JP3602297B2 - DC power cable - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a DC power cable that improves dielectric strength by removing distortion of an electric field due to space charge.
[0002]
[Prior art]
Conventionally, polyethylene and crosslinked polyethylene have been widely used as insulators of ordinary AC high-voltage power cables such as CV cables because of their excellent dielectric strength and dielectric properties.
[0003]
[Problems to be solved by the invention]
By the way, when a cable having an insulator made of polyethylene, cross-linked polyethylene, or the like is applied to high-voltage DC power transmission, it is known that some problems occur. The biggest problem is that a long-lived space charge is easily formed in an insulator by applying a high DC voltage. This space charge is generally said to be electronic, holey, or ionic, because it is trapped in a region related to the crystal structure of polyethylene. Further, the polyethylene because it is a good non-polar substances insulating, hardly causes leakage of trapped charge, therefore, a long lifetime space charge. When the insulator space charge is accumulated by the application of the direct current, the electric field strength near the conductor increases, which causes a disadvantage that the breakdown voltage of the cable decreases.
[0004]
In order to solve the above-mentioned inconveniences, there has been proposed a DC power cable in which an appropriate amount of carbon black is added to an insulator to reduce the accumulation of space charges and thereby increase the dielectric strength (Japanese Patent Laid-Open No. 61-253712). ).
[0005]
The gist of the proposed addition condition is that an insulating composition obtained by adding 0.2 to 5% by weight of carbon black to a thermoplastic resin under the following conditions was used as an insulator. The condition is that the ratio of the oil absorption (cc / 100 g) of the mineral oil to the specific surface area (m ² / g) measured by the BET method is 0.7 or more, 1.5 or less, and the carbon content is 97% or less. It is a carbon black having a weight percent or more and an average particle size of 10 to 100 nm (nanometer).
[0006]
However, in the case of this proposal, the DC breakdown characteristics are improved, but on the other hand, the added carbon black may also act as a foreign substance. That is, there is a problem that the lightning impulse destruction property, which is another property required for the power cable, tends to be lower than that of the non-added (unfilled) crosslinked polyethylene.
[0007]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and it is an object of the present invention to provide a DC power cable capable of improving DC breakdown characteristics and greatly improving lightning impulse breakdown characteristics.
[0008]
[Means for Solving the Problems]
The present invention has the following configuration to solve the above problems.
According to a first aspect of the present invention, there is provided a DC power cable characterized in that an insulating composition obtained by adding 0.2 to 5% by weight of carbon black to a thermoplastic resin under the following conditions is used as an insulator.
(A) The ratio of the oil absorption (cc / 100 g) of the mineral oil to the specific surface area (m ² / g) measured by the BET method is 0.7 or more and 3.5 or less, and
(B) a carbon content of 97% by weight or more, and
(C) The presence ratio of coarse carbon black having a particle size of 300 nm or more is 1% or less.
[0009]
According to another aspect of the invention, the added carbon black has an average particle size of DC power cable according to claim 1, characterized in that a 10 to 100 nm.
[0010]
Here, the specific surface area is an amount of a predetermined substance (N ₂ , Ar, etc.) adsorbed per 1 g of carbon black, and is expressed as a surface area per g. This is because it is difficult to measure the surface area of each particle.
On the other hand, the oil absorption is a literal amount of oil absorption, and is for observing the particle structure of carbon black.
[0011]
Examples of the thermoplastic resin include polyethylene (low density polyethylene, high density polyethylene), polypropylene, ethylene vinyl acetate copolymer (EVA), ethylene ethyl acrylate copolymer (EEA), ethylene propylene rubber (EPR), and the like. These mixtures can be used. In addition, it is of course possible to use it after crosslinking.
[0012]
On the other hand, typical types of carbon black include SAF carbon and acetylene carbon.
[0013]
According to the first aspect of the present invention, the lightning impulse breakdown voltage can be improved by setting the proportion of the coarse carbon black having a particle size of 300 nm or more to 1% or less by the configuration (c). did it. The reason for this is that, in many cases, impulse destruction is caused by conductive projections as a starting point of destruction. If the existence ratio of large carbon particles (300 nm or more) is large, coarse particles formed by agglomeration of carbon particles naturally become large. The probability of touching or approaching the conductor also increases. This is because such agglomerated coarse particle carbon near the inner and outer conductors is considered to affect impulse breakdown.
[0014]
Also, other configurations (a), it is possible to prompt the leakage of spatial electric load, etc. (b). Hereinafter, the reason will be described.
The resistivity (specific resistance) of the insulator composition is ρ (Ω-m), the temperature coefficient of the insulation resistance is α (1 / ° C.), and the electric field coefficient (stress coefficient of the insulation resistance) is β (mm / kv). If the electric field strength applied to the insulator is E (kv / mm),
ρ = ρ ₀ exp− (αT + βE) (1)
It is known that the following relationship holds.
[0015]
Then, the addition of carbon black, the temperature coefficient α is reduced while the field factor β is increased, promoting leakage of the spatial electric load in insulator composition. This is because, when the electric field coefficient β increases, the resistivity ρ decreases, so that the electric field in a high stress portion (a portion where a strong electric field is applied) is relieved. This is because the maximum electric field Emax that has appeared in FIG. Thus, the electric field distribution in the insulator composition moves in the direction of uniformity, and the accumulation of space charges is reduced. The reason for limiting each numerical value will be described.
[0016]
(1) The reason why the addition amount of carbon black is 0.2 to 5% by weight.
If the addition amount is 0.2% or less, the above-mentioned effects cannot be sufficiently obtained. If the addition amount is 5% or more, the resistivity ρ and the electric field coefficient β increase remarkably, which may cause thermal destruction.
[0017]
