JPS585516B2 - Kakiyou Polyethylene Cable Nosetsuzokuhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for connecting intermediate or terminal ends of crosslinked polyethylene cables using a mold.

Conventionally, a mold is attached to the cable connection part, and 20 to 50 kg of polyethylene compound with a crosslinking agent added from an extruder is added.
The method of extruding an insulating reinforcing body by applying pressure to a pressure of g/cm 2 and filling it into a mold and crosslinking it by heating from the outside is widely used because a connection part having relatively stable performance can be obtained.

However, the connection made by the above method is prone to voids at the interface between the surface of the cable insulator and the molded insulation reinforcing body, resulting in electrical weaknesses such as dielectric breakdown when used in the connection of an ultra-high voltage cable.

It is known that the main cause of this void generation is the roughness of the pencil front portion of the cable insulator and the surface roughness of the outer semiconducting layer removed portion, and that microscopic depressions become voids.

Therefore, in order to prevent voids, it is sufficient to smoothen the surface of the cable insulator, and several methods have been proposed for this purpose.

However, either method increases the number of work steps and is unfavorable in terms of efficiency.

The object of the present invention is to eliminate the above-mentioned drawbacks and to provide a means for reliably preventing the occurrence of voids in conventional working processes, the purpose of which is to provide a means for reliably preventing the formation of voids in conventional work processes, the content of which is to The desired area was surrounded by a mold, and 80 kg/cm2 of polyethylene compound with a crosslinking agent was added.
A method for connecting a crosslinked polyethylene cable is characterized in that the mold is filled with the above pressure and then crosslinked to form an insulation reinforcement.

The present invention will be explained in detail based on the illustrated embodiments.
In the figure, 1 and 1' are cross-linked polyethylene cables to be connected, and the cable insulators 2 and 2' at the ends thereof are shaped like pencil sharpeners, and the core wires 3 and 3' that have been centered are connected by a sleeve 4. Then, an internal semiconducting layer 5 is applied on the core wires 3, 3' and the sleeve 4 exposed to the outside.

In order to prevent this internal semiconductive layer 5 from deforming or moving during extrusion molding, which will be described later, a semiconductive cloth and an irradiated polyethylene tape are further wound around the upper layer of the semiconductive layer 5, and heat fusion treatment is performed. is preferred.

In addition, 6 and 6' are the outer semiconducting layers of the cables 1 and 1', and 7
, 7' are shielding layers, and 8, 8' are sheaths.

Then, a mold 9 is attached around the connection part, and an uncrosslinked polyethylene compound 11 mixed with a crosslinking agent is fed from an extruder 10.
is filled into the space inside the mold 9 through the conduit 12.

When filling, the filling pressure of Compound 11 is important; conventionally it was 20 to 50 kg/cm2, but it is now 80 kg/cm2.
/cm2 or more, and the pressure is adjusted while being monitored by, for example, a Bourdon tube type pressure gauge 13.

A heating wire coil 14 is embedded in the mold 9, and the mold 9 is preheated to such an extent that the pound 11 does not lose its fluidity and does not cause crosslinking or reaction, as shown in FIG. When filling is completed, the mold 9 is raised to the crosslinking temperature.

Cable insulator 2 without insulation reinforcement during heating,
Since it is desirable that no heat be applied to the 2' portion, the temperature distribution inside the mold 9 is highest in the center, and
The density of the heating wire coil 14 embedded in the mold 9 is adjusted so as to have a temperature distribution along the .

In some cases, it may be effective to cut the mold 9 into a plurality of pieces and insert a heat insulating material into the ends of the mold 9 to prevent heat transfer.

The pressure of the compound 11 in the mold 9 is 8 at the end of filling.
Even if it is 0 kg/cm2 or more, it temporarily decreases because some leakage occurs from the mold 9, and as the compound 11 is heated for crosslinking, it increases again and reaches equilibrium.

When the mold 9 is removed after the mold 9 is cooled and the compound 11 is cured after the bridging is completed, the cable insulator 2,
An insulating reinforcement 11' having the same quality as 2' is obtained.

Furthermore, the connection is completed by applying anti-corrosion treatment to the periphery of the insulating reinforcing body 11' using an external semiconductive layer, a shielding layer, and a sheath.

In the connection obtained by such a method, the filling pressure of the compound 11 is high, so the compound 11 sufficiently penetrates into the recesses on the surface of the cable insulators 2 and 2', and no voids are generated and electrical connection is maintained. Good characteristics can be obtained.

FIG. 3 shows the relationship between filling pressure and dielectric breakdown voltage based on the results of an AC breakdown test on a 110 kV x 100 mm2 cable.

When the filling pressure is 60 kg/cm2 or less, the breakdown voltage is around 200 kV, but when it is 80 kg/cm2 or more, the voids almost disappear and the breakdown voltage is 340 kV or more, which means that the cable has the same strength as a normal cable section. However, the effect brought about by the filling pressure difference is extremely significant.

After the test, the sample was disassembled and the cable insulators 2, 2'
As a result of observing the interface between the material and the insulating reinforcement 11', no voids were found in the method of the present invention;
It was observed that many voids were generated in the case where the filling pressure was less than kg/cm2.

In addition to this method, cable insulator 2,
If heat treatment is performed by wrapping a thin, smooth-surfaced tape such as Mylar tape around the pencil-sharpened part 2', the work process will increase slightly, but the surface of the cable insulators 2 and 2' will become smooth and voids will be eliminated. This has the effect of further reducing the occurrence of.

Furthermore, in order to prevent voids from occurring at the interface, the pressure during crosslinking may be increased instead of increasing the pressure during filling, but the principle is the same and the same effect can be obtained.

However, as shown in Figure 2, the pressure during crosslinking is
It is difficult to control the pressure to an arbitrary value, and is not practical.

As explained above, the crosslinked polyethylene cable connection method according to the present invention stabilizes electrical performance by increasing the filling pressure of the crosslinked polyethylene compound in the mold to 80 kg/cm2 or more to prevent the generation of voids. There is no need to intentionally treat the surface of the cable insulator that forms the interface, and the process is almost the same as the conventional method.

[Brief explanation of drawings]

The drawings are diagrams for explaining the method of connecting cross-linked polyethylene cables according to the present invention. Figure 1 is a longitudinal cross-sectional view of the connection part, and Figure 2 shows the temperature at the center of the mold and the inside of the mold over time. FIG. 3 is a graph showing the relationship between the breakdown voltage and the filling pressure. 1 and 1' are crosslinked polyethylene cables, 2 is a cable insulator, 9 is a mold, 10 is an extruder, 11 is a crosslinked polyethylene compound rim, 13 is a Bourdon tube type pressure gauge, and 14 is a heating wire coil.

Claims (1)

[Claims] 1. Surround the intermediate or terminal portion of the cross-linked polyethylene cable with a mold, fill the mold with a polyethylene compound containing a cross-linking agent under a pressure of 80 kg/cm2 or more, and then perform cross-linking to reinforce the insulation. A method for connecting a cross-linked polyethylene cable, characterized by molding the body.