JPH0132731B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention particularly relates to an insulated connection for a rubber or plastic insulated cable with a novel edge cut structure. In a long single-core cable, a potential is induced in the sheath by electromagnetic induction of conductor current, but this potential can be reduced by using the so-called cross-bond method. In such a cross-bond system, an insulated connection part is used as a cable intermediate connection part. The insulating connection portion is formed by electrically insulating the insulating shielding layer using some means. Conventionally, the edge cutting structure of the insulated connection part of this type of rubber or plastic insulated cable is as follows.
As shown in the figure, on the reinforcing insulating layer provided on the two connected conductors 1 and 1', a connecting part insulating shielding layer 5 is provided coaxially to form a slit 8, and a slit 8 is formed in the vertical direction. It is known to have an insulating shielding layer on the edge. The insulated connection part of such a crosslinked polyethylene insulated cable is manufactured as follows. First, the insulator layers 3 and 3 at the ends of the two cables to be connected are each shaved into a pencil shape as shown in the figure, and after connecting the conductors 1 and 1' with a compression sleeve, etc., The inner semiconductive layer 2 is formed by a conductive tape or a semiconductive heat shrink tube. Next, a rubber or plastic insulating tape, such as a self-adhesive insulating tape, is wound around the cable insulator layers 3, 3 on the internal semiconducting layer 2, and then heated and pressurized to fuse them together. Alternatively, a desired mold (not shown) is formed around the internal semiconducting layer 2.
After injection molding a molten resin thereon, the connecting portion reinforcing insulating layer 4 is formed by heat-sealing by appropriate means. Furthermore, an insulating shielding layer 5 made of a semiconducting layer having a slit portion 8 coaxially provided on the outer periphery of the connecting portion reinforcing insulating layer 4 is provided to complete the connecting portion. However, the insulated connections of such conventional rubber and plastic insulated cables have a number of drawbacks. That is, (a) the tip of the insulating shielding layer 5 forming the slit 8 is deformed when the tape winding layer for forming the reinforcing insulating layer 4 is heated and fused together. This increases the electric field at the tip, so
The formed connection becomes easy to break from this tip. (b) When creating the slits 8 in the insulating shielding layer 5, it is difficult to make them coaxially on a concentric circle, which tends to cause disturbances in the electric field. In view of these drawbacks, the slit 8 shown in Figure 1 is
On the outer periphery of the insulation reinforcing layer 4 that covers the cable conductor joints of rubber or plastic insulated power cables as shown in Figure 2, a volume specific resistivity of 10 ⁶ to 10 ¹² Ωcm at AC , dielectric constant 6~100
An insulating shielding layer 6 is provided through a high dielectric constant and high resistance layer 7 having a high dielectric constant,
A high resistance type insulated connection was proposed. Here, the basis for the values of this high dielectric constant and high resistance layer is the volume resistivity
If the resistivity is less than 10 ⁶ Ω・cm and the dielectric constant is more than 100, the impulse voltage that enters the cable line will cause flash shorting, while if the specific volume resistivity is more than 10 ¹² Ω・cm and the dielectric constant is less than 6, the connection will fail. This is because if an electric current is applied to the parts, the electric field will concentrate on the tips of the insulating shielding layer 6 and the high dielectric constant, high resistance layer 7 shown in FIG. 2, and they will easily break down. Conventionally, there is a method of forming a high resistance layer having the above resistance range on the circumference of the insulator by appropriately adjusting the carbon content for such a high dielectric constant and high resistance type edge cut. There was a problem in that the resistance value of the high-resistance layer containing only the above-mentioned materials tends to fluctuate due to thermal history such as heat cycling. The object of the present invention is to eliminate the above-mentioned drawbacks of high dielectric constant, high resistance type insulated connections and provide a stable and simple insulated connection. That is, for the high dielectric constant, high resistance layer (edge cut portion) 7 in FIG. 2, based on 100 parts by weight of the base resin,
This insulating connection part is characterized by using a composition in which 50 to 700 parts by weight of silicon carbide and 2 to 60 parts by weight of carbon are mixed and blended. Base resins include low density polyethylene, medium density polyethylene, high density polyethylene, ethylene-propylene copolymer, ethylene-ethyl acrylate copolymer, ethylene-
Vinyl acetate copolymer, ethylene α-olefin
Polyene terpolymer (for example, Mitsui Petrochemicals elastomer (ethylene/1-butene/5-ethylidene-2-norbornene terpolymer)), a single material or a blend of two or more of these materials, or a blend of two or more of these materials. A crosslinked product is suitable. Next, to briefly explain the reason for the limitation in quantity in the present invention, it is impossible to blend silicon carbide in an amount of less than 50 parts by weight based on 100 parts by weight of the base resin because the electrical resistance will change depending on the thermal history. . Moreover, if it exceeds 700 parts by weight, the composition becomes very hard and difficult to process, so it is not possible. Further, if the carbon content is less than 2 parts by weight, the desired dielectric constant resistance cannot be obtained, so it is not acceptable.On the other hand, if it exceeds 60 parts by weight, the composition becomes hard and difficult to process, so it is not acceptable. The effects and features of the structure of this invention are that, compared to a high dielectric constant, high resistance layer containing only carbon black, the inclusion of silicon carbide makes it difficult for carbon black to move even when subjected to thermal history;
It is characterized by almost no change in resistivity. The method for forming the edge cut portion is as follows. That is, (1) the above-mentioned composition tape is attached to the connecting portion reinforcing insulating layer 4;
Roll it up. In some cases, after winding the tape, it is heat-fused to the connecting portion reinforcing insulating layer 4. (2) A tube made of the above compounded composition is prepared in advance according to the outer diameter of the designed connecting portion reinforcing insulating layer 4, and after molding the reinforcing insulating layer 4, the tube is placed on this reinforcing insulating layer 4. Insert, cover and heat fuse. (3) After molding the reinforcing insulating layer, a mold is placed on the insulating layer, and the above compounded composition is injected or extruded according to the design of the edge cut portion. Furthermore, it is heat-fused to the insulating layer. Here, the thickness and length of the high dielectric constant and high resistance layer vary depending on the rated voltage class, but for example, for a 66KV class cable, the thickness is 1 to 3 mm, and the separation distance between the insulation shielding layers is 50 to 50 mm. 100mm is preferred. Example 1 After sharpening the insulators 3 and 3 of a 600 mm ² 154 KV cross-linked polyethylene insulated cable, connect the conductors 1 and 1' with a compression sleeve (not shown), and then apply semi-conductive tape (manufactured by Nippon Unicar Co., Ltd.). Product name DFDJ0580
After winding the tape over the conductor connection part, it was heat-molded at a temperature of 150°C for 4 hours. after that,
A mold (not shown) was attached around the formed conductive layer 2, and a crosslinking agent-containing polyethylene composition [HFDJ4201 (trade name, manufactured by Nippon Unicar Co., Ltd.)] was extruded into the mold using a 30 mm extruder. The set temperature of this extruder (not shown) was 120°C. Next, after cooling, the mold was removed, and a 3 mm thick tape of the composition shown in Table 1 was applied to the high dielectric constant and high resistance layer shown in FIG. 2 of the formed connection reinforcing insulator layer 4. ,
The above semiconductive tape was wrapped around the edges at a distance of 100 mm and other parts. Place the thus obtained connection into a vulcanizing tube (not shown), and add 8 kg of nitrogen gas to the tube (not shown).
After heating at a temperature of 210° C. for 6 hours in a cm ² atmosphere, it was cooled under gas treatment. The thickness of the joint reinforcing insulator layer 4 was 25 mm. After forming the connection part, the high dielectric constant and high resistance layer was tested for volume specific resistivity and impulse flash voltage withstand AC, and then electricity was applied for 8 hours every day for 200 days to maintain the conductor temperature at 90°C. After conducting heat cycle tests, we conducted volume resistivity and impulse flash breakdown voltage tests of the high dielectric constant and high resistance layers under alternating current.
The obtained results are also listed in Table 1.

