JPS63178407A - Dc power cable - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention relates to a DC power cable that improves the dielectric strength and other characteristics of a base polymer by eliminating distortion in the electric field caused by space charges. be.

"Prior Art" Conventionally, polyethylene and crosslinked polyethylene have been widely used as insulators for ordinary AC high voltage power cables such as CV cables because of their excellent dielectric strength and dielectric properties.

[Problems to be Solved by the Invention] By the way, it is known that several problems occur when a cable having an insulator made of polyethylene, crosslinked polyethylene, or the like is applied to high-voltage DC power transmission. The biggest problem is that by applying a high DC voltage, long-lived space charges are likely to be formed in the insulator. This space charge is generally said to be electronic, hole-based, or ionic, and is said to be caused by electric charges being trapped in regions related to the crystal structure of polyethylene.

Furthermore, since polyethylene is a non-polar material with good insulation properties, trapped charges are less likely to leak, resulting in space charges having a long life. When a space charge is accumulated in the insulator due to the application of direct current, the electric field strength near the conductor increases, causing a disadvantage that the breakdown voltage of the cable decreases.

The present invention was made against this background, and an object of the present invention is to provide a DC power cable with increased dielectric strength by reducing the accumulation of space charges that adversely affect the insulator.

"Means for Solving the Problems" In order to achieve the above object, the inventors first of all
The first step was to find a means to prevent the accumulation of space charges in the insulator and remove distortion of the electric field.Secondly, the second step was to improve the dielectric strength of polyethylene, the base polymer, and to reduce the We have found a means (second means) to prevent dielectric breakdown from occurring even if there is strain.

In the first means, an insulator as an insulating composition is formed by adding 0.2 to 5% by weight of carbon black to the thermoplastic resin. In addition, as the carbon black, BE
3. The ratio of the oil absorption amount (cc/100 g) of mineral oil to the specific surface area (m"/g) measured by the T method is 0.7 or more.
5 or less, and the hydrogen content relative to carbon black is 0
, 6% by weight or less, and an average particle size of 10 to 100n+n,
That is, 10 to 100 millimicrons are used,
Furthermore, this carbon black is added to the thermoplastic resin at a rate of 0.
The insulating composition is constituted by adding 2 to 5% by weight.

Here, the specific surface area used in the description of carbon black is the amount of a predetermined substance (for example, N1, Ar, etc.) adsorbed per gram of carbon black, and is expressed as a surface area per gram. This is because it is difficult to measure the surface area of each particle. On the other hand, oil absorption is literally the amount of oil absorbed, and is a measure of the particle structure of carbon black. Further, the average particle size of carbon black is given by: Average particle size = ΣN1 - Di/ΣNi, where the number of particles in each particle size section is set as Di, the center value of the Ni1 particle size section. Further, typical types of carbon black include SAF carbon and acetylene carbon.

On the other hand, in the second means, the thermoplastic resin used as the insulator is mixed with 0.1-
It is formed by copolymerizing at a ratio of 1% by weight (resin indicated by code A in Table 2), and it is also formed by blending an aromatic monomer with polyethylene at a ratio of 0.1 to 1% by weight. (symbol B in Table 2)
resin shown).

In addition, in the following explanation, when referring to the entire thermoplastic resin, "thermoplastic resin" or simply "resin" is used.
When referring to the polyethylene contained in this resin, the term "base polymer" is used.

"Function" To explain the first means, leakage of space charges can be promoted by adding carbon black to the insulating composition. The reason for this will be explained below.

The resistivity (specific resistance) of the above insulating composition is ρ (Ω-m), the temperature coefficient of insulation resistance is α (1/'C), and the electric field coefficient (
If the stress coefficient of insulation resistance is β (mm/kV) and the electric field strength applied to the insulator composition is E (kV/mm), then ρ=ρ. It is known that the relationship exp-(αT+βE) (1) holds true.

When carbon black is added, the electric field coefficient β increases while the temperature coefficient α decreases, promoting space charge leakage in the insulator composition. This is because when the electric field coefficient β increases, the electric field becomes high and the resistivity ρ decreases, so the electric field in high stress parts (areas where a strong electric field is applied) is relaxed, and when the temperature coefficient α decreases, the conductor temperature increases. This is because the maximum electric field E max that appeared on the shielding side when it was high is reduced. In this way, the electric field distribution within the insulator composition moves toward uniformity, reducing space charge buildup.

Next, the reasons for various numerical limitations will be explained.

(1) Reason for adding carbon black in an amount of 0.2 to 5% by weight.

If the surface addition amount is 0.2% or less, the above-mentioned effects cannot be sufficiently obtained. Moreover, if it exceeds 5%, the resistivity ρ decreases and the electric field coefficient β increases significantly, leading to a risk of thermal breakdown.

(2) Reason why oil absorption m/specific surface area is 0.7 or more and 3.5 or less.

When the amount of carbon black added increases, the distance between the particles decreases, and under a high electric field, current flows between the particles due to the tunnel effect. For this reason, the electric field coefficient β becomes larger than necessary, causing thermal breakdown. Therefore, it is essential to reduce the resistivity ρ in equation (1) with a small addition amount.

