JP3139719B2 - Connection method of cross-linked polyethylene insulated power cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved method for connecting a crosslinked polyethylene insulated power cable.

[0002]

2. Description of the Related Art Crosslinked polyethylene insulated power cables are:
Due to its excellent insulation properties and ease of handling, it is rapidly following the path of higher voltage, and is being used for 275KV-class long-haul lines. Connections are indispensable for long-distance lines, but the so-called extrusion-molded connection method is adopted for the 275KV class.

The connection method of the conventional extrusion mold type is performed as follows. First, the outer semiconductive layer of the crosslinked polyethylene insulated power cable to be connected is peeled to a predetermined dimension to expose the cable insulator, and the cable insulator is shaped into a predetermined shape. Thereafter, the cable conductor is compression-connected by a conductor connection tube, and an internal semiconductive layer is formed at the connection portion.

[0004] Next, the connecting portion is covered with a mold, and a non-crosslinked polyethylene containing a crosslinking agent is extruded therein to form a connecting portion insulator. After cutting and shaping the connecting portion insulator into a predetermined shape, a semiconductive heat-shrinkable tube is put on the outer periphery of the outer portion, and the outer portion is heated and shrunk to form a connecting portion external semiconductive layer. Crosslink by heating under pressure.

[0005]

In the above connection method, when the outer semiconductive layer of the cable is peeled off and when the connection insulator is cut into a predetermined shape, the surface of the insulator is carefully scraped off using a power tool or a glass piece. However, at this time, the surface of the cable insulator or the connecting portion insulator is likely to be finely scratched. If the connecting portion external semiconductive layer is formed on the damaged insulator surface and crosslinked, when the connecting portion external semiconductive layer is melted, it may flow into fine scratches on the insulator surface and become conductive protrusions. is there. These protrusions become electrical defects, and significantly lower the withstand voltage characteristics of the connection portion.

[0006]

SUMMARY OF THE INVENTION The present invention provides a method for connecting a crosslinked polyethylene insulated power cable which solves the above-mentioned problems. After that, a semiconductive heat-shrinkable tube whose melting point is higher than the melting point of the connecting portion insulator and lower than the cross-linking temperature of the connecting portion insulator is laid over the connecting portion insulator and the cable outer semiconductive layer on both sides thereof. In this manner, the connection portion insulator is shrunk by heating, and then the connection portion insulator is cross-linked by heating under pressure.

As the semiconductive heat-shrinkable tube, it is desirable to use a tube having high-density polyethylene as a base polymer.

[0008]

According to the connection method of the present invention, when the connection insulator is cross-linked by heating under pressure, the connection insulator and the cable insulator first begin to melt in the process of increasing the temperature. At this time, the semiconductive heat-shrinkable tubing is not melted, so the smooth inner surface of the semiconductive heat-shrinkable tubing is pressed against the surface of the connection insulator and the cable insulator by the pressure from the outer periphery, and the insulation between them is reduced. The body surface is smoothed. When the temperature further rises, the semiconductive heat-shrinkable tube melts and fuses to the connecting portion insulator and the cable insulator. After that, when the temperature required for the cross-linking has been reached, the connection insulator is cross-linked by maintaining the temperature for a predetermined time.

As described above, according to the connection method of the present invention, the surface smoothing process of the connecting portion insulator and the cable insulator and the bridging of the connecting portion insulator are continuously performed. In the process, a connection portion having no defect such as a conductive protrusion can be obtained in the connection portion external semiconductive layer.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for connecting a crosslinked polyethylene insulated power cable according to the present invention will be described below in detail with reference to the drawings. The cable used in the examples had a voltage of 275
KV, cross-linked polyethylene insulated power cable conductor size 2000 mm ^2.

Embodiment 1 First, in FIG. 1, before connecting the crosslinked polyethylene insulated power cables 11a and 11b, a semiconductive heat-shrinkable tube 13 is extrapolated to the cables together with parts required for connection. The semiconductive heat-shrinkable tube 13 is made of high-density polyethylene having a melting point of 129 ° C. as a base polymer,
This is obtained by adding carbon for imparting conductivity and an antioxidant.

