper) tape around a conductor and impregnating it with insulating oil, and are widely used for high-power transmission. rate,
Improvement was requested due to the large dielectric loss tangent. In recent years, with the increase in power transmission voltage, there has been a strong demand for improvements in these characteristics, and new insulating materials made of laminate composites of insulating paper and polyolefin resin are coming into practical use. There are two types of configurations for this type of laminate insulator: In other words, (a) an extruded polyoffine resin layer with insulating paper laminated on both sides, (b) an extruded polyoffine resin layer with insulating paper on one side and a stretched polyoffine film on the other side. However, (a) Since the ratio of insulating paper to the whole is large, the dielectric constant (ε) and dielectric loss tangent (tanδ) are larger than (b), but (a) has better dielectric strength characteristics and oil absorption and swelling are also higher than (a). It's smaller. For example, conventional laminate insulation types (a) and (b) of 125μ thickness were made using extruded polypropylene sheets with insulation paper and stretched polypropylene film of 40μ thickness, respectively, and the dielectric properties at 80°C in oil immersion condition were 100 Table 1 shows a comparison of the thickness swelling ratios after immersion in oil for 3 days at ℃.

[Table] This kind of thickness swelling actually causes a big problem for OF cables. Specifically, when it swells by oil absorption, the compressive force that acts between the tapes becomes large within the range where the swelling force does not cut the paper. (1) The tape will not move when the cable is bent, resulting in paper breaks, wrinkles, etc. (2) The flow resistance of the insulating oil will increase, and local negative pressure will occur when oil pressure fluctuates during operation, creating concerns about long-term reliability. Therefore, with the conventional swelling degree, there is a limit to improving the inductive properties by increasing the proportion of polyolefin, and the extruded resin layer fraction is approximately 40% or less in the insulator with the configuration (a), and (b) The disadvantage of this structure is that it is only practical if the insulation fraction is 50% or more and the extruded resin layer fraction is 20% or less. The degree of swelling of the extruded polyolefin layer is as follows: polypropylene, polybutene-1, polymethylpentene-1
There is no big difference between 1. Furthermore, the swelling properties of the stretched film are about 1/5 that of the extruded sheet, and there is no significant difference between the resins. Taking the above points into consideration, the inventors of the present invention have conducted intensive studies on methods for suppressing oil absorption and swelling of extruded polyolefin layers, and have found that oil absorption and swelling properties can be significantly improved by kneading a specific hydrocarbon oil into polyolefin. This discovery led to the present invention. That is, the present invention provides polyolefin resin 100
part by weight and 5 to 30 parts by weight of a hydrocarbon insulating oil with an initial boiling temperature of 300°C or higher, a sheet obtained by melt-extruding the cellulose insulating paper on one side and the insulating paper or the polyolefin on the other side. This relates to a sheet-like insulator made by gluing stretched resin films together. A preferable power cable can be obtained by providing the sheet-like insulator on a shearing layer provided on the conductor and a wound layer of cellulose insulating paper, and then providing the shearing layer thereon. The polyolefin resin is preferably polypropylene, polybutene-1, or polymethylpentene-1 for the reasons mentioned above. First of all, regarding insulating oil, all conventional insulating oils for OF cables are hydrocarbon-based, and most have a temperature of initial boiling [JIS 2254 Petroleum Products Distillation Test Method].
On the other hand, the extrusion resin temperature in the production of laminated insulators is about 300°C, which is about 220 to 260°C, which is below 300°C. Therefore, when a kneaded material containing hydrocarbon oil with an initial boiling temperature of 300°C or less is extruded, the hydrocarbon oil evaporates from the surface of the melt, resulting in (1) sheet-like objects (paper, film) to be pasted together; Problems arise, such as the oil condensing on the surface, resulting in no adhesive strength, and (2) the oil being oxidized and degraded on the molten surface and in the gaseous state, resulting in poor tanδ. For this reason, in the present invention, a hydrocarbon-based insulating oil with an initial boiling temperature of 300°C or higher is used. Oils suitable for this include mineral oil-based heavy electrical insulating oil, heavy alkylbenzene-based insulating oil [JIS C
