JPH0229613Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a power cable that has an insulator, a metal sheath, an anticorrosion layer, etc. provided on a conductor, and the metal sheath includes stainless steel. FIG. 1 shows a conventional example of a power cable such as an OF cable. The power cable shown in the figure is composed of a conductor 1, an insulator 2 provided on the conductor 1, a metal sheath 3a made of aluminum, lead, etc., and a corrosion protection layer 4.
ensures oil sealing and power cable protection and worker safety. In the power cable configured in this way, when the electrical resistance of the metal sheath 3a becomes low, the eddy current loss caused by the current flowing in the adjacent power cable becomes excessive, reducing the power transmission current. In order to reduce such eddy current loss, there is a proposal to use stainless steel, which has a high electrical resistivity, alone as the material for the metal sheath 3a, but although using stainless steel alone can reduce eddy current loss, stainless steel has a high electrical resistivity. Since this is large, in the event of a ground fault, the temperature of the metal sheath 3a will rise excessively, resulting in burnout of the power cable. The present invention was devised in view of the problems of the prior art described above, and its purpose is to provide a power cable having a metal sheath with low eddy current loss during power transmission and high current capacity in the event of a ground fault. . In other words, the power cable of the present invention has a metal sheath, a bare conductor layer formed by winding a large number of bare copper wires arranged in a spiral shape around the outer circumference of an insulator, and a metal sheath formed around the outer circumference of the bare conductor layer. It is characterized in that it is formed with a stainless steel sheath that is provided in contact with any of the many bare copper wires in the layer. In the process of obtaining the configuration of the present invention, it was also considered to use a conductor with an insulating coating as the shunt line. In other words, if a large number of bare copper wires are arranged side by side and placed on an insulator, the adjacent copper wires will come into electrical contact with each other, similar to when a copper tube is placed on an insulator. This is because eddy current loss appears to be significant in such copper tubes. By applying an insulating coating to each copper wire, it was attempted to electrically isolate the adjacent wires, thereby reducing eddy current loss. However, if each copper wire is coated with insulation as described above, it will be difficult to shunt the current in the event of a ground fault.
A new problem arose. In other words, if we consider a case where a ground fault occurs between a conductor and one copper wire, the one copper wire that has a ground fault and the many other copper wires adjacent to it will be electrically isolated; This is because the wire is electrically isolated from the stainless steel sheath, and as a result, the ground fault current will concentrate on that one copper wire, making it difficult to distribute it to many other copper wires. be. As mentioned above, if the ground fault current flows in a concentrated manner in one copper wire, the temperature of the metal sheath will rise significantly in the event of a ground fault, resulting in widespread damage to the power cable in the event of a ground fault. occurs. Furthermore, there is also the problem that providing an insulating coating increases manufacturing costs. As a result of intensive research by the inventors, it was found that even with the configuration of the present invention, that is, a large number of bare copper wires arranged side by side, the increase in eddy current loss is so small that it can be practically ignored. The reason for this is that when a large number of bare copper wires are lined up, there is unavoidable contact resistance between the adjacent copper wires, and this contact resistance is caused by the contact resistance between the adjacent copper wires and the outer conductor layer wrapped in metal tape. This is because the presence of contact resistance appears to suppress the flow of current between the copper wires and between the copper wires and the outer conductor layer. Since such contact resistance is sufficiently lower than that of the insulating coating material, it will not interfere with the flow of earth fault current between the copper wires under a ground fault, and none of the copper wires will be exposed to the outside. By incorporating it into the conductor layer, an equipotential state is created, which enables uniform branching of the ground fault current throughout each copper wire. Based on the above knowledge, the present invention has the above-mentioned configuration, that is, a large number of bare copper wires are wound in a spiral shape on an insulator, and a metal is placed on top of the insulator to make contact with each of the bare copper wires. A tape-wrapped outer conductor layer is provided, and a stainless steel sheath is provided on top of the outer conductor layer. In addition, it has been considered to provide such a shunting conductor outside the stainless steel sheath, but since the ground fault current from the conductor is shunted through the stainless steel sheath, which has a high electrical resistivity, the result is not necessarily satisfactory. Moreover, since the stainless steel sheath is corrugated, it becomes difficult to wind the shunt conductor thereon, making it difficult to conduct electricity within the shunt conductor itself, which is not desirable in terms of manufacturing. It didn't happen. Therefore, in the present invention, a bare conductor layer for shunting current is provided on an insulator, and it is suppressed by an outer conductor layer wrapped with metal tape, and further, the outer conductor layer is covered with a stainless steel sheath from the outside. This is to ensure reliable contact between the conductor layer and the bare conductor layer. Hereinafter, an explanation will be given based on FIG. 2 showing an embodiment of the present invention. In FIG. 2, the same parts as in FIG. 1 of the conventional example are given the same reference numerals. The metal sheath 3b, which is the key point of improvement, consists of a bare conductor layer 3c provided on the outer periphery of the insulator 2, an outer conductor layer 3d provided on the surface of this bare conductor layer 3c, and a metal sheath 3b provided on the outer periphery of this outer conductor layer 3d. It was formed with a stainless steel sheath 3e. The bare conductor layer 3c is formed by winding a large number of bare copper wires (copper wires without an insulating layer on the surface) in a spiral shape around the outer periphery of the insulator 2. Further, the outer conductor layer 3d is formed by winding a metal tape around the surface of the bare conductor layer, so that it is wrapped in a restrained winding state around each copper wire of the bare conductor layer 3c. By doing this, in the event of a ground fault, the flow is shunted to the bare conductor layer made of twisted bare copper wires close to the conductor 1 side and having good conductivity, and the bare conductor layer is constructed via the outer conductor layer. Since the current can be uniformly divided into each copper wire, a temperature rise in the metal sheath 3b at the time of a ground fault is suppressed. Eddy current loss caused by current flowing in the adjacent power cable is suppressed by the stainless steel sheath 3d having a high electrical resistivity on the corrosion protection layer 4 side, that is, on the outside. In addition, bare copper wires can be lined up and connected to each other through adjacent parts or through an outer conductor layer wrapped with metal tape, but there is unavoidable contact resistance between these wires and between the copper wire and the outer conductor layer. This suppresses eddy currents from flowing across the lines. Therefore, it is possible to simultaneously satisfy the contradictory demands of reducing the eddy current loss of the metal sheath 3b during energization and increasing the ground fault capacity of the metal sheath 3b during a ground fault. In addition, although this embodiment shows an example in which a round copper wire with a circular cross section is used as the bare copper wire, the present invention is not limited thereto, and a rectangular bare copper wire may also be used. Furthermore, it is desirable that the total cross-sectional area of the bare copper wires of the bare conductor layer 3c be set to a size such that the temperature of the bare conductor layer 3c due to ground fault current is below a permissible value. Table 1 shows the results of examining the characteristics of the above examples. This study examined the eddy current loss factor, temperature rise, and temperature rise of a conventional product that uses aluminum as the metal sheath, and the invented product that uses a stainless steel sheath, bare conductor layer (copper wire), and outer conductor layer (metal tape). was measured.

