JPH11127516A - Extrusion mold connecting construction method for cross-linking polyethylene power cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an extrusion mold connecting construction method for a cross-linking polyethylene power cable, wherein the deformation of a cable insulator is prevented and a good connection part can be formed. SOLUTION: In an extrusion mold connecting construction method of a cross- linking polyethylene power cable, stripping a cable insulator 6a, 6b of the two cross-linking polyethylene power cables which are to be connected, exposing a conductor 1a, 1b, applying an internal semiconducting electrical layer 3 onto a conductor connection part connecting the fellow conductors 1a, 1b, next providing an extruding metal mold 4 over the cable insulator 6a 6b of both the cables, extruding non-crosslinking polyethylene in the inside of the metal mold 4, forming a reinforced insulating layer, and applying an external semiconducting electrical layer onto the reinforced insulating layer, chromaticity of an internal surface of the extruding metal mold 4 is formed in a manner, such that a central part 4a in a lengthwise direction thereof is black unit as compared with both end parts 4b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an extrusion molding connection method for a crosslinked polyethylene power cable.

[0002]

2. Description of the Related Art Crosslinked polyethylene power cables are rapidly following the path of high voltage due to their excellent insulation properties and ease of handling, and long-distance lines of 275 kV class are being constructed. Cable connections are essential for long-distance lines. A 275 kV-class crosslinked polyethylene power cable is covered with a split mold over the stripped cable insulator, and the insulating resin is extruded from the small extruder into the mold. A connecting part using an extruded molding connecting method, which is coated and crosslinked by heating and pressing in a state of being integrated with the extruded insulating resin, is employed.

[0003] A general description of the extrusion molding connection method will be given with reference to FIG. The working steps of this method are as follows. 1) First, the conductor 1 of the cable stripped to a predetermined size
a and 1b are compression-connected to each other using the conductor connection pipe 2, and the conductor connection pipe 2 is connected by a semiconductive tape or a semiconductive shrink tube.
An internal conductive layer 3 is formed thereon. 2) Next, cover the mold 4 in two parts, and put the inner space 5
The extruded insulating resin is extruded from a small extruder (not shown). However, prior to extrusion, the inner surface of the mold 4, the surfaces of the cable insulators 6a and 6b, and the surface of the inner conductive layer 3 are preheated to a predetermined temperature by a heater (not shown) incorporated in the mold 4, and Prevents resin solidification inside the mold. 3) Next, after the mold 4 was disassembled, the extruded insulating resin was cut into a predetermined reinforcing insulator shape, covered with a semiconductive shrinkable tube, and extruded in a pressurized container under gas pressure. Heat and crosslink the insulating resin.

[0004]

In the above-mentioned extrusion molding connection method, when the mold 4 is preheated, the cable insulator portions A of the cable insulators 6a and 6b inside the mold 4 which are closer to both ends of the mold 4 are connected. Is relatively close to the inner surface of the mold 4,
During preheating of the mold 4, the temperature tends to be higher than other parts. That is, inside the mold 4, the temperature distribution is such that the temperature of the inner semiconductive layer portion B located at the center in the longitudinal direction is the lowest, and the temperature increases as approaching both ends of the mold 4.
Therefore, when the temperature of the internal semiconductive layer is raised to a temperature that satisfies the preheating condition, the temperature of the cable insulator portion A made of cross-linked polyethylene becomes too high, and the pressure in the mold 4 increases due to the inflow of resin. In addition, there is a problem that the cable insulator portion A is easily softened and deformed.

In order to solve this problem, as a preheating condition of the mold 4, the temperature of the cable insulator portion A is set to a temperature at which the cable insulator does not deform, and the temperature of the internal semiconductive layer portion B is set. It is necessary to increase the temperature at which the extruded resin does not solidify, in other words, to reduce the temperature difference between the inner semiconductive layer portion B and the cable insulator portion A.

Therefore, as a solution to this problem, a mold built-in heater is divided so that the temperature at the center of the mold 4 is higher than that at both ends, and the temperature difference between the both ends and the center of the mold 4 is increased. Is conceivable. However, even with this method,
Due to heat conduction in the mold wall and convective heat transfer in the mold, the temperature of the cable insulator portion A rises more than necessary. For example, as shown in FIG. 1, the heater built into the mold is divided into a mold center 4 a and both ends 4 b, 4 b, and the center heater 4 is divided into three parts.
The temperature of the internal semiconductive layer portion B is lower than that of the cable insulator portion A by about 20 ° C. A temperature difference occurs. Alternatively, there is a possibility that the temperature difference can be further reduced by dividing the heater built into the mold into five or seven parts and gradually decreasing the control temperature from the center to both ends. The increase in locations
It has a significant impact on equipment costs and on-site workability, and is not realistic.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a conductor connection in which conductors of two cross-linked polyethylene power cables to be connected are peeled off and exposed. Apply an inner semiconductive layer on the part, then provide an extrusion mold over the cable insulator of both cables, extrude uncrosslinked polyethylene inside the mold to form a reinforcing insulating layer, In the extrusion molding connection method for a crosslinked polyethylene power cable to which a semiconductive layer is applied, the chromaticity of the inner surface of the extrusion die is characterized in that the central portion in the longitudinal direction is closer to a black body than other portions. Is what you do.

