JPH04150714A - Insulation block for power cable joint and power cable joint - Google Patents

Abstract

PURPOSE:To obtain an insulation block for power cable joint having enhanced contact tightness and reduced outer diameter at the joint by enlarging the minimum inner diameter larger than the outer diameter of the core of the power cable thereby imparting thermal contraction properties while furthermore profiling such that the insulator profile is recovered at the joint of the power cable upon thermal contraction. CONSTITUTION:A crosslinked polyethylene insulated power cable is cut substantially as long as a cable joint, a central conductor is pulled out to produce a tubular crosslinked polyethylene insulator having inner and outer peripheral surfaces applied with semiconductive layers which is then profiled as shown on the drawing. Thus profiled insulator 23 is then heated to a predetermined temperature and a mandrel is pushed therein thus enlarging the inner diameter larger than the outer diameter of the core of the cable. It is then cooled and the mandrel is drawn out thus producing an insulation block 21 having profile as shown on the drawing. Since the insulation block 21 is heated and then cooled under forcibly enlarged state, it has thermal contraction properties and recovered to the original profile upon heating.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a technology for connecting crosslinked polyethylene insulated power cables.

[Prior art]

As the application of cross-linked polyethylene insulated power cables to ultra-high voltage lines progresses, shortening the time required for connection work has become a major issue in streamlining line construction.

In other words, the mold method is a connection technology for cross-linked polyethylene insulated power cables with a voltage class of 154 Kv or higher.
Although stable and high performance can be expected, the drawback is that it takes a long time to connect.

Recently, so-called prefabricated joints, in which insulating parts preformed in a factory are assembled on-site, have been developed and are about to be put into practical use. However, prefabricated joints use epoxy resin and rubber for the reinforcing insulator, which cannot be used due to the high electrical stress compared to cross-linked polyethylene, which limits the ability to reduce the size of the connection. However, on 275KV and 500KVK class lines, the places where it can be applied are limited due to space constraints.

Therefore, as a connection method that combines the high performance of the mold method with the simplicity of prefabricated joints to some extent, the connection insulator is prefabricated in the factory as an uncrosslinked or crosslinked insulating block, and then cables are connected on site. A so-called block molding method has been proposed, in which the cable is attached to the cable and integrated with the cable by applying pressure and heating to crosslink it.

〔assignment〕

Figure 7 is an insulating block that has been used conventionally.
There are two types of insulating block 11: a split-type insulating block 11 shown in FIG. 8, and a cylindrical insulating block 13 shown in FIG.

The split-type insulating blocks 11 are difficult to design because high electrical stress is applied to the adhesive interface between the insulating blocks 11, and the internal conductive layer of the connection part flows into the joint of the insulating blocks 11, resulting in a conductive layer. There is a phenomenon of protrusions, and it has been difficult to take measures to prevent this.

On the other hand, in the case of the cylindrical insulating block 13, it is inserted into the cable insulator in advance, connected to the conductor, and then pulled back to the cable connection position. It is necessary to lengthen the stripping process, which increases the overall length of the connection. Furthermore, since the inner diameter of the insulating block is equal to the outer diameter of the cable insulator, the outer diameter of the connection portion also becomes larger. Furthermore, in order to insert a highly rigid cylindrical insulating block into the cable, it is necessary to provide a clearance between the insulating block and the cable insulator, and if this clearance is provided, sufficient adhesion with the cable insulator cannot be obtained. [Means for solving the problem and its effects] The invention of claim 1 provides an insulating block for connecting cross-linked polyethylene insulated power cables that solves the above problems. The structure consists of a cylindrical cross-linked polyethylene insulator cut from a cross-linked polyethylene insulated power cable, expanded in diameter so that the minimum inner diameter is greater than the core outer diameter of the cross-linked polyethylene insulated power cable to be connected, and heat-shrinkable. It is characterized in that the outer shape is processed so that it assumes the shape of an insulator of a cross-linked polyethylene insulated power cable connection part when it is heat-shrinked.

The external shape of the crosslinked polyethylene insulator may be processed before or after the diameter expansion process.

In this invention, the reason why a cylindrical crosslinked polyethylene insulator cut from a crosslinked polyethylene insulated power cable is used is to ensure the same quality as the cable insulator in the connection part insulating block.

