JPH0377603B2 - - Google Patents

Description

[Detailed description of the invention]

<Technical Field of the Invention> The present invention relates to a power cable capable of eliminating ground faults and preventing the spread of fire. <Background art of the invention and its problems> In the case of a power cable, for example, a cross-linked polyethylene insulated power cable (hereinafter referred to as CV cable),
When a ground fault occurs, the coating layer is scattered on the conductor at the ground fault. In this case, if the insulation layer is flammable such as cross-linked polyethylene (XLPE), the heat generated during the ground fault will ignite and spread the fire to nearby flammable objects such as other power cables. There is a risk of a serious fire accident. In the case of conventional CV cables, the polyvinyl chloride (PVC) sheath is generally hardened to increase mechanical strength, so in the event of a ground fault, it will be scattered over a considerable area along with the insulation layer, and the remaining cross-linked polyethylene When it ignites and burns, there is nothing to cover this part, so the combustion progresses, leading to a serious fire accident. <Object of the Invention> The present invention has been made in view of the above-mentioned current situation, and its purpose is to provide a sheath with a certain degree of flexibility to the polyvinyl chloride composition as a power cable for ground fault countermeasures. It has flame retardant properties, so that when the insulating layer is scattered during a ground fault, the tearing is small, and it is then restored to cover the ground fault area. Even if the insulating layer ignites, it will be temporarily stopped and the fire will be extinguished naturally. The point is to get the cable you want. <Structure of the Invention> In order to achieve the above object, the present invention provides a sheath with a shore D hardness of 25 to 55 and an elongation rate of 300 to 500.
%, has physical properties with an oxygen index (OI) of 30 or more
It uses a PVC-based composition. A composition with such physical properties is, for example, a mixture of 100 parts by weight of polyvinyl chloride (PVC) and 5 to 50 parts by weight of NBR, and 100 parts by weight of a base resin, and 20 to 70 parts by weight of a plasticizer. Part by weight, nonflammable inorganic substance 20~
A composition containing 70 parts by weight can be mentioned. The power cable according to the present invention uses, as a sheath material, a PVC composition that has appropriate flexibility as evidenced by the Shore D hardness mentioned above, and has appropriate elasticity from its elongation rate. When the internal insulating layer is scattered due to the impact of a ground fault, only the scattering holes in the insulating layer are scattered, and then it returns to its original state to some extent due to its elasticity. ) is eventually covered by the sheath. Therefore, the insulating layer becomes difficult to burn, and the fire tends to self-extinguish. In the present invention, if the shore D hardness of the sheath exceeds 55 and the elongation rate is less than 300%, it will be too hard and have poor recovery properties, making it inconvenient for use as a sheath for this type of flameproof cable. If it is less than 25 and the growth rate exceeds 500%, then on the contrary,
It is undesirable because it is too soft and causes severe trauma during wire extension. In the PVC-based composition of the present invention, any PVC can be used as long as it is commonly available in the general market, and is not particularly limited. Examples include Vinicron 3000H (manufactured by Mitsui Toatsu) and Vinicron 4000M (manufactured by Mitsui Toatsu). In addition, NBR mixed into PVC is a copolymer of acrylonitrile 20~40 and butadiene 80~60, which gives heat resistance and strong elasticity to the PVC composition of the present invention, and prevents ground faults from occurring. Also, to prevent the sheath from being damaged and flying off. These general commercial products include Chemi Gum P-8B-1A2,
Chemi Gum P-83 (manufactured by Gutdeyer), Nitzpol
1203J (manufactured by Nippon Zeon), etc. Plasticizers used in the compositions of the invention are typically
Any plasticizer used as a plasticizer for PVC, such as phthalate ester, phosphate ester, trimellitic acid, etc., may be used, but trimellitic acid is preferred from the viewpoint of flame retardancy. The nonflammable inorganic substance used in the present invention is selected from, for example, antimony trioxide, hydrated alumina, hydrated magnesium, clay, talcum zinc compound, borate, etc., or a combination of two or more of these. Examples include things. In particular, antimony trioxide is essential for imparting flameproofing and flame retardant properties, and hydrated alumina, zinc borate, and the like are preferred. In addition, when NBR is less than 5 parts by weight in the base resin of the composition of the present invention, Shore D
