"DIAGNOSTICS OF ELECTRICAL EQUIPMENT OF POWER PLANTS AND SUBSTATIONS Textbook Ministry of Education and Science of the Russian Federation Ural Federal University ..."
DIAGNOSTICS
ELECTRICAL EQUIPMENT
ELECTRICAL STATIONS
AND SUBSTATIONS
Tutorial
Ministry of Education and Science of the Russian Federation
Ural Federal University
named after the first President of Russia B. N. Yeltsin
Diagnostics of electrical equipment
power plants and substations
Tutorial
Recommended by the methodological council of UrFU for students enrolled in the direction 140400 - Electric power and electrical engineering Yekaterinburg Publishing house of the Ural University UDC 621.311: 658.562 (075.8) ББК 31.277-7я73 Д44 Authors: A.I. Khalyasmaa, S. A. Dmitriev, S. E. Kokin , D. A. Glushkov Reviewers: Director of United Engineering Company LLC A. A. Kostin, Ph.D. econom. Sciences, prof. AS Semerikov (Director of JSC "Yekaterinburg Electric Grid Company") Scientific editor - Cand. tech. Sciences, Assoc. A. A. Suvorov Diagnostics of electrical equipment of power plants and substations: a tutorial / A. I. Khalyasmaa [and others]. - Yekaterinburg: Publishing House 44 to the Urals. University, 2015 .-- 64 p.
ISBN 978-5-7996-1493-5 In modern conditions of high wear and tear of power grid equipment, an assessment of its technical condition is a mandatory and inalienable requirement for the organization of its reliable operation. The manual is intended to study the methods of non-destructive testing and technical diagnostics in the electric power industry to assess the technical condition of power grid equipment.
Bibliography: 11 titles. Rice. 19. Tab. 4.
UDC 621.311: 658.562 (075.8) ББК 31.277-7я73 ISBN 978-5-7996-1493-5 © Ural Federal University, 2015 Introduction Today, the economic state of the Russian energy industry forces us to take measures to increase the service life of various electrical equipment.
In Russia, the total length of 0.4–110 kV power grids currently exceeds 3 million km, and the transformer capacity of substations (SS) and transformer stations (TP) is 520 million kVA.
The cost of fixed assets of the networks is about 200 billion rubles, and the degree of their depreciation is about 40%. Over the 90s, the volume of construction, technical re-equipment and reconstruction of substations has sharply decreased, and only in the last few years there has been some activity in these areas again.
The solution to the problem of assessing the technical condition of electrical equipment of electrical networks is largely associated with the introduction of effective methods instrumental control and technical diagnostics. In addition, it is necessary and indispensable for the safe and reliable operation of electrical equipment.
1. Basic concepts and provisions of technical diagnostics The economic situation that has developed in recent years in the energy sector compels us to take measures aimed at increasing the service life of various equipment. The solution to the problem of assessing the technical condition of electrical equipment of electrical networks is largely associated with the introduction of effective methods of instrumental control and technical diagnostics.
Technical diagnostics (from the Greek "recognition") is an apparatus of measures that allows you to study and establish signs of malfunction (operability) of equipment, establish methods and means by which a conclusion is given (a diagnosis is made) about the presence (absence) of a malfunction (defect) ... In other words, technical diagnostics makes it possible to assess the state of the investigated object.
Such diagnostics are mainly aimed at finding and analyzing the internal causes of equipment malfunction. External causes are determined visually.
According to GOST 20911–89, technical diagnostics is defined as "a field of knowledge covering the theory, methods and means of determining the technical state of objects." The object, the state of which is determined, is called the object of diagnostics (OD), and the process of investigating OD is called diagnostics.
The main purpose of technical diagnostics is, first of all, the recognition of the state technical system in conditions of limited information, and as a consequence, increasing the reliability and assessing the residual life of the system (equipment). Due to the fact that different technical systems have different structures and purposes, it is impossible to apply the same type of technical diagnostics to all systems.
Conventionally, the structure of technical diagnostics for any type and purpose of equipment is shown in Fig. 1. It is characterized by two interpenetrating and interconnected directions: the theory of recognition and the theory of controllability. Recognition theory studies recognition algorithms as applied to diagnostic problems, which can usually be considered as classification problems. Recognition algorithms in technical diagnostics are partially based on
1. Basic concepts and provisions of technical diagnostics on diagnostic models that establish a connection between the states of a technical system and their displays in the space of diagnostic signals. Decision rules are an important part of the recognition problem.
Inspection is the property of a product to provide a reliable assessment of its technical condition and early detection of malfunctions and failures. The main task of the theory of controllability is to study the means and methods of obtaining diagnostic information.
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Rice. 1. The structure of technical diagnostics
Application (selection) of the type of technical diagnostics is determined by the following conditions:
1) the purpose of the controlled object (scope of use, operating conditions, etc.);
2) the complexity of the controlled object (the complexity of the structure, the number of controlled parameters, etc.);
3) economic feasibility;
4) the degree of danger of the development of an emergency and the consequences of failure of the controlled object.
The state of the system is described by a set of parameters (features) that determine it; when diagnosing the system, they are called diagnostic parameters. When choosing diagnostic parameters, priority is given to those that meet the requirements of reliability and redundancy of information about the technical state of the system in real operating conditions. In practice, several diagnostic parameters are usually used simultaneously. Diagnostic parameters can be parameters of working processes (power, voltage, current, etc.), associated processes (vibration, noise, temperature, etc.) and geometric values (clearance, backlash, beating, etc.). The number of measured diagnostic parameters also depends on the types of devices. Diagnostics of electrical equipment of power plants and substations for system diagnostics (which are used to obtain the data itself) and the degree of development of diagnostic methods. For example, the number of measured diagnostic parameters of power transformers and shunt reactors can reach 38, oil circuit breakers - 29, SF6 circuit breakers - 25, surge arresters and arresters - 10, disconnectors (with a drive) - 14, oil-filled instrument transformers and coupling capacitors - 9 ...
In turn, the diagnostic parameters must have the following properties:
1) sensitivity;
2) the breadth of change;
3) unambiguity;
4) stability;
5) informativeness;
6) the frequency of registration;
7) availability and convenience of measurement.
The sensitivity of the diagnostic parameter is the degree of change in the diagnostic parameter when the functional parameter is varied, i.e., the greater the value of this value, the more sensitive the diagnostic parameter to the change in the functional parameter.
The uniqueness of the diagnostic parameter is determined by its monotonically increasing or decreasing dependence on the functional parameter in the range from the initial to the limiting change in the functional parameter, i.e., each value of the functional parameter corresponds to a single value of the diagnostic parameter, and, in turn, to each value of the diagnostic parameter, there corresponds a single value for a functional parameter.
Stability sets the possible deviation of the diagnostic parameter from its mean value after repeated measurements under constant conditions.
Latitude of change - the range of change of the diagnostic parameter corresponding to the given value of the change in the functional parameter; thus, the larger the range of variation of the diagnostic parameter, the higher its informative value.
Informativeness is a property of a diagnostic parameter, which, if insufficient or redundant, can reduce the efficiency of the diagnostic process itself (the reliability of the diagnosis).
The frequency of registration of the diagnostic parameter is determined based on the requirements technical exploitation and the manufacturer's instructions, and depends on the rate of possible formation and development of the defect.
1. Basic concepts and provisions of technical diagnostics The availability and convenience of measuring the diagnostic parameter directly depend on the design of the diagnostic object and the diagnostic tool (device).
In various literature you can find different classifications diagnostic parameters, in our case, for the diagnosis of electrical equipment, we will adhere to the types of diagnostic parameters presented in the source.
Diagnostic parameters are classified into three types:
1. Parameters information type representing the object characteristic;
2. Parameters representing the current technical characteristics of the elements (nodes) of the object;
3. Parameters that are derivatives of several parameters.
Information type diagnostic parameters include:
1. Object type;
2. Time of commissioning and period of operation;
3. Repair work carried out at the facility;
4. Technical characteristics of the object obtained during testing at the factory and / or during commissioning.
The diagnostic parameters representing the current technical characteristics of the elements (nodes) of the object are most often the parameters of the working (sometimes accompanying) processes.
Diagnostic parameters that are derivatives of several parameters include, first of all, such as:
1. Maximum temperature of the hottest point of the transformer at any load;
2. Dynamic characteristics or derivatives thereof.
To a large extent, the choice of diagnostic parameters depends on each specific type of equipment and the diagnostic method used for this equipment.
2. Concept and diagnostic results
Modern diagnostics of electrical equipment (by purpose) can be conditionally divided into three main areas:
1. Parametric diagnostics;
2. Diagnostics of malfunctions;
3. Preventive diagnostics.
Parametric diagnostics is the control of standardized parameters of equipment, detection and identification of their dangerous changes.
It is used for emergency protection and equipment control, and diagnostic information is contained in the aggregate of deviations of the values of these parameters from the nominal values.
Diagnostics of malfunctions is the determination of the type and size of a defect after registering the fact of the occurrence of a malfunction. Such diagnostics is part of the maintenance or repair of equipment and is carried out based on the results of monitoring its parameters.
Preventive diagnostics is the detection of all potentially dangerous defects at an early stage of development, monitoring their development and, on this basis, a long-term forecast of the equipment condition.
Modern diagnostic systems include all three areas of technical diagnostics in order to form the most complete and reliable assessment of the equipment condition.
Thus, the diagnostic results include:
1. Determination of the condition of the diagnosed equipment (assessment of the condition of the equipment);
2. Identification of the type of defect, its scale, location, reasons for its appearance, which serves as the basis for making a decision on the subsequent operation of the equipment (withdrawal for repair, additional inspection, continued operation, etc.) or on the complete replacement of equipment;
3. Forecast on the terms of subsequent operation - an assessment of the residual life of the electrical equipment.
Therefore, it can be concluded that in order to prevent the formation of defects (or detect them at the early stages of formation) and maintain the operational reliability of equipment, it is necessary to use equipment control in the form of a diagnostic system.
2. Concept and results of software diagnostics general classification, all methods of diagnosing electrical equipment can be divided into two groups, also called control methods: non-destructive and destructive testing methods. Non-destructive testing (NDT) methods are methods for controlling materials (products) that do not require destruction of material samples (products). Accordingly, destructive testing methods are methods for controlling materials (products) that require the destruction of material samples (products).
All OLS, in turn, are also subdivided into methods, but depending on the principle of operation (physical phenomena on which they are based).
Below are the main MNCs, according to GOST 18353-79, which are most often used for electrical equipment:
1) magnetic,
2) electric,
3) eddy current,
4) radio wave,
5) thermal,
6) optical,
7) radiation,
8) acoustic,
9) penetrating substances (capillary and leak detection).
Within each type, methods are also classified according to additional criteria.
We will give each OLS method clear definitions used in the normative documentation.
Magnetic control methods, according to GOST 24450-80, are based on the registration of stray magnetic fields arising over defects, or on the determination of the magnetic properties of the controlled products.
Electrical control methods, according to GOST 25315–82, are based on recording the parameters of the electric field interacting with the control object, or the field that occurs in the control object as a result of external influence.
According to GOST 24289–80, the eddy current control method is based on the analysis of the interaction of an external electromagnetic field with the electromagnetic field of eddy currents induced by a driving coil in an electrically conductive object of control by this field.
Radio wave control method is a non-destructive control method based on the analysis of the interaction of electromagnetic radiation of the radio wave range with the object of control (GOST 25313–82).
Thermal control methods, according to GOST 53689-2009, are based on recording the thermal or temperature fields of the controlled object.
Visual-optical control methods, according to GOST 24521-80, are based on the interaction of optical radiation with the object of control.
Diagnostics of electrical equipment at power plants and substations Radiation control methods are based on the registration and analysis of penetrating ionizing radiation after interaction with the controlled object (GOST 18353–79).
Acoustic control methods are based on the use of elastic vibrations excited or arising in the control object (GOST 23829–85).
Capillary control methods, according to GOST 24521–80, are based on the capillary penetration of indicator liquids into the cavities of surface and through discontinuities of the material of the objects of control and registration of the resulting indicator traces by a visual method or using a transducer.
3. Defects in electrical equipment Assessment of the technical condition of electrical equipment is an essential element of all major aspects of the operation of power plants and substations. One of its main tasks is to identify the fact of serviceability or malfunction of equipment.
The transition of the product from a working condition to a faulty one occurs due to defects. The word defect is used to denote each individual non-conformity of the equipment.
Defects in equipment can occur at different points in its life cycle: during manufacture, installation, setup, operation, testing, repair - and have various consequences.
There are many types of defects, or rather their varieties, electrical equipment. Since acquaintance with the types of diagnostics of electrical equipment in the manual will begin with thermal imaging diagnostics, we will use the gradation of the state of defects (equipment), which is more often used in IR control.
There are usually four main categories or degrees of defect development:
1. Normal condition of the equipment (no defects);
2. A defect in the initial stage of development (the presence of such a defect does not clearly affect the operation of the equipment);
3. A highly developed defect (the presence of such a defect limits the ability to operate the equipment or shortens its life span);
4. A defect in an emergency stage of development (the presence of such a defect makes the operation of the equipment impossible or unacceptable).
As a consequence of the identification of such defects, depending on the degree of their development, the following are accepted possible solutions(measures) to eliminate them:
1. Replace the equipment, its part or element;
2. Carry out the repair of the equipment or its element (after that, conduct an additional survey to assess the quality of the repair performed);
3. Leave in operation, but reduce the time between periodic inspections (more frequent control);
4. Conduct other additional tests.
Diagnostics of electrical equipment of power plants and substations When identifying defects and making decisions on the further operation of electrical equipment, one should not forget about the issue of reliability and accuracy of the information received about the state of the equipment.
Any NDT method does not provide complete reliability in assessing the state of an object.
The measurement results include errors, so there is always the possibility of a false test result:
A healthy object will be declared unusable (a false defect or an error of the first kind);
The defective object will be considered good (a detected defect or a type II error).
Errors in NDT lead to various consequences: if errors of the first kind (false defect) only increase the volume of restoration work, then errors of the second kind (undetected defect) entail emergency damage equipment.
It is worth noting that for any type of NDT, a number of factors can be identified that affect the measurement results or the analysis of the data obtained.
These factors can be conditionally divided into three main groups:
1. Environment;
2. Human factor;
3. The technical aspect.
The "environment" group includes such factors as meteorological conditions (air temperature, humidity, cloudiness, wind strength, etc.), time of day.
The "human factor" is understood as the qualifications of the personnel, professional knowledge of the equipment and the competent conduct of the thermal imaging control itself.
"Technical aspect" means the information base about the diagnosed equipment (material, passport data, year of manufacture, surface condition, etc.).
In fact, there are many more factors influencing the result of NDT methods and data analysis of NDT methods than those listed above. But this topic is of separate interest and is so vast that it deserves a separate book.
It is because of the possibility of making mistakes for each type of NDT there is its own normative documentation governing the purpose of NDT methods, the procedure for carrying out NDT, NDT tools, analysis of NDT results, possible types of defects in NDT, recommendations for their elimination, etc.
