JPH10162659A - Of cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the positive electrode impulse dielectric breakdown strength of an OF(oil-filled) cable having an insulating layer of PP laminated paper and improve its pulse dielectric breakdown characteristic by providing a layer wound in turn with kraft paper and a plastic film having the positive electrode impulse dielectric breakdown strength higher than the negative electrode impulse dielectric breakdown strength. SOLUTION: A shield layer 3 wound with carbon paper is provided on the outer periphery of a conductor 1, and an auxiliary insulating layer 4 is provided on the shied layer 3. The auxiliary insulating layer 4 is wound with kraft paper and a plastic film in turn, and it has the thickness off 0.2-2mm. The plastic film having the positive electrode impulse dielectric breakdown strength higher than the negative electrode impulse dielectric breakdown strength is used. The reduction of the positive electrode impulse dielectric breakdown strength caused by the polypropylene (PP) laminated paper forming a main insulating layer 5 is supplemented, and the positive electrode impulse dielectric breakdown strength of an OF cable can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OF cable having a small polarity effect on impulse breakdown strength.

[0002]

2. Description of the Related Art As an insulating layer of an OF cable for ultrahigh-voltage power transmission, polypropylene-laminated paper (hereinafter referred to as PP) obtained by laminating a polypropylene film and kraft paper has recently been used.
Abbreviated as laminated paper. ) And impregnated with an insulating oil such as alkylbenzene oil are widely used. This is because AC cables have excellent dielectric properties and dielectric breakdown properties by using PP laminated paper. Also, because of its excellent DC breakdown characteristics, application to DC cables is also being studied.

However, the OF cable using the PP laminated paper has a disadvantage that impulse breakdown characteristics are not good. This is because the use of PP laminated paper has a large polar effect on the impulse breakdown strength, and the negative impulse breakdown strength is sufficiently high but the positive impulse breakdown strength is low.
As a result, the impulse breakdown characteristics of the cable are reduced.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to increase the positive impulse breakdown strength of an OF cable having an insulation layer of PP laminated paper, thereby improving the impulse breakdown characteristics.

[0005]

The object of the present invention is achieved by providing an alternating winding layer of kraft paper and a plastic film having a positive impulse breakdown strength higher than a negative impulse breakdown strength on the conductor side. Will be resolved. Examples of the plastic include polyphenylene oxide and polyvinyl fluoride.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
FIG. 1 shows an example of an OF cable according to the present invention. In the figure, reference numeral 1 denotes a conductor. The conductor 1 is a stranded conductor, and a spiral 2 serving as a passage for insulating oil is inserted into the center of the conductor. A shielding layer 3 wrapped with carbon paper or the like is provided on the outer periphery of the conductor 1, and a sub-insulating layer 4 is provided on the shielding layer 3.

The sub-insulating layer 4 has a thickness of 0.1 mm formed by alternate winding of kraft paper and plastic film.
It is an insulating layer of 2 to 2 mm. Examples of the plastic film used here include a film having a thickness of 50 to 200 μm made of plastic whose positive impulse breakdown strength is higher than that of the negative impulse breakdown strength. Specific examples of the plastic having a positive impulse breakdown strength higher than the negative impulse breakdown strength include polyphenylene oxide (PP
O), polyvinyl fluoride (PVF), polystyrene (P
S) may be mentioned, but polystyrene may cause crazing in insulating oil, so its use conditions are limited, and practical ones are polyphenylene oxide or polyvinyl fluoride.

[0008] The kraft paper used here is a normal insulating paper for power cables, such as kraft paper having a thickness of 0.05 to 0.2 mm satisfying the characteristics specified in JIS-C-2307, or deionized water washing. Kraft paper is used.
By alternately winding the kraft paper and the plastic film, the respective layers of the sub-insulating layer 4 can be sufficiently impregnated with the insulating oil.

When the thickness of the sub-insulating layer 4 is less than 0.2 mm, the effect of improving the positive impulse breakdown strength cannot be obtained.
If it exceeds 2 mm, wrinkles will be generated in the plastic film layer when the cable is bent, and when a polyvinyl fluoride film is used as the plastic film, the dielectric loss of polyvinyl fluoride is large, so that the entire cable is Since the dielectric properties are reduced, the thickness is preferably thinner, most preferably 0.2 to 1 mm.

