JPH1032911A - Method of manufacturing reinforcing insulator for block mold joint and method of connecting power cable - Google Patents

Abstract

(57) Abstract: In a method of manufacturing a reinforcing insulator for a block mold joint and a method of connecting a power cable, mechanical strength at an interface between the insulator of the power cable and the reinforcing insulator at a high temperature is increased. SOLUTION: Before a power cable 2 connecting step, the power cable 2 is preliminarily manufactured from a material containing a synthetic resin and a cross-linking agent for cross-linking the synthetic resin. In the method of manufacturing the reinforcing insulator 4 for a block mold joint to be fused with the insulator 2a at the connection end of the power cable 2, a material containing a cross-linking agent was melted and molded to produce a molded product in the shape of the reinforcing insulator. Thereafter, by adding a cross-linking agent to the molded article, the cross-linking agent concentration of the surface portion 4d in contact with the insulator 2a of the power cable 2 is made higher than the other portions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a reinforcing insulator for a block mold joint and a method for connecting a power cable.

[0002]

2. Description of the Related Art Conventionally, a block mold joint (BMJ) has been widely used as an intermediate connection method of power cables. This block mold joint uses a substantially cylindrical reinforcing insulator manufactured in advance at a factory or the like, and inserts the connection end of the pre-treated power cable into the reinforcing insulator, and connects the conductors at the connection end to each other. Then, by heating the reinforcing insulator, the reinforcing insulator is crosslinked, and the reinforcing insulator and the insulator of the power cable are fused together.

[0003] As described above, the block mold joint is a method using a reinforced insulator manufactured prior to the power cable connecting step, and is reinforced using a portable small extruder and an extrusion die at the cable connection site. A so-called extrusion mold joint (E
Compared to MJ), there is an advantage that the number of work steps on site is small.

The reinforcing insulator used for the block mold joint is obtained by molding a cross-linking agent-containing polyethylene of the same material as the insulator of the power cable by an appropriate molding method. Generally, the molding of a reinforced insulator
Since various molding machines such as an extrusion molding machine or an injection molding machine are used, it is necessary to raise the melting point of the polyethylene containing a crosslinking agent, which is a molding material, to a temperature equal to or higher than the melting point and to once melt the molding material.

[0005]

By the way, peroxide is generally used as the cross-linking agent, and dicumyl peroxide (DCP) is a typical one. A crosslinking agent such as dicumyl peroxide decomposes at a high temperature to generate a radical, and the polyethylene molecular chain is cross-linked by the radical. When the crosslinking reaction proceeds, the viscosity of the resin increases, and the resin does not flow at a certain point.

Therefore, when polyethylene containing a cross-linking agent is used as a molding material, it is necessary to perform molding at a temperature equal to or higher than the melting point of the resin and under conditions that can ensure the fluidity of the resin in the cavity. Therefore, when forming a reinforced insulator by an extrusion molding machine or the like, in order to keep the decomposition of the cross-linking agent as low as possible, various measures such as lowering the molding temperature and shortening the molding time have been employed.

However, in the method of suppressing the decomposition of the cross-linking agent by lowering the molding temperature, if the temperature is lowered too much, the fluidity of the resin is rather deteriorated, and the molding material is not sufficiently filled in the cavity, and the molded product is not filled. There is a problem that the surface is roughened.

In the method of shortening the molding time, when using a molding machine of the same scale, it is necessary to increase the extrusion speed and the injection speed. In this case, the resin generates shear heat in the molding machine, and the molding temperature rises. Therefore, there is a problem that a larger-scale molding machine is required to shorten the molding time without increasing the molding temperature.

In any case, since a necessary heat history is applied when molding the reinforcing insulator, the cross-linking agent in the molding material is decomposed in accordance with the heat history to increase the degree of cross-linking of the reinforcing insulator. Therefore, conventionally, the connection of the power cable is performed using a reinforcing insulator to which a crosslinking reaction has already progressed to some extent, so that the fluidity of the resin in the heating crosslinking process of the block mold joint is low, and the reinforcing insulation between the power cable insulator and the power cable insulator. Long time heating is required for fusion bonding with the body.