The table below shows the main regulatory documents that must be followed when carrying out diagnostics using the main methods of non-destructive testing.
3. Defects in electrical equipment
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4.1. Thermal control methods: basic terms and purpose Thermal control methods (TMK) are based on the measurement, assessment and analysis of the temperature of controlled objects. The main condition for the use of diagnostics using thermal OLS is the presence of heat fluxes in the diagnosed object.
Temperature is the most versatile reflection of the condition of any equipment. In virtually any operation other than normal operation of the equipment, a change in temperature is the very first indication of a malfunctioning condition. Temperature reactions under different operating modes, due to their versatility, arise at all stages of the operation of electrical equipment.
Infrared diagnostics is the most promising and effective direction of development in the diagnostics of electrical equipment.
It has a number of advantages and benefits over traditional test methods, namely:
1) the reliability, objectivity and accuracy of the information received;
2) personnel safety during equipment inspection;
3) no need to turn off equipment;
4) no need to prepare the workplace;
5) a large amount of work performed per unit of time;
6) the ability to identify defects at an early stage of development;
7) diagnostics of most types of substation electrical equipment;
8) low labor costs for the production of measurements per piece of equipment.
The use of TMK is based on the fact that the presence of almost all types of equipment defects causes a change in the temperature of defective elements and, as a result, a change in the intensity of infrared
4. Thermal control methods (IR) radiation, which can be recorded by thermal imaging devices.
TMK for diagnostics of electrical equipment at power plants and substations can be used for the following types of equipment:
1) power transformers and their high-voltage bushings;
2) switching equipment: power switches, disconnectors;
3) measuring transformers: current transformers (CT) and voltage (VT);
4) surge arresters and overvoltage limiters (SPD);
5) busbars switchgears(RU);
6) insulators;
7) contact connections;
8) generators (frontal parts and active steel);
9) power lines (power lines) and their structural elements (for example, power transmission line supports), etc.
TMK for high-voltage equipment, as one of the modern methods of research and control, was introduced into the "Scope and standards of testing of electrical equipment RD 34.45-51.300-97" in 1998, although it was used in many power systems much earlier.
4.2. Main instruments for inspection of TMK equipment
A thermal imaging measuring device (thermal imager) is used to inspect TMK's electrical equipment. According to GOST R 8.619-2006, a thermal imager is an optoelectronic device designed for contactless (remote) observation, measurement and registration of the spatial / spatial-temporal distribution of the radiation temperature of objects in the field of view of the device by forming a temporal sequence of thermograms and determining the surface temperature object by known emissivity and shooting parameters (ambient temperature, atmospheric transmission, observation distance, etc.). In other words, a thermal imager is a kind of television camera that captures objects in infrared radiation, allowing you to get a picture of the distribution of heat (temperature difference) on the surface in real time.
Thermal imagers come in various modifications, but the principle of operation and design are approximately the same. Below, in Fig. 2 shows the appearance of various thermal imagers.
Diagnostics of electrical equipment of power plants and substations a b c
Rice. 2. Appearance thermal imager:
a - professional thermal imager; b - stationary thermal imager for continuous control and monitoring systems; c - the simplest compact portable thermal imager The range of measured temperatures, depending on the brand and type of thermal imager, can be from –40 to +2000 ° C.
The principle of operation of a thermal imager is based on the fact that all physical bodies are heated unevenly, as a result of which a picture of the distribution of infrared radiation is formed. In other words, the operation of all thermal imagers is based on fixing the temperature difference "object / background" and on converting the received information into an image (thermogram) visible to the eye. A thermogram, according to GOST R 8.619-2006, is a multi-element two-dimensional image, each element of which is assigned a color / or gradation of one color / gradation of screen brightness, determined in accordance with the conditional temperature scale. That is, the temperature fields of objects are considered in the form of a color image, where the color gradations correspond to the temperature gradations. In fig. 3 shows an example.
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palettes. The connection of the color palette with the temperature on the thermogram is set by the operator himself, that is, thermal images are pseudo-color.
The choice of the color palette of the thermogram depends on the range of temperatures used. Changing the color palette is used to increase the contrast and the effectiveness of visual perception (information content) of the thermogram. The number and types of palettes depend on the manufacturer of the thermal imager.
Here are the main, most commonly used palettes for thermograms:
1. RGB (red - red, green - green, blue - blue);
2. Hot metal (colors of hot metal);
4. Gray (gray);
7. Inframetrics;
8. CMY (cyan - cyan, magenta - magenta, yellow - yellow).
In fig. 4 shows a thermogram of fuses, by example of which you can consider the main components (elements) of a thermogram:
1. Temperature scale - defines the relationship between colors area of the thermogram and its temperature;
2. Zone of abnormal heating (characterized by a color range from the upper part of the temperature scale) - an item of equipment with an increased temperature;
3. Temperature cut line (profile) - a line passing through a zone of abnormal heating and a node similar to the defective one;
4. Temperature graph - a graph displaying the temperature distribution along the temperature cut line, ie along the X-axis - ordinal numbers of points along the length of the line, and along the Y-axis - the temperature values at these points of the thermogram.
Rice. 4. Thermogram of fuses Diagnostics of electrical equipment of power plants and substations In this case, the thermogram is a fusion of thermal and real images, which is not provided in all software products for analyzing thermal imaging diagnostics data. It is also worth noting that the temperature graph and the temperature cut line are elements of the analysis of thermogram data and it is impossible to use them without the help of software for processing a thermal image.
It should be emphasized that the distribution of colors on the thermogram is chosen arbitrarily and in this example it divides defects into three groups: green, yellow, and red. The red group unites serious defects, the green group includes incipient defects.
Also, for non-contact temperature measurement, pyrometers are used, the principle of which is based on measuring the power of thermal radiation of the measurement object, mainly in the infrared range.
In fig. 5 shows the appearance of various pyrometers.
Rice. 5. Appearance of the pyrometer The range of measured temperatures, depending on the brand and type of the pyrometer, can be from –100 to +3000 ° C.
The fundamental difference between thermal imagers and pyrometers is that pyrometers measure the temperature at a specific point (up to 1 cm), and thermal imagers analyze the entire object as a whole, showing all the difference and temperature fluctuations at any point.
When analyzing the results of IR diagnostics, it is necessary to take into account the design of the diagnosed equipment, methods, conditions and duration of operation, manufacturing technology and a number of other factors.
Table 2 discusses the main types of electrical equipment at substations and the types of defects detected using IR diagnostics according to the source.
4. Thermal control methods
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Currently, thermal imaging control of electrical equipment and overhead power lines is provided for by RD 34.45-51.300-97 "Scope and standards for testing electrical equipment."
5. Diagnostics of oil-filled equipment Today, substations use a sufficient number of oil-filled equipment. Oil-filled equipment is one that uses oil as the quenching, insulating and cooling medium.
Today, substations use and operate oil-filled equipment of the following types:
1) power transformers;
2) measuring current and voltage transformers;
3) shunt reactors;
4) switches;
5) high-voltage bushings;
6) oil-filled cable lines.
It is worth emphasizing that a significant proportion of oil-filled equipment in operation today is used at the limit of its capabilities - over its standard operating life. And along with other pieces of equipment, the oil is also aged.
Particular attention is paid to the condition of the oil, since under the influence of electric and magnetic fields, its initial molecular composition changes, and also, due to operation, its volume may change. That, in turn, can pose a danger both to the operation of the equipment at the substation and to the maintenance personnel.
Therefore, correct and timely oil diagnostics is the key to reliable operation of oil-filled equipment.
Oil is a refined fraction of oil obtained during distillation, boiling at temperatures ranging from 300 to 400 ° C. Depending on the origin of the oil, it has different properties, and these distinctive properties of the feedstock and production methods are reflected in the properties of the oil. In the energy field, oil is considered the most common liquid dielectric.
In addition to petroleum transformer oils, it is possible to manufacture synthetic liquid dielectrics based on chlorinated hydrocarbons and organosilicon fluids.
5. Diagnostics of oil-filled equipment To the main types of oil Russian production, most often used for oil-filled equipment, include the following: TKp (TU 38.101890-81), T-1500U (TU 38.401-58-107-97), TCO (GOST 10121-76), GK (TU 38.1011025-85), VG (TU 38.401978–98), AGK (TU 38.1011271–89), MVT (TU 38.401927–92).
Thus, oil analysis is carried out to determine not only oil quality indicators, which must comply with the requirements of regulatory and technical documentation. The condition of the oil is characterized by its quality indicators. The main indicators of the quality of transformer oil are given in clause 1.8.36 of the PUE.
Table 3 shows the most frequently used today indicators of the quality of transformer oil.
Table 3 Indicators of the quality of transformer oil
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Diagnostics of electrical equipment of power plants and substations Oil contains about 70% of information about the condition of the equipment.
Mineral oil is a complex multicomponent mixture of aromatic, naphthenic and paraffinic hydrocarbons, as well as relative amounts of oxygen, sulfur and nitrogen-containing derivatives of these carbons.
1. Aromatic series are responsible for stability against oxidation, thermal stability, viscosity-temperature and electrical insulating properties.
2. Naphthenic series are responsible for the boiling point, viscosity and density of the oil.
3. Paraffin rows.
The chemical composition of oils is determined by the properties of the original petroleum feedstock and production technology.
On average, for oil-filled equipment, the frequency of inspection and the scope of equipment testing is once every two (four) years.
The dielectric strength, characterized by the breakdown voltage in a standard arrester or the corresponding electric field strength, changes with wetting and contamination of the oil and can therefore serve as a diagnostic indicator. When the temperature drops, excess water is released in the form of an emulsion, which causes a decrease in breakdown voltage, especially in the presence of contaminants.
Information about the presence of oil moisture can also be given by its tg, but only with large amounts of moisture. This can be explained by the small effect on the tg of the oil of the water dissolved in it; a sharp increase in the tg of the oil occurs when an emulsion occurs.
In insulating structures, the bulk of the moisture is in solid insulation. Moisture exchange constantly occurs between it and the oil, and in unsealed structures also between oil and air. With a stable temperature regime, an equilibrium state occurs, and then the moisture content of the oil can be used to estimate the moisture content of solid insulation.
Under the influence of an electric field, temperature and oxidizing agents, the oil begins to oxidize with the formation of acids and esters, at a later stage of aging - with the formation of sludge.
Subsequent sludge deposition on the paper insulation not only impairs cooling, but can also lead to insulation breakdown, since sludge is never evenly deposited.
5. Diagnostics of oil-filled equipment
Dielectric losses in oil are determined mainly by its conductivity and grow as aging products and impurities accumulate in the oil. The initial tg values of fresh oil depend on its composition and degree of refining. The dependence of tan on temperature is logarithmic.
Oil aging is determined by oxidative processes, exposure to an electric field and the presence of structural materials (metals, varnishes, cellulose). As a result of aging, the insulating properties of the oil deteriorate and sludge forms, which impedes heat transfer and accelerates the aging of cellulosic insulation. Elevated operating temperatures and the presence of oxygen (in unsealed structures) play a significant role in accelerating oil aging.
The need to control the change in the oil composition during the operation of transformers raises the question of choosing such an analytical method that could provide a reliable qualitative and quantitative determination of the compounds contained in the transformer oil.
To the greatest extent these requirements are met by chromatography, which is a complex method that combines the stage of separating complex mixtures into individual components and the stage of their quantitative determination. Based on the results of these analyzes, the condition of the oil-filled equipment is assessed.
Insulating oil tests are carried out in laboratories, for which oil samples are taken from the equipment.
Methods for determining their main characteristics, as a rule, are regulated by state standards.
Chromatographic analysis of gases dissolved in oil reveals defects, for example, of a transformer at an early stage of their development, the alleged nature of the defect and the degree of damage present. The state of the transformer is assessed by comparing the quantitative data obtained from the analysis with the boundary values of the gas concentration and by the rate of growth of the gas concentration in the oil. This analysis for transformers with a voltage of 110 kV and above should be carried out at least once every 6 months.
Chromatographic analysis of transformer oils includes:
1) determination of the content of gases dissolved in oil;
2) determination of the content of antioxidant additives - ions, etc .;
3) determination of moisture content;
4) determination of nitrogen and oxygen content, etc.
Based on the results of these analyzes, the condition of the oil-filled equipment is assessed.
The determination of the electrical strength of the oil (GOST 6581–75) is carried out in a special vessel with standardized dimensions of the electrodes when the voltage of the industrial frequency is applied.
Diagnostics of electrical equipment at power plants and substations Dielectric losses in oil are measured by a bridge circuit at an alternating electric field strength of 1 kV / mm (GOST 6581–75). The measurement is performed by placing the sample in a special three-electrode (shielded) measuring cell (vessel). The tan value is determined at temperatures of 20 and 90 C (for some oils at 70 C). Typically, the vessel is placed in a thermostat, but this significantly increases the time spent on testing. A vessel with a built-in heater is more convenient.
A quantitative assessment of the content of mechanical impurities is carried out by filtering the sample followed by weighing the sediment (GOST 6370–83).
Two methods are used to determine the amount of water dissolved in oil. The method regulated by GOST 7822–75 is based on the interaction of calcium hydride with dissolved water. The mass fraction of water is determined by the volume of released hydrogen. This method is tricky; results are not always reproducible. The preferred method is the coulometric method (GOST 24614–81), based on the reaction between water and Fischer's reagent. The reaction takes place when current passes between the electrodes in a special apparatus. The sensitivity of the method is 2 · 10–6 (by weight).
The acid number is measured by the amount of hydroxydetaly (in milligrams) spent to neutralize acidic compounds extracted from the oil with a solution of ethyl alcohol (GOST 5985–79).
Flash point is the lowest oil temperature at which, under test conditions, a mixture of vapors and gases with air is formed, capable of flashing from an open flame (GOST 6356-75). The oil is heated in a closed crucible with stirring; testing the mixture - at regular intervals.
Small internal volume (inputs) of equipment with a value of even insignificant damage contributes to a rapid increase in the concentration of accompanying gases.
In this case, the appearance of gases in the oil is rigidly associated with a violation of the integrity of the insulation of the bushings.
In this case, additional data can be obtained on the oxygen content, which determines the oxidative processes in the oil.
Typical gases produced from mineral oil and cellulose (paper and cardboard) in transformers include:
Hydrogen (H2);
Methane (CH4);
Ethane (C2H6);
5. Diagnostics of oil-filled equipment
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Examples of major equipment for oil composition analysis:
1. Moisture meter - designed to measure the mass fraction of moisture in transformer oil.
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3. Meter of dielectric parameters of transformer oil - designed to measure the relative permittivity and dielectric loss tangent of transformer oil.
Rice. 8. Meter of dielectric parameters of oil
4. Automatic transformer oil tester - used to measure the dielectric strength of insulating liquids for breakdown. The breakdown voltage reflects the degree of contamination of the liquid with various impurities.
Rice. 9. Transformer oil tester
5. Monitoring system for transformer parameters: monitoring the content of gases and moisture in transformer oil - monitoring on a working transformer is carried out continuously, data recording is carried out at a specified frequency in the internal memory or sent to the dispatcher.
