JPS6228015Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is applicable to single-core power cables that require a relatively hard protective layer, such as termite-proof sheathed cables.
This article relates to a single-core power cable that is excellent in preventing trauma, and this single-core power cable is often used as a triplex type cable (three single-core cables twisted together).

Termite-proof sheathed cables are conventionally coated with a sheath (protective layer).
Termite repellents, such as those containing organic chlorine-based chemicals, have been often used in the past, but in recent years, due to problems such as toxic pollution caused by chemicals, it has become possible to make the sheath material itself less susceptible to being eaten by termites, etc., without using chemicals. Hard plastic materials such as high density polyethylene and nylon have come into use. Even with normal power cables, the cables are pulled in through the manhole,
During installation, the cable is damaged by the edge of the manhole, which requires the provision of a relatively hard protective layer that is highly abrasive.

However, in single-core power cables with relatively hard protective layers, ordinary low-density polyethylene or
It has been discovered that cables with protective layers made of soft materials such as PVC suffer from problems that are not present.

The problem is as explained below. Normally, power cables are designed so that they can be used at a conductor temperature of 90°C by energizing the conductor. During a power outage, the cable will return to normal temperature, and in actual use, the cable will undergo a heat cycle between 90°C or higher when an overcurrent flows and normal temperature.

The inventor conducted a heat cycle of a termite-proof sheathed cable with a relatively hard sheath between 105℃ and room temperature by energizing the conductor, and found that the shielding copper tape wrapped around the outside of the cable insulation It was found that vertical wrinkles occur in the length direction of the cable. In some cases, the wrinkles dug into the insulation, and when the tape was removed, the insulation was dented. The reason why vertical wrinkles occur on the tape is considered as follows. As the conductor temperature increases, the insulation expands and the copper tape stretches accordingly. However, when the power goes out and the insulator cools and contracts to its original diameter, the sheath also cools and contracts, but once the copper tape is stretched,
This is thought to be because it does not return to its original state and buckles due to the tightening force of the outer sheath. In fact, this phenomenon is not observed in cables whose sheaths are made of soft materials such as ordinary low-density polyethylene or PVC. This phenomenon is also not observed in the case of three-core bulk sheathed cables. The reason for this is thought to be that the intervening layer or the gap between the cores relaxes the tightening force of the sheath.

Looking at the bending elastic modulus at room temperature as a measure of hardness, a normal low-density polyethylene sheath is 20Kg/mm ²
In contrast, high-density polyethylene is 50Kg/mm ² or more, nylon 66 is 140Kg/mm 2 or more, and nylon 610 is 140Kg/mm ² or more.
It is 120Kg/mm2 or ^more .

In view of the above, the inventor conducted extensive research into a single-core power cable having a relatively hard sheath and in which the copper tape shielding layer does not wrinkle when current is passed through the conductor or during a power outage, and has now completed this invention.

The gist of this invention is that when compressed, the thickness of a copper tape shielding layer provided on an insulating core consisting of a conductor, an insulator, and an external semiconducting layer decreases by at least 4.5% of the thickness of the insulator. A single-core power cable is provided with a buffer layer, and a protective layer made of a thermoplastic resin with a bending modulus of elasticity of 50 kg/mm ² or more is provided on the outer side of the buffer layer.

This idea will be explained based on the drawings. The figure shows a cross-sectional view of a single-core power cable of the invention, in which 1 is a conductor, 2 is an insulator, and 3 is an outer semiconducting layer, from which an insulating core is formed. A copper tape shielding layer 4 is provided on this insulating core, ie the outer semiconducting layer 3. A buffer layer 5 whose thickness decreases by 5% or more of the thickness of the insulator 2 when compressed is provided on the outside of the copper tape shielding layer 4, and the buffer layer 5 has a flexural modulus of elasticity.
A protective layer 6 made of a thermoplastic resin of 50 kg/mm ² or more is provided.

