KR810002132B1 - Insulating layers for electrical cables - Google Patents

Abstract

Elec. Insulators for high-voltage cables were mamufd. Biaxially oriented isotactic polypropylnen films of thickness<200μ, wt. av. mol. wt. 43,000, crystallinity 40-90%, tensile strength>5daN/mm2, elasticity 175-450 daN/mm2 were the nonimpregnation materials for elec. insulators. The polypropylene film tapes were wound around the cables and heated to 100-135≰C for the increase of crystallinty by film shrinkage.

Description

Electrical insulation materials

The present invention relates to insulators of linear current conductors, such as electrical cables, in particular high voltage cables.

Currently, electrical insulators of cable conductors are manufactured by one of two methods, one of which is to extrude an insulating synthetic polymer onto a conductor. However, the extrusion method of the polymer has the drawback of reducing the dielectric and viscoelasticity of the polymer, and this type of insulator is easily broken, so it has to be used only for cables of relatively low voltage. Another method is to wind the conductor around using a tape that is made of paper impregnated with a dielectric liquid and that can be combined with a polymer tape. Since the tape is sometimes wound on the conductor in the presence of dielectric oil or gas under pressure, it infiltrates the wires of oil or gas and increases the insulation effect of the wound tape. The cables insulated in this way must then be manufactured so that no water or air can pass through them, and they are now covered with lead.

Since the extruded polymer has various limitations when used as an insulator, the submarine cable is currently insulated using the above-described tape, that is, a tape wound on a conductor in the presence of oil or gas under pressure. However, due to soaked oil or gas, there are significant limitations on the depth and length of such cables that can be enclosed in the cable. In general, such cables are suitable for depths of less than 500 m and the maximum load capacity of cables with such insulators is 300 MW, so the voltage should not exceed 250 to 300 KV.

It is therefore an object of the present invention to feature a tape formed from a film of axially oriented polymer, having a thickness of 200 microns or less, having a high crystallinity and a high tensile strength, high elastic modulus and adhesion. The present invention provides an electrical insulator for insulating a linear current conductor.

Another object of the present invention is to provide a cable, characterized in that it consists of an insulator surrounding the conductor, which is formed by successively winding the conductor around with a linear current conductor and at least one tape (tape as described above). have.

It is a further object of the present invention to provide a method of insulating a current conductor, characterized in that the conductor is wound under tension with at least one tape (tape as described above) to superimpose a continuous layer of tape.

In order to increase the adhesiveness of the tape, the film preferably has a constant thickness and a uniform surface, and the film thickness is preferably 10 to 50 microns, in particular 10 to 25 microns.

Layer of the tape is tightly coiled to produce a conductor because there is a high elastic modulus in tension, and 175 and 450daN / mm ² of 5daN / mm ² the insulation will have a cohesive strength. In addition, when the conductor is deformed in the longitudinal direction, for example when the conductor is a cable and the cable is wound around the drum, the layers of tape do not slip against each other.

It is preferred that the tape be oriented in both directions and able to shrink when heated. To make the layer of insulator more dense, the tape shrinks on the conductor by heating the tape on or after use in the current conductor, making the layer of insulator more dense.

The temperature at which the tape is heated is below the softening point of the tape, preferably in the range of 5 to 40 ° C below the softening point.

If the film forming the tape is oriented in both axial directions, it is preferred that the tape be produced by conventional methods, the film having a temperature between the softening point and the melting point, and T and T-100 ° C. (T is the melting point of the polymer used). The ratio between the unextended length and the elongated length at the temperature between 3 and 7 is extended in the axial direction.

When winding the tape, air, or dielectric gas, seeps into the tiny spiral space between the tape layers at the side edges of the tape. This space is limited in the radial direction of the insulating layer relative to the thickness of the tape. Dielectric gas permeates into the insulating layer but is not necessary for the dielectric properties of the insulator provided by the tape. However, when or after winding the tape, the insulation of the tape layer can be further increased by carefully introducing a dielectric gas into each side edge of the tape. Such gas may be one or a mixture thereof as described below.

air

The tape may be made of any suitable homo polymer, copolymer or ter polymer.

Films can be prepared from stereoregular homopolymers having stereoregularity and of the general formula (-CH ₂ -CHR) n.