Next, the cable outer semiconductive layers 15a, 15b of the cables 11a, 11b are stripped off by a predetermined length to expose the cable insulators 17a, 17b, and their ends are tapered, and the cable conductors 19a, 17b are processed. , 19b are exposed.
Then, the cable conductors 19a and 19b are compression-connected by the conductor connection tube 21, and the connection portion inner semiconductive layer 23 is formed thereon by a semiconductive tape or a semiconductive heat shrink tube.

Thereafter, a two-piece mold (not shown) is put over the cable insulators 17a and 17b on both sides, and a non-crosslinked polyethylene containing a crosslinking agent is extruded therein by a small extruder. The connection insulator 25 is formed. After this cools down to a predetermined temperature, the mold is removed, and the connecting portion insulator 25 is shaped into a predetermined shape using a power tool or a piece of glass in a simple clean room.

Next, the semiconductive heat-shrinkable tube 13 previously extrapolated to the cable is pulled back and set so as to straddle the connecting portion insulator 25 and the cable external semiconductive layers 15a and 15b on both sides thereof. Thereafter, for example, hot air is blown by a dryer or the like to be heated and shrunk, and the connection portion insulator 25, the cable insulators 17a and 17b, and the cable outer semiconductive layers 15a and 15b
In close contact.

Thereafter, as shown in FIG. 2, a gas barrier layer 27 for cross-linking and a heater (not shown) are attached, and a pressurizing and heating device 29 is further attached. The connection insulator 25 is crosslinked by heating and pressurizing with an active gas. At this time, in order to prevent foaming of the polyethylene, the temperature of the connecting portion insulator and the cable insulator are individually controlled using, for example, a temperature sensor.

FIG. 3 shows a pattern of a rise in the temperature of the connecting portion insulator at the time of crosslinking. Incidentally, as described above, high-density polyethylene, which is the base polymer of the semiconductive heat-shrinkable tube 13, has an extremely high melting point of 129 ° C.
(About ℃).

According to the temperature rise pattern in the crosslinking step shown in FIG. 3, during the process of raising the temperature from room temperature (Tr: 25 ° C.) to the crosslinking temperature (Tm: about 150 ° C.)
When the temperature exceeds about 105 ° C., the surfaces of the connection insulator 25 and the cable insulators 17a and 17b begin to melt. At this time, since the semiconductive heat-shrinkable tube 13 is not melted, the smooth inner surface of the semiconductive heat-shrinkable tube 13 is pressed against the connection portion insulator 25 and the cable insulators 17a and 17b by a pressing force, and the The surface of the insulator is smoothed. Thereafter, when the temperature rises to about 129 ° C., the semiconductive heat-shrinkable tube 13 melts, and the connection insulator 25 and the cable insulator 17 are melted.
a, 17b and the cable outer semiconductive layers 15a, 15b. If the temperature further rises and reaches a cross-linking temperature of, for example, 150 ° C., the connection insulator 25 is cross-linked by maintaining this for, for example, 5 hours.

When the heat capacity of the connecting portion is small, the time required for raising the temperature from the melting point of the connecting portion insulator and the cable insulator to the crosslinking temperature is short, and the time required for the smoothing process is short. As shown in FIG. 4, it is possible to intentionally set the temperature rise stagnation time for the smoothing process. That is, the connecting portion insulator 25 and the cable insulators 17a, 17b
Is in a molten state, and when the temperature reaches a temperature at which the semiconductive heat-shrinkable tube 13 is not melted, for example, 120 ° C., for example, it is maintained for one hour to perform a smoothing treatment. In this way, even if the heat capacity of the connection portion is small, the surfaces of the connection portion insulator 25 and the cable insulators 17a and 17b can be surely smoothed.

Example 2 In this example, a semiconductive heat-shrinkable tube was made of a linear low-density polyethylene having a melting point of 127 ° C. as a base polymer, and carbon for imparting conductivity and an antioxidant were used. The composition added and blended was used.
The same cable as in Example 1 was used, and an extrusion-molded connection was manufactured by the same means.

An electrical breakdown test was performed on the connection parts manufactured according to Examples 1 and 2 and the connection part according to the conventional method. The results are as follows.

