JPH1186635A - Dc cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a lengthy cable by providing an insulating layer consisting of a cross-linked polyethylene, including a specified quantity or less of a polarized inorganic filler in the insulating layer, including no benzene ring in the cross-linked polyethylene, and performing the crosslinking by use of an organic peroxide which generates a volatile decomposition residue having a boiling point, not exceeding a specified temperature. SOLUTION: To polyethylene, 5phr or less of a polarized inorganic filler is added, and an organic peroxide having no benzene ring and generating a decomposition residue having a boilding point will not exceed 100 deg.C such as 2,5-dimethyl-2,5-dihexane or dibutyl peroxide is added thereto as a cross-linking agent to prepare a compound. The compound is extrusion-molded around a conductor, together with inner and outer semiconductor layers, and the polyethylene is crosslinked by heating to form a cross-linked polyethylene insulating layer. Thus, a lengthy DC cross-linked polyethylene cable can be provided without causing rise in resin pressure, even by lengthy continuous extrusion molding.

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 bridge which has excellent DC insulation characteristics and lightning impulse resistance, has no deformation at the time of molding, and can produce a long cable. It relates to a polyethylene cable.

[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. A decrease in the volume resistivity increases the leakage current of the insulator, and may cause the insulator to thermally break down due to Joule heat. Since the decomposition residue of the cross-linking agent volatilizes through the inner and outer semiconductive layers, it is distributed largely in the middle layer portion of the insulating layer, and the volume resistivity of the portion is particularly reduced. For this reason, the load of the voltage applied to the outer layer and the inner layer under DC application becomes large, and the effective thickness of the insulator decreases. 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.

[0005] Such disadvantages in the DC properties of crosslinked PE cables have been ameliorated by the addition of a polar inorganic filler such as magnesium oxide to the crosslinked polyethylene insulation layer as described above. If the added amount of the filler is less than 5 phr, a sufficient effect of improving the volume resistivity cannot be obtained, so that 10 to 40 phr of the filler is generally used.

[0006]

However, according to the conventional direct-current cable, when a polar inorganic filler exceeding 5 phr is added to the insulating layer, coarse particles or agglomeration of the filler are caused in the insulating compound. May occur. The coarse particles and agglomeration of the filler cause clogging in a screen mesh provided on the front surface of the extruder for removing foreign matter in the resin in a process of continuously extruding the insulator. When the mesh is clogged, the resin pressure is excessively increased (for example, 3 MPa), making it difficult to continue extrusion molding, and making it impossible to manufacture a long cable.

Further, if a polar inorganic filler exceeding 5 phr is added to the insulating layer, the cable insulator may be deformed due to a change in flow characteristics such as viscosity of the molten resin extruded in the extrusion process. is there.

Further, when a polar inorganic filler exceeding 5 phr is added to the insulating layer, the dielectric strength against DC application is improved, but the dielectric strength against lightning impulse is rather reduced.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a direct current having a crosslinked polyethylene insulator, which is excellent not only in direct current insulation characteristics but also in lightning impulse resistance characteristics and can produce a long cable without deformation of the insulator. Cable for use in a vehicle.

[0010]

In order to achieve the above object, the present invention provides a DC cable having an insulating layer made of crosslinked polyethylene, wherein the insulating layer contains a polar inorganic filler of 5 phr or less, and The present invention provides a DC cable in which a crosslinked polyethylene is crosslinked with an organic peroxide which has no benzene ring and produces a volatile decomposition residue having a boiling point not exceeding 100 ° C.

The organic peroxide is, for example, 2,5-dimethyl-
2,5-di (tert-butylperoxi) -hexane (2,5-dimethyl @ 2,5 di (tert-butylperoxy) hexane) and dibutylperoxide (dibutyl peroxide). In practice, these two are preferred.

Magnesium oxide (MgO) is suitable as a polar inorganic filler to be added to the insulating layer in order to obtain excellent DC insulation characteristics.
Is preferred. MgO has a great effect of suppressing the reduction of volume resistivity and the accumulation of space charge due to the residue of decomposition of an organic peroxide crosslinking agent such as DCP, thereby improving the DC insulation characteristics. Purity 9
This effect is particularly excellent with MgO of 9% or more.

A polar inorganic filler such as MgO is subjected to a surface treatment,
For example, it may be treated with vinylsilane. Further, the polar inorganic filler may be subjected to a pulverization treatment such as jet pulverization.

In order to avoid an increase in the resin pressure in the continuous extrusion step in the production process, the amount of the filler must be 5 phr or less. In order to obtain excellent DC insulation characteristics, it is preferable to add the filler in an amount of 0.5 phr or more.

