JPH1042421A - Manufacture of reinforced insulator block for power cable connecting section and structure of power cable connecting section using the block - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of voids by improving the mechanical strength at a boundary. SOLUTION: The inside diameter of a reinforced insulating block 1 is made smaller than the outside diameter of a power cable connecting section 2, and at the same time, the molded block 1 is crosslinked. After crosslinking, the by-product generated by the crosslinking reaction is removed by volatilization by keeping the block 1 in a state, where the block 1 is heated to a temperature lower than the melting point. Then the block 1 is expanded, so that the inside diameter of the block 1 can become larger than the outside diameter of the connecting section 2 by heating the block to a temperature higher than the melting point, and the internal surface of the expanded block 1 is impregnated with a crosslinking agent after the block 1 has been cooled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a reinforcing insulator block for a power cable connection portion and a structure of a power cable connection portion using the block.

[0002]

2. Description of the Related Art Several methods have been proposed for connecting power cables. For example, as a reinforcing insulator, a resin containing a cross-linking agent molded in a tape shape in advance is wound around a connection point between the pencilled cable conductors,
There is a method of covering the whole with a cross-linking mold and cross-linking the mold, that is, a method called a tape mold joint (TMJ). In the TMJ method, since the tape is wound at the construction site, there is a high risk of foreign matter being taken into the reinforcing insulator, and the reliability is poor. As another method, in order to obtain a more reliable connection part, as a connection part of a 275 KV class CV cable, a polyethylene resin containing a cross-linking agent was extruded and injected into a mold previously set in the cable connection part by an extruder. Thereafter, there is a method of performing mold crosslinking, that is, a method called an extrusion mold joint (EMJ).
Although this method is excellent in performance, it is necessary to bring an extruder to the construction site, requires a large space, and also requires a resin extrusion process, correction molding after extrusion, etc.,
There was a disadvantage that the construction time was long. Accordingly, a method called block mold joint (BMJ) has been developed as a method that requires high reliability and requires a short construction time.
In the BMJ method, a reinforcing insulator block formed in advance at a factory or the like is used as a reinforcing insulator, and a connection portion is attached to the block and the mold is crosslinked. As a conventional example of this method, a method described in Japanese Patent Application Laid-Open No. 62-31315 is known. This means that after electrically connecting the cable conductors to be connected, a reinforcing insulator block is applied to this connection, and this block is heated to melt soften and vulcanize / crosslink, and pressurized from the outside. The gap is crushed to form an insulating layer. Pressing and crushing the gap means that the inner diameter of the block is formed larger than the outer diameter of the cable connection.

In the conventional BMJ method, the inner diameter of the reinforcing insulator block is formed larger than the outer diameter of the cable connection portion in consideration of the ease of insertion of the connection cable, the dimensional error of the cable, and the like. The gap created by the pressure difference, heating and melting is closed. Therefore, unless an appropriate pressurizing / heating method is adopted, the gap may not be completely closed in some cases, and a gap may be formed in some places, which may lower the insulating function. In addition, there is a possibility that a by-product generated by a chemical reaction in the cross-linking mold step may deteriorate insulation performance.

Therefore, there is no gap between the connection portion and the block, no by-products due to cross-linking are generated when the block is attached to the connection portion, and a power cable connection portion having excellent insulation performance is obtained. For the purpose of providing an insulator forming method, the present applicant has previously proposed "a method of forming an insulator at a power cable connection portion" in Japanese Patent Application No. 6-336276.

[0005]

[Problems to be Solved by the Invention] Japanese Patent Application No. Hei 6-33627
In No. 6, since no cross-linking agent is present in the reinforcing insulator and the cable insulator, fusion occurs through the interface after the molding step, but no cross-linking point is formed between the reinforcing insulator and the molecular chain of the cable insulator. At a temperature equal to or higher than the melting point, the mechanical strength of the interface may decrease compared to bulk crosslinked polyethylene. In addition, when DCP is used as a cross-linking agent, it is known that, among the by-products generated by the cross-linking reaction, cumyl alcohol further generates water due to heat at the time of cross-linking. It has been found that water in low density polyethylene, when its concentration exceeds 250 ppm, forms a large number of voids due to agglomeration, and the voids, when grown large, can sometimes be detrimental to the insulating properties. The amount of water generated varies depending on the heat history at the time of cross-linking, and when exposed to high temperatures during actual use, it is generated by the reaction of residual cumyl alcohol, which may cause voids.

Therefore, the present invention provides a method of manufacturing a reinforcing insulator block for a power cable connecting portion which can improve the mechanical strength of the interface between the power cable connecting portion and the reinforcing insulator block and eliminate the occurrence of voids. It is an object of the present invention to provide a structure of a power cable connecting portion using the block.

