JP2834533B2 - Method of forming power cable connection - Google Patents

Description

The present invention relates to an improvement in a method for connecting a crosslinked polyethylene power cable.

(Prior art)

Crosslinked polyethylene power cables are rapidly following the path of higher voltage due to their excellent insulation properties and ease of handling, and their practical application to long-haul lines up to the 275 KV class is progressing. A long-haul line requires a highly reliable connection, but the 275KV class employs a so-called molded connection. This mold connection portion is covered with a split mold so as to straddle the cable insulator on both sides of the cable conductor connection portion, and an insulating resin is injected into the mold with a small extruder to mold and mold. After forming a reinforced insulator by shaping into a shape and coating an external conductive layer thereon, the whole is heated and pressurized to form a crosslink.

The conventional method of forming the mold connection is
This will be described in more detail with reference to FIG.

First, the cables 11a and 11b stripped to predetermined dimensions are connected to each other by compression using the conductor connection tube 13. Next, an internal semiconductive layer 15 is formed on the conductor connection tube 13 using a semiconductive tape and a semiconductive heat-shrinkable tube. Then, the upper and lower molds 17a and 17b are placed so as to sandwich the cable. Mold
A small extruder 21 is connected to 17a by a pipe 19, and the insulating resin 23 is injected into the cavities of the dies 17a and 17b by using this. When the injected insulating resin 23 has cooled and solidified, the molds 17a and 17b are dismantled. Exposed insulating resin 23
Is cut into a reinforced insulator 25 as indicated by the dotted line, a semiconductive heat-shrinkable tube (not shown) is coated, and then heat-molded while pressurizing the gas using a pressurized container.

〔Task〕

Some of the above connection tasks include cable insulators 27a, 2
There is an operation of stripping the outer semiconductive layer of 7b. This is to strip the outer semiconductive layer with a sheet of glass or the like to finish it smoothly, and in some cases, to further smooth the surface with fine sandpaper or the like. This work is performed in a dust-controlled clean room to remove dust and dirt,
Nevertheless, foreign matter, dust, fine particles of sandpaper and the like often adhere to the surface of the cable insulator.

In order to remove these, spraying dry gas from which static has been removed onto the insulator surface or wiping it with a lint-free cloth impregnated with a solvent has been used. It is difficult. In addition, when attaching a mold to a cable, foreign matter adhering to the inner surface of the mold or foreign matter mixed in from outside during mold assembly may adhere to the surface of the cable insulator.

Foreign matter adhering to the surface of the cable insulator is difficult to remove after the mold is mounted, and if the insulating resin is injected as it is, the range of A shown in FIG. Since the surface and the insulating resin are integrated, there is a danger that they will remain as foreign matter at the interface and become electrical defects. In particular, the slope rising portion 28 of the reinforcing insulator 25
In the vicinity of a and 28b, a high stress substantially equal to the stress applied to the outer semiconductive layer of the cable is applied, so that it is easy to cause an electrical defect.

In a conventional disassembly inspection after the electrical breakdown test of the connection portion, it has been confirmed that such foreign matter at the interface is a starting point of electrical breakdown.

As described above, the electrical effect caused by the foreign matter remaining on the interface becomes more severe as the insulation thickness of the cable becomes thinner and the applied voltage class of the connection part becomes higher, which is a major obstacle to the expansion of the applicable range of the mold connection part. ing.

[Solutions to solve the problem]

The present invention provides a method for forming a power cable connection portion capable of almost completely removing foreign substances on the surface of a cable insulator in order to solve the above-described problems. Put the mold in two so as to straddle the cable insulator, inject the insulating resin into the mold and mold it to form the reinforcing insulator. Before performing the cleaning, the surface of the cable insulator and the conductor connection portion in the mold is cleaned by a cleaning agent spraying device attached with the mold to remove extraneous matter.