In addition, the inner diameter has been enlarged to be larger than the cable core diameter to enable insertion over the cable core, shorten the length to strip the cable protection layer, shorten the overall length of the connection part, and provide heat shrinkability. This is to reduce the outer diameter of the connection part.

Furthermore, the external shape was processed to take the shape of an insulator at the connection part when it is heat-shrinked, which not only increases the adhesion with the cable insulator, but also reduces the outer diameter of the connection part. This is to make it possible to configure a connection part with the same diameter as the power cable.

In addition, if the cross-linked polyethylene insulator is cut from the cross-linked polyethylene insulated power cable after the insulation test is completed (invention of claim 2), the reliability of the insulation performance as the connection part insulation block will be more reliable. Become something.

Further, if the cross-linked polyethylene insulator is coated with a semi-conductive layer cut from a cross-linked polyethylene insulated power cable together with the cross-linked polyethylene insulator on at least one of its inner peripheral surface and outer peripheral surface, ), it is possible to omit or simplify the formation work of the inner semiconducting layer or the outer semiconducting layer during the connection work, and it is possible to prevent defects from occurring at the interface between the crosslinked polyethylene insulator and the inner or outer semiconducting layer.

To connect a cross-linked polyethylene insulated power cable using an insulating block as described above, insert the insulated block into one side of the cross-linked polyethylene insulated power cable to be connected, connect the cable conductor, and then pull the insulated block back to connect the conductor. The insulating block is set so as to straddle the cable insulators on both sides of the connection, and the insulating block is heated to shrink, and then further pressurized and heated to integrate with the cable insulator.
The following steps are taken (invention of claim 4).

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 and FIG. 2 show an example of an insulating block for connecting a cross-linked polyethylene insulated power cable according to the present invention in the order of manufacturing steps.

First, cut a cross-linked polyethylene insulated power cable (not shown) to the same length as the cable connection part, pull out the central conductor, and then cut the cross-linked polyethylene insulated power cable (not shown) into a cylindrical cross-linked polyethylene cable with a semiconductive layer on the inner and outer circumferential surfaces. Get an insulator. In this case, it is desirable to use a cross-linked polyethylene insulated power cable that has passed an insulation test (extrusion test).

Next, the insulator obtained as described above is shaped as shown in Figure 1. That is, the cylindrical crosslinked polyethylene insulator 23
On the inner surface of the cable, a predetermined length of the inner semiconductive layer 25 of the cable is left in the center, and cylindrical inner surfaces 27a and 27b are formed at both ends of the inner semiconductive layer 25, and an inner tapered portion 29a is formed at both ends. , 29b. It is desirable that the inner taper portions 29a, 29b have the same dimensions as the taper portion formed on the insulator of the cable to be connected, or slightly smaller dimensions.

Further, on the outer surface of the crosslinked polyethylene insulator 23, a predetermined length of the outer semiconductive layer 31 of the cable is left, and cylindrical outer surfaces 33a and 33b are formed at both ends thereof.

Next, the cross-linked polyethylene insulator 23, which has been shaped as shown in Figure 1, is heated to a predetermined temperature, for example, about 130°C, and a mandrel is pushed into it, so that the inner diameter becomes equal to or larger than the outer diameter of the core of the cable to be connected. Expand the diameter to. Thereafter, it is cooled and the mandrel is pulled out, thereby obtaining an insulating block 21 having a shape as shown in FIG. 2. This insulating block 21 has heat shrinkage because it is heated and forcibly expanded in diameter and then cooled and solidified.
Return to the shape of. Therefore, by using this insulating block 21, a power cable connection section can be easily constructed.

Regarding the heating temperature during diameter expansion, if the temperature is too high, foaming will occur due to residual methane gas in the insulator, and if the temperature is too low, the insulator will be strained and cracks will occur during diameter expansion with a mandrel. Decide by taking into account.

The method for connecting power cables using this insulating block 21 will be described later, but if a semiconductive layer is provided on the outer periphery of the cable conductor connection portion during connection, the semiconductive layer 25 on the inner surface of the crosslinked polyethylene insulator 23 is In addition, when the outer periphery of the insulating block 21 is covered with a semiconductive heat-shrinkable tube or the like to form an external semiconductive layer, the semiconductive layer on the outer surface of the crosslinked polyethylene insulator 23 can be removed. It is also possible to eliminate layer 31.

