JPS6132888B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in a method for installing overhead covered electric wires, and its purpose is to prevent stress corrosion and disconnection of the overhead covered electric wires, thereby increasing their service life. Traditionally, overhead covered electric wires are made by installing a separator made of polyester or the like on a conductor made of hard copper wire or stranded wire, and covering it with a rubber or plastic insulator on the outside, or by directly covering the conductor with the above-mentioned insulator. In all of these conductors, residual stress exists during wire drawing, stranding, or drum winding. Overhead covered wires with this structure are used for outdoor high voltage,
When used in a low-voltage distribution line passageway, moisture such as rainwater travels through the wire retention section, branch section, etc., and enters the installation through the section where the covering insulation is stripped off. If moisture remains in this gap for a long time, corrosion cells such as oxygen concentration cells will be applied to the conductor with residual stress, which will cause stress corrosion cracking in the conductor.
This eventually causes the phenomenon that the conductor breaks. Although it was previously thought that stress corrosion cracking does not occur in pure metals, it has recently become clear that most of the corrosion and disconnection phenomena in insulated copper wires are due to such factors. Before overhead distribution lines are manufactured and shipped, the conductors, hard copper wire and hard copper stranded wire, go through various processes, including wire drawing, twisting, and several times of winding. After examining the tensile residual stress during the process, we found that hard copper stranded wire, which is comparable to hard copper wire, has a non-uniform residual strain of 0.20 to 0.30% in the length direction strain on the same circumference before being shipped. I made sure of that. Furthermore, these electric wires are then used as overhead wires, and the amount of strain in the length direction during overhead wires is only 0.05% or less. Therefore, the non-uniform residual strain during the manufacture of the wire and the strain during the overhead wire are superimposed on the overhead wire. In particular, we found that the nonuniform residual strain that occurs during the manufacturing of electric wires is extremely large compared to the strain that occurs during overhead wire manufacturing, and that this has an adverse effect on stress corrosion cracking. As a result of intensive research into the relationship between the non-uniform residual strain in the length direction that occurs during the manufacturing of electric wires and the life of stress corrosion cracking, the inventors of the present invention found that by reducing the uneven residual strain in the length direction of electric wires, stress corrosion cracking can occur. It was discovered that the lifespan of That is, the present invention provides a method for manufacturing an insulated wire for overhead power distribution by extruding and coating the outside of a hard copper stranded conductor with an insulator, and installing the same, in which a straightening roll or straightening machine is used at the time of manufacturing or installing the insulated wire. The method is characterized in that after the non-uniform residual strain in the longitudinal direction of the conductor or the insulated wire is reduced to 0.15% or less, the overhead wire is installed in this state. In the method of the present invention, the non-uniform residual strain in the length direction of the electric wire is caused by the fact that after the electric wire is stretched in a straight line with a constant tension (5 to 10 kg/mm ² ), when the electric wire is released, the electric wire is not directly above the electric wire. The uniform residual strain is assumed to be 0, and the state of bending with a certain degree of curvature is considered to be non-uniform residual strain, and the magnitude of the non-uniform residual strain is generally ε=r/R (ε:
amount of strain, r: radius of wire, R: radius of curvature of wire bending). Therefore, the non-uniform residual strain in the length direction of the wire is 0.15
% or less can be achieved by applying excessive tension to the wire using a straightening machine or a straightening roll when manufacturing or installing the wire. Next, the relationship between non-uniform residual strain in the length direction of a wire and stress corrosion cracking is shown in FIG. As is clear from Figure 1, there is a certain relationship between non-uniform residual strain and stress corrosion cracking life, and there is a transition point when the non-uniform residual strain is around 0.20%, and when the non-uniform residual strain is reduced to 0.15% or less. It can be seen that by doing so, the lifespan against stress corrosion cracking is significantly improved. Next, examples of the present invention will be described. On the outside of a hard copper stranded conductor with a wire diameter of 2 mm and 19 strands.