Diagnostics of electrical equipment of power plants and substations Fig. 10. Monitoring system of transformer parameters
6. Diagnostics of transformer insulation: determination of aging or moisture content in transformer insulation.
Rice. 11. Diagnostics of transformer insulation
7. Automatic meter of moisture content - allows you to determine the water content in the microgram range.
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6. Electrical methods of non-destructive testing Currently in Russia there is a surge of interest in diagnostic systems that allow diagnostics of electrical equipment by non-destructive testing methods. JSC FGC UES in the "Regulations on the technical policy of JSC FGC UES in the distribution electric grid complex" clearly formulated the general development trend in this matter: diagnostics of the cable condition with prediction of the cable insulation condition ”(NRE № 11, 2006, clause 2.6.6.).
Electrical methods are based on the creation of an electric field in a controlled object either by direct exposure to an electrical disturbance (for example, a direct or alternating current field), or indirectly, using non-electrical disturbances (for example, thermal, mechanical, etc.). The electrical characteristics of the control object are used as the primary informative parameter.
The conditionally electrical method of non-destructive testing for diagnosing electrical equipment can be attributed to the method of measuring partial discharges (PD). The external manifestations of the processes of development of the CR are electrical and acoustic phenomena, gas evolution, glow, heating of insulation. That is why there are many methods for determining the PD.
Today, three methods are mainly used to detect partial discharges: electrical, electromagnetic and acoustic.
According to GOST 20074–83, CR is called a local electrical discharge that shunts only part of the insulation in an electrical insulation system.
In other words, PD are the result of the occurrence of local concentrations of the electric field strength in the insulation or on its surface, exceeding the electric strength of the insulation in some places.
Why and why is PD measured in isolation? As you know, one of the main requirements for electrical equipment is the safety of its operation - excluding the possibility of human contact with live parts or their thorough isolation. That is why the reliability of insulation is one of the mandatory requirements for the operation of electrical equipment.
During operation, the insulation of high-voltage structures is exposed to prolonged exposure to operating voltage and repeated exposure to internal and atmospheric overvoltages. Along with this, insulation is exposed to thermal and mechanical influences, vibrations, and in some cases moisture, which leads to a deterioration in its electrical and mechanical properties.
Therefore, reliable operation of the insulation of high-voltage structures can be ensured if the following conditions are met:
1. The insulation must withstand, with sufficient reliability for practice, possible overvoltages in operation;
2. Insulation must with sufficient reliability for practice withstand the long-term operating voltage, taking into account its possible changes within the permissible limits.
When choosing the permissible operating electric field strengths in a significant number of types of insulating structures, the characteristics of the PD in insulation are decisive.
The essence of the partial discharge method is to determine the value of the partial discharge or to check that the value of the partial discharge does not exceed the set value at the set voltage and sensitivity.
The electrical method requires the contact of measuring instruments with the object of control. But the possibility of obtaining a set of characteristics that allow a comprehensive assessment of the PD properties with the determination of their quantitative values has made this method very attractive and accessible. The main disadvantage of this method is its strong sensitivity to various kinds of interference.
The electromagnetic (remote) method allows you to detect an object with PD using a directional receiving microwave antenna-feeder device. This method does not require contacts of measuring instruments with the controlled equipment and allows for an overview scan of a group of equipment. The disadvantage of this method is the lack of a quantitative assessment of any characteristic of the PD, such as the charge of PD, PD, power, etc.
The use of diagnostics by the method of measuring partial discharges is possible for the following types of electrical equipment:
1) cables and cable products (couplings, etc.);
2) complete gas-insulated switchgear (GIS);
3) measuring current and voltage transformers;
4) power transformers and bushings;
5) motors and generators;
6) arresters and capacitors.
6. Electrical methods of non-destructive testing
The main risks of partial discharges are related to the following factors:
· Impossibility of their detection by the method of conventional tests with increased rectified voltage;
· The risk of their rapid transition to the state of breakdown and, as a consequence, the creation of an emergency on the cable.
Among the main equipment for detecting defects using partial discharges, the following types of equipment can be distinguished:
1) PD-Portable Fig. 13. Portable system for registering partial discharges Portable system for registering partial discharges, which consists of a VLF voltage generator (Frida, Viola), a communication unit and a unit for registering partial discharges.
1. Simplified scheme of the system: does not imply pre-charging with direct current, but gives the result online.
2. Small dimensions and weight, allowing the system to be used as a portable one or to be mounted on almost any chassis.
3. High measurement accuracy.
4. Simplicity of operation.
5. Test voltage - Uo, which allows diagnostics of the condition of 35 kV cable lines up to 13 km long, as well as 110 kV cables.
2) PHG-system A universal system for diagnosing the condition of cable lines, which includes the following subsystems:
· PHG high voltage generator (VLF and rectified direct voltage up to 80 kV);
Diagnostics of electrical equipment of power plants and substations · measurement of the tangent of the loss angle TD;
· Measurement of partial discharges with localization of the PD source.
Rice. 14. Universal system of registration of partial discharges
The features of this system are:
1. Simplified scheme of the system operation: does not imply pre-charging with direct current, but gives the result in online mode;
2. Versatility: four devices in one (test setup with rectified voltage up to 80 kV with primary burning function (up to 90 mA), VLF voltage generator up to 80 kV, loss tangent measurement system, partial discharge registration system);
3. Possibility of gradual formation of a system from a high voltage generator to a cable line diagnostics system;
4. Simplicity of operation;
5. Possibility of carrying out full diagnostics of the cable line condition;
6. Possibility of cable tracing;
7. Assessment of the dynamics of aging of insulation based on data archives based on test results.
With the help of the system data, the following tasks are solved:
· Verification of the performance characteristics of the test objects;
· Planning maintenance and replacement of couplings and cable sections and carrying out preventive measures;
· Significant reduction in the number of forced downtime;
· Increase in the service life of cable lines due to the use of a sparing level of test voltage.
7. Vibration diagnostics Dynamic forces act in each machine. These forces are the source of not only noise and vibration, but also defects that change the properties of the forces and, accordingly, the characteristics of noise and vibration. We can say that functional diagnostics of machines without changing their operating mode is the study of dynamic forces, and not vibration or noise itself. The latter simply contain information about dynamic forces, but in the process of converting forces into vibration or noise, some of the information is lost.
Even more information is lost when the forces and the work they do are converted into thermal energy. That is why, of the two types of signals (temperature and vibration), vibration should be preferred in diagnostics. Speaking simple language, vibration is mechanical vibrations of the body about the equilibrium position.
Over the past several decades, vibration diagnostics have become the basis for monitoring and predicting the condition of rotating equipment.
The physical reason for its rapid development is the huge amount of diagnostic information contained in the vibrational forces and vibration of machines operating in both nominal and special modes.
Currently, diagnostic information about the state of rotating equipment is extracted from the parameters of not only vibration, but also other processes, including working and secondary ones, occurring in machines. Naturally, the development of diagnostic systems goes along the path of expanding the information received, not only due to the complication of signal analysis methods, but also due to the expansion of the number of controlled processes.
Vibration diagnostics, like any other diagnostics, includes three main areas:
Parametric diagnostics;
Diagnostics of malfunctions;
Preventive diagnostics.
As mentioned above, parametric diagnostics is used for emergency protection and equipment control, and diagnostic information is contained in the aggregate of deviations of the values of these parameters. Parametric diagnostic systems usually include several channels for monitoring various processes, including vibration and temperature of individual equipment units. The amount of used vibration information in such systems is limited, that is, each vibration channel controls two parameters, namely the magnitude of the normalized low-frequency vibration and the rate of its growth.
Usually vibration is normalized in a standard frequency band from 2 (10) Hz to 1000 (2000) Hz. The magnitude of the controlled low-frequency vibration does not always determine the real state of the equipment, but in a pre-emergency situation, when chains of rapidly developing defects appear, their connection grows significantly. This allows you to effectively use equipment emergency protection equipment in terms of the magnitude of low-frequency vibration.
The most widely used are simplified vibration alarm systems. Such systems are most often used for the timely detection of errors by the personnel operating the equipment.
Diagnostics of malfunctions in this case is vibration maintenance of rotating equipment, called vibration adjustment, which is carried out according to the results of monitoring its vibration, primarily to ensure safe vibration levels of high-speed critical machines with a rotation speed of ~ 3000 rpm and above. It is in high-speed machines that increased vibration at the rotational speed and multiple frequencies significantly reduces the service life of the machine, on the one hand, and on the other, is most often the result of the appearance of individual defects in the machine or foundation. Identification of a dangerous increase in machine vibration in steady-state or transient (starting) modes of operation with the subsequent determination and elimination of the reasons for this increase is the main task of vibration adjustment.
Within the framework of vibration adjustment, after detecting the reasons for the increase in vibration, a number of service works are performed, such as alignment, balancing, changing the vibrational properties (detuning from resonances) of the machine, as well as replacing the lubricant and eliminating those defects in machine components or foundation structures that entailed dangerous growth vibration.
Preventive diagnostics of machinery and equipment is the detection of all potentially dangerous defects at an early stage of development, monitoring their development and, on this basis, a long-term forecast of the condition of the equipment. Vibration preventive diagnostics of machines as an independent direction in diagnostics began to form only at the end of the 80s of the last century.
The main task of preventive diagnostics is not only the detection, but also the identification of incipient defects. Knowledge of the type of each of the detected defects can dramatically increase the reliability of the forecast, since each type of defect has its own rate of development.
7. Vibration diagnostics Preventive diagnostics systems consist of measuring instruments for the most informative processes occurring in a machine, tools or software for analyzing measured signals and software for recognizing and long-term prediction of the state of the machine. The most informative processes usually include machine vibration and its thermal radiation, as well as the current consumed by the electric motor used as an electric drive, and the composition of the lubricant. To date, only the most informative processes have not been identified, which make it possible to determine and predict the state of electrical insulation in electrical machines with high reliability.
Preventive diagnostics based on the analysis of one of the signals, for example, vibration, has the right to exist only in those cases when it allows you to detect an absolute (more than 90%) number of potentially dangerous types of defects at an early stage of development and to predict the trouble-free operation of the machine for a sufficient period to prepare for current repairs. At present, such a possibility cannot be realized for all types of machines and not for all industries.
The greatest success in preventive vibration diagnostics is associated with the prediction of the condition of low-speed loaded equipment used, for example, in metallurgy, paper and printing industries. In such equipment, vibration does not have a decisive effect on its reliability, that is, special measures to reduce vibration are rarely used. In this situation, the vibration parameters most fully reflect the state of the equipment units, and taking into account the availability of these units for periodic vibration measurement, preventive diagnostics gives the maximum effect at the lowest cost.
The most difficult issues of preventive vibration diagnostics are solved for reciprocating machines and high-speed gas turbine engines. In the first case, the useful vibration signal is many times blocked by vibration from shock impulses arising when the direction of movement of inertial elements is changed, and in the second - by flow noise, which creates a strong vibration interference at those control points that are available for periodic vibration measurement.
The success of preventive vibration diagnostics of medium-speed machines with a rotation speed of ~ 300 to ~ 3000 rpm also depends on the type of machines being diagnosed and on the peculiarities of their operation in different industries. The tasks of monitoring and predicting the state of widespread pumping and ventilation equipment are most easily solved, especially if they use rolling bearings and an asynchronous electric drive. Such equipment is used practically in all branches of industry and in the city economy.
Preventive diagnostics in transport has its own specifics, which is performed not in motion, but at special stands. First, the intervals between diagnostic measurements in this case are not determined by the real state of the equipment, but are planned according to the mileage data. Secondly, there is no control of the equipment operating modes in these intervals, and any violation of the operating conditions can dramatically accelerate the development of defects. Thirdly, diagnostics is carried out not in the nominal operating modes of the equipment, in which the defects develop, but in special bench tests, in which the defect may not change the controlled vibration parameters, or change them differently than in the nominal operating modes.
All of the above requires special improvements to the traditional systems of preventive diagnostics in relation to different types of transport, their experimental operation and generalization of the results obtained. Unfortunately, such work is often not even planned, although, for example, the number of preventive diagnostic systems used on the railways is several hundred, and the number of small firms supplying these products to industry enterprises exceeds a dozen.
A working unit is a source of a large number of vibrations of various nature. The main dynamic forces acting in rotary-type machines (namely, turbines, turbochargers, electric motors, generators, pumps, fans, etc.), exciting their vibration or noise, are presented below.
Of the forces of mechanical nature, it should be noted:
1. Centrifugal forces, determined by the imbalance of rotating units;
2. Kinematic forces determined by the unevenness of the interacting surfaces and, first of all, the friction surfaces in the bearings;
3. Parametric forces, determined primarily by the variable component of the stiffness of rotating nodes or rotation supports;
4. Friction forces, which can not always be considered mechanical, but almost always they are the result of the total action of a multitude of micro-impacts with deformation (elastic) of contacting microroughnesses on the friction surfaces;
5. Forces of an impact type arising from the interaction of individual friction elements, accompanied by their elastic deformation.
Of the forces of electromagnetic origin in electrical machines, the following should be distinguished:
7. Vibration diagnostics
1. Magnetic forces, determined by changes in magnetic energy in a certain limited space, as a rule, in a limited section of the air gap;
2. Electrodynamic forces, determined by the interaction of a magnetic field with an electric current;
3. Magnetostrictive forces, determined by the effect of magnetostriction, ie, by a change in the linear dimensions of a magnetic material under the influence of a magnetic field.
Of the forces of aerodynamic origin, the following should be distinguished:
1. Lift forces, ie forces of pressure on a body, for example, an impeller blade moving in a stream or streamlined by a stream;
2. Friction forces at the boundary of the flow and stationary parts of the machine (inner wall of the pipeline, etc.);
3. Pressure pulsations in the flow, determined by its turbulence, separation of vortices, etc.
Below are examples of defects detected by vibration diagnostics:
1) unbalance of the rotor masses;
2) misalignment;
3) mechanical weakening (manufacturing defect or normal wear and tear);
4) grazing (rubbing), etc.
Unbalance of the rotating masses of the rotor:
a) manufacturing defect of the rotating rotor or its elements at the factory, at the repair facility, insufficient final inspection of the equipment manufacturer, shocks during transportation, poor storage conditions;
b) improper assembly of equipment during initial installation or after repairs;
c) the presence of worn, broken, defective, missing, insufficiently firmly fixed, etc. parts and assemblies on the rotating rotor;
d) the result of the influence of the parameters of technological processes and the peculiarities of the operation of this equipment, leading to uneven heating and bending of the rotors.
Misalignment The relative position of the centers of the shafts of two adjacent rotors in practice is usually characterized by the term "alignment".
If the axial lines of the shafts do not coincide, then they speak of poor alignment quality and the term "misalignment of two shafts" is used.
Diagnostics of electrical equipment of power plants and substations
The quality of the alignment of several mechanisms is determined by the correct installation of the shaft line of the unit, controlled by the centers of the shaft support bearings.
