RU2342724C1 - Isolator with inorganic composite rod - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention is attributed to electric engineering in particular to high-voltage suspended and base rod composite insulators for air lines and open distributing devices. In the insulator containing rod made of composite material and reinforced by glass fibers, inorganic phosphate bonding material serves as matrix of bearing rod composite material. Bonding material is selected from following group: magnezium, aluminium, chrome, zirconium-phosphate bonding materials, combined on their basis bonding materials and alcaline polyphosphate solutions.

EFFECT: making the isolator resistant to adverse effects during service, reliability and durability improvement.

3 dwg

Description

Technical field

The invention relates to electrical engineering, in particular to high-voltage suspended and support rod composite insulators of overhead power lines (VLEP) and open switchgears (outdoor switchgear), designed for a voltage of mainly 6-1150 kV.

State of the art

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

Among the classical rod insulators, ceramic (porcelain) insulators occupy the main place. 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 composite insulators (suspension and tension insulators, VL line-to-line spacers). The basis of composite polymer insulators is a fiberglass rod, consisting of epoxy (phenol-formaldehyde, cycloaliphatic) resin and reinforcing glass fibers (glass roving). The IEC 1109/1 / standard was first developed, and on its basis the bulk of recent polymer composite insulators was created.

Starting from the 60s, the design of these insulators is also found in most patents related to rod polymer 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 filaments is described in detail in patent US 3557447 Jan. 1971. All insulators used in the world today use a core made of thermosetting polymer reinforced with glass filaments. In particular, in patents US 4604498 Aug. 1986, US 4,212,696 Jul. 1980, US 6051796 Apr. 2000, US 3134164 May 1964, US 4246696 Jan. 1981, US 4,217,466 Aug. 1980, SU 983758 of 12/23/1983 expressly indicates the use of glass fibers and a polymer matrix 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. In general, after the introduction of the IEC 1109 standard, a fiberglass rod with an epoxy matrix and reinforcing glass fibers is an integral element of a composite polymer insulator and does not undergo changes, despite the existing operational problems.

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” during 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 the fiberglass matrix material in combination with mechanical stress. When the acid first contacts the resin of the matrix and then 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 as a result of the lack of resistance of the resin material to acid or other adverse factors. 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 in composite insulators subjected to ordinary 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 significant drawback of rods based on polymer thermosetting resins (epoxy, polyester, phenolic, etc.) is their susceptibility to external adverse effects: solar radiation, temperature, weathering, ozone, moisture, electric arc, tracking, corona discharges, etc. Especially negatively affects the operation of high-voltage insulators is the resistance of the fiberglass rod to the effects of surface currents and internal partial discharges. When leakage currents pass along the surface of an epoxy or other polymeric organic resin, the surface burns and char. The thermal decomposition of organic resins results in products containing carbon, and carbon is known to be a good electrical conductor. As a result of the action of surface currents on the resin of the matrix of the fiberglass rod, a conductive path is formed, which quickly leads to the destruction of the insulator, short circuit and breakdown of the insulator. The same mechanism, with slight changes, operates with partial discharges in the internal cavities of the insulator. It is for the protection of fiberglass that protective shells made of polymer-resistant, resistant to the effects of leakage currents of silicone rubber are used on polymer insulators. The result of thermal decomposition of silicone rubber is silicon dioxide, a dielectric. And to eliminate partial discharges inside, vacuum is used in the manufacture and strict control of the level of partial discharges during control tests before shipment of finished insulators to the consumer.

All of these shortcomings were deprived of traditional ceramic insulators. They were made of electrical porcelain and had a monolithic design. The main disadvantage of porcelain insulators is fragility, low mechanical strength, very low impact strength, the possibility of a wire falling in case of breakage. All supporting porcelain insulators have a weak spot near the lower metal flange. Usually in this place, the insulator breaks down under mechanical stress. Composite polymer insulators do not collapse under the influence of only mechanical operational loads, since glass reinforcing threads have tensile strength several times greater than the strength of porcelain. Porcelain has acceptable compressive strength only. Fiberglass rods work great for tensile and bending. They are almost impossible to break. Under load, they bend like a fiberglass rod, but do not break. This property of fiberglass is used in polymer insulators and, in particular, in the supporting rod insulation design RU 2173902 from 1999.12.23, which is the prototype of the proposed insulator.

OBJECTS OF THE INVENTION

The invention solves the problem of creating an insulator with a supporting rod that is resistant to adverse operating factors and to the effects of mechanical dynamic shock loads.