[0007]

In order to achieve the above-mentioned object, according to the manufacturing method of the present invention, an inner diameter of a reinforcing insulator block is formed smaller than an outer diameter of a power cable connection portion, and this block is bridged. Molded with resin, cross-links the formed reinforcing insulator block, after cross-linking, heats and stores the reinforcing insulator block at the melting point or below to volatilize and remove by-products generated by the cross-linking reaction, Heating the body block above the melting point, expanding the inner diameter of this block to be larger than the outer diameter of the power cable connection,
After cooling the expanded reinforcing insulator block, the inner diameter of the block is impregnated with a crosslinking agent, and the inner diameter of the reinforcing insulator block is formed smaller than the outer diameter of the power cable connection portion. This block is molded with a resin that does not contain a crosslinking agent, and the molded reinforcing insulator block is impregnated with a crosslinking agent to be crosslinked, and after crosslinking, the reinforcing insulator block is heated and stored at a melting point or lower to be generated by a crosslinking reaction. The by-products are volatilized and removed, and then the reinforcing insulator block is heated above its melting point to expand the inner diameter of this block to be larger than the outer diameter of the power cable connection. After cooling the insulator block, the inside diameter of the block is impregnated with a crosslinking agent. Further, the structure according to the present invention is such that the reinforcing insulator block is attached to the power cable connection portion, and the applied block is heated and cross-linked, and further heated and pressurized, and the block is connected to the power cable connection portion. Are fused.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below. The reinforcing insulator block 1 shown in FIG. 1 has an inner diameter smaller than the outer diameter of the power cable connecting portion 2 at the time of molding. It is molded with a resin containing a crosslinking agent. The thus formed reinforcing insulator block 1 is cross-linked, and the cross-linked reinforcing insulator block 1 is subjected to a heat treatment at a melting point or lower and stored, and the by-products due to the cross-linking are volatilized and removed. The reinforcing insulator block 1 in FIG. 1 shows a state before being attached to the power cable connection portion 2 in which by-products are removed and the inner diameter is smaller than the outer diameter of the power cable connection portion 2. . The reinforcing insulator block 1 shown in FIG. 1 in which by-products generated by the cross-linking reaction are removed and the inner diameter of which is smaller than the outer diameter of the power cable connection portion 2 is heated at a temperature equal to or higher than the melting point, The inner diameter is increased using an appropriate device or jig so that the inner diameter is larger than the outer diameter of the power cable connection portion 2. After cooling the reinforcing insulator block 1 having an increased inner diameter, a cross-linking agent is impregnated near the inner surface of the block 1. The concentration of the cross-linking agent at the time of impregnation may be an amount necessary and sufficient to obtain a gel fraction required for a reinforcing insulator or a cable insulator, and may be an amount necessary to obtain a minimum required degree of cross-linking. , It is more desirable to add about twice as much. The step of impregnating the crosslinking agent may be performed before the step of expanding the diameter of the reinforcing insulator. In this way, the diameter is increased and then cooled, and the reinforcing insulator block 1 impregnated with the crosslinking agent is in the state shown in FIG. In this state, the power cable is inserted and the conductors of both cables are connected. Since the inner diameter of the reinforcing insulator block 1 is increased, the insertion of the power cable is performed smoothly. In the state shown in FIG. 2, the reinforcing insulator block 1 is heated and pressed at a temperature equal to or higher than the melting point. When the heating temperature of the reinforcing insulator block 1 exceeds the melting point,
Since the inner diameter of the reinforcing insulator block 1 is originally formed smaller than the outer diameter of the power cable connecting portion 2, it contracts and the gap between the reinforcing insulator block 1 and the power cable connecting portion 2 is easily closed.

As shown in FIG. 2, after the power cable is inserted and connected, the reinforcing insulator block 1 is heated and pressurized to fuse the closed interface, and at the same time, the crosslinking reaction proceeds, and the reinforcing insulator and the cable are insulated. A crosslinked network structure grows between the molecular chains of the body by crosslinking, and the mechanical strength equivalent to bulk crosslinked polyethylene is obtained. At this time, since the by-products due to the crosslinking are volatilized and removed in advance in the reinforcing insulator block 1, the by-products generated by the heating easily diffuse in the reinforcing insulator and volatilize out of the reinforcing insulator. As a by-product, it is desirable to control the concentration of water and cumyl alcohol which causes the generation of water. Desirably, the water present after crosslinking is below 250 ppm. This makes it possible to prevent the generation of microvoids.

FIG. 3 shows an example of a power cable 10 in which a conductor 11 is covered with an insulating layer 12, and the ends of the power cable 10 to be connected are pencil-bonded to each other.
1 can be connected to each other by using a connector 13. A power cable 10 as shown in FIG. 3 is inserted from both ends of the reinforcing insulator block 1 to connect the conductors 11 to each other. The configuration of the power cable connection unit 2 includes various connection means other than the example shown in FIG.