There are many reasons for the appearance of misalignments in operating equipment. These are the processes of wear, the influence of technological parameters, a change in the properties of the foundation, the curvature of the supply pipelines under the influence of a change in temperature outside, a change in the operating mode, etc.
Mechanical weakening Quite often, the term "mechanical weakening" is understood as the sum of several different defects present in the structure or resulting from the peculiarities of operation: most often vibrations during mechanical weakening are caused by collisions of rotating parts with each other or collisions of moving rotor elements with stationary structural elements, for example, with clips bearings.
All these reasons are brought together and have here the general name "mechanical weakening" because in the spectra of vibration signals they give approximately the same qualitative picture.
Mechanical weakening, which is a defect in manufacturing, assembly and operation: all kinds of excessively loose landings of parts of rotating rotors, coupled with the presence of nonlinearities of the "backlash" type, which also occur in bearings, couplings, and the structure itself.
Mechanical weakening resulting from natural wear and tear of the structure, features of operation, as a result of the destruction of structural elements. The same group should include all possible cracks and defects in the structure and foundation, increase in clearances that have arisen during the operation of the equipment.
Nevertheless, such processes are closely related to the rotation of the shafts.
Grazing
The touching and "rubbing" of equipment elements against each other of various root causes occur during the operation of the equipment quite often and by their origin can be divided into two groups:
Normal structural rubbing and rubbing in of various types seals used in pumps, compressors, etc .;
The result, or even the last stage, is the manifestation of other structural defects in the unit, for example, wear of supporting elements, a decrease or increase in technological gaps and seals, and a curvature of structures.
Grazing in practice is usually called the process of direct contact of the rotating parts of the rotor with the stationary structural elements of the unit or foundation.
7. Vibration diagnostics Contacting in its physical essence (in some sources the terms "friction" or "mashing" are used) can have a local character, but only at the initial stages. In the last stages of its development, grazing usually occurs continuously throughout the entire turnover.
The technical support of vibration diagnostics is high-precision vibration measurement and digital signal processing, the capabilities of which are constantly growing, and the cost is decreasing.
The main types of vibration control equipment:
1. Portable equipment;
2. Stationary equipment;
3. Equipment for balancing;
4. Diagnostic systems;
5. Software.
Based on the results of vibration diagnostics measurements, signal forms and vibration spectra are compiled.
Comparison of the waveforms, but already with the reference one, can be carried out using another information spectral technology based on narrowband spectral analysis of signals. When using this type of signal analysis, diagnostic information is contained in the ratio of the amplitudes and initial phases of the main component and each of its multiples in frequency.
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Diagnostics of electrical equipment of power plants and substations Fig. 16. Shapes and spectra of vibration of the transformer core during overload, accompanied by magnetic saturation of the core Vibration signal spectra: their analysis shows that the appearance of magnetic saturation of the active core is accompanied by distortion of the shape and growth of vibration components at the harmonics of the supply voltage.
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The magnetic particle method is based on the identification of stray magnetic fields arising over defects in a part during its magnetization, using a ferromagnetic powder or magnetic suspension as an indicator. This method, among other methods of magnetic control, has found the greatest application. Approximately 80% of all ferromagnetic parts to be inspected are checked with this method. High sensitivity, versatility, relatively low labor intensity of control and simplicity - all this ensured its wide application in industry in general and in transport in particular.
The main disadvantage of this method is the complexity of its automation.
The induction method involves the use of a receiving inductor that is moved relative to a magnetized workpiece or other magnetized controlled object. An EMF is induced (induced) in the coil, the value of which depends on the speed of the relative movement of the coil and the characteristics of the magnetic fields of the defects.
The method of magnetic flaw detection, in which the measurement of magnetic field distortions arising in the places of defects in products made of ferromagnetic materials is carried out by flux gates. A device for measuring and indicating magnetic fields (mainly constant or slowly varying) and their gradients.
The Hall effect method is based on the detection of magnetic fields by Hall transducers.
The essence of the Hall effect is the appearance of a transverse potential difference (Hall EMF) in a rectangular semiconductor plate as a result of curvature of the path of an electric current flowing through this plate under the influence of a magnetic flux perpendicular to this current. The Hall effect method is used to detect defects, measure the thickness of coatings, control the structure and mechanical properties of ferromagnets, and register magnetic fields.
The ponderomotive method is based on measuring the force of separation of a permanent magnet or an electromagnet core from a controlled object.
In other words, this method is based on the ponderomotive interaction of the measured magnetic field and the magnetic field of the frame with a current, an electromagnet or a permanent magnet.
The magnetoresistive method is based on the detection of magnetic fields by magnetoresistive transducers, which are a galvanomagnetic element, the operating principle of which is based on the Gaussian magnetoresistive effect. This effect is associated with a change in the longitudinal resistance of a current carrying conductor under the influence of a magnetic field. In this case, the electrical resistance increases due to the curvature of the trajectory of charge carriers under the influence of a magnetic field. Quantitatively, this effect manifests itself in different ways and depends on the material of the galvanomagnetic cell and its shape. This effect is not typical for conductive materials. It mainly manifests itself in some semiconductors with high carrier mobility.
Magnetic particle flaw detection is based on the identification of local stray magnetic fields arising above the defect using ferromagnetic particles that play the role of an indicator. The stray magnetic field arises above the defect due to the fact that in the magnetized part the magnetic lines of force encountering a defect on their way, they go around it like an obstacle with a low magnetic permeability, as a result of which the magnetic field is distorted, individual magnetic lines of force are displaced by the defect to the surface, leave the part and enter it back.
The stray magnetic field in the defect zone is the greater, the larger the defect and the closer it is to the surface of the part.
Thus, magnetic non-destructive testing methods can be applied to all electrical equipment consisting of ferromagnetic materials.
9. Acoustic control methods Acoustic control methods are used to control products, radio waves in the material of which do not attenuate strongly: dielectrics (glass fiber, plastics, ceramics), semiconductors, magnetodielectrics (ferrites), thin-walled metal materials.
The disadvantage of non-destructive testing by the radio wave method is the low resolution of devices based on this method, due to the small depth of penetration of radio waves.
Acoustic NDT methods are divided into two large groups: active and passive methods. Active methods are based on the emission and reception of elastic waves, passive - only on the reception of waves, the source of which is the object of control itself, for example, the formation of cracks is accompanied by the occurrence of acoustic vibrations, detected by the acoustic emission method.
Active methods are divided into methods of reflection, transmission, combined (using both reflection and transmission), natural vibrations.
Reflection methods are based on the analysis of the reflection of pulses of elastic waves from inhomogeneities or boundaries of the test object, the transmission methods are based on the influence of the parameters of the test object on the characteristics of the waves transmitted through it. Combined methods use the influence of the parameters of the test object both on the reflection and on the transmission of elastic waves. In the methods of natural vibrations, the properties of the control object are judged by the parameters of its free or forced vibrations (their frequencies and the magnitude of losses).
Thus, according to the nature of the interaction of elastic vibrations with the controlled material, acoustic methods are divided into the following main methods:
1) transmitted radiation (shadow, specular-shadow);
2) reflected radiation (echo-pulse);
3) resonant;
4) impedance;
5) free vibrations;
6) acoustic emission.
By the nature of the registration of the primary informative parameter, acoustic methods are divided into amplitude, frequency, and spectral.
9. Acoustic control methods Acoustic methods of non-destructive testing solve the following control and measuring tasks:
1. The transmitted radiation method reveals deep-seated defects such as discontinuity, delamination, non-riveted, non-riveted;
2. The method of reflected radiation detects defects such as discontinuity, determines their coordinates, sizes, orientation by sounding the product and receiving the echo signal reflected from the defect;
3. The resonant method is mainly used to measure the thickness of the product (sometimes it is used to detect the zone of corrosion damage, non-penetration, delamination in thin places made of metals);
4. The acoustic emission method detects and registers only cracks developing or capable of developing under the action of a mechanical load (it qualifies defects not by size, but by the degree of their danger during operation). The method has a high sensitivity to the growth of defects - it detects an increase in the crack by (1 ... 10) microns, and measurements, as a rule, take place under operating conditions in the presence of mechanical and electrical noise;
5. The impedance method is intended for testing adhesive, welded and soldered joints with a thin skin glued or soldered to stiffeners. Defects in adhesive and soldered joints are detected only from the side of input of elastic vibrations;
6. The free vibration method is used to detect deep-seated defects.
The essence of the acoustic method consists in creating a discharge in the place of damage and listening to sound vibrations arising above the place of damage.
Acoustic methods are applied not only to large equipment (for example, transformers), but also to equipment such as cable products.
The essence of the acoustic method for cable lines is to create a spark discharge at the place of damage and listen on the track on the track caused by this discharge of sound vibrations that arise over the place of damage. This method is used to detect all types of damage on the track, provided that an electric discharge can be generated at the site of damage. For the occurrence of a stable spark discharge, it is necessary that the value of the contact resistance at the point of damage exceeds 40 ohms.
The audibility of sound from the surface of the earth depends on the depth of the cable, the density of the soil, the type of cable damage and the discharge power. The listening depth ranges from 1 to 5 m.
The use of this method on openly laid cables, cables in channels, tunnels is not recommended, since due to the good propagation of sound through the metal sheath of the cable, a big mistake can be made in determining the location of the damage.
As an acoustic sensor, sensors of a piezo or electromagnetic system are used, which convert mechanical vibrations of the ground into electrical signals arriving at the input of an audio frequency amplifier. Above the place of damage, the signal is the greatest.
The essence of ultrasonic defectoscopy lies in the phenomenon of propagation of ultrasonic vibrations in the metal with frequencies exceeding 20,000 Hz, and their reflection from defects that violate the solidity of the metal.
Acoustic signals in equipment caused by electrical discharges can be detected even against a background of noise: vibration, noise from oil pumps and fans, etc.
The essence of the acoustic method consists in creating a discharge in the place of damage and listening to sound vibrations arising above the place of damage. This method is used to detect all types of damage, provided that an electrical discharge can be generated together with the damage.
Reflection methods In this group of methods, information is obtained from the reflection of acoustic waves in the OC.
The echo method is based on the registration of echo signals from defects - discontinuities. It is similar to radio and sonar. Other reflection methods are used to search for defects that are poorly detected by the echo method, and to study the parameters of defects.
The echo-mirror method is based on the analysis of acoustic impulses, specularly reflected from the bottom surface of the OC and the defect. A variant of this method designed to detect vertical defects is called the tandem method.
The delta method is based on the use of wave diffraction at a defect.
Part of the transverse wave incident on the defect from the emitter is scattered in all directions at the edges of the defect, and partly turns into a longitudinal wave. Some of these waves are received by the P-wave receiver located above the defect, and some are reflected from the bottom surface and also enter the receiver. Variants of this method assume the possibility of moving the receiver over the surface, changing the types of waves emitted and received.
The time-diffraction method (TDM) is based on the reception of waves scattered at the ends of the defect, and both longitudinal and transverse waves can be emitted and received.
9. Acoustic control methods Acoustic microscopy differs from the echo method by increasing the frequency of ultrasound by one or two orders of magnitude, the use of sharp focusing and automatic or mechanized scanning of small objects. As a result, it is possible to record small changes in the acoustic properties in the OC. The method allows you to achieve a resolution of hundredths of a millimeter.
Coherent methods differ from other reflection methods in that, in addition to the amplitude and time of arrival of pulses, the phase of the signal is also used as an information parameter. Due to this, the resolving power of reflection methods is increased by an order of magnitude and it becomes possible to observe images of defects that are close to real ones.
Transmission methods These methods, in Russia more often called shadow methods, are based on observing changes in the parameters of an acoustic signal (through signal) transmitted through the OC. At the initial stage of development, continuous radiation was used, and a sign of a defect was a decrease in the amplitude of the end-to-end signal caused by the sound shadow formed by the defect. Therefore, the term "shadow" adequately reflected the content of the method. However, in the future, the fields of application of the considered methods have expanded.
The methods began to be used to determine the physical and mechanical properties of materials when the controlled parameters are not associated with discontinuities that form a sound shadow.
Thus, the shadow method can be viewed as a special case of the more general concept of "passing method".
When controlling by transmission methods, the emitting and receiving transducers are located on opposite sides of the OC or the controlled area. In some methods of passage, the transducers are placed on one side of the OC at a certain distance from each other. Information is obtained by measuring the parameters of the end-to-end signal transmitted from the emitter to the receiver.
The amplitude transmission method (or the amplitude shadow method) is based on recording a decrease in the amplitude of the through signal under the influence of a defect that impedes the passage of the signal and creates a sound shadow.
The temporary transmission method (temporary shadow method) is based on the measurement of the pulse delay caused by the bending of the defect. In this case, in contrast to the velocimetric method, the type of elastic wave (usually longitudinal) does not change. In this method, the information parameter is the time of arrival of the end-to-end signal. The method is effective for inspecting materials with large ultrasonic scattering, for example, concrete, etc.
The multiple shadow method is similar to the amplitude transmission method (shadow), but the presence of a defect is judged by the amplitude Diagnostics of electrical equipment of power plants and substations of the end-to-end signal (shadow pulse), which has repeatedly (usually twice) passed between the parallel surfaces of the product. The method is more sensitive than the shadow or specular-shadow method, since the waves pass through the defect zone several times, but it is less resistant to noise.
The varieties of the transmission method discussed above are used to detect defects such as discontinuity.
Photoacoustic microscopy. In photoacoustic microscopy, acoustic oscillations are generated as a result of the thermoelastic effect when the OC is illuminated by a modulated light flux (for example, a pulsed laser) focused on the OC surface. The energy of the light flux, absorbed by the material, generates a heat wave, the parameters of which depend on the thermophysical characteristics of the OC. The heat wave leads to the appearance of thermoelastic vibrations, which are recorded, for example, by a piezoelectric detector.
The velocimetric method is based on recording the change in the velocity of elastic waves in the defect zone. For example, if a flexural wave propagates in a thin product, the appearance of delamination causes a decrease in its phase and group velocities. This phenomenon is recorded by the phase shift of the transmitted wave or the delay in the arrival of the pulse.
Ultrasound tomography. This term is often used to refer to various defect imaging systems. Meanwhile, initially it was used for ultrasound systems, in which they tried to implement an approach that repeats X-ray tomography, i.e., through sounding of the OC in different directions with the highlighting of the OC features obtained at different directions of the beams.
Laser detection method. Known methods of visual representation of acoustic fields in transparent liquids and solid media, based on the diffraction of light on elastic waves.
Thermoacoustic control method is also called ultrasonic-local thermography. The method consists in the fact that powerful low-frequency (~ 20 kHz) ultrasonic vibrations are introduced into the OC. At the defect, they turn into warmth.
The greater the effect of the defect on the elastic properties of the material, the greater the value of elastic hysteresis and the greater the release of heat. The rise in temperature is recorded with a thermal imager.
Combined methods These methods contain features of both reflection and transmission methods.
The mirror-shadow (MF) method is based on measuring the amplitude of the background signal. In terms of the execution technique (the echo signal is recorded), this is a reflection method, and in terms of its physical nature (they measure the attenuation by a defect of a signal that has passed the OK twice), it is close to the shadow method, therefore it is referred not to transmission methods, but to combined methods.