FIG. 3 and FIG. 4 show another embodiment of the crosslinked polyethylene insulated power cable connection insulating blower according to the present invention in the order of manufacturing steps.

First, cut the cross-linked polyethylene insulated power cable to the same length as the cable connection, pull out the center conductor,
Obtaining the crosslinked polyethylene insulation is similar to the previous example.

Next, the insulator thus obtained is shaped as shown in Figure 3. That is, the inner surface of the cylindrical cross-linked polyethylene insulator 23 has an outer surface of the inner semiconducting layer formed at the center thereof to fit into the inner semiconducting layer of the connecting section formed on the compression connecting section of the cable conductor. An inner surface processing portion 35 having an inner diameter slightly smaller than the diameter is formed, and inner surface tapered portions 29a, 2 are formed at both ends thereof.
9b, and cylindrical inner surfaces 3Qa, 30b having an inner diameter larger than the outer diameter of the cable core are formed at both ends thereof. It is desirable that the inner taper portions 29a, 29b have the same size as the taper portion formed on the insulator of the cable to be connected, or slightly smaller size.

Further, on the outer surface of the crosslinked polyethylene insulator 23, a predetermined length of the outer semiconductive layer 31 of the cable is left, and outer surface tapered portions 39a and 39b are formed at both ends thereof.

Thereafter, the diameter of the cross-linked polyethylene insulator 23 is expanded in the same manner as in the previous example so that the inner diameter is larger than the outer diameter of the core of the cable to be connected, and an insulating block 21 having a shape as shown in FIG. 4 is obtained. . This insulating block 21 has heat shrinkability and returns to the shape shown in FIG. 3 when heated.

In the above embodiments, the insulating block 21 was manufactured after the outer shape was processed and then the diameter was expanded, but the outer shape may be processed after the diameter was expanded. When the outer shape is processed after the diameter has been expanded, the heat shrinkage rate (diameter expansion rate) of each part will be the same, so the cross-sectional shape will be approximately as shown in Figure 1 or Figure 3, and the minimum inner diameter will be smaller than the outer diameter of the cable core. It becomes something big.

The insulation block 21 of the two embodiments described above is made of DCP (dicumyl peroxide) at about 50°C.
By immersing the cable in the cable for 2 hours and diffusing a small amount of DCP (crosslinking agent) on and near the surface, the crosslinking reaction is promoted in the subsequent pressurization and heating process, improving the adhesive strength with cable insulation, etc. can be done.

Figure 5 shows an example of the method for connecting cross-linked polyethylene insulated power cables according to the present invention.
75KV 1400m5” (insulator outer diameter 103++
n, outer semiconductive layer outer diameter 105-1, inner semiconductive layer outer diameter 4
9111-) cross-linked polyethylene insulated power cable.

The insulating block used was made from the same cable and had the structure shown in Figure 2, and its expanded inner diameter was 110 m.

In this connection method, first, the ends of the cables to be connected are stripped to a predetermined length and shape, and then necessary parts such as the insulation block 21 and the bridging gas barrier layer are inserted into the cables. Next, the cable conductors 41a and 41b are welded together to form a welded joint 43. When welding and connecting, a two-split water cooling device (not shown) is installed on the cable conductors 41a, 41b to be welded so that the internal conductive layers 45a, 45b and cable insulators 47a, 47b are not affected by heat. Install and weld while cooling.

Furthermore, when performing welding connections, it is recommended to cover the insulating block 21 with a heat insulating material (not shown) so that the insulating block 21 inserted into the cable does not shrink due to radiant heat.

After welding and connecting the cable conductors 41a and 41b, the insulating block 21, which had been inserted into the cable in advance, is placed in the center of the connection, and a two-split heat shrinking device (not shown) is set on its outer periphery. The insulating block 21 is heated and shrunk. The insulating block 21 includes an internal semiconducting layer 2
5 is provided integrally with the crosslinked polyethylene insulator 23, so when the insulating block 21 contracts, the internal semiconducting layer 25 becomes the internal semiconducting layer of the connection part, and the crosslinked polyethylene insulator 23 serves as reinforcing insulation of the connection part. It becomes a layer.