The connection portion according to the first embodiment has a breakdown voltage
The concentration was in the range of 1200 to 1260 KV (the number of samples n = 3).
The connection portion according to the second embodiment has a breakdown voltage of 1290 to 1350 KV.
(N = 3). The connection part by the conventional method had a breakdown voltage of 860 to 910 KV (n = 2), and all were broken by the processing part of the connection outside semiconductive layer. When the fracture holes were examined, the starting points of the fracture were all conductive protrusions of the semiconductive layer outside the connection portion.

As described above, it has been confirmed that the connection portions according to the first and second embodiments of the connection method according to the present invention have much better electric characteristics than the connection portions according to the conventional connection method.

The base polymer of the semiconductive heat-shrinkable tube used in the present invention is not limited to the high-density polyethylene or the linear low-density polyethylene used in the examples. The base polymer only needs to have a certain conductivity as a compound, and have a melting point higher than the melting point of the connecting portion insulator and lower than the crosslinking temperature of the connecting portion insulator.

As the base polymer of the semiconductive heat-shrinkable tube, olefin resins such as general low density polyethylene, ethylene ethyl acrylate copolymer and ethylene ethyl acrylate copolymer can be used. Further, a blend of two or more polymers may be used. Although the melting point of the base polymer depends on the rate of rise to the cross-linking temperature, a melting point higher than the melting point of the connection insulator by 2 ° C. or more is practical when temperature measurement errors are considered.

[0025]

As is apparent from the above description, according to the method for connecting a crosslinked polyethylene insulated power cable according to the present invention, the melting point of the semiconductive heat-shrinkable tube for the external semiconductive layer at the connection portion is determined by the following method. Since the temperature is higher than the melting point of the insulator and lower than the cross-linking temperature of the connection insulator, if the temperature is increased to bridge the connection insulator, the connection insulator and the cable insulator will melt. When the heat treatment begins, the semiconductive heat-shrinkable tubing does not melt. At this time, the smooth inner surface of the semiconductive heat-shrinkable tubing is pressed against the connection insulator and the cable insulator by the pressing force, and the surface of the insulator is shrunk. Is smoothed.

When the temperature further rises, the semiconductive heat-shrinkable tube melts and fuses to the connection portion and the insulator of the cable,
Thereafter, when the cross-linking temperature is reached, the connecting portion insulator is cross-linked.

Therefore, even if there are some scratches on the surface of the insulator of the connection portion, the damage is corrected smoothly, and the external semiconductive layer of the connection portion does not dig into the surface of the insulator as a protrusion, so that the electrical connection is surely achieved. Thus, a connection portion of a crosslinked polyethylene insulated power cable having high performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an intermediate step in one embodiment of a method for connecting a crosslinked polyethylene insulated power cable according to the present invention.

FIG. 2 is a sectional view showing a final step in the same manner.

FIG. 3 is a graph showing one pattern of temperature rise at the time of crosslinking in one embodiment of the method for connecting a crosslinked polyethylene insulated power cable according to the present invention.

FIG. 4 is a graph showing another pattern.

[Explanation of symbols]

11a, 11b: Cross-linked polyethylene insulated power cable 13: Semi-conductive heat-shrinkable tube 15a, 15b: Cable outer semi-conductive layer 17a, 17b: Cable insulator 19a, 19b: Cable conductor 21: Conductor connection tube 23: Connection inner half Conductive layer 2
5: Connection insulator 27: Gas barrier layer for crosslinking 29: Pressurized heating device

Continued on the front page (72) Inventor Susumu Sakuma 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd. (72) Inventor Tetsuo Matsumoto 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. Inside the company (72) Inventor Yoshihisa Takahashi 1-3-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Inside Tokyo Electric Power Company

Claims (2)

(57) [Claims] 1. A semiconductive material whose melting point is higher than the melting point of the connecting part insulator and lower than the cross-linking temperature of the connecting part insulator, after forming the connecting part insulator by extrusion molding of uncrosslinked polyethylene and shaping. The heat-shrinkable tube is covered with the connecting portion insulator and the outer semiconductive layer of the cable on both sides thereof so as to be heated and shrunk, and thereafter, the connecting portion insulator is pressurized and heated to crosslink. Connection method of cross-linked polyethylene insulated power cable. 2. The method for connecting a crosslinked polyethylene insulated power cable according to claim 1, wherein the semiconductive heat-shrinkable tube is made of high-density polyethylene as a base polymer.