By the way, carbon black, which has a large ratio of oil absorption to specific surface area, can lower the resistivity ρ with a small amount.
Good results can be obtained if this ratio is 0.7 or more. On the other hand, if this ratio is greater than 3.5, the degree of agglomeration of particles increases, the apparent particle size increases, and miscibility with thermoplastic resins such as polyethylene deteriorates. In particular, this effect is large in acetylene carbon because the particles are connected in a chain. Also, SAF, l5AF, l-1sAF
, CF, SCF, and HAP carbon, the above ratios are 0, 7 to 1.
It has been experimentally confirmed that a range of 5 is particularly good.

(3) The reason why the hydrogen content in carbon black is 0.6% by weight or less.

When the hydrogen content is high, the number of π electrons increases and the movement of electrons is hindered. Therefore, in order to obtain the desired resistivity ρ,
A large amount of carbon black must be added, which is not preferred for the same reason as (2) above. Therefore, the lower the hydrogen content, the better, and good results can be obtained if it is 0.6% by weight or less.

(4) The reason why the average particle size of carbon black is lθ to 100 millimicrons.

This particle size is the optimum value that does not disturb the crystal structure of the insulator such as polyethylene. Disturbance of the crystal structure reduces the electrical performance of the insulator. Grains.

If the diameter is larger than this, the dispersion and mixing of carbon black will deteriorate. Moreover, if it is smaller than this, manufacturing is difficult and impractical.

Next, the second means (1) for improving the dielectric strength of polyethylene, which is the base polymer, will be explained.
The thermoplastic resin A used as the insulator composition was formed by copolymerizing ethylene with an aromatic monomer at a ratio of 0.1 to 1% by weight, and the aromatic monomer used in this copolymerization As a monomer, S tyrene shown in the upper row of Table 3 was used.

A 1lyl S tyrene shown in the middle row, 4-(3-B utenyl) S tyrene or 3-(3-B utenyl) S tyrene shown in the bottom row
e etc. are appropriate.

(1) Reason for selecting aromatic monomer for copolymerization with ethylene.

Aromatic monomers have a benzene ring, and the resonance effect of the benzene ring absorbs the electronic energy around it. That is, since dielectric breakdown of the resin is caused by the energy of electrons flowing through the polymer, the dielectric breakdown strength of the base polymer is improved by the benzene ring of the aromatic monomer absorbing the surrounding electron energy.

In addition, as shown in the schematic diagram in Table 2, the aromatic monomer is bonded to the polyethylene chain (main chain) that is the base polymer in the copolymer, so the polyethylene chain receives and absorbs the electronic energy. can also be absorbed by its benzene ring.

(2) Addition amount of aromatic monomer to ethylene.
Reason for setting it at 1-1% by weight.

It has been observed that when the amount of aromatic monomer added is 1% by weight or more, the crystal structure of polyethylene is disturbed, and when the amount is 0.1% by weight or less, the electron energy absorption effect does not occur effectively. This has been experimentally confirmed.

Next, a second means (n) for improving the dielectric strength of polyethylene, which is the base polymer, will be explained. This second means (■) differs from the second means (I) described above in the composition of the thermoplastic resin (resin indicated by code B in Table 2), and this thermoplastic resin is made of polyethylene. 0.1-1 aromatic monomer! It is formed by blending at a ratio of ffi%.

The aromatic monomers used in the blend with the polyethylene include 5-tyrene shown in the upper row of Table 3, A 11yL S tyrene shown in the middle row, and A 11yL S tyrene shown in the lower row, similar to the aromatic monomers used in the copolymerization. 4
-(3-B utenyl) S tyrene or 4-(3-B --utenyl) S tyrene
etc. are appropriate.

In the thermoplastic resin configured in this way, the main chain of polyethylene, which is the base polymer, is not bonded to the benzene ring, so the main chain of the base polymer receives and receives the electronic energy indirectly. can only be absorbed. In other words, while the copolymer (resin A) combined with the base polymer can directly absorb electron energy, the blended resin B can only absorb electron energy indirectly. Since it cannot absorb energy, it is likely to be less effective than resin A.

However, from the perspective of manufacturing resin B, the polymerization temperature,
While it is difficult to produce resin A in terms of controlling reaction conditions such as polymerization time or selecting a reaction initiator, resin B can be produced relatively easily by selecting an appropriate solvent. There is an advantage.

"Example" Power cables using various insulator compositions shown in Table 1 as insulators were manufactured. In this case, the power cable has a conductor cross-sectional area of 200 mm" and an insulator thickness of 3 mm,
The inner and outer semiconducting layers and the insulator are formed by coextrusion.

A DC breakdown test was conducted on the above power cable, and the results shown in Table 1 were obtained. In Table 1, insulator compositions No. 1 to No. I8 are No. 1 to No. 19 to No. I8 for those containing no aromatic monomer.

30 shows the results of a DC destructive test for a sample containing a predetermined amount of aromatic monomer.

