JPS5824881B2 - power cable - Google Patents

Description

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

Traditionally, in plastic insulating capacitors made of polyethylene or cross-linked polyethylene, trace amounts of water mixed in during manufacturing or use interact with the electric field to form a deterioration called water tree in the insulator, causing moisture to be supplied. It is known that if there is a problem, the insulation performance will deteriorate significantly.

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, but it is difficult to reduce them, and currently, insulators are impregnated with electrically negative gases such as SF6 or electrically insulating oils such as silicone oil. A method of filling voids has been studied and is already known, but even if such a method is adopted, it is still insufficient in preventing water trees.

Another possible method is to provide a metal sheath on the cable or a layer containing a desiccant such as calcium oxide to prevent the moisture itself, which causes water tree formation, from entering the insulator. However, the current situation is that the cost is high and that satisfactory results have not yet been obtained.

In view of the above-mentioned problems, the inventors of the present invention have conducted intensive research into an electric cable that can prevent water tree deterioration even if bonds 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. As a result, they discovered that it is very effective to form the electrical cable insulator from a polyolefin composition containing a specific thermoplastic polyester.

The present invention was made based on such knowledge, and 100 parts by weight of polyolefin contains a softening point of 190°C or less,
Thermoplastic polyester resin 1-2 with a molecular weight of 100,000 or less
The present invention provides an electrical cable with good water resistance, in which a composition containing 8 parts by weight and a crosslinking agent is coated on a conductor directly or via a shielding layer and crosslinked.

The polyolefin used in the present invention is low-density polyethylene (for example, NUC9025 manufactured by Nippon Unicar Co., Ltd.), high-density polyethylene (for example, Shorex 500 manufactured by Showa Yuka Co., Ltd.),
3) There are ethylene-vinyl acetate copolymers, ethylene-propylene copolymers, etc., but low-density polyethylene is particularly suitable for ultra-high voltage insulation.

The thermoplastic polyester resin used in the present invention has good processability,
In terms of water resistance, it is appropriate to have a softening point of 190°C or less and a molecular weight of 100,000 or less, such as Toyobo Membrane's Byron 500, Byron 300, and Byron 290.
, Byron GX-250, etc.

The appropriate amount of this substance to be added is 1 to 28 parts by weight, preferably 3 to 15 parts by weight, per 100 parts by weight of the base polymer.If it is less than this, it will not have any effect on water resistance, and if it is more than this, the mechanical properties will deteriorate. This is not preferable because it increases the amount of moisture absorbed.

As the crosslinking agent, a common crosslinking agent such as dicumyl peroxide is used.

Of course, anti-aging agents, voltage stabilizers, etc. may be added if necessary.

The composition used in the present invention can also be formed into a tape or sheet shape and used for insulating the connection parts and terminal parts of electric cables.

Next, an example will be described.

EXAMPLE Each component shown in Table 1 was kneaded and press-crosslinked at 170°C for 15 minutes to prepare a one-inch thick sheet.

In addition, a composition consisting of each component shown in Table 1 was extruded and coated on the conductor with a general-purpose semiconducting composition using a three-layer co-extrusion method, crosslinked, and a metal shielding tape was wound around the conductor to form a sheath. A cross-linked polyethylene insulated cable of 22KVIX1001nJII2 was prepared.

The surface of the sheet was forcibly scratched with 150 mesh sandpaper, and 2KV, 3KHz was applied for 7 days in the presence of 2N saline, and then the number of water trees in 25U2 was observed under a microscope.

For the cable, IN salt water was forcibly poured into the conductor and from the outside, and after immersion voltage was applied at 30KV for one year, the cable insulation was taken out and a length of 1OcIrL was
．． 5WIJIL was sliced into round slices and the state of water trees generated from the interface was observed.

Almost similar results were obtained for the sheet sample and the cable sample.
The number of water trees in sheet sample 25-Oki or cable 10 crrL is shown in Table 1 with 1 or less ◎, several trees ○, and several tens water trees X.

As is clear from the above results, the power cable of the present invention significantly improves the occurrence of water trees and is extremely effective.

Claims (1)

[Claims] 1 100 parts by weight of polyolefin has a softening point of 190°C
The following features are characterized in that a composition containing 1 to 28 parts by weight of a thermoplastic polyester resin with a molecular weight of 100,000 or less and a crosslinking agent is coated on a conductor directly or via a shielding layer to cause crosslinking. Electric power cable.