JPH0258724B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] This invention relates to improvements in large-sized conductors used in power cables, and in particular to improvements in divided conductors. [Prior art] [Problem to be solved by the invention] In recent years, due to the rise in energy costs associated with petrochemical production and the difficulty in acquiring land, high voltage has been developed as a means of reducing loss and increasing capacity of underground power transmission lines. , increasing the size of the conductor and cooling the cable have been adopted,
Since the loss generated in cables increases as the capacity increases, there is an urgent need to develop technology to reduce loss from the perspective of reducing the cooling burden and saving energy. Regarding conductors, they are becoming larger and larger, and it is now common to use large cables with a conductor cross-sectional area of 2000 ^mm2 . In addition, 2500mm ² cables have already been used in some areas, and large-sized cables of 3000mm ² or larger are expected to be put into practical use in the next few years. With this trend toward larger conductor sizes, the degree of increase in conductor AC effective resistance relative to DC resistance is becoming larger and larger. + proximity effect coefficient) has been strongly demanded. As a countermeasure to this problem, multi-segmented conductors, wire insulation, etc. have been considered. The relationship between the conductor size and the skin effect coefficient is shown in Figure 1. As the size increases, the skin effect coefficient, which is a factor in increasing the AC effective resistance, increases. efforts have been made to reduce the
When the conductor size is 2000 mm ² or more, the skin effect coefficient exceeds 10% and cannot be ignored even if the conductor is divided. Therefore, it has been found that application of wire insulation etc. is highly effective in reducing the effective AC resistance for areas over 2500 mm ² to 3000 ^{mm 2} . To explain strand insulation here, contact resistance between bare copper strands alone is not sufficient to reduce the skin effect, so this is a method that attempts to forcibly insulate between strands. When applied to a segmented conductor, the current moving in the semi-mechanical direction is suppressed, and the strands in the segment are twisted and transferred between the center and outer parts of the segmented conductor. Since the portion becomes the outer portion, and conversely, the outer portion moves to the center portion, the inductance of each strand becomes substantially uniform, and at the same time, the current distribution within the segment is made uniform, and the skin effect is reduced. Conventionally, enamel coating has been considered as a method of insulating wires, and it has been recognized that it is somewhat effective against the proximity effect and skin effect, but it is difficult to insulate wires with enamel coating in order to obtain the specified characteristics. In addition to selecting the coating material, it is necessary to apply a relatively thick film of 34 to 64 μm, which results in a large finished outer diameter of the strands, which in turn increases the outer diameter of the conductor that is twisted together.For example, 2500 mm. In the case of cable conductor ² , the outer diameter is approximately 3 mm due to the use of enamel.
(equivalent to 300 mm ² ), and the process of enamel coating each strand is time-consuming and expensive. In addition, when connecting cable conductors, it is necessary to completely remove the enamel film when connecting by crimping the sleeve, and this removal process requires chemicals, which is very time-consuming. When making connections, a large amount of harmful gas is generated due to the thermal decomposition of the enamel.
There are drawbacks such as the need for a large-scale exhaust gas system. Furthermore, with wire insulation using enamel coating, since the stainless steel tape wrapping and internal shielding layer are insulated from the internal conductor, abnormal voltage that does not occur with normal cables can cause electrical discharge, which may cause thermal decomposition deterioration of the enamel coating. There is. For these reasons, enamelling of wire insulation has not been put to practical use. [Means for Solving the Problems] The present invention was developed as a result of intensive studies in view of the above-mentioned circumstances, and the present invention has been made as a result of intensive studies in view of the above-mentioned circumstances. As a result of repeated research, we discovered that forming this on the surface of a copper wire provides excellent wire insulation performance. By applying this to the special structure of split, compressed, and stranded cables, we have succeeded in solving the problems of conventional technology and providing a cable conductor that is effective against the skin effect and proximity effect. . Here, the volume resistivity of the cupric oxide (CuO) film is ρ = 10 ⁴ to 10 ⁶ Ω·cm (specific value), and the thickness of the CuO film is 0.3 to 3.0 μm, preferably 0.5 to 3.0 μm. It is 1.0 μm. In other words, each of the sector-shaped parts constituting the divided conductor, whose size gradually decreases, is insulated from each other by cupric oxide, and is arranged at a pitch of a certain length (usually 20 to 30 cm). It is twisted together. Since this fan-shaped part is coated with a film of cupric oxide that has semiconducting resistance, the contact resistance between the copper wires is sufficiently large compared to the contact between copper wires, so that The directional resistance is electrically independent, and the wires have a twisted wire structure. Therefore, each of the sector-shaped parts described above can equivalently have a substantially uniform inductance, and since the center part and the outer part of the divided conductor are transferred while being twisted, the inductance of the divided conductor is uniform in each sector-shaped part. Since the current flows, the skin effect can be effectively reduced. As shown in FIG. 2, the strand insulation used in the present invention comprises a strand 10 which is insulated by providing a cupric oxide film 14 on the surface of each copper wire 12, for example, a copper strand. 12 can be heated to over 300°C to form a film 14 of cupric oxide on its surface, or by various chemical methods, such as heating copper oxide in an oxidizing agent mixture of sodium chlorite and caustic soda. Surface oxidation is performed by immersing the wire to form a cupric oxide film 1.
4 can be obtained, that is, a wire insulator. Since the wire insulation in the present invention is the inherent resistance value of the cupric oxide film, in the above-mentioned structure that is the subject of the present invention, in other words, since it is 10 ⁴ to 10 ⁶ Ω-cm, each copper constituting the conductor The potential difference between the wires is
It has a low resistance of about 1 mV, which is sufficient to insulate against this voltage. Even if a high voltage is applied to the conductor, the potential sharing is small, so it is possible to prevent the occurrence of discharge due to abnormal voltage or charging current. Furthermore, as mentioned above, in the present invention, since the present invention has a cupric oxide film, no discharge occurs, but the insulation by the conventional enamel film, that is, the volume resistivity of the enamel film is ρ'=10 ¹³ to 10 ¹⁵ Ω・cm high,
Since the coating thickness is thick and the capacitance is distributed, and the voltage sharing becomes high, discharge occurs between the wires that make up the conductor, and as a result, the contact resistance of the conductor becomes zero, and the provision of the coating becomes meaningless. This results in degraded gas (e.g. OF
In the case of cables, C ₂ H _2, etc.) occur, which deteriorates the insulating oil and the insulator, but the cupric oxide film of the present invention, which has a resistivity in the semiconducting range, does not nothing happens. In the present invention, the thickness is preferably about 0.3 μm to 3.0 μm, regardless of the method of forming the copper oxide film.
A film with a thickness of about 0.5 to 1.0 μm was formed, and a film with a volume resistivity ρ of 10 ⁴ to ^{10 6} Ω·cm was obtained. [Example] In the present invention, a copper wire provided with such a cupric oxide film is used, for example, as shown in FIG.
It constitutes the cable conductor, and a cupric oxide film is formed on the entire surface of the copper wire. That is, the segment 20 is constructed by twisting and compressing a plurality of copper wires, and each copper wire of the segment 20 is made of a copper wire 10 having a cupric oxide film. Note that although the figure shows a case where the number of segments is six, it is not limited to this. In the cable conductor having a cupric oxide film according to the present invention, since cupric oxide has excellent heat resistance, it is possible to connect conductors with the same diameter at a flexible joint, which is indispensable for submarine cables. A strand with a cupric oxide coating and an enamel-coated strand used in the present invention were prepared, and their properties were compared and tested as shown in the table below.

