JPH0261767B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of manufacturing an oil-impregnated plastic power cable filled with an insulating gas.

[Object of the Invention] In order to improve the drawbacks of conventional power cables having insulating layers formed by extruding plastic insulating materials, the present inventor provided an insulating layer containing insulating oil to plastic and sealed an insulating gas inside the cable. A solid-state power cable and its manufacturing method were proposed.

In particular, it has been found that drying the plastic insulating layer is extremely effective in preventing the occurrence of water trees caused by moisture in the insulating layer, which is a drawback in solid power cables, and this has already been proposed. The invention also seeks to provide a method for manufacturing solid insulated power cables that completely eliminates moisture in the plastic insulation layer.

[Disclosure of the Invention] The present invention involves placing a plastic insulated power cable core in which an insulating layer is formed on a conductor by extrusion molding, placing the core in a tank, heating the core from the inside with the conductor's heat by passing electricity through the conductor, and heating the core from the inside using the heat generated by the conductor. The tank is evacuated to dry the core, the core is vacuum-coated to form a metal sheath, and then insulating oil is filled into the metal sheath and heated. The method of manufacturing a power cable is characterized in that the insulating layer is impregnated with the insulating oil while the cable is kept under pressure, the insulating oil is removed after the insulating layer is returned to room temperature, and an insulating gas is sealed.

The present invention will be explained below with reference to embodiments shown in the drawings.

The conductor to which the present invention is applied is a stranded conductor of copper or aluminum, or an aggregate of compressed stranded wire segments, and may be a hollow conductor having a hollow portion at the center of the conductor or a solid conductor having no hollow portion.

These conductors are passed through an extruder, and at least PE, PP, or polystyrene is supplied as a plastic insulating material, with crosslinking agents, oxidation stabilizers, etc. added as necessary, and an insulating layer is formed on the conductors by extrusion molding. do. This is called the core. This process is no different from the conventional one.

An insulating layer is thus formed on the conductor, and the core wound around the cable drum is subjected to a vacuum heating and drying process as shown in FIG.

In the figure, 1 indicates a tank. The tank 1 is configured such that the top cover 8 can be opened at the flange 2, and the tank 1 is equipped with a drawer part 3, and a caterpillar 4 for drawing out the core is provided in the middle of the drawer part 3. Furthermore, a gate valve 5 for opening and closing the internal pressure of the tank 1 is provided.

The upper lid 8 of the tank 1 is opened, the cable drum 6 with the core 9 wound thereon is housed, both ends of the core 9 are connected to the DC power source 7, the upper lid 8 is closed, and the gate valve 5 is closed and energized. Although not shown, the tank 1 is heated while being evacuated. Required temperature from inside the core, e.g. 70-150
℃, and on the other hand, the water in the plastic insulating layer is removed very efficiently and with good quality by heating from the tank wall by steam heating with a coiled pipe (not shown) and evacuating it with a vacuum pump. be done. At this time, if the hollow conductor described above is applied, it is even more convenient to remove moisture from the conductor side.

The process of covering the metal sheath in FIG. 2 is shown.

As shown in the figure, this step is carried out in tandem with the heating drying step. In the figure, 10 is an aluminum press connected to the drawer section (FIG. 1), and 11 is a corrugator that corrugates the aluminum sheath covered by the aluminum press 10.

Open the gate valve 5 at a pressure slightly higher than normal pressure, and press the core 9 into the aluminum press 1 with the catalyst pillar 4.
After being coated with aluminum, it is corrugated and wound onto a drum 13. After the core 9 is tightened by the corrugator 11, the caterpillar 4 releases its engagement with the core 9 when it is naturally extruded by the force of the aluminum press 10. This process makes it possible to obtain a power cable with an aluminum sheath 12, which is wound around the drum 13.

A third cable is attached to both ends of the aluminum sheath of this power cable.
As shown in the figure, attach the metal tubes 14, 14',
The cable drum 15 wrapped with this cable is stored in the tank 16, and for example, although not shown,
The cable sheath is heated to a temperature of 80 to 150°C by electrical heating of the conductor and heating using a steam coil installed on the wall of the tank 16 as a heat source, and purified and degassed insulating oil is extracted from the metal pipe 14 at one end. For example, an insulating oil blended with at least one of DDB, polybutene, mineral oil, or another insulating oil is selected and introduced, and the metal tube 14' at the other end is evacuated to impregnate the insulating oil.

