JP2548770B2 - DC cable - Google Patents

Description

TECHNICAL FIELD The present invention relates to a DC cable, and more particularly to a DC cable using an extruded polymer insulating material as an insulating material formed on the outer periphery of a core conductor. is there.

[Prior Art] Conventionally, cross-linked polyethylene having polyethylene as a base material has been widely used as an insulating material of a power cable for AC high voltage because of its excellent withstand voltage and dielectric properties.

Cross-linked polyethylene having such polyethylene as a base material is widely used as an insulating material in a DC cable for transmitting and distributing a DC voltage.

[Problems to be Solved by the Invention] However, when the extruded polymer-insulated cable made of the above-mentioned insulating material is applied to high-voltage DC transmission, some problems occur.

The big problem is that space voltage is formed in the insulator by applying high DC voltage, and a local high electric field is generated in the insulator to reduce the substantial insulation thickness of the cable. Therefore, the outer diameter of the cable becomes large.

It is said that the cause of this space charge formation is the imperfections in the molecular structure of polyethylene itself and various additives (such as antioxidants and crosslinking decomposition residues).

Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a DC cable with reduced space charge accumulation and excellent insulation performance.

[Means for Solving the Problems] A direct current cable according to the present invention is a direct current cable in which an insulating material made of polyethylene or crosslinked polyethylene is formed on an outer peripheral portion of a core conductor, and the hindered or semi-hindered phenol is added to polyethylene or crosslinked polyethylene. The present invention is characterized in that a type antioxidant is added to form an insulating material.

[Function] Space charge accumulation was reduced and insulation performance was improved by adding a hindered or semi-hindered phenolic antioxidant to polyethylene or cross-linked polyethylene as an insulating layer in a DC cable to form an insulating material. It is a thing.

[Examples] Examples of the present invention will be described in detail below. A total of 10 kinds of samples, a sample A consisting only of low density polyethylene and samples B to J in which the base material is low density polyethylene and various antioxidants are added, are mixed in a weight part as shown in Table 1. Made in proportion.

Material a: low-density polyethylene Material b: 4,4'-thio-bis (3-methyl-6-t-butyl-phenol) Material c: 4,4'-thio-bis (6-t-butyl-ortho-
Cresol) Material d: 2,2-thio [diethyl-bis-3- (3,5-di-
t-Butyl-4-hydroxyphenol) propionate] Material F: 2,6-di-t-butyl-para-cresol Material F: 1,3,5-tri-methyl-2,4,6-tris (3, 5-di-t-butyl-4-hydroxy-benzyl) benzene Material: 2,2'-methylene-bis (4-methyl-6-t-)
Butyl-phenol) Material H: Tetrakis [methylene-3- (3,5-di-t-
Butyl-4-hydroxy-phenyl) propionate]
Methane Material Re: di-stearyl-thio-di-propionate Material: Polymer-of-2,2,4-tri-methyl-1,2-
Di-hydroquinoline Each of Samples A to J is formed in a sheet shape and has a plate thickness of 0.1 mm.
Thermal stimulation current measurements were performed on ~ J.

The measurement conditions at this time were that the electrode diameter was 20 mm, the initial bias was 5 kV, and the temperature was 30 ° C, and then a direct current voltage was applied for 10 minutes, followed by rapid cooling to -10 ° C, grounding the electrode, and the above-mentioned initial bias. While applying a collecting bias of the same polarity at 180 V, the temperature was raised by 2 ° C. per minute and the current up to 90 ° C. was measured.

Further, the leakage current amount for each temperature was subtracted from the above-described thermal stimulation current, and the current of the subtracted amount was integrated over time to obtain the charge accumulation amount of each of the samples A to J. The results are shown in Table 2.

As is clear from Table 2, the sample A to which the antioxidant is not added has the smallest charge accumulation amount, and the addition of the antioxidant increases the charge accumulation amount. However, considering the long-term deterioration of the cable insulator, it is essential to add an antioxidant.