9. Acoustic control methods The echo-shadow method is based on the analysis of both transmitted and reflected waves.
The reverberation-through (acoustic-ultrasonic) method combines the features of the multiple shadow method and the ultrasound reverberation method.
On the OC of small thickness, at some distance from each other, direct emitting and receiving transducers are installed. The radiated pulses of longitudinal waves, after multiple reflections from the walls of the OC, reach the receiver. The presence of inhomogeneities in the OC changes the conditions for the passage of pulses. Defects are registered by changes in the amplitude and spectrum of the received signals. The method is used to control PCM products and joints in multilayer structures.
Methods of natural vibrations These methods are based on the excitation of forced or free vibrations in the OC and the measurement of their parameters: natural frequencies and the magnitude of losses.
Free vibrations are excited by short-term exposure to OK (for example, mechanical shock), after which it vibrates in the absence of external influences.
Forced vibrations are created by the action of an external force with a smoothly variable frequency (sometimes long pulses with a variable carrier frequency are used). Resonance frequencies are recorded by increasing the amplitude of oscillations when the natural frequencies of the OC coincide with the frequencies of the disturbing force. Under the influence of the exciting system, in some cases, the natural frequencies of the OC change slightly, therefore the resonance frequencies are somewhat different from the natural ones. The vibration parameters are measured without interrupting the action of the exciting force.
Distinguish between integral and local methods. Integral methods analyze the natural frequencies of the OC as a whole, and local methods analyze its individual sections. The informative parameters are the frequency values, the spectra of natural and forced oscillations, as well as the figure of merit and the logarithmic damping decrement that characterize the loss.
Integral methods of free and forced vibrations provide for the excitation of vibrations in the entire product or in a significant part of it. The methods are used to control the physical and mechanical properties of products made of concrete, ceramics, metal casting and other materials. These methods do not require scanning and differ high performance, but do not provide information on the location and nature of the defects.
The local method of free vibrations is based on the excitation of free vibrations in a small section of the OC. The method is used to control layered structures by changing the frequency spectrum in the part of the product excited by impact; for measuring thicknesses (especially small) pipes and other OCs by exposure to a short-term acoustic pulse.
Diagnostics of electrical equipment of power plants and substations The local method of forced oscillations (ultrasonic resonance method) is based on the excitation of oscillations, the frequency of which is smoothly changed.
To excite and receive ultrasonic vibrations, combined or separate transducers are used. When the excitation frequencies coincide with the natural frequencies of the OC (loaded with a transceiver transducer), resonances arise in the system. A change in thickness will cause a shift in resonance frequencies, the appearance of defects - the disappearance of resonances.
The acoustic-topographic method has features of both integral and local methods. It is based on the excitation of intense bending vibrations of a continuously varying frequency in the OC and registration of the distribution of the amplitudes of elastic vibrations on the surface of the controlled object using a finely dispersed powder applied to the surface. A smaller amount of powder settles on the defective area, which is explained by an increase in the amplitude of its oscillations as a result of resonance phenomena. The method is used to control connections in multilayer structures: bimetallic sheets, honeycomb panels, etc.
Impedance methods These methods are based on the analysis of changes in the mechanical impedance or input acoustic impedance of the part of the OC surface with which the transducer interacts. Within the group, the methods are divided according to the types of waves excited in the OC and by the nature of the interaction of the transducer with the OC.
The method is used to control connection defects in multilayer structures. It is also used to measure hardness and other physical and mechanical properties of materials.
I would like to consider the method of ultrasonic flaw detection as a separate method.
Ultrasonic flaw detection is applied not only to large equipment (for example, transformers), but also to cable products.
The main types of equipment for ultrasonic flaw detection:
1. Oscilloscope, allowing to register the waveform of the signal and its spectrum;
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10. Acoustic emission diagnostics Acoustic emission is a powerful technical tool for non-destructive testing and material assessment. It is based on the detection of elastic waves generated by the sudden deformation of a stressed material.
These waves travel from the source to the sensor (s), where they are converted into electrical signals. AE instruments measure these signals and display data, on the basis of which the operator evaluates the state and behavior of the energized structure.
Traditional methods of non-destructive testing (ultrasonic, radiation, eddy current) detect geometric inhomogeneities by radiating some form of energy into the structure under study.
Acoustic emission takes a different approach: it detects microscopic movements rather than geometric irregularities.
Fracture growth, inclusion fracture, and liquid or gas leakage are examples of hundreds of acoustic emission-producing processes that can be detected and effectively investigated with this technology.
From the AE point of view, a growing defect produces its own signal, which travels meters, and sometimes tens of meters, until it reaches the sensors. The defect can not only be detected remotely;
it is often possible to find its location by processing the difference in arrival times of waves at different sensors.
Advantages of the AE control method:
1. The method ensures the detection and registration of only developing defects, which makes it possible to classify defects not by size, but by their degree of danger;
2. Under production conditions, the AE method allows detecting crack increments by tenths of a millimeter;
3. Integral property of the method provides control of the entire object using one or more AE transducers, fixedly mounted on the surface of the object at a time;
4. The position and orientation of the defect does not affect the detectability;
10. Acoustic emission diagnostics
5. The AE method has fewer restrictions related to the properties and structure of structural materials than other non-destructive testing methods;
6. Control of areas inaccessible to other methods (thermal and waterproofing, design features) is carried out;
7. The AE method prevents catastrophic destruction of structures during testing and operation by assessing the rate of development of defects;
8. The method determines the location of the leaks.
11. Radiation method of diagnostics X-ray, gamma radiation, neutrino fluxes, etc. are used. Passing through the thickness of the product, the penetrating radiation is attenuated in different ways in defective and defect-free sections and carries information about the internal structure of the substance and the presence of defects inside the product.
Radiation control methods are used to control welded and brazed seams, castings, rolled products, etc. They belong to one of the types of non-destructive testing.
With destructive test methods, random control is carried out (for example, by cut samples) of a series of the same type of product and its quality is statistically evaluated without establishing the quality of each specific product. At the same time, high quality requirements are imposed on some products, which necessitate complete control. Such control is provided by non-destructive testing methods, which are mainly amenable to automation and mechanization.
Product quality is determined, according to GOST 15467-79, by a set of product properties that determine its suitability to meet certain needs in accordance with its purpose. This is a capacious and broad concept, which is influenced by a variety of technological and design-operational factors. For an objective analysis of product quality and its management, not only a set of non-destructive testing methods are involved, but also destructive tests and various checks and control at various stages of product manufacturing. For critical products, designed with a minimum margin of safety and operated in difficult conditions, one hundred percent non-destructive testing is used.
Radiation non-destructive testing is a type of non-destructive testing based on the registration and analysis of penetrating ionizing radiation after interaction with the controlled object. Radiation control methods are based on obtaining defectoscopic information about an object using ionizing radiation, the passage of which through the substance is accompanied by the ionization of atoms and molecules of the medium. The results of the control are determined by the nature and properties of the ionizing radiation used, the physical and technical characteristics of the controlled object, the type and its own.
Distinguish between directly and indirectly ionizing radiation.
Directly ionizing radiation - ionizing radiation, consisting of charged particles (electrons, protons, a-particles, etc.), which have sufficient kinetic energy to ionize the medium upon collision. Indirectly ionizing radiation - ionizing radiation consisting of photons, neutrons or other uncharged particles that can directly create ionizing radiation and / or cause nuclear transformations.
X-ray films, semiconductor gas-discharge and scintillation counters, ionization chambers, etc. are used as detectors in radiation methods.
Purpose of methods Radiation methods of flaw detection are designed to detect macroscopic discontinuities of the material of controlled defects arising during manufacturing (cracks, porosity, cavities, etc.), to determine the internal geometry of parts, assemblies and assemblies (wall thickness and deviations of the shape of internal contours from those specified in the drawing in parts with closed cavities, improper assembly of units, gaps, loose fit in joints, etc.). Radiation methods are also used to detect defects that have appeared during operation: cracks, corrosion of the inner surface, etc.
Depending on the method of obtaining primary information, a distinction is made between radiographic, radioscopic, radiometric control and the method of registration of secondary electrons. In accordance with GOST 18353–79 and GOST 24034–80, these methods are defined as follows.
Radiographic means a method of radiation monitoring based on converting a radiation image of a controlled object into a radiographic image or recording this image on a storage device with subsequent conversion into a light image. A radiographic image is the distribution of the density of blackening (or color) on an X-ray film and photographic film, the light reflectance on a xerographic image, etc., corresponding to the radiation image of the controlled object. Depending on the type of detector used, a distinction is made between radiography itself - registration of a shadow projection of an object onto an X-ray film - and electroradiography. If a color photographic material is used as a detector, that is, the gradations of the radiation image are reproduced in the form of a color gradation, then one speaks of color radiography.
Diagnostics of electrical equipment of power plants and substations Radioscopic is understood as a method of radiation monitoring based on converting the radiation image of the controlled object into a light image on the output screen of the radiation-optical converter, and the resulting image is analyzed during the monitoring process. When used as a radiation-optical converter of a fluorescent screen or in a closed television system of a color monitor, a distinction is made between fluoroscopy or color radioscopy. X-ray machines are mainly used as radiation sources, less often accelerators and radioactive sources.
The radiometric method is based on the measurement of one or more parameters of ionizing radiation after its interaction with the controlled object. Depending on the type of ionizing radiation detectors used, scintillation and ionization methods of radiation monitoring are distinguished. Radioactive sources and accelerators are mainly used as radiation sources, and X-ray devices are also used in thickness measurement systems.
There is also a method of secondary electrons, when a flux of high-energy secondary electrons formed as a result of the interaction of penetrating radiation with a controlled object is recorded.
By the nature of the interaction of physical fields with the controlled object, the methods of transmitted radiation, scattered radiation, activation analysis, characteristic radiation, and field emission are distinguished. The methods of transmitted radiation are practically all classical methods of X-ray and gamma flaw detection, as well as thickness measurement, when various detectors record radiation that has passed through the controlled object, i.e., useful information about the controlled parameter is carried, in particular, by the degree of attenuation of the radiation intensity.
The method of activation analysis is based on the analysis of ionizing radiation, the source of which is the induced radioactivity of the controlled object, which arose as a result of exposure to it by primary ionizing radiation. Induced activity in the analyzed sample is created by neutrons, photons, or charged particles. According to the measurement of the induced activity, the content of elements in various substances is determined.
In industry, in prospecting and prospecting for minerals, methods of neutron and gamma activation analysis are used.
In neutron activation analysis, radioactive neutron sources, neutron generators, subcritical assemblies, and, less often, nuclear reactors and charged particle accelerators are widely used as sources of primary radiation. In gamma activation
11. Radiation diagnostic method for analysis, all kinds of electron accelerators (linear accelerators, betatrons, microtrons) are used, allowing for highly sensitive elemental analysis of samples of rocks and ores, biological objects, products of technological processing of raw materials, high-purity substances, fissile materials.
The methods of characteristic radiation include methods of X-ray radiometric (adsorption and fluorescence) analysis. In essence, this method is close to the classical X-ray spectral method and is based on the excitation of the atoms of the determined elements by the primary radiation from the radionuclide and the subsequent registration of the characteristic radiation of the excited atoms. The X-ray radiometric method has a lower sensitivity in comparison with the X-ray spectral method.
But due to the simplicity and portability of the equipment, the ability to automate technological processes and the use of monoenergetic radiation sources, the X-ray radiometric method has found wide application in the mass express analysis of technological or geological samples. The method of characteristic radiation also includes methods of X-ray spectral and X-ray radiometric measurements of coating thickness.
The field emission method of non-destructive (radiation) control is based on the generation of ionizing radiation by the substance of the controlled object without activating it during the control process. Its essence lies in the fact that with the help of an external electrode with a high potential (electric field with a strength of the order of 106 V / cm) from the metal surface of the controlled object it is possible to induce field emission, the current of which is measured. Thus, you can control the quality of surface preparation, the presence of dirt or films on it.
12. Modern expert systems Modern systems for assessing the technical condition (OTS) of high-voltage electrical equipment of stations and substations involve automated expert systems aimed at solving two types of tasks: determining the actual functional state of equipment in order to adjust the life cycle of equipment and predicting its residual resource and solving technical economic tasks, such as the management of production assets of network enterprises.
As a rule, among the tasks of European OTS systems, unlike Russian ones, the main goal is not to extend the service life of electrical equipment, due to the replacement of equipment after the end of its service life specified by the manufacturer. Strong enough differences in the normative documentation for maintenance, diagnostics, testing, etc. of electrical equipment, the composition of equipment and its operation do not allow the use of foreign OTS systems for Russian power systems. In Russia, there are several expert systems that are actively used today at real power facilities.
Modern OTS systems The structure of all modern OTS systems in general is approximately similar and consists of four main components:
1) database (DB) - the initial data, on the basis of which the OTS of the equipment is performed;
2) knowledge base (KB) - a set of knowledge in the form of structured rules for data processing, including all kinds of experience of experts;
3) the mathematical apparatus with the help of which the mechanism of operation of the OTS system is described;
4) results. Usually, the "Results" section consists of two subsections: the results of the OTS of the equipment themselves (formalized or non-formalized assessments) and control actions based on the assessments obtained - recommendations on the further operation of the evaluated equipment.
Of course, the structure of OTS systems may differ, but most often the architecture of such systems is identical.
As input parameters (DB), data obtained in the course of various methods of non-destructive testing, testing of modern expert systems of equipment, or data obtained from various monitoring systems, sensors, etc. are usually used.
As a knowledge base, various rules can be used, both presented in the RD and other regulatory documents, and in the form of complex mathematical rules and functional dependencies.
The results, as described above, usually differ only in the “type” of assessments (indices) of the equipment condition, possible interpretations of the classifications of defects and control actions.
But the main difference between OTS systems from each other is the use of different mathematical devices (models), on which the reliability and correctness of the system itself and its operation as a whole depend to a greater extent.
Today, in Russian OTS systems of electrical equipment, depending on their purpose, various mathematical models are used - from the simplest models based on conventional production rules to more complex ones, for example, based on the Bayesian method, as presented in the source.
Despite all the unconditional advantages of the existing OTS systems, in modern conditions they have a number of significant disadvantages:
· Focused on solving a specific problem of a specific owner (for specific schemes, specific equipment, etc.) and, as a rule, cannot be used at other similar facilities without serious processing;
· Use different-scale and different information, which can lead to possible unreliability of the estimate;
· Do not take into account the dynamics of changes in the OTS equipment criteria, in other words, the systems are not trainable.
All of the above, in our opinion, deprives modern OTS systems of their versatility, which is why the current situation in the Russian power industry forces us to improve existing or look for new methods for modeling OTS systems.
Modern OTS systems should have the properties of data analysis (introspection), search for patterns, forecasting and, ultimately, learning (self-learning). Such opportunities are provided by artificial intelligence methods. Today, the use of artificial intelligence methods is not only a generally recognized direction of scientific research, but also a completely successful implementation of the actual application of these methods for technical objects in various spheres of life.
