JPH1186636A - Dc cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a satisfactory DC insulating characteristic and lightning impulse intensity resistance and reduce the thickness of an insulating layer by providing an insulating layer, consisting of a cross-linked polyethylene and containing a polarized inorganic filler, and including a maleic anhydride denatured(MAH) polyethylene in this insulating layer. SOLUTION: The addition quantity of MAH polyethylene is set to 1-10 phr, the denaturation quantity is set to 0.1% or more, and the added quantity of a polarized inorganic filler is set to 0.5-5 phr. A part of polyethylene is kneaded with the polarized inorganic filler to form a master batch having high filling property, and the remaining part of the polyethylene is mixed thereto to a prescribed filling concentration. The MAH polyethylene is added in the mixing of the master batch with the polyethylene, and a cross-linking agent is further added thereto to form a compound. The compound is extrusion molded on a conductor with inner and outer semiconductor layers, and cross-linked by heating. As a result, the reduction in resistance to lightning impulse intensity by the polarized inorganic filler can be prevented to dispense with the increase in thickness of the insulating layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC cable, and more particularly to a DC crosslinked polyethylene cable having excellent DC breaking strength and impulse breaking strength.

[0002]

2. Description of the Related Art A cable having a cross-linked polyethylene as an insulating layer (hereinafter referred to as a cross-linked PE cable) is widely used for alternating current. Generally, an organic peroxide such as dicumyl peroxide (hereinafter, referred to as DCP) is used for crosslinking polyethylene.

Japanese Patent Publication No. 57-21805 discloses that a polar inorganic filler such as magnesium oxide is added to an insulating layer in order to improve the insulation performance instability when a crosslinked PE cable is used for direct current. It has been disclosed.

[0004] In a crosslinked PE cable using a crosslinker such as DCP, a stable insulation performance is obtained because the decomposition residue of the crosslinker lowers the volume resistivity of the crosslinked polyethylene insulator and increases the charge accumulation. Could not be obtained. The decrease in the volume resistivity increases the leakage current of the insulator, and the Joule heat leads to thermal breakdown of the insulator. Since the volume resistivity is particularly lowered in the middle layer portion of the insulating layer where a large amount of the decomposition residue of the cross-linking agent is distributed, the load of the voltage applied to the outer layer and the inner layer under DC power application increases.
The effective thickness of the insulator is reduced. In addition, the increase in charge accumulation locally generates a high electric field in the insulator, causing a low voltage breakdown or the like, or causes a dielectric breakdown when the polarity is reversed or when an impulse of the opposite polarity is introduced.

The drawbacks in the DC properties of such crosslinked PE cables have been ameliorated by the addition of polar inorganic fillers as described above.

[0006]

However, a direct current case obtained by adding a polar inorganic filler such as magnesium oxide to a crosslinked polyethylene insulator (hereinafter referred to as a crosslinked PE insulator).
According to Bull, the adhesiveness between the polar inorganic filler and the polyethylene is poor, so that voids are generated at the interface, and the lightning impulse strength is likely to be reduced. In order to ensure a sufficient lightning impulse strength of the cable, it is necessary to make the thickness of the insulator larger than that required from the DC withstand voltage, and the outer diameter of the cable must be increased. Did not.

[0007] Accordingly, an object of the present invention is to provide a crosslinked PE having excellent direct-current insulation characteristics and improved lightning impulse strength.
An object of the present invention is to provide a DC cable having an insulator.

Another object of the present invention is to provide a DC cable having satisfactory DC insulation characteristics and lightning impulse strength, and having a reduced insulating layer thickness.

[0009]

According to the present invention, there is provided a direct current cable having an insulating layer comprising a crosslinked polyethylene and containing a polar inorganic filler, wherein the insulating layer is modified with maleic anhydride. Disclosed is a direct current cable characterized by containing polyethylene.