The single-core power cable of this invention has the above structure, so that the copper tape is stretched by 5% or more beyond its elastic limit due to the thermal expansion of the insulation. In this case, when cooled to room temperature, the clamping force caused by the contraction of the protective layer outside the copper tape shielding layer is weakened by the compression of the buffer layer, and no wrinkles are generated in the copper tape. The reason why the reduction in thickness of the buffer layer due to compression is 4.5% or more of the insulation thickness is that if it is less than 4.5%, when the contraction of the protective layer exceeds the compressible range of the buffer layer, the clamping force caused by the contraction of the protective layer is applied to the copper tape shielding layer, which may cause wrinkles.

Examples will be shown below to clarify the significance of this invention.

Example 1 A buffer layer was provided by wrapping a jute, which is often used as an intermediary in multi-core cables, without much tightening, on the copper tape shielding layer on the insulating core with a conductor outer diameter of 17 mm and an insulator thickness of 4.5 mm, and then After wrapping the juute with cotton tape to prevent it from coming apart, it was extruded and coated with nylon 66 (flexural modulus 130Kg/mm ² ) to a thickness of 2.5mm, a protective layer (inner diameter 40mm) was applied, and a 6KV-strength polyethylene film was applied. Created a single core power cable.

When the buffer layer of this cable was compressed and its thickness reduced, it was found to be about 5% of the insulator thickness.
After this cable was subjected to 10 electrical heat cycles between the conductor temperature of 105°C and room temperature, the cable was disassembled, but no wrinkles were observed in the copper tape shielding layer.

Example 2 A copper tape shielding layer was wound on the insulating core used in Example 1, and a polyester nonwoven fabric was butt-wound on it, and then a protective layer similar to Example 1 was provided, and a 6KV-200mm ² cable was prepared. After conducting a heat cycle between the conductor temperature of 105℃ and room temperature,
When this cable was disassembled and the copper tape shielding layer was examined, no wrinkles were observed.

The thickness of this polyester nonwoven fabric was reduced by about 4.5% (about 0.2 mm) of the insulator thickness by compression.

Example 3 Instead of the protective layer material (nylon 66) of Example 2,
A similar cable was made using high-density polyethylene (flexural modulus 50 Kg/mm ² ). A similar heat cycle test was conducted, but no wrinkles were observed in the copper tape.

Comparative example A shielding layer was provided by wrapping copper tape on the same insulating core as in Example 1, and cotton tape (0.2 mm thick) was placed on top of it.
A protective layer of high-density polyethylene (flexural modulus of elasticity 50 Kg/mm ² ) was extruded thereon. When the cable was disassembled after a similar heat cycle, vertical wrinkles were observed in the copper tape. The thickness of the cotton tape decreased by 1.0 mm or less (approximately 2% or less of the insulating layer) due to compression.

[Brief explanation of the drawing]

The figure is a cross-sectional view of the single-core power cable of this invention. DESCRIPTION OF SYMBOLS 1...Conductor, 2...Insulator, 3...Outer semiconducting layer, 4...Copper tape shielding layer, 5...Buffer layer, 6...
…protective layer.

Claims (1)

[Claims for Utility Model Registration] (1) A copper tape shielding layer provided on the outer side of an insulating core consisting of a conductor, an insulator, and an external semiconductive layer, whose thickness when compressed is 4.5 times the thickness of the insulator. Provide a buffer layer that reduces the bending elastic modulus by more than %.
Single core power cable with a protective layer made of thermoplastic resin of 50Kg/mm2 or ^more . (2) The single-core power cable according to claim (1), in which the buffer layer is made of nonwoven fabric, jute, foamed polyurethane tape, or foamed polyurethane extrusion coating layer. (3) The single-core power cable according to claim 1, wherein the thermoplastic resin having a bending modulus of elasticity of 50 Kg/mm ² or more is high-density polyethylene or nylon.