RU2531295C1 - Electrical paper - Google Patents

Abstract

FIELD: textiles, paper.

SUBSTANCE: invention relates to the field of production of electrically insulating paper materials obtained from sulphate unbleached cellulose and designed to isolate the electrical power cables for voltage up to 35 kV inclusive, for insulation of telephone cables and winding wires, for the manufacture of different electrically insulating products. In order to improve stretchability and dynamic strength (energy of rupture) in the machine direction, as well as dielectric properties and processability the electrical paper has a deformed surface structure in the form of low-observable micro-folds obtained as a result of operation of micro-creping, elongation in the machine direction (5-15%) and the specific electrical conductivity of aqueous extract with the irrigation modulus of 1:50 in the range of (35-110) mcS/cm.

EFFECT: invention enables to obtain the high-quality and high-reliability power cable with impregnated paper insulation.

8 cl, 1 tbl

Description

The invention relates to the field of production of electrical insulating paper materials obtained from unbleached sulfate pulp and intended for insulation of power electric cables up to and including 35 kV, for insulation of telephone cables and winding wires, for the manufacture of various electrical insulating products.

The use of paper insulation is due to the fact that this insulation is chemically stable, resistant to electric fields, can work for a long time at elevated temperatures (70-85) ° C, more economical in comparison with other types of insulation materials (plastics, rubber) used in cables to transmit electricity. Electrical insulating paper consists of sulphate pulp fibers arranged in such a way that a mechanically strong web is formed.

Known two-layer and four-layer electrical insulating cable paper (Milov B.G. and other electrical insulating paper. M., 1974, S. 113-123), each layer of which is made of unbleached sulfate pulp. This paper has a reduced density and insufficiently high mechanical and dielectric characteristics, which limits its use for insulation of power cables and does not provide high reliability during operation.

Cable paper of brand K, KM and KMP (prototype) according to GOST 23436-83, year of input 1985, Russia, the characteristics of which are given in the table, is also known. Cable paper according to the prototype is made of natural fiber color from sulfate unbleached softwood pulp of softwood or softwood pulp with the addition of hardwood pulp according to the normative and technical documentation. The addition of hardwood pulp reduces the cost of cable paper, but at the same time, the strength characteristics of the paper and its heat resistance are reduced. Paper is made of machine smoothness (using a machine calender). Cable paper of brand K is two-layer, and KM and KMP are multilayer.

The disadvantages of paper cable prototype:

- reduced elongation in the machine direction;

- reduced dynamic strength in the machine direction;

- increased rigidity and brittleness;

- increased breakage and production losses when winding cable insulation;

- reduced cable insulation speed;

- reduced resistance to cracking and tearing after testing the cable for resistance to repeated bending;

- reduced heat resistance.

All these shortcomings of paper cable according to the prototype significantly reduce the manufacturability of cable manufacturing, the quality of paper insulation and cable performance.

An object of the invention is the development of paper cable, not inferior to the prototype in dielectric characteristics, but more durable, flexible, heat-resistant, technological, having high resistance to cracking in the composition of the cable and providing high-quality and highly reliable power cables with impregnated paper insulation.

The technical result is achieved by the fact that the paper cable has a deformed surface structure in the form of subtle micro-folds obtained as a result of the microcreping operation, the relative elongation in the machine direction (5-15)% and the specific electrical conductivity of the water extract with a hydraulic module 1:50 in the range (35- 110) μS / cm.

A common feature of the prototype and the proposed technical solution is the manufacture of single or multi-layer paper cable from sulfate unbleached pulp. At the same time, the proposed paper differs from the known deformed surface structure in the form of subtle micro folds obtained as a result of the microcreping operation, machine elongation (5-15)% and the specific electrical conductivity of the water extract with a hydraulic module 1:50 in the range (35-110 ) μS / cm.

Advantages of the new paper:

- high elongation in the machine direction;

- high dynamic strength in the machine direction;

- high elasticity;

- high resistance to cracking and tearing of paper tapes after repeated bending in the composition of the cable;

- high manufacturability and productivity when applying paper tapes to the cable;

- high dielectric characteristics;

- high heat resistance.