Conclusion Reliability and uninterrupted operation of power electrical complexes and systems is largely determined by the operation of the elements that make them up, and, first of all, power transformers, which ensure the coordination of the complex with the system and the transformation of a number of power parameters into the required values for its further use.
One of the promising directions for increasing the efficiency of the operation of electrical oil-filled equipment is the improvement of the system of maintenance and repair of electrical equipment. At present, the transition from the preventive principle, strict regulation of the repair cycle and the frequency of repairs to maintenance based on the standards of scheduled preventive maintenance, is being carried out by a radical way of reducing the volume and cost of maintenance of electrical equipment, the number of maintenance and repair personnel. A concept has been developed for the operation of electrical equipment according to its technical condition through a deeper approach to the appointment of the frequency and volume of technical maintenance and repairs based on the results of diagnostic examinations and monitoring of electrical equipment in general and oil-filled transformer equipment in particular as an integral element of any electrical system.
With the transition to the system of repairs based on the technical condition, the requirements for the system for diagnosing electrical equipment are qualitatively changed, in which the main task of diagnostics is to predict the technical condition for a relatively long period.
The solution to such a problem is not trivial and is possible only with an integrated approach to improving the methods, tools, algorithms and organizational and technical forms of diagnostics.
An analysis of the experience of using automated monitoring and diagnostics systems in Russia and abroad made it possible to formulate a number of tasks that must be solved to obtain the maximum effect when implementing online monitoring and diagnostics systems at facilities:
1. Equipping substations with means of continuous control (monitoring) and diagnostics of the state of the main equipment should be carried out in a comprehensive manner, creating unified projects for automation of substations, the conclusion in which the issues of control, regulation, protection and diagnostics of the state of equipment will be resolved interconnected.
2. When choosing the nomenclature and the number of continuously monitored parameters, the main criterion should be to ensure an acceptable level of risk of operation of each specific apparatus. In accordance with this criterion, the most complete control should first of all cover equipment operating outside the specified service life. The costs of equipping with means of continuous monitoring of equipment that have reached the standardized service life should be higher than that of new equipment with higher reliability indicators.
3. It is necessary to develop principles for a technically and economically sound distribution of tasks between individual subsystems of the APCS. To successfully solve the problem of creating fully automated substations for all types of equipment, criteria should be developed that are formalized physical and mathematical descriptions of serviceable, defective, emergency and other states of devices as a function of the results of monitoring the parameters of their functional subsystems.
List of bibliographic references
1. Bokov GS Technical re-equipment of Russian electrical networks // News of electrical engineering. 2002. No. 2 (14). C. 10-14.
2. Vavilov VP, Aleksandrov AN Infrared thermographic diagnostics in construction and power engineering. M.: NTF "Energoprogress", 2003. S. 360.
3. Yashchura AI The system of maintenance and repair of general industrial equipment: a reference book. M.: Enas, 2012.
4. Birger IA Technical diagnostics. M.: Mechanical engineering,
5. Vdoviko VP Methodology of the high voltage electrical equipment diagnostics system // Electricity. 2010. No. 2. P. 14–20.
6. Chichev SI, Kalinin VF, Glinkin EI Monitoring and control system for electrical equipment of substations. M.: Spectrum,
7. Barkov A. V. Basis for the transfer of rotating equipment for maintenance and repair according to the actual state [Electronic resource] // Vibrodiagnostic systems of the Association VAST. URL: http: // www.vibrotek.ru/russian/biblioteka/book22 (date of access: 20.03.2015).
Title from the screen.
8. Zakharov OG Search for defects in relay-contactor circuits.
M.: NTF "Energopress", "Energetik", 2010. P. 96.
9. Swee P. M. Methods and means of diagnostics of high voltage equipment. M.: Energoatomizdat, 1992.S. 240.
10. Khrennikov A. Yu., Sidorenko MG Thermal imaging inspection of electrical equipment of substations and industrial enterprises and its economic efficiency. No. 2 (14). 2009.
11. Sidorenko MG Thermal imaging diagnostics as a modern monitoring tool [Electronic resource]. URL: http://www.centert.ru/ articles / 22 / (date of access: 20.03.2015). Title from the screen.
INTRODUCTION
1. BASIC CONCEPTS AND PROVISIONS OF TECHNICAL DIAGNOSTICS
2. CONCEPT AND RESULTS OF DIAGNOSTICS
3. DEFECTS OF ELECTRICAL EQUIPMENT
4. THERMAL CONTROL METHODS
4.1. Thermal control methods: basic terms and purpose
4.2. The main instruments for the inspection of TMK equipment ... 15
Students' work; 4. Sample questions for the exam; 5. List of used literature. 1. Explanatory note Methodological instructions for performing extracurricular independent work in the profession ... "INDUSTRIES)" for students of the specialty 1-25 02 02 Management MINSK 2004 THEME 4: "DECISION-MAKING AS A PROSPECTIVE DIRECTION OF INTEGRATION ..." / Methodological manual ... "INCREASING THE QUALIFICATION OF THE FEDERAL TAX SERVICE", ST. PETERSBURG. Friendship of Peoples Approved about the LBC RIS of the Academic Council of the Russian University ... "Federal Education Agency GOU VPO" Siberian State Automobile Academy (SibADI) "VP Pustobaev LOGISTICS OF PRODUCTION Textbook Omsk SibADI UDC 164.3 LBC 65.40 P 893 Reviewers: Doctor of Economics, Prof. S.M. Khairova; Doctor of Economics, Prof ... "
"Research methods: 1. Diagnostic interview with family history. 2. Test of frustration tolerance of Rosenzweig 3. Test" determination of the orientation of the personality of Bass. "4. Test of anxiety Tamml-Dorky-Amen. Book: Diagnosis of Suicidal Behavior .... "
“Ministry of Education and Science of the Russian Federation, ITMo University I.Yu. Kotsyuba, A.V. Chunaev, A.N. Shikov Methods for assessing and measuring the characteristics of information systems study guide St. Petersburg Kotsyuba I.Yu., Chunaev A.V., Shikov A.N. Methods for assessing and measuring the characteristics of information systems. Educational aid ... "
“1 METHODOLOGICAL RECOMMENDATIONS for the development and adoption by organizations of measures to prevent and combat corruption Moscow Contents I. Introduction .. 3 1. Goals and objectives of the Methodological Recommendations. 3 2. Terms and definitions .. 3 3. The circle of subjects for whom the Methodological Recommendations have been developed .. 4 II. Regulatory legal support. 5..."
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Methods for diagnosing electrical equipment
Monitoring and diagnostics of overhead lines
1.3.1 General information
The reliability of electricity supply, that is, the power supply of a large number of consumers distributed throughout the country, is mainly determined by the state of the overhead line. For this reason, close attention is paid to monitoring and diagnostics of overhead lines, especially recently, when the level of technology has provided reliable communication of numerous sensors and devices that exchange digital data.
Monitoring in the application to technology - ϶ᴛᴏ a discrete process realized with the help of digital equipment automatic collection, transmission, storage and analysis of instant data on parameters that change over time and characterize the state of the object of management and / or control. The discreteness or frequency of collecting information about the parameters is determined by the type and state of the object. In the process of monitoring, the discreteness can change if it is provided for by the algorithm of work. Monitoring is carried out at a live facility in operation. The object of control in this case is the overhead line.
Monitoring tasks:
Providing subdivisions making decisions with reliable operational information;
Informing about emergency situations on overhead lines (icing, wire breakage, short circuit occurrence);
Assessment of the current technical condition of the facility;
Instant detection of faults and indication of the exact location of their location (for example, support number);
Solving other information and analytical tasks (nature of the load, phase symmetry, etc.).
From the tasks being solved it is clear that monitoring is part of an automated control system for an object, in which a person makes the final decision.
All types of inspections (on foot, on horseback, on cars, helicopters, airplanes, from space) on the tasks being solved are not a computer-based episodic form of monitoring. Inspections will remain indispensable for solving many problems, for example, determining the state of the foundations of supports and guys, checking the quality of grounding, diagnosing the condition of supports, the quality of the connection of wires and cables, etc. That is, until cheap reliable sensors appear that take into account changes in the parameters necessary to solve the listed tasks.
Technical diagnostics- ϶ᴛᴏ assessment of the technical condition of the object starting with the determination of the location and nature of the existing problematic elements and ending with the transition of the object to an inoperative state. Diagnostics is carried out on the basis of the use of modern methods and tools and solves the problem of ensuring the safety, functional reliability and efficiency of a technical object͵ as well as reducing the cost of its maintenance and reducing losses from downtime as a result of failures.
Diagnostic tests are performed on disconnected equipment. With the help of diagnostic monitoring systems, the problem is solved effective management operation and repair of equipment.
It is difficult to find a physical phenomenon or process that is not used for diagnostic purposes. Let's consider some of them that have found wide application in the electric power industry.
Physicochemical methods... Energy impact on insulation electrical devices leads to its changes at the molecular level. This happens regardless of the type of insulation and ends with chemical reactions with the formation of new chemical compounds, and under the influence of an electromagnetic field, temperature, vibration, the processes of decomposition and synthesis occur simultaneously. Analyzing the number and composition of emerging new chemical compounds, one can draw conclusions about the state of all elements of the insulation. The easiest way to do this is with liquid hydrocarbon insulation, such as mineral oils, since all or almost all of the new chemical compounds formed remain in a closed volume.
The advantage of physicochemical methods of diagnostic control is their high accuracy and independence from electric, magnetic and electromagnetic fields and from other energetic influences, since all research is carried out in physicochemical laboratories. The disadvantages of these methods are the relative high cost, and the delay from the current time, that is, non-operational control.
Method for chromatographic control of oil-filled equipment. This method is based on chromatographic analysis of various gases released from oil and insulation in case of defects inside oil-filled electrical equipment. Algorithms for detecting defects at an early stage of their occurrence, based on the analysis of the composition and concentration of gases, are common, well-developed for diagnosing oil-filled electrical equipment and are described in.
Assessment of the condition of oil-filled equipment is carried out on the basis of control:
Limiting gas concentrations;
The rate of rise of gas concentrations;
Gas concentration ratios.
Insulation dielectric characteristics control method. The method is based on measuring dielectric characteristics, which include leakage currents, capacitance values, dielectric loss tangent ( tg δ) and etc.
Posted on ref.rf
The absolute values of tgd, measured at voltages close to the operating voltage, as well as its increments with changes in the test voltage, frequency and temperature, characterize the quality and degree of aging of the insulation.
AC bridges (Schering bridges) are used to measure tgd and insulation capacitance. The method is used to control high-voltage instrument transformers and coupling capacitors.
Infrared thermography method. Losses of electrical energy for heating elements and assemblies of electrical equipment during operation depend on their technical condition. By measuring infrared radiation caused by heating, it is possible to draw conclusions about the technical condition of electrical equipment. Invisible infrared radiation is converted by thermal imagers into a signal visible to humans. This method is remote, sensitive, allowing to register temperature changes in fractions of a degree. For this reason, its readings are highly susceptible to influencing factors, for example, the reflectivity of the measurement object, temperature and environmental conditions, since dust and humidity absorb infrared radiation, etc.
Assessment of the technical condition of elements and assemblies of electrical equipment under load is carried out either by comparing the temperature of the same type of elements and assemblies (their radiation should be approximately the same), or by exceeding the permissible temperature for a given element or assembly. In the latter case, thermal imagers should have built-in equipment for correcting the influence of temperature and environmental parameters on the measurement result.
Vibration diagnostics method. To control the technical condition of the mechanical units of electrical equipment, the connection between the parameters of the object (its mass and structural rigidity) with the spectrum of frequencies of natural and forced vibration is used. Any change in the parameters of an object during operation, in particular the rigidity of the structure due to its fatigue and aging, causes a change in the spectrum. The sensitivity of the method increases with an increase in informative frequencies. State estimation based on the displacement of low-frequency spectrum components is less effective.
Insulation partial discharge control methods. The processes of the appearance and development of defects in insulators of overhead lines, regardless of their material, are accompanied by the appearance of electrical or partial discharges, which, in turn, generate electromagnetic (in the radio and optical ranges) and sound waves. The intensity of the manifestation of discharges depends on the temperature and humidity of the atmospheric air and is associated with the presence of atmospheric precipitation. Such a dependence of the received diagnostic information on atmospheric conditions requires combining the procedure for diagnosing the intensity of discharges in the overhead insulation of power transmission lines with the extreme importance of mandatory monitoring of the ambient temperature and humidity.
All types and ranges of radiation are widely used for monitoring. The acoustic emission method works in the audio range. A known method for monitoring the optical radiation of the PR using an electron-optical flaw detector. It is based on the registration of the space-time distribution of the luminescence brightness and the determination of defective insulators by its nature. For the same purposes, radio engineering and ultrasonic methods are used with varying efficiency, as well as the method of monitoring ultraviolet radiation using an electronic optical flaw detector "Filin".
Ultrasonic sounding method. The speed of propagation of ultrasound in the irradiated object depends on its state (presence of defects, cracks, corrosion). This property is used to diagnose the state of concrete, wood and metal, which are widely used in the energy sector, for example, as a material for supports.
Methods for diagnosing electrical equipment - concept and types. Classification and features of the category "Methods for diagnosing electrical equipment" 2017, 2018.
To assess the technical condition of the object, it is necessary to determine the current value with the standard. However, the structural parameters in most cases cannot be measured without disassembling the unit or assembly, but each disassembly and violation of the mutual position of the worn-in parts lead to a reduction in the residual resource by 30-40%.
For this, when diagnosing, the values of structural indicators are judged by indirect, diagnostic signs, the qualitative measure of which is diagnostic parameters. Thus, the diagnostic parameter is a qualitative measure of the manifestation of the technical condition of the vehicle, its assembly and indirectly, the determination of the quantitative value of which is possible without disassembling them.
When measuring diagnostic parameters, interferences are inevitably recorded, which are caused by design features the diagnosed object and the selectivity of the device and its accuracy. This complicates the diagnosis and reduces its reliability. Therefore, an important stage is the selection of the most significant and effective diagnostic parameters from the identified initial set, for which they must meet four basic requirements: stability, sensitivity and information content.
The general process of technical diagnostics includes: ensuring the functioning of the object in the specified modes or test impact on the object; capturing and transforming signals expressing the values of diagnostic parameters by means of sensors, their measurement; making a diagnosis based on the logical processing of the information received by comparing it with the standards.
Diagnostics is carried out either during the operation of the car itself, its units and systems at specified load, speed and thermal conditions (functional diagnostics), or when using external drive devices, with the help of which test influences are applied to the car (test diagnostics). These influences should provide maximum information about the technical condition of the vehicle at optimal labor and material costs.
Technical diagnostics determines a rational sequence of checks of mechanisms and, on the basis of studying the dynamics of changes in the parameters of the technical state of units and units of a machine, solves the issues of predicting the resource and failure-free operation.
