JP2677869B2 - Assembling method of connection box for power cable - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for assembling a connection box for a power cable having a rubber stress cone on a cable insulator of a power cable, and more particularly to a method for mounting a rubber stress cone. Related to the improvement of.

[Conventional technology]

A power cable junction box having a rubber stress cone on a cable insulator of a power cable uses a rubber stress cone having an inner diameter smaller than the outer diameter of the power cable, and gives a surface pressure by drawing a fit. In order to keep the stress cone close to the power cable side when assembling the connection box, the outer conductive layer of the cable was removed, and a conductive tape containing a cross-linking agent was wrapped and heat-molded. The inner diameter of the stress cone was determined by measuring the diameter of the cable insulator after manufacturing the power cable.

[Problems to be solved by the invention]

However, in such a conventional technique, it is uneconomical to prepare several types of stress cones having different inner diameters according to the outer diameter of the power cable at the site where the junction box is assembled. In addition, the rising portion of the stress cone conductive layer or its vicinity is electrically weak due to the influence of the stress on the cable outer conductive layer side. On the other hand, this stress is determined by the thickness of the cable insulator, so the cable insulator For power cables or high-voltage cables with a small thickness,
This stress increased and it was easy for dielectric breakdown to occur at the interface between the stress cone and the cable insulator. In recent years, there is an increasing demand for power cables in which the cable insulator of the power cable is thin. However, such a power cable is electrically weak at the cable insulator portion, and there is a risk of dielectric breakdown.

An object of the present invention is to provide a method for assembling a junction box for a power cable, which avoids the above-mentioned drawbacks and prevents dielectric breakdown even if the cable insulator is thin or the applied voltage is high.

[Means for solving the problem]

The present invention, in order to solve the above problems, when assembling a power cable connection box having a rubber stress cone on the cable insulator of the power cable, after removing the cable outer conductive layer of the power cable, An insulating reinforcement layer of insulating polyethylene containing a cross-linking agent is applied on the cable insulator, and then an external conductive auxiliary layer of conductive or semiconductive polyethylene is provided from the cable external conductive layer to the vicinity of the rising portion of the rubber stress cone conductive layer. This insulating and conductive or semi-conductive polyethylene is heat-molded separately or simultaneously, and finally, a rubber stress cone is mounted over the insulating reinforcing layer and the external conductive auxiliary layer so as to be mounted. A method for assembling a cable connection box is provided.

[Action]

In this way, after removing the cable outer conductive layer, the insulation reinforcement layer of insulating polyethylene is applied on the cable insulator, which increases the thickness of the cable insulator. Since the electrically weak parts in the vicinity are reinforced, the electrical characteristics can be improved without causing dielectric breakdown. Therefore, the power cable or high voltage cable with a small thickness of the cable insulator, which has recently been in demand, is increasing. Can be applied to.

〔Example〕

Embodiments of the present invention will be described in detail with reference to the drawings.
The drawing shows the upper half of the main part of a junction box 10 for a power cable assembled by the method of the present invention.
Is composed of a cable conductor 14, a cable insulator 16 provided thereon, and a cable outer conductive layer 18 provided on the cable insulator 16. An insulating jacket (not shown) is provided on the cable outer conductive layer 18.

This power cable 12 is used when assembling the junction box 10.
The cable outer conductive layer 18 and the cable insulator 16 are sequentially removed and gradually peeled. As can be seen from the drawings, the outer end 18a of the cable outer conductive layer 18 is tapered. Then, a polyethylene tape containing a cross-linking agent is wound around the exposed cable insulator 16 to form the insulating reinforcing layer 22. In this case, the end of the winding layer of this polyethylene tape on the side of the outer conductive layer 18 is formed so as to form a smooth taper 22a. The thickness of the insulating reinforcing layer 22 is determined by the characteristics of the rising portion of the conductive layer of the stress cone 20.

Next, the rising portion of the conductive layer 21 of the stress cone 20 is formed on the insulating reinforcing layer 22 from the tapered end portion 18a of the outer conductive layer 18.
A polyethylene tape containing a conductive or semi-conductive cross-linking agent is wound up to the vicinity of 21a to form the external conductive auxiliary layer 24.

The cross-linking agent-containing polyethylene tape of the insulating reinforcing layer 22 and the outer conductive auxiliary layer 24 is heated and molded. The heat molding may be performed separately for the insulating reinforcing layer 22 and the external conductive auxiliary layer 24.