[Table] As is clear from the measurement results in the above table, the eddy current loss factor of the power cable of the present invention is approximately one order of magnitude lower than that of conventional power cables that use aluminum for the metal sheath, and The temperature rise of the metal sheath was 17°C, lower than the value for the stainless steel sheath alone. In this way, the eddy current loss factor and temperature rise of the present product were both reduced because the metal sheath was made of a stainless steel sheath, a bare conductor layer made of spirally wound numerous bare copper wires provided inside the stainless steel sheath, and a metal tape wound. This is because the ground fault current is shunted by the bare conductor layer near the conductor and the outer conductor layer, and the eddy current loss is reduced by the stainless steel sheath. As is clear from the above explanation, according to the power cable of the present invention, a metal sheath is provided by winding a large number of bare copper wires in a spiral shape on a stainless steel sheath and an insulator inside the sheath. It is made up of a bare conductor layer, and an outer conductor layer wrapped with metal tape, which is placed around the outer periphery of the layer and in contact with any of the many bare copper wires in the layer. The intended purpose of providing a power cable having a metal sheath with low eddy current losses and high current carrying capacity in the event of a ground fault is fully achieved.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional diagram of a conventional power cable.
FIG. 2 is an explanatory cross-sectional view showing one embodiment of the power cable according to the present invention. In the symbols, 1 is a conductor, 2 is an insulator, 3b is a metal sheath, 3c is a bare conductor layer, 3d is an outer conductor layer, 3e is a stainless steel sheath, and 4 is an anticorrosion layer.

Claims (1)

[Scope of utility model registration request] In a power cable having an insulator provided on a conductor, a metal sheath, and an anti-corrosion layer, the metal sheath is provided by winding a large number of bare copper wires in a spiral shape around the outer periphery of the insulator. a bare conductor layer, an outer conductor layer formed by winding a metal tape and provided on the surface of this conductor layer in contact with any of the many bare copper wires in the layer; A power cable characterized by being formed with a stainless steel sheath.