As is clear from Table 1, in the power cables of the present invention (No. 19 to No. 27) (using copolymers), by adding a predetermined amount of aromatic monomer, the DC breakdown voltage can be significantly reduced. improved.

To explain with an example, when comparing Composition No. 3 and Composition No. 24, No. 26 under substantially the same test conditions, the DC breakdown voltage of Composition No. 3 was 96 (kV).
/mm), and the DC breakdown voltages of compositions No., 24, No., and 26 were 120 (kV/mm) and 144, respectively.
(kV/n+m), so the composition No. 3
It was found that the value of DC breakdown voltage was improved by copolymerizing a predetermined amount of aromatic monomer with each of the above. Similarly, composition No. 9 and composition No. 23
, No., and 25, their DC breakdown voltages range from 96 (kV/mm) to 120.144 (kV/mm).
V/mm), the above No. 9
It was found that the DC breakdown voltage value was improved by copolymerizing the composition with a predetermined amount of aromatic monomer.

Moreover, composition No. 20 and composition No. 23 and No.

As can be seen by comparing the DC breakdown voltage with Composition No. 24, or the DC breakdown voltage between Composition No. 21 and Composition No. 25 to No. 27, these compositions contain aromatic monomers in the same ratio. Even if carbon black were present, it was observed that there was no relative improvement in DC breakdown voltage in the absence of carbon black.

That is, the DC breakdown voltage of compositions No. 23, No. 24 is 128.120 (kV 7 mm), and the composition No.
The DC breakdown voltage of composition No. 20 is 112 (kV /n+m), and the DC breakdown voltage of compositions No. 25 to No. 27 is 152.144.144 (kV 7 mm).

Since the DC breakdown voltage of No. 21 was 136 (kV 7mm), it was recognized that the DC breakdown voltage was improved when both the aromatic monomer and carbon black were contained.

On the other hand, as is clear from Table 1 above, the power cables of the present invention (using No. 28 to No. 300 blend products)
By blending a predetermined amount of aromatic monomer, the DC breakdown voltage was significantly improved, similar to that using a copolymer.

To explain with an example, as can be seen by comparing composition No. 19 and composition No. 30, which have almost the same test conditions,
The DC voltage breakdown of composition NO19 is 96 (kV/mm),
The DC breakdown voltage of composition No. 30 was 144 (kV/mm
), it was found that the DC breakdown voltage value was improved by blending a predetermined amount of aromatic monomer into the composition N093.

Furthermore, as can be seen by comparing the DC breakdown voltage values of Composition No. 29 and Composition No. 30, even if aromatic monomers are blended in the same ratio in these compositions, the presence of carbon black is It was observed that in the case where there was no relative improvement in the DC breakdown voltage. That is, composition N
The DC breakdown voltage of composition No. 02 is 128 (kV/mm), and the DC breakdown voltage of composition No. 30 is 144 (kV 7mm).
), it was found that the DC breakdown voltage was improved when both the aromatic monomer and carbon black were contained.

"Effects of the Invention" As explained above, according to the present invention, a specific amount of carbon black is added to the thermoplastic resin forming the insulator,
Furthermore, since the thermoplastic resin contains an aromatic monomer in a specific proportion, the resonance effect of the benzene ring of the aromatic monomer attracts surrounding electron energy and prevents the formation of space charges. In addition to this, it is possible to improve the dielectric strength of the base polymer constituting the resin. As a result, it is possible to increase the DC breakdown voltage of the cable.

Claims (5)

[Claims] (1) An insulating composition is prepared by adding 0.2 to 5% by weight of the following carbon black to a thermoplastic resin made by copolymerizing ethylene with an aromatic monomer at a ratio of 0.1 to 1% by weight. A DC power cable characterized by being used as a. (a) The ratio of the oil absorption amount (cc/100g) of 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) the carbon black The hydrogen content is 0.
Carbon black less than 6% by weight. (2) The DC power cable according to claim 1, wherein the carbon black satisfies the following conditions. (a) Specific surface area (m^2/g) measured by the above BET method
The ratio of oil absorption amount (cc/100g) of mineral oil to 0.
7 or more and 1.5 or less, and (b) carbon black having an average particle size of 10 to 100 nm. (3) As an insulator, an insulating composition is prepared by adding 0.2 to 5% by weight of the following carbon black to a thermoplastic resin made by blending polyethylene with an aromatic monomer at a ratio of 0.1 to 1% by weight. A DC power cable characterized by its use. (4) The DC power cable according to claim 3, wherein the carbon black satisfies the following conditions. (a) The ratio of the oil absorption amount (cc/100g) of 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) the carbon black The hydrogen content is 0.
Carbon black less than 6% by weight. (5) The DC power cable according to claims 3 and 4, wherein the carbon black satisfies the following conditions. (a) Specific surface area (m^2/g) measured by the above BET method
The ratio of oil absorption amount (cc/100g) of mineral oil to 0.
7 or more and 1.5 or less, and (b) carbon black having an average particle size of 10 to 100 nm.