Even if the insulating block 21 is heat-shrinked, the interface 5 between the crosslinked polyethylene insulator 23 and the cable insulators 47a and 47b
A fitting error occurs between 3a and 53b, creating a gap, and the gap is not filled even after pressurizing and heating, and the interface 53a
, 53b may occur. To prevent this phenomenon, either make the cable step stripping dimension slightly wider as shown by the dotted line in Figure 5, or
Alternatively, as described above, a cross-linked polyethylene insulator 23 whose internal tapered portions 29a and 29b are made slightly smaller in size than the tapered portion of the cable insulator is used.

In this way, residual stress can be applied to the crosslinked polyethylene insulator 23 when the insulation block 21 is thermally shrunk. This action ensures interfacial adhesion,
Poor adhesion at the interface due to dimensional errors can be avoided.

Once the insulating block 21 has shrunk, the semiconductive heat shrink tubes 49a and 49b inserted into the cable in advance are returned to the outer semiconductive layer 31 and the outer semiconductive layer 51 of the cable.
Set it so as to cover the space between a and 51b.

Next, a crosslinking gas barrier layer that has been inserted into the cable in advance is attached to the outer periphery of the connection, and the entire connection is pressurized and heated using a pressure tube. Through this crosslinking process, the interface 53a between the crosslinked polyethylene insulator 23 and the cable insulator
, 53b are fused and integrated to complete reinforcing insulation at the connection portion. At this time, the above-mentioned DCP improves the adhesive force at the interface. Further, the semiconductive heat-shrinkable tubes 49a and 49b are heat-shrinked to form the outer semiconductive layer 31 and the outer semiconductive layer 5 of the cable.
1a and 51b are connected, and an external conductive layer of the connection portion is formed.

Finally, a shielding layer is formed on the outer semiconducting layer of the connection to complete the connection.

FIG. 6 shows another embodiment of the method for connecting a cross-linked polyethylene insulated power cable according to the present invention. The cable used was the same as in the previous example. The insulating block used is a cross-linked polyethylene insulator with the same conductor cross-sectional area as the cable to be connected, the same internal conductive layer structure, and an insulation thickness of 32 fi (the insulation thickness of the cable to be connected is 27 m), which has been inspected before shipping. It is cut from a power cable, processed into the shape shown in Figure 3, and then expanded in diameter to the shape shown in Figure 4.

In this connection method, first, the ends of the cables to be connected are stripped to a predetermined length and shape, and then necessary parts such as the insulation block 21 and the bridging gas barrier layer are inserted into the cables. Next, the cable conductors are compressed and connected using an ordinary compression connection sleeve 57, and a connection internal semiconductive layer 59 is formed on the outer periphery of the cable conductor.

After that, the insulation block 21 that had been inserted into the cable in advance
is placed in the center of the connection part, and the insulating block 21 is heated and shrunk in the same manner as in the previous embodiment. When the insulating block 21 contracts, the crosslinked polyethylene insulator 23 directly serves as a reinforcing insulating layer at the connection portion. The subsequent steps are the same as in the previous example.

By the way, even if the insulating block 21 is heat-shrinked, a fitting error will occur at the interfaces 53a, 53b between the crosslinked polyethylene insulator 23 and the cable insulators 47a, 47b, resulting in a gap, and even if the insulation block 21 is subsequently heated under pressure, the gap will not be closed. Otherwise, poor adhesion between the interfaces 53a and 53b and between the crosslinked polyethylene insulator 23 and the internal semiconducting layer 59 may occur. In order to eliminate adhesion defects at the interfaces 53a and 53b, as in the previous embodiment, the cable step-stripping dimension should be slightly shifted by k to make it thicker, as shown by the dotted line in Figure 6.
Or inner tapered part 2 of cross-linked polyethylene insulator 23
It is sufficient to use cables 9a and 29b whose dimensions are slightly smaller than the dimensions of the tapered portions of cable insulators 47a and 47b.

Furthermore, poor adhesion between the cross-linked polyethylene insulator 23 and the internal semi-conductive layer 59 is caused by the fact that the internal diameter of the cross-linked polyethylene insulator 23 before diameter expansion is slightly smaller than the outer diameter of the internal semi-conductive layer 59, as explained in FIG. This can be solved by keeping it.

〔Effect of the invention〕

As explained above, the present invention has the following effects.

■ The connection insulation block uses a cylindrical crosslinked polyethylene insulator cut from a crosslinked polyethylene insulated power cable, so it can guarantee the same high level of quality as the cable insulation, and the reliability of the connection. Improves sex. In particular, if a crosslinked polyethylene insulator cut from a crosslinked polyethylene insulated power cable after an insulation test is used, the reliability of the insulation performance as a connection part insulation block will be more reliable.

■ The insulating block has an inner diameter larger than the cable core diameter, so it can be inserted over the cable core.
Therefore, the peeling length of the cable protection layer can be shortened, and the total length of the connection portion can be shortened.

■ The insulation block is heat-shrinkable, and its external shape is processed so that it takes on the shape of an insulator at the connection part when it is heat-shrinked, so it can improve adhesion to cable insulation, etc. , the outer diameter of the connection part can be reduced.

■ If you use a crosslinked polyethylene insulator that has a semiconducting layer cut out from a crosslinked polyethylene insulated power cable along with the crosslinked polyethylene insulator on at least one of its inner and outer circumferential surfaces, internal semiconductivity will be removed during connection work. The formation of the layer or outer semiconducting layer can be omitted or simplified, and defects at the interface between the crosslinked polyethylene insulator and the inner or outer semiconducting layer are eliminated.

[Brief explanation of the drawing]

Figures 1 and 2 are sectional views showing one embodiment of the insulating block according to the present invention in the order of manufacturing steps, and Figures 3 and 4 are sectional views showing other embodiments of the insulating block according to the present invention in the order of manufacturing steps. Cross-sectional view, Figure-5 is a cross-sectional view showing an example of a method for connecting a cross-linked polyethylene insulated power cable using the insulating block shown in Figure-2, and Figure-6 is a cross-sectional view showing an example of a method for connecting a cross-linked polyethylene insulated power cable using the insulating block shown in Figure-4. A sectional view showing another embodiment of a method for connecting an insulated power cable, FIG. 7 is a perspective view showing a conventional split-type insulation block, and FIG. 8 is a perspective view showing a conventional cylindrical insulation block. 21: Insulation block 23: Cross-linked polyethylene insulator 25; Internal semiconductive layer 31: External semiconductive layer 35: Inner surface processed portion 41a, 41b: Cable conductor 43: Welded connection portion 45a, 45b: Cable internal semiconductive layer 47 a ,
47 b: 'r-pull WjAm bodies 49a, 49b
: Semiconductive heat shrinkable tubes 51a, 51b two cables External semiconductive layer 57: Compression connection sleeve 59: Connection part internal semiconductive layer -

Claims (1)

[Claims] 1. Consisting of a cylindrical cross-linked polyethylene insulator cut from a cross-linked polyethylene insulated power cable, the diameter is expanded so that the minimum inner diameter is equal to or larger than the core outer diameter of the cross-linked polyethylene insulated power cable to which it is connected. It is given contractility,
An insulating block for connecting a cross-linked polyethylene insulated power cable, characterized in that the insulating block for connecting a cross-linked polyethylene insulated power cable is processed to have an outer shape so that it assumes the shape of an insulator at a connecting portion of the cross-linked polyethylene insulated power cable when it is thermally shrunk. 2. The insulating block according to claim 1, wherein the crosslinked polyethylene insulator is cut from a crosslinked polyethylene insulated power cable after an insulation test. 3. The insulating block according to claim 1 or 2, wherein the cross-linked polyethylene insulator has a semi-conductive layer on at least one of its inner circumferential surface and outer circumferential surface, and this semi-conductive layer comprises a cross-linked polyethylene insulator. characterized in that it is a semiconducting layer of a cross-linked polyethylene insulated power cable cut out with its body. 4. Using the insulating block according to any one of claims 1, 2, or 3, inserting the insulating block into one side of the connecting cross-linked polyethylene insulated power cable, connecting the cable conductor, and then pulling back the insulating block. Set it so that it straddles the cable insulators on both sides of the conductor connection, heat the insulating block to shrink it, and then pressurize it further.
A method for connecting a cross-linked polyethylene insulated power cable, characterized by heating and integrating it with a cable insulator.