JPH02155416A - Molded joint method of cable - Google Patents

Abstract

PURPOSE:To make a withstand breakdown voltage higher by covering the inside edge part of a joint part, where one side edge part of an external semiconductor layer arranged on the inside and the other side edge part are piled in a lap-like manner while and insulated state is maintained, with an electric field relaxation layer by means of an admixture. CONSTITUTION:The edge part 7a of one side external semiconductive layer 7 is arranged on the inside and the edge part 8a of the other side external semiconductive layer 8 is overlapped upon said edge part 7a, with an electric field relaxation layer 10 between them. Said layer 10 is formed when a base material rubber, 100 pts.wt. plastics and 30-250 pts.wt. conductive zinc white are blended together. Said layers 7, 8 are pressed and wound from above by a tape 11 and melt-molded subsequently. In this manner, it is possible to obtain an high withstand breakdown voltage.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a mold joint construction method, and particularly to a method for improving breakdown voltage by relaxing the electric field at the two-divided edge of an external semiconducting layer. This is related to the construction method that was developed.

<Prior Art> Generally, an external semiconductive layer is provided at the mold joint part of a cable, for example, a Cv cable.
This external semiconductive layer may be continuous over the entire length of the joint, or it may be divided into two along the circumferential direction at appropriate points and overlapped in a lap shape with their edges insulated. There is.

The reason for adopting such a two-division system is to reduce the increase in electric field in the sheath caused by electromagnetic induction and the sheath circuit loss.

<Problems to be Solved by the Invention> However, when such a divided structure is adopted, stress such as electric field concentration tends to be concentrated on the edge of the external semiconducting layer, so it is difficult to select the edge composition material and the shape. Not only does molding require careful attention, but how to alleviate this electric field stress plays an important role in improving breakdown voltage.

In particular, in recent years, the voltage of C■ cables has been rapidly increasing, so improvements in this respect are strongly desired.

Therefore, the inventors conducted a deeper study and found that if at least the inner edge of the outer semiconducting layer (the tip of the outer inner layer semiconducting electrode) is covered with an electric field relaxation layer, the electric field stress at the edge will be alleviated, leading to destruction. We have found that it is possible to improve the voltage.

On the other hand, the concept of such an electric field relaxation layer has long been adopted in the field of cables themselves, such as C cables, but the admixtures at that time are generally additives such as acetohenone in the base resin. organic matter and carbon blank,
Alternatively, it is known that metal oxides such as titanium oxide are added (EPRr Report El-4
28, U.

S, P, 3885,085, 17th Electrical Insulating Materials Symposium ■-3, etc.).

However, in the case of materials to which the above-mentioned organic substances have been added, concentration changes occur over many years due to diffusion transfer, which tends to cause changes in properties, and in the case of carbon blanks, it is difficult to It is difficult to obtain a material that exhibits a good volume resistivity, and furthermore, because the color of the mixture is black, the same color as the semiconducting layer, it is difficult to distinguish it from the semiconducting layer, making terminal processing such as connection difficult. Furthermore, when metal oxides are added, the effect will not be seen unless they are added in a fairly large amount, and this large amount of addition causes deterioration of physical properties and mechanical properties, making it impractical.

The present invention has been made in view of the conventional situation, and focuses on conductive zinc white as an additive for the above-mentioned electric field relaxation layer used in the mold joint of the cable.
It is complete.

<Means for Solving the Problems and Their Effects> The feature of the present invention is that the external semiconductive layer coated on the outer periphery of the molded resin insulator is divided into two along the circumferential direction, and one At least the inner edge of the outer semiconductive layer (the tip of the outer inner layer semiconductive electrode) at the mold joint part of the cable where the edge goes inside and the other edge is overlapped in a lap shape while maintaining insulation. is covered with an electric field relaxation layer made of a mixture of base rubber, 100 parts by weight of plastic, and 30 to 250 parts by weight of conductive zinc white, and then,
This is a cable mold joint construction method in which the entire joint part is heated and melted to be molded.