[0010] Crosslinked PE for obtaining excellent DC insulation properties
As the polar inorganic filler to be added to the insulating layer, magnesium oxide (MgO) is suitable, and in particular, MgO having a purity of 99% or more is preferable (for example, see JP-B-57-21805 and JP-A-7-21850). Described), it is preferred to add at least 0.5 phr.
On the other hand, in order to prevent the resin pressure from excessively increasing in the continuous extrusion step in the production process, the amount of the filler should be 5 phr.
It is preferable to set the following.

As a base resin (base material), high density,
Any of medium density, low density or ultra low density polyethylene, linear low density polyethylene, etc. may be used.

As the polyethylene crosslinking agent, DC is usually used.
Although P is used, the present invention is also effective for organic peroxide crosslinking agents other than DCP.

The maleic anhydride-modified polyethylene is, for example, a polyethylene grafted with maleic anhydride. The modification amount with maleic anhydride is preferably 0.1% or more, but even if it is slightly less than 0.1%, the effect can be obtained by increasing the addition amount. High density, medium density, low density or ultra low density polyethylene as raw material polymer (unmodified polyethylene),
Any of linear low density polyethylene and the like may be used.
The same polyethylene modified as the base resin (base material) is preferred in terms of compatibility, but a different polyethylene may be modified.

The added amount of the maleic anhydride-modified polyethylene is from 1 phr to 10 phr in order to obtain the sufficient effect of the present invention.
The following is preferred. If you select the amount of denaturation, polyethylene 100
Less than 2 parts by weight per part is sufficiently effective. 10ph
If it exceeds r, foreign substances are mixed and moldability is deteriorated.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the DC cable according to the present invention will be described in detail. In the embodiment of the DC cable of the present invention, a conductor, an inner semiconductive layer formed on the outer periphery thereof, and a crosslinked PE insulator formed on the outer periphery thereof;
The crosslinked PE insulator includes at least an outer semiconductive layer formed on the outer periphery thereof and a sheet formed on the outer periphery thereof. The crosslinked PE insulator is made of polyethylene, maleic anhydride-modified polyethylene (hereinafter, referred to as MAH polyethylene), It consists of a polar inorganic filler such as magnesium and is cross-linked using an organic peroxide cross-linking agent such as DCP.

The preferable addition amount of MAH polyethylene is 1
10 to 10 phr, a preferable modification amount is 0.1% or more, and a preferable addition amount of the filler is 0.5 to 5 phr.

To manufacture the DC cable according to the present invention, a part of polyethylene and a polar inorganic filler are kneaded to prepare a master batch having a high filler concentration, and this is mixed with the remaining part of the polyethylene. (Kneading) to a predetermined filler concentration, MAH polyethylene is added at the time of mixing the master batch and the polyethylene, and a compound containing a crosslinking agent is extruded onto a conductor together with the inner and outer semiconductive layers, and molded. Crosslink by heating to obtain a crosslinked PE cable. MAH polyethylene may be added during the kneading process of the master batch (before or during kneading).

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the DC cable according to the present invention will be described in detail below. [Example 1] Sheet-like samples having different compositions as shown in Table 1 were prepared and used as Samples No. to No. 1. Samples H to H are insulating compositions containing the MAH polyethylene of the present invention, and Samples A and B are comparative compositions. Sample A is only low-density polyethylene, and Sample B is low-density polyethylene with only magnesium oxide added. Denaturation rate 0.07 for samples c, d and e
%, Denaturation rate is 0.16% for samples,
Male and maleic anhydride-modified low-density polyethylenes (modified PE-1, modified PE-2, and modified PE-3 in this order) having a modification ratio of 0.34% are shown in Table 1 (parts by weight). Added in. In Table 1, () shows the modification rate of MAH polyethylene.

[0019]

[Table 1]

The samples were heat-pressed into a sheet having a thickness of 1 mm, and the elongation characteristics at a low temperature of each sample were evaluated. Table 2 shows the results of measuring the elongation at a pulling speed of 200 mm / min for five dumbbell pieces of each composition at a temperature of -50 ° C. Table 2 shows the average, minimum, and maximum values of the five pieces.

