RU2328787C1 - Insulator with composite rod that is reinforced with high module organic fibers - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to high voltage suspended rod polymer insulators of overhead transmission lines (OT), designed predominantly for voltage 6-1150 V. Polymer rod insulator contains terminators and protective coating, bearing rod is made from composite polymer material, which is reinforced with organic fibers with high module of elasticity and strength.

EFFECT: absence of brittle fracture.

2 dwg

Description

Technical field

The invention relates to electrical engineering, in particular to high-voltage suspended rod polymer insulators of overhead power lines (VLEP), designed for a voltage of mainly 6-1150 kV.

State of the art

In recent years, the production and use of polymer insulators in high voltage electrical installations in many countries has been steadily expanding.

The use of these insulators on 35-750 kV overhead lines can significantly reduce the cost of construction and operation of power lines. World practice shows that the use of progressive polymer insulation on overhead lines will continue to increase steadily.

In the use of polymer insulators, along with the undoubted achievements, a number of serious unsolved problems remain. Therefore, manufacturers of insulators rather sparingly inform interested specialists about their achievements and shortcomings, keeping in secret not only the aspects of technology and design features of insulators, but also the experience of their operation.

Non-ceramic insulators are divided into composite insulators, consisting of several types of polymers and solid insulators from one polymer material. The most widespread in the world and in Russia were composite insulators. The IEC 1109 (1992) standard applies only to linear (suspension and tension insulators, VL line-to-line spacers) composite insulators. The IEC 1109 standard [1] was developed first, and on its basis the bulk of polymer composite insulators of recent times was created.

Starting from the 60s, the design of these insulators is also found in most patents related to rod composite insulators. They are all united by a common design: a fiberglass power rod, a protective shell made of a tracking-resistant polymer (polyolefin, silicone, etc.), metal flanges at the ends for fixing the insulator. A fiberglass rod usually consists of a matrix based on a thermosetting polymer, such as epoxy, and reinforcing thin unidirectional fibers. A method of manufacturing fiberglass with glass fibers is described in detail in US patent 3,557,447 Jan. 1971. All insulators used in the world today use a rod reinforced with glass filaments. In particular, in patents US 4,604,498 Aug. 1986, US 4,212,696 Jul. 1980, US 6,051,796 Apr. 2000, US 3,134,164 May 1964, US 4,246,696 Jan. 1981, US 4,217,466 Aug. 1980, SU 983758 of 12/23/1983 expressly indicates the use of glass fibers in a composite power rod. In the patents of the Japanese company NGK Insulators Ltd., for example, EP 0617433 of 03.25.1994 describes an insulator with a polymer rod reinforced with strong fibers, without indicating the material of the rod. The core and material of this patent are not protected.

Some types of composite suspension insulators manufactured by various factories since the beginning of the 70s turned out to be mechanically fragile, which led to a number of serious accidents even after a short period of their operation. These failures in the operation of the insulators occurred under mechanical loads significantly less than the nominal, and the fracture surface of fiberglass significantly differed from that observed in laboratory mechanical tests. This type of fracture, later called the “brittle fracture”, was reproduced in laboratory conditions when a relatively low tensile load with simultaneous acid exposure was applied to the fiberglass core. In [2], recommendations are given for identifying brittle fracture of a fiberglass rod of composite insulators. The main visually observed characteristics of a brittle fracture of fiberglass: a smooth (without fragments) fracture surface, mainly located perpendicular to the axis of the rod (only some fibers protrude from the resin), the presence of several fracture planes (cracks) formed along the length of the rod, the fracture surfaces are clean, not visible a large number of broken fibers. In contrast to the “brittle fracture”, with the usual destruction of fiberglass by tensile load, many broken fibers (not crystalline, but white), small particles of glass and resin are visible, and the fracture surface is at an angle of 45 degrees to the axis of the rod.