[Action]

After covering the mold and before injecting the insulating resin, the surface of the cable insulator is cleaned by a cleaning agent spraying device and dust and foreign matter are discharged outside. The surface is surely kept clean,
No foreign matter remains at the interface between the cable insulator and the molded reinforcing insulator.

〔Example〕

Hereinafter, an embodiment of a method for forming a power cable connecting portion of the present invention will be described in detail with reference to FIGS.

The cables 11a and 11b, which have been stripped to predetermined dimensions, are compression-connected using the conductor connection tube 13. A semiconductive polyethylene tape is wound thereon, and the internal semiconductive layer 15 of the connection portion is formed by a heating mold. Next, the cable insulator surface
27a, 27b, 29a, and 29b are shaved using a sheet glass etc., and after finishing the entire surface, foreign substances adhering to the surface are electrostatically removed (removed by spraying nitrogen gas with an air gun equipped with a filter).
Then, the two-part extrusion dies 17a and 17b whose inner surfaces have been cleanly cleaned are set.

Holes 31a, 31b, 31c are provided at the ends of the molds 17a, 17b in the axial direction.
Are formed. These holes 31a, 31b and 31c are formed at upper and oblique lower portions at intervals of 120 ° in the circumferential direction as shown in FIG. In each of the holes 31a, 31b, 31c,
Injection nozzles 33a, 33b, 33c rotatable and movable in the longitudinal direction are inserted in the holes, and these injection nozzles are provided with the cleaning agent container 35 and the pressurized supply device 37 and the valve 39,
They are connected by pipes via 41a, 41b and 41c. In the middle of this pipe, a nitrogen gas cylinder 43 is branched and connected via a valve 45.

A discharge hole 49 communicating with a vacuum suction device 47 disposed outside is formed in a lower portion of the mold 17b.

First, cleaning is performed by the upper spray nozzle 33a using the above apparatus. For cleaning, open the valves 39 and 41a and clean the detergent container 35.
The fluorocarbon inside is sent out from the pressurized supply device 37 to the injection nozzle 33a, and from the injection nozzle 33a, the cable insulator surfaces 27a, 27
B, 29a, 29b and the inner semiconductive layer 15 are evenly sprayed in the circumferential direction and the longitudinal direction on the upper surface to wash away foreign matter. Next, one of the injection nozzles on both sides, for example,
Cleaning is performed with 33b, and finally, cleaning is performed with the other spray nozzle 33c.
At this time, the inner surfaces of the molds 17a and 17b are also cleaned as necessary. The order of spraying is from the upper surface to the side surface, the lower surface, so that the foreign matter in another place does not flow and adhere to the once removed part, even in the longitudinal direction, considering the flowing direction of the solution,
27a, 27b to 29a, 29b, below 29a, 29b to 27a, 2
It is desirable to carry out in the order of 7b.

The sprayed cleaning agent is discharged out of the discharge hole 49 by the vacuum suction device 47 so that the once removed foreign matter does not adhere to the surface of the cable insulator again.

When the spray cleaning of all the cable insulator surfaces is completed, close the valve 39 and open the valve 45 to open the nitrogen gas cylinder 43.
And the nitrogen gas is blown off from the injection nozzles 33a, 33b, 33c to replace the inside of the mold with an inert gas. Then mold 17
The surface of the cable insulator is preheated by a heater (not shown) built in a, 17b. This preheating volatilizes the cleaning agent adsorbed on the insulator surface under reduced pressure and high temperature, discharges it to the outside, raises the temperature of the cable insulator, and injects the insulating resin and cable insulator that are injected later. This is performed in order to improve the interfacial adhesion with the substrate.

When the preheating of the cable insulation surface is completed, spray nozzle
33a, 33b, 33c are removed, and plugs (not shown) are inserted into the holes 31a, 31b, 31c to close the holes. The discharge hole 47 is similarly closed.