Wherein R is one of those described below:

Examples of other homopolymers that can be used as the film are as follows;

Poly- (4,4'-diphenylene propanecarbonate) in polycarbonates, poly- (hexamethylene adipamide) in polyamides, poly- (ethylene terephthalate) in polyesters, poly (arylene oxide ) Poly- (oxyphenylene), polysulfones, polyvinylidene halides, polyvinyl halides, poly (methyl methacrylate), poly- (tetrafluoroethylene), poly- (monochlorotrifluoro) Roethylene), poly- (vinylene chloride), 6, 6.6, 6.10, 10 and 11 polyamides.

Preferred copolymers and terpolymers for preparing films are synthesized from the monomers of the homopolymers described above. Examples of the terpolymer that can be used to produce the film include fluorinated ethylene-propylene terpolymers.

All the polymers mentioned above have an average molecular weight between 200,000-700,000, preferably between 350,000-500,000 and a polymer index of 2-10.

The percent crystallinity is 40-90%, preferably 50-80%.

Since the average molecular weight of the polymer is large, strong cohesion between molecules is known, and as a result, there are virtually no pores between the molecules, the film made of such a polymer is opaque as a complete film which does not tear even when stretched and does not have any pores. It can be classified as film.

The high crystallinity of these polymers means that the films made from these polymers have high tensile, elastic and dielectric strengths.

In a preferred embodiment, the tape is made from a biaxially oriented film of stereoregular polypropylene having the following properties;

The film thus produced has a high dielectric strength for direct current of 630 KV / mm or more, a low dielectric constant of 2.2 and a low loss factor of 2 × 10 ⁻⁴ .

The film tape is wound on a conductor to be insulated under tension within the elastic limits of the tape. For example, a tape formed from a film 25 microns thick and 20 mm wide can be wound under a tension of 500 g. Preferably, the tension should not be less than 0.4 daN / mm ² . The degree of overlap between successive layers of tape varies with the degree of insulation required, i.e. the maximum voltage and current to be conducted by the conductor.

If the layer of tape is to be further densified, besides winding the tape on the conductor under tension, the tape is heated to shrink the tape during or after use in the conductor. For polypropylene tapes with stereoregularity, the tapes are heated to a temperature between 100 and 135 ° C. below the softening point of the polypropylene. The polypropylene film has the additional advantage of increasing the crystallinity when heated in this way.

As an example, submarine cables for very high voltages using direct current are constructed as follows.

That is, a conductive core of an electrically conductive metal such as aluminum or aluminum alloy, aluminum having a steel support, or copper; Anhydrous semiconductor layers of polyethylene or extruded ethylene-polypropylene copolymers or other materials; An electrical insulation layer of tape as described above (the tape was formed of a stereoregular polypropylene film); A semiconductor layer similar to the semiconductor layer covering the core, screening; And anti-corrosion protection.

In this way, an electrical insulator is provided, and an electrical insulation method is provided in which an electric cable conductor is provided with a synthetic insulation layer. The insulation layer is formed of a polymer in the form of a film to maintain dielectric and viscoelasticity of the polymer used. The insulating layer consists of a plurality of overlapped tape layers that provide a plurality of polymer-polymer interfaces that inhibit conduction of current. These electrical properties are combined with the mechanical properties of the tape itself to obtain a dense insulating layer.

The insulating layer does not need to contain dielectric gases or oils to sufficiently insulate and provides much more reliable insulation than either extruded synthetic insulators or conventional tape wound insulators. The thickness of the insulation layer can vary depending on the degree of insulation provided and in accordance with the nominal operating voltage of the current conductor.

The insulator provided by the above-described insulating layer can be used sufficiently even at 500 MW to 1,000 MW in a very high voltage and load capacity, for example, a potential tendency in a conductor of 80 KV / mm. Since the insulating layer has excellent mechanical properties, the cable formed with such an insulating layer can be submerged in a depth of 500 m or more.

Although the present invention has been described with respect to the insulator of the electrically conductive cable to be used underwater for high pressure, the insulator of the present invention can also be used for the insulation of low voltage carrying cables, underground cables, telephone cables, AC and DC cables.

Claims (1)

As described above in detail, the determination of thickness, 40-90% less than 200 microns, even, 5daN / mm ² or more tension, 175-450daN / mm ² modulus of elasticity, and a film of a polymer oriented in the axial direction having a self adhesion A non-impregnated material for electrical insulation for insulating linear current conductors, characterized in that it is composed of a tape formed of: a.