As the main material polyethylene constituting the insulator, any of high-density, medium-density, low-density, ultra-low-density polyethylene, linear low-density polyethylene and the like may be used. The polyethylene is not limited to a homopolymer, but may be a copolymer, a graft, or a mixture thereof. Copolymers include, for example, ethylene and olefins (propylene and the like), alkyl acrylates (ethyl acrylate,
Copolymers with methyl methacrylate), vinyl esters (vinyl acetate, etc.), styrene, etc., having a molecular ratio of ethylene of 50% or more, and grafts made of, for example, polyethylene or ethylene polymer and maleic anhydride , Vinyl silane and the like.

Maleic anhydride-modified polyethylene, for example, maleic anhydride-grafted polyethylene, is added to polyethylene such as high-, medium-, low- or ultra-low-density polyethylene, linear low-density polyethylene, etc. for 1 phr to 10 phr.
r or less may be added, thereby further improving the lightning impulse strength. The amount of denaturation with maleic anhydride is
0.1% or more is preferable.

[0017]

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 according to the present invention, a conductor, an inner semiconductive layer formed on the outer periphery thereof, a cross-linked polyethylene insulating layer formed on the outer periphery thereof, and an outer semiconductive layer formed on the outer periphery thereof are provided. A cross-linked polyethylene insulation layer comprising polyethylene and a polar inorganic filler of 5 ph.
organic compounds such as 2,5-dimethyl 2,5-di (tert-butylperoxy) hexane and dibutyl peroxide which do not have a benzene ring and the boiling point of the decomposition residue does not exceed 100 ° C. Add peroxide,
A compound is prepared, the compound is extruded around the conductor together with the inner and outer semiconductive layers, and the polyethylene is crosslinked by heating. The polyethylene may be any of high density, medium density, low density or ultra low density polyethylene, linear low density polyethylene and the like, and includes homopolymers, copolymers and grafts. It is preferable that the filler contains 0.5 phr or more in the insulating layer.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a DC cable according to the present invention will be described below in detail. Example 1 Insulating compositions A to F having the compositions (expressed in parts by weight) shown in Table 1 were prepared. The composition A is a composition containing no magnesium oxide, and the compositions B to F contain magnesium oxide. Compositions E and F are compositions according to the present invention using 2,5-dimethyl @ 2,5-di (tert-butylperoxy) hexane (abbreviated as DBPH) as a cross-linking agent. This is a comparative composition using dicumyl peroxide (DCP).

[0019]

[Table 1]

Each of the compositions A to F has a thickness of 0.1 mm.
The sample was subjected to heat press molding into a sheet shape as described above to obtain samples I to F. Volume resistivity and thermal stimulation current (TS
C) was measured. Table 2 shows the results.

[0021]

[Table 2]

The volume resistivity is as follows: temperature 90 ° C., applied electric field 80
It was calculated from the leakage current 10 minutes after voltage application under kV / mm. In TSC, a DC voltage of 5 kV was applied as an initial bias at a temperature of 30 ° C. for 10 minutes, then rapidly cooled to −10 ° C., the electrodes were grounded, and a collecting bias of 180 kV having the same polarity as the above-mentioned bias was applied. The temperature was raised at a rate of 2 ° C. per minute while measuring the current until the temperature reached 90 ° C. Usually, in this TSC measurement, when space charge is accumulated by the initial bias, a current peak having the same polarity as that of the initial bias is observed. The deterrent effect can be determined.

As is clear from Table 2, TSC peak was observed in the sample A without MgO added, but no TSC peak was observed from Samples B to F with MgO added. That is, this indicates that the charge accumulation was prevented by the addition of MgO.

Samples A and B using DCP as a crosslinking agent
Between C and D, the volume increases as the amount of MgO added increases.
The resistivity is rising. However, the sample d, namely MgO
Is 1 phr, the volume resistivity is low.¹⁴Ωc
m level. 2 × 10 ^FifteenVolume resistivity of Ωcm or more
Must be added at least 5 phr of MgO to obtain
Is shown. Sample E using DBPH as a crosslinking agent,
In (F), the amount of MgO added is the same and cross-linked with DCP
The volume resistivity increased compared to the samples C and D, and was approximately 2 × 10
^FifteenIt exhibited a volume resistivity of Ωcm and higher.

Example 2 Tables 1 and 2 were used to produce cables 1, 2, and 3 having a conductor cross-sectional area of 200 mm ² and an insulating layer thickness of 9 mm by extrusion molding. An extruder equipped with a 325 mesh screen mesh was used for molding. Table 3 shows the rise in resin pressure when about 1 ton of resin was extruded continuously over 24 hours.