[Table] Therefore, it is much thinner than enamel coating, and the outer diameter of the conductor does not increase. Unlike enamel coating, special coating and baking equipment is not required, and the film forming method is simple, resulting in low cost. Also, since the resistivity is as mentioned above,
A conventional conductor shielding structure can be used. Next, we prototyped a strand insulated conductor with a cupric oxide film and measured its effective AC resistance. The measurement method was to apply a predetermined current to the conductor, and use an AC potentiometer to measure the current, potential drop, and phase of voltage and current, and calculate the AC effective resistance. The cable length was 7 to 8 m, and the effective measurement length was approximately 5 m. After removing the cupric oxide film from both ends of the cable, the rods were compressed and attached to current-carrying terminals. The test conductors are shown in the table below.

[Table] The results of measuring the skin effect coefficient are shown below, and it can be seen that the present invention is superior. Here, the skin effect coefficient λ is the AC effective resistance r _ac , r _ac
If the DC resistance at the measured temperature is r _dc , it is calculated from λ=r _ac −r _dc /r _dc . Skin effect coefficient measurement results

【table】

〔Effect of the invention〕

In the present invention, by forming a cupric oxide film on all the wires, the skin effect proximity effect is reduced and the various effects described above are achieved, compared to the case where this wire is partially used. In particular, it is easy to manufacture by forming a stranded wire structure and then oxidizing it, which is also advantageous in terms of manufacturing cost.Also, when removing the oxide film when connecting conductors, it can be done without sorting the wires. Therefore, from this point of view as well, it can be said that the structure is highly workable. In addition, the present invention uses a copper wire with a volume resistivity ρ=10 ⁴ ~
Since a CuO film with a resistance of 10 ⁶ Ω・cm and a film thickness of approximately 0.5 to 1.0 μm is used, the proximity effect and skin effect in the wire conductor can be kept to a minimum compared to split compression shaping, and the film is It is thin, has stable characteristics, and is easy to manufacture. Proximity effects and skin effects in wire conductor cables can be kept to a minimum compared to split compression shaping, and the outer diameter and weight do not increase. In addition, it is stable against insulating oil, and the film can be easily removed by mechanical means such as sandblasting and honing during connection, resulting in various effects such as easy welding connection.

[Brief explanation of drawings]

Figure 1 is a diagram of the relationship between skin effect coefficient and conductor cross-sectional area.
FIG. 2 is a cross-sectional view of the insulated wire used in the present invention,
FIG. 3 is a sectional view showing an embodiment of the cable conductor according to the present invention. DESCRIPTION OF SYMBOLS 10... Insulated strand, 12... Copper strand, 14... Cupric oxide film, 20... Segment.

Claims (1)

[Claims] 1. A split compression-shaped stranded wire conductor made by twisting and compressing copper strands, characterized in that a CuO film is formed on the entire surface of the copper strands. 2. In a cable in which a CuO film is formed on the entire surface of the copper wire of a divided compression-formed stranded wire conductor made by twisting and compressing copper wires,
The cable conductor according to claim 1, wherein the CuO film has a volume resistivity ρ of 10 ⁴ to ^{10 6} Ω·cm.