Examples of the base rubber or plastic used in the electric field relaxation layer include ethylene propylene rubber, chlorinated polyethylene rubber, and ethylene-vinyl acetate copolymer (
EVA), polyethylene, crosslinked polyethylene, polypropylene, ethylene-ethyl acrylate copolymer (E
EA), ethylene-α-olefin diene copolymer, etc., and in forming the electric field relaxation layer, 30 to 250 parts by weight of conductive zinc white is added to 100 parts by weight of these alone or in combination. Mix and make.

Here, conductive zinc white refers to 0.01 to 5% zinc oxide.
It is doped with aluminum oxide, mixed in powder form, and fired at high temperature in a reducing atmosphere. The conductive zinc white produced in this way generally weighs 200 kg/
It exhibits a volume resistivity of 10,310' Ω-cm or less under a pressure of 10,310' Ω-cm, and exhibits a grayish-white to white color.

The reason why the amount of conductive zinc white is set at 30 to 250 parts by weight per 100 parts by weight of the rubber or plastic base material is that if the amount is less than 30 parts by weight, it will not function as an electric field relaxation layer. If the amount exceeds 250 parts by weight, the mechanical properties will deteriorate and the electrical resistance will drop too much to lose the electric field relaxation effect. Although there are some differences depending on the type of base rubber and plastic, for example, when the base plastic is a crystalline polymer such as polyethylene, the more preferable blending amount is 30 to 30.
150 parts by weight is good.

Furthermore, processing aids such as crosslinking agents, anti-aging agents, lubricants, etc. can be added to the rubber and plastic of this electric field relaxation layer as appropriate, within a range that does not impair their electrical properties. .

The composition of the external semiconductive layer of the joint portion is ethylene-ethyl acrylate copolymer (EEA).
, a base resin such as ethylene vinyl acetate copolymer (EVA), or ethylene-acrylic acid copolymer (EAA), conductive powder such as carbon or metal, and some crosslinking agent such as dicumyl peroxide (DCP). , 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-
Examples include those to which 3,2,5-dimethyl-2,5-di(t-butylperoxy)hexane and the like are added. The blending amount of each of these components depends on the materials used, but 1 part by weight of the conductive powder is added to 100 parts by weight of the base resin.
0 to 70 parts by weight, and 0.2 to 1 part by weight of the crosslinking agent, and coated on the molded resin insulator as an external semiconductive layer. The gel fraction at that time (based on the extraction method when immersed in xylene at 110° C. for 24 hours) is preferably adjusted to a range of 10 to 50%. This is because when the gel fraction is less than 10%, adhesion with the molded resin insulator is good, but the degree of crosslinking is insufficient, resulting in poor shape retention, resulting in crushed edges, protrusions, and sharp edges. This is because shapes are likely to occur and cause electrical breakdown, and if the gel fraction exceeds 50%,
Shape retention is enhanced by a sufficient degree of crosslinking, but mold resin! ! This is because the adhesion to the edge deteriorates, and voids are likely to occur at the edge due to minute peeling, etc., which also causes electrical breakdown.

Next, a specific example of the construction method of the present invention will be explained with reference to FIG.

In the figure, F and F are cables that are connected to each other, and J is a joint portion thereof.

In the construction method of the present invention, the covering part (insulator, etc.) 2.2 of the reconnection end part of the cables F and F to be connected is scraped off (benzine ring treatment) and exposed, and the side conductor 1.1 part is shaped into a cylindrical shape. The conductor is inserted into a metal crimp sleeve 3 from both sides, and then the crimp sleeve 3 is crushed to connect the conductor.

Next, wrap a semiconductive tape around this connection, for example.
The material is heated and melted to be crosslinked to form a crosslinked internal semiconductive layer 4. Of course, this internal semiconducting layer 4 is connected to the cable F,
Connection processing is performed with the internal semiconducting layers 5, 5 on the F side.

Thereafter, an insulator 6 is formed by wrapping, for example, an uncrosslinked composition tape containing a crosslinking agent around this portion. In addition to this tape wrapping, when forming the insulator 6,
For example, an extrusion mold may be set in this portion, and molded resin may be extruded as the insulator 6 using a normal method.

A semiconductive tape is wrapped around the outer periphery of this insulator 6,
A two-part outer semiconductive layer 7.8 is formed. At this time, the edge 7a of one of the outer semiconductive layers 7 is placed inside, and the edge 8a of the other outer semiconductive layer 118 is overlapped thereon in a lap shape with the electric field relaxation layer 10 interposed therebetween. .