This destruction is currently being studied in many countries. Based on these observations, the following mechanism of brittle fracture was adopted: most often it occurs inside the metal reinforcement of insulators, where the distribution of mechanical stresses over the cross section of the rod is especially uneven, or at a distance of 5-10 cm above the lower terminal, where in the absence of shields the greatest electric field strength is observed. A crack initiating brittle fracture under the action of a tensile load propagates slowly until, due to a gradual decrease in the cross section of the rod, the mechanical stress rises to a sufficiently high level that breaks the fibers. Examination of the surface of brittle fracture using a microscope reveals "stop lines" where cracks begin. Evaluation of many brittle fractures shows that they are associated with low mechanical stress, slow propagation of cracks, their initiation on the surface of a fiberglass rod. A mandatory fact that accompanies brittle fracture is the presence of contact with fiberglass active chemicals, especially an acid solution, i.e. brittle fracture is associated with corrosion of fiberglass material in combination with mechanical stress. When the acid contacts the glass fibers, an ion exchange occurs between the acid and the glass lattice. This leads to increased loads on the surface of the fiberglass, causing spiral cracks on the surface of the glass. It is known that fiberglass rods of composite insulators are made of fiberglass placed in a polymer resin. High mechanical strength of the rods is determined by fiberglass. Cracks begin in the resin and usually cease to spread near fiberglass. If the acid reaches the glass fiber (usually this occurs near or on the surface of the rod), the fiber breaks in the plane of propagation of the crack. Tears occur gradually: fiber by fiber. Acid can also migrate longitudinally, causing a gradual spread of “brittle fracture” along the rod. In this case, as the crack propagates, the mechanical stress in front of the crack increases and, therefore, the crack propagates faster and faster. At the final stage, when the crack propagation velocity reaches the speed of sound in fiberglass, the fracture mode changes from “brittle” to normal.

The considered phenomenon of “brittle fracture” can be observed on composite insulators subjected to normal atmospheric influences, since some acids of various concentrations can be contained in atmospheric air. Nitric acid can also form on the surface of the insulator during electrical discharges in a humid environment. The danger of a "brittle fracture" increases sharply if the edges of the insulator containment shell are damaged and the core is exposed. A particularly sensitive fracture zone is the transition from the insulator shell to its end fittings.

Here materials with different coefficients of thermal expansion are used and they must be interconnected so as to avoid the penetration of moisture into the inner cavity of the reinforcement, i.e. ensure the tightness of the connection.

The likelihood of a “brittle fracture” cannot be ruled out when using unidirectional fiberglass rods with a longitudinal orientation of glass fibers, since the destruction of one fiber directed along the applied mechanical load leads to an increase in the stress of the remaining fibers of this direction and provides the basis for the development of fracture.

In the insulator described in CN 1141718 and CN 1267063, "Liquid polyester modified anticorrosion stress-resistant core rod for high-voltage composite insulator", an attempt was made to solve this problem by using corrosion-resistant type E glass coated with liquid polyester for glass fibers. The isolator according to the latest patent is a prototype, since the goals set in it are identical to those achieved in our isolator. The prototype introduces additional protection of the glass in the composite rod and increases its reliability, but the solution according to this patent did not completely exclude the possibility of a “brittle fracture”.

OBJECTS OF THE INVENTION

The aim of the invention is to eliminate the corrosion of glass fibers in the composite rod of polymer suspension insulators, to eliminate the occurrence of “brittle fracture”, and as a result, to eliminate the possibility of destruction of the insulator and falling wires to the ground.