Technical diagnostics is the process of determining the technical condition of the diagnostic object with a certain accuracy. Diagnostics ends with the issuance of an opinion on the need for the performing part of maintenance or repair operations. The most important requirement for diagnostics is the ability to assess the state of an object without disassembling it. Diagnostics can be objective (carried out with the help of control and measuring instruments, special equipment, instruments, tools) and subjective, made with the help of the sensory organs of the checking person and the simplest technical means.
Table 1: List of diagnostic parameters for vehicles with gasoline engines
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Name |
Value for GAZ-3110 vehicles |
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Engine and electrical system |
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Initial ignition timing |
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Clearance between breaker contacts |
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Angle of the closed state of the breaker contacts |
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Voltage drop across breaker contacts |
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Battery voltage |
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Voltage limited by the regulator relay |
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Voltage in the network of electrical equipment |
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The gap between the electrodes of the candles |
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Breakdown voltage on candles |
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Electric capacity of the capacitor |
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Generator power |
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Starter power |
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Rotation frequency crankshaft when starting the engine |
1350 rpm |
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Starter current consumption |
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Aggregate drive belt deflection at a given force |
810 mm at 4 kgf (4 daN) |
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Light-lighting equipment |
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Direction of maximum beam intensity |
coincides with the reference axis |
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The total luminous intensity measured in the direction of the reference axis |
not less than 20,000 cd |
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Luminous intensity of signal lights |
700 cd (max.) |
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Flashing frequency of direction indicators |
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Time from the moment the direction indicators are turned on until the first flash appears |
If two or more elements fail in the system, the process of troubleshooting by the combination method becomes much more complicated, but the test methodology remains the same. In this case, additional combinations of several functional elements appear, leading to new code numbers. With the combination search method, the average number of checks is equal to the average number of parameters (tests) used to unambiguously determine the failure of one or more functional elements. The number of checks should not be less than the minimum number of checks mmin, determined by the expression: where i is the number of functional elements in the system. The maximum number of checks is equal to the number of functional elements, then nmax = N. The average search time for a failed element with m checks is:
where tпk, t0 is the average time k-th check and the processing time for all test results, respectively. The advantage of the combination diagnostic method lies in the simplicity of logical processing of the results. Disadvantages: a large number of mandatory checks, difficulties in application when the number of failures is more than two. In practice, there is a certain differentiation in the application of methods for finding failures in electrical products and relay protection and automation equipment. The method of sequential group checks is used when connecting functional elements in series, the method of sequential element-by-element checks can be even more widely used, but the search time during its implementation is very significant. The combination method is convenient for analysis complex schemes control of electrical equipment with a large number of branches, but it is difficult to implement with a simultaneous number of failures of more than two. Complex use is recommended different ways diagnostics: at the system level - a combination method; at the block level, a method of sequential group checks, and at the level of individual nodes, a method of sequential item-by-item checks. 5.4 Technical means of diagnosisThe implementation of technical diagnostics processes is carried out using built-in control elements and special diagnostic equipment. For a long time, diagnostic systems were built on the basis of the use of general-purpose devices and installations - ammeters, voltmeters, frequency meters, oscilloscopes, etc. The use of such tools took a lot of time to assemble and disassemble control and test circuits, required relatively high qualifications of operators, contributed to erroneous actions, etc. . NS. Therefore, in the practice of operation, built-in control devices began to be introduced, which are additional equipment that is part of the diagnostic system and works in conjunction with it. Usually, such devices control the functioning of the most critical parts of the system and provide a signal when the corresponding parameter goes outside the set limits. Recently, special diagnostic devices based on complex equipment have become widespread. Such devices (for example, stand-alone test panels) are made in the form of separate blocks, suitcases or combined stands, in which the circuits are pre-assembled, providing for an appropriate volume of diagnostic operations. The diagrams of complete devices used in the operation of electrical equipment are very diverse and depend on the specific type of diagnosed equipment, as well as on the purposes of application (performance testing or search for failures). However, complete devices do not allow enough objective to judge the state of the diagnosed object, because even in the case of a positive outcome, erroneous conclusions are possible, since the entire diagnosis process depends on the subjective qualities of the operator. Therefore, at present, automated diagnostic tools have begun to be introduced into the practice of operation. Such tools are built on the basis of information and measurement systems and are intended not only to control the functioning of the object of the diagnosis, but also to search for a failed element with a given diagnosis depth, to quantify individual parameters, process the results of the diagnosis, etc. The current trend in the development of diagnostic tools is the creation of universal automated tools that work according to a shift program, and therefore are suitable for a wide class of electrical equipment for power supply systems. 5.5 Features of technical diagnostics of electrical equipment5.5.1 Tasks of diagnostic work during the operation of electrical equipmentThe use of diagnostics makes it possible to prevent failures of electrical equipment, determine its suitability for further operation, and reasonably set the timing and scope of repair work. It is advisable to diagnose as when using the existing system scheduled preventive repairs and technical maintenance of electrical equipment (PPREsh system), and in the case of a transition to a new, more advanced form of operation associated with the use of diagnostics based on the current state. When applying a new form of maintenance of electrical equipment in agriculture, the following should be carried out: Maintenance according to schedules, · Planned diagnostics after certain periods of time or operating time; At maintenance diagnostics is used to determine the operability of the equipment, check the stability of adjustments, identify the need for repair or replacement of individual units and parts. In this case, the so-called generalized parameters are diagnosed, which carry a maximum of information about the state of electrical equipment - insulation resistance, temperature of individual nodes, etc. During scheduled inspections, parameters are monitored that characterize the technical condition of the unit and make it possible to determine the residual life of units and parts that limit the possibility of further operation of the equipment. Diagnostics carried out during routine repairs at maintenance and repair points or at the installation site of electrical equipment allows, first of all, to assess the condition of the windings. The residual life of the windings must be greater than the period between current repairs, otherwise the equipment must be overhauled. In addition to the windings, the condition of bearings, contacts and other assemblies is assessed. In the event of maintenance and routine diagnostics, the electrical equipment is not disassembled. If necessary, remove the protective screens of ventilation windows, terminal covers and other quick-detachable parts that provide access to the units. A special role in this situation is played by an external examination, which makes it possible to determine damage to the terminals, the case, to establish the presence of overheating of the windings by darkening the insulation, to check the condition of the contacts. In order to improve the conditions for diagnosing electrical equipment used in agriculture, it is recommended to place it in a separate power unit located outside the main premises. In this case, checking the condition of electrical equipment can be carried out using specialized mobile laboratories. Docking with the power unit is carried out using connectors. The personnel in the auto laboratory can check the condition of the insulation, the temperature of individual units, adjust the protections, that is, carry out% of the total required amount of work. During current repairs, electrical equipment is disassembled, which allows a more detailed examination of the condition of the product and identifies faulty elements. 5.5.2 Basic parameters of diagnosticsAs diagnostic parameters, you should choose the characteristics of electrical equipment that are critical to the service life of individual nodes and elements. The wear process of electrical equipment depends on the operating conditions. Operating modes and environmental conditions are of decisive importance. The main parameters checked when assessing the technical condition of electrical equipment are: for electric motors: the temperature of the winding (determines the service life), the amplitude-phase characteristic of the winding (allows you to assess the state of the coil insulation), the temperature of the bearing assembly and the clearance in the bearings (indicate the performance of the bearings). In addition, for electric motors operated in damp and especially damp rooms, you should additionally measure the insulation resistance (allows you to predict the service life of the electric motor); for ballast and protective equipment: loop resistance "phase - zero" (control of compliance with protection conditions), protective characteristics of thermal relays, resistance of contact transitions; for lighting installations: temperature, relative humidity, voltage, switching frequency. In addition to the main ones, a number of auxiliary parameters can be estimated, which give a more complete picture of the state of the diagnosed object. 5.5.3 Technical diagnostics and prediction of the residual life of the windings of electrical productsThe windings are the most important and vulnerable component of the apparatus. From 90 to 95% of all electric motor failures are due to winding faults. The complexity of the current and overhaul windings account for 40 to 60% of the total work. In turn, the most unreliable element in the windings is their insulation. All this indicates the need for a thorough check of the condition of the windings. On the other hand, it should be noted that it is difficult to diagnose windings. During operation, electrical equipment is under the influence of the following factors: Loads, Ambient temperature, Overloads from the side of the working machine, Voltage deviations, Deterioration of cooling conditions (clogging of the surface, work without ventilation), · High humidity. Among the various processes affecting the service life of the insulation of apparatus, thermal aging is the determining one. In order to predict the condition of the insulation, one needs to know the rate of heat aging. Insulation of units operating for a long time is subject to thermal aging. In this case, the service life of the insulation is determined by the heat resistance class of the insulating material and the operating temperature of the winding. Thermal aging is an irreversible process that occurs in a dielectric and leads to a monotonic deterioration of its dielectric and mechanical properties. The first work in the field of quantifying the dependence of service life on temperature relates to electric motors with class A insulation. The rule of "eight degrees" is established, according to which an increase in the temperature of the insulation for every 8 ° C reduces its service life in half. Analytically, this rule can be described by the expression
where Тsl.0 is the service life of the insulation at a temperature of 0 ° C, h; Q - insulation temperature, 0С. The rule of "eight degrees" is widely used due to its simplicity. It is possible to carry out approximate calculations on it, but it is not possible to obtain reliable results, since this is a purely empirical expression obtained without taking into account a number of factors. In the process of diagnosing electric motors, the temperature of the stator housing is usually measured; for this, the thermometer is inserted into a recess drilled in the housing and filled with transformer or machine oil. The obtained temperature measurements are compared with the permissible values. The temperature of the electric motor housing should not exceed 120 ... 150 0С for electric motors of the 4A series. More accurate assessment results temperature regime can be obtained by placing a thermocouple in the stator winding. A universal means of diagnosing the thermal state of electric motors is infrared thermography, which provides monitoring of its condition without taking it out for repair. Non-contact IR thermometers measure the surface temperature of an object from a safe distance, making them extremely attractive for operating rotating electrical machines. The domestic market has a significant number of thermal imaging cameras, thermal imagers, thermographs of domestic and foreign production for these purposes. In addition to direct temperature measurement in this situation, an indirect method can be used - taking into account the current consumption. An increase in the current value above the nominal value is a diagnostic sign of abnormal development of processes in an electric machine. The current value is a fairly effective diagnostic parameter, since its value determines the active power losses, which in turn are one of the main reasons for the heating of the winding conductors. Overheating of the electric motor can be long-term and short-term. Long-term overcurrents are caused by load conditions, poor power quality. Short-term overloads occur mainly when starting an electric machine. In terms of magnitude, long-term overloads can be (1 ... 1.8) Inom, and short-term (1.8 Inom. Steady-state temperature rise of the winding asynchronous motor ty under overload can be found by the expression where DРсн - calculated constant power losses (losses in steel) at nominal operating conditions, W; DРмн - calculated variable power losses in conductors (copper losses) at nominal operating conditions of the electric motor, W; kн - the multiplicity of the load current in relation to the rated current; A is the heat transfer of the electric motor. At the same time, both when using current as a diagnostic parameter and when measuring the winding temperature using special built-in sensors, the ambient temperature is not taken into account, it is also necessary to remember about the variable nature of the applied load. There are also more informative diagnostic parameters that characterize the state of thermal processes in an electric motor - for example, the rate of thermal wear of insulation. However, its definition presents significant difficulties. The results of investigations carried out in the Ukrainian branch of GOSNITI showed that one of the possible means of determining the technical state of hull and phase-to-phase insulation is the measurement of leakage currents. To determine the leakage currents between the case and each of the phases of the electric motor, a DC voltage from 1200 to 1800 V is applied and the corresponding measurements are made. The difference in the values of the leakage currents of different phases by 1.5 ... 2 or more times indicates the presence of local defects in the insulation of the phase with the highest current value (cracking, ruptures, abrasion, overheating). Depending on the state of the insulation, the presence and type of defect, when the voltage rises, an increase in the leakage current is observed. Surges and fluctuations in leakage currents indicate the appearance of short-term breakdowns and conductive bridges in the insulation, i.e., the presence of defects. To measure leakage currents, commercially available devices IVN-1 and VS-2V can be used or a fairly simple installation based on a rectifier bridge and an adjustable voltage transformer can be constructed. Insulation is considered to be in good condition if no current surges are observed when the voltage rises, the leakage current at a voltage of 1800 V does not exceed 95 μA for one phase (230 μA for three phases), the relative increment of currents is no more than 0.9, the phase leakage current unbalance does not exceed 1.8. 5.5.4 Determination of the strength level of turn-to-turn insulationTurn-to-turn insulation damage is one of the most common causes of failure of electric motors and other equipment. The technical condition of turn-to-turn insulation is characterized by breakdown voltage, which reaches 4 ... 6 kV. It is practically impossible to create such a voltage on the turn-to-turn insulation of electric motors and other devices for testing purposes, since in this case a voltage exceeding tens of kilovolts must be applied to the insulation of the windings in relation to the case, which will lead to breakdown of the case insulation. Provided that the probability of breakdown of the housing insulation is excluded, a voltage of no higher than 2.5 ... 3 kV can be applied to the windings of electric machines with a voltage of 380 V. Therefore, it is really possible to determine the breakdown voltage of only defective insulation. In the place of the turn circuit, an arc usually occurs, leading to the destruction of the insulation in a limited area, then the process expands over the area. The smaller the distance between the conductors and the greater their compression force, the faster the breakdown voltage decreases. It has been experimentally established that when the arc is burning, the breakdown voltage between the turns decreases from 1 V to 0 in time s. Due to the fact that the breakdown voltage at the site of a defect when it occurs is quite large (400 V and more), and overvoltages in the turns occur for a short time and do not reach the breakdown value often, a considerable time passes from the moment a defect occurs in the insulation to a complete turn circuit. ... These data indicate that, in principle, it is possible to predict the residual life of the insulation if we have data on its actual state. To diagnose turn-to-turn insulation, devices of the CM, EL series or the VChF 5-3 device can be used. Devices such as SM and EL allow you to determine the presence of a coil short circuit. When using them, two windings are connected to the terminals of the device, and a high-frequency pulse voltage is applied to the latter. The presence of turn short circuits is determined by the curves observed on the screen of the cathode-ray tube. In the absence of a turn circuit, a combined curve is observed, in the presence of short-circuited turns, the curves are bifurcated. The VChF 5-3 device allows you to determine the presence of a defect in the coil insulation and the breakdown voltage at the place of damage. It is recommended to determine the technical condition of the 380 V turn-to-turn insulation when a high-frequency voltage of 1 V is applied to the winding, which can be considered as not affecting the dielectric strength of the insulation, since the average impulse strength of the turn-to-turn insulation is 8.6 kV, and the minimum is 5 kV. It should be remembered that existing devices allow you to get a certain result only with respect to windings that already have a defect, and do not provide complete information about the technical state of defect-free insulation. Therefore, to prevent sudden failures due to breakdown of coil insulation, diagnostics should be carried out at least once a year for new products and at least once every two months or at least 250 hours of operation for repaired devices or operating more than three years, which will allow detecting a defect. at an early stage of development. Disassembly of an electric machine when diagnosing coil insulation is not required, since an EL type apparatus can be connected to the power contacts of the magnetic starter. However, it should be remembered that if the rotor of an induction motor is damaged, it can create magnetic asymmetry, commensurate with the asymmetry created by the stator windings, and the real picture may be distorted. Therefore, it is better to diagnose windings for the presence of turn-to-turn closures on a disassembled electric motor. 