When the hardness exceeds 55 and the elongation rate is about 300%,
Unable to obtain the specified physical properties, or
If NBR exceeds 50 parts by weight, the shore D hardness will be less than 25 and the elongation will be more than 500%.
In this case as well, it is not possible to obtain physical properties within a predetermined range, which is not preferable. Moreover, if the plasticizer is less than 20 parts by weight, the elongation rate will be about 250% and the shore D hardness will be about 60, which is not preferable. On the other hand, plasticizer
If it exceeds 70 parts by weight, bleeding may occur from the surface of the sheath, the oxygen index may be less than 30, and the hardness may deteriorate.
20.Strength decreases when elongation reaches 600%. Furthermore,
If the nonflammable inorganic substance is less than 20 parts by weight, the oxygen index cannot reach 30, and the nonflammability is insufficient.
If the amount exceeds 70 parts by weight, the elongation rate will be 200%,
Not only does oil resistance (70°C x 4 hours) deteriorate, but also the tensile strength and flex cracking resistance become poor, which is undesirable. Next, an example of the power cable of the present invention is shown in FIG. 1. In the figure, 1 is a conductor, which is usually made of twisted wires made of copper, aluminum, or an alloy mainly composed of these materials. On the outside of this conductor 1, an inner semiconducting layer 2, a crosslinked polyethylene insulating layer 3 and an outer semiconducting layer 4 are successively provided. Note that the inner semiconducting layer 2 and the outer semiconducting layer 4 may be omitted in the case of a power cable for low voltage (for example, 600 V or less). A shielding layer 5 is provided outside the external semiconducting layer 4 . This shielding layer 5 is formed by winding a metal tape or a filament on the outer semiconducting layer 4 . Note that this shielding layer 5 may be omitted similarly when the external semiconducting layer 4 is not provided. A sheath 6, which is a feature of the present invention, is provided on the shielding layer 5. As described above, this sheath 6 has a shore D hardness of 25 to 55, an elongation rate of 300 to 500%, and an oxygen index of 30 or more. The method for manufacturing the power cable of the present invention thus constructed may be any known method. For example, an inner semiconducting layer 2, an insulating layer 3, and an outer semiconducting layer 4 are coated on the outside of the conductor 1 by extrusion sequentially or two or more of these layers are coated on the outside of the conductor 1, and then the sheath 6 is coated thereon by a normal extrusion method. Extrusion molding may be carried out using the following method. <Example> A sheath according to the formulation shown in Table 1 was applied on a 154KV, 1×2000mm ² CV cable core. This example 1~
2 has Shore D hardness of 30-55 and elongation rate of 350-
500% and its thickness is approximately 5 mm. In addition, in the case of Comparative Example 1, the Shore D hardness and elongation rate do not satisfy the conditions of the present invention. Regarding the prototype cable with the above sheath, approx.
A 2.5m sample was taken, a nail was driven into it, and a voltage of 14.6KV x 5KA was applied for 2 seconds between the conductor and the shielding layer to create a ground fault. The results were as shown in the ground fault experiment column of Table 1.

[Table] <Effects of the Invention> According to the power cable of the present invention, as described above, a polyvinyl chloride composition with a novel formulation is used as the sheath material, and its shore D hardness is 25 to 25.
55. Since the elongation rate is 300 to 500% and the oxygen index (OI) is 30 or more, it is suitable for use as a ground fault prevention cable. Even if it burns, its physical properties close the cracks in the sheath, making it possible to obtain an excellent cable that naturally extinguishes the fire.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the power cable of the present invention. DESCRIPTION OF SYMBOLS 1...Conductor, 2...Inner semiconducting layer, 3...Insulating layer, 4...Outer semiconducting layer, 6...Sheath.

Claims (1)

[Claims] 1. In a power cable having a sheath made of a polyvinyl chloride composition as the outer layer of the insulating layer, the sheath material is a base resin 100 in which 100 parts by weight of polyvinyl chloride is mixed with 5 to 50 parts by weight of nitrile butadiene rubber (NBR). Plasticizer 20 parts by weight
Using a polyvinyl chloride composition containing ~70 parts by weight and 20 to 70 parts by weight of a nonflammable inorganic material, the sheath has a shore D hardness of 25 to 55, an elongation rate of 300 to 500%,
Power cable with an oxygen index of 30 or higher.