RU2788308C1 - Method and device for continuous control of humidity of paper-oil insulation of high-voltage oil-filled equipment - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to measurement of absolute humidity of paper in coil insulation of high-voltage oil-filled equipment. A preset number of paper samples used as internal insulation of equipment is impregnated with transformer oil. Several capacitors are assembled next to each other, in each of which an insulation layer is made of one of paper samples. The assembly is calibrated, while it is immersed into transformer oil with the known humidity. The assembly is immersed into a tank with transformer oil of high-voltage oil-filled equipment. Electrical capacity of each assembly capacitor is measured. Humidity of a specific paper sample is determined by the measurement results and calibration data.

EFFECT: increase in the reliability and efficiency of determination of absolute actual humidity of paper insulation of oil-filled electrical devices.

12 cl, 7 dwg

Description

The field of technology to which the invention belongs

The present invention relates to a method for measuring the absolute moisture content of paper in coiled insulation of high-voltage oil-filled equipment, such as a power transformer, as well as to a device for implementing this method.

State of the art

The presence of moisture (water) in the paper-oil insulation of high-voltage oil-filled equipment can adversely affect the operation of such equipment. In a working power oil-filled transformer, even at a constant load, there is an uneven distribution of moisture in different parts of the insulation. It is known that coiled insulation has a lower moisture content than main insulation barriers due to the tendency to equalize the partial pressure of water vapor under the influence of a temperature gradient. This fact is explained by the fact that the barrier insulation is heated by oil, and the coil insulation is heated directly from the magnetic circuit, which in a working power transformer always has a higher temperature than oil. In a working transformer, there is a constant redistribution of water between solid insulation and oil due to temperature changes with changes in load and atmospheric conditions. In the case of an increase in the temperature of a solid insulation, the partial pressure of water vapor in it increases, and under the action of a partial pressure gradient, moisture passes from the solid insulation to the oil. Under sudden changes in conditions, the transformer oil may become supersaturated with moisture and free water will be released in the form of an emulsion. Under the influence of an electric field, water bubbles can line up in chains, because. water is inherently polar and will form conductive bridges or deposit on the surface of solid insulation. All this leads to a decrease in the electrical strength of the insulation (http: //leg.co.ua/transformatory/praktika/vlagosoderzhanie-izolyacii-transformatora-pri-ego-ekspluatacii.html) and, ultimately, to its breakdown. In this regard, the measurement of the moisture content of the insulation during the operation of the transformer is an urgent and important task.

To measure the moisture content of oil-paper insulation, various methods and devices are used.

RF patent No. 2756508 (published on October 1, 2021) describes a system for monitoring the technical condition of a transformer based on the condition of the oil poured into this transformer. In this system, a solid insulation moisture sensor is specified as an integral part. However, the implementation of this sensor and even the principle of its operation in this document are not disclosed.

US Pat. No. 8,149,003 (published April 3, 2012) describes a method and apparatus for determining the moisture content of a transformer insulation. This patent describes in a general way a method in which the dielectric properties of the insulation are determined, its model is built and it is refined depending on the conductivity of the liquid used. As in the previous document, this patent does not disclose the details of both the method and the apparatus.

In US patent No. 10180407 (published on January 15, 2019) and in the continuation and development of its US patent No. 10502702 (published on December 10, 2019), capacitive humidity sensors are disclosed, made using the technology of multilayer MOS (metal-oxide-semiconductor) field-effect transistors and containing reference and measuring capacitors. These sensors are quite difficult to manufacture and use.

The principle of measuring the moisture content of the insulation of power transformers by measuring the dielectric frequency response using a set of capacitors is also disclosed in the publications of international applications WO 2008/026997 (published on March 6, 2008) and WO 2015/155270 (published on October 15, 2015). However, the devices proposed in these applications are quite complex.

In the RF utility model patent No. 155510 (published on October 10, 2015), a very simple capacitive-type humidity sensor is described in the form of two flanges, between which capacitor electrodes are fixed, separated by a layer of paper insulation, which plays the role of a dielectric layer. This document is accepted as the closest analogue.

However, this sensor has limited functionality due to the long settling time of the measured value, which is determined by the diffusion of moisture in the paper and may be unacceptable for the purposes of continuous monitoring of the moisture content of oil-paper insulation of high-voltage equipment. The characteristic time of diffusion processes is proportional to the square of the size from the edges to the point farthest from them in the paper - this is the path that moisture needs to travel in the paper, so reducing these dimensions would reduce the measurement time. In addition, in this sensor, one type of paper is used as the dielectric layer in the capacitor, while the coiled insulation in the equipment can be of varying degrees of aging.