Each SP of the plastic material used for the above plastic insulation layer and the insulation oil impregnated with it.
It is possible to use a combination of materials with a value (solubility index: the closer the SP values of plastic and insulating oil are, the stronger their kinship is, and the greater the degree to which they will dissolve into each other and mix into one) is 8 or more. The above-mentioned insulating oils are preferably used corresponding to the plastic materials used as the insulating layer, such as the already mentioned PE, PP, polystyrene, etc.

Thereafter, the temperature is maintained at an appropriate temperature, for example 80 to 150°C, for a certain period of time, for example 1 day to 1 week. During this post-impregnation heating time, the insulating oil penetrates into the amorphous microvoids of the plastic insulation layer, causing a so-called swelling of the plastic insulation layer. At this time, if the inside of the tank is pressurized to the required pressure, for example with air, and the oil pressure inside the metal sheath is increased accordingly, the metal seal can be pressurized and heated in a balanced state without being deformed by the oil pressure, and the plastic insulation layer can be impregnated. Impregnation inside becomes even smoother. As an example, when pressure is applied at 3 kg/cm ² , impregnation can be carried out in about half the time compared to when pressure is not applied. After that, the insulating oil is removed from the metal sheath after being cooled to room temperature. However, when the insulating oil is heated and pressurized, the insulating oil penetrates into the micro voids and cools the insulating oil to room temperature. As a result, the remaining microvoids are almost completely eliminated. In this case, it is effective to turn the drum on its side, pressurize the gas from the top side, and drain the insulating oil from the bottom side. Although dry air may be used as the gas for removing the insulating oil, it is preferable to use an insulating gas consisting of at least one of SF ₆ , N ₂ , CFC, etc. After removing the insulating oil, the insulating gas is Enclosed in a filled state. In this case, the insulating gas is sealed at a high temperature (drying temperature higher than the operating temperature), and considering the shrinkage characteristics of the gas, the insulating gas is kept at room temperature so that even if the temperature drops, the microvoids and amorphous materials are sufficiently filled with the insulating gas. Maintain positive pressure to penetrate the plastic insulation layer.

After this, a corrosion-resistant layer is coated on the outside of the metal sheath in a separate process, and the cable is completed.

The vacuum metal coating method used in the examples is already within the applicable range of coating technology for OF cables that are commonly used.

[Operations and Effects of the Invention] As explained above, the present invention involves placing a cable core in which a plastic insulating layer is formed by extrusion on a conductor and heating it from the inside and outside to dehydrate the moisture in the core. The vacuum-coated metal sheath is heated and filled with insulating oil, kept in a heated and pressurized state, the insulating layer is impregnated with the insulating oil, and once returned to room temperature, the insulating oil is filled with the insulating oil. Since we use a method to remove oil and fill in insulating gas, there are no microvoids, and by filling with insulating gas, we can sufficiently increase the dielectric strength. A power cable that is electrically stable over a long period of time can be manufactured without requiring supply, processing, etc.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of vacuum and heating drying of a cable core in the present invention. FIG. 2 shows the steps for implementing the present invention. FIG. 3 also shows the process of implementing the present invention. 1... Tank, 2... Flange, 3... Core drawer, 4... Catapillar, 5... Gate valve, 6, 13, 15... Cable drum, 7...
DC power supply, 8... Tank top lid, 9... Cable core, 10... Aluminum press, 11... Corrugator, 12... Aluminum sheath, 14, 14'...
Metal pipe, 16...tank.

Claims (1)

[Claims] 1. A plastic insulated power cable core with an insulating layer formed by extrusion molding on a conductor is placed in a tank, the core is energized through the conductor, and the conductor's heat is heated from the inside as well as from the outside. After the core is dried by drawing a vacuum inside, the core is vacuum-coated to form a metal sheath, and then insulating oil is filled into the metal sheath while heated, and heated and pressurized. A method for manufacturing a power cable, characterized in that the insulating layer is impregnated with the insulating oil, the insulating oil is removed after the insulating layer is returned to room temperature, and the insulating gas is sealed.