JPS5846802B2 - power cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrical cable cable with improved water resistance.

Traditionally, in plastic insulating cables made of polyethylene or cross-linked polyethylene, trace amounts of moisture mixed in during manufacturing or use interact with the electric field to form a deterioration called water tree in the insulator, resulting in moisture loss. It is known that if there is a supply, it will develop and significantly reduce insulation performance.

The causes of such water trees are thought to be the presence of foreign matter or voids in the polyethylene insulator, and defects at the interface between the insulator and the inner or outer semiconducting layer. Various measures have been taken in manufacturing to reduce these emissions, but it is difficult to reduce them, and currently, insulators are impregnated with electrically negative gases such as SF 6 or electrically insulating oils such as silicone oil. Therefore, a method of filling the voids has been studied and is already known, but even if such a method is adopted, it is still insufficient in terms of preventing water trees.

We are also considering ways to prevent the moisture itself, which causes water trees, from entering the insulator by providing a metal sheath on the cable or a layer containing a desiccant such as calcium oxide. However, the current situation is that it is costly and that satisfactory results have not yet been obtained.

In view of the above-mentioned problems, the present inventors have conducted intensive research into an electric cable that can prevent water tree deterioration even if voids or foreign matter are present in the insulator, and can be manufactured using a manufacturing method and cost that are almost the same as conventional ones. I just proceeded.

It has been found that it is very effective to form the electrical cape semiconductive layer with a semiconductive composition containing 0.5 to 15% by weight of an epoxy resin that does not contain a curing agent.

The reason for this is thought to be that during long-term use of the cable, the epoxy resin added to the semiconductive layer penetrates into the interface with the insulator and into the interior, significantly improving the water resistance of the insulator.

The present invention has been made based on such knowledge, and is an electrical cable having a semiconductive layer mainly covered with a conductor or a crosslinked polyethylene insulator, in which the semiconductive layer is made of 0 epoxy resin containing no curing agent. .5-15% by weight
The present invention provides an electrical cable having good water resistance and formed from the added semiconductive composition.

Epoxy resins used in the present invention include bisphenol epoxy, alicyclic epoxy, long chain aliphatic epoxy, heterocyclic epoxy, and dicrycidyl ester epoxy.

These preferably have a molecular weight of 3000 or less from the viewpoint of processability.

A commercially available product is Araldite CY-1 manufactured by Ciba Geigy.
79, CY-182, CY-350, CT-200,0
There are Y-250, GY-260, etc.

These epoxy resins are added alone or in combination to a general-purpose semiconducting composition in an amount of 0.5 to 15% by weight.

If it is less than this, there is no effect on improving the water resistance of the insulator, and if it is more than this, the electrical and mechanical properties of the semiconducting layer will deteriorate, which is not preferable.

Note that epoxy resin is usually used after being cured with a hardening agent, but in the present invention, not only is the epoxy resin not effective in terms of water resistance when it is hardened, but rather the hardening agent that remains unreacted can be used when electricity is applied. Since it contributes to the generation and development of water trees, it is necessary to use it without curing.

Next, an example will be described.

Example Various epoxy resins shown in Table 1 were added to the above composition,
A semiconductive composition was obtained by kneading in a conventional manner.

This is extruded and coated onto the conductor and the crosslinked polyethylene insulating layer using a three-layer co-extrusion method to form an inner semiconductive layer and an outer semiconductive layer, and then a metal shielding tape and a holding tape are wound around it to form a sheath. In step 22, a cross-linked polyethylene cable of 1 x 100 m4 was obtained.

1N saline solution was forcibly introduced into these cables from the conductor and the outside, and immersion voltage was applied at 33 KV for one year.

After that, take out the cable insulator and cut it to a length of 10 cm.
The sample was sliced into 5 ynm slices, and the generation of water trees generated from the interface between the inner semiconducting layer and the outer semiconducting layer was observed using a microscope.

Cable 10 crn The number of water tree occurrences is 1 or less ◎
, several numbers are indicated by ○, and dozens of numbers are indicated by X, as shown in Table 1.

As is clear from the above results, by adding an epoxy resin containing no curing agent to the semiconductive layer, an electrical cable with good water resistance can be obtained, which is extremely useful.

Claims (1)

[Claims] 1. In an electrical cable having a semiconductive layer coated on a conductor or a crosslinked polyethylene insulator, the semiconductive layer has an epoxy resin containing no hardening agent of 0.5 to 15%.
An electrical caple characterized in that it is formed of a semiconducting composition containing % by weight of a semiconductive composition.