Disclosure of invention

The objective of the present invention is to overcome the shortcomings of the existing state of the art and achieve a technical result, which consists in increasing the reliability and efficiency of determining the absolute actual moisture content of the paper insulation of oil-filled electrical devices, as well as in providing the possibility of obtaining a more accurate estimate of the aging rate of solid insulation, including when determination of the load capacity of oil-filled power transformers.

To solve this problem and achieve the specified technical result in the first object of the present invention, a method for measuring the moisture content of paper-oil insulation of high-voltage oil-filled equipment is proposed, in which: impregnating with transformer oil a predetermined number of paper samples used as internal insulation of high-voltage oil-filled equipment; provide an assembly of several capacitors next to one another, in each of which the insulating (dielectric) layer is made from one of the paper samples; the assembly is calibrated when it is immersed in transformer oil with a known moisture content; the assembly is immersed in a tank with transformer oil of high-voltage oil-filled equipment; measure the electrical capacitance of each capacitor assembly; determine the moisture content of a particular paper sample from the measurement results and calibration data.

A feature of the method according to the first object of the invention is that paper in different samples may differ in its characteristics, selected from the group including paper grade, paper thickness, paper polymerization degree.

Another feature of the method according to the first aspect of the invention is that the same transformer oil can be chosen for the impregnation of the paper as is used in high-voltage oil-filled equipment.

Another feature of the method according to the first object of the invention is that the impregnation can be carried out in a vacuum.

Another feature of the method according to the first object of the invention is that each of the capacitor assemblies can be perforated in advance for better penetration of oil into the paper.

Another feature of the method according to the first aspect of the invention is that capacitance measurements can be performed after the dynamic equilibrium of the moisture in the oil and paper has been established.

Finally, another feature of the method according to the first object of the invention is that the assembly can be provided with a transformer oil moisture sensor and take its readings into account when determining the moisture content of a particular paper sample.

To solve the same problem and achieve the same technical result in the second object of the present invention, a device for measuring the moisture content of paper-oil insulation of high-voltage oil-filled equipment is proposed, containing: a common base made of a dielectric material; a predetermined number of capacitor plates of a dielectric material placed side by side on the base; selected according to the number of capacitor plates and each laid between a common base with a corresponding capacitor plate, paper samples used as internal insulation in equipment, pre-impregnated with transformer oil; in this case, the capacitor plates from the side facing the common base, and the sections of the common base facing them, are covered with a metallization layer and provided with electrical leads laid along the common base.

A feature of the device according to the second object of the invention is that paper in different samples may differ in its characteristics, selected from the group including paper grade, paper thickness, paper polymerization degree.

Another feature of the device according to the second object of the invention is that in the capacitor plates, in the areas of the common base opposite these plates and in the paper samples between them, perforation can be made for better penetration of transformer oil into the paper samples.

Another feature of the device according to the second object of the invention is that the common base with capacitor plates placed on it can be inserted into a perforated protective cover designed for installation in a tank with transformer oil of high-voltage oil-filled equipment, leaving electrical leads outside the tank.

Another feature of the device according to the second object of the invention is that it may further comprise a transformer oil moisture sensor located on a common base next to the capacitor plates.

Finally, another feature of the device according to the second object of the invention is that it may further comprise a temperature sensor mounted on a common base next to the capacitor plates.

It should be specially noted that the use of perforated plates and, accordingly, perforation in paper samples provides an additional technical result in the form of an improvement and, consequently, an acceleration of the dynamics of moisture migration from oil to paper and vice versa with a change in oil moisture, which reduces the duration of dynamic equilibrium. And the use of an oil moisture sensor in this case provides another additional technical result in the form of control in achieving a dynamic balance between the moisture content of paper and oil.

Brief description of the drawings

The present invention is illustrated in the drawings, in which like elements are identified by the same reference numerals.

On FIG. 1 shows an embodiment of a device according to the second aspect of the present invention.

On FIG. 2 shows the base and the capacitor plate separately.

On FIG. 3 is a sectional view of the device of FIG. 1 when immersed in transformer oil.

On FIG. 4 shows the serial assembly of the device capacitors according to the second aspect of the present invention.

On FIG. 5 shows a parallel assembly of device capacitors according to the second aspect of the present invention.

On FIG. 6 shows the device of FIG. 1 inserted into a perforated protective case.

On FIG. 7 shows the device of FIG. 1 with oil moisture sensor installed.

