JPS6219031B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for connecting a power cable in which a copper oxide film is formed on the surface of copper wires to insulate the wires from each other. Power cables, especially high power AC cables,
A conductor is formed by twisting a large number of copper wires together, and an insulating outer layer is provided on this.Some conductors are compression-molded into a fan-shaped cross section, and several pieces of this are twisted together. ing. Also, some of these power cables are provided with a cooling insulating oil flow path in the center. In power cables having such a structure, power loss occurs due to the skin effect where current concentrates on the outer layer of the conductor, and power loss is particularly noticeable in high-power AC cables. To prevent this, the concentration of current on the skin is suppressed by insulating the wires from each other. Various methods are known for insulating wires from each other, but the most effective method in terms of performance and productivity is coating the wire surface with copper oxide with a thickness of 0.1 to 3 μm. The method of forming a film is disadvantageous in terms of cost. From this point of view, power cables coated with copper oxide to insulate the strands from each other have recently been used, but these cables have discrete points in their connection method. For example, in a compression connection using a connector, even if some of the strands (the outermost layer of strands) come into electrical contact with the connector, all the strands are electrically connected because the strands are insulated from each other. Not yet. The same thing happens with other connection methods, such as welding and brazing. Therefore, in order to achieve a highly reliable cable connection, when connecting the cable,
It is required to remove the insulation coating (copper oxide) from the wire. A known method for removing copper oxide coatings is pickling with a mineral acid solution such as sulfuric acid, but since it uses a corrosive substance, treatment work must be carried out to avoid it remaining inside the cable. Cleaning operations must be abolished, and since acidic and toxic liquid containing copper is discharged, sufficient attention must be paid to environmental pollution. For this reason, attempts have been made to reduce copper oxide using a reducing solution, but this method has the drawback of using a toxic solution. In view of this, as a result of various studies, the present invention has succeeded in efficiently and effectively removing the copper oxide coating on bare wires without using toxic liquids, and has developed a highly reliable power cable connection method. In the connection of power cables in which a copper oxide film is formed on the surface of copper wires to insulate the wires from each other, the outer insulation layer is removed from the terminals of the cables to be connected to make the wires protrude. The cable is connected after the copper oxide on the surface of the wire is chemically reduced by bringing the wire into contact with a hydrazine solution. That is, in the present invention, in order to connect a power cable in which a copper oxide film is formed on the surface of a copper wire to insulate the wires from each other, the outer insulating layer is first removed from the terminal end of the cable to be connected by stripping or the like. A group of wires is made to protrude, and then a hydrazine solution is brought into contact with the protruding group of wires to chemically reduce the copper oxide on the surface of the wires. Hydrazine solutions are aqueous or organic solutions containing hydrazine, hydrazine hydrade (NH ₂ NH ₂・H ₂ O), etc. Hydrazine and hydrazine hydrade are usually commercially available as concentrated aqueous solutions, which can be mixed with water. Dilute or dilute with polar organic solvents. Examples of polar organic solvents include alcohols such as methanol, ethanol, and propanol, acetone,
Ketones such as methyl ethyl ketone and aldehydes such as formaldehyde and acetaldehyde are used. The concentration of hydrazine, hydrazine hydrade, etc. is the main factor of reducing power and reduction rate.
% or more is desirable. In addition, the liquid temperature is an important acceleration factor, and it is industrially advantageous to use the liquid at a temperature of 30°C or higher. Hydrazine has reactions that produce ammonia and hydrated amide as by-products, and although it is not simple, copper oxide is reduced by the following formula. 2CuO＋NH ₂・NH ₂ →2Cu＋N ₂ +2H ₂ O Excess hydrazine reacts with oxygen in the atmosphere or decomposes catalytically, producing nitrogen,
Hydrogen changes to ammonia. 2NH ₂・NH ₂ →N ₂ +2H ₂ 3NH ₂・NH ₂ →H ₂ +4NH ₃ 2NH ₂・NH ₂ →N ₂ +H ₂ +2NH _3In this way, hydrazine has a slight tendency to corrode copper, but after the reaction it corrodes to a large extent. Since the parts are gasified, there is no need for rigorous cleaning, and the residue does not deteriorate the cable or insulating oil. These characteristics are not available with other reducing agents, such as metal hydrides such as sodium borohydride (NaBH ₃ ), formic acid (HCOOH), and the like. That is, metal hydrides are strong reducing agents, but they produce ionic reduction products such as sodium and boric acid,
Furthermore, since formic acid is an acid, it causes disadvantages such as producing copper formate. In the present invention, it is more advantageous to use a polar organic solution as the hydrazine solution than an aqueous solution. For example, if an alcohol solution is used, the reduction rate will be more than twice as high at the same temperature, speeding up the work. Also, since the surface tension of the liquid is low, it quickly penetrates between the strands of wire, making the work even faster. Furthermore, the copper oxide on the surface of the strands is reduced and then dried before connection, and drying is easy. These features work effectively for cable connection work. In order to reduce the copper oxide on the surface of the wire according to the present invention, the outer insulating layer is peeled off to make the wire group at the end of the cable protrude, and this is immersed in a hydrazine solution to reduce the copper surface. I pulled it up at a place,
It is common to dry with hot air. In addition, if the group of wires protruding from the cable end is heated to 70-80℃, rapid processing can be performed at a temperature of 40-50℃ without heating the solution, and reduction and drying can be done within 5 minutes. You will also be able to complete it. The solution penetrates between the strands due to capillary force and spreads beyond the connection part, but to prevent this, a penetration length can be set and further spread can be prevented by an appropriate method. In particular, when penetration must be avoided, a circular body with an air supply port or exhaust port on the inside is attached tightly to the outer peripheral surface of the wire group away from the immersed part, and compressed air is supplied from the air supply port. Pressure feed to form an air curtain, or
Alternatively, the permeate can be shut off by suctioning from the exhaust port with a vacuum pump or the like. It is more effective to attach the annular body tightly around the wire group to completely isolate it from the outside air. It will be even more effective if you try to make it work. When connecting power cables, there are many cases in which the cables are jointed from below, such as underground, to the power receiving section above. In such cases, a method is adopted in which the protruding strands are surrounded by a tank and the hydrazine solution is injected into the tank, but in order to prevent liquid leakage and penetration, it is necessary to devise measures such as attaching the annular body. It is. Furthermore, as a simple method, it is effective to drop a hydrazine solution onto the group of wires to be reduced or to apply it using a brush. The strands of wire that have been reduced in this way can be cleaned with water or a solvent, or without cleaning.
After drying, normal connection work can be performed. Next, examples of the present invention will be described. Example 1 88 copper wires with a diameter of 2.3 mm coated with copper oxide with a thickness of about 1.5 μ were twisted together and then compression-molded into 6 segments (cross section 2000 mm ² ), which were then combined with an insulating outer layer. Connected the power cable. First, about 50 cm of the outer insulating layer at the end of the cable was peeled off to expose the wires. Next, from the tip of the wire group
A 10cm long rubber cylinder is placed over the 15cm position, both ends of which are sealed with tape, and air is injected using a compressor through the hole provided on the side of the cylinder, extending up to 10cm from the tip of the wire group. It was immersed in a 15% ethanol solution of hydrazine hydrade at 30°C, pulled out after 2 minutes, then immersed in ethanol to a depth of 15 cm for 30 seconds, and then dried with a dryer for 3 minutes. When this table was dismantled and the inside of the reduced wire group was examined, the black color of copper oxide was not visible at all. Further, the two cables treated above were compressed and connected using a copper sleeve. When the electrical resistance of this connection was measured, it was 8.5 μΩ. For comparison, a wire connected in the same manner without removing the copper oxide on the surface of the wire had a resistance of 100 μΩ or more. Furthermore, the electrical resistance of the connection part of a similar cable twisted without coating the surface of the wires with copper oxide was 7.8 μΩ. Example 2 Hydrazine hydrade at 30°C in Example 1
The hydrazine hydrade solution shown in Table 1 was used in place of the 15% ethanol solution, and the treated interior was examined and the electrical resistance of the connected joints was measured in the same manner. The results are also listed in Table 1.