On the sub-insulating layer 4, a main insulating layer 5 formed by winding ordinary PP laminated paper is provided. On this main insulating layer 5, carbon paper or the like is wound. A shielding layer 6 is provided. Further, an aluminum corrugated sheath 7 is provided outside the shielding layer 6, and an anticorrosion layer 8 is provided on the sheath 7. The insulating oil is filled in the sheath 7 in a pressurized state, and the gaps between the main insulating layer 5 and the sub-insulating layer 4 and the kraft paper are impregnated with the insulating oil to form the OF cable of the present invention. .

In the OF cable having such a structure, the sub-insulating layer 4 made of a plastic film having a positive impulse breakdown strength higher than the negative impulse breakdown strength causes an extremely large electric field stress when a voltage is applied. Since it is provided directly above the conductor 1, the main insulating layer 5
The sub-insulating layer 4 compensates for the decrease in the positive impulse breakdown strength caused by the PP laminated paper, and the positive impulse breakdown strength of the OF cable is increased to be substantially the same as the negative impulse breakdown strength. And the polarity effect of the impulse breakdown strength becomes small.

Further, in the present invention, as the sub-insulating layer 4, a double-sided laminated paper obtained by laminating kraft paper on both sides of the above-mentioned polyphenylene oxide or polyvinyl fluoride film is wound on the shielding layer 3. Layers may be employed, which will exhibit a similar effect. Further, in the present invention, a wound layer in which only kraft paper is wound can be provided between the shielding layer 3 and the sub-insulating layer 4. By providing this wound layer, the impulse breakdown strength can be further improved. This is preferable because the polarity effect can be reduced.

Hereinafter, a specific example will be shown to clarify the operation and effect. (Example 1) A 0.3 mm thick shielding layer is formed by winding carbon paper on a stranded wire conductor having a cross-sectional area of 2500 mm ² , and a 0.1 mm thick kraft paper and a 0.1 mm thick polyphenylene oxide are formed thereon. The film and the film were alternately wound to form a sub-insulating layer having a thickness of 0.5 mm. Further, a 170 μm-thick PP laminated paper (PP film thickness: 100 μm) is wound on the sub-insulating layer to form a sheet having a thickness of 2 μm.
A 5 mm main insulating layer is formed, a carbon paper is wound thereon to form a 0.2 mm thick shielding layer, an aluminum sheath is provided thereon, and a branched alkylbenzene oil (JIS-C-23220 2) is provided inside the sheath. (Type 1 oil) was filled under pressure to obtain an OF cable. The lightning impulse positive polarity dielectric breakdown strength and negative polarity dielectric breakdown strength of this OF cable were measured. Table 1 shows the results.

Example 2 OF Example 1 was repeated except that a 0.1 mm thick polyvinyl fluoride film was used in place of the polyphenylene oxide film.
A cable was prepared and the same measurement was performed. Table 1 shows the results.

(Conventional Example) An OF cable was prepared in the same manner as in Example 1 except that no sub-insulating layer was provided, and the same measurement was performed. Table 1 shows the results.

[0016]

[Table 1]

[0017]

As described above, in the OF cable of the present invention, the impulse breakdown strength of the positive impulse is increased and is substantially the same as the impulse breakdown strength of the negative polarity. The polarity effect is small.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of an OF cable of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Conductor, 4 ... Sub insulation layer, 5 ... Main insulation layer

Claims (3)

[Claims] 1. An OPC having an insulating layer formed by winding a polypropylene laminated paper on a conductor and impregnating the conductor with an insulating oil.
An OF cable according to claim F, wherein an alternating winding layer of kraft paper and a film made of plastic having a positive impulse breaking strength higher than the negative impulse breaking strength is provided on the conductor side in the F cable. 2. The OF cable according to claim 1, wherein the alternately wound layer is a layer formed by winding a laminated paper of kraft paper and a film made of the plastic. 3. The OF cable according to claim 1, wherein the plastic is polyphenylene oxide or polyvinyl fluoride.