JPH1166947A - Covered electric wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve stress corrosion cracking resistance of a conductor, and lengthen its service life by setting the impurity content of the conductor totaling a specific quantity or less except for the silver content. SOLUTION: The impurity quantity of a conductor is set totaling 60 ppm or less except for silver. It is desirably set no more than 40 ppm, and is particularly set not more than 20 ppm. Purity of the conductor is desirably set not less than 99.995%, and since the conductor is constituted of copper on which the total content of Ni, S and H as an impurity is 5 ppm or less, stress corrosion cracking resistance can be improved further. Heat treatment is desirably performed on the conductor under a condition of not causing recrystallization. When heat treatment is performed on an impurity quantity-limited conductor under a conduction of not causing complete recrystallization such as to maintain strength equal to a hard copper wire, the stress corrosion cracking resistance can be improved further. The conductor of a covered conductor has an insulating covering on an outer periphery. The conductor may be either of a single track and a stranded wire by interwisting plural strands.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a covered electric wire having a conductor coated with an insulating material such as polyethylene. In particular, the present invention relates to a covered distribution line installed between utility poles.

[0002]

2. Description of the Related Art Overhead power distribution lines installed between telephone poles are:
A conductor obtained by twisting a plurality of hard copper wires is used, and an insulating coating of polyethylene, polyvinyl chloride, or the like is applied to the twisted wire.

[0003]

On the surface of each of these twisted hard copper wires, the repulsive force of the twisted wire to release the twist, the winding habit when wound on the drum, and the tension accompanying the erection , A residual tensile stress appears.

On the other hand, when rainwater enters the covered electric wire, the inside of the covered electric wire becomes an easily corrosive environment, and an oxide film is formed on the surface of the hard copper wire. If such a tensile residual stress and a corrosive environment are present at the same time, they affect each other to cause stress corrosion cracking in the hard copper wire, and as a result, the coated electric wire may be disconnected.

[0005] In order to reduce disconnection due to stress corrosion cracking of the covered wire, it is necessary to prevent rainwater from entering the inside of the covered wire,
Measures such as the use of conductor discoloration prevention materials and the reduction of stranded wire repulsion have been taken. However, no measures have been proposed for improving the stress corrosion cracking resistance of the conductor itself. For example, if a soft copper wire is used as the conductor of the covered electric wire, the tensile residual stress due to the stranded wire repulsive force or winding habit can be reduced, and the occurrence of stress corrosion cracking can be suppressed, but the tensile strength decreases. Therefore, in practice, a soft copper wire cannot be used as a conductor of a covered electric wire.

Accordingly, a main object of the present invention is to provide a covered electric wire which can improve the stress corrosion cracking resistance of a conductor and extend the life thereof while maintaining the electrical and mechanical properties of the covered electric wire. Is to do.

[0007]

A covered electric wire according to the present invention is a covered electric wire having an insulating coating on the outer periphery of a conductor, wherein the conductor is made of copper having a total amount of impurities other than silver of 60 ppm or less. And The conductor here may be either a single wire or a stranded wire obtained by twisting a plurality of strands.

The cross section of the conductor broken by stress corrosion cracking and the conductor surface near the cross section are always covered with a black oxide film. It is considered that the breakage of the conductor due to the formation of such an oxide film is caused by the following phenomenon.

First, the surface of the conductor strand becomes dry or wet due to the influence of rainwater or the like that has entered between the insulating coating layer of the covered electric wire and the stranded conductor. An oxide film is formed on the surface of the conductor wire by the repetition of the dry and wet. When a tensile stress is applied to the conductor surface, the oxide film formed on the conductor wire surface is broken, and an oxide film is further formed on the newly appearing surface. Such a phenomenon is repeated many times, cracks develop, and finally the conductor strands are broken.

In the present invention, by limiting the impurities other than silver in the conductor as described above, the growth rate of the oxide film on the conductor surface is reduced and the oxide film is cracked in a corrosive environment such as a rain-water cycle. And improve stress corrosion cracking resistance.

The total content of impurities other than silver is 60 ppm
The reason for this is that if the content exceeds 60 ppm, the effect of improving the stress corrosion cracking resistance is reduced.
The total content of these impurities is preferably 40 ppm or less, particularly preferably 20 ppm or less.