When manufacturing and installing a 60 mm ² OE wire (19/2.0) (outdoor polyethylene electric wire) using extrusion coating of 2.5 mm thick polyethylene, the wire was installed with non-uniform residual strain in the longitudinal direction of the conductor as shown below. Example (1) After the conductors were twisted, the conductors were passed through a straightening machine to give a non-uniform residual strain of 0.02% in the longitudinal direction of the conductors, and then an insulated wire coated with polyethylene on the outside was wired. Example (2) After twisting the conductors, the conductors were passed through straightening rolls (5 rolls of 50 mm diameter arranged on the top, bottom, left and right) to make the non-uniform residual strain in the longitudinal direction of the conductors 0.01%, and then the outside of the conductors was An insulated wire coated with polyethylene was used as an overhead wire. Example (3) After twisting the conductors, a tension of 40 kg/mm ² was applied to the conductors to make the non-uniform residual strain in the longitudinal direction of the conductors 0.02%, and then an insulated wire coated with polyethylene on the outside was attached to the overhead line. did. Example (4) After the conductors are twisted, the outside is coated with polyethylene to produce an overhead insulated wire, and then passed through a straightening machine.
An electric wire with a non-uniform residual strain of 0.05% in the longitudinal direction of the electric wire was wired. Example (5) A straightening roll was used instead of immediately after straightening in Example (4), and an electric wire with a nonuniform residual strain of 0.03% was wired. Example (6) When installing electric wires, the electric wires pulled out from the drum were passed through a straightening machine, and the electric wires were installed with a non-uniform residual strain of 0.06% in the longitudinal direction of the electric wires. Example (7) When installing electric wires, the electric wires pulled out from the drum are passed through a straightening roll to reduce the uneven residual strain in the longitudinal direction of the electric wires to 0.1%.
The electric wires were installed overhead. Example (8) When installing electric wires, the electric wires pulled out from the drum were loaded with 40 kg/
A tension of mm ² is applied to create a non-uniform residual strain in the longitudinal direction of the wire.
An electric wire with a concentration of 0.12% was installed. Comparative Example (1) When installing an electric wire, the electric wire pulled out from the drum was passed through a straightening machine to create an electric wire with a non-uniform residual strain of 0.2% in the longitudinal direction of the electric wire. Comparative Example (2) After the conductors were twisted, they were passed through straightening rolls to give a non-uniform residual strain of 0.25% in the longitudinal direction of the conductors, and an insulated wire covered with polyethylene on the outside was wired. Comparative Example (3) After the conductors were twisted, the outside of the conductors was coated with polyethylene by a conventional method, and an insulated wire with a non-uniform residual strain of 0.3% in the longitudinal direction of the conductors was wired. The above-mentioned erection method requires an erection tension of 10 kg/
An overhead line was installed between utility poles with a span length of 30 m at ^mm2 . In addition, in order to measure the stress corrosion cracking of each of these insulated wires, we stripped off the insulation over a 100 cm central portion of the wires (30 m long), exposed the conductors, and placed them in a hard vinyl chloride airtight container in advance.
The above conductor was immersed in a solution containing 1N, NH ₄ OH + 2N, H ₂ SO ₄ and heat cycled at 80°C and 20°C, and the experiment was continued until stress corrosion broke. The results are shown in Table 1.

【table】

[Table] As detailed above, the method of the present invention has remarkable effects such as significantly increasing the life span of overhead power distribution lines against stress corrosion cracking.

[Brief explanation of the drawing]

The figure is a relationship curve diagram between non-uniform residual strain in the longitudinal direction of a conductor and the period until stress corrosion cracking occurs.

Claims (1)

[Claims] 1. In a method of manufacturing an insulated wire for overhead power distribution by extruding and coating the outside of a hard copper stranded conductor with an insulator, and installing the same, the conductor is Or, a method for installing an overhead distribution line, which comprises reducing the non-uniform residual strain in the longitudinal direction of the insulated wire to 0.15% or less and then installing the line in this state.