JPS5828113A - Method of producing of cable - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an OF cable, and particularly to a method for manufacturing an OF cable using a polyolefin plastic film or a combination of a polyolefin plastic film and kraft paper as an insulator.

In recent years, from the perspective of saving energy, increasing power transmission capacity, and making cables more compact, ultra-high voltage OF lines of 275 to 500 K'V are using plastic film, alternately wrapped with kraft paper, or Cables using composite insulating paper made by laminating plastic film and kraft paper together have been developed and put into practical use.

Good electrical properties for a plastic material, that is, ε×
-δ (ε: permittivity, -δ: dielectric loss angle) is small, impulse and AC withstand voltage performance is high, and economically excellent polyolefin materials are used. Among them, polypropylene, polymethylpentene, and polyethylene are commonly used. be.

However, as is well known, these materials are made from petroleum, so among the insulating oils used in OF cables, they are very different from dodecylbenzene (DDB), which is commonly used as ultra-high voltage insulating oil. They have similar characteristics. For example, the sp value (solubility parameter), which is an index showing the similarity of properties, is extremely similar between the plastic material and the insulating oil at around 8. Insulators using Blastinok film are insulated in insulating oil, and the insulating oil permeates into the plastic film depending on the temperature of the insulating oil, so swelling is inevitable and the thickness of a single tape increases. Generally, the upper limit temperature for OF cable usage is 85°C.
The insulating tape made of polyolefin plastic film may be several inches thicker than before it is impregnated, and it is essential to solve this problem for cables made of polyolefin plastic material.

In addition, if we try to improve the electrical characteristics of an OF cable that uses both kraft paper and plastic film, we will naturally have to increase the proportion of plastic film used, but if we increase that, we will need to increase the proportion of plastic film used.
Since the thickness increases due to swelling in the insulating oil at the operating temperature of the cable, it is necessary to take measures against swelling of the insulating tape itself or the insulating layer during the insulating layer forming process prior to impregnation.

Specifically, as a countermeasure for this, if kraft paper is interposed as alternating rolls or is present in a composite tape made by laminating plastic film and kraft paper, as is already known, kraft paper One method is to wind a material that has been pre-humidified (see Japanese Patent Publication No. 52-38237). As a cultural countermeasure, there is a method of wrapping one or both of kraft paper tape and plastic film tape, or a composite insulating tape made of plastic film and kraft paper with so-called embossed concavities and convexities. Furthermore, both of these methods may be used in combination.

Now, if you adopt these methods, there will be too many gaps between the insulating tapes when the Gupple is impregnated with insulating oil at room temperature immediately after manufacturing is completed, so the cable cloth, bending and twisting when -ψ゛ is completed. The insulating tape wound around the wall may move irregularly, and even if the tape is wound so as not to overlap the gap between the chap winding layers, it may collapse and become heavy, resulting in poor impulse voltage resistance and AC This may impair pressure resistance or cause damage to the tapes.

In addition, when the cross-sectional area of the conductor increases and the weight of the conductor increases, the insulation tape swells and becomes thicker due to the high temperature caused by electricity after the cable is installed, causing the gaps between the insulation tapes to disappear properly. Before it reaches the appropriate hardness, the lower insulating layer that bears the load of the conductor will sag and become hard due to the weight of the conductor.
The upper insulating layer, which does not receive the load of the conductor, will have an extra gap in contrast to the lower insulating layer, so if it is bent or twisted in this state, this will cause the aforementioned gap irregularity. Not only is the damage to the insulating tape greater, but also the insulation layer thickness will not return to a uniform hardness over the entire circumference of the cable due to swelling after actual use. Subsequent thermal expansion and contraction of the cable (turning on electricity,
(Stretching and contraction of the cable due to disconnection) can damage the insulation tape and reduce AC and impulse performance.

Above we have explained the basic method for manufacturing OF keguru using a combination of polyolefin plastic film or polyolefin plastic film and kraft paper, and the problems that still occur even with the above basic method. It provides a means to solve the problem, i.e. during the OF cable manufacturing process.
In particular, immediately after wrapping insulating tape, vacuum heating and drying, extruding the metal sheath and impregnating it with insulating oil,
Maintaining the cable at the maximum operating temperature (generally 85°C) for a necessary time to sufficiently swell the already wound insulating tape in the metal sheath and increasing the thickness of the insulating tape to a stable thickness; It is characterized by making the cable uniformly hard in the circumferential direction before proceeding to the next process, and by adding such addition fp4+ and swelling treatment processes, subsequent handling of the cable can be made easier. The present invention aims to provide an OF cable that is no different from the conventional OF cable using only kraft paper, which not only solves all of the above-mentioned problems, but also has excellent electrical performance.

The implementation of the present invention will be described below.

Traditionally, ordinary OF cables are manufactured and shipped by the following steps: 〇Conductor manufacturing - Insulation cheap winding - Vacuum heating drying - Aluminum or lead metal sheath extrusion coating - Co-immersion - Polyethylene or vinyl chloride anti-corrosion layer tubing - Inspection - Shipment of cut - Installation.

As can be understood from the above description, the heat swelling treatment in the present invention is carried out immediately after the metal sheath coating is completed and the insulating oil is impregnated therein.

At this stage, the anticorrosive layer of polyethylene or vinyl chloride is not applied, so the anticorrosive layer itself is not exposed to the high temperature caused by heating to 85°C. The predetermined temperature in the heat swelling treatment is generally the maximum operating temperature of the cable (for example, 8
5° C.), but it goes without saying that the temperature can be slightly higher or lower than this maximum temperature.