Description and implementation example

When using glass fibers, it is impossible to exclude glass corrosion under the influence of adverse atmospheric influences and completely exclude the possibility of “brittle fracture” and the fall of an insulator with a live wire to the ground. On the other hand, it is impossible not to use high-strength glass filaments, since the supporting rod must withstand tensile loads of more than 70 kN, and the tension of the wires of overhead power lines, especially in emergency operation, can exceed 400 kN. A rod made of monolithic without reinforcement with thin unidirectional threads of any polymer cannot withstand such loads. There is a conflict situation: glass unidirectional threads should be and at the same time - they should not be. This conflict was resolved in the proposed insulator, where the glass filaments in the composite power rod were replaced with organic filaments with a high modulus of elasticity. Such filaments appeared in the late 1980s [3] and now there are many types of organic filaments that are comparable in properties to glass filaments: polyparaphenylene terephthalamide, polybenzothiazole, polybenzoxazole, polyvinyl alcohol, polyethylene and other fibers based on rigid-chain and flexible-chain polymers, liquid crystal polyacrylene and polyimide polymers. The trademarks for these fibers are Kevlar (Dupont Nemur), CBM, Armos, Thurlon, Econol, Vectran, IVSAN, Teclimon (Mitsui Co. Japan), Espelen (Tverkhimvolokno NGO), Spectra (Ellide Co., USA), Daynema (DSM , Holland) and others.

The most famous high-strength and high-modulus organic fibers are aramid fibers based on liquid crystal polyamides (Kevlar, Twaron, Terlon fibers) and their copolymers (CBM, Armos, Tehnora fibers). The first of them in 1971 appeared Kevlar fiber (Fiber D, PRD - the original name), created by the American company Dupont de Nemours. Later similar fibers Twaron and Thurlon were developed respectively by Akzo (Holland) and NPO Khimvolokno (Russia). Of the copolymer fibers, first of all, we note domestic fibers of the CBM brand (the original name is VNIIVLON) and the Armos brand, developed by NPO Khimvolokno (Russia), manufactured on an industrial scale since the late 1970s. A similar fiber of Technor is produced by the Japanese company Teijin. Currently, the range of organic fibers is very extensive. By modifying the composition, drawing conditions and heat treatment, it is possible to vary their elastic strength properties in accordance with the requirements of consumers. For example, more than 12 types of Kevlar fiber are produced with a strength of 2 to 3.8 GPa and an elastic modulus of 70 to 190 GPa.

Organic fibers with a high modulus of elasticity are highly resistant to the action of mineral acids, are not susceptible to corrosion and leaching, unlike glass used in glass fibers. Composite plastics with reinforcing organic fibers are used in the aerospace industry, and begin to be used in mechanical engineering, where high specific characteristics of the material are required.

The main disadvantage of organic fibers with a high modulus of elasticity and composite materials based on them is their high cost in comparison with glass fibers and fiberglass. However, given that in the structure of the cost of an insulator the bearing rod takes up no more than 9%, the rise in price of the total cost of the entire insulator is negligible. The properties that an insulator acquires are more valuable.

The production technology of a composite polymer material reinforced with organic fibers with a high modulus of elasticity is identical to the technology for the production of composites based on glass fibers, and is not difficult. The materials used for the matrix can be both thermoplastics and thermosets. The only difference is the use of high modulus organic polymers for reinforcing fibers. In particular, rods up to 80 mm in diameter are manufactured by pultrusion. The method consists in drawing a beam of thin organic filaments impregnated with a polymer matrix through a die and then curing the polymer matrix as a result of an irreversible reaction for thermosets or lowering the temperature for thermosets. Using this technology, up to 85% of all polymer composite rods reinforced with fibers (glass, carbon, boric, basalt, ceramic, organic, etc.) are manufactured.

Bearing rods for insulators made of composite polymer material reinforced with organic fibers with a high modulus of elasticity, unlike fiberglass ones, have a number of properties necessary and manifested during the operation of high-voltage insulators with a load. In the manufacture of an experimental batch of high-voltage insulators for voltage of 110 kV, 220 kV at the applicant enterprise and subsequent studies, it was proved that the purpose of the invention was achieved.

Insulators made on the basis of an organoplastic rod successfully withstood the effects of contamination with solutions of mineral acids, alkalis and salts. Insulator tests were carried out under extreme operating conditions in accordance with the recommendations of CIGRE [4] and the international standard IEC1102 [1]. In additional comparative tests for the effects of organic acids, insulators showed slightly worse results than similar insulators made on the basis of fiberglass rods. Exposure to such acids under actual operating conditions does not occur. All harmful effects according to the generally accepted testing methods for polymer high-voltage insulators were applied during the tests and the insulators successfully passed these tests.

