JPH071969B2 - Method for forming connection part of cross-linked polyethylene insulated power cable - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for forming a connecting portion, in which a reinforcing insulating layer of a connecting portion of a crosslinked polyethylene insulated power cable (CV cable) is formed by extrusion molding using a mold. Regarding improvement.

(Prior Art and Problems to Be Solved) The performance of the extrusion mold type connection portion of the CV cable largely depends on the degree of adhesion between the cable insulating layer and the reinforcing insulating layer formed by extrusion.

FIG. 1 is an explanatory view of a method for forming a CV cable connection portion by extrusion molding. In the drawings, (1) is a cable insulating layer made of cross-linked polyethylene, (2) is a semiconductive layer inside the cable on the cable conductor (3), (4) is a connecting sleeve of the cable conductor (3), and (5) is a cable. A connecting part inner semi-conducting layer applied over the cable conductor connecting sleeve (4) over the inner semi-conducting layer (2) of the cable for electric field relaxation of the connecting part of the conductor (3).

An uncrosslinked structure including a conductor connection part of the cable, a mold (6) mounted over the cable insulating layer (1), and a cross-linking agent mixed in an internal space (7) of the mold (6) by an extruder. The polyethylene mixture is injected, and then heated and pressed to crosslink the polyethylene injected into the internal space (7) and integrally molded to form a reinforced insulating layer.

In the formation of the reinforcing insulating layer, the step of injecting the polyethylene mixture into the mold (6) is called an extrusion step, and the step of crosslinking the erythylene mixture and integrally molding is called a crosslinking step. In the process, the polyethylene mixture is simply injected into the mold (6) with an extruder, and the adhesiveness at the interface between the cable insulation layer and the reinforcing insulation layer, which is important for the performance of the connection part, depends on the processing, heating, etc. in the crosslinking process. It has been considered to depend on the conditions.

However, as a result of the inventor's deep study on the degree of adhesion at the interface, it was found that the factor of the pressing step also greatly influences the adhesion at the interface. That is, in order to improve the adhesion of the interface, it is necessary to sufficiently heat the surface (A) of the cable insulating layer in the mold (6) before injecting the polyethylene mixture into the mold (6). Was important, and it was confirmed that the adhesiveness of the interface depends on the temperature condition of the cable insulating layer surface (A).

(Example) As shown in Fig. 1, a cable conductor connecting portion is included, a mold (6) is set over the cable insulating layer (1), and a bridge is formed in the internal space (7) of the mold (6). Before injecting the uncrosslinked polyethylene mixture containing the agent, preheat the mold (6) with a heater (not shown) attached to the mold (6) to insulate the cable insulation layer surface (A). It is made to reach the melting point temperature (the temperature measured by a differential calorimeter) of the crosslinked polyethylene, which is the body, and then the polyethylene mixture is injected from the mixture injection hole (8) of the mold (6).

By doing so, the interface between the cable insulating layer (1) and the reinforcing insulating layer in the mold (6) has already been heat-sealed at the end of the extrusion process of the polyethylene mixture, and the subsequent crosslinking Problems such as peeling in the process can be prevented.

When heating the cable insulation surface (A) described above, the X mark near the conductor has the lowest temperature.
It is necessary to keep the mark point above the melting point temperature of the crosslinked polyethylene.

By the way, the results of measuring the AC breakdown voltage for two types of extrusion mold connection of a 154KV, 2000mm ² CV cable are shown in the table below. The melting point temperature of cross-linked polyethylene is 110.
℃.

(Effect of the Invention) According to the above-described method for forming the connection portion of the present invention, the surface of the cable insulating layer in the mold is allowed to reach a temperature equal to or higher than the melting point of the crosslinked polyethylene before the resin is injected into the mold. Since the interface between the cable insulation layer and the reinforced insulation layer is already heat-fused in the extrusion process, it has a considerable adhesive strength, and its adhesiveness is maintained even in the cross-linking process to prevent interfacial peeling. It can be prevented. Therefore, the variation of the breakdown voltage is small, and the breakdown is reduced especially at a low voltage.

[Brief description of drawings]

FIG. 1 shows an explanatory view of a method for forming a connecting portion by extrusion molding of a CV cable. 1 ... Cable insulating layer, 3 ... Cable conductor, 4 ... Conductor connecting sleeve, 6 ... Mold, A ... Surface of cable insulating layer in mold.

Claims (2)

[Claims] 1. A method for forming a reinforcing insulating layer of a connecting portion of a crosslinked polyethylene insulated power cable by extrusion molding using a mold, wherein the cable insulating layer in the mold is preheated before injecting resin into the mold. A method for forming a connecting portion of a crosslinked polyethylene insulated power cable, characterized in that the surface is kept at a temperature equal to or higher than the melting point of the crosslinked polyethylene. 2. The connection of a crosslinked polyethylene insulated power cable according to claim 1, wherein the surface of the cable insulating layer at least near the conductor connecting portion is kept at a temperature equal to or higher than the melting point of the crosslinked polyethylene. Forming method.