[Table] As is clear from Table 1, the characteristics of the edge cut parts after heat cycle thermal history are much more stable than those of the comparative example in all the insulated connections according to this example compared to the conventional ones. . Example 2 After sharpening the insulators 3 and 3 of a 250 mm 66 KV cross-linked polyethylene insulated cable, connect the exposed conductors 1 and 1' with a compression sleeve (not shown).
A tape made of DFDJ0580) was wound onto the conductor connection portion and then heat-molded at a temperature of 150°C for 3 hours. Thereafter, a mold (not shown) was attached around the formed conductive layer 2, and a crosslinkable polyethylene composition (HFDJ4201 manufactured by Nippon Unicar) was extruded into the mold using a 30 mm extruder so that the insulation thickness was 12 mm. . The extruder (not shown) was set at 120°C. Next, after cooling, the mold was removed, and a 2 mm thick tape of the composition shown in Table 2 was applied to the high dielectric constant and high resistance layer shown in FIG. 2 of the formed connection reinforcing insulator layer 4. Then, the above semi-conductive tape was wrapped around the edge cut distance of 70 mm at the point 6 in Figure 2. Place this connection into a vulcanizing tube (not shown) and use 8 kg of nitrogen gas/
cm ² and an ambient temperature of 210° C. for 4 hours, and cooled under gas processing to form a connection part. After forming the connection part, the high dielectric constant and high resistance layer was tested for volume specific resistivity and impulse flash voltage withstand AC, and then electricity was applied for 8 hours every day for 200 days to maintain the conductor temperature at 90°C. After conducting heat cycle tests, we conducted volume resistivity and impulse flash breakdown voltage tests of the high dielectric constant and high resistance layers under alternating current. The obtained results are also listed in Table 2. As is clear from Table 2, it can be seen that the characteristics of the edge cut parts after heat cycle thermal history are much more stable than those of the comparative example in all of the insulated joints according to this example, compared to the conventional ones. .