[0010] In addition to such a problem of a decrease in the fluidity of the resin, a crosslinking agent diffuses from the reinforcing insulator side to the power cable insulator side at the interface between the insulator of the power cable and the reinforcing insulator at the time of heating and crosslinking. It is possible that
In that case, the degree of cross-linking at the interface is lower than that of the surroundings, and there is a possibility that the mechanical strength at the interface is lower at temperatures higher than the melting point than at other parts.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and is directed to a reinforcing insulator for a block mold joint having improved mechanical strength at an interface between an insulator of a power cable and a reinforcing insulator. It is an object to provide a manufacturing method and a power cable connection method.

[0012]

The present invention has the following configuration to achieve the above object. According to the first aspect of the present invention, before the power cable connecting step, the power cable is manufactured in advance by using a material containing a synthetic resin and a cross-linking agent for cross-linking the synthetic resin, and is heated and cross-linked during the power cable connecting step. In the method of manufacturing a reinforcing insulator for a block mold joint to be fused and fused with the insulator at the connection end of the power cable, after manufacturing a molded product in the shape of a reinforcing insulator by melting and molding a material containing a crosslinking agent, By adding a cross-linking agent to the manufactured molded product, the concentration of the cross-linking agent at the surface portion in contact with the insulator of the power cable is made higher than that of the other portions. It is a method of manufacturing the body.

According to a second aspect of the present invention, the manufactured molded article is immersed in a liquid crosslinking agent for a certain period of time, and then taken out of the liquid crosslinking agent and left standing and stored at a predetermined temperature for a certain period of time. The method according to claim 1, wherein the concentration of the cross-linking agent on the surface portion is made higher than that of the other portions.

According to a third aspect of the present invention, there is provided a method for connecting a power cable using a reinforcing insulator for a block mold joint, wherein a material containing a cross-linking agent is melted and molded to produce a molded product in the shape of a reinforcing insulator. By adding a cross-linking agent to the manufactured molded product, the concentration of the cross-linking agent at the surface portion in contact with the insulator of the power cable is made higher than at other portions, and the molded product having the surface portion at a high concentration is obtained. A power cable connection method characterized in that the power cable is heated and cross-linked after being attached to the connection end of the power cable.

According to a fourth aspect of the present invention, there is provided the method for connecting a power cable according to the third aspect, wherein the molded article is heated and cross-linked in a pressurized state.

According to the present invention, a cross-linking agent is added to the molded article so that the concentration of the cross-linking agent at the surface of the power cable in contact with the insulator is higher than at other parts. The mechanical strength at the interface between the insulator and the reinforcing insulator can be improved. That is, when the concentration of the cross-linking agent inside the molded article is uniform as in the related art, the degree of cross-linking of the surface portion is reduced due to the diffusion of the cross-linking agent to the power cable side. Although there is a possibility that the mechanical strength of the interface, particularly at high temperatures, may decrease, according to the present invention, the concentration of the cross-linking agent on the surface portion in contact with the insulator is higher than that of the other portions. At the time of fusion bonding of the connection end portion to the insulator, even if the cross-linking agent on the surface portion is diffused, the degree of cross-linking is the same as other portions (similar to the bulk power cable insulator and the reinforcing insulator). Can also be obtained near the interface.