[Table] Example 3 Eighteen copper wires each having a diameter of 2.3 mm and coated with copper oxide having a thickness of 0.3 μm were twisted together, and a power cable having a polyethylene insulating layer provided thereon was connected. First, 15 cm of the insulation layer at the end of the cable was peeled off to expose the strands of wire, and a 50% methanol solution of hydrazine hydride was applied with a brush to a 10 cm area from the tip while blowing hot air. It was applied once every 2.5 minutes and treated for 5 minutes. Subsequently, it was dried for 5 minutes. This was compressed and connected using a copper sleeve, and the electrical resistance of the connection was measured and found to be 5.9 μΩ. The electrical resistance of the untreated connection was 100 μΩ or more, and the electrical resistance of the same type of cable without copper oxide coating was 5.5 μΩ. As described above, according to the present invention, it is possible to quickly and effectively remove copper oxides from the surface of copper wire without producing harmful side effects or waste products, and it is possible to remove copper oxides from the surface of copper wires even in minute gaps compared to conventional methods. Not only can the removal process be done in a short time, but copper oxide can also be completely removed from twisted strands, which is a remarkable effect in solving the connection problems of stranded insulated cables. It is something that plays.

Claims (1)

[Claims] 1. In the connection of a power cable in which a copper oxide composite film is formed on the surface of copper wires to insulate the wires from each other,
The cable is connected after removing the insulating outer layer from the end of the cable to be connected to make the strands protrude and contacting them with a hydrazine solution to chemically reduce the copper oxide on the surface of the strands. How to connect the power cable. 2. The method for connecting power cables according to claim 1, which uses a hydrazine solution in which hydrazine is dissolved in a polar organic solvent capable of dissolving hydrazine.