JPH0366769B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an OF cable, in particular an outer part of the entire insulation layer consisting of alternating windings of kraft paper and lead-resistant (heat-resistant) plastic film.
This is related to OF cable.

In recent years, ultra-high voltage, large capacity OF cables (275-500KV)
Low-loss insulation materials using various plastic materials have been developed to reduce dielectric loss (tanδ) and increase power transmission capacity, as well as to improve dielectric strength and create more compact OF cables. It has come to be put into practical use. As these insulating materials, we are particularly interested in industrial productivity, cost, track record,
From the viewpoint of performance etc., polyethylene and polypropylene are most likely to be used.

The structure of an OF cable that uses polyethylene or polypropylene as part of the insulating material is (a) polyethylene film tape or polypropylene film tape and kraft paper wrapped alternately, (b) polyethylene film or polypropylene film on one or both sides. (c) When using composite insulating paper that is made by laminating and integrating kraft paper, (c) When using composite insulating paper that is made by laminating and integrating polypropylene mixed paper on one or both sides of polypropylene nonwoven fabric, (d) When using polyethylene or There are cases where polypropylene mixed paper is used.

In particular, a product made by laminating and integrating polypropylene film and kraft paper is called PPLP, and OF cables using PPLP have excellent electrical performance, mechanical performance, industrial productivity, and economic efficiency, and have a proven track record at present. It has become the mainstream OF cable using plastic.

However, an insulating layer made of polyethylene undergoes deterioration such as dissolution of the polyethylene when the temperature exceeds 100°C in insulating oil, and an insulating layer made of polypropylene begins to deteriorate at a temperature of 130°C or more.

OF cables are generally connected by processing the metal sheaths at both ends with a lead worker.
In the conventional "normal lead method" that uses normal solder, the melting point of the solder reaches approximately 250°C, so when using polyethylene or polypropylene as part of the insulating layer, it is necessary to The outer insulating layer near the sheath begins to deteriorate under the influence of heat.

A detailed explanation of the OF cable connection will be omitted, but
In addition, ``low-temperature solder long lead injection method'', ``metal sheath under oil pouring lead method'', and ``lead-free connection method'' have been developed.
Although it has been put into practical use, if the conventional ordinary lead construction method could be applied to OF cables with an insulating layer containing plastic, it would improve compatibility with conventional cable connections, commonality of construction technology, This is preferable in terms of economy, reliability based on track record, etc.

It has been found that when ordinary lead work is applied to OF cables having an insulation layer containing polyethylene or polypropylene, the outer 2-6 mm insulation layer close to the metal sheath is thermally affected.

Therefore, in order to use ordinary lead work for low-loss, high dielectric strength OF cables that have an insulation layer containing polyethylene or polypropylene, it is necessary to install lead-resistant work 2 to 6 mm from the outside of the insulation layer, which is affected by the heat of the lead work. It has already been proposed to use kraft paper, a composite insulating material made by laminating polymethylpentene and kraft paper, or a composite insulating material made by laminating fluoroethylene propylene and kraft paper. The idea was to use composite insulating materials such as However, although kraft paper is the cheapest and has the highest heat resistance, it has a higher εtanδ than PPLP or the above-mentioned composite materials, which increases the εtanδ of the entire cable.

Composite insulation materials made by laminating and integrating polymethylpentene and kraft paper are (a) expensive because polymethylpentene itself is not as versatile as polyethylene or polypropylene and has poor industrial productivity; ) The adhesion with kraft paper is poor and it is difficult to integrate the composite, making it more expensive, and the thermocompression bonding process to improve adhesion causes thermal deterioration of the kraft paper, resulting in a decrease in electrical and mechanical properties. Or,
(c) Polymethylene pentene film and kraft paper tend to separate when impregnated with insulating oil and exposed to high operating temperatures (e.g., 85°C) due to deflection of the crystallinity or residual stress of the plastic due to thermocompression bonding.

In addition, an insulating material made by laminating and integrating fluoroethylene propylene and kraft paper causes roughly the same phenomenon as the insulating material made by laminating and integrating polymethylpentene film and kraft paper.
In addition, fluoroethylene propylene is more expensive than polymethylpentene, and tends to be less versatile as a composite insulating material.

The inventor proposed an OF cable in which kraft paper was wrapped around the outside of the insulation layer as a lead-resistant material.
As already explained, the problem is that εtanδ becomes large. On the other hand, in the present invention, the outer side 2 of the insulating layer
The OF cable has an insulating layer made by alternately wrapping heat-resistant plastic film tape and kraft paper tape around the ~6mm thick part, and attempts to supply lead-resistant OF cables at low cost. It is something.

Examples of heat-resistant plastic films include plastic films made of polymethylpentene, plastic films made of fluoroethylene propylene, and films made of tetrafluoroethylene plastic (trade name: Teflon).

These plastic film tapes alone
It has also been proposed to form an outer insulating layer, but
Compared to kraft paper, single wraps of plastic film (a) have inferior impulse voltage resistance, and (b) there are no gaps between the films, so when manufacturing cables, it is difficult to avoid vacuuming before filling with insulating oil. (c) The formation of insulating oil passages is also poor, so it is necessary to apply embossing etc. to the film in advance, and (d) polymethylpentene layer alone is difficult to form due to the increase in thickness due to swelling in insulating oil. Continuous experiments have confirmed that there are problems such as the insulating layer becomes too thick, the mechanical properties against bending etc. are poor, and (e) the amount of expensive film used increases, which affects the product cost. As aforementioned,
The idea was to form an outer insulating layer by alternately wrapping heat-resistant plastic film and kraft paper around the lead wire.