(2) The reason that oil absorption / specific surface area is 0.7 or more and 3.5 or less.
When the amount of carbon black is increased, the distance between the particles is reduced, and a current flows between particles under a high electric field due to a tunnel effect. For this reason, the electric field coefficient β becomes unnecessarily large, which causes thermal destruction. Therefore, it is essential to reduce the resistivity ρ of the equation (1) with a small amount of addition. By the way, carbon black having a large ratio of the oil absorption amount to the specific surface area can reduce the resistivity ρ with a small amount, and good results can be obtained if this ratio is 0.7 or more.
[0018]
On the other hand, when this ratio is larger than 3.5, the degree of aggregation of the particles increases, the apparent particle diameter increases, and the mixing with a thermoplastic resin such as polyethylene deteriorates. In particular, acetylene carbon has a large effect because the particles are connected in a chain.
When any one of SAF, ISAF, I-ISAF, CF, SCF, and HAF carbon black is used, the above ratio is in the range of 0.7 to 1.5. I was assured.
[0019]
(3) The reason why the carbon content of carbon black is 97% by weight or more.
Carbon black contains impurities such as ash, O ₂ , and H ₂ , and when these impurities are large, the electrical characteristics are deteriorated. Therefore, the higher the purity of carbon, the better.
[0020]
(4) The reason for the 10~100nm an average particle diameter of the carbon black (Claim 2).
The average particle size of the carbon black, when the number of particles among the particles size range Ni, the center value of the grain径径interval was Di,
Average particle size = ΣNi · Di / ΣNi
Given by
This carbon black having an average particle size of 10 to 100 nm is an optimal value that does not disturb the crystal structure of an insulator such as polyethylene. Disturbing the crystal structure lowers the electrical performance of the insulator. On the other hand, if the particle size is larger than the above range, the dispersion and mixing of the carbon black will be poor. On the other hand, if it is smaller than this, it is difficult to manufacture and it is not practical.
[0021]
As described above, the direct current characteristics are improved by removing the carbon black particles having a particle diameter of 300 nm or more to remove 1% or less of the coarse particles of the carbon black, thereby improving the direct current characteristics and the lightning impulse. Breakage characteristics can be improved.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
A DC power cable was manufactured using the insulating material according to the present invention (the present invention), and a power cable was manufactured using a comparative insulating material (the comparative product).
[0023]
That is, in the power cable of the present invention, the insulator used was an insulating composition obtained by adding 0.2 to 5% by weight of carbon black under the following conditions to crosslinked polyethylene. In this case, the ratio of the oil absorption (cc / 100 g) of the mineral oil to the specific surface area (m ² / g) measured by the BET method is 0.7 or more and 3.5 or less, and the carbon content is 97% by weight. % Of the carbon black, and the maximum particle size of the carbon black is 300 nm, and coarse particles exceeding 300 nm are removed to reduce the proportion of coarse carbon black having a particle size of 300 nm or more to 1% or less. .
[0024]
The comparative power cable used an insulating composition containing 0.2 to 5% by weight of carbon black under the following conditions as an insulator. In this case, the ratio of the oil absorption (cc / 100 g) of the mineral oil to the specific surface area (m ² / g) measured by the BET method is 0.7 or more and 3.5 or less, and the carbon content is 97% by weight. % Or more, and the average particle size of the carbon black is 10 to 100 nm , and the maximum particle size is not specified.
[0025]
Each of the power cables of the present invention and the comparative product has a conductor sectional area of 800 mm ² and an insulator thickness of 20 mm, and is formed by simultaneously extruding the inner and outer semiconductive layers and the insulator.
[0026]
The DC power cables of the above-described present invention product and the comparative product were actually manufactured, and the insulator of each DC power cable was observed under a microscope, thereby investigating the size distribution of the carbon particles. FIG. 1 shows the results of the investigation.
[0027]
Further, a lightning impulse breakdown test and a DC breakdown test were performed on these DC power cables, and the results were obtained as shown in FIG. From FIG. 2, it is understood that the lightning impulse breakdown voltage and the DC breakdown voltage of the power cable of the present invention are significantly improved. Therefore, it is understood that the present invention is superior to the comparative product.
[0028]
【The invention's effect】
According as the invention of claim 1 described above, by reducing the accumulation of space electric load by adding a specific amount of a particular carbon black in the thermoplastic resin forming the insulator, the DC breakdown voltage of the power cables The carbon black to be added can significantly improve the lightning impulse destruction characteristics by suppressing the presence ratio of coarse carbon black having a particle size of 300 nm or more to 1% or less. Therefore, the DC breakdown characteristics and the lightning impulse breakdown characteristics can be simultaneously improved, and the overall dielectric strength of the DC power cable can be improved.
According to the second aspect of the present invention, the DC breakdown voltage further increases, and the DC breakdown characteristics can be improved.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram of a result of an investigation on the distribution of carbon particle sizes of a product of the present invention and a comparative product.
FIG. 2 is an explanatory diagram showing the electrical performance of a product of the present invention and a comparative product in comparison.

Claims (2)

A DC power cable, wherein an insulating composition obtained by adding 0.2 to 5% by weight of carbon black under the following conditions to a thermoplastic resin is used as an insulator.
(A) the ratio of the oil absorption (cc / 100 g) of the mineral oil to the specific surface area (m ² / g) measured by the BET method is 0.7 or more and 3.5 or less, and
(B) a carbon content of 97% by weight or more, and
(C) The presence ratio of coarse carbon black having a particle size of 300 nm or more is 1% or less. The added carbon black, a DC power cable according to claim 1, wherein the average particle size of 10 to 100 nm.

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