JPH0626448B2 - Method for forming connection part of cross-linked polyethylene insulated power cable - Google Patents

Description

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. .

(Prior art and problems to be solved) When the reinforcing insulating layer of the connection portion of the CV cable is formed by extrusion molding using a mold, resin is usually used in a cooling process after completion of extrusion injection of the molding resin into the mold. Supplemental injection of resin is performed for the purpose of compensating for the volume contraction accompanying the temperature decrease of. Conventionally, this supplementary injection at the time of cooling depends on experience, and the technical roots have not always been clear, so optimization has not been performed quickly when the insulation thickness or conductor size of the cable has changed.

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

Including the conductor connection part of the above cable, the cable insulation layer
The mold (6) is installed by jumping to (1), and the internal space (7) of the mold (6)
Injecting an uncrosslinked polyethylene mixture containing a cross-linking agent by an extruder, and then heating the mixture under pressure to crosslink the polyethylene mixture injected into the mold (6),
The reinforced insulating layer is formed by integrally molding. In the drawing, (8) is a polyethylene mixture injection hole.

The performance of the connection portion of the CV cable thus formed by extrusion molding largely depends on the degree of adhesion between the cable insulation layer and the reinforcing insulation layer formed by extrusion. It is considered that this is because the volume contraction of the cable insulating layer and the connecting portion reinforcing insulating layer during cooling is concentrated near the interface between the two, and micro defects at the interface are amplified.

As a measure for solving such problems and obtaining a connection part having a good adhesiveness at the interface, the inventors of the present invention have found that the cable insulating layer in the mold at the time of preheating before injecting the polyethylene mixture into the mold. The surface is made to reach the melting point temperature of cross-linked polyethylene (the temperature measured by a differential calorimeter) or higher, and then the polyethylene mixture is extruded and injected into the mold so that the interface is at the end of extrusion injection of the polyethylene mixture. It has been found out that the above problems have already been heat-sealed and that problems such as peeling due to subsequent crosslinking can be prevented.

However, in this case, the mold is also at a temperature above the melting point of the cross-linked polyethylene in order to improve the flow of the injected polyethylene mixture, and when the injection of the mixture into the mold is completed and the cooling process is started, If this is left as it is, the mold will cool first, and the admixture in contact with the mold will also solidify. As a result, the effect of supplemental injection of the admixture does not extend to the end part in particular, stress is applied in the direction of peeling the interface at the interface near the end part, and defects such as minute voids existing there are amplified. I knew it would be done.

(Means for Solving Problems) The present invention solves the above problems and provides an improved method for forming a connection part, which is characterized by a mold and a surface of a cable insulating layer in the mold. Is heated to a temperature equal to or higher than the melting point of the cross-linked polyethylene, and an uncross-linked polyethylene mixture containing a cross-linking agent is extruded and injected into the mold, and in the cooling process,
The temperature of the mold is kept above the melting point of the crosslinked polyethylene until the temperature of the interface between the cable insulating layer and the reinforcing insulating layer formed by extrusion becomes equal to or lower than the melting point of the crosslinked polyethylene.

(Example) As shown in FIG. 1, the cable conductor connecting portion is included, and the mold (6) is mounted by jumping on the cable insulating layer (1), and is inserted into the internal space (7) of the mold (6). Before extrusion-injecting an uncrosslinked polyethylene mixture containing a crosslinking agent, the mold (6) is preheated by a heater (not shown) attached to the mold (6) and the inside of the mold (6) is The surface of the cable insulating layer is allowed to reach the melting point temperature of the cross-linked polyethylene, which is an insulator, and then the polyethylene mixture is injected from the mixture injection hole (8) of the mold (6).

Then, in the cooling process, the temperature of the mold (6) is controlled until the temperature at the interface between the cable insulating layer (1) in the mold (6) and the reinforcing insulating layer by extrusion falls below the melting point of the crosslinked polyethylene. And keep above the melting point. At this time, the temperature of the interface is cooled by heat escaping from the conductor (3) side in the length direction. After that, by supplementally injecting the polyethylene mixture into the mold (6), a positive pressure can be maintained throughout the interface, and defects at the interface are not amplified, and a good connection portion can be obtained.

By the way, 154 kV. The following table shows the results of measuring the AC breakdown voltage for two types of extrusion mold connection of a 2000 mm ² CV cable.

(Effects of the Invention) According to the above-described method for forming a connecting portion of the present invention, the mold is used until the temperature of the interface between the in-mold cable insulating layer and the connecting portion reinforcing insulating layer becomes equal to or lower than the melting point of the crosslinked polyethylene in the cooling process. Since the temperature is maintained at or above that temperature, the interface is always kept at a positive pressure during supplemental implantation, and micro defects on the interface are not amplified. Therefore, the dielectric breakdown due to the interface is reduced, and a good extrusion-molded connecting portion can be obtained.

[Brief description of drawings]

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

Claims (1)

[Claims] 1. A method of forming a reinforced insulating layer at a connection portion of a crosslinked polyethylene insulated power cable by extrusion molding using a mold, wherein the mold and the surface of the cable insulating layer in the mold are crosslinked polyethylene and a temperature not lower than the melting point. In the mold, the cross-linking agent was extruded and the uncrosslinked polyethylene mixture was extruded and the temperature of the interface between the cable insulation layer and the reinforced insulation layer formed by extrusion fell below the melting point of the crosslinked polyethylene. A method for forming a connecting portion of a crosslinked polyethylene insulated power cable, characterized in that the temperature of the mold is kept at a temperature equal to or higher than the melting point of the crosslinked polyethylene until the temperature reaches a certain level.