JPS60202616A - Electrically insulated thermally shrinkable tube and connector of power cable using same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a heat-shrinkable tube for electrical insulation and a connecting portion of a plastic insulated power cable using the same.

(Background of the Invention) The connection portion of a plastic insulated cable having a plastic insulation layer made of polyethylene, cross-linked polyethylene, etc.
Like the cable main body, an inner semiconducting layer, an insulating layer, an outer semiconducting layer, and an outer protective layer are sequentially provided on the outer periphery of the cable, covering the conductor connection portion and the cable insulating layer. In forming these layers, there are methods such as forming each layer by tape wrapping or inserting a rubber molded product that integrates each layer, but each method has advantages and disadvantages. As a simple connection method, a heat shrink tube connection method is adopted in which an electric field relaxation layer is used instead of the internal semiconductive layer, and both layers are formed by heat shrinking using heat shrink tubes.

However, a major technical problem with such cable connections is that when electricity is applied for many years, the insulation performance gradually deteriorates and the breakdown voltage begins to drop. For this reason, measures such as using thicker insulating tubes or increasing the number of insulating tubes have been taken in anticipation of the reduction in insulation due to deterioration. We, the inventors, have conducted various studies on this deterioration over time, and have found that this deterioration phenomenon is caused by microvoids occurring in the insulating tube or moisture existing between the conductor and the tube. It was found that this is due to water trees generated at the interface. In particular, it has been found that when used in a stretched and strained state, such as in a shrink tube, trees are more likely to form compared to unstrained polyethylene.

As a result, the deterioration phenomenon is prevented by suppressing the tree caused by the microscopic defects peculiar to shrink tubes.
It is no longer necessary to take into account deterioration due to aging, and we have succeeded in reducing the thickness of the shrinkable tube.

(Disclosure of the Invention) The present invention solves the above-mentioned problems and provides a heat-shrinkable tube for electrical insulation that has a thin wall thickness and stable insulation performance over a long period of time, and a connection portion for an electric power cable using the same. It is something.

Figure 1 shows a heat-shrinkable electrically insulating tube (1) according to the present invention.
, which is a longitudinal cross-sectional view showing that the main composition is a composition in which an ethylene-vinyl acetate copolymer is blended with a copolymer of ethylene and an α-olefin having 4 to 8 carbon atoms. As the α-olefins, butene-1, pentene-1, octene-1, and those having substituents such as methyl groups and ethyl groups on their main chains are used. Furthermore, various types of ethylene-vinyl acetate copolymers can be used, ranging from those with a low residual vinyl content that are crystalline to those that are rubbery and have no crystallinity. At this time, it is of course possible to add anti-aging agents, processing aids, etc. that are usually added to heat-shrinkable tubes.

When this non-shrinkable tube is coated on a conductor to form an insulating layer, it is possible to suppress the generation of trees within the heat-shrinkable tube or from the interface between the non-shrinkable tube and the conductor, compared to when conventional polyethylene heat-shrinkable tube is used. In comparison, ethylene-α olefin copolymer alone, ethylene-
Even compared to the case of vinyl acetate copolymer alone, it was possible to form an insulating layer that was thinner and resistant to electrical damage for a longer period of time.

FIG. 2 is a longitudinal cross-sectional view of an embodiment of the power cable connection part according to the present invention, in which (1) is the cable conductor, (2) is the cape/l' insulation layer made of polyethylene, cross-linked polyethylene, etc., and (3) is the cable conductor.
(4) is the internal semiconducting layer of the cable; (4) is the metal thin layer made by winding a metal tape such as copper or aluminum;
(5) is a cable sheath made of extruded plastic such as polyethylene or vinyl chloride resin, and +61 is a connection portion of the cable conductor (1).

An electric field relaxation tube layer (7) for relaxing the electric field at the conductor connection part (6) is provided on the connection part (6) of the cable conductor (1) and the outer periphery of the cable insulation layer (2), and on the In the present invention, an insulating tube layer (A) made of the above-described heat-shrinkable tube is further provided with an outer semiconducting tube layer (8) and an outer protective layer (9) in this order.

The formation of the tube layer is no different from the conventional method of forming cable connections using heat-shrinkable tubes, and each tube may be provided separately and heat-shrinked.For example, the electric field relaxation tube and the insulating tube may be integrated in advance. Toshidamono, or in the example, there is no tree generation at all, and the tearing time is significantly improved. Furthermore, compared to the case of using α-olefin alone or ethylene-vinyl acetate copolymer alone, both tree properties and breaking time are significantly improved.

Example ■ A tube with an inner diameter of 20 mm and a wall thickness of 8' mm was made by extrusion using the composition shown in Table 2, and after crosslinking by electron beam irradiation,
The tube was expanded to obtain a heat-shrinkable tube with an inner diameter of 40'mm.

Using this tube, a 22 KV, 150 mm cross-linked polyethylene insulated polyvinyl chloride cable connection was formed as shown in FIG. An alternating current voltage of 60 KV was applied to the above connection part in water at room temperature. After 400 hours of power application, the connection was disconnected and the state of tree formation was examined, and the time until the connection was broken was measured for connections created in the same way. The results are shown in Table 2.

Table 2 Note 1 The α-olefin and EVA used are the same as in Table 1.

Note 2 Tree characteristics ×: Nori Many occurrences Δ: Nori
Slight occurrence ◎: No sories (effects of the invention) As described above, the heat shrinkable tube of the present invention and the power cable terminal connection section using the same do not cause trees to occur, which could not be avoided with conventional heat shrinkable tubes. First, the insulation breaking properties are also significantly improved. Therefore, unlike conventional methods, there is no need to use thick insulation to account for insulation loss.
This has the effect of maintaining stable insulation properties for a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a heat shrinkable tube according to the present invention, and FIG.
The figure is a longitudinal cross-sectional view of an embodiment of the power cable connection part of the present invention using the above-mentioned heat-shrinkable tube. A: Heat shrinkable tube of the present invention, 2: Cable insulation layer, 6: Conductor connection portion, 7: Electric field relaxation tube layer, 8: External semiconducting tube layer. 1 illustration of prayer 2

Claims (8)

[Claims] (1) An electrically insulating heat-shrinkable tube characterized in that its main composition is a composition in which an ethylene-vinyl acetate copolymer is blended with a copolymer of ethylene and an α-olefin having 4 to 8 carbon atoms. (2) The heat-shrinkable tube for electrical insulation according to claim 1, wherein the α-olefin is butene-1. (3) The heat-shrinkable tube for electrical insulation according to claim 1, wherein the α-olefin is pentene-1. (4) The heat-shrinkable tube for electrical insulation according to claim 1, wherein the α-olefin is octene-1. (5) In a cable connection part in which an electric field relaxation tube layer, an insulating tube layer, and an external semiconducting layer are sequentially provided on the outer periphery of the cable conductor connection part and the cable insulation layer, the insulation tube layer is combined with ethylene and carbon number 4. A connection part for an electric power cable, characterized in that the main composition is a composition obtained by blending an ethylene-vinyl acetate copolymer with the α-olefin copolymer of 1 to 8, and is made by shrinking a heat-shrinkable tube. (6) The connection portion for an electric power cable according to claim 5, wherein the α-olefin is Butyshi-1. (7) The connection portion for an electric power cable according to claim 5, wherein the α-olefin is pentene-1. (8) The electrical cable connection part according to claim 5, wherein the α-olefin is octene-1.