JPH01202107A - Mold joint construction for cable - Google Patents

Abstract

PURPOSE:To suppress the generation of voids and improve insulating characteristic, by stepped-stripping off the connecting end of a power cable to expose the core for connection, and by discharging air to introduce inert gas and to perform resin-molding. CONSTITUTION:The covering section 2 of the connecting end section 1 of a CV cable to be connected to is stepped-stripped off for connection and is penciling-processed, and a conductor is connected with a pressure-fitting sleeve. After that, the connected section is wound up with a semiconductive tape 3, and after it is heat-fused, it is set in an extrusion-molding metallic mold and is vacuum-led, and nitrogen gas is permitted to flow in. Then, resin is extruded into the metallic mold. After that, the connected section is taken out of the metallic mold, and the joint section is shaped and is covered with a semiconductive tube and is thermally shrunk to form an external semiconductive layer. The molding metallic mold is set again with the connected section, and the section is heated and is pressure-applied with the nitrogen gas and is fusion- molded. As a result, the generation of micro-voids at investigated points A-F is suppressed, and insulating characteristic is improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a cable mold joint construction method,
In particular, the present invention relates to a construction method for suppressing the generation of voids in joints.

<Prior Art> An example of a mold joint construction method for a conventional cable, for example, a C■ cable, is as follows. First, the covering parts of the connecting ends of both cables that are to be connected to each other are shaved off into a conical shape (penciling process), and the wing parts are inserted into cylindrical metal crimp sleeves from both sides. The conductor connection is made by crushing the crimp sleeve.

Next, if necessary, an internal semiconductive layer is formed using a semiconductive tape. After this, an extrusion mold is set and the mold resin is extruded in the air or in nitrogen gas. After the resin has cooled, the mold is removed, and if necessary, an external semiconductive layer is formed using a semiconductive layer heat shrink tube, etc., and finally,
Set the mold for molding, heat and pressurize it,
The resin is melt-molded.

However, in recent years, the voltage of C■ cables has been rapidly increasing, and with this, high reliability has been required of cable joint technology.

<Problems to be Solved by the Invention> In the case of the conventional mold joint method described above, the method of extruding the mold resin in nitrogen gas is superior in that it provides better heat aging resistance than that in air. However, it was still insufficient in terms of microvoid suppression and electrical properties.

Therefore, the inventors of the present invention conducted extensive studies and found that in order to further suppress the generation of voids and improve the electrical characteristics in this mold joint part, the effects of dissolved moisture and dissolved oxygen present on the cable side itself must be was found to be extremely large. It was also found that the amount of dissolved water and dissolved oxygen increases as the CV cable size increases and the coating becomes thicker due to higher voltage, and the effects thereof tend to increase. .

As a result of various experiments, we performed vacuum treatment as a pretreatment prior to resin molding, and then injected inert gas to replace the moisture and oxygen dissolved in the cable with inert gas. It was found that the effect of suppressing the generation of large voids and the improvement of electrical properties can be obtained.

The present invention has been made from this viewpoint.

A feature of the present invention is that after connecting the conductors of the cable, it is evacuated, then inert gas is injected, and then resin molded. This is in the cable mold joint construction method.

The conditions for evacuation performed in the present invention are not particularly limited, but preferably the degree of vacuum is 10 Torr or less for 2 hours or more, and the temperature is in the range of 50 to 120°C. Also,
The inert gas used is nitrogen (N2), argon (
Examples include gases such as Ar) and neon (Ne).

This evacuation is performed after the conductor is connected and after the extrusion mold is set. After this evacuation, an inert gas is subsequently injected, and by this evacuation and gas injection, dissolved moisture and dissolved oxygen in the connecting portion, particularly the cable, are replaced by the inert gas. In other words, a water-free and oxygen-free state is achieved, giving good results to the subsequent extrusion of the mold resin and melt molding of the resin, effectively suppressing the generation of microvoids in the joint part, and at the same time providing good electrical properties. can get.

<Example> Next, an example of the construction method of the present invention and a comparative example of the conventional construction method will be described.

First, as a test cable, 275Kv, 2500m
A mold joint (EMJ) part was made using the following process using a C■ cable of 1.5 m'', and an AC withstand voltage test and microvoid observation were attempted.

For connection, scrape (penciling) the sheathing part (insulator, etc.) of the reconnection end of the above ℃v cable to expose it, and put both conductor parts into a cylindrical metal crimp sleeve. It was inserted from both sides, and the crimp sleeve was then crushed to connect the conductors. Next, a semiconductive tape was wrapped around this connection portion and heated and melted to promote crosslinking to form an internal semiconductive layer, and then an extrusion mold was set.

After setting this mold, (1) In the case of Example I of the present invention, the degree of vacuum is 10 Torr.
After vacuuming at 50°C for 2 hours, nitrogen gas (normal pressure) was subsequently blown away.

(2) In the case of Example ① of the present invention, the degree of vacuum is 10 Torr.
A vacuum was drawn at 120° C. for 2 hours, and then nitrogen gas (normal pressure) was blown away.

(3) In the case of Comparative Example I, nitrogen gas was blown away without pretreatment.

(4) In the case of Comparative Example (■), no treatment was performed, that is, the inside of the mold was left in the atmosphere (air).

After this, the mold resin was extruded into the mold. The extrusion conditions at that time were a resin temperature of 135°C and a pencil ring interface temperature on the cable side of 125°C.

After extruding the molded resin, it was cooled under nitrogen gas at an applied pressure of 6 kg/cm'', the mold was removed, and the shape of the joint portion was adjusted by glass cutting or the like.

Further, a semiconductive heat-shrinkable tube was placed over this and heat-shrinked to form an external semiconductive layer.

Since the degree of crosslinking between the extrusion mold resin part and the external semiconducting layer part of each connection part made in this way is still insufficient, a mold for molding is further set in each connection part, and a 200° C (heater temperature) for 10 hours, 6.5
It was pressurized with nitrogen gas of Kg/cm'' to melt and mold, and then cooled by controlling the temperature so that the cooling progressed from the conductor side toward the outer semiconducting layer.

Regarding the four types of joints manufactured in this way (Examples ■~■, Comparative Examples I~■), we investigated the occurrence of microvoids through an AC withstand voltage test and a subsequent disassembly investigation, and the results are shown in Table 1 and It was as shown in Table 2.

In addition, each test and investigation was performed on two samples on each side (sample 1.
2) I went one by one. The locations where microvoids were investigated and measured were points A-F in FIG.

In FIG. 1, 1 is a conductor, 2 is a covering part such as an insulator,
3 is an extrusion mold part.

From Table 1 above, it can be seen that the height measurements carried out in accordance with the present invention have higher breakdown voltage and superior electrical properties than comparative products. Furthermore, from Table 2, it can be seen that the actual height measurement of the present invention has a smaller number of microvoids than the comparative product, and has a large effect of suppressing the generation of voids.

<Effects of the Invention> As is clear from the above description, the present invention provides a cable that can effectively suppress the generation of voids caused by thermal history during molding, has a high AC breakdown voltage, and has excellent electrical properties. We can provide the mold joint construction method. In particular, it is possible to provide a highly reliable and optimal mold joint construction method that is compatible with the recent increase in the voltage of cables.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the investigation points where the occurrence of microvoids in the mold joint portion was investigated according to the present invention. Number to

Claims (1)

[Claims] A mold joint construction method for a cable, which is characterized in that after connecting the conductors of the cable, the cable is evacuated, then inert gas is injected, and then resin molding is performed.