JPS63150811A - 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 Field of Application) The present invention relates to the modification of polyethylene polymer.

(Prior Art) Crosslinked polyethylene cables (XLPg cables), which utilize the excellent insulating properties of polyethylene and have completely improved thermal properties through crosslinking, are widely used.

(Problems to be improved by the invention) The weak point of this XLPg cable is that water trees occur due to moisture in the insulator and the presence of local abnormal electric fields, which is a phenomenon unique to the cable, which deteriorates the insulation performance of the cable. . Water trees in the XLPE insulation layer are thought to occur when water is concentrated in polyethylene, which is a hydrophobic polymer, when there is a locally abnormal electric field. Therefore, it has polar groups and is hydrophilic to some extent. By blending certain polymers, it is possible to prevent water from concentrating in local abnormal electric field areas and improve the water tree property.
In fact, some VC proposals have already been made to improve water resistance by blending ethylene vinyl acetate copolymer (gVA) or ethylene ethyl acrylate copolymer + gBA) (z). Even with the insulating composition of Ushikoko et al., the water tree suppression effect is still insufficient, especially under severe conditions such as distribution class power cables where VC is immersed in water. It is desired to improve the water resistance of

(Means for Solving the Problems) In view of the above-mentioned circumstances, the present invention has been made based on intensive studies on polar polymers, and it has been found that maleic anhydride grafted polyethylene grafted with a predetermined amount of maleic anhydride is effective. I found it. The grafting rate of maleic anhydride used here is 0.5 to IO% by weight, and this
'LjjH 2 to 4 parts per 100 parts by weight of polyethylene
By blending 0 parts by weight, an excellent constant voltage capacitor can be provided.

The base polyethylene constituting the maleic anhydride grafted polyethylene used in the present invention includes low density polyethylene (LDPB>), medium density polyethylene (MD
PB), high density polyethylene (HDPgl), linear polyethylene, or a combination thereof is preferred.

The maleic anhydride-grafted polyethylene resin blend used in the present invention is used by coating the outside of the conductor, but if flow of the insulator at high temperatures is a problem, crosslinking is required. This method of crosslinking treatment is chemical crosslinking using organic peroxides.

Crosslinking may be performed by irradiation with radiation such as an electron beam or by silane crosslinking using a silanizing agent.

(Function) The insulating layer of the present invention unexpectedly has the effect of preventing the occurrence of water trees, but if it is less than 10% by weight of the grafted poly, it is not effective in suppressing water trees, and if it exceeds 10% by weight, the dielectric properties This is not preferable because it worsens insulation resistance. or,
Low density polyethylene (LDPE), medium density polyethylene (MDPg), high density polyethylene (HDPg) can be used as the base polyethylene to which maleic anhydride is grafted.
L, linear polyethylene, etc. can be used, but considering the extrusion processability into cables and the flexibility of the insulator, L
It is more desirable to use DPBi-based polyethylene.

Further, in the present invention, the above-mentioned graft polyethylene blend t
2 to 40 parts by weight for 100 parts of polyurethane, and it is important to note that if it is less than 2 parts by weight, there will be no water tree deterrent effect, and 40 parts by weight will not be effective.
If the amount exceeds 100 parts by weight, the electrical properties, particularly the dielectric properties and insulation resistance of the power cable will deteriorate.However, when carrying out the present invention, 2 to 40 parts by weight of grafted polyethylene may be added to 100 parts by weight of polyethylene. The deterrent effect of water trees is stable.

Even better electrical properties, especially dielectric properties and insulation resistance, can be obtained as a power cable.

VC in the insulating composition used in the present invention contains a predetermined amount of a crosslinking agent (in the case of chemical crosslinking) and an anti-aging agent.

Other additives may be added as necessary.

(Example) Examples of the present invention will be described below.

(Example 1) 100 weight low density polyethylene with melt index (M, I) 1.2! For 1 part, various maleic anhydride grafted polyethylene (graft it...approximately 2%
) were blended in varying amounts, 2 parts by weight of dicumyl oxide as a crosslinking agent, and 0 parts by weight of 4゜4'-thiobis-6(-tert-butyl-3-methylphenol) as a deterioration inhibitor.
．． 2 parts were added and kneaded to prepare a composition. Each composition was press-molded under conditions of 180° C. and IQ min, and the following tests were conducted. After press molding each composition, the gel fraction Vi was 85% or more after immersion drying in xylene at 80° C. for 24 hours.

(1) Water tree test: As shown in Figure 1, a coated layer 2 of conductive paint is provided on the bottom surface of the test sample 1 with a thickness of 5 baits to serve as a ground electrode, and a water tank 4 is placed on the top surface of the test sample 1. A voltage of 10 kV, L kHz is applied to the water electrode. The structure was such that voltage could be applied from the high voltage electrode 3, and after applying the above voltage for 30 days, the sample was boiled and water trees were observed.

The occurrence density of water trees of 50μ or more was observed and expressed as a relative number to the number of occurrences of 100 in the comparison sample (currently used XLPg).

(11) Dielectric loss tangent (tan δ) measurement: 1 electric thick sheet VC
A pressure of 1 kV, 508 zt was applied, and the above tests were performed using a Schering bridge. The results are shown in Table 1.

Table 1 Maleic anhydride graph) LDPE: Mitsui Petrochemical 7)
'? -LF500 (MI=1.11 maleic anhydride graph) M D P B: Mitsui Petrochemical Atmer N
gO50 (MI=3.51 anhydrous maleic graph) HDPE: Mitsui Petrochemical Atmer HB310 (MI=0.121 (Example 2) Conductive power cable using the compositions of samples AI and Ya5 in Table 1 as insulators Nine to make.

The cable structure has a conductor cross-sectional area of 200.7. It consists of a three-layer structure with an insulation thickness of 3 mm, an internal extruded semiconductive layer, and an external extruded semiconductive layer, and no external shielding or sheathing is required.

Table 2 shows the results of the following submersion charging test for each of the above cables.

Water immersion test: 1k in 70℃ warm water with conductor water injection
After applying an electric current of 10 kV at Hz for 190 days, A
Voltage of C (50Hz)'fr: 5 kV/30m1n
The breakdown voltage was determined by increasing the voltage under step-up conditions.

Table 2 (Effects of the Invention) As can be seen from the above comparative tests, the present invention significantly suppresses the occurrence of water trees by incorporating a predetermined amount of maleic anhydride grafted polyethylene into the composition constituting the insulator. It is possible to prevent a decrease in breakdown voltage after flooding due to electrification.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the water tree test. ■=Sample 2: Conductive paint 3: High voltage electrode 4: Tap water

Claims (2)

[Claims] (1) On the outside of the conductor, an insulating layer is formed of a composition consisting of 100 parts by weight of polyethylene and 2 to 40 parts by weight of maleic anhydride grafted polyethylene with a maleic anhydride grafting amount of 0.5 to 10% by weight. A power cable characterized by (2) The power cable according to claim 1, wherein the polyethylene is low-density polyethylene and is crosslinked.