JPH0879935A - Plastic power cable jointing method - Google Patents

Abstract

PURPOSE: To obtain a plastic power cable jointing method employing an insulator block in which the bonding strength on the interface between the insulator block and a cable insulator is enhanced while eliminating corona discharge. CONSTITUTION: A tubular insulator block is applied to a conductor joint and the end part of cable insulator and then the insulator block is heated and pressed thus fusing and integrating the insulator block and the cable insulator. In such method for jointing a plastic power cable, the insulator block comprises a core metal pipe coated with a fluororesin and an insulation material is extruded on the core, having thermal conductivity of 5×10<-3> cal/sec/cm<2> / deg.C or above, between the inner and outer faces of the insulator block. It is cooled on the inside of the pipe upon finishing extrusion thus producing the insulator block being employed in plastic power cable joint.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to C used at high voltage.
The present invention relates to a connecting method using an insulator block of a plastic power cable such as a V cable.

[0002]

2. Description of the Related Art Conventionally, for connecting a plastic power cable such as a CV cable used at high voltage, an insulating material which is the same as or similar to the cable insulator is extruded on a conductor connecting portion and then cross-linked if necessary. The so-called extrusion mold type connection method of performing

On the other hand, in recent years, as disclosed in, for example, Japanese Patent Publication No. 6-64845 and Japanese Patent Laid-Open No. 5-76125, a material which has been extruded at a connecting place is formed into a cylindrical shape by being preformed in a factory. An insulator block is produced, and the insulator block is mounted on the conductor connecting portion and the end portion of the cable insulator to be connected on site, and the insulator block is heated and pressed to be fused and integrated with the cable insulator, A so-called block mold type connection method has been proposed.

[0004]

However, in the block mold type connecting method as described above, since the preformed insulator block is inserted on the cable insulator after the removal of the outer semiconductive layer, the outer semiconductive layer is inserted. A gap is required between the cable insulator after removing the conductive layer and the inner diameter of the preformed insulating block. For this reason, in the case of heat fusion, the interface with the cable insulator is less likely to adhere than in the extrusion mold type connection method, and there is a problem that corona discharge occurs at the relevant portion during voltage application and leads to destruction.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above problems and provides a method for connecting a plastic power cable which has good interface adhesion and does not generate corona discharge. The core of the body block is a metal pipe coated with a fluororesin, and the thermal conductivity between the inner surface and the outer surface is 5 × 10 ^-3 cal / sec / cm ² / ° C.
It is intended to use the one manufactured by extruding the insulating material on the core as described above and cooled from the inside of the pipe at the time of cooling after the completion of the extrusion.

[0006]

As a result of intensive studies on the above problems, the present inventors have concluded that the insulator block should be manufactured so as to have a large residual shrinkage strain. Therefore, a method of manufacturing an insulator block having a large residual shrinkage strain was examined. As a result, a desired large residual shrinkage strain can be obtained by extruding an insulating material on a pipe-shaped core that satisfies the following two requirements and cooling the inside of the pipe during cooling after the extrusion. It was found that it can be obtained. (1) The core has a metal pipe coated with a fluororesin. (2) The thermal conductivity between the inner surface and the outer surface of the core is 5 × 10 ^-3 ca.
l / sec / cm ² / ° C or higher. That is, compared with unreacted cross-linked polyethylene insulation that forms the insulation block, a large residual shrinkage strain can be obtained by using a core mainly composed of a metal pipe whose shrinkage degree is small at the time of cooling and rapidly cooling from the inside can get.

Here, the reason why the core coats the metal pipe with the resin is that when the core has a metal surface, the hardness difference between the core and the unreacted cross-linked polyethylene material extruded thereon is too large, and This is because it is unavoidable that the inner surface of the insulator block is damaged when the cable is removed. The reason why the fluorine-based resin is used as the coating resin is that it is very easy to peel off from the unreacted cross-linked polyethylene resin and the inner surface of the insulating block is not easily damaged when the resin is removed. On the other hand, the thermal conductivity between the inner surface and the outer surface of the core is 5 × 10 ^-3 cal / sec /
The reason for using cm ² / ° C is to improve heat transfer on the inner surface for quick cooling from the inside.

[0008]

Example A crosslinked polyethylene compound was extruded at 120 ° into a mold in which a core coated with a fluororesin was set on a stainless steel pipe to prepare an unreacted crosslinked polyethylene block. At this time, the cross-linked polyethylene block was produced by changing the coating thickness of the fluororesin. Further, in each case, two conditions were performed, namely, cooling by blowing a wind of about 20 ° C. inside the pipe and cooling with the airtight.

These crosslinked polyethylene blocks are covered on a CV cable core from which the outer semiconductive layer has been scraped off, and a semiconductive heat-shrinkable tube is further formed thereon to form an outer semiconductive layer, which is then covered with a crosslinked can. Heat molding was performed under a nitrogen gas pressure of 5 kg / cm ² . At this time, the scraping amount was adjusted so that the difference between the inner diameter of the insulator block and the outer diameter of the cable obtained by scraping the outer semiconductive layer was 6 mm in diameter. After the completion of the molding, the state of adhesion at the interface was observed with an optical microscope to evaluate the presence or absence of interface peeling. Table 1 shows the above experimental conditions and results.

[0010]

[Table 1]

From the results shown in Table 1, the thermal conductivity is 5 × 10 ^-3 cal
It was found that peeling did not occur at the interface when cooling was performed from the inner surface of the pipe having a core of / sec / cm ² / ° C or higher and having a core. The fact that the difference in thermal conductivity affects the cooling speed at the time of manufacturing the block and obtained such results is that when cooling in the pipe is not performed, peeling occurs at the interface regardless of the thermal conductivity. It is clear from the fact that In Comparative Example 5, the core was processed without providing the fluororesin layer, but the inner surface of the insulator block was scratched when the core was removed. It was confirmed that this scratch remained as peeling even after molding.

[0012]

As described above, according to the method for connecting a plastic power cable of the present invention, the insulation block and the cable insulation are well adhered to each other and there is no peeling at the interface, and corona discharge occurs at this portion. A good connection can be obtained without any occurrence.

Claims (1)

[Claims] 1. A plastic power cable in which a cylindrical insulator block is mounted on a conductor connecting portion and an end portion of a cable insulator to be connected, and the insulator block is heated and pressed to be fused and integrated with the cable insulator. In the connection method of No. 3, the insulator block has a metal core coated with a fluororesin on a metal pipe, and the thermal conductivity between the inner surface and the outer surface is 5 × 10 ⁻³ cal / sec / Characterized by being manufactured by extruding an insulating material onto a core having a cm ² / ° C or higher, and by being cooled from the inside of the pipe at the time of cooling after the end of extrusion. How to connect a plastic power cable.