Further, when a conductor having a limited amount of impurities as described above is subjected to a heat treatment under conditions that do not cause complete recrystallization such as maintaining the strength equivalent to that of a hard copper wire, stress corrosion cracking resistance is further improved. Performance can be improved. This is presumably because, in addition to suppressing the growth rate of the oxide film on the conductor surface and suppressing cracking of the oxide film, local corrosion such as pitting corrosion is less likely to occur. This heat treatment is preferably performed after drawing to a predetermined wire diameter. In the case where the conductor is a stranded wire, the stress corrosion cracking resistance can be further improved by performing heat treatment after twisting a plurality of strands. This is because the effect of reducing lattice defects is less likely to be lost in the process of processing the electric wire.

Further, in the above-mentioned electric wire, when the conductor is copper having a purity of 99.995% or more, the stress corrosion cracking resistance can be further improved as compared with the conventional hard copper wire.

Even when the conductor is made of copper having a total content of Ni, S and H as impurities of 5 ppm or less, the stress corrosion cracking resistance is further improved as compared with the conventional hard copper wire. Can be. This is presumably because Ni, S, and H adversely affect stress corrosion cracking resistance.

[0015]

Embodiments of the present invention will be described below. A copper wire having a wire diameter of 8 mmφ having a purity and an impurity amount shown in Table 1 was produced. This copper wire is cold drawn to a wire diameter of 2m.
mφ to obtain a conductor wire for a covered electric wire. Each of these wires is
Nine wires were assembled into a stranded wire, and a conductor for a covered electric wire was prototyped.
After stranded wire processing, sample No. 1 was sample No. 1-1 without heat treatment and sample No. 1 was subjected to heat treatment at 230 ° C. for 2 hours.
No.1-2 was prototyped. When the crystal structure of the strand of Sample No. 1-2 was observed, it was not recrystallized.

[0016]

[Table 1]

A tensile test, a conductor resistance test and a stress corrosion cracking susceptibility test were conducted on the stranded conductor for a coated wire manufactured as a trial. As shown in FIG. 1, the stress corrosion cracking susceptibility test was conducted in 1 (liter) of aqueous solution of copper acetate ammonia (40 g of copper acetate).
+ 1000 ml of pure water + ammonia water, pH = 5.5, temperature 35 ° C) and a stranded wire sample 2 immersed in a state where a bending stress (bending radius = 150 mm) is applied, and the number of test days until cracks are generated is stress corrosion. The crack life was determined. The results of the stress corrosion cracking susceptibility test were shown as a ratio when the stress corrosion cracking life of the conventional example (sample No. 6) was set to 1.0, and expressed as the degree of improvement in stress corrosion cracking resistance. Table 2 shows the test results.

[0018]

[Table 2]

In the case of a coated electric wire conductor in which 19 strands each having a wire diameter of 2.0 mmφ are twisted, it is necessary that the tensile strength is 23634 N or more and the conductor resistance is 0.313 Ω / km (20 ° C.) or less. However, as shown in Table 2, each embodiment satisfies these requirements. In addition, it can be seen that all the examples show 3.2 times or more of the excellent stress corrosion cracking resistance improvement as compared with the conventional example. In particular, the heat-treated Example 1-2 shows an extremely excellent degree of improvement in stress corrosion cracking resistance. On the other hand, in the comparative example (sample No. 5) having a large amount of impurities other than silver, the stress corrosion cracking resistance is not improved.

[0020]

As described above, the coated electric wire of the present invention can obtain high stress corrosion cracking resistance by limiting the amount of impurities other than silver in the conductor.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a stress corrosion cracking susceptibility test.

[Explanation of symbols]

 1 Ammonia copper acetate aqueous solution 2 Twisted wire sample

Claims (4)

[Claims] 1. A covered electric wire having an insulating coating on the outer periphery of a conductor, wherein the conductor is made of copper whose total amount of impurities other than silver is 60 ppm or less. 2. The coated electric wire according to claim 1, wherein the conductor is heat-treated under conditions that do not cause recrystallization of the conductor. 3. The coated electric wire according to claim 1, wherein the purity of the conductor is 99.995% or more. 4. The method according to claim 1, wherein the total content of Ni, S, and H as impurities is 5 ppm or less.
3. The coated electric wire according to any one of the above items 3.