2320 Electrical Insulating Oil Class 2 No. 2], polybutene-based insulating oil [JIS C 2320, Class 3, No. 2, No. 3], etc., but all of these have similar effects. The appropriate amount of the hydrocarbon insulating oil to be kneaded into the polyolefin resin is in the range of 5 to 30 parts by weight per 100 parts by weight of the resin. Even if it is added, the swelling rate does not change much, and some of the kneaded oil begins to separate on the surface. The relative permittivity (ε) of the polyolefin resin at 80°C is approximately 2.2, and the dielectric loss tangent (tanδ) is 0.01%.
However, the smaller the tan δ, the more desirable the insulating oil is, so it is preferable to use an insulating oil with a tan δ of 0.05% or less. In the present invention, the kneaded product of polyolefin resin and hydrocarbon insulating oil is melt-extruded to form a sheet consisting of an extruded resin layer, and insulating paper and stretched polyolefin film are placed on both sides of the sheet, and the above-mentioned (a) structure or (b) shall be a sheet-like insulator of composition. In the case of sheet insulators not according to the present invention, only the configuration (a) with ε of 2.75 or more and tan δ of 0.07% or more, and the configuration (b) with ε of 2.70 or more are practical. Therefore, the OF cable using this has ε2.7, tanδ
It cannot fall below 0.06%. On the other hand, the insulator made of a polyolefin mixture kneaded with 20% by weight of insulating oil according to the present invention has an oil absorption swelling rate of about 2%, so in configuration (a), ε2.45 or more and tanδ 0.03% or more , (b) In the configuration ε
A range of 2.35 or more and tan δ 0.02% or more can be put to practical use. Therefore, in a cable using this, it is possible to reduce the capacitance tan δ value of the entire cable. Also, for example, the ε of the entire cable is
2.7. Even when tanδ is set to 0.06%, laminated insulators with different characteristics can be combined, so in order to improve the withstand voltage in the OF cable design,
It is also easy to adopt a structure in which an insulating tape with a large ε is placed on the conductor side, and insulating tapes with a small ε are placed sequentially toward the outer periphery. OF cables made by combining configurations (a) and (b) above have dielectric strength characteristics, especially in terms of lightning impulse withstand voltage, positive polarity is 10% higher than negative polarity.
~20% lower characteristics. In order to eliminate this difference in characteristics and increase the breaking strength in positive polarity to the same level as negative polarity, the cable of the present invention has the following configuration. In other words, the thin layer on the conductor is covered with carbon paper,
Or a combination of carbon paper and metallized paper, or metalized paper with a thickness of 80 to 100 mm as an insulating layer.
μ insulating paper (ε: about 3.5) is wound to a layer thickness of 1 mm or more and 2.0 mm or less, and the sheet-like insulating tape of the present invention is placed on the inside with a thin sheet and a large dielectric constant. The outside has a thick sheet and a low dielectric constant (thickness: 120, 150,
By winding three types of about 200μ (for ε about 2.8, 2.6, and 2.3) to a specified thickness, and further providing a flexible layer such as carbon paper or metallized paper on the outermost layer just above the conductor. and configure it. The power cable having the above structure has significantly improved oil absorption and swelling compared to conventional cables, and has excellent electrical properties, so it is suitable as an OF cable for transporting large amounts of power. The effects of the present invention will be explained below with reference to Examples. Example 1 Polypropylene, polybutene-1, and polymethylpentene-1 were kneaded with polybutene oil with an average molecular weight of about 1300, heavy alkylbenzene (JIS C 2320, Type 2 No. 2), and heavy mineral oil with an initial distillation temperature of 320°C, The mixture was melt extruded to make a 100μ thick sheet. The thickness of this material was measured, and the material was immersed in alkylbenzene-based OF cable oil at 100° C. for 3 days to absorb oil and swell, and the thickness was measured. Table 2 shows the results of calculating the thickness swelling ratio based on the thickness before swelling treatment.
It was as follows.