5.5.5 Diagnostics and prediction of winding insulation resistanceDuring operation, the windings of electrical devices are subject to either thermal aging or aging due to moisture. The insulation of electrical equipment that is little used during the day or year and is located in damp or especially damp rooms is subjected to humidification. The minimum non-working period for electric motors, at which humidification begins, is from 2.7 to 5.4 hours, depending on the size. Units that are idle for more than the duration of the given pauses for two or more hours should be diagnosed to determine the state of the frame and phase-to-phase insulation. It is recommended to check the technical condition of the windings by the value of the insulation resistance direct current or the absorption coefficient https://pandia.ru/text/78/408/images/image029_23.gif "width =" 84 height = 25 "height =" 25 ">, (5.11) where Rн - insulation resistance after adjustment, MOhm; kt - correction factor (depends on the ratio of the measured temperature and the most probable in the given room); Ri - measured insulation resistance, MOhm. The predicted value of the insulation resistance during the third forthcoming measurement is calculated by the expression https://pandia.ru/text/78/408/images/image031_22.gif "width =" 184 "height =" 55 ">, (5.15) where Ipv is the rated current of the fuse-link, A; Iem - rated current of the electromagnetic release, A; Uf - phase voltage, V; Zph. o - total resistance of the "phase - zero" circuit, Ohm. The compliance of the protection with the conditions of stable start-up of the electric drive is checked https://pandia.ru/text/78/408/images/image033_10.jpg "width =" 405 "height =" 173 src = "> Figure 5.9 - Diagram of a test tube for a fluorescent lamp with a starter ignition circuit: 1 - test tube, 2 - pins, 3 - control lamps such as NG127-75 or NG127-100, 4 - probe The test tube is made of transparent insulating material such as Plexiglas. For the convenience of work, it is recommended to make it detachable. For 40 W lamps, the tube length without pins shall be 1199.4 mm. The technology for checking the condition of the luminaire using a test tube is as follows. The tube is inserted into the lighting fixture instead of the faulty fluorescent lamp. Voltage is supplied, and according to a special table, which contains possible list faults, the damaged node is determined. The insulation condition of the luminaire is checked by connecting the probe 4 to the metal parts of the housing. Troubleshooting lighting installations can be performed by external signs, having a corresponding diagnostic table. During maintenance of lighting installations, the level of illumination is checked, the insulation resistance of wires is monitored, the state of the control and protective equipment is assessed. For lighting installations, the service life can be predicted. According to the nomograms developed at VNIIPTIMESH (Figure 5.10), depending on environmental conditions (temperature and relative humidity), voltage values and frequency of switching on the lighting installation, the mean time between failures is determined. Example 5.3... Determine the service life of a fluorescent lamp for the following initial data: relative humidity 72%, voltage 220 V, ambient temperature + 15 ° C. Solution. The solution to the problem is shown on the nomogram (Figure 5.10). For the given baseline conditions, the service life of the luminaire is 5.5 thousand hours. shortcodes "> 5.1 Basic concepts and definitionsThe diagnosis in translation from Greek means "recognition", "determination". Technical diagnostics- this is the theory, methods and means by which a conclusion is made about the technical state of the object. To determine the technical condition of electrical equipment, it is necessary, on the one hand, to establish what should be monitored and in what way, and on the other hand, to decide what funds will be required for this. In this problem, two groups of questions are visible: Analysis of the diagnosed equipment and the choice of control methods to establish its actual technical condition, · Construction of technical means for monitoring the state of equipment and operating conditions. So, to make a diagnosis, you need to have the object and means of diagnosis. Any device can be the object of the diagnosis if it can be in two mutually exclusive states - operable and inoperative. At the same time, it is possible to distinguish elements in it, each of which is also characterized by different states. In practice, a real object in research is replaced by a diagnostic model. The actions specially created for the purpose of diagnosing a technical condition and supplied to the object of the diagnosis from the means of diagnosis are called test influences. Distinguish between monitoring and diagnostic tests. A controlling test is a set of sets of input influences that make it possible to check the operability of an object. A diagnostic test is a set of sets of input influences that make it possible to search for a malfunction, that is, to identify a failed element or a faulty node. The central task of diagnostics is to find faulty elements, that is, to determine the place, and possibly the cause of the failure. For electrical equipment, such a problem arises at various stages of operation. Because of this, the diagnosis is effective remedy increasing the reliability of electrical equipment during its operation. Troubleshooting steps in installation usually includes next steps: · Logical analysis of available external signs; · Drawing up a list of malfunctions that can lead to a failure; · choice the best option checks; · Transition to the implementation of the search for a faulty node. Let's take a look at the simplest example. The electric motor together with the actuator does not rotate when voltage is applied to it. Possible reasons - the winding is burnt out, the motor is jammed. Therefore, the stator winding and bearings must be checked. Where to start diagnosing? Easier with the stator winding. The checks begin with it. Then, if necessary, the engine is disassembled and the technical condition of the bearings and other elements is assessed. Troubleshooting methods. Each specific search is in the nature of a logical study, which requires knowledge, experience, intuition of the personnel serving electrical equipment. Moreover, in addition to knowledge of the equipment design, signs of normal functioning, possible reasons failure, it is necessary to know the methods of troubleshooting and be able to choose the correct method from them. There are two main types of search for failed elements - sequential and combinational. With the first method, the hardware checks are performed in a certain order. The result of each check is immediately analyzed, and if the failed element is not identified, then the search continues. The order of performing the operations of the diagnosis can be strictly fixed or depend on the results of previous experiments. Therefore, programs that implement this method can be subdivided into conditional, in which each subsequent check starts depending on the outcome of the previous one, and unconditional, in which checks are performed in some predetermined order. With human participation, flexible algorithms are always used to avoid unnecessary checks. To optimize the troubleshooting procedure when using the method under consideration, the probabilities of failure of the elements should be specified. With an exponential law of distribution of operating time to failure: where Qi (t) is the probability of failure of the i-th element; li is the failure rate of the i-th element under the given operating conditions; t is time. When using the combinational method, the state of an object is determined by performing a specified number of checks, the order of which is irrelevant. Failed elements are identified after all tests have been performed by analyzing the results obtained. This method is characterized by situations when not all the results obtained are necessary to determine the state of the object. The average time to detect a failure is usually used as a criterion for comparing different troubleshooting systems. Other indicators can also be applied - the number of checks, the average speed of obtaining information, etc. In practice, in addition to the methods under consideration, the heuristic method of diagnosis is often used. Strict algorithms do not apply here. A certain hypothesis is put forward about the expected place of failure. Search in progress. Based on the results, his hypothesis is refined. The search continues until the faulty node is identified. Often this approach is used by a radio master when repairing radio equipment. In addition to searching for failed elements, the concept of technical diagnostics also covers the processes of monitoring the technical condition of electrical equipment in the conditions of its intended use. In this case, the person operating the electrical equipment determines the compliance of the output parameters of the units with the passport data or technical specifications (TU), identifies the degree of wear, the need for adjustments, the need to replace individual elements, and specifies the timing of preventive measures and repairs. 5.2 Monitoring the technical condition of electrical installationsElectrical installation model. The functioning of any technical system can be considered as a reaction to input influences. For example, for mechanical systems such influences are forces and moments, for electrical equipment - voltages and currents. Schematically, the model of an electrical installation can be represented in the form of some two-terminal network (Figure 5.1), the input of which receives a set of input influences (signals) X = x (t), and at the output a set of output signals Y = y (t) is obtained. Any system has many properties, the definition of which is associated with the establishment of the system's response to the input action.
Figure 5.1 - Scheme of the system functioning Consider, for example, the static characteristic of a relay element with a deadband (Figure 5.2)
Figure 5.2 - Static characteristic of the relay element It can be seen from the figure that when the input value reaches the values ± x1, the shape of the output signal changes sharply. System state space. Assessment of the condition of electrical equipment is an essential aspect of many operational processes. In this case, it is necessary to strive to achieve a sufficiently accurate assessment, because the correctness of making a decision on further methods and forms of carrying out operational measures depends on this. The state of the system is considered known if the value of each of its parameters from a given set is known. Since we are talking about a set of properties (parameters), it makes sense to consider the state of system A in the state space at some moment in time. Of the many properties, those without which the system cannot be used for its intended purpose in the given conditions are usually distinguished. These properties are commonly referred to as functional or basic. The parameters corresponding to these properties were given a similar name. For electrical installations, for example, such parameters are voltage, current, frequency, etc. Auxiliary parameters are those parameters that characterize the performance of their particular tasks by the nodes, for example, the transformation ratio of an individual transformer. Non-functional properties can characterize ease of use, environmental protection, etc. There are usually three main regions of the state space: · The area of serviceable states P, in which all parameters are within the established tolerances; · The area of defective states Q, in which only auxiliary (non-functional parameters) can be outside the established tolerances; · The area of inoperative states S, for which the values of the functional parameters do not meet the requirements of the normative and technical documentation. The last two areas constitute the area of the faulty state of the electrical installation. Figure 5.3 shows a plot of these areas for a two-dimensional system.
Figure 5.3 - System state space With a relatively large number of parameters characterizing the system, its possible states can be presented in the form of a table of states (Table 5.1). Table 5.1 - Table of states
The table shows that the state of P3 corresponds to the good state of the system, since all its parameters are within the established limits. The rest of the Pn - 1 states are faulty. If each of the parameters characterizes a well-defined element, then the given table can be converted into a table of malfunctions (Table 5.2), which reflects the influence of each of the system elements on its output parameters. Table 5.2 - Table of malfunctions
The possibility of a system transition from one state to another can be quantified using a probabilistic measure. System information. The process of receiving, processing and receiving information that assesses the state of the system to the requirements for it and ensures that a decision is made or the issuance of control actions is called control. Information about a controlled object is usually obtained by measurement, which is understood as the process of comparing a measured value with a reference value. However, the control of the state of the system (its quality) cannot be reduced only to measurements, since even if all the elements are in good working order, their mutual connections can be violated, and the deviations of individual parameters can be compensated for. Another important aspect of control is the fact that quality assessment is viewed as a process that takes place over time. From these positions, under the control of the technical state, one should understand the determination of the state of an object at a given moment in time by obtaining and analyzing technical information that characterizes this object. Often, the concept of control and measurement are identified. However, this cannot be considered correct. When measuring, some physical quantity is compared with another, selected as a unit of measurement. During control, as well as during measurements, a comparison operation is performed, however, if the main result of measurement is a quantitative determination of the measured value, then the main result of control is not only obtaining quantitative values of the parameters, but also making a certain judgment about the subsequent actions to control the object. Consider, as an example, the actions of the dispatcher of a power grid enterprise. In this case, the operator is interested not only in the operation of individual network elements, but also in the general (external to the element) situation, which he judges by the light signals of the mnemonic diagram and the monitored parameters. The peculiarities of the control process of various objects are expressed in control methods. Currently, the following control methods are most widely used: external examination, performance check based on external signs, checks using control and measuring equipment. Visual inspection consists in a comprehensive visual check of the condition of electrical equipment. During external examination it is necessary to make sure: there are no contamination, damage and breakdowns of equipment, loosening of the degree of tightening of nuts and bolts; the presence of markings and seals; serviceability of switching devices; compliance with the filling level of electrical installations with liquid dielectrics, etc. Despite the obvious shortcomings of this method associated with the subjectivity of the assessment and high labor intensity, it still remains one of the most important methods of control. Checking by external signs carried out visually and by ear by observing the movement of devices, the state of the alarm, the perception of specific noise characteristic of a certain mode of operation of the electrical installation. This check provides information on the presence or absence of internal damage and clear signs of a malfunction. Both considered methods, along with simplicity, have a significant drawback - they do not provide a quantitative assessment of the state of the controlled object, thereby do not provide adjustment and adjustment work, do not allow predicting the further state of the electrical installation. Testing with instrumentation does not have the disadvantages inherent in the two previous methods, however, it differs in the complexity and high cost of equipping electrical installations with instrumentation and devices. Nevertheless, this method has become widespread in determining the technical condition of electrical equipment, identifying failures, ensuring adjustment and repair work, restoring operability. The algorithm of the control and measuring equipment during control and its structure are completely determined by the control tasks, which, in turn, are determined by the functional purpose of the electrical installation, the degree of its complexity, the place of control and other requirements. 5.3 Methods for finding faults in electrical installationsMethod of successive element-by-element checks. The application of the method requires the availability of statistical data characterizing the likelihood of malfunctions in equipment elements, and data on labor costs for checks. In this case, the minimum ratio is used as an optimality criterion: where ti is the check time of the i-th element; ai - conditional probability of failure of the i-th element. With the distribution of the operating time to failure according to the exponential law where Qi is the probability of failure of the i-th element; n is the number of elements. After analyzing the object of the diagnosis, and determining the ratio ti / ai, they are arranged in ascending order. In this case, the optimality criterion will look like:
The first check is carried out for which the condition is satisfied. The main advantage of the method is the ability to optimize the program in terms of the total diagnosis time. The disadvantages of the method include the limited possibilities of its application in complex interconnections of functional elements, the need to have data on the search time for the failed element and the failure rates, as well as the uncertainty in the choice of the sequence of checks in case of equality of relations:
If the probability of occurrence of faults is equal, i.e., a1 = a2 = ... = an, the search is carried out in a sequence determined by the minimum time spent on checks. Method of sequential group checks. If there are no initial data on the reliability of elements, then the half-partition method can be the optimal method for finding faulty elements. The essence of this method lies in the fact that a section of a circuit with series-connected elements is divided into two equal parts (Figure 5.4) and the left or right part is equally selected for verification. https://pandia.ru/text/78/408/images/image012_41.gif "width =" 83 "height =" 32 "> is minimal, with the probability of a negative outcome. By calculating the values for all checks and using the proposed criterion, you can select the place of the first check. After the first check is selected, the diagram is divided into two parts, which are considered as independent objects. For each of them, the failure rates of their elements are determined (the sum of the coefficients must be equal to 1). A list of possible checks and a test is selected for which the probabilities of outcomes are closest to 0.5. This process continues until the faulty element is found. Example 5.1. Let an object be given, consisting of 5 elements, the functional connections between which are shown in Figure 5.5. The letters A, B, C, D, E, F, G denote the input and output signals of the elements. Failure rates of elements b1 = 0.2 are known; b2 = 0.1; b3 = 0.3; b4 = 0.3; b5 = 0.1. It is required to compose an algorithm for searching for a malfunction of an object that provides the minimum average number of checks.
Figure 5.5 - Object diagram Solution . To draw up a troubleshooting algorithm, you must first generate a list of possible checks on the object. Let's represent it in the form of table 5.3. Table 5.3 - List of possible checks
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