JPH047647Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a rubber/plastic cable termination with excellent corona properties. Conventionally, the termination of a high-voltage cable, especially a rubber-plastic insulated cable, is carried out from the cable outer semiconducting layer 1 or the cable shielding layer 2, where electrical stress is concentrated, to the cable insulation layer 3, as shown in FIG. High dielectric constant heat shrink tube 4
-a is known to be closely coated. However, in the cable termination section with such a configuration, the third
As shown in the figure, a gap G tends to occur at the boundary between the cable outer semiconducting layer 1 and the cable insulating layer 3, and this gap degrades the corona discharge characteristics at the cable terminal end. For this reason, silicone grease is applied to the gap at the end of a coneless type cable that uses a heat-shrinkable tube, but in such cases, the silicone grease spreads to areas other than where it is needed. There are problems such as dripping and insufficient filling. Furthermore, as shown in FIG. 4, Japanese Patent Application Laid-Open No. 52-21695 discloses that a semi-conductor is provided at the stepped portion between the cut end of the semi-conducting layer 1 of the cable and the cable insulator 3 so as to communicate with the semi-conducting layer of the cable. A conductive compound or a soft tape-like material 5 is smoothly arranged or wrapped to fill the stepped portion, and a heat-shrinkable tube 4-a with a high dielectric constant is placed over it, or heat-shrinkable. A method of terminating a cross-linked polyethylene vinyl sheathed cable by wrapping it with a plastic tape 4-b and shrinking it by heat has been disclosed. However, with this method, it is not possible to provide sufficient shrinkage force to the heat-shrinkable tube 4-a or the heat-shrinkable tape 4-b, and furthermore, when the heat-shrinkable tube 4-a is used, air bubbles are prevented. Easy to get caught in
Further, in the case of the heat-shrinkable tape 4-b, there is a step at the interface due to the tape edge, which becomes an electrically discontinuous surface, so that there is a problem that sufficient electrical characteristics cannot be exhibited. Furthermore, as shown in FIG. 5, Utility Model Application Publication No. 56-161931 discloses that an unvulcanized rubber tape 6, preferably a volume resistivity A method of terminating a cable is disclosed in which an insulating unvulcanized rubber tape 6 having a diameter of about 10 ¹⁰ Ω-cm is wound, and a high dielectric constant self-adhesive tape 4-c is wound on top of this winding. ing. However, this method requires the use of tape as a material with a high dielectric constant, and has the disadvantage that it requires a high degree of skill and a long working time. The present invention aims to eliminate these conventional drawbacks and provide a cable termination that has excellent corona characteristics and is also easy to work with. As an embodiment of the present invention is shown in FIG. 1, at the cable end of a rubber-plastic cable, the cable is formed between the cable external semiconducting layer 1 exposed by stripping the cable and the cable insulating layer 3. A semiconductive coating layer 7 is formed by coating and drying an oil-based sticky semiconductive paint with a viscosity of 80 to 300 cps on the outer circumference of the boundary.
is formed, and an electric field relaxation layer is provided around the outer periphery. That is, while the conventional method improves the corona discharge characteristics by filling the gap G between the cable semiconducting layer 1 and the cable insulating layer 3 with a suitable material, the present invention improves the corona discharge characteristics as shown in FIG. Next, an oil-based semiconductive paint is applied around the boundary between the external semiconductive layer 1 and the insulating layer 3 so that the gap G is within the upper surface of the coating film, and is dried to form an adhesive semiconductive coating layer 7. The aim is to improve the corona characteristics by moving the semi-conductive part to the outside of the gap G and substantially eliminating the influence of the gap G. Accordingly, in the present invention, the oil-based semiconductive paint that forms a sticky coating upon drying refers to a coating whose volume resistivity is 10 ⁵ Ω-cm or less. As a result of intensive research by the present inventors, the desirable semiconductive paint is (a) based on a polymer such as polyisobutylene or polybutene, which has adhesive properties and has excellent adhesion to the insulating layer, and (b) Viscosity is 80~300cps
It was found that the range of If this coating material is used, the resulting semiconductive coating layer 7 has good adhesion to the cable insulation layer 3 made of an insulator. Moreover, a cable terminal with excellent corona properties can be obtained. The reason for limiting the viscosity to 80 to 300 cps is that semiconductive paints with a viscosity within this range have good film-forming ability, so that the gap G is within the upper surface of the paint film. This is because the corona characteristics are stabilized to a high level by forming the semi-conductive portion 7 and moving the semiconductive portion to the outside of the gap G to substantially eliminate the influence on the gap. To explain further, the viscosity