Detailed description of embodiments

The device according to the second object of the present invention can be made as follows.

The device for measuring the moisture content of oil-paper insulation of high-voltage oil-filled equipment contains an assembly of several capacitors placed next to one another. On FIG. 1-5, for greater clarity, an example of such an assembly with a single capacitor is shown. The assembly contains a common base 1 made of a dielectric material, which can be fiberglass, getinaks or any other insulating material. A predetermined number of capacitor plates 2 can be made from the same material. FIG. 2 shows those sides of the common base 1 and the capacitor plate 2 which, when assembled, face each other. Meanwhile, shown in FIG. 2, the side of the capacitor plate 2 and the corresponding section of the common base 1, facing this capacitor plate 2 in the assembled state, are covered with a metallization layer 4 and provided with signal leads 5 and 6 laid along the common base 1. Instead of metallization, a foil textolite with an etched topology can be used. connections. Thus, the metallized surfaces of the capacitor plate 2 and the section of the common base 1 facing it during assembly form the capacitor plates.

Reference numerals 8 mark the mounting holes for attaching the capacitor plate 2 to the common base 1, and reference numeral 9 marks the contact hole for connecting the metallization layer 4 of the capacitor plate 2 with the signal terminal 6 on the common base 1. Those skilled in the art will understand that the metallization layer 4 around mounting holes 8 is spaced from their edges in order to avoid contact with the fasteners used, for example, screws (not shown).

Between the common base 1 and the corresponding capacitor plate 2 is laid a sample 3 of paper used as insulation in high-voltage oil-filled equipment. This paper sample 3 plays the role of a dielectric spacer for the resulting capacitor. The paper in different samples 3 can be the same, but it is preferable that the paper in different samples differ in its characteristics. For example, paper samples 3 may differ in grade, in thickness, in degree of polymerization (by degree of aging).

Each such sample 3 is pre-impregnated with transformer oil. Preferably, for this impregnation of paper samples 3, the same transformer oil is selected as used in the high-voltage oil-filled equipment for which moisture measurements are carried out using the device according to the second aspect of the present invention. At the same time, it is advisable to carry out such impregnation in a vacuum to exclude air cavities and speed up the impregnation process.

In the capacitor plates 2 and in the areas of the common base 1 facing them, perforation 7 is preferably made for better penetration of the transformer oil into the paper samples 3. Perforation holes are also made in the paper samples 3 themselves, since moisture enters the paper through the ends of the paper sheets. On FIG. 3 arrows show the penetration of transformer oil 10 through perforation holes 7 into paper samples 3.

On FIG. 4 and 5 show, respectively, a series assembly and a parallel assembly of capacitors. Wherein reference numerals 11 and 12 denote the signal terminals of the second capacitor, and reference numerals 13 and 14 denote the signal terminals of the third capacitor.

As shown in FIG. 6, in the device according to the second object of the present invention, the common base 1 with capacitor plates 2 placed on it can be inserted into a perforated protective cover 15 intended for installation in a tank with transformer oil of high-voltage oil-filled equipment. This cover 15 can be made of any oil-resistant non-magnetic material: metal (aluminum, titanium, brass) or plastic (Teflon, polystyrene, etc.). In this case, the signal leads (not shown in Fig. 6) remain outside the tank.

According to FIG. 7, the device according to the second object of the present invention may additionally contain a transformer oil moisture sensor 16, which is located on a common base 1 next to the capacitor plates 2. Reference position 17 denotes the outputs of this sensor 16. As such a sensor, you can use a dielcometric humidity sensor or any other, known to experts and presented on the market.

The device according to the second object of the present invention may further comprise a temperature sensor (not shown) mounted on a common base 1 next to the capacitor plates 2, similarly to the transformer oil humidity sensor 16. This can be a sensor of any design that allows you to take readings and transmit the results in the form of electrical signals. Those skilled in the art will appreciate that, as shown in FIG. 7, the location of any sensor is purely illustrative, and any of the two indicated sensors can be placed, including on the reverse side of the common base 1.

The method according to the first object of the present invention is implemented using the described device as follows.

Samples of paper used as insulation (predominantly coiled) in high-voltage oil-filled equipment (for example, in a power transformer) are impregnated with transformer oil, preferably the same one that is filled with this equipment. These samples can be made from the same paper to improve the accuracy of subsequent measurements. However, it is preferable that the paper in the samples be different: it can be cable paper with a different degree of polymerization (SP), characterizing the degree of its aging (see, for example, "Guidelines for assessing the state of paper insulation of windings of power transformers and shunt reactors by the degree of polymerization » - https://library-full.nadzor-info.ru/doc/51317). For example, fresh paper (DR≈1200), medium aged paper (DR≈600) and aged paper (DR≈300) can be selected.