The "surface portion" refers to a portion having a predetermined depth from the surface in contact with the insulator of the power cable into the reinforcing insulator, and the predetermined depth is desirably about 5 mm. Further, the `` high concentration '' refers to a concentration necessary for the degree of cross-linking at the interface and the degree of cross-linking of the insulator to be substantially equal after fusion-bonding the connection end of the power cable to the insulator, It is desirable that the concentration of the crosslinking agent be at least about 1.5 times the other part.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an exploded view of an intermediate connecting portion by a block mold joint according to the present embodiment. FIG. 2 is a front view of the reinforcing insulator according to the present embodiment. FIG. 3 is an enlarged cross-sectional view of an intermediate connecting portion by the block mold joint according to the present embodiment. FIG. 4 is a cross-sectional view of the intermediate connecting portion in the step of heating and crosslinking the block mold joint according to the present embodiment.

In this embodiment, as shown in FIG. 1, before the power cable 2 is connected, the power cable 2 is manufactured in advance using a material containing polyethylene and a cross-linking agent for cross-linking the polyethylene. This is a method of manufacturing a reinforcing insulator for block mold joint (hereinafter, referred to as a “reinforcing insulator”) 4 that is heated and cross-linked during the connecting step and is fused to the insulator 2a at the connection end of the power cable 2.

The reinforcing insulator 4 is made of the same material as the insulator 2a of the power cable 2, and a material containing a cross-linking agent is melted and molded to produce a molded product in the form of a reinforcing insulator. It is produced by adding a crosslinking agent to the article. Hereinafter, the forming step and the step of adding the crosslinking agent according to the method of manufacturing the reinforcing insulator 4 will be sequentially described.

(Process of Forming Reinforced Insulator 4) Reinforced Insulator 4
The molding method in the molding step is not particularly limited, and a typical method is, for example, a method using a molding machine such as an extrusion molding machine or an injection molding machine. The molded product of the reinforcing insulator 4 obtained by an arbitrary molding machine has a substantially cylindrical shape as shown in FIGS.
Insertion holes 4a, 4a into which the connection end of the power cable 2 is inserted are provided at both ends in the axial direction. The insertion holes 4a, 4a
Tapered holes 4b, 4b into which the insulator 2a of the power cable 2 fits are connected inward of each other. Further, a conductor connection hole 4c through which a conductor 2b (described later) of the power cable 2 is inserted is formed between the tapered holes 4b.

The reinforcing insulator 4 is provided in the conductor connection hole 4.
A high-pressure shield ring 6 made of aluminum having c as an inner hole, and an internal semiconductive layer 8 covering the peripheral surface and both ends in the axial direction of the high-pressure shield ring 6 from the outside are incorporated by insert molding or the like.

(Step of adding cross-linking agent) A cross-linking agent such as dicumyl peroxide is added to the molded product of the reinforcing insulator 4,
The concentration of the cross-linking agent in the surface portion 4a of the power cable 2 that is in contact with the insulator 2a is set higher than in other portions. The method for adding the cross-linking agent is not particularly limited as in the case of the above-mentioned molding method, but in the present embodiment, the following steps (1) and (2) are sequentially performed to obtain a molded article of the reinforcing insulator 4. A concentration gradient of the cross-linking agent can be provided inside.

(1) A surface portion 4d of the molded reinforcing insulator 4 which comes into contact with the insulator 2a of the power cable 2.
(See FIG. 1) is immersed in the liquid crosslinking agent for a certain period of time, and then taken out of the liquid crosslinking agent and left standing and stored at room temperature or in a heated state for a certain period of time to obtain a cross-linking agent for the surface portion 4d. Make the density higher than the other parts. The surface portion 4d is a surface near the inside of the insertion hole 4a and the tapered hole 4b. The method of adding the crosslinking agent only to the surface portion 4d is not particularly limited. For example, a method of flowing a liquid crosslinking agent only to the surface portion 4d,
A method in which the reinforcing insulator 4 is immersed in a liquid crosslinking agent in a state where the surface of the other portion except the surface portion 4d is masked is used. (2) The reinforcing insulator 4 is stored at a low temperature so that the high concentration of the cross-linking agent in the surface portion 4d does not decrease due to diffusion. The storage temperature is a temperature at which the diffusion of the cross-linking agent is sufficiently slow with respect to the storage period, and is a temperature determined by the diffusion coefficient of the cross-linking agent.