Description and implementation example

When using fiberglass composite insulators, it is impossible to completely eliminate the damage caused by adverse atmospheric influences and completely exclude the possibility of a “brittle fracture” and fall of the insulator with the wire under voltage to the ground. On the other hand, it is impossible not to use high-strength composite materials, 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. For supporting insulators, lateral bending loads reach 10 kN. A rod made monolithic without reinforcing from any polymer cannot withstand such loads. Ceramic monolithic materials have all the necessary electrical properties, but do not have the mechanical properties of composite polymers. A conflict arises: there should be a composite material and at the same time there should not be a composite material. It was possible to resolve this conflict in the proposed isolator. The supporting insulating core is made of inorganic composite material reinforced with glass fibers. The matrix connecting the glass fibers is made on the basis of an inorganic phosphate binder.

The chemical process that initiates the hardening of phosphate systems is the acid-base interaction of a liquid protonated medium with solids of a basic nature. Any acid-base reaction in heterogeneous dispersed solid-liquid systems is a synthesis of binders and materials. The simplest phosphate binders are formed by acid-base phosphoric acid interaction systems. The conditions for the manifestation of astringent properties in phosphate binders change with a change in the chemical characteristics of the solid phase as a base. A decrease in the ionic potential of the cation in the oxide or in the work function of the electron causes an increase in its basic properties. In accordance with this, there is an increase in the chemical activity of the oxide with respect to acid and a transition from phosphate systems that harden only under conditions stimulating the chemical interaction of components (heating, mechanochemical activation, etc.) to systems hardening under normal conditions, and then to objects exhibiting astringent properties only with a decrease in the intensity of interaction of the solid phase and the matrix. So for oxides of silicon, titanium, aluminum, zirconium, magnesium, chromium, cobalt, the activation of the process of interaction with phosphoric acid is required for the manifestation of astringent properties. Oxides of iron, nickel, copper harden under normal conditions. Oxides of magnesium, zinc, cadmium, calcium, barium require passivation of the interaction process. Based on these properties, oxides for phosphate binders are selected. Some natural materials used in the electrical insulating industry can be used in phosphate bonds. An example of electrical insulation systems can be mica phosphate materials - the result of the interaction of mica minerals (phlogopite and muscovite) with aluminochromophosphate solutions. The most widely used in practice are magnesium, aluminum, chromium, zirconium phosphate bonds, as well as combined ligaments based on them and alkaline polyphosphate solutions. This is due to a wide range of compositions and properties, good adhesive and thermophysical characteristics of the ligaments.

As tests have shown, the use of phosphate bonds for the manufacture of composite rods made it possible to significantly increase the heat resistance, arc resistance, and resistance to tracking and leakage currents of insulators. Composite rods based on thermosetting resins required special protection against adverse factors during operation. Composite rods based on a phosphate matrix and glass reinforcing yarns do not require measures to protect against the effects of the atmosphere, ozone, ultraviolet radiation, precipitation and pollution. The mechanical properties of inorganic composite rods are primarily determined by the properties of the reinforcing fibers, the characteristics of the glass roving used. On this basis, the basic mechanical properties of an inorganic composite material are comparable to those of polymer composites. The main properties used in insulators include high mechanical tensile and bending strength, resistance to dynamic shock loads, the absence of brittleness, the absence of a break in the loss of mechanical strength and, as a consequence, the impossibility of the wire falling to the ground.

The high resistance of inorganic composite rods to adverse effects allows them to be used in insulators without a protective silicone or other coating. Until now, fiberglass rod-based polymer insulators have necessarily been required to be protected by a track-proof, resistant to the atmosphere, electric arc, ultraviolet, etc. protective sheath made of silicone rubber. In the case of violation of the tightness of the silicone shell or its destruction (for example, as a result of biting by birds), the fiberglass rod quickly broke down and the insulator failed with its complete destruction. The proposed insulators are devoid of this significant drawback.

Insulators with an inorganic composite rod based on phosphate bonds have all the advantages of polymer composite insulators, but are not exposed to adverse operating factors even without a protective sheath.

The production technology of a composite material based on inorganic phosphate bonds is identical to the technology for the production of composites based on thermosets, and is not difficult. The only difference is the use of a matrix of phosphate binders for the material, instead of thermosetting polymer resins. In particular, rods up to 80 mm in diameter are manufactured by pultrusion. The method consists in drawing a thin glass filament impregnated with a matrix binder through a die and then curing the matrix as a result of an irreversible reaction when heated in an oven to temperatures from 80 to 300 degrees Celsius. Using this technology, up to 85% of all polymer composite rods reinforced with glass or other fibers are made, while the filaments are also impregnated with a polymer that irreversibly hardens as a result of a chemical reaction at an elevated temperature from 80 to 180 degrees Celsius. Increasing the temperature to 300 degrees is not difficult.

