JPH0129284B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is suitable for tracing a pipeline or the like that transports a fluid such as sulfur that has a very high viscosity at room temperature to adjust the viscosity of the fluid to a moderately low level, especially at 180°C. The present invention relates to an insulated wire for skin current heating tubes that is suitable for heating to high temperatures in the region exceeding . [Prior Art] Generally, it is difficult to transport relatively high viscosity fluids with low fluidity, such as heavy oil, by pipelines, so the fluid transport pipes that make up the pipelines are heated and transported. BACKGROUND ART The viscosity of fluids has been adjusted to be low to facilitate the transportation of highly viscous fluids over long distances. A typical example of heating means for such a fluid transport tube is a skin current heating tube, which is actually widely used. The basic principle of the skin current heating tube is, for example,
This is specifically disclosed in the Publication No. 12128, and it will be explained based on FIG. One end of the insulated wire 2 is connected to one end of the skin current heating tube 1, and the other end of the insulated wire is connected to an AC power source 3 using commercial AC equipment, and the insulated wire 3 is connected to one end of the skin current heating tube 1. A current closed circuit is formed through the skin current heating tube 1. With the above configuration, the current flowing through the skin current heating tube 1 becomes a so-called skin current that concentrates on the inner surface of the tube, and virtually no longer flows on the outer surface. Therefore, even if tracing is carried out on the fluid transport pipe 4, which is the object to be heated, no current is passed through the transport pipe 4, and the fluid transport pipe 4 is heated by the Joule heat generated in the highly magnetic steel pipe 1, and the fluid transport pipe 4 is then transported. The viscosity of the fluid 5 in the pipe is adjusted appropriately. Now, if we look at the insulated wires used as described above, they are small (nominal diameter A specified by JIS G3452-65 is 25; outer diameter 34 mm, thickness about 3.2 mm).
It has appropriate flexibility and heat resistance as well as high electrical insulation performance because it is drawn into a long and thin high magnetic steel pipe 1, heated in a heat-generating steel pipe, and high voltage is generated by long-distance tracing construction. Conventionally, silicone rubber-covered electric wires have been adopted as a wire that satisfies these demands. However, insulating coatings made of silicone rubber are generally used at temperatures below 180°C due to their heat resistance, and are not suitable for pipelines that need to transport fluids at higher temperatures (for example, sulfur pipelines). , cannot be hired. Therefore, it has been considered to use fluororesin-based insulators as a coating material for insulated wires for skin current heating tubes that are heated to temperatures exceeding 180°C. [Problems to be Solved by the Invention] According to such a fluororesin-insulated electric wire, under conditions where ionization (corona discharge state) occurs, that is, under high voltage application exceeding 3 KV, for example, the fluorine resin as a coating material High-energy gaseous ions from corona discharge collide with the resin insulator on its inner surface, which is under the influence of a strong electric field on the side in contact with the stranded wires of the conductor, causing mechanical erosion and deterioration. The problem was that it gradually progressed outward and eventually reached the outside of itself, leading to dielectric breakdown, making it impossible to use it stably for a long period of time. Therefore, it can generally only be used in low-voltage circuits of 600V or less, and cannot perform long-distance tracing at once, which is the original feature of skin current heating tubes, and can only be applied to short tubes. I couldn't do it. When the skin current heating tube becomes short, it is necessary to have a large number of AC power supply equipment or their relay devices scattered around, which increases the number of incidental equipment and makes it difficult to manage current supply, which is not practical. In view of the above-mentioned problems of the prior art, the present invention aims to take advantage of the features of fluororesin insulators, which have excellent heat resistance, as coating materials in skin current heating tubes that are subjected to high-temperature heating, particularly in excess of 180°C. The object of the present invention is to provide an insulated wire for a skin current heating tube, which compensates for the insulator's vulnerability to corona discharge and provides long-term stability even when used under high voltage. [Means for Solving the Problems] According to the present invention, an inorganic tape is provided in which an insulating layer mainly made of an inorganic material is provided directly above a current-carrying conductor, and a fluororesin is coated or adhered directly above the insulating layer. This object is achieved by winding the tape and further providing a fluororesin-based insulating layer on the tape winding layer. [Function] According to the insulated wire for skin current heating tubes having the above-mentioned characteristics, the insulating layer mainly made of inorganic material applied directly on the conductor not only maintains the temperature rating at a high temperature but also maintains the corona discharge voltage value. This has the effect of increasing the corona resistance, thereby improving corona resistance. In addition, since there is an inorganic tape layer coated or attached with a fluororesin on the insulating layer mainly made of inorganic material, corona resistance can be reinforced, and the insulating layer mainly made of inorganic material can be used as a current conductor. Even if a small amount of moisture or adhesives or other solvents contained in the tape vaporizes when heated by electricity, it is blocked by the tape wrapping layer and does not affect the fluororesin insulation layer. Therefore, problems caused by foaming of the fluororesin insulating layer due to the vaporized gas are eliminated. In this way, it is possible to improve the corona resistance properties by using an insulating layer mainly made of inorganic materials, and to eliminate the effects of the fluororesin insulating layer, which can be affected by heating conditions on the insulating layer mainly made of inorganic materials. By providing this, it is possible to achieve both improvement in heat resistance characteristics and improvement in corona resistance characteristics. Furthermore, by providing a fluororesin insulating layer as the outermost layer, even if water intrudes into the tube, the fluororesin's excellent water resistance allows it to be used with electricity without any problems, resulting in excellent long-term stability. ing. [Embodiment] FIG. 2 shows a preferred embodiment of the insulated wire for a skin current-generating tube according to the present invention, in which an inorganic material is mainly used directly above the current-carrying conductor 21 made of a stranded wire conductor with excellent flexibility. An insulating layer 22 is formed, and a layer 23 made of a fluororesin-coated inorganic tape is provided around this insulating layer 22 mainly made of an inorganic material. An insulating layer 24 is formed. With an insulated wire constructed in this way, the heat resistance rating can of course be improved by employing the fluororesin-based insulating layer 24, and an insulating layer mainly made of an inorganic material is provided directly above the conductor 21, which becomes hot when current is applied. 22, it is possible to maintain a high corona discharge voltage value without any hindrance to maintaining the temperature rating at a high temperature, improving not only heat resistance characteristics but also corona resistance characteristics. be able to. In addition, since a fluororesin-based insulating layer is formed as the outermost layer, even if water intrudes into the pipe, the water resistance of the fluororesin allows it to be used as is, ensuring stable energization over a long period of time. can be made possible. Furthermore, since the fluororesin-based insulating layer 24 is formed with the fluororesin-coated tape wrapping layer 22 interposed between the insulating layer 22 mainly made of inorganic material, the heat generated when the conductor 21 is energized causes the insulating layer 22 mainly made of inorganic material to 22 is heated and released from itself is blocked by the fluororesin-coated inorganic tape wrapping layer 23 and does not reach the fluororesin-based insulating layer 24. This solves the problem that layer 4 foams under conditions of humidity and heat. Note that the inorganic tape is made from glass cloth, a sheet-like material mixed with mica/glass short fibers, or the like. In order to confirm the improvement in the corona resistance of the insulated wire of this example, the corona discharge voltage value was measured. The results are shown in Table 1 below. In the table, sample W ₁ is a comparative example in which a stranded wire conductor with a size of 22 mm ² is extruded and coated with a tetrafluoroethylene resin having a perfluoroalkoxy group side chain to a thickness of 1.2 mm. In addition, sample W ₂ consists of a 1.08 mm thick glass mica layer on a stranded wire conductor of the same size as above, a 0.07 mm thick glass layer coated with fluororesin of the same material as above, and a 0.07 mm thick glass layer coated with fluororesin of the same material as above. This is an example of the present invention in which fluororesin insulator layers with a thickness of 2.0 mm were successively formed by extruding fluororesin.

