SU1095889A3 - High voltage electric cable - Google Patents

Abstract

Conductors of electric cables are insulated by overlapping winding of a tape. The tape is a pore- and void-free and 200 mu thick and is wound under sufficient tension to obtain coherent grip, i.e., no-slip between adjacent or overlapping layers. The tape is made of a highly crystalline (40-90, pref. 50-80%) polymer having a high wt. average mol. wt. (2-7 x 105, pref. 3.5-5 x 105) with high strength (>=5 daN/mm2) and elastic modulus (175-450 daN/mm2). The tape is suitable for cables used underwater at =500 m. for power capacities =1000 MW. It is similar to oil-impregnated paper wound insulation. Extruded coatings are slow to apply and so porous that max. immersion depths are 500 m. and power loadings 300 MW.

Description

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This invention relates to high-voltage electrical cables. An electrical cable is known with insulation made in the form of strips of paper impregnated with a liquid dielectric lj. However, the limiting voltage for such cables is 250-300 kV. Immersion of such a cable under water is possible to a depth of less than 500 m (the oil and gas trapped to make insulation are strongly opposed when the cable is submerged under a wire). It is also known that polymer materials have found wide use in the manufacture of insulation in cable technology polypropylene zj. Polypropylene has high mechanical strength, is wear-resistant, resistant to various aggressive media, has a high melting point and can work for a long time at T 100-120 ° C. The disadvantages of polypropylene, which limit its use in cable technology, are their high rigidity and their tendency to oxidation at extreme temperatures and upon contact with copper, and low cold resistance. Therefore, for the manufacture of high-voltage cables operating, in particular, under water at great depths, polypropylene has not been used up to now. The closest to the technical essence of the invention is a high-voltage electrical cable, in which the insulation is made in the form of a tape made of a fluoroplast-4-based polymer film wound with tension around the core. However, when using this insulation, it is advisable to use a dielectric liquid as a spread which has a strong resistance, reducing the depth to which the cable must be submerged under water, and reduces the length of this cable. The disadvantage of this cable based on fluoroplast-4 is also low reliability of operation and relatively short service life of the cable, which is caused, in particular, by the low corona resistance of fluoroplast-4. The purpose of the invention is to increase the reliability of cable operation and increase its service life. The goal is achieved by insulating a high-voltage electrical cable with insulation in the form of a polymer film tape wound around a core of a polymeric film and insulating from a biaxially flat-stretched film 10-50 µm thick from isotactic stereo-regular polypropylene with an average molecular weight of 200,000-700,000 , a polymolecular coefficient of 2-10, a crystallinity coefficient of 40-90%, an elastic modulus of 1750-4500 N / mm, a tensile strength equal to or greater than 50 N / mm. Due to this insulation isolation, it is not required An additional impregnation, since the van der Waals forces, with appropriate tension, ensure adhesion of the polymer film layers. In addition, the deformation of such insulation does not go beyond its elasticity. All this leads to an increase in reliability, the cable during its operation and an increase in its service life. For the manufacture of a high-voltage electrical cable according to the invention, a biaxially oriented film of isotactic plipropylene is used, which is characterized by the following parameters: thickness 25 μm; average molecular weight of 430,000; tensile strength in the longitudinal direction 14 daN / mm (1400 kgfA: m); tensile strength in transverse bending of 25 daN / mm (2500 kgf / cm); the degree of crystallinity of more than 50%. This film has a high dielectric strength for direct current, which is more than 530 kV / mm, and has a low dielectric constant of 2.2, a low loss coefficient having an order value. A tape made of such a film is wound on an insulated product when the tension is within the elasticity of the tape. So, for example, a tape made of a film 25 µm thick and 20 mm wide can be wound at 500 g. It is desirable that the tension is not less than 0.4 daN / mm, or AO kgf / cm. Overlap against each other successive layers of the tape varies depending on the degree of insulation required, i.e. from the maximum voltage and maximum electric current passing through the product. For the purpose of additional sealing of NIN layers of the tape, along with winding the tape on the product, during tension, it can be heated to 100-135 ° C, which allows an increase in the degree of criticality of the material. Example. As a cable to an aluminum conductor of 800 mm with insulation from polypropylene film of 16 m, the operating voltage is 550 kV; current strength 1000 A; cable service life of 30 years; cable length 100 km. Such a cable can be compared with classic impregnated cables whose permissible voltages are limited to 400 kV (actual characteristic 300 kV). Dielectric strength in cold condition, kV / mm: Impregnated paper 160 Multi-layer polypropylene 360 Average voltage gradient permissible in operation, kV / mm: Impregnated paper 25 Multi-layer polypropylene .35 Below are the characteristic properties of the original polypropylene: Isotacticity,% Mass-average molecule521000 shaped weight Average molecular weight by number Polymolecularity index 50 parts Ash content per milliliter Melting rate, min (2.16 kg at) 2 g / 10 Melting point Characteristic properties of biaxially oriented The first film of isotactic polypropylene is shown below. Macromolecular characteristics: Average molecular weight by number 65000 Average molecular weight by weight 4,30000 Polymolecularity index 6, 6 Mechanical characteristics, anH / mm; Elasticity limit along the machine3.7 (1.3%) Modulus of elasticity along the machine292t Modulus of elasticity in the transverse direction440 Rupture of tensile stress in the direction of the machine 14 Discontinuity at stretch. in the transverse direction25 Physical characteristics: Thickness, μm 25 Average graininess, μm 0.09 Crystallinity,% 55 Water absorption,% 0.01 Thermal characteristics: film stability up to T - is complete. In tab. 1 shows the characteristics of the cable model. In tab. 2 shows the test results of a cable with a length of 30 m for durability. The cable with insulation according to the invention imposes 5001000 I / W loads with a conductor potential gradient of 80 kV / mm. Due to the good mechanical properties of the insulation layer, the cable can be immersed under water to a depth of more than 500 m. The cable can be used as a low-voltage, underground telephone cable, as a direct and alternating current conductor. Table Conductor 1x50 mm ARC of 19 1.67 mm wires, twisted to the left Semi-conductive tape, nylon substrate, width 24 mm, with overlap of 30%

S1095889 Continuation of the table. one

Poluprovo-. PRC screen

151 ribbon of isotactic biaxially oriented polypropylene, laid by crossing layers in a spiral, 10% loustot

Continued table. one

one

Semiconducting

20.80 PRC screen

Crepe coal paper tape, 80 g, overlaid with 20% overlap

21.70 25.70

Lead shell

table 2

Claims (1)

HIGH-VOLTAGE ELECTRICAL CABLE with insulation in the form of a polymer film tape wound ¹ with a tension around the core, characterized in that, in order to increase the reliability of operation and increase the service life of the cable, the insulation is made of a biaxially flat-elongated film with a thickness of 10-50 microns from isotactic stereo-regular polypropylene with an average molecular weight of 200,000-700,000, a polymolecularity coefficient of 2-10, a crystallinity coefficient of 40-90%, an elastic modulus of 1750-4500 N / mm ² , a tensile strength equal to or large 50 N / mm ² SU w, 1095889>