The reason for limiting the range to 80 to 300 cps is that semiconductive paints with a viscosity of 80 cps or less have low viscosity, resulting in high fluidity and low adhesion to the surfaces of semiconductive layer 1 and insulating layer 3. This is because the semiconductive paint flows while the paint film is drying, making it impossible to form the necessary semiconductive paint layer, and conversely, the viscosity decreases.
This is because a semiconductive paint of 300 cps or more has too high a viscosity and has poor fluidity, making it impossible to form a uniform semiconductive coating layer. In water-based paints,
Since it takes time for the coating film to dry, the workability is poor and the adhesiveness is poor, and an oil-based semiconductive paint is required to ensure good workability. In addition, in order to develop an even higher level of corona generation voltage, for example, 45KV or more with a 33KV cable, 100~
Must be within 200cps. Further, in the embodiment, a high dielectric constant heat-shrinkable tube is used as the electric field relaxation layer 4, but a high dielectric constant tape or a rubber stress cone may also be used. Examples of the present invention will be explained below in comparison with comparative examples. Examples 2 to 5, Comparative Examples 1 to 6 A 33KV class cross-linked polyethylene insulated cable was stripped in stages, and the conductor 8 was 6.5 cm, the insulator, that is, the cross-linked polyethylene insulation layer 3 was 45 cm, and the outer semiconducting layer 1 was 1 cm.
cm, exposing 1 cm of the cotton tape layer and 3 cm of the copper shielding layer, respectively. Next, the semiconductive paint shown in the Comparative Examples and Examples described later is applied with a brush to the cable insulating layer 3 on the circumference in a width of 2 cm so that the end part covers the cable semiconductive layer 1. A conductive layer 7 is formed. Furthermore, a high dielectric constant heat shrink tube 4 is attached to the outer periphery of the tube.
-a was coated on the insulating layer 3 so that the extra length was 20 cm and then shrunk. The terminal end of this cable was tested to measure corona generation voltage using a discharge detector. The semiconductive paints used in Examples and Comparative Examples are as follows. The viscosity of the semiconductive paint was measured using a B-type rotational viscometer. Comparative Example 1 Water-based graphite paint...Product name: Corohite, manufactured by Nippon Graphite Industries Co., Ltd. This water-based paint was adjusted to have a viscosity of 150 cps. Comparative Example 2 Oil-based paint...Product name RA- manufactured by Fujikura Kasei Kogyo Co., Ltd.
3 (Rubber is used as the base polymer.) This oil-based paint was adjusted to a viscosity of 150 cps. Comparative Examples 3, 4, 5, 6 and Examples 2, 3 Polyisobutylene...100 parts by weight Carbon Black (trade name Vulcan XC-72)
...40 parts by weight were kneaded in a paint mill and then diluted with trichlene to prepare semiconductive paints having the following viscosities. Viscosity (cps) Comparative example 3 1600 〃 4 800 〃 6 400 Example 2 200 〃 3 100 Comparative example 5 60 Example 4 Polybutene...100 parts by weight Carbon black (product name Vulcan XC-72)
After kneading 40 parts by weight in a paint mill, the mixture was diluted and adjusted to a viscosity of 150 cps with trichlene. Example 5 Polyisobutylene...100 parts by weight Carbon Black (trade name: KETSUCHEN BLACK)
EC)...After kneading 15 parts by weight in a paint mill,
The viscosity was diluted and adjusted to 150 cps with toluene. In Comparative Examples 1 and 2, no adhesiveness was observed in any of the coating layers 10 formed by applying and drying the semiconductive paint. On the other hand, the coating layer 7 formed by coating and drying the coating materials used in Examples 2 to 5 was found to have excellent adhesiveness. Further, Table 1 shows the results of measuring the corona generation voltage for each cable end portion obtained in the comparative example and the example.

[Table] As is clear from Table 1, the cable termination of the present invention has excellent corona resistance, and its practical value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a main part of an embodiment of the present invention, and FIGS. 2 to 5 are schematic cross-sectional views showing examples of conventional cable terminations. 1... External semiconducting layer, 2... Shyahei layer, 3...
...Insulating layer, 4...Electric field relaxation layer, 4-a...High dielectric constant heat-shrinkable tube, 4-b...High dielectric constant heat-shrinkable tape, 4-c...High dielectric constant self-bonding tape , 5... Semiconductive compound or soft tape, 6... Unvulcanized rubber tape, 7... Adhesive semiconductive coating layer, 8... Conductor, graphite... Sheath, 1
0...protective layer, G...gap at the boundary.

Claims (1)

[Scope of utility model registration request] At the end of a rubber or plastic cable, an oil-based semiconducting material with a viscosity of 80 to 300 cps is applied to the outer periphery of the boundary between the cable external semiconductive layer 1, which is exposed by peeling off the cable, and the cable insulation layer 3. Adhesive semiconductive coating layer 7 after coating and drying of paint
What is claimed is: 1. A cable termination section characterized by forming an electric field relaxation layer on the outer periphery of the cable termination section.