Example 1 Using a resin containing a cross-linking agent (DCP), a reinforcing insulator block having an inner diameter smaller by 5% than the outer diameter of a cable connecting portion was formed. Next, after the same block was crosslinked, it was stored at a temperature lower than the melting point, and by-products generated by the crosslinking reaction were volatilized and removed. Subsequently, the block was heated to a melting point of + 10 ° C., the inner diameter was increased by 5% with respect to the outer diameter of the cable connection portion, and the block was cooled while maintaining its shape. A liquefied cross-linking agent (DCP) was impregnated into the inner diameter of the reinforcing insulator block, and a reinforcing insulator block 1 having a cross-linking agent concentration at a thickness of 5 mm from the surface equal to the cross-linking agent concentration blended in the cable insulator was manufactured. . A BMJ was assembled using the block thus formed as a reinforcing insulator.

Example 2 The concentration of the crosslinking agent for impregnating the inner diameter of the expanded block in Example 1 was doubled.

Example 3 Using a resin containing a cross-linking agent (DCP), a reinforcing insulator block having an inner diameter smaller by 5% than the outer diameter of a cable connecting portion was formed. After crosslinking the block, the block was heated and stored at a temperature lower than the melting point, and by-products generated by the crosslinking reaction were volatilized and removed. Next, a liquefied crosslinking agent (DC) is applied to the inner diameter of the reinforcing insulator block.
P) was impregnated to produce a reinforcing insulator block 1 having a cross-linking agent concentration at a thickness of 5 mm from the surface equal to the cross-linking agent concentration incorporated in the cable insulator. Subsequently, the block was heated to a melting point of + 5 ° C., the inner diameter was increased by 5% with respect to the outer diameter of the cable connection portion, and the block was cooled while maintaining its shape. The block formed in this way is used as a reinforcing insulator.
I assembled BMJ.

Example 4 The concentration of the cross-linking agent for impregnating the inner diameter of the expanded block in Example 3 was doubled.

Example 5 A reinforcing insulator block having an inner diameter smaller by 5% than the outer diameter of a cable connecting portion was formed by using a resin containing no crosslinking agent.
After the reinforcing insulator block was impregnated with a cross-linking agent (DCP), the block was cross-linked, and heated and stored at a melting point or lower, and by-products generated by the cross-linking reaction were volatilized and removed. Subsequently, the block was heated to a melting point of + 10 ° C., the inner diameter was increased by 5% with respect to the outer diameter of the cable connection portion, and the block was cooled while maintaining its shape. Liquefied cross-linking agent (DC
P) was impregnated, and a reinforcing insulator block 1 was manufactured in which the cross-linking concentration at a thickness of 5 mm from the surface was equal to the cross-linking agent concentration incorporated in the cable insulator. A BMJ was assembled using the block thus formed as a reinforcing insulator.

Example 6 The concentration of the cross-linking agent for impregnating the inner diameter of the expanded block in Example 5 was doubled.

EXAMPLE 7 A reinforcing insulator block having an inner diameter smaller by 5% than the outer diameter of a cable connecting portion was formed by using a resin without a crosslinking agent.
After the reinforcing insulator block was impregnated with a cross-linking agent (DCP), the block was cross-linked, and heated and stored at a melting point or lower, and by-products generated by the cross-linking reaction were volatilized and removed. Next, the inside diameter of the reinforcing insulator block is impregnated with a liquefied crosslinking agent (DCP),
A reinforcing insulator block 1 was manufactured in which the cross-linking agent concentration at a thickness of 5 mm from the surface was equal to the cross-linking agent concentration incorporated in the cable insulator. Subsequently, the same block is melted at + 5 ° C
The inner diameter was increased by 5% with respect to the outer diameter of the cable connection part, and cooled while maintaining its shape. A BMJ was assembled using the block thus formed as a reinforcing insulator.

Example 8 The concentration of the cross-linking agent for impregnating the inner diameter of the expanded block in Example 7 was doubled.

All the above-mentioned examples were manufactured under the condition that the water content after block crosslinking was 200 ppm or less.

COMPARATIVE EXAMPLE 1 A block of a reinforcing insulator having an inner diameter 5% smaller than the outer diameter of a cable connecting portion was formed, and after the block was crosslinked, it was heated and stored at a temperature lower than the melting point, and a by-product produced by the crosslinking reaction was removed. Volatilized and removed. Subsequently, the block was heated to the melting point + 10 ° C., the inner diameter was increased by 5% with respect to the outer diameter of the cable, and the block was cooled while maintaining its shape. A BMJ was assembled using the block thus formed as a reinforcing insulator.