[0008] By the way, the temperature of the extrusion die rises,
Although the temperature of the internal semiconductive layer and the cable insulator in the mold rises, the transfer of thermal energy in this case is due to convective heat transfer in the mold interior space and heat radiation from the mold inner surface. Of these, energy transfer by thermal radiation is greatly affected by the chromaticity of the mold inner surface. That is, when the temperature is constant,
The closer the chromaticity is to a black body (having the highest thermal radiation energy density at a given temperature), the greater the thermal radiation energy density. Therefore, by partially changing the chromaticity of the inner surface of the mold (heat radiating surface), the temperature distribution of the internal semiconductive layer and the cable insulator (heat receiving surface) facing the inner surface of the mold can be adjusted. Therefore, as described above, when the chromaticity of the inner surface of the extrusion die is set such that the central portion in the longitudinal direction is closer to a black body than the other portions, the temperature of the inner surface of the die is equal throughout. In this case, the inner semiconductive layer portion facing the center of the mold receives a relatively higher density of thermal radiation energy than the cable insulator portion facing the end of the mold. Further, if the temperature of the central portion in the longitudinal direction of the extrusion die is higher than the other portions, the convective heat transfer occurs because the inner semiconductive layer portion receives a higher density of heat radiation energy than the cable insulator portion. The temperature difference between the inner semiconductive layer portion and the cable insulator portion can be reduced, including the transfer of thermal energy by the heat transfer.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an explanatory cross-sectional view of one embodiment of an extrusion molding connection method for a crosslinked polyethylene power cable according to the present invention. The steps of the connection method according to the present embodiment are as follows. That is, 1) First, strip to a predetermined size and remove the cable (275k
V, 2000 mm ² ), and the conductors 1 a and 1 b are compression-connected with the conductor connection pipe 2. 2) Next, a conductive tape or a semiconducting shrink tube is wound around the conductor connecting tube 2 and heated and molded to form an internal semiconductive layer 3. 3) Next, the mold 4 is placed between the ends of the cable insulators 6a and 6b via the heat-resistant cushion layer 10. The mold 4 has a built-in heater (not shown) divided into a central portion 4a and both end portions 4b and 4b, and an inner surface of the mold central portion 4a is treated with black Teflon coating.
The inner surfaces of b and 4b are subjected to a silver-white treatment by chrome plating, and the chromaticity of the inner surface of the mold central portion 4a is closer to a black body than the chromaticity of the inner surfaces of the mold end portions 4b and 4b. The length of the mold 4 is 800
mm, and the inner diameter of the central portion 4a is 135 mm. 4) Next, the control temperature of the mold central portion 4a is increased
The temperature is set to be 20 ° C. higher than the control temperatures b and 4b, and the inside of the mold 4 is heated and heated by energizing the built-in heater.

When the mold 4 is heated under the above-mentioned conditions and the temperature is raised to a temperature suitable for extruding the uncrosslinked polyethylene, the temperature difference between the inner semiconductive layer portion B and the cable insulator portion A is almost zero. Met. Further, when the uncrosslinked polyethylene was extruded into the heated mold 4 by a small extruder (not shown), the extrusion could be performed as usual, and the cable insulator portion A was not deformed at the time of extrusion. A good extrusion mold connection was formed. In the figure, 7
a, 7b, 8a, 8b are cable semiconductive layers, 9a, 9b
Is a sheath.

In the above embodiment, the chromaticity is changed by dividing the inner surface of the mold 4 into three parts. However, the inner surface of the mold 4 is divided into five parts, and a gray area between black and silver-white between the center and both ends is formed. Even with the provision, the same result as in the above embodiment was obtained. On the other hand, when the chromaticity of the inner surface of the mold 4 is made uniform as a conventional example, the temperature difference between the inner semiconductive layer portion B and the cable insulator portion A is 20 ° C.
When the temperature of the inner semiconductive layer portion B was sufficiently increased, the cable insulator portion A was deformed. From the above,
When the chromaticity is changed by dividing the inner surface of the mold 4 into at least three parts and the chromaticity of the central part is relatively close to a black body, a good extrusion mold connection part can be formed.

[0012]

According to the present invention, there is an excellent effect that the deformation of the cable insulator can be prevented and a good extruded mold connection can be formed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of a method of connecting a crosslinked polyethylene power cable by extrusion molding according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1a, 1b Conductor 2 Conductor connection pipe 3 Inner semiconductive layer 4 Die 4a Central part 4b End part 5 Inner space 6a, 6b Cable insulator 7a, 7b, 8a, 8b Cable semiconductive layer 9a, 9b Sheath 10 Heat resistant cushion layer A Cable insulator B Inner semiconductive layer

Claims (1)

[Claims] 1. An inner semiconductive layer is applied on a conductor connection connecting two exposed conductors of a crosslinked polyethylene power cable to be connected by stripping the cable insulation and then extruding over the cable insulation of both cables. A mold for extruding uncrosslinked polyethylene into the mold to form a reinforced insulating layer, and applying an external semiconductive layer on the reinforced insulating layer. An extrusion molding die connection method for a crosslinked polyethylene power cable, wherein the chromaticity of the inner surface of the mold is closer to a black body at a central portion in the longitudinal direction than at other portions.