The impregnation of the paper with transformer oil is preferably carried out under vacuum in order to speed up the impregnation and improve the quality of the impregnation.

Paper samples impregnated with transformer oil are placed on a common base 1, covering each paper sample 3 with its capacitor plate 2, which is attached to the common base 1 with suitable fasteners through mounting holes 8. Metallization 4 of each capacitor plate 2 is connected through a contact hole 9 to the corresponding signal output 6, 12, 14 (see Fig. 1, 6, 7).

It should be noted that in the common base 1, in the capacitor plates 2 and in the paper samples 3, perforations 7 can be made to better penetrate the oil into the paper, as shown in FIG. 3.

On the common base 1, an oil moisture sensor 16 and a temperature sensor can be placed (see Fig. 7). It should be emphasized that the capacitor plates 2 and said sensors are placed on a common base 1 in close proximity to each other to ensure the identity of the temperature conditions and the moisture content of the oil.

An assembly of one or more capacitors prepared in this way is immersed in transformer oil with a known moisture content and the finished assembly is calibrated. To do this, measure the electrical capacitance of each capacitor assembly at different moisture content of the transformer oil, and the results of these measurements are stored in the memory of a suitable computing tool, for example, a personal computer or controller. Computing means may be included in the device according to the second object of the present invention.

The method according to the first object of the present invention is implemented using the device according to the second object of the present invention as follows.

First, a predetermined number of samples 3 of paper used as internal insulation of high-voltage oil-filled equipment, such as a power transformer, is impregnated with transformer oil. Paper samples 3 can be either identical or different in their characteristics, which are selected from the group including paper grade, paper thickness, paper polymerization degree. The impregnation is preferably carried out in a vacuum, and the same transformer oil can be chosen for impregnating the paper as used in the high-voltage oil-filled equipment being tested (power transformer).

Transformer oil impregnated paper samples 3 are used as an insulating layer in several capacitors arranged side by side in an assembly. In each of the capacitors of this assembly, the insulating layer is made from one of the impregnated paper samples. As noted above, perforations 7 can be made in the capacitor plates for better penetration of oil into the paper located between the capacitor plates. In addition, an oil moisture sensor 16 and a temperature sensor may be placed adjacent to the assembly capacitors.

After preparing such an assembly of capacitors, it is calibrated by immersing it in transformer oil with a known and constant humidity. Then the calibrated assembly is immersed in a tank with transformer oil of controlled high-voltage oil-filled equipment (power transformer). This assembly can be inserted into the perforated protective case 15.

To measure the moisture content of paper-oil insulation of high-voltage oil-filled equipment, the electric capacitance of each capacitor of this assembly installed in the transformer oil tank of the equipment under test is measured.

In operating high-voltage oil-filled equipment, the duration of complete moisture equilibrium between oil and paper is unacceptable for the purposes of measuring the moisture content of coiled insulation, given the temperature instability and low rates of moisture migration from oil to paper and back. Moisture migration occurs due to changes in oil temperature, both during daily fluctuations in ambient temperature, and due to changing electrical load. The present invention makes it possible, without waiting for the onset of an equilibrium state, to measure the actual (rather than equilibrium) moisture content of the coiled insulation under current conditions, determined by the rate of moisture migration into the paper and back with a change in temperature. Thus, more accurate results of monitoring the moisture content of paper under current conditions will be obtained in a continuous mode without taking the equipment (power transformer) out of operation.

To date, in accordance with regulatory documents (see, for example, Guidelines for determining the moisture content of solid insulation of windings of power transformers (shunt reactors) based on the results of measuring dielectric characteristics. Approved by RAO UES of Russia on June 21, 2007), the moisture content of paper insulation windings of power transformers can be determined by an indirect method without paper sampling during measurements on disconnected (out of service) equipment. The capacitance and dielectric loss tangent of the winding insulation are measured, as well as the dielectric loss tangent of the oil at the same temperature, and the average moisture content of the solid insulation is calculated from these data using the dependencies of the solid insulation loss tangent of the transformer windings on temperature and humidity. For calculations, among other things, it is necessary to know the design of the equipment, namely the geometric parameters of the internal solid insulation.