Then, comparing the charge accumulation amounts of the samples B to J to which the antioxidant is added, it can be seen that the sample C, D, E, F, and H have a relatively small charge accumulation amount. The common features of the materials C, D, E, F, and H added to these samples C, D, E, F, and H are that the hindered phenol type as shown in Fig. 1 or the same as shown in Fig. 2. It is a semi-hindered phenol type structure.

Further, if the hindered phenol type as shown in FIG. 3 is used, the charge accumulation amount is increased as in the sample B to which the material B is added.

Therefore, polyethylene containing a hindered or semi-hindered phenol type antioxidant has a small amount of charge accumulation.

On the other hand, the amount of the antioxidant used is preferably 0.025 to 0.25 part by weight for 100 parts by weight of the low-density polyethylene, if the above-mentioned materials C, C, C, C, and C are used. 0.2
If it exceeds 5 parts by weight, charge accumulation in the insulator increases when a direct current is applied, and if it is 0.025 parts by weight or less, the effect as an antioxidant decreases.

The antioxidants according to the present invention may, of course, be the materials (a) to (m) listed below in addition to the above-mentioned materials c, e, and f.

(A) 4,4'-methylene-bis (2,6-di-t-butyl-
(Phenol) (b) 2,4-dimethyl-6-t-butyl-phenol (c) bis (3-methyl-4-hydroxy-5-t-butyl-benzyl) sulfide (d) 2,6-di-t -Butyl-phenol (e) 2,6-di-t-butyl-α-dimethylamino-p
-Cresol (f) 2,4,6-tri-t-butyl-phenol (g) tris (3,5-di-t-butyl-4-hydroxy-phenyl) isocyanurate (h) tris [β- ( 3,5-di-t-butyl-4-hydroxy-phenyl) propionyl-oxyethyl] isocyanurate (i) hexamethylene glycol-bis [β- (3,5-
Di-t-butyl-4-hydroxy-phenol) propionate] (j) 6- (4-hydroxy-3,5-di-t-butyl-
Anilino) 2,4-bis-octyl-thio-1,3,5-triazine (k) n-octidedecyl-3- (4'-hydroxy-
3 ', 5'-di-t-butylphenol) propionate (l) N, N'-hexamethylene-bis (3,5-di-t-butyl-4-hydroxy-hydrocyanamide) (m) 2,6 -Di-t-butyl-4-ethyl-phenol [Advantages of the Invention] As described above, the DC cable according to the present invention has a small amount of charge accumulated in the insulating material, and therefore the cable breakdown voltage caused by this charge. And the breakdown voltage at the time of polarity reversal are eliminated, and the stability of DC insulation can be improved.

Since the thickness of the insulating material can be reduced accordingly, the cable can be made smaller and lighter without deteriorating various insulating materials.

[Brief description of drawings]

FIG. 1 is a structural diagram showing a hindered phenol type antioxidant used in this invention, FIG. 2 is a structural diagram showing a semi-hindered phenol type antioxidant used in this invention, FIG. FIG. 3 is a structural diagram showing a rehindered phenol type antioxidant.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akifumi Katagai 5-1-1, Hidaka-cho, Hitachi, Ibaraki Prefecture, Electric Cable Research Institute, Hiritsu Electric Cable Co., Ltd. (72) Hisaya Shirai, 5 Hidaka-cho, Hitachi-shi, Ibaraki 1st-1st, inside the Electric Cable Research Institute, Nitrate Electric Cable Co., Ltd. (72) Inventor, Mamoru Kanaoka 5-1-1, Hidakacho, Hitachi City, Ibaraki Inside Electric Cable Research Institute

Claims (1)

(57) [Claims] 1. A direct current cable in which an insulating material made of polyethylene or cross-linked polyethylene is formed on the outer periphery of a core conductor, and the insulating material is formed by adding a hindered or semi-hindered phenol type antioxidant to polyethylene or cross-linked polyethylene. DC cable characterized by doing.