[Table] Example 2 Two mixtures made by kneading 20 parts by weight of alkylbenzene-based OF cable oil and heavy alkylbenzene per 100 parts by weight of resin into polypropylene were extruded at 280°C, using 40μ thick insulating paper. (a) A sheet-like insulator with a total thickness of 125μ was made. Each insulator was vacuum dried at 120°C and impregnated with degassed alkylbenzene OF cable oil at 80°C. The dielectric properties were measured and an adhesion test was conducted. The results are shown in Table 3.

[Table] The adhesion test in this case was conducted as follows. Prepare a test piece with a width of 15 mm and a length of 250 mm, and
Vacuum dried at 120°C and kept at 80°C for 20 days. After cooling, the paper layer of one test piece is peeled off in the length direction by 50 mm, the peeled paper and the remaining sheet are peeled off using a tensile tester, and the average peel strength is measured over the new peeled length of 150 mm. Adhesive force. Example 3 Using a mixture of polymethylpentene-1 and 20 parts by weight of polybutene oil with an average molecular weight of about 1,300 per 100 parts by weight of resin, a mixture was prepared using insulating paper with a thickness of 40μ.
(a) Sheet insulators with a thickness of 125μ and 160μ,
A 210μ thick sheet insulator of configuration (b) was made from a 120μ thick polymethylpentene-1 film. The dielectric properties of this material (80℃ in oil immersion state) are:
For the 125μ thickness, ε: 2.75 and tan δ: 0.075%, for the 160μ thickness, ε: 2.67 and tan δ: 0.063%, and for the 210μ thickness, ε: 2.38 and tan δ: 0.035. A hollow conductor with an effective conductor cross-sectional area of 2000 mm ² , 1 sheet of 100μ thick carbon paper, and 100μ carbon paper with one side insulated.
Wrap one sheet of thick insulation paper, then 10 layers of 100μ thick insulating paper (80℃ in oil immersion, ε: 3.5, tanδ 0.20%) (thickness 1.0
mm), and then wrapped with sheet insulators of 125μ, 160μ, and 210μ in this order (with the insulating paper surface facing the conductor side) to obtain an insulating layer thickness of 19.0 mm. Four sheets of metallized paper were wrapped as an outer layer. After drying as required, it was impregnated with degassed alkylbenzene OF cable oil and covered with an aluminum sheath to obtain an OF cable. For comparison, OF cables similar to those described above were made using only 125μ, 150μ, and 210μ thick laminate insulators (no insulating paper layer) made of polypropylene resin and having a pP fraction of 36 to 40% in the structure (a). The dielectric properties of these cables at 80℃ and the lightning impulse breakdown voltage of both positive and negative polarities at room temperature were measured. The above results were as shown in Table 4.

【table】

Claims (1)

[Claims] 1. 100 parts by weight of polyoffine resin and an initial boiling temperature of 300 parts by weight.
A sheet obtained by melt-extruding a kneaded product with 5 to 30 parts by weight of hydrocarbon insulating oil at a temperature of ℃ or higher is laminated with cellulose insulating paper on one side and cellulose insulating paper or a stretched film of the above-mentioned polyoffine resin on the other side. 2. 100 parts by weight of polyoffine resin and an initial boiling temperature of 300
A sheet obtained by melt-extruding a kneaded product with 5 to 30 parts by weight of hydrocarbon insulating oil at a temperature of ℃ or higher is laminated with cellulose insulating paper on one side and cellulose insulating paper or a stretched film of the above-mentioned polyoffine resin on the other side. A power cable that is made by winding a sheet-shaped insulating tape on a conductor, a sheathing layer provided on the conductor, and a wound layer of cellulose-based insulating paper, and then providing a sheathing layer on top of that layer.