As described above, this electric field relaxation layer 10 is made by blending 30 to 250 parts by weight of conductive zinc white with 100 parts by weight of base rubber or plastic.

These outer semiconducting layers 7 and 8 are connected to cables F and F.
Connect to the external semi-conducting N9.9 on the side.

On the external semiconducting conductors N7 and 8 formed in this way,
Further, it is wrapped with a restraining tape 11, and then a molding die is set, and the uncrosslinked or insufficiently crosslinked insulator 6, outer semiconducting layer 7
．． 8 portions and 10 portions of the electric field relaxation layer are melt-molded.

During this molding, the inner edge 7a of the outer semiconductive layer 7 is
As a result, a high breakdown voltage can be obtained.

<Example> Compounds of each composition shown in Table 1 (Examples I~■,
Comparative Examples I~■) were extruded at 120°C into a tape shape with a thickness of 0.1 mm and a medium size of 100 mm, and a width of 2
An electric field relaxation tape of 0 mm was used.

On the other hand, the C cable (154Kv, 1
200mm”) (7) Scrape off the covering (insulator, etc.) at the connection end into a conical shape (penciling process), connect the conductors with a crimp sleeve, then wrap semiconductive tape, An internal semiconductive layer was formed and tape molded by heating.

Next, a polyethylene tape containing a cross-linking agent corresponding to the insulator part is wrapped around the mold shape, and then the above-mentioned pipe is wrapped around the appropriate part of the tape, for example, near the right end of the joint part, as shown in Figure 1 above. Attach the inner edge of the shape, and wrap a semiconductive EEA tape containing a crosslinking agent in the left direction from above to form one outer semiconductive layer,
Above the inner edge of the pipe shape (upper right part of Figure 1 above)
The above-mentioned electric field relaxation tape was wrapped around it to form an electric field relaxation layer.

Thereafter, on the inner edge and the electric field relaxation layer, a semiconductive EEA tape containing a crosslinking agent was wrapped around the conical part in the right direction in a partially wrapped manner to form the other outer semiconductive layer.

Further, a Teflon tape, for example, was wrapped thereon as a restraining tape, and the mold was cross-linked by heating under nitrogen gas pressure.

The AC breakdown voltage value and breakdown location of the joint portion thus prepared were investigated, and the results shown in Table 2 were obtained.

Table 2 From Table 2 above, in the case of the example products of the present invention, a high AC breakdown voltage value was obtained, and the breakdown occurred at a location other than the inner edge of the outer semiconducting layer, and the durability at the inner edge was low. An improvement in breakdown voltage was confirmed. On the other hand, in the case of comparative example products, the AC breakdown voltage value is also low, and it can be seen that the breakdown occurs in many cases from the tip of the inner edge.

<Effects of the Invention> As is clear from the above description, according to the present invention, in the two-divided mold joint part of the external semiconducting layer,
Since the inner edge of the outer semiconductive layer (the tip of the outer inner layer semiconductive electrode) is covered with an electric field relaxation layer made of rubber or plastic with conductive zinc white added, the electric field stress at the edge is effectively alleviated. A cable mold joint construction method with excellent electrical properties can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an embodiment of the cable mold joint construction method according to the present invention. In the diagram, F, F...cable, J...joint part, 1, l...conductor, 2.2 3 ・ ・ 4 ・ ・ 6 ・ ・ 7.8 7 a ・ 8 a ・ 10・ １１ ・ Covering part (insulator), crimp sleeve, inner semiconducting layer, molded resin insulator, outer semiconducting layer, inner edge, outer edge, electric field relaxation layer, suppressing tape,

Claims (1)

[Claims] The outer semiconducting layer coated on the outer periphery of the molded resin insulator is divided into two along the circumferential direction, one edge is inside,
At the molded joint part of the cable, on which the other edge is overlapped in a lap shape while maintaining insulation, at least the inner edge of the outer semiconductive layer is coated with 30 parts by weight of conductive zinc white on 100 parts by weight of base rubber and plastic. A cable mold joint construction method characterized in that the cable is covered with an electric field relaxation layer made of a mixture containing up to 250 parts by weight, and then the entire joint part is heated and melted and molded.