JPS624802B2 - - Google Patents

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 viewpoint of energy saving, increasing power transmission capacity, and making cables more compact,
For ultra-high voltage OF lines, cables have been developed and put into practical use that use plastic film as the insulator, alternately wrapped with kraft paper, or composite insulating paper made by laminating plastic film and kraft paper together. It's here.

As a plastic material, it has good electrical properties, i.e., small ε×tanδ (ε: dielectric constant, tanδs dielectric loss angle), high impulse and AC withstand voltage performance, and economically excellent polyolefin materials, especially polypropylene. Polymethylpentene and polyethylene are common.

However, as is well known, these materials are made from petroleum, so they are very different from dodecylbenzene (DDB), which is commonly used as an ultra-high voltage insulating oil among the insulating oils used in OF cables. They have similar properties. For example, the sp value (solubility parameter), which is an index showing the similarity in properties, is approximately 8 for the plastic material and the insulating oil, and is extremely similar.

For this reason, insulators using plastic film made from the aforementioned polyolefin plastic film material will inevitably swell in insulating oil as the insulating oil permeates into the plastic film depending on the temperature of the insulating oil. The thickness of a single piece of insulating tape increases in proportion to the rise in temperature. in general
At the upper limit operating temperature of OF cables of 85°C, the thickness of the above-mentioned polyolefin-based insulating tape using plastic film may increase by several percent compared to before impregnation.The solution to this problem is to use polyolefin-based plastic material. This is essential for cables that use

Also, if we are trying 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 have to increase the amount of plastic film used in the cable. Since the thickness increases due to swelling in the insulating oil at the operating temperature, it is necessary to take measures against swelling of the insulating tape itself or the insulating layer during the insulating layer formation 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). Other countermeasures include 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 bumps. It will be done. Furthermore, both of these methods may be used in combination.

Now, if these methods are adopted, there will be too much gap between the insulating tapes when the cable is impregnated with insulating oil at room temperature immediately after the cable is manufactured, so it will be difficult to wrap the cable against bending and twisting until the cable is completely installed. The rolled insulating tape tends to move irregularly, and the tapes are not aligned with each other. Even if the gap in one gap-wound layer does not overlap with the gap in the gap-wound layer immediately above and below, this may cause the tape to collapse. In some cases, it may become heavy due to
This may impede the impulse voltage resistance performance and AC voltage resistance performance, or may cause damage to the tapes.

Also, as 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.
Before the gaps between the insulating tapes disappear and the appropriate hardness is achieved, the lower insulating layer, which bears the load of the conductor, collapses and becomes hard due to the weight of the conductor, and the upper insulating layer, which does not bear the load of the conductor, collapses. An extra gap will be created in the insulating layer as opposed to the lower insulating layer, so if it is bent or twisted in this condition, this will cause the aforementioned gap irregularities and damage to the insulating tape. Not only this, but even when the cable swells after actual use, the thickness of the insulating layer will not return to a uniform hardness over the entire circumference of the cable, and the thermal expansion and contraction of the cable will be reduced. (Expansion and contraction of the cable when the power is turned on and off) may damage the insulating tape and reduce AC and impulse performance.

The basic method for manufacturing an OF cable using a polyolefin plastic film or a combination of a polyolefin plastic film and kraft paper and the problems that still occur even with the basic method have been explained above, and the present invention solves these problems. It provides a means to solve the problem.
That is, during the OF cable manufacturing process, immediately after winding insulating tape, etc., vacuum heating and drying, extruding the metal sheath, and impregnating it with insulating oil,
The maximum operating temperature of the cable (generally 85℃),
Hold for the required time to sufficiently swell the insulating tape already wound inside the metal sheath, increase the thickness of the insulating tape to the required thickness, and make it uniformly hard in the circumferential direction of the cable. By adding this heating and swelling treatment process, the subsequent handling of the cable is completely different from the case of OF cables that only use conventional kraft paper. The object of the present invention is to not only eliminate all of the above-mentioned problems, but also to obtain an OF cable with excellent electrical performance.

Examples of the present invention will be described below.

Conventionally, ordinary OF cables are manufactured and shipped through roughly the following steps.

Conductor manufacturing → Insulating tape wrapping → Vacuum heating drying → Aluminum or lead metal sheath extrusion coating → Impregnation →
Polyethylene or vinyl chloride anti-corrosion layer tubing → inspection → cutting and shipping → 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.