[0026]

[Table 3]

As is apparent from Table 3, D is used as a crosslinking agent.
In the composition using CP and 20 phr of MgO, 2
Four hours later, the resin pressure rose to 3 MPa. In the case of the composition (1 phr) containing less MgO, the rise in the resin pressure was smaller. Composition E using DBPH as a cross-linking agent had a 5 phr addition of MgO, which was larger than that of D, but the resin pressure after 24 hours was even lower. This result indicates that the crosslinking agent is DCP
It shows that the increase in resin pressure after continuous extrusion is reduced by changing from DBPH to DBPH. This is probably because the scorch time of DBPH is longer than that of DCP, so that "burn resin" is less generated.

No deformation of the insulator was observed in any of the cables 1, 2, and 3. Conductor temperature 9 for cables 1, 2 and 3
A dielectric breakdown test was performed at 0 ° C. using a direct current and an impulse. Table 4 shows the results.

[0029]

[Table 4]

As can be seen in Table 4, the crosslinking agent DC
Of cables 1 and 2 using P, 20 phr of MgO
Although the cable 1 using has sufficiently high DC breakdown strength, it has poor impulse resistance. Cable 2 with small amount of added MgO
Conversely, the impulse withstand strength is high, but the DC breakdown strength is low. On the other hand, the cable 3 using DBPH as a cross-linking agent has excellent DC breaking strength and impulse resistance.

From the above results, by using DBPH as a cross-linking agent and reducing the MgO filler added to the cross-linked polyethylene insulation layer to 5 phr or less, excellent DC breakdown strength and impulse resistance were obtained, and long extrusion was achieved. A long case with excellent insulation properties
It was confirmed that bulls could be manufactured. The increase in resin pressure was prevented because the MgO filler was reduced to 5 phr or less, so that clogging of the screen mesh due to coarse particles and aggregation of the filler did not occur. DC as crosslinker
Compared with the case of using P, the volume resistivity is high even when the added amount of the MgO filler is reduced, because the boiling point of the decomposition residue of the crosslinking agent is low, so that the decomposition residue remaining in the insulating layer is small,
It may also be due to the fact that the crosslinker molecule has no benzene ring.

[0032]

According to the DC cable of the present invention, an organic peroxide having no benzene ring and having a boiling point of a decomposition residue not exceeding 100 ° C., such as DBPH, is used as a crosslinking agent. Since the amount of the polar inorganic filler required to obtain excellent insulation characteristics (DC insulation characteristics and lightning impulse strength) can be reduced to 5 phr or less, deformation of the insulator during cable molding can be reduced. Since there is no clogging of the screen mesh due to coarse particles or agglomeration of the filler, there is no increase in resin pressure even in long continuous extrusion molding. -You can get a bull.

According to the direct current cable of the present invention, the crosslinked PE cable for direct current has no benzene ring such as DBPH as a cross-linking agent, and the decomposition residue has a boiling point of 100 ° C.
By using an organic peroxide that does not exceed 5 phr, excellent direct current insulation characteristics and lightning impulse strength can be obtained simultaneously even if the amount of a polar inorganic filler such as magnesium oxide is reduced to 5 phr or less, which is smaller than the conventional amount. That is, a highly reliable DC cable can be realized. Since the DC insulating property (volume resistivity) is improved for the same amount of the filler, the insulating layer can be thinned, and the cable can be reduced in size and weight. As described above, such a highly reliable, compact and lightweight DC cable can be obtained as a long product.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI // H01B 7/02 H01B 7/02 F

Claims (5)

[Claims] 1. A direct current cable having an insulating layer made of cross-linked polyethylene, wherein the insulating layer contains a polar inorganic filler of 5 phr or less, and the cross-linked polyethylene has no benzene ring and a boiling point. A direct current cable characterized by being crosslinked with an organic peroxide that generates volatile decomposition residues not exceeding 100 ° C. 2. The direct current cable according to claim 1, wherein said polar inorganic filler is magnesium oxide. 3. The DC cable according to claim 1, wherein the polar inorganic filler is contained in the insulating layer in an amount of 0.5 phr or more. 4. The direct current cable according to claim 1, wherein the organic peroxide is 2,5-dimethyl @ 2,5 di (tert-butylperoxy) hexane or dibutyl peroxide. 5. The direct current cable according to claim 4, wherein said organic peroxide is 2,5-dimethyl @ 2,5 di (tert-butylperoxy) hexane.