The resin molding is performed in this state. That is, the extruder 21 injects and fills the insulating resin 23 into the cavity through the connecting pipe 19. Cooling is performed while applying pressure to the filled insulating resin 23.
a and 17b are dismantled and shaped into a predetermined reinforcing insulator shape. The surfaces of the reinforced insulator and cable insulator that have been shaped are spray-washed with anhydrous alcohol using the above-mentioned pressurized supply device, dried with a hot air blower equipped with a submicron filter at the tip, and subjected to semiconductive heat shrinkage. After coating the tube, the whole was pressurized and heated to crosslink.

The test results of the mold connection manufactured by the above-described embodiment and the mold connection by the conventional connection method are shown below.

The cable used was a 275 KV 2000 mm ² cross-linked polyethylene power cable, the insulation outer diameter of which was 112 mm,
The outer diameter of the outer conductive layer is 115 mm, and the outer diameter of the inner conductive layer is 58 mm.

According to the present invention, a voltage of 610 KV was applied for 12 hours to the mold connecting portion, and the AC breakdown voltage was obtained by increasing the voltage in steps of 50 KV / 1 hour. As a result of disassembling and examining the mold connection portion, no foreign matter was found at the interface between the reinforcing insulator and the cable insulator, and the effect of cleaning by spraying a cleaning agent, which is a feature of the present invention, was confirmed.

When performing an AC destruction test under the same test conditions as the mold connection part according to the prior art, 910 KV, near the rise of the insulating slope in 35 minutes,
It penetrated and fractured from the outside toward the conductor. As a result of investigating the fracture hole, the starting point of the fracture was a conductive foreign substance at the interface between the cable insulator and the reinforcing insulator 0.5 mm inside the outer conductive layer.

In the above embodiment, chlorofluorocarbon is used as the cleaning agent. However, similar effects can be obtained by using alcohol, trichlorethane, or the like. Although three injection nozzles 33 were used,
As long as the surface of the cable insulator can be sufficiently cleaned, two or one cable may be used.

〔The invention's effect〕

According to the method for forming the power cable connection portion of the present invention described above, after the mold is covered and before the insulating resin is injected, the surface of the cable insulator and the conductor connection portion are formed by the cleaning agent spraying device attached to the mold. In the step of molding the insulating resin, the surfaces of the cable insulator and the conductor connecting portion are reliably kept clean. Therefore, no foreign matter remains at the interface between the cable insulator and the conductor connecting portion and the injection-molded reinforcing insulator. Therefore, there is no remarkable effect that electric breakdown caused by foreign matter at the interface can be prevented and a stable and high-performance connection portion can be obtained.

[Brief description of the drawings]

1 and 2 are a longitudinal sectional view and a left side view of a method of forming a power cable connecting portion of the present invention, and FIG. 3 is a longitudinal sectional view of a conventional method of forming a power cable connecting portion. 11a, 11b: Stripped cable 13: Conductor connection tube, 15: Internal semiconductive layer 17a, 17b: Split mold, 21: Small extruder 23: Insulating resin, 25: Reinforced insulator 27a, 27b, 29a, 29b: Cable insulator surface 28a, 28b: Slope rising portion 31a, 31b, 31c: Injection nozzle hole 33a, 33b, 33c: Injection nozzle 35: Cleaning agent container, 37: Pressurized supply device 39, 41a, 41b, 41c , 45: Valve 43: Nitrogen gas cylinder, 47: Vacuum suction device 49: Discharge hole

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01R 4/70-4/72 H01R 43/00 H02G 1/14 H02G 15/08

Claims (1)

(57) [Claims] 1. A case in which a split mold is placed so as to straddle a cable insulator on both sides of a cable conductor connection portion, and an insulating resin is injected into the mold and molded to form a reinforcing insulator. In, before covering the mold and before injecting the insulating resin, by the detergent spraying device attached with the mold,
A method for forming a power cable connection portion, comprising cleaning the surfaces of a cable insulator and a conductor connection portion in a mold to remove extraneous matter.