Since the polyethylene or vinyl chloride anticorrosion layer is not applied at this stage, the anticorrosion layer itself is not exposed to high temperatures by heating to 85°C. The predetermined temperature in the heating and swelling treatment generally means the maximum operating temperature of the cable (for example, 85° C.), but it goes without saying that the temperature may 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, an alternately wound layer of polyolefin plastic film and kraft paper, or an integrated layer of polyolefin plastic film and kraft paper. It is applied to products that use polyolefin plastic film for part or all of the insulating layer, such as those that have a wound layer of composite paper laminated on the surface.

Immediately after impregnating the cable with insulating oil, the metal sheathed cable, while still wrapped in a drum, can be placed in a special oven and heated with steam to keep it at, say, 85°C, or it can be heated in a vacuum drying tank (generally higher than 85°C). reuse (used to dry insulation layers at high temperatures),
A metal sheathed cable is placed in the drum together with the drum, and the drum is heated at a predetermined temperature for a predetermined period of time with atmospheric air introduced.

Another method is to cover the drum and blow hot air into it, and in the case of an aluminum sheath,
There is also a method of heating this with electricity.

Further, when impregnating with insulating oil, it is effective to use insulating oil that has been heated to a predetermined temperature, for example, 85° C., because it can accelerate the subsequent heating and swelling treatment.

Although examples of cable heating methods have been listed above, since the present invention does not relate to heating itself, any other heating method may be used.

Here, we will explain an example in which multiple layers of PPLP tape (composite tape consisting of 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. Figure 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 evaporate, and the drying ends at point C.
If impregnated with insulating oil at room temperature, the thickness of the PPLP tape will be approximately 3-4% at point A after impregnation.
If we enter the heat swelling treatment process at this point,
Depending on the type and size of the cable, approximately 6~
Swelling reaches saturation in 24 hours and the thickness increases (point B).
Humidity control or embossing 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 of penetration of the insulating oil. Conversely, 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 increase in thickness due to swelling is saturated varies depending on the type of plastic film, the degree of crystallinity of the molecules in the film, and the surrounding conditions of the film.

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

As mentioned above, in OF cables, when the swelling of the plastic film is fully saturated at the highest temperature in actual use (generally 85°C), the insulating tape should be rolled so that it becomes equal to or slightly thinner than the thickness when the tape was wound. Since the insulating tape is subjected to humidity control processing and embossing before winding, the heating and swelling treatment performed immediately after the impregnation process according to the present invention is carried out at a predetermined temperature (the highest actual operating temperature of the OF cable). (generally 85℃) for a specified period of time (the time required for the increase in thickness due to swelling to reach saturation, which is determined by the type and degree of crystallinity of the plastic film used and the surrounding conditions of the film). be.

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. After that, when the tapes forming the insulating layer are dried, the kraft paper wears down to point C in FIG. 1, and 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 the conventional manufacturing method, the next process is extrusion coating of polyethylene or vinyl chloride anticorrosion layer in this state, and from then on until the completion of installation.
To give the cable various bends and twists,
As mentioned above, there was a risk of damage to the cable. 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 FIG. 1 when the tape is wound.
You can clearly see that it has become more resistant to twisting.

In addition, as the insulating oil permeates into the plastic film due to the heat swelling treatment described above, the microscopic voids in the plastic film are also impregnated. The breakdown voltage is also improved by 10 to 30%, and the dielectric loss angle tan δ is also improved in the direction of decreasing, so that it exhibits good electrical characteristics even in the initial stage of practical use.

[Brief explanation of the drawing]

Figure 1 is an example of a composite insulating tape that integrates a polyolefin plastic film and kraft paper that has been subjected to moisture control or embossing during the period from the drying process to the end of the heat swelling treatment process.
FIG. 3 is a diagram showing a state of substantial thickness change of a PPLP tape.

Claims (1)

[Claims] 1. In manufacturing OF cables in which part or all of the insulating layer is formed from a polyolefin plastic film, a metal sheath is applied and the cable is heated and swollen at the stage where it is impregnated with insulating oil. A method for manufacturing an OF cable, comprising the step of causing swelling in an insulating layer formed entirely of polyolefin plastic film.