[Table] Example 3 After sharpening the insulator layers 3 and 3 of a 250 mm 66 KV ethylene-propylene rubber insulated cable, the conductor 1 was exposed with a compression sleeve (not shown).
After connecting 1', apply semi-conductive tape (manufactured by Nippon Unicar)
A tape made of DFDJ0580) was wound onto the conductor connection portion, and then heated and molded at a temperature of 150°C for 3 hours.
Thereafter, an ethylene-propylene copolymer tape (Nodel 2722 manufactured by du pout) was applied on the semiconductive layer 2 formed.
(made into a tape) was wound so that the insulation thickness was 20 mm, and further, in order to create the edge cut portion 7 shown in FIG. 2 on the insulator 4, a tape made of the composition shown in Table 2 Semi-conductive tape was wrapped around the area shown in Figure 2, 6, with a thickness of 2 mm and an edge cut distance of 70 mm. Place this connection into a vulcanizing tube (not shown) and use nitrogen gas
Kg/cm ² and an ambient temperature of 210° C. for 4 hours, and then cooled under gas pressure to form a connection part. After forming the connection part, the specific volume resistivity of the edge cut part at AC is 2×10 ⁹ Ω・cm, and the impulse flash voltage is
It was heated at 140KV. After performing 200 heat cycles on this connection part under the condition that the conductor temperature was 90°C and energized for 8 hours and energized for 16 hours, the above test was performed, but there was no change in the characteristics. Example 4 After sharpening the insulators 3 and 3 of a 600 mm ² 154 KV cross-linked polyethylene insulated cable, connect the exposed conductors 1 and 1' with a compression sleeve, and then apply semiconductive tape (Furukawa Electric Co., Ltd.) on the conductor connection part. Co., Ltd.'s product name: Conductive C Tape) is wound around the semiconductive layer 2, and an insulating tape (product name: Fco No. 31, made by Furukawa Electric Co., Ltd.) based on ethylene propylene rubber is wound on the semiconductive layer 2 to an insulation thickness of 50 mm.
The wire was wound to form a connecting portion reinforcing insulator layer 4. At the edge cut portion 7 shown in FIG. 2 on this reinforcing insulating layer 4, a tape of the same composition as shown in Table 1 is used, and at other locations, the same semiconductive tape as used for the semiconductive layer 2 is used. I made an insulated connection part by winding each. After making the connection, the specific volume resistivity of the cut edge part at alternating current is 2×10 ⁹ Ω・cm, and the impulse flash voltage is
It was heated at 120KV. A heat cycle test was conducted in which the conductor temperature was 90°C by energizing the connection for 8 hours every day for 200 days, but the characteristics of the edge cut portion did not change. Example 5 After sharpening the insulators 3 and 3 of a 66KV250mm ² polyethylene insulated cable, connect the exposed conductors 1 and 1' with a compression sleeve, and then apply semiconductive tape (polyethylene (NUC9025) 100
A tape made of a compound prepared by mixing 70 parts of carbon black (Vulcan Next, insulating tape (made of polyethylene (NUC9025))
Wound so that the insulation thickness is 12 mm, and then
In order to create the edge cut portion 7 shown in the figure, a tape made from Composition 4 of Example 2 was wound to a thickness of 2 mm. Next, connect this connection with nitrogen gas at 8 kg/cm ² and at an ambient temperature of 130°C.
was heated for 2 hours to form an insulated connection part. After making the connection, the specific volume resistivity of the cut edge part at alternating current is 2×10 ⁷ Ω・cm, and the impulse flash voltage is
It was 110KV. A heat cycle test similar to that in Example 1 was conducted on this connection, but there was no change in the characteristics of the edge cut portion.

[Brief explanation of drawings]

FIG. 1 is a schematic partial vertical cross-sectional view showing an example of a conventional insulated connection part of a rubber or plastic insulated cable, and FIG. 2 is a schematic partial vertical cross-sectional view showing an embodiment of the insulated connection part of the present invention. 1, 1'...Conductor, 2...Inner semiconducting layer, 3...
... Cable insulator layer, 4 ... Connection part reinforcing insulator layer, 5 ... Connection part insulation shielding layer, 6 ... Connection part insulation shielding layer, 7 ... High dielectric constant, high resistance layer, 8 ... Slit part (Edge cutting part).

Claims (1)

[Claims] 1. In a connection part of a rubber or plastic insulated power cable in which an insulating shielding layer is provided on the outer periphery of an insulating reinforcing layer covering a cable conductor connecting part, the insulating shielding layer is made of plastic as a base, and the 100%
Provided in a state in which left and right sides were opposed in the longitudinal direction through a high dielectric constant, high resistance layer made of a mixture of 50 to 700 parts by weight of silicon carbide and 2 to 60 parts by weight of carbon black. An insulated joint for rubber and plastic insulated power cables characterized by: