JPH05103408A - Technique for connecting extrusion molds for electric cable - Google Patents

Abstract

PURPOSE:To form a reinforced insulating layer of an even quality by increasing a crosslinker continuously from the beginning to the end when a base resin and an anti-oxidizing agent are melt kneaded and injected by a extruder into a metallic die the connecting ends of which are covered at a laying site. CONSTITUTION:The ends of electric cables 1a and 1b are gradationally stripped at a laying site to allow the conductor to be exposed and coupled by compression. Then, after the inner semiconductor layer is formed, the conductor is set into a metallic die 7 which is divided into two parts. A base resin and an anti-oxidizing agent are melt kneaded from a hopper 10 to an extruder 9 by supplying the pellets which are kneaded in advance in a plant. A crosslinker is supplied from a supplier 11 in a gradually increased quantity. Thus, both of them are melt kneaded and injected into the metallic die 7 through an injection inlet 7a. Also, a mixture of a base resin, anti- oxidizing agent and crosslinker is prepared in the plat from the outset, and cast into the hopper at the laying site for kneading, and then, a crosslinker adjuster is being injected from the supplier 11 in a gradually reduced quantity. In this way, a reinforced insulator can be easily produced at the laying site without containing any foreign particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extrusion molding type connection method for power cables, which is performed at a cable laying site.

[0002]

2. Description of the Related Art A power cable having an insulating layer formed of a crosslinked polyolefin such as crosslinked polyethylene has excellent insulation properties and is easy to handle. It is beginning to be used. For example, using this power cable, 2
Construction of a long-distance line of 75 kV class is underway.

In constructing such a long-distance line,
Since it is impossible to construct the entire length of the laying with a single power cable, it is unavoidable to extend the power cable by connecting power cables of appropriate length to each other. The extrusion molding type connection method has been conventionally used for the interconnection of such power cables at a construction site. The extrusion molding type connection method will be described below with reference to FIG.

First, the power cables 1a and 1b to be connected
The conductors 2a, 2b are exposed by exposing the conductors 2a, 2b by stepping off each end of the conductors, and the conductors 2a, 2b and the conductor connecting pipe 3 are inserted into the conductor connecting pipe 3 and compression-connected to each other.
The inner semiconductive layer 4 is formed on the outer side of the substrate using a semiconductive tape or a semiconductive heat shrinkable tube. Then, the outside of this connecting portion is covered, for example, a mold (not shown) divided in two is arranged, and a polyolefin resin composition containing a polyolefin resin, an antioxidant and a cross-linking agent as essential components is melted. It is melted at a temperature above and below the crosslinking temperature and cast into the mold. This casting is done using a small extruder located at the installation site.

After the casting is completed, the connecting portion is cooled, the die is removed, the outer side of the formed casting resin layer is cut into a predetermined shape, and then a semiconductive tape or a semiconductive heat shrinkable tube is placed on the outside. To form the outer semiconductive layer 6. Next, this connection A is set in a pressure vessel and heated at the crosslinking temperature while pressurizing with gas. Thus, the cross-linking reaction of the polyolefin resin occurs in the cast resin layer, and the reinforcing insulator layer 5 made of the cross-linked polyolefin resin composition is formed.

[0006]

However, the above-mentioned conventional extrusion mold type connecting method has the following problems. The first problem is that the casting resin layer is heated only from the outside and the heat conductivity of the casting resin layer is not good. Therefore, in the process of heat crosslinking, the casting resin layer is separated from the outer layer portion and the inner layer portion. There is a problem that a temperature gradient is generated between the two, the cross-linking conditions are different between the outer layer portion and the inner layer portion, and the cross-linking of the casting resin layer does not proceed simultaneously in terms of time as a whole.

That is, although the outer layer portion is heated to a predetermined temperature in the initial stage of heat crosslinking to allow a sufficient crosslinking reaction to proceed, at that time, the inner layer is not yet heated to the predetermined temperature. This means that the crosslinking reaction has not proceeded in some parts. Therefore, the total cross-linking of the casting resin layer is defined by the cross-linked state of the inner layer portion.

This means that when the casting resin layer as a whole is completely crosslinked, until the crosslinking reaction of the inner layer portion is completed,
That is, it is necessary to continue heating the outer layer portion where the crosslinking reaction has already been completed in the initial stage of heating. However, such heating is excessive heating for the outer layer portion, and is not only completely wasteful in terms of thermal energy, but also causes a difference in the degree of decomposition of the crosslinking residue between the outer layer portion and the inner layer portion, This may cause differences in the cross-linked state, composition, structure, etc. between the two layers. For example, due to this excessive heating, moisture may be generated in the outer layer portion,
Since the whole is pressurized, even if this moisture does not grow into voids, it is possible that the characteristics of the formed reinforcing insulating layer are deteriorated.

The second problem is a problem that a high melting point resin is used as a base resin as a recent tendency. High-melting-point resins have begun to be used as the base resin in order to improve the insulating property and heat resistance of the reinforcing insulating layer in the connection portion. When performing the extrusion mold connection method using the high melting point resin, when casting the resin composition consisting of the high melting point resin, the antioxidant and the crosslinking agent into the mold from a small extruder, In order to remove foreign substances that are mixed in the resin composition and also cause dielectric breakdown of the formed reinforcing insulation layer, a screen mesh is attached to the extrusion port of the small extruder and poured into the mold. Typed.

In this case, since the base resin used has a high melting point and the screen mesh has resistance,
It is necessary to raise the extrusion temperature from the small extruder to a high temperature to sufficiently melt the resin composition and increase its fluidity.
However, when the extrusion temperature is raised, the temperature approaches the decomposition temperature of the crosslinking agent contained in the resin composition,
Alternatively, the decomposition temperature may be exceeded, and as a result, the crosslinking reaction may occur before the casting into the mold. Such problems can of course be avoided by lowering the extrusion temperature, but in that case, it is very difficult to cast into the mold because the base resin is not sufficiently melted. Becomes

An object of the present invention is to solve the above-mentioned problems in the extrusion mold type connection method for power cables and to provide an extrusion mold type connection method for power cables that enables highly reliable connection.

[0012]

In order to achieve the above-mentioned object, in the present invention, at the installation site of a power cable, a mold is arranged by enclosing the mutual connection portions of the power cable and arranging a mold. A resin composition containing a resin, an antioxidant, and a cross-linking agent as essential components is melt-kneaded by using an extruder and then extruded and injected into a mold, which is then heat-crosslinked to reinforce the insulation at the connecting portion. In the extrusion mold type connection construction method of the power cable forming a layer, in the laying site, bring a kneaded material containing a base resin and an antioxidant and not a cross-linking agent in the resin composition, and put this in an extruder. Extrusion mold type connection of a power cable, characterized in that the resin composition is melted and kneaded while being fed into the extruder while increasing the amount of the crosslinking agent stepwise or continuously from the initial stage to the end of extrusion. In addition, a kneaded material containing a base resin, an antioxidant and a cross-linking agent but not a cross-linking regulator is brought into the laying site, and the kneaded material is put into an extruder, and from the initial stage of extrusion. Provided is an extrusion mold type connection construction method for a power cable, which is characterized in that the resin composition is melted and kneaded by supplying it to an extruder while reducing the amount of a crosslinking regulator stepwise or continuously until the end.

The base resin used in the method of the present invention may be any as long as it is used as the base resin of the reinforcing insulating layer in the conventional extrusion mold type connection method, for example, low density polyethylene. , Polyolefin resin such as ultra low density polyethylene, linear low density polyethylene, ethylene ethyl acrylate copolymer, ethylene vinyl acetate copolymer, ethylene acrylic acid copolymer, and fluororesin such as polytetrafluoroethylene Can be raised. Among these, crystalline polyethylene having a high melting point is suitable for use because the reinforcing insulating layer obtained has excellent insulating properties and heat resistance.

The antioxidant is also not particularly limited and includes, for example, 4,4-thiobis (3-methyl-6-t-butylphenol) and bis [2-methyl-4- (3-n-alkylthio). Propionyloxy) -5-t-butylphenyl] sulfide, 2,5-di-t-butylhydroquinone, 2,6-di-t-butyl-p-cresol, 2,
2'-thiodiethylenebis- [3- (3,5-di-t-
Butyl-4-hydroxyphenyl) propionate],
Examples include dilauryl thiodipropionate and distearyl thiodipropionate. These may be used alone or in combination of two or more. Among these antioxidants, 4,4-thiobis (3-methyl-6-t-butylphenol) and bis [2-methyl-4- (3-
n-Alkylthiopropionyloxy) -5-t-butylphenyl] sulfide is particularly preferred.

Further, an organic peroxide is used as the crosslinking agent. As the organic peroxide, for example, m- (t
-Butylperoxyisopropyl) -isopropylbenzene, p- (t-butylperoxyisopropyl) -isopropylbenzene, dicumyl peroxide, t-butylcumyl peroxide, α, α'-bis (t-butylperoxy-m-isoprop)- Benzene etc. can be given.

The cross-linking regulator added as necessary in order to suppress excessive progress of cross-linking includes, for example,
There is 2,4-diphenyl-4-methyl-1-pentene, which has not only the effect of suppressing crosslinking, but also has the ability to dissolve many of the above-mentioned organic peroxides, and the crosslinking of the base resin. It is suitable because it also has the function of increasing the degree.

The method of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic view of an example of an apparatus used when carrying out the method of the present invention. First, as in the case of the conventional extrusion molding type connection method, as shown in FIG.
At the installation site, the conductors 2a of the power cables 1a, 1b,
2b is compression-connected using the conductor connecting tube 3, and the inner semiconductive layer 4 is formed on the outer side thereof. Then, for example, a mold 7 that is divided into two is arranged by enclosing it (FIG. 1).

An injection port 7a for a molten resin, which will be described later, is provided at a substantially central portion of the die 7, and the injection port 7a is connected to an extrusion port 9a of a screw type extruder 9 through a flow path 8. ing. At the other end of the extruder 9, a hopper 10 and
Further, a cross-linking agent or a cross-linking regulator supplying device 11 described later.
Are arranged.

The construction method of the present invention is carried out by assembling the above-described apparatus example at a cable laying site. Then, as the base resin which itself crosslinks to form the reinforcing insulating layer, the base resin from which the foreign matter has been removed by using the above-mentioned screen mesh in the factory is used as described later. Based on the above apparatus example, the method of the present invention will be described for the case where the molten resin first extruded and injected into the mold 7 essentially comprises the base resin, the antioxidant and the cross-linking agent and does not contain the cross-linking regulator. ..

In the construction, first, in the hopper 10,
Pellets of the kneaded material composed of the base resin and the antioxidant are charged and supplied to the extruder 9. The pellets are manufactured in advance in the factory and are delivered to the installation site. Therefore, since the crosslinking agent is not added at the time of manufacturing the pellets in the factory, the foreign matter removing operation can be performed at a high temperature without considering the decomposition temperature of the crosslinking agent. Therefore, the pellets fed into the hopper 10 and fed to the extruder 9 are those in which the foreign matter has already been removed, and in the extrusion injection into the mold 7, there is no need to perform the foreign matter removal operation again. Is becoming

A cross-linking agent is further supplied from the supply device 11 to the kneaded product which is charged into the extruder 9 and melted and kneaded therein, and both are melted and kneaded by a screw of the extruder 9 while being extruded. It is transferred to 9a. A molten resin having a desired composition is extruded and injected from the injection port 7a of the mold 7 into the mold through the flow path 8.

Here, unlike the conventional case, in the extruder 9, since it is only necessary to uniformly add the cross-linking agent, the extrusion temperature is at a relatively low temperature at which the molten state of the base resin is secured. Therefore, it is possible to solve the problem that cross-linking proceeds by the action of the cross-linking agent before extrusion and injection into the mold 7. By the way, the injection port 7a of the mold 7 is usually provided at a substantially central position of the mold 7.
Therefore, when the molten resin is extruded and injected into the die 7 from the injection port 7a, generally, the molten resin is cast along the inner wall of the die in the initial stage of the extrusion and the inside of the die gradually. The center is filled. That is, in the obtained cast resin layer, the outer layer portion is made of the cast resin cast at a relatively early stage, and the inner layer portion is made of the cast resin cast at a later stage. The tendency is to occur.

Utilizing this fact, in the above-described construction method of the present invention, when the cross-linking agent is supplied from the supply device 11 to the molten kneaded material, the supply amount thereof is adjusted with time to Such an effect can be achieved. That is, the supply amount of the cross-linking agent is reduced in the initial stage of extrusion injection, and the supply amount of the cross-linking agent is increased stepwise or continuously as the extrusion injection is advanced.

In this way, the casting resin layer formed in the mold 7 has a relatively small content of the crosslinking agent in the outer layer portion, and the content of the crosslinking agent in the inner layer portion is relatively small. It is in a relatively large amount. Therefore, at the time of heat crosslinking by heating from the outside of this casting resin layer, the crosslinking reaction of the outer layer portion having a small content of the crosslinking agent is delayed, and the crosslinking reaction of the inner layer portion having a large content of the crosslinking agent is promoted. In the end, the crosslinking between the outer layer portion and the inner layer portion proceeds substantially at the same time.
Therefore, the above-mentioned inconvenience caused by excessive heating of the outer layer portion can be eliminated.

Next, the molten resin extruded and injected into the mold is
The case where the base resin, the antioxidant, the cross-linking agent, and the cross-linking modifier are mixed will be described. In the factory, a mixture of base resin and antioxidant is screened beforehand to remove foreign substances, and then a cross-linking agent is added to the mixture to form a kneading mixture of the base resin, antioxidant and cross-linking agent. Prepare things. Therefore, in this kneaded material, the foreign matter has already been removed.

The kneaded product conveyed from the factory to the laying site is put into the extruder 9 from the hopper 10 of the extruder and melted and kneaded. Then, the cross-linking regulator is supplied from the supply device 11, melt-kneaded by the extruder 9 and extruded and injected into the mold 7. At this time, in the initial stage of extrusion injection, the supply amount of the crosslinking regulator is increased, and as the extrusion injection proceeds, the supply amount of the crosslinking regulator is reduced stepwise or continuously.

The casting resin layer formed in the mold 7 has the same content of the crosslinking agent in both the outer layer portion and the inner layer portion, but the content of the crosslinking regulator in the outer layer portion is the same. However, the inner layer portion has a smaller content of the crosslinking regulator. Therefore, during the heat-crosslinking of the extrusion-injected resin layer, the crosslinking reaction of the outer layer portion tends to be suppressed, and the crosslinking reaction of the inner layer portion tends to be accelerated. The cross-linking between the outer layer portion and the inner layer portion of the cast resin layer will proceed at substantially the same time. Therefore, the inconvenience caused by excessive heating of the outer layer portion can be eliminated.

[0028]

Example 1 Both ends of a 275 kV cross-linked polyethylene power cable having a conductor cross-sectional area of 2000 mm ² were connected according to a conventional method,
A mold 7 was arranged on the outer side of the mold to prepare for an extrusion mold connection method.

First, in a factory, polyethylene having a melting point of 129 ° C. and 4,4′-thiobis (3-methyl-6-t-butylphenol) were kneaded into pellets. An extruder equipped with a screen mesh was extruded at a temperature of 160 ° C. to remove foreign matters. Then, carry this kneaded material to the laying site, and use the hopper 1
It was charged into a screw type extruder 9 from 0, heated and melted, and flowed in the extruder at a flow rate of 100 g / min.

A heater is provided over the entire length of the extruder 9, and the temperature is observed at 5 points from the upstream side to the downstream side, and the temperature is 130-
The temperature was controlled so as to be within the range of 135 ° C. While flowing the melt-kneaded product, dicumyl peroxide was continuously supplied thereto from the supply device 11 at a supply rate of 25 g / min for about 60 minutes, and then at a supply rate of 3 g / min for about 30 minutes.

In this way, the mold 7 is used for about 90 minutes.
After the molten resin composition was cast into the mold, the entire extrusion injection work was stopped, the mold 7 was removed, the outer shape of the cast resin layer was shaped, and the external semiconductive layer was formed thereon. Then, a pressure vessel is provided so as to surround this connecting portion, and the inside of the pressure vessel is filled with N ₂ gas.
Apply pressure of 8 kg / cm ^{2 with} gas, and apply ² from the outside of the connection.
Heat at 20 ° C. for about 13 hours.

When the insulation breakdown of the three connected power cables was examined, the insulation breakdown occurred at 1290 to 1350 kV. Moreover, only one piece was broken at the connecting portion, and the other two pieces were broken at portions other than the connecting portion. Example 2 The same power cable as in Example 1 was prepared for the extrusion molding type connection method.

First, in a factory, linear low-density polyethylene having a melting point of 127 ° C. and bis [2-methyl-4- (3-n-
Alkylthiopropionyloxy) -5-t-butylphenyl] sulfide was kneaded to form pellets, and the pellets were extruded at a temperature of 160 ° C. from an extruder equipped with a # 1000 screen mesh at the extrusion port to remove foreign matters. , M- (t-butylperoxyiopropyl)
-2.5 parts by weight of a cross-linking agent prepared by mixing isopropylbenzene and p- (t-butylperoxyisopropyl) -isopropylbenzene in a ratio of 3: 2 is added to 100 parts by weight of the composition after removing foreign matter. Kneaded

The kneaded product thus obtained was conveyed to the site of laying, charged into the extruder 9 from the hopper 10 to be heated and melted, and flowed in the extruder 9 at a flow rate of 100 g / min. Extruder 9 temperature 1
While controlling the temperature at 40 to 145 ° C. and continuing to flow the melt-kneaded product, 2,4-diphenyl-4-methyl-1-pentene is continuously supplied from the supply device 11 at a supply rate of 0.7 g / min for about 30 minutes. Then, the supply was continued at a supply rate of 0.5 g / min for about 30 minutes, and further at a supply rate of 0.3 g / min for about 30 minutes.

In this way, the mold 7 is used for about 90 minutes.
After the molten resin composition was extruded and injected into the mold, the whole casting operation was stopped, the mold 7 was removed, the outer shape of the cast resin layer was shaped, and the external semiconductive layer was formed thereon. Then, a pressure vessel is provided so as to surround this connecting portion, and the inside of the pressure vessel is filled with N ₂ gas.
Apply pressure of 8 kg / cm ^{2 with} gas, and apply ² from the outside of the connection.
Heat at 20 ° C. for about 13 hours.

When the dielectric breakdown of the three connected power cables was examined, the dielectric breakdown occurred at 1290 to 1380 kV. Moreover, there was not one broken at the connecting portion, and all were broken at places other than the connecting portion.

[0037]

As is apparent from the above description, the extrusion mold type connection method of the present invention is a method of adding a crosslinking agent or a crosslinking regulator at the site of installation using the base resin from which foreign substances have been removed in advance at the factory. Therefore, it is possible to arbitrarily adjust the supply amount of the cross-linking agent or the cross-linking regulator, which makes it possible to form a reinforcing insulating layer in which the outer layer portion and the inner layer portion are homogeneous, and the reliability of the connection portion is improved. You can improve your sex.

Further, since the foreign matter of the base resin is removed when the cross-linking agent is not contained, it is possible to remove the foreign matter of the base resin at high temperature without considering the occurrence of the crosslinking reaction. Therefore, as the base resin, a resin having a high melting point can be used, whereby a reinforced insulating layer having excellent insulating properties and heat resistance can be formed.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an apparatus used when carrying out a construction method of the present invention.

FIG. 2 is a cross-sectional view showing a connection portion formed by an extrusion mold type connection method.

[Explanation of symbols]

 1a, 1b Power cable 2a, 2b Conductor of power cable 1a, 1b 3 Conductor connecting pipe 4 Inner semiconductive layer 5 Reinforcement insulator layer 6 External semiconductive layer 7 Mold 7a Mold 7 inlet 8 Flow path 9 Extruder 9a Extrusion port of small extruder 10 Hopper 11 Cross-linking agent or cross-linking regulator supply device

Claims (3)

[Claims] 1. A resin composition containing a base resin, an antioxidant, and a cross-linking agent as essential components in a power cable laying site, in which a mold is arranged so as to cover the mutual connection portions of the power cables. After melt-kneading using an extruder, extrusion-injecting into a mold, and then heat-crosslinking it to form a reinforcing insulator layer in the connection part in the extrusion mold-type connection method of the power cable, at the laying site Is a kneaded product containing a base resin and an antioxidant in the resin composition and not containing a crosslinking agent,
This power cable is characterized in that the resin composition is melted and kneaded by feeding it into the extruder while gradually or continuously increasing the amount of the cross-linking agent from the initial stage to the end of the extrusion while being fed into the extruder. Extrusion mold type connection method. 2. A resin composition containing a base resin, an antioxidant, a cross-linking agent, and a cross-linking regulator in a power cable laying site, in which a mold is arranged so as to cover the mutual connection portions of the power cables. After melt-kneading using an extruder, extrusion-injecting into a mold, and then heat-crosslinking it to form a reinforced insulating layer in the connection part in the extrusion mold-type connection method of the power cable, at the laying site A kneaded product containing a base resin, an antioxidant, and a crosslinking agent but not a crosslinking modifier is introduced into the extruder, and this is put into an extruder, and the crosslinking modifier is gradually added from the initial stage to the end of extrusion. Alternatively, an extrusion mold type connection construction method for a power cable, characterized in that the resin composition is melted and kneaded while being continuously reduced in amount and supplied to an extruder. 3. The base resin is a polyolefin resin, the cross-linking agent is an organic peroxide, and the cross-linking regulator is 2,4-diphenyl-4-methyl-1-pentene. The extrusion molding type connection construction method for the power cable according to 1 or 2.