In the present invention, if at least the surface portion 4d has a high concentration, in some cases, the surface portion of the entire molded product, that is, the entire surface including the surface portion 4d and the outer surface portion of the molded product has a high concentration. You may. Further, in the present invention, the formability may be improved by molding using a smaller amount of a crosslinking agent than the amount usually required for the reinforcing insulator 4, and in that case, the crosslinking after the molding may be performed. In the step of adding the agent, a sufficient amount of the cross-linking agent may be added to the entire reinforcing insulator 4, and the surface portion 4d may have a high concentration.

(Connecting Step of Power Cable 2) Next, a method of connecting the power cable 2 by a block mold joint using the reinforcing insulator 4 obtained in the above steps (1) and (2) will be described. As shown in FIG. 1, the power cables 2 and 2 to be connected are single-core CV cables, and their connection ends are a conductor 2b, an inner semiconductive layer 2c, a tapered insulator 2a, and an outer Pretreatment is performed so that the semiconductive layer 2d, the cushion layer 2e, and the aluminum sheath 2f are sequentially exposed. 2 g of anticorrosion layer outside of aluminum sheath 2f
Is coated. Further, an engagement fitting 10a for connecting a conductor having a groove 10a1 is fitted to the end of the conductor 2b of one power cable 2 (shown on the left side in FIG. 1), and the other power cable 2 (shown in FIG. 1). At the tip of the conductor 2b (shown on the right), a protrusion 10b1 that can be fitted into the groove 10a1 is provided.
Is fitted.

When connecting the power cables 2, 2, first, as shown in FIG. 1, the connection ends of the power cables 2, 2 are inserted into insertion holes 4a, 4a in a reinforcing insulator 4 previously manufactured in a factory or the like.
And the insulator 2a at the connection end is fitted into the tapered hole 4b of the reinforcing insulator 4 to attach the reinforcing insulator 4, and the protrusion 10b1 of the engaging fitting 10b is engaged with the engaging metal as shown in FIG. The conductor 2 is inserted into the groove 10a1 of the fixture 10a.
b and 2b are connected to each other. Also, each connected conductor 2
b, 2b are conductor connection holes 4 of the high-pressure shield ring 6;
c is in contact with the inner surface.

Next, as shown in FIG. 4, an external semiconductive layer 12 is provided on the surface of the reinforcing insulator 4, and a flexible heater 14 is arranged around the external semiconductive layer 12. A temperature controller 16 is connected to the flexible heater 14. A seat 18 is fitted on the outer surface of the aluminum sheath 2g of each power cable 2, and a bridging mold 20 is set on the seat 18 so as to include the reinforcing insulator 4 and the flexible heater 14. The outer semiconductive layer 12 and the seat 18 attached to the reinforcing insulator 4 are covered with a gas seal layer 22.

Then, the cross-linking mold 2 is removed from the gas cylinder 24.
The nitrogen gas adjusted by the gas pressure controller 26 is put into the chamber 0 to pressurize the inside of the cross-linking mold 20, and the reinforcing insulator 4 is heated by the flexible heater 14 in this pressurized state. By this heating, the crosslinking agent in the reinforcing insulator 4 is decomposed, and the polyethylene molecular chains are cross-linked by radicals generated by the decomposition. At the same time, the reinforcing insulator 4 and the insulator 2a of the power cable 2 are fused by this heating.

(Comparative Evaluation between Embodiment and Comparative Example) The above-described reinforcing insulator 4 according to the present embodiment and a reinforcing insulator manufactured by a conventional method were compared and evaluated.