Restrictions on the choice of paper for the manufacture of insulation of power cables impose conditions for the manufacture and operation of cables:

- mechanical load on the paper when cutting it into tapes with a width of (14-30) mm at a speed of up to 500 m / min;

- mechanical load on paper tapes when applied to the cable;

- thermomechanical and chemical load on paper tapes in the composition of the cable when it is dried and impregnated with an oil-rosin compound at temperatures up to 145 ° C;

- thermomechanical load on paper tapes in the composition of the cable when applying aluminum or lead sheath on them;

- difficult-deformed state of paper tapes in the composition of the cable during repeated bending during manufacturing, testing, storage, laying and operation;

- long-term (25-30 years) thermochemical load on paper tapes impregnated with oil-rosin compound in the composition of the cable at temperatures up to 80 ° C;

- thermomechanical load on paper tapes in the composition of the cable during storage at a temperature of ± 50 ° C in drums;

as well as the required characteristics of insulating cable paper: thickness, density, maximum breaking stress and elongation in both directions, maximum heat resistance and durability.

Of all the existing cable papers of the prototype with a thickness of up to 140 microns, the maximum strength has three-layer cable paper brand KMP-140 (table) with a nominal thickness of 140 microns and a density of 0.78 g / cm ³ . Nevertheless, after mechanical testing of the cable for winding in accordance with GOST 18410-98, KMP-140 paper may have transverse tears in the belt insulation of up to 6 mm and in phase insulation of more than 6 mm to two torn tapes. Paper cable grade K does not pass the test in the composition of the cable for winding the number and length of transverse tears. Folds, pockets, tears and tears of paper tapes violate the integrity of the impregnated paper insulation, as a result of which in the places of defects the electric field strength increases and the electric strength of the cable insulation decreases. This circumstance can lead to premature failure (breakdown) of the cable.

In order to exclude transverse and longitudinal tears, folds, pockets and cracks of paper tapes after testing the cable for winding, the inventors developed paper cable microcreated with a thickness of (90-150) microns and a density of (0.65-0.80) g / cm ³ manufactured from 100% softwood sulphate unbleached pulp. Microcreated cable paper differs from ordinary crepe paper with a very small crepe, almost invisible to the naked eye, so its thickness is almost equal to the thickness of uncreated base paper. This paper, unlike crepe paper, cannot be stretched by hand. The advantages in the properties possessed by microcreped paper are explained by giving the fibers increased elastoplastic properties and high flexibility due to their preliminary deformation in the process of microcreping without destroying the paper structure, as with macrocreping.

One of the main distinctive properties of microcreated paper is its increased elongation (5-15)% in the machine direction, which is 2.5-5 times higher than that of cable paper according to the prototype. Microcreated cable paper in comparison with the cable paper of the prototype has lower tensile strength in the machine direction (1.2-1.5 times lower). However, due to the high relative elongation in practice, it turns out to be better than the more tensile, but less tensile cable paper of the prototype. This is due to the high dynamic strength (burst energy according to TU 5433-004-50289046-2005, commissioning year 2005, Russia), determined by calculation by the formula:

E = K × P × L, J / m ² , where

K = 0.41 - coefficient for machine direction;

K = 0.48 - coefficient for the transverse direction;

P - destructive force, N;

L is the elongation,%.

The bursting energy of cable microcreped paper in the machine direction is two to three times higher than that of cable paper according to the prototype of one thickness, therefore, cable microcreated paper is able to withstand much greater dynamic and bending loads in the cable. Tensile and dynamic strength in the machine direction are some of the most important operational properties of an insulating material. The use of microcreated cable paper as phase and zone insulation of the cable ensures smooth and very dense winding of paper without the formation of folds and air cavities in the insulation. This helps increase the electrical strength and reliability of paper insulation. At the same time, tears and breakage of paper tapes in the process of isolation are eliminated. Insulation of the cable can be carried out at higher speeds, while paper tapes of greater width can be used in comparison with cable paper according to the prototype. Microcreated cable paper has high resistance to mechanical damage (tears, cuts, punctures, tears), is moisture-proof and heat-resistant, has a low cost, therefore, it most satisfies the above requirements for material for cable insulation. After testing the cable for winding, it was found that the cable microcreated paper does not have mechanical damage (tears, cracks, tears, folds), remains flexible and elastic after impregnation with a dielectric composition in all layers of phase and zone insulation. The microcreped highly porous surface of the paper helps to keep the viscous dielectric composition of MP-2 from flowing along the cable on inclined sections of cable lines.