Finally, the rubber stress cone 20 is attached through the outer conductive auxiliary layer 24 so as to straddle the outer conductive auxiliary layer 24 and the insulating reinforcing layer 22. In the drawings, reference numeral 26 is an epoxy porcelain tube, and an insulating process is performed across the porcelain tube 26 and an insulating jacket of a power cable (not shown).

Next, referring to specific examples of the present invention, when assembling a junction box by the method of the present invention to a power cable of 19 mm in which the thickness of the cable insulator is relatively thin, an insulation reinforcing layer of 4 mm is used on site.
When formed with, the same electrical characteristics as a junction box assembled into a power cable with a cable insulator having a thickness of 23 mm could be obtained. The electrical stress in the junction box of this structure is the most severe at the tip of the taper of the insulating reinforcing layer formed by molding in the field, but since this part is integrated by the mold, the stress cone conductive layer The characteristics are better than the above, and the same characteristics as the mold joint are obtained.

According to the illustrated embodiment of the present invention, the conductive layer rising portion 2 of the stress cone 20 extends from the tip of the taper 22a of the insulating reinforcing layer 22.
The stress increases up to 1a, and foreign matter may enter and be caught when the polyethylene tape containing the crosslinking agent is wound. Therefore, this portion of the insulating reinforcement layer 22 and the outer conductive auxiliary layer 24 may be formed by covering with a polyethylene heat-shrink tube, which is foreign material controlled at the factory. This polyethylene heat shrink tube has insulation reinforcement layer 22
The outer reinforcement layer 22 and the outer conductive auxiliary layer 24 may be separated, or the inner reinforcing layer 22 and the outer conductive auxiliary layer may be formed as an integrated double tube in which the inner layer is the insulating layer and the outer layer is the conductive layer. The 24 parts may be formed at the same time. still,
When using a heat-shrinkable tube in this way, adhesion with a cable that has already been cross-linked becomes a problem, but this is because one or two layers of polyethylene tape containing a cross-linking agent is wrapped around the cable and the heat-shrinkable tube is wound on it. It can be avoided by wrapping. In the winding of the tape of one or two layers, the foreign matter can be visually monitored, so that the foreign matter can be prevented from being caught.

In this way, since the stress of the stress cone conductive layer rising portion 21a can be controlled by the insulating reinforcement layer 22 applied on site, the cable insulator 16 can obtain good electric characteristics even in a power cable and a high voltage cable. You can

〔The invention's effect〕

According to the present invention, as described above, an insulating reinforcing layer is provided on the exposed cable insulator to suppress stress in the rising portion of the rubber stress cone conductive layer, so that the power cable and the high-voltage cable have a thin cable insulator. However, good electrical characteristics can be obtained, and since the insulation reinforcement layer and the external conductive auxiliary layer to be molded are thin, it can be applied by the same method as the conventional external conductive mold method, so workability is not reduced. In addition, since the inner diameter of the rubber stress cone is larger than the conventional one, this rubber stress cone can be moved closer to the cable side during assembly, which improves workability and increases the inner diameter of the stress cone to the insulation reinforcement layer and the external conductive auxiliary layer. The advantage is that it can be easily adapted to the diameter of the mold part.

[Brief description of the drawings]

The drawing is a cross-sectional view of the upper half of a junction box for power cables assembled by the method of the present invention. 10 …… Junction box, 12 …… Power cable, 14 …… Cable conductor, 16 …… Cable insulator, 18 …… Cable outer conductive layer, 20 …… Rubber stress cone, 21 …… Conductive layer, 21a…
… Conductive layer rising part, 22 …… Insulation reinforcement layer, 24 …… External conductive auxiliary layer.

Claims (1)

(57) [Claims] Claim: What is claimed is: 1. When assembling a connection box for a power cable having a rubber stress cone on the cable insulation of the power cable, after removing the cable outer conductive layer of the power cable, an insulating property is provided on the cable insulation. An insulating reinforcing layer of polyethylene is applied, and then an external conductive auxiliary layer of conductive or semiconductive polyethylene is provided from the cable external conductive layer to the vicinity of the rising portion of the rubber stress cone conductive layer, and the insulating and conductive or semiconductive layer is provided. Assembly of a power cable connection box, characterized in that the heat-resistant polyethylene is separately or simultaneously heat-molded, and finally the rubber stress cone is mounted over the insulating reinforcing layer and the external conductive auxiliary layer. Method.