JP2002245867A - Oil impregnated dc solid cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oil impregnated dc solid cable preventing the deoiling void in the gaps caused by the shrinkage of an insulation oil, spreading between insulation paper layers during a current loaded cooling heat cycle. SOLUTION: For the oil impregnated solid cable with rolled layers of insulation paper impregnated with high viscosity oil, the insulation layer is composed by alternately laying an insulation layer made by winding only craft paper, and an insulation layer made by winding plastic laminate paper.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC oil immersion solid cable, and more particularly to a DC oil immersion solid cable suitable for an ultra-high pressure long submarine cable of 300 to 500 kV class or more.

[0002]

2. Description of the Related Art As an ultra-high voltage DC cable of 300 to 500 kV class, an OF cable of a type in which low viscosity oil is impregnated and hydraulic pressure is applied is used. However, 50-1
If the length is longer than 00 km, it becomes difficult to maintain the oil pressure. Therefore, a so-called solid cable is used in which the insulating layer is impregnated with high-viscosity oil and oil pressure is not applied so as not to remove oil.

[0003]

In the above-described DC oil immersion solid cable, no oil pressure is applied, and the viscosity of the insulating oil is high. Occurs. When the applied voltage is increased (300 to 500 kV class or more), a high DC electric field is applied to the voids, and the insulating paper layers are spread by electromechanical stress, thereby reducing the breakdown voltage. In particular, this problem becomes a severe condition in a voltage application verification test in which a voltage 1.5 to 2 times the operating voltage is applied.

In addition, voids in the oil gap are caused by thermal expansion of insulating oil,
The conductor allowable temperature of the oil-immersed solid cable is about 50 to 60 ° C.
There is a problem that the temperature is considerably lower than the temperature.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a DC oil immersion solid cable which suppresses the spread of oil elimination voids between insulating paper layers due to the contraction of insulating oil during cooling by applying heat cycle. .

[0006]

SUMMARY OF THE INVENTION The expansion of oil gaps between deoiled void insulating paper layers due to contraction of insulating oil during cooling in a current-carrying heat cycle increases the pressure between the insulating layers (that is, improves the tightness of the insulating layers). Do) can be suppressed.

According to the present invention, there is provided an oil-immersed solid cable in which a high-viscosity oil is impregnated in an insulating paper winding insulating layer, wherein the insulating paper winding insulating layer comprises a plurality of kraft paper insulating layers and a plurality of plastic laminated paper winding insulating layers. The gist of the present invention is that it is composed of alternating insulating layers.

In a kraft paper insulating layer solid cable, after the kraft paper is wound around the conductor, moisture is removed in the insulating paper drying step, the paper thickness is reduced, and the insulating layer surface pressure is reduced. In plastic laminated paper, especially polyolefin-based polypropylene (PP) laminated paper, PP swells to some extent with insulating oil, and thus has the effect of increasing the surface pressure. The oil-immersed solid cable is impregnated with high-viscosity oil, so that it is lubricated at a high temperature of, for example, 120 ° C., and swells greatly.

Therefore, when the kraft paper layer and the plastic laminated paper layer such as PP laminated paper are alternately arranged, the decrease in the surface pressure due to the removal of moisture of the kraft paper is compensated for by the increase in the surface pressure due to the swelling of the laminated paper, and the insulation layer is tightened. And the spread of the deoiled voids between the insulating paper layers during the heat cycle of the application heat cycle can be suppressed. That is, it is possible to prevent the breakdown voltage from being lowered during cooling in the applied heat cycle during the applied-current verification test.

Here, when using PP laminated paper,
The PP fraction is preferably from 20 to 80%. If it is less than 20%, the effect of increasing the surface pressure is small, and if it is more than 80%, the paper to be laminated becomes thin paper, which causes a problem in manufacturing laminated paper.

The number of windings of the insulating paper for each of the kraft paper insulating layer and the laminated paper insulating layer is preferably 5 to 30. If the number is five or less, the number of alternate laminations increases and the workability is poor. In the case of 30 sheets or more, the thickness of each kraft paper layer and laminate paper layer becomes large, and the effect of compensating the surface pressure between laminations becomes small.

[0012] Also, the laminated insulating paper having a small PP fraction on the inner layer side and a laminated paper having a large PP fraction on the outer layer side having a structure of the alternating insulating layer, or the number of wound laminated layers of the laminated paper on the inner layer side is small. By increasing the number of layers of laminated paper on the outer layer side, step insulation can be achieved. By using step insulation, the dielectric constant of the inner layer side is higher than that of the outer layer side, and the insulation resistance is reduced, so that the electric field is alleviated and the characteristics with respect to impulse voltage and DC voltage are improved.