[0021]

[Table 2]

As is apparent from Table 2, the average value of the elongation is 104% and the variation is about 9% in the case of the sample A, ie, the polyethylene not containing MgO. In the sample B to which MgO is added, the average value of elongation increases and the variation between samples becomes very large. This is polyethylene and Mg
It is estimated that the adhesion of the interface of O is unstable.

In the sample to which MAH polyethylene was added,
Except for Sample C, the elongation was close to that of polyethylene without the addition of MgO. Maleic anhydride modification amount is 0.0
The average elongation and the fluctuation of the elongation decreased as the amount of the modified polyethylene increased in the samples C to E of 7%, but the fluctuation rate decreased to nearly 20% for the first time at 5 phr of the sample E. 3 phr for samples with 0.16% denaturation
In (Sample G), the elongation percentage was equal to that of polyethylene without addition at 1 phr (Sample L) in which the denaturation amount was 0.34%, and the fluctuation rate became close to 20%.

The results were obtained by adding maleic anhydride-modified polyethylene to MgO-added polyethylene.
This is considered to indicate that the adhesion between the filler and the polyethylene was improved and the state of the interface was improved.

Example 2 Using a compound obtained by adding DCP as a cross-linking agent to a composition corresponding to the sample B and the sample G in Table 1, a conductor cross-sectional area of 200 mm ² and an insulating layer thickness of 9 were used.
mm cables 1 and 2 were manufactured.

A dielectric breakdown test was performed on each cable. Table 3 shows the results.

[Table 3]

From Table 3, it can be seen that the cable 1 to which the MAH polyethylene was not added had a high DC breaking strength but the impulse resistance was inferior, whereas the cable 2 to which the modified polyethylene was added had both a DC breaking strength and an impulse resistance. It is recognized that it is excellent.

From the above results, it was confirmed that by adding maleic anhydride-modified polyethylene to the crosslinked polyethylene insulating layer containing MgO, a DC cable excellent in both DC breaking strength and impulse resistance was obtained. .

[0029]

As described above, the DC cable of the present invention is used.
According to the cable, in a DC cable having a crosslinked polyethylene insulator, excellent DC insulation characteristics are maintained, and the lightning impulse strength is improved. That is, since a polar inorganic filler such as MgO is added to the cross-linked polyethylene insulating layer, a decrease in volume resistivity and an increase in charge accumulation based on the decomposition residue of a peroxide cross-linking agent such as DCP are prevented. Since maleic anhydride-modified polyethylene is added, excellent lightning impulse strength can be obtained even when a polar inorganic filler is present in the insulating layer. It is estimated that the addition of maleic anhydride-modified polyethylene improves the adhesion between the filler and the polyethylene.

Further, according to the DC cable of the present invention, since the maleic anhydride-modified polyethylene is added together with the polar inorganic filler, a decrease in lightning impulse strength due to the filler is prevented, so that the thickness of the insulating layer is increased. Even without this, a crosslinked PE cable for DC having excellent DC insulation characteristics and sufficient lightning impulse strength can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08L 23:26)

Claims (5)

[Claims] 1. A DC cable having an insulating layer comprising a crosslinked polyethylene and containing a polar inorganic filler, wherein the insulating layer contains maleic anhydride-modified polyethylene. 2. The direct current cable according to claim 1, wherein said polar inorganic filler is magnesium oxide. 3. The direct current cable according to claim 1, wherein the maleic anhydride-modified polyethylene has a modification amount of 0.1% or more. 4. The amount of the maleic anhydride-modified polyethylene added is 1 phr to 10 phr.
Or any of the three DC cables. 5. The amount of the polar inorganic filler added is 0.5.
The direct current cable according to any one of claims 1 to 4, which is not less than phr and not more than 5 phr.