JPH0229614Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a power cable that has an insulator, a metal sheath, an anti-corrosion 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., a corrosion protection layer 4, and the like. 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 the eddy current loss can be reduced if stainless steel is used alone, 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 with a metal sheath that has low eddy current loss during power transmission and high current capacity in the event of a ground fault. . That is, the power cable of the present invention includes a metal sheath, a diversion bare conductor layer provided by winding a large number of bare copper wires arranged in a spiral around the outer periphery of an insulator, and this diversion bare conductor layer. It is characterized by being formed with a stainless steel sheath provided around the outer periphery of the layer and 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 providing an insulating coating to each copper wire, the adjacent wires are electrically isolated, thereby reducing eddy current loss. However, if each copper wire is coated with insulation as described above, it becomes 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 with the 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 also occurs between the stainless steel sheath that contacts them. This is because the presence of contact resistance seems to suppress the flow of current between the copper wires and between the copper wire and the stainless steel sheath. Since this contact resistance is sufficiently lower than that of the insulating coating material, it does not interfere with the flow of ground fault current between the copper wires under a ground fault, and all of the copper wires are made of stainless steel. By incorporating it into the sheath, an equipotential state is created, which enables ground fault current to be shunted throughout each copper wire. Based on the above findings, the present invention has the above-mentioned configuration, in which a large number of bare copper wires are arranged in a spiral manner and wound around an insulator, and a stainless steel sheath is placed on top of the wires so that each copper wire is in contact with the other wires. It was established. In addition, it has been considered to provide such a shunting conductor outside the stainless steel sheath, but since the ground fault current is shunted through the stainless steel sheath, which has a high electrical resistivity, satisfactory results cannot necessarily be obtained. In addition, the corrugation of the stainless steel sheath makes it difficult to wind the shunt conductor thereon, making it undesirable in terms of manufacturing. Therefore, in the present invention, a diversion bare conductor layer is provided inside the stainless steel sheath. 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 the improvement, is formed by a diversion bare conductor layer 3c provided on the outer periphery of the insulator 2, and a stainless steel sheath 3d provided on the outer periphery of this diversion bare conductor layer 3c. The diversion 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. Each bare copper wire is inscribed in a stainless steel sheath 3d provided on the outside thereof. By doing this, in the event of a ground fault, the current is shunted to the shunt bare conductor layer formed by twisting bare copper wires close to the conductor 1 and having good conductivity, thereby suppressing the temperature rise in the metal sheath 3b at the time of a ground fault. be done. Eddy current loss caused by the 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 in contact with each other through adjacent parts or through a stainless steel sheath, but due to the unavoidable contact resistance between these wires and between the copper wire and the stainless steel sheath, This suppresses the flow of eddy current across the 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. 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 for diversion be set to a size such that the temperature of the bare conductor layer 3c for diversion due to ground fault current is below a permissible value. The results of examining the characteristics of the above examples are shown in the table below. In this study, we measured the eddy current loss factor and temperature rise of a conventional product that uses aluminum as the metal sheath, and the invented product that uses a stainless steel sheath and a bare conductor layer for diversion (multiple copper wires). It is something.

[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 reason why both the eddy current loss factor and the temperature rise of the invented product are reduced is that the metal sheath is formed by a stainless steel sheath and a diversion bare conductor layer made of a large number of spirally wound bare copper wires that are in contact with the inside of the stainless steel sheath. This is because the ground fault current was shunted by the diversion bare conductor layer close to the conductor, and the eddy current loss was reduced by the stainless steel sheath. As is clear from the above description, according to the power cable of the present invention, the metal sheath is a shunt bare conductor provided by winding a large number of bare copper wires arranged in a spiral shape on an insulator. Since it is formed of a layer and a stainless steel sheath provided on the outer periphery of the layer in contact with any of the many bare copper wires in the layer, eddy current loss during power transmission is small. The intended objective of providing a power cable with a metal sheath having a high current carrying capacity during 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 diversion bare conductor layer, 3d is a stainless steel sheath, and 4 is an anticorrosive 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. and a stainless steel sheath provided around the outer periphery of the diversion bare conductor layer and in contact with any of the many bare copper wires in the layer. power cable.