JPS5952493B2 - How to manufacture power cables - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a power cable.

Rubber-plastic power cables of, for example, 20 kV or more that have been commonly used in the past are constructed as follows.

That is, an inner semiconductive layer formed by extrusion coating of a semiconductive mixture containing carbon powder, a rubber plastic insulating layer, and an outer semiconductive layer formed by extrusion coating of the above semiconductive mixture are provided on the conductor in this order. The layers were simultaneously vulcanized in heated and pressurized steam, and the layers were cross-linked and integrated using a cross-linking agent mixed into each layer in advance. However, in the manufacturing method of such power cables, the semiconductive mixture layer and the rubber-plastic insulation layer are usually softened during thermal crosslinking, and when this is heated under pressure, the internal semiconductive layer is softened. It has the disadvantage that it sinks into the conductor, degrading the electrical properties of the resulting power cable.

Although it is always strongly desired to improve the production efficiency of power cables, the conventional methods described above require a certain amount of crosslinking time, which is determined by the cable size, and there is a certain limit to increasing the production speed. I couldn't escape it.

Here, the inventors believe that the above-mentioned sinking of the semiconducting layer into the conductor is caused by the softening of the semiconducting layer during steam heating and by applying pressure from the outside. After careful consideration, we focused on the fact that it is difficult to shorten the crosslinking time because there are limits to improving thermal efficiency such as permeation, and as a result, we found that a ferromagnetic material was blended in advance into the semiconductive mixture. It has been discovered that the above problem can be substantially solved by irradiating high frequency waves and causing internal heat generation due to the ferromagnetic material's current loss and magnetic hysteresis loss, thereby cross-linking the semiconducting mixture. was completed.

That is, the present invention involves coating a conductor with a semiconductive mixture containing a crosslinking agent and a ferromagnetic material, and then coating the outside with an insulating layer and an external semiconductive coating material, and then irradiating the conductor with high frequency. A method for manufacturing a power cable, characterized by:

The drawing shows one embodiment of the invention, in which 1J is a conductor, 2 is an inner semiconducting layer, 3 is an insulating layer, and 4 is an outer semiconducting layer.

In this invention, the resin material for the inner and outer semiconductive layers is mainly polyolefin such as polyethylene, ethylene copolymer, chlorinated polyethylene, or a mixture thereof, as in conventional power cables,
If necessary, an antioxidant such as 4,4'-thiobis (6-tert-butyl-3-methylphenol) may be added.

In this invention, the semiconductive mixture refers to a semiconductive mixture that, as is well known, contains, for example, a polyolefin copolymer and also contains 10 to 7 parts of carbon black per 100 parts of the resin composition.
Approximately 0 parts were mixed. Next, as the crosslinking agent used in this invention, dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)
Organic peroxides such as hexane, 2,5-bis(tertiary-butylperoxy)2,5-dimethyl-3-hexyne, quinone dioxime, sulfur, etc., are commonly used in the above resins. 0.5 to 100 parts of composition
It is mixed in a proportion such as 5 parts. In this invention, ferrites such as Fe, O, ferrite, COFe2O4 ferrite, NiFe2O, ferrite, etc. are used as the ferromagnetic material, and these are used in an amount of 5 to 5% per 100 parts of the resin composition.
It is good to mix about 0 parts, particularly preferably 10 to 30 parts. If the amount of the ferromagnetic material is less than this range, the semiconducting mixture will not be crosslinked quickly; if the amount exceeds this range, extrusion coating properties and processability will deteriorate, both of which are undesirable.

After coating the conductor with each of the above layers, 10 to 1
000KHz of high frequency is irradiated, but specifically, a coil is wound around a cylinder, it is connected to a high frequency oscillator, and a cable is passed through the cylinder, and high frequency is irradiated at the same time as heating from the outside. The above-mentioned irradiation amount can be changed as appropriate within this range depending on the cable structure, wire speed, composition or thickness of the semiconducting layer, etc.
As described above, this invention mixes a ferromagnetic material into a semiconductive mixture that has been mixed with a crosslinking agent in advance, coats it on a conductor to form a semiconductive layer, and further coats an insulating layer and an external semiconductive layer. , the crosslinking is caused by internal heat generation due to the presence of the ferromagnetic material by irradiation with high frequency waves.

Therefore, since the internal semiconducting layer is quickly crosslinked, production efficiency is improved, and since no pressurizing conditions are applied, there is no deterioration in the characteristics of the power cable due to sinking of the internal semiconducting layer into the conductor. The industrial effects are extremely large.

The present invention will be specifically explained below with reference to Examples.

The composition of Table 1 (parts by weight) was applied to the conductors of Examples 1 to 3 and comparative examples (copper conductor 150 mm2).
Extrusion coated with a semi-conductive mixture of 0.25 mm thick, an insulating layer of 2.3 mm thick polyethylene Inumoto Unicar Co., Ltd., 9025), and an outer conductive layer (0.25 mm thick).
This was immediately heated to 180° C. in a vulcanized tube and subjected to high-frequency induction heating at 10 KHz for 5 minutes to crosslink it to obtain a 6 kV 150 sq CV cable.

The resulting power cable was evaluated to see if the internal semiconducting layer had sunk into the conductor as described above, and to check the degree of crosslinking, and the results are shown in Table 2.

According to the results in the table above, it is clear that the crosslinking degree of the conductive layer in the upper part of the product of the present invention is significantly improved compared to the comparative example, there is no sinking into the conductor at all, and the electrical holding property is significantly improved. . The above cited example was carried out at a line speed of 7 m/min, but when this was increased by 1.5 times under the same conditions, in the comparative example, the gel fraction decreased to 30% and the above-mentioned indentation increased further, and the above-mentioned indentation was maintained. It was clear that the speed improvement described above was possible.

[Brief explanation of drawings]

The drawing is a cross-sectional view of the power cable of the invention. DESCRIPTION OF SYMBOLS 1... Conductor, 2... Inner semiconducting layer, 3... Insulating layer, 4... Outer semiconducting layer.

Claims (1)

[Claims] 1. A power source characterized by coating a conductor with a semiconductive mixture containing a crosslinking agent and a ferromagnetic material, and then coating the outside with an insulating layer and an external semiconductive coating material, and then irradiating the conductor with high frequency waves. Cable manufacturing method.