Here, the reinforcing insulator 4 according to this embodiment is
Is a method in which a cross-linking agent is added to the surface portion 4d of the reinforcing insulator 4 in the addition steps (1) and (2) to make the surface portion 4d higher in concentration than other portions. The concentration of the cross-linking agent in the surface portion 4d (in a range of 5 mm in depth from the surface) is 200 to 200% of the lowest concentration of the cross-linking agent in other portions in the reinforcing insulator 4.
The concentration was 225%. The storage temperature at a low temperature in the adding step (2) was about 10 ° C.

The reinforced insulator according to the comparative example is a reinforced insulator having the same shape as that of the above embodiment manufactured only by melting and molding polyethylene containing a cross-linking agent. Intermediate connection of power cables by block mold joint was performed by the same method as the embodiment.

For each of the above embodiment and comparative example, the mechanical strength at the high temperature (120 ° C.) at the interface between the reinforcing insulator and the insulator of the power cable after the connection of the power cable was evaluated.

Table 1 shows the results of the evaluation. In Table 1, the mechanical strength of the interface according to the comparative example is a relative value when the example is normalized to 1.

[0035]

[Table 1]

(Operation / Effect of the Method of Manufacturing Reinforced Insulator and Connecting Method of Power Cable) In this embodiment, since the surface portion 4d has a high concentration, the insulator 2a is used during the connecting step of the power cable. Even if the cross-linking agent diffuses to the side, the degree of cross-linking at the interface A can be kept high, and as can be seen from Table 1, the mechanical strength at the interface A under high temperature is significantly improved as compared with the comparative example. Can be done.

This embodiment is a preferred embodiment of the present invention, and the technical scope of the present invention is not limited to this embodiment.

[0038]

As described above, according to the present invention, the mechanical strength at the high temperature at the interface between the insulator of the power cable and the reinforcing insulator can be increased.

[Brief description of the drawings]

FIG. 1 is an exploded view of an intermediate connecting portion by a block mold joint according to the present embodiment.

FIG. 2 is a front view of a reinforcing insulator according to the embodiment.

FIG. 3 is an enlarged cross-sectional view of an intermediate connecting portion by a block mold joint according to the embodiment.

FIG. 4 is a cross-sectional view of an intermediate connecting portion in a heating and crosslinking step of the block mold joint according to the embodiment.

[Explanation of symbols]

 2 power cable 2a insulator 4 reinforcing insulator 4d surface

Claims (4)

[Claims] 1. A method for manufacturing a power cable, comprising: a step of connecting a power cable before the power cable connecting step, wherein the power cable is manufactured in advance using a material containing a synthetic resin and a cross-linking agent for cross-linking the synthetic resin;
A method for producing a reinforcing insulator for a block mold joint, which is thermally cross-linked and fused to an insulator at a connection end of a power cable, wherein a material containing a cross-linking agent is melted and molded to form a molded product in the shape of a reinforcing insulator. A block mold, characterized in that after production, a cross-linking agent is added to the manufactured molded article so that the concentration of the cross-linking agent at the surface portion in contact with the insulator of the power cable is higher than at other portions. A method for manufacturing a reinforced insulator for a joint. 2. After the manufactured molded article is immersed in a liquid crosslinking agent for a predetermined time, the molded article is taken out of the liquid crosslinking agent, and is allowed to stand and stored at a predetermined temperature for a predetermined time to obtain the surface portion. 2. The method for producing a reinforcing insulator for a block mold joint according to claim 1, wherein the concentration of the cross-linking agent is higher than that of the other parts. 3. A method of connecting a power cable using a reinforced insulator for a block mold joint, comprising: forming a reinforced insulator-shaped molded product by melting and molding a material containing a cross-linking agent; By adding a cross-linking agent to the surface of the power cable, the cross-linking agent concentration at the surface portion in contact with the insulator is made higher than other portions, and the molded product having the surface portion at a higher concentration is connected to the power cable connection end. A method for connecting a power cable, wherein the power cable is heated and cross-linked after being attached to a portion. 4. The method of connecting a power cable according to claim 3, wherein the molded article is heated and cross-linked in a pressurized state.