Further, in the OF cable to which the present invention is applied, the insulating layer wrapped with insulating tape includes a single layer of polyolefin plastic film, alternately wound layers of polyolefin plastic film and kraft paper, and an integrated layer of polyolefin plastic film and kraft paper. Applicable to products that use polyolefin plastic film for part or all of the insulating layer, such as products that have a wound layer of composite paper laminated on the paper.

Immediately after impregnating the cable with insulating oil, the metal sheathed cable, still wrapped in a drum, is placed in a special oven and heated with steam to maintain it at, say, 85°C, or it is placed in a vacuum drying tank (generally at 85°C). (used to dry the insulating layer at a higher temperature) is reused, the metal sheathed cable is placed inside the drum together with the drum, and the drum is heated at a specified temperature for a specified period of time in the atmosphere.

There is also a method of covering the drum with a cover and blowing hot air into it, and in the case of an aluminum sheath, there is also a method of heating it with electricity.

In addition, when impregnating with insulating oil, the temperature must be set at a predetermined temperature, for example, 85°C.
It is effective to use insulating oil heated to C to accelerate the subsequent heating and swelling treatment.

Examples of cable heating methods have been listed above, but since misfire 1 is not related to heating itself, it does not matter what heating method is used for the pond.

Here, an example will be described in which multiple layers of PPLP tape (a composite tape consisting of a polypropylene plastic film and kraft paper laminated on both sides) are gap-wound as an insulating layer. It goes without saying that the PPLP tape that has been pre-humidified or embossed is used as described above. FIG. 1 shows the substantial change in thickness of the PPLP tape during the period from the drying process to the heating and swelling process.

As the drying begins, the moisture in the kraft paper of the PPLP tape begins to drain, and when the drying process ends at 6 points, the process begins.
Depending on the type and size of the cable, the swelling reaches saturation and increases in thickness in approximately 6 to 24 hours (point B). Humidity control or -cV,y boss processing is performed so that the tape thickness at point B is equal to or slightly smaller than the thickness at point 0 before drying starts.

To explain the heat swelling treatment in more detail, since swelling is a phenomenon in which insulating oil penetrates between the molecules of the plastic film, it depends on the temperature of the insulating oil, which determines the rate at which the insulating oil penetrates. In other words, if you keep the temperature of the insulating oil constant and give it a sufficiently long time, the plastic film will show a certain amount of swelling and the thickness will stop increasing at a certain value. That is, the increase in thickness of the plastic film in the insulating oil at a certain temperature is saturated at a constant value. However, the time at which the thickness increase due to swelling is saturated varies depending on the type of plastic film, the degree of crystallinity of molecules in the film, and the surrounding conditions of the film.

- As an example, the thickness increase due to swelling in DDB insulating oil of a composite insulating tape made of polypropylene or polyethylene film and kraft paper covered on both sides is 85%.
At ℃, it reaches saturation in about 6 to 24 hours. On the other hand, the increase in thickness due to swelling in DDB insulating oil of a composite insulating tape formed by covering polymethylpentene film and kraft paper on both sides saturates at approximately 12-72H at 85°C.

As mentioned above, for OF cables, when the swelling of the plastic film is fully saturated at the highest temperature in actual use (generally 85 degrees Celsius), the insulating tape is wrapped with tape so that it is exactly the same thickness as when it was wrapped, or slightly tingling. Since the insulating tape is subjected to humidity control processing and embossing beforehand, the heat swelling treatment carried out immediately after the impregnation according to the present invention is carried out at a predetermined temperature (meaning the highest temperature at which the OF cable is actually used). , generally 85°C) for a predetermined time (the time at which the increase in thickness due to swelling is saturated, which is determined by the type and degree of crystallinity of the plastic film used and the surrounding conditions of the film). .

In actual cable manufacturing, first, we use an insulating tape that has been moisture-conditioned or embossed in advance so that it has the characteristics shown in Figure 1, so that its thickness does not decrease, that is, to maintain the state at point 0 in Figure 1. Hold it and wrap the tape to the required thickness over the conductor. Thereafter, when dried, each tape forming an insulating layer was reduced to 27 strips of paper up to point 6 in Figure 1.
:5・The insulating layer becomes rough.

After that, when the metal sheath is extruded and coated and impregnated with insulating oil at room temperature, the insulating layer is cooled by the insulating oil, the plastic film layer contracts, and the thickness of the insulating tape is further reduced to A in Figure 1. Furthermore, the insulating layer becomes rough. In conventional manufacturing methods, the next process is extrusion coating with a polyethylene or vinyl chloride anticorrosion layer in this state, and the cable is then subjected to various bends and twists until the installation is completed, causing damage to the cable as described above. There was fear. However, in the present invention, the thickness of the insulating tape is returned to a state where there is no unnecessarily large gap between the tapes by heating and swelling treatment, that is, close to the zero point in Figure 1 when the tape is wound. You can clearly see that it is getting stronger.

Due to the heat-swelling treatment that I explained, the insulating oil permeates into the plastic film, so the microscopic voids in the plastic film are also impregnated, and the AC Both the withstand voltage and impulse withstand voltage are 10 to 30%, and the dielectric loss angle is -
δ is also improved in the direction of decreasing, and good electrical characteristics are exhibited even in the initial stage of practical use.

[Brief explanation of drawings]

Figure 1 shows the actual state of PPLP tape, which is an example of a composite insulating tape that integrates a moisture-controlled or embossed polyolefin plastic film and kraft paper, from the drying process to the heating swelling process. It is a figure which shows the state of thickness change.

Claims (1)

[Claims] (1) In the manufacture of OF cables in which part or all of the insulating layer is made of polyolefin plastic film, the metal sheath is applied and the insulating oil is impregnated.
)7 A method for manufacturing an OF cable, comprising the step of subjecting the cable to a heating swelling treatment to produce necessary swelling.