To increase the elasticity and strength, microcreated cable paper can be made from sulphate pine unbleached pulp. To improve the dielectric characteristics, microcreated cable paper can be made of ECB grade unbleached sulphate coniferous electrical insulating cellulose. To increase the mechanical and electrical strength, microcreated cable paper can be made from a mixture of unbleached sulphate pulp and bacterial cellulose. To reduce the cost, microcreated cable paper can be made from a mixture of sulphate unbleached softwood pulp and sulphate unbleached softwood pulp. To impart water-repellent properties, fix microcreps and increase mechanical strength, microcreated cable paper can be made with gluing with rosin glue, or oxidized starch, or a mixture thereof.

Microcreated cable paper is manufactured using the following technology. Wood, preferably coniferous, is freed from the bark, washed with water and ground into wood chips. Chips along the conveyor enters the brewing workshop. In the cooking shop, wood chips are cooked in an aqueous solution of sodium hydroxide and sodium sulfide with a pH of 13-14, at a temperature of (155-175) ° C and a pressure of up to 1.2 MPa. Cooking time - (1-3) hours. After wood chips are cooked, sulfate cellulose is obtained with a yield of (45-55)% with a degree of penetration (delignification) of 30-46 Kappa units, determined according to GOST 10070-74, year of introduction 1975, Russia. Cellulose is washed with demineralized water and cleaned of impurities. The washed and cleaned pulp is pumped into pools for the manufacture of paper pulp. From the pools, the pulp is fed to disk mills, which undergo two- or three-stage grinding to a degree of grinding in conventional Schopper-Riegler degrees 25-45 ° SH, determined on a Schopper-Riegler device according to ISO 5267-1. At the first stage, grinding is carried out at an increased concentration of cellulose in an aqueous suspension (15-45)%. This significantly increases the mechanical strength and extensibility of the paper. After grinding, the pulp is fed into a stirring pool, where it is diluted with water and mixed, if necessary, with gum rosin, or oxidized starch, or a mixture thereof. From the mixing basin, the pulp is fed into the machine pool, to which aluminum sulfate is also supplied, if necessary. Well-mixed, cleaned and diluted with water paper pulp is fed from the headbox to one or more nets of the paper machine (PM). A paper web of a certain thickness is formed on a PM net and excess water is removed. The final molding of a single or multilayer paper web and the removal of excess moisture occurs in the press section of the machine. The final drying of the paper is carried out by the contact method on paper drying cylinders. Additional paper can also be dried by convective drying in a drying chamber by blowing with hot air. Convective drying provides free shrinkage of the paper and increase its strength. To ensure high elongation of paper in the machine direction, the surface structure of the web is deformed in the form of subtle micro folds across the web resulting from the microcreping operation. Microcreping of paper is carried out at the Klupak installation, located at the end of the drying part of the paper machine, at a relative web moisture content of (60-85)%. At the Klupak plant, a relatively wet web passes between the drying cylinder and the endless rubber web. Due to the elastic properties of rubber, the paper web is initially stretched, and then shrinks, resulting in microcrepa formed on its surface. To increase the density of the paper and the uniformity of thickness along the length of the web, microcreated cable paper can be sealed on a machine calender or supercalender. Due to the high degree of penetration (delignification) and washing of cellulose with demineralized water, microcreped cable paper has increased dielectric characteristics determined by the specific electrical conductivity of the water extract according to GOST 8552-88, commissioned year 1989, Russia, with a hydraulic module of 1:50. The higher the degree of penetration (delignification) of the pulp, the lower the electrical conductivity of the water extract and the higher the dielectric characteristics of the paper. The unit of conductivity of a paper paper is microsiemens per centimeter (μS / cm). Hydro module 1:50 corresponds to the ratio of one weight part of absolutely dry substance (paper) to fifty weight parts of water.