To tighten the test conditions, the insulators were made without protective silicone shells. The organoplastic core was made on the basis of cycloaliphatic tracking-resistant resin and aramid fibers produced by Kamenskvolokno OJSC. As a result of testing these insulators, it was revealed that live insulators could operate without a protective silicone shell. In accordance with the accelerated testing program, the calculated period of operation of the insulator was more than 10 years. It should be borne in mind that a high-voltage insulator based on a fiberglass rod without a protective shell is destroyed within 3-4 months.

Mechanical tests showed higher tensile strength. Under the influence of long dynamic tensile forces, insulators made on the basis of an organoplastic rod showed results that are 15-20 times higher than the characteristics of insulators made on the basis of fiberglass rods. Under the influence of dynamic loads, fatigue fractures in the organoplastic rods of the insulator occurred much later than in fiberglass ones. This makes it possible to predict a significant increase in the service life of these insulators, since suspension insulators experience dynamic stresses during vibration of the wires. In additional tests of organoplastic insulator rods for compression, worse results were obtained than similar ones for fiberglass insulator rods. But this drawback does not affect the operation of the insulator, since during operation only tensile loads act on the insulator. Compressive loads are tested by the rods only at the factory during manufacture, during the operation of crimping metal flanges on the rod. This operation must be carried out more carefully, observing the pressing pressure regimes. When crimping flanges, it is also necessary to use round dies and radial comprehensive compression to more carefully carry out this operation.

The main result of the use of the proposed insulator based on a composite polymer material reinforced with organic fibers with a high modulus of elasticity is the absence of a “brittle fracture”. At the applicant enterprise, rods were made by impregnating reinforcing organic fibers with a matrix binder under pressure. For the production of cores, CBM aramid fibers manufactured by Kamenskvolokno OJSC were used, and ED-20 epoxy-diane resin was used as a binder. As a result of lengthy tests simulating the conditions of occurrence of a “brittle fracture”, not a single case of this type of destruction was revealed. Control samples of insulators with a fiberglass rod showed destruction in 3 cases out of 10. Fiberglass rods were made according to the same technology using glass roving manufactured by Tverstekloplastik OJSC for reinforcing and the same epoxy resin ED-20 as a binder. The tests were carried out for 8 months according to the CIGRE method [4].

Based on the foregoing, it can be concluded that the electrical, operational and mechanical characteristics of the proposed insulators are significantly improved in comparison with traditional ones based on a fiberglass supporting rod. Also, the proposed insulators exclude the possibility of a “brittle break” and a fall of the wire for this reason.

The design of the insulator is illustrated by drawings.

In all the drawings, the following notation:

1 - insulator flanges for fastening to fittings and support

2 - electrical insulating core made of composite polymer material reinforced with organic fibers with a high modulus of elasticity

3 - silicone protective shell

4 - reinforcing organic fibers with a high modulus of elasticity

5 - polymer matrix composite rod

Figure 1 is a view of a composite insulator with a rod reinforced with organic fibers.

Figure 2 - view of the insulating rod, consisting of a polymer matrix and organic high-modulus fibers.

Literature

1. IEC 1109 (1992). Composite insulators for a.c. overhead lines with a nominal voltage greater than 1000 V. Definitions, test methods and acceptance criteria.

2. Guide for the identification of brittle fracture of composite insulator FPR rod. Working Group 03 of CIGRE Study Committee 22. Electra, 1992, No. 144, 61-65.

3. Moore, John W., "PRD-49 A New Organic High Modulus Reinforcing Fiber", published by E.I. DuPont de Nemours and Co., Inc., Textile Fibers Department, Wilmington, Del., 18 pages.

4. CIGRE Study Committee 22, W.G. 10, 1983. Technical basis for nominal requirements for composite insulators. Electra, No. 88, 1983, 89-114.

Claims (1)

A polymer rod insulator containing a power supporting rod, terminators and a protective sheath, characterized in that the rod is made of a composite polymer material reinforced with organic fibers with a high modulus of elasticity.

Images