Comparative Example 2 A reinforcing insulator block was formed using a resin containing a crosslinking agent having an inner diameter 5% larger than the outer diameter of the cable connection portion. A BMJ was assembled using the block thus formed as a reinforcing insulator.

Comparative Example 3 Using a resin containing a cross-linking agent (DCP), a reinforcing insulator block having an inner diameter smaller by 5% than the outer diameter of the cable connecting portion was formed. After the cross-linking, the block was stored at a temperature lower than the melting point, and by-products generated by the cross-linking reaction were volatilized and removed. continue,
The block was heated to a melting point of + 10 ° C., the inner diameter was increased by 5% with respect to the outer diameter of the cable, and the block was cooled while maintaining its shape. The liquefied crosslinking agent (D
CP) to produce a reinforced insulator block having a crosslinker concentration at a thickness of 5 mm from the surface equal to the crosslinker concentration incorporated in the cable insulation. A BMJ was assembled using the block thus formed as a reinforcing insulator.

Comparative Example 4 The concentration of the cross-linking agent for impregnating the inner diameter of the expanded block in Comparative Example 3 was doubled.

In Comparative Examples 3 and 4, the production was performed under the condition that the sum of the water after the block crosslinking and the water generated from the remaining cumyl alcohol was about 300 ppm.

With respect to the reinforcing blocks of Examples 1 to 8 and Comparative Examples 1 to 4, the mechanical strength (pulling) of the reinforcing insulator block / cable insulator interface at room temperature (25 ° C.) and 120 ° C. after the BMJ was applied. Peeling test)
Was carried out. Further, the moisture and the concentration of cumyl alcohol after the mold were measured, and the amount of moisture that could be generated from cumyl alcohol was compared with the sum of the above-mentioned amounts of moisture. The result is
The results are shown in Table 1 below.

[0026]

[Table 1]

The strength is expressed as a relative value when the strength at the test temperature of Comparative Example 2 is set to 1. Water content is Comparative Example 1
Are expressed as relative values when the water content is set to 1. Comparative Example 2 had the largest amount of water that could be generated, but had a value of 250 ppm or less. In Comparative Example 1, the water content was the lowest at 1.00, but a value of 100 ppm or less was obtained.

[0028]

As described above, by using the above-mentioned reinforcing insulator block, the mechanical strength at the interface between the reinforcing insulator block and the cable insulator at a temperature near the melting point and at a temperature higher than the melting point is greatly improved. It has become possible to increase the mechanical strength of the connection portion under the above temperature.
In addition, by controlling the by-products after crosslinking at an appropriate concentration or less during block production in advance, the amount of generated water can be reduced, and the generation of voids can be suppressed regardless of molding conditions.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a reinforcing insulator block in a first molded state.

FIG. 2 is a cross-sectional view of a reinforcing insulator block just before a power cable is inserted.

FIG. 3 is a sectional view showing a power cable inserted into a reinforcing insulator block in the state of FIG. 2;

[Explanation of symbols]

 1 Reinforced insulator block 2 Power cable connection

Claims (3)

[Claims] 1. An inner diameter of a reinforced insulator block is formed smaller than an outer diameter of a power cable connection portion, and the block is formed of a resin containing a crosslinking agent, and the formed reinforced insulator block is crosslinked. The reinforcing insulator block is heated and stored at a temperature lower than the melting point to volatilize and remove by-products generated by the crosslinking reaction. Then, the reinforcing insulator block is heated at a temperature equal to or higher than the melting point so that the inner diameter of the block is outside the power cable connection portion. The reinforcing insulator block for a power cable connection part, characterized in that the diameter of the reinforcing insulator block is increased to be larger than the diameter, and after cooling the expanded reinforcing insulator block, the inner diameter of the block is impregnated with a crosslinking agent. Production method. 2. The reinforcing insulator block has an inner diameter smaller than an outer diameter of a power cable connecting portion, and the block is formed of a resin containing no cross-linking agent, and a cross-linking agent is applied to the formed reinforcing insulator block. After the crosslinking, the reinforcing insulator block is heated and stored at a temperature lower than the melting point to volatilize and remove by-products generated by the cross-linking reaction. A power cable characterized in that the inner diameter is enlarged so as to be larger than the outer diameter of the power cable connection portion, and the expanded diameter of the reinforcing insulator block is cooled and then the block inner diameter is impregnated with a crosslinking agent. A method for manufacturing a reinforcing insulator block for a connection portion. 3. A reinforcing insulator block manufactured by the method according to claim 1 or 2 is attached to a power cable connection portion, and the applied block is heated and cross-linked, and further heated and pressed. The structure of the power cable connection part formed by fusing the block and the power cable connection part.