The essence of the invention is illustrated by the following examples. The table shows the options for samples of paper cable according to the prototype and paper cable microcreated, as well as their main characteristics. The breaking force, elongation and break energy of all paper samples are given in the machine direction. Microcreated cable paper samples were made from 100% sulphate pine unbleached pulp without gluing with rosin glue and oxidized starch with different degree of penetration (delignification) of the pulp and different elongation in the machine direction. The manufacturability of all variants of cable paper according to the prototype and cable micro-crepe paper was tested in the manufacture of power electric cables with impregnated paper insulation. As can be seen from the table, microcreated cable paper in terms of basic characteristics is not inferior to prototype cable paper and surpasses it in mechanical characteristics in the machine direction (relative elongation and burst energy), in tear resistance in the transverse direction, in dielectric characteristics (K-120 paper) and manufacturability. At the same time, the optimal elongation in the machine direction of microcreated cable paper used for the manufacture of cable insulation should be in the range of (5-15)%. With a relative elongation of less than 5%, microcreated cable paper (option 1) does not withstand the process loads in the manufacture and testing of cable. This paper breaks during increased dynamic loads and cable bends. An elongation of 15% is the technological limit for micro-creped cable paper. Elongation of more than 15% has ordinary crepe paper, which is not suitable for cable insulation. Microcreated cable paper (option 3) with the elongation in the machine direction of 10% has the highest burst energy in the machine direction and the greatest adaptability. The optimum conductivity (E) of the aqueous extract of microcreped cable paper with a hydraulic module of 1:50 should be in the range (35-110) μS / cm. When E is less than 35 μS / cm, the complexity of manufacturing and the cost of paper significantly increase. When E is more than 110 μS / cm, the dielectric characteristics of paper are significantly reduced, which leads to an electrical breakdown of impregnated paper insulation and cable failure. The most optimal from the point of view of dielectric characteristics and cost is microcreated cable paper (option 3) with a specific electrical conductivity of a water extract with a hydraulic module 1:50 of 48 μS / cm.

Microcreated cable paper has passed comprehensive tests at cable plants in Russia and the CIS countries with positive results. The release of new insulating material has been arranged.

Table Name of characteristic Cable paper options for the prototype Cable Microcreated Paper Options K-120 KM-140 KMP-140 one 2 3 four Fiber Composition:  - unbleached sulfate pulp,%, one hundred one hundred one hundred one hundred one hundred one hundred one hundred according to GOST 7500-85 Mixed Mixed Mixed Coniferous Coniferous Coniferous Coniferous Degree of penetration - - - thirty 32 38 46 Paper design Two-layer machine smoothness Three-layer machine smoothness Three-layer machine smoothness Single-layer microcreated Single-layer microcreated Single-layer microcreated Single-layer microcreated Nominal thickness, microns, according to GOST 12769-85 120 140 140 140 140 140 140 Nominal mass 1 m ² , g, according to GOST 27015-86 94 109 109 109 108 105 one hundred

Table continuation Name of characteristic Cable paper options for the prototype Cable Microcreated Paper Options K-120 KM-140 KMP-140 one 2 3 four Nominal density, g / cm ³ , according to GOST 27015-86 0.78 0.78 0.78 0.78 0.77 0.75 0.72 Destructive force, N, according to ISO 1924-3 128 157 167 140 130 120 70 Elongation,%, according to ISO 1924-3 2.0 2.2 2.2 4.0 5,0 10.0 15.0 Burst energy, J / m ² , according to ISO 1924-3 105 142 151 230 266 492 430 Tear resistance in the transverse direction, N, according to GOST 13525.3-97 1,5 1.9 2.1 3.0 3.3 3.8 3,5

Table continuation Name of characteristic Cable paper options for the prototype Cable Microcreated Paper Options K-120 KM-140 KMP-140 one 2 3 four The specific electrical conductivity of a water extract, with a water module of 1:50, μS / cm, according to GOST 8552-88 60 35 40 115 110 48 35 Mass fraction of ash,%, according to GOST 7629-93 1,0 0.6 0.8 1,0 0.9 0.6 0.8 Manufacturability Low Low Low Low Average High Average

Claims (8)

1. Paper single or multi-layer cable paper from unbleached sulfate pulp, characterized in that it has a deformed surface structure obtained as a result of microcreping, relative elongation in the machine direction (5-15)% and specific electrical conductivity of water drawing with a hydraulic module 1: 50 within (35-110) μS / cm. 2. Paper cable according to claim 1, characterized in that the microcreping operation is carried out at the Klupak installation. 3. Paper cable according to claim 1, characterized in that it is made from sulphate pine unbleached pulp. 4. Paper cable according to claim 1, characterized in that it is made from sulfate coniferous unbleached electrical insulating cellulose grade ECB. 5. Paper cable according to claim 1, characterized in that it is made from a mixture of sulphate unbleached pulp and bacterial cellulose. 6. Paper cable according to claim 1, characterized in that it is made from a mixture of sulfate unbleached softwood pulp and sulfate unbleached hardwood pulp. 7. Cable paper according to claim 1, characterized in that it is glued with rosin glue, or oxidized starch, or a mixture thereof. 8. Paper cable according to claim 1, characterized in that it is sealed on a machine calender.