JPH0510893B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a molded joint for a DC plastic cable.

[Prior Art] Figures 2 and 3 are schematic diagrams showing the structure of the upper right half of a conventional DC plastic cable mold joint. The conductors 5 of a plastic cable (the DC plastic cable on the right side is omitted) are connected using a conductor connecting tube 1, and a joint insulator 3 is formed around it by tape wrapping or extrusion. It is constructed by heating the body 3 and integrating it.

[Problem to be solved by the invention] By the way, when a DC voltage is applied to this mold joint, there will be no problem if the cable insulator 2 and the joint insulator 3 are made of the same material, but if the materials are different. There is a problem, especially when the volume resistivity is different. In other words, the potential distribution inside the cable insulator 2 and the joint insulator 3 is determined by the distribution of resistance values in the relevant parts, and the potential gradient is small where the volume resistivity is low, and the potential gradient is small where the volume resistivity is high. becomes large, and as a result, a partial electric field concentration occurs near the area between the cable insulator 2 and the joint insulator 3. For example, joint insulator 3 rather than cable insulator 2.
When analyzing the electric field of a mold joint with a large volume resistivity, the result is approximately as shown in Figure 3. As can be seen from this figure, the equipotential lines 6 are crowded near the rising portion A of the joint insulator 3, and an electric field is concentrated in the portion A. In the opposite case, i.e. cable insulator 2
If we analyze the electric field of a molded joint in which the volume resistivity of the joint insulator 3 is smaller than that shown in FIG. As can be seen from this figure, the equipotential lines 6 are crowded near the rising part B of the cable insulator 2, causing electric field concentration in the part B, which causes a problem in that the withstand voltage performance is significantly reduced. .

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a molded joint for a DC plastic cable that has excellent DC withstand voltage performance.

[Means for Solving the Problems] The molded joint for a DC plastic cable according to the present invention has an additive that reduces the volume resistivity of the insulator, which is thermally diffused into both the cable insulator and the joint insulator. It is something.

[Function] In the present invention, as a result of thermally diffusing the additive, the volume resistivity does not change abruptly from the cable insulator to the joint insulator, but changes gradually, so the potential at that part The distribution is uniform throughout and no electric field concentration occurs.

[Embodiment] In an embodiment of the present invention, unlike the conventional examples shown in FIGS. 2 and 3, an additive 4 (pyrene, for example) is added to the joint insulator 3 (for example, polyethylene)
1267 Tetrahydropyrene) is added in advance to reduce the volume resistivity of the joint insulator 3 to 1/10~
Reduce it to 1/100. Since the melting points of polyethylene and pyrene are almost the same, when polyethylene is heated above its melting point and molded together with the cable insulation 2 (for example, crosslinked polyethylene), pyrene is also in a molten state. Therefore, part of the pyrene migrates into the cable insulator 2 due to thermal diffusion at the interface between the joint insulator 3 and the cable insulator 2. FIG. 1 shows this state. As a result, the volume resistivity after the insulator is cooled does not change abruptly from the cable insulator 2 to the joint insulator 3, but changes gradually.

Therefore, when a DC voltage is applied to the mold joint of the present invention, the potential distribution in the vicinity between the two becomes uniform throughout, and the DC withstand voltage performance is stabilized without causing electric field concentration.

Incidentally, when the electric field of the mold joint of this embodiment is analyzed, it is generally as shown in FIG. 1. Thus, it can be seen that the equipotential lines 6 are evenly distributed throughout the vicinity between the cable insulator 2 and the joint insulator 3, and there is no electric field concentration.

[Effects of the Invention] According to the present invention, a molded joint with excellent DC withstand voltage performance without causing electric field concentration can be obtained, and cables with different characteristics can also be connected.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the state of additive migration and potential distribution in the mold joint for DC plastic cables of the present invention, and Figs. 2 and 3 show the structure of the conventional mold joint for DC plastic cables and the related art. FIG. 3 is a schematic diagram showing the state of potential distribution in a mold joint. 1... Conductor connection tube, 2... Cable insulator, 3
... joint insulator, 4 ... additive, 5 ... conductor, 6 ... equipotential line.

Claims (1)

[Scope of Claims] 1. In a molded joint in which DC plastic cables are connected to each other, a joint insulator is further molded around the cables, and the insulators are heated and integrated, the insulators of the cables and the joint insulators are integrated. 1. A mold joint for a DC plastic cable, characterized in that an additive for reducing the volume resistivity of the insulator is thermally diffused into both sides of the mold joint. 2. The mold joint for a DC plastic cable according to claim 1, wherein the additive is pyrene, phenylnaphthalene or acetophenone. 3. The cable insulation is cross-linked polyethylene,
3. A molded joint for a DC plastic cable according to claim 1, wherein the joint insulator is polyethylene, and the additive is thermally diffused at a temperature higher than the melting point of the joint insulator.