Another regulated indirect method without sampling paper can determine the moisture content of cardboard (Appendix B in STO RusHydro 02.03.77-2011 Hydroelectric power plants. Extending the life of the main equipment during operation. Norms and requirements) in the internal insulation of power transformers. However, the weakest element of the transformer insulation system is the winding insulation, and it is necessary to control the moisture content of this particular insulation. At the same time, the transformer is transferred to a special mode of operation for warming up to 65±5°C with exposure for three days, during which the moisture content of the oil is measured, followed by conversion to the moisture content of the cardboard.

It is known from practice that three days are not enough to establish a complete balance of moisture between oil and paper insulation of power transformers (the characteristic duration is 1-3 months). Therefore, in both regulated methods, the moisture content value is obtained not yet for the equilibrium distribution of moisture between paper and oil, but not in the operating mode, which often leads to overestimated results of the moisture content of solid insulation due to the combination of oil temperature at the time of sampling and the previous operating mode ( the nature of the change in load) equipment.

At the same time, in accordance with the present invention, with the simultaneous use of an oil moisture sensor, it is possible to calculate the equilibrium moisture content of the turn insulation, which will make it possible to determine the difference between the moisture content value determined by the indirect method and the actual moisture content value and the time parameters of moisture migration.

It should be noted that if oil moisture and temperature sensors are not provided, measurements begin after a predetermined period of time determined from previous test results or from reference data.

According to the results of the measurements taken, taking into account the data of the previous calibration, the moisture content of a particular paper sample is determined.

Thus, the present invention achieves the above technical result, which consists in increasing the reliability and efficiency of determining the absolute actual moisture content of the paper insulation of oil-filled electrical devices by directly measuring the moisture content without recalculation from the moisture content of the oil or the dielectric characteristics of the oil and between the winding insulation.

The present invention also provides the possibility of refining the assessment of the aging rate of solid insulation, including when determining the load capacity of oil-filled power transformers and autotransformers.

Claims (22)

1. A method for measuring the moisture content of paper-oil insulation of high-voltage oil-filled equipment, in which: - impregnate with transformer oil a predetermined number of samples of paper used as internal insulation of the said equipment; - provide an assembly of several capacitors next to one another, in each of which the insulating layer is made of one of the mentioned paper samples; – carry out the calibration of the mentioned assembly when it is immersed in transformer oil with a known humidity; - immerse said assembly in a tank with transformer oil of said high-voltage oil-filled equipment; - measure the electric capacitance of each capacitor of the mentioned assembly; – determine the moisture content of a particular paper sample from the results of said measurements and the data of said calibration. 2. The method according to claim 1, in which the paper in different samples is different in its characteristics, selected from the group including paper grade, paper thickness, paper polymerization degree. 3. The method according to claim 1, wherein the same transformer oil is selected for said paper impregnation as used in said high voltage oil-filled equipment. 4. Method according to claim 1 or 3, wherein said impregnation is carried out under vacuum. 5. The method according to claim 1, in which perforation is performed in advance in each of the capacitors of the mentioned assembly for better penetration of oil into the paper. 6. The method according to claim 1, in which said capacitance measurements are performed after establishing a dynamic balance of moisture in the transformer oil of the equipment and the paper of the capacitor assembly. 7. The method according to claim 1, wherein said assembly is provided with a transformer oil moisture sensor and its readings are taken into account in said moisture determination of a particular paper sample. 8. A device for measuring the moisture content of oil-paper insulation of high-voltage oil-filled equipment, comprising: – common base made of dielectric material; - a predetermined number of capacitor plates made of dielectric material, placed on the mentioned base next to one another; - selected according to the number of mentioned capacitor plates and each laid between a common base with a corresponding capacitor plate, paper samples used as internal insulation of the said equipment, pre-impregnated with transformer oil; - at the same time, the said capacitor plates from the side facing the common base, and the sections of the common base facing them, are covered with a metallization layer and provided with signal leads laid along the common base. 9. The device according to claim. 8, in which the paper in different samples is different in its characteristics, selected from the group including paper grade, paper thickness, paper polymerization degree. 10. The device according to claim 8, in which perforation is made in the said capacitor plates, in the areas of the common base opposite these plates and in the paper samples between them for better penetration of transformer oil into the mentioned paper samples. 11. The device according to claim 8, in which the common base with capacitor plates placed on it is inserted into a perforated protective case designed for installation in a tank with transformer oil of the mentioned high-voltage oil-filled equipment, leaving the mentioned signal leads outside of the tank. 12. The device according to claim 8 or 11, further comprising a transformer oil moisture sensor and a temperature sensor located on a common base next to said capacitor plates.

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