〔Effect of the invention〕

As is clear from the above explanation, according to the insulated wire for a skin current heating tube of the present invention, a fluororesin insulator with excellent heat resistance is used as a coating material, especially in a skin current heating tube that is subjected to high-temperature heating exceeding 180°C. To provide this type of insulated wire for skin current heating tubes, which makes use of the characteristics of the fluororesin insulator, which compensates for the weakness of the fluororesin insulator against corona discharge, and which provides long-term stability even when used under high voltage. The purpose of the present invention has been more than fully achieved, and it has now become possible to provide this type of insulated wire for skin current heating tubes that can be heated at high temperatures and installed in long lengths, that is, can be used at high voltages.
This eliminates the need to increase the number of auxiliary equipment such as power supply equipment, making it possible to provide a skin current heating tube that is easy to maintain and is economically advantageous.

[Brief explanation of drawings]

1A and 1B are a cross-sectional explanatory view and a side explanatory view showing an example in which a skin current heating tube is traced to a high viscosity fluid transport pipe, and FIGS. 2A and 2B are a cross-sectional view and a side view showing an example in which a skin current heating tube is traced to a high viscosity fluid transport pipe, and FIGS. 2A and B are for a skin current heating tube according to the present invention. A cross-sectional explanatory view and a side explanatory view showing an example of an insulated wire, and FIG. 3 are explanatory views showing a test situation of an insulated wire for a skin current heating tube. In the figure, 1 is a skin current heating tube, 2 is a current conductor,
3 is a power supply, 4 is a high viscosity fluid transport pipe, 5 is a high viscosity fluid passage, 21 is a current conductor, 22 is an insulating layer mainly composed of an inorganic substance, 23 is a fluororesin-containing tape wrapping layer, 24
is a fluororesin-based coating layer.

Claims (1)

[Claims] 1. In an insulated wire for a skin current-generating tube that is inserted into a highly magnetic metal tube and connected to the end of the metal tube to form a current closed circuit passing through the inner skin of the metal tube, an inorganic material is placed directly above the current-carrying conductor. An insulating layer consisting mainly of An insulated wire for skin current heating tubes.