[0013]

Embodiments of the present invention will be described below. FIG. 1 is a sectional view showing an example of a DC oil immersion solid cable of the present invention. Although this cable is not shown around the conductor 1 in order from the center, it is provided with an appropriate internal shield, and 16 sheets of 100 g of density 1.0 g / cm ³ are provided on the outside thereof.
μm thick kraft paper insulating layer and 16 sheets of 120 μm thick PP laminated paper (30 μm paper / PP /
(Construction of 30μ paper) Insulating layers are alternately formed (however, a kraft paper layer is provided immediately above the conductor and immediately below the shielding layer). The insulating layer has a conductor cross-sectional area of 200% under 40% relative humidity.
It is wound up on a conductor of 0 mm ² and the insulation thickness is 20
mm.

After performing a predetermined vacuum overheating drying,
Kinematic viscosity at 60 ° C. at 1300 cst, 120 ° C.
After completion of impregnation with a high viscosity oil having a kinematic viscosity of 120 cst, 2 kg /
cm ^TwoIt was gradually cooled to room temperature under pressure.

On the insulating layer, a shielding layer 4 and a lead coating 5 were applied, and although not shown, a polyethylene anticorrosion layer and an iron wire sheath were applied to obtain a submarine cable structure.

As the high-viscosity insulating oil, those having a kinematic viscosity at 60 ° C. of about 500 to 10,000 cst and a kinematic viscosity at 120 ° C. of about 50 to 500 cst are used. Kraft paper of alternating winding configuration is used for DC cable 0.9
High density paper of ~ 1.2 g / cm ³ is good.

For comparison, a submarine cable having the same structure using only 100 μm kraft paper was manufactured.

For the two cables, 8 hours when the conductor temperature is room temperature 及 び 50 ° C. and when the conductor temperature is room temperature⇔70 ° C.
A DC heat cycle section energizing test was performed at n and 16 hr off.

The initial DC voltage is 400 kV.
The voltage was increased by 50 kV step-up for each heat cycle, and the breakdown voltage under DC heat cycle application was determined.

In each case, destruction occurred during heat cycle cooling, and the destruction tests were as shown in Table 1.

[0021]

[Table 1] From the results in Table 1, it can be seen that the cable of the example has a breakdown voltage intensity that is 2-3 times higher than the cable of the comparative example.

Next, another embodiment of the present invention is shown in FIG.
FIG. 2 similarly shows a cross section of a DC oil immersion solid cable, in which the plastic fraction of the laminated paper is gradually increased from the conductor side toward the sheath side in the configuration of the alternating insulating layers.

FIG. 3 shows still another embodiment of the present invention. In the structure of the alternating insulating layer, the number of windings of the inner layer side laminated paper is reduced, and the number of windings of the outer layer side laminated paper is reduced. It is the one that increased.

[0024]

As described above, by using the kraft paper layer / plastic laminate paper layer as an alternately wound insulating layer, the reduction in paper thickness due to moisture removal of kraft paper is offset by the increase in paper thickness due to oil swelling of the laminate paper. As a result, the insulation layer surface pressure is kept high, preventing the expansion of deoiling voids during heat cycle cooling under DC application, and providing a highly reliable ultra-high-voltage DC cable because the breakdown voltage can be reduced. can do.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a DC oil immersion solid cable of the present invention.

FIG. 2 is a sectional view showing another embodiment of the DC oil immersion solid cable of the present invention.

FIG. 3 is a sectional view showing another embodiment of the DC oil immersion solid cable of the present invention.

[Explanation of symbols]

 1,21,31 Conductor 2,22,32 Kraft paper insulating layer 3,23,33 PP laminated paper insulating layer 4,24,34 Shielding layer 5,25,35 Lead coating

Claims (5)

[Claims] 1. A direct current oil immersion solid cable in which a high viscosity oil is impregnated in an insulating paper winding insulating layer, wherein the insulating paper winding insulating layer comprises a plurality of kraft paper insulating layers and a plurality of plastic laminated paper insulating layers. A direct current oil immersion solid cable comprising an alternating insulating layer. 2. The plastic laminated paper is a composite insulating paper in which kraft paper is laminated and integrated on one or both sides of a polypropylene film or a polypropylene fiber cloth, and a polypropylene fraction is 20 to 80%. 2. The direct current oil immersion solid cable according to 1. 3. The multi-layer insulation layer of kraft paper and the multi-layer insulation layer of plastic laminated paper, wherein the plurality of layers are 5 to 30 sheets.
DC oil immersion solid cable described. 4. The DC oil immersion solid according to claim 1, wherein in the structure of the alternating insulating layers, laminated paper having a small plastic fraction on the inner layer side and laminated paper having a large plastic fraction on the outer layer side are used. cable. 5. The direct-current oil immersion solid according to claim 1, wherein in the structure of the alternating insulating layers, the number of windings of the laminated paper is reduced on the inner layer side and the number of windings of the laminated paper is increased on the outer layer side. cable.