Examples of the present invention and comparative examples to be compared thereto will be described below.

FIG. 1 shows a cross section of an embodiment of an OF cable according to the present invention.

Although not shown in the figure, the surface of the conductor 2 having the oil passage 1 is provided with an appropriate internal seal, and a PPLP tape of εtanδ=2.65×0.07% (85°C) is applied to the surface of the conductor 2.
The inner insulating layer 3 is formed by winding to a thickness of 4 mm, and on the outside, polymethylpentene film with an εtanδ of 2.2×0.02% (85°C) and kraft paper with an εtanδ of 3.2×0.18% (85°C) are alternately coated with a thickness of 4 mm. An insulating layer 4 is formed by winding the insulating layer 4, which is then subjected to external sheathing (not shown), covered with a metal sheath 5, heated and evacuated to be filled with insulating oil, and then an anti-corrosion layer made of PVC. 6 will be provided.

In these respects, there is no difference from the conventional OF cable manufacturing process. More than 500KV
We obtained a prototype OF cable, but since polymethylpentene film swells in insulating oil and increases its thickness, kraft paper has a low density (0.6 g/cm ³ ) and a large thickness of 200 μm. The density was 0.5 to 1.0 g/cm ³ , preferably 0.6 to 0.78.
g/cm ³ and thickness of 80 to 300 μm, preferably 100 to 200 μm.

In addition, the kraft paper used had been pre-hydrated to control its humidity (see Japanese Patent Publication No. 52-38237). Although it was not necessary in this case, a polymethylpentene film with embossing was used. Instead of humidity control, polymethylpentene film and/or kraft paper with embossing may be used.

As a result, εtanδ=2.67×0.065% (85℃)
Got 500KV OF cable. As mentioned above, the thickness of the outer insulating layer is determined so that the heat during lead work does not affect the plastic film used for the inner insulating layer. However, polyethylene,
In the case of polypropylene, it has been confirmed that a range of 2 to 6 mm is usually sufficient.

For comparison, kraft paper with ε tan δ = 3.2 x 0.18% (85°C) was used only for the outer 4 mm insulating layer. As a result, εtanδ=2.68×0.072% (85
℃) got 500KV OF cable.

From the above results, it is clear that a cable excellent in terms of εtanδ can be obtained by the present invention, but especially in the case of the outer insulation layer using plastic film tape, the film surface is covered with fibers and is soaked in oil. Therefore, it is noteworthy that the impulse voltage withstand performance has improved dramatically.

According to the present invention, it is possible not only to eliminate most of the problems associated with wrapping a lead heat-resistant plastic film alone on the outside of the insulating layer, but also to solve the problems of the heat-resistant plastic film and kraft paper that have already been proposed. Problems that arise with composite insulating materials include (a) thermal deterioration of the kraft paper, which deteriorates its electrical performance because kraft paper and heat-resistant materials are laminated and integrated through a high-temperature, long-term heat treatment process; (mainly tan δ) deteriorates, (b) the crystallinity of the plastic is biased, the thickness increases due to swelling of the plastic after impregnation with insulating oil due to residual stress, and furthermore, when immersed in oil with kraft paper, There is no need to worry about lowering the bonding strength of the composite film or (c) reducing the processing speed and making the composite film more expensive since it is necessary to heat and pressurize for a long time for composite formation. These problems are solved by the alternating wrapping of heat-resistant plastic film and kraft paper of the present invention.

When performing lead work, even though it is a heat-resistant plastic, if polymethylpentene plastic film is used, if the temperature exceeds 150°C in insulating oil, it will begin to melt or change in quality, so lead work that has been used in the past is not recommended. However, it is necessary to be very careful, but plastic films made of Teflon (trade name) and fluoroethylene propylene do not change in quality at the above-mentioned temperatures, so special precautions are not required when working with lead.

As explained above, the OF cable of the present invention is
For most of the inside of the insulating layer, an inexpensive plastic with slightly inferior lead resistance but excellent in other properties is used, and for the outside, an expensive but durable plastic is used to make ordinary lead work possible. Plastic with excellent lead workability,
By using it in the form of a film, it eliminates the disadvantages of laminating and integrating with kraft paper, while by alternately winding it with kraft paper, it overcomes the disadvantages of using only a film. Ultra-high pressure, large capacity OF with excellent characteristics and economical efficiency
It is a cable, and its practical use is expected from both the manufacturing and practical aspects.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention. 1...Oil passage, 2...Conductor, 3...Inner insulation layer made of PPLP, 4...Outer insulation layer made of polymethylpentene and kraft paper, 5...Metal sheath,
6...PVC anti-corrosion layer.

Claims (1)

[Scope of Claims] 1. The outside 2 to 6 mm thickness of the insulating layer is made of alternating windings of lead-resistant plastic film tape and kraft paper tape, and the remaining inside insulating layer is made of an insulating layer containing polyethylene or polypropylene. OF cable characterized by the following. 2. The OF cable according to claim 1, characterized in that polymethylpentene, fluoroethylene propylene, or tetrafluoroethylene is used as the lead-resistant plastic. 3. The OF cable according to claim 1, characterized in that when polymethylpentene is used as the lead-resistant plastic, the kraft paper that is alternately wound is subjected to a humidity control process in advance. 4. When polymethylpentene is used as the lead-resistant plastic, one or both of the plastic film and kraft paper that are alternately wound is used that has been embossed in advance. Range 1
OF cable as described in section. 5. A patent characterized in that when polymethylpentene is used as a lead-resistant plastic, the kraft paper that is alternately wound is subjected to moisture control processing in advance, and the polymethylpentene film is embossed. As stated in claim 1
OF cable.