JPH06243736A - Power cable - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to reduce the required cross-sectional area of the metal wire shielding layer. A power cable in which a metal wire shielding layer 1 is applied on a cross-linked extrusion type outer semiconductive layer 5 and a sheath 8 is applied to the outer periphery of the metal wire shielding layer 1 via a holding tape 7 is provided.
The metal wire shielding layer 1 is characterized by being filled with a semiconductive admixture 9 whose main component is a thermoplastic material having a melting point lower than that of the sheath 8. [Effect] Dissipation of heat generated by the ground-fault current is better than before.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to power cables.

[0002]

2. Description of the Related Art When a ground fault occurs in a power system in which a cable is used, the ground fault current flows through a metal shielding layer of the cable. The required cross-sectional area of this metal shielding layer is designed so that the temperature of the outer sheath does not exceed the limit value inherent to the material within the transit time of the ground fault current. JCS Standard No. 16
According to No. 8D, this limit is 140 ° C. for cross-linked polyethylene insulated polyethylene sheath (CE) cables and 150 ° C. for cross-linked polyethylene insulated vinyl sheath (CV) cables.

Therefore, as shown in FIG. 2, a metal wire shield layer 1 using a metal wire must be used as a metal shield layer of a cable used in a system having a large ground fault current. A so-called wire shield in which a copper wire is wound horizontally is generally adopted. In the figure, 2 is a conductor, 3 is an inner semiconductive layer, 4 is an insulator, 5 is an outer semiconductive layer, 6 is a void, 7 is a holding tape, and 8 is a sheath.

[0004]

In the above prior art, since the air gap exists adjacent to the metal wire shielding layer, the heat generated by the ground fault current is very poorly dissipated and the temperature of the metal wire shielding layer easily rises. . That is, there has been a problem that the thickness of the metal wire must be increased or the number of metal wires must be increased in order to secure the required cross-sectional area of the metal wire shielding layer.

In order to solve this drawback, it is conceivable that the pressing tape is simply omitted and the sheath is fully extruded to fill the voids with the sheath material. In this case, the sheath material which is an insulating material serves as the metal wire shielding layer. It flows into the space between the outer semiconductive layers during extrusion, which causes a new defect that electrical contact between the two is incomplete, and the function as the metal wire shielding layer is lost.

The present invention has been made in view of the above points, and an object of the present invention is to provide a power cable capable of reducing the required cross-sectional area of the metal wire shielding layer.

[0007]

The above object can be achieved by filling a space between metal wire shielding layers with a semiconductive mixture containing a thermoplastic material having a melting point lower than that of a sheath as a main component.

[0008]

Since the above means is provided, the heat generated by the ground fault current can be dissipated better than before.

[0009]

EXAMPLES Next, the present invention will be specifically described by way of examples.

[Embodiment 1] FIG. 1 shows an embodiment of the present invention. Since the same parts as those of the prior art are designated by the same reference numerals, the description thereof will be omitted. In this embodiment, the metal wire shielding layer 1 is filled with a semiconductive mixture 9 containing a thermoplastic material having a melting point lower than that of the sheath 8 as a main component. By doing so, the heat generated by the ground fault current is better dissipated than before, and the heat generation of the metal wire shielding layer 1 due to the ground fault current is suppressed. It is possible to obtain a power cable whose area can be reduced.

That is, the metal wire shielding layer 1 in which metal wires are wound in a horizontal direction is formed on the outer semiconductive layer 5, and then the semiconductive mixture 9 is placed in the space corresponding to the space between the metal wire shielding layers 1. Is filled, and if necessary, a holding tape 7 is applied, and the sheath 8 is pushed to complete the cable.

The admixture 9 is made semiconductive so that it does not lose its electrical contact when it enters between the outer semiconductive layer 5 and the metal wire shielding layer 1. Further, the main component of the semiconductive admixture 9 is set lower than the melting point of the sheath 8 because the temperature when the heat generation of the metal wire shielding layer 1 due to the ground fault current is consumed for melting the semiconductive admixture 9 Then, the sheath 8 is intended to be healthy.

Further, the external semiconductive layer 5 is limited to the cross-linking type because the metal wire shielding layer 1 is in direct contact with the external semiconductive layer 5, so that at the same time as the semiconductive admixture 9 is generated at the time of ground fault heat generation. This is to prevent melting.

As described above, according to this embodiment, at the time of a ground fault, since there is no air layer around the metal wire shielding layer and the semiconductive admixture is present, the heat dissipation is remarkably improved and the semiconductive admixture is further improved. Since the heat is absorbed by the melting of the object, the required cross-sectional area of the metal wire shielding layer can be made smaller than that in the conventional case.

Therefore, an inexpensive cable can be supplied, and at the same time, expensive metal resources such as copper and aluminum can be saved.

Although the effect is slightly lowered, a similar effect can be expected by using a material of the pressing tape having a lower melting point than that of the sheath without applying the semiconductive mixture. However, in this case, once the ground fault occurs and the pressing tape melts, the metal wire shielding layer and the sheath come into direct contact with each other, so that it is considered that the effect is not so great at the second and subsequent ground faults.

[0017]

As described above, according to the present invention, since the semiconductive mixture containing a thermoplastic material having a melting point lower than that of the sheath as a main component is filled between the metal wire shielding layers, the heat generated by the ground fault current can be prevented. Dissipation becomes better than in the past, heat generation of the metal wire shielding layer due to ground fault current is suppressed, and a power cable that can reduce the required cross-sectional area of the metal wire shielding layer can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view of an embodiment of a power cable of the present invention.

FIG. 2 is a vertical sectional side view of a conventional power cable.

[Explanation of symbols]

 1 Metal Wire Shielding Layer 5 External Semiconducting Layer 7 Holding Tape 8 Sheath 9 Semiconducting Admixture

Claims (3)

[Claims] 1. A power cable in which a metal wire shielding layer is provided on a cross-linked extruded outer semiconductive layer, and a sheath is provided on the outer periphery of the metal wire shielding layer via a holding tape,
A power cable characterized in that a semi-conductive mixture containing a thermoplastic material having a lower melting point as a main component is filled between the metal wire shielding layers. 2. The thermoplastic material is polyethylene, EV
The power cable according to claim 1, which is A. 3. The power cable according to claim 1, wherein the sheath is made of a vinyl admixture.