It is possible to use the process of two stages. At the first stage, the reinforcing fibers are impregnated with a phosphate binder, drawn through a die and pre-dried. In the second stage, the rods are placed in a furnace with the temperature necessary to activate the process of acid-base interaction of a phosphate binder (for example, 300 degrees Celsius), where the final curing of the inorganic composite takes place.

It is possible to manufacture products using other methods traditionally accepted in the production of polymer composite materials. Such methods are: winding reinforcing threads pre-impregnated with a phosphate binder onto a mandrel, laying out material pre-impregnated in a phosphate binder from a reinforcing fabric or a chaotic bundle of threads, pressing blanks from an impregnated fabric or unidirectional reinforcing material in heated molds.

Using the winding method, they create the most durable structures with minimum weight, which is achieved by orientation of the reinforcing fibers in the direction of action of the main loads. At the applicant enterprise, all methods of manufacturing composite materials based on phosphate binders were tested. The main type of ligaments used in the manufacture of experimental batches of products were aluminophosphate ligaments and aluminochromophosphate ligaments. Composition of material for the carrier rods are usually insulators was: alyumohromfosfatnaya aluminophosphate ligament or ligament in a molar ratio of P ₂ O ₅ / Al ₂ O ₃ within 3,0-3,2-8-25%, alumina powder with a content of Al ₂ O ₃ not less than 95% and grain size M5-M20 up to 70%, reinforcing glass fibers from E glass - from 15% to 70%.

Bearing rods for insulators based on phosphate bonds, unlike fiberglass ones, have a number of properties that are necessary and manifest when operating 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 inorganic composite rod have 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 [3] and the international standard IEC1102 [1]. In additional comparative tests for the effects of organic acids, insulators showed better 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. 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 1 day to 3 months.

Mechanical tests showed higher tensile strength. Under the influence of long dynamic bending and tensile forces, insulators made on the basis of an inorganic composite rod showed results that are 15-20 times higher than the characteristics of insulators made of electrical porcelain. Under the influence of dynamic loads, fatigue fractures in the proposed insulator rods occurred much later than in china. This makes it possible to predict a significant increase in the service life of these insulators, since suspension insulators during vibration of wires and supporting insulators in the composition of disconnectors experience precisely dynamic loads.

The result of the use of the proposed insulator based on an inorganic rod is the absence of a "brittle fracture" in suspended insulators, resistance to the effects of adverse factors in operation. At the applicant plant, rods were made by impregnating the reinforcing fibers with a phosphate matrix binder under pressure. For the production of rods, glass filaments manufactured by Tverstekloplastik OJSC were used, as a binder, a composition of aluminophosphate binder with a molar ratio of P ₂ O ₅ / Al ₂ O ₃ in the range of 3-3.5 and alumina powder with α-Al ₂ content were used About ₃ not less than 95% and grit M5-M20. 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 and as a binder - epoxy resin ED-20 with PEPA hardener (polyethylene polyamine ) The tests were carried out for 8 months according to the CIGRE method [3].

The main result of the use of a rod based on an inorganic phosphate binder is the high stability of the insulator based on it to all types of adverse effects: ultraviolet, ozone, acids, moisture, electric arc, leakage currents, tracking, erosion, etc. The insulator can work while maintaining operability without protective shells and coatings. At the same time, the mechanical characteristics of the insulator, resistance to dynamic shock loads, vibrations is comparable with polymer composite insulators based on a fiberglass rod.

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 fracture" and the fall of the wire for this reason on the ground.

The design of the insulator is illustrated by drawings.

In all the drawings, the following notation:

1 - flanges of the insulator for mounting to fittings and support,

2 - electrical insulating composite rod based on a matrix with a phosphate binder,

3 - silicone protective shell,

4 - reinforcing high modulus fibers,

5 - inorganic matrix of a composite rod based on a phosphate binder.

Figure 1 is a view of a composite suspension insulator with a composite rod, based on an inorganic matrix of a phosphate binder.

Figure 2 is a view of a composite support insulator based on a rod with an inorganic matrix of a phosphate binder.

Figure 3 is a view of an electrical insulating rod consisting of an inorganic phosphate matrix and high modulus fibers.

Used publications:

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

Claims (1)

An insulator containing a support rod made of a composite material reinforced with glass fibers, characterized in that the matrix of the composite material of the support rod is an inorganic phosphate binder selected from the group: magnesium, aluminum, chromium, zirconium phosphate binders, combined binders based on them and alkaline polyphosphate solutions.

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