Diagnostics Of Power Transformers Research Articles

APPLICATION OF THE DECISION TREE ALGORITHM TO EVALUATE THE RESULTS OF CHROMATOGRAPHIC ANALYSIS OF TRANSFORMER OIL

Power oil-filled transformer is the main link in the process of conversion and transmission of electrical energy in electrical networks at almost all voltage classes. At the moment in our country more than 50% of them are operated with significant excess of service life, which increases the requirements to their proper technical control and full-fledged diagnostics of all its main components.
 
 The aim of the research is to consider the ways of simplification and automation of the process of technical diagnostics of power oil-filled equipment by means of application of artificial intelligence methods, namely the decision tree algorithm for evaluation of the results of chromatographic analysis of transformer oil.
 
 Materials and Methods. As input data, the results of chromatographic analysis of dis-solved gases in transformer oil conducted from December 11, 2009 to December 12, 2020 for two power transformers of voltage class 110 kV installed in the power system of one of the regions of our country were considered and analyzed. As a software application used for diagnosing the technical condition of a power transformer using artificial intelligence methods, we selected the free application Deductor Academic 5.3 Build 0.46.
 
 Research results. The article considers the application of a promising method (decision tree algorithm) of interpretation of data obtained as a result of chromatographic analysis of dissolved gases in transformer oil. The analysis data were processed by means of artificial intelligence methods, the result of which was the reliability and accuracy of determining the technical condition of the power oil-filled transformer.
 
 Conclusions. According to the results of the study, a decision tree algorithm is proposed for the implementation of artificial intelligence in solving the problem of power transformer diagnostics using chromatographic analysis results.

Design and Optimization of Power Transformer Diagnostics

From year to year, humanity’s dependence on electricity supplies is growing, which affects virtually all areas that improve the comfort of people’s lives [...]

Applied Complex Diagnostics and Monitoring of Special Power Transformers

As a major component in electric power systems, power transformers are one of the most expensive and important pieces of electrical equipment. The trouble-free operation of power transformers is an important criterion for safety and stability in a power system. Technical diagnostics of electrical equipment are a mandatory part of preventing accidents and ensuring the continuity of the power supply. In this study, a complex diagnostic methodology was proposed and applied for special power transformers’ risk estimation. Twenty special power transformers were scored with the proposed risk estimation methodology. For each transformer, dissolved gas analysis (DGA) tests, transformer oil quality analysis, visual inspections of all current equipment on-site and historical data for the operation of each electrical research were conducted. All data were collected and analyzed under historical records of malfunctioning events. Statistical data for expected fault risk, based on long-term records, with such types of transformers were used to make more precise estimations of the current state of each machine and expected operational resource. The calculated degree of insulation polymerization was made via an ANN-assisted predictive method. Assessment of the collected data was applied to allow detailed information of the state of the power transformer to be rated. A method for risk assessment and reliability estimation was proposed and applied, based on the health index (HI) for each transformer.

Features of spectral vibration diagnostics of traction power transformers in high-speed motion

This paper uses spectral analysis methods to develop a mathematical model and algorithms for evaluating the diagnosed signals corresponding to certain defects of windings and magnetic circuits of traction power transformers. A distinctive feature of the study is at certain frequencies of spectral dependences, taking into account the effects associated with defect formation that have a different cause of their manifestation, for example, wide-field fluctuations and changes in the shape and width of spectral peaks. The presence of random fluctuations caused the application of the normal Gaussian distribution law of the measured values of the spectra. To solve the problem of identifying the diagnosed spectra corresponding to certain defects of the power transformer, algorithms for identifying the vector of diagnostic features based on the method of statistical recognition theory for large amounts of information are proposed.

Structure and distribution of function between the stages of the information and measurement system for diagnostics of traction substations and contact network installations

The article presents the results of the study of the multistage information-measuring system (IMS) of the diagnostic of traction power supply objects combined with the operational-dispatch control allowing to ensure reliability, attributing to unit value of the IMS. Taking into account the introduction of functional redundancy in the structure of duplicate channels of diagnostics of each stage. he upper level of the complex should maintain processing of information received more frequently from previous devices and issue of certain tasks to the operating personnel for the work of maintenance according to the actual condition of the diagnosed facility. Based on mathematical models of reliability of primary converters and information processing devices on probabilistic indicators. The functional block-circuits of the multi-stage IMS for obtaining and converting information on the example of power transformer diagnostics and contact network devices are disclosed. It has been shown that, given the vulnerability of communication channels, it is advisable to transmit information in large flows, for example, related to spectral analysis, to process at the lower stages of the IMS, and through communication channels to transmit their integral indicators.

Monitoring of power transformers using thermal model and permission time of overload

<p><span>This paper presents the problem of increasing the reliability of electricity</span> supply to consumers. Uninterrupted power supply to electricity consumers depends on the reliability of power supply system in general and power transformers in particular, the accident rate of which is quite high. The causes of the problem are the location of transformer substations at a considerable distance from the service centers, their spreading out over a large area, missing information about the current modes of their operation and so on. One of the ways to solve this problem is development and implementation a system for continuous diagnostics of power transformers. Failure analysis of power transformer based on fault tree is considered, the diagnostic parameters are determined. The insulation wear rate and permission operating time under overload have been defined with help of equivalent heat circuit. It is proposed to use a permission time as a parameter to diagnose the operation mode and increase the efficiency of maintenance of substations through remote monitoring based on the global service mobile (GSM) network. Remote diagnostics allows to receive an information about emergency situation timely. It helps to reduce operating costs, to ensure the reliability and quality of electricity supply for consumers.</p>

Diagnostics of power transformers operating for many years in the power supply system through gases in the composition of transformer oil

Oiled power transformers and autotransformers 40-60 years ago are still in operation in Uzbekistan. At the same time, diagnostic methods for determining faults in transformers and autotransformers remained the same. This article partially analyzes the factors affecting the oils of power transformers and autotransformers used in the agricultural sector. It is known that transformer oil performs the functions of cooling and insulation. During use, the oil is in direct contact with air through the respiratory system. There is a process of transition of moisture and various gases in the composition of the air into the composition of the oil. By the composition of gases, it is possible to determine the reasons for the deterioration in the quality of the main and additional insulation of oil-immersed power transformers. The issues of influence on the state of insulation of marsh gases appearing inside (at the bottom) of the tank of oil transformers and partial discharges in oil-gas medium have been little studied.

Development of a fuzzy expert system for power transformer diagnostics

In this paper, an expert information system for assessing the technical condition of a power transformer is developed. The system will work on the basis of the fuzzy logic device, and provide operational information about the state of the power transformer. The paper uses fuzzy inference algorithms. The R programming language is used to write a program that uses fuzzy logic. We analyzed the data of chromatographic analysis of gases dissolved in oil, as well as the data of thermal imaging images, identifying the most heated points in power transformers. A database of fuzzy logic rules has been formed. Several examples of defuzzification of the results obtained by the center of gravity method are given. As a result of the program, a three-dimensional graph was obtained that characterizes the surface of the fuzzy output. The developed software package allows you to detect defects in working electrical equipment at an early stage of their development, which not only prevents a sudden shutdown of production as a result of an accident, but also significantly reduces the cost of repairing equipment and increases its service life

Non-Contact High Voltage Measurement in the Online Partial Discharge Monitoring System

The article presents an innovative system for non-contact high voltage (HV) measurement, which extends the measurement capabilities of a portable partial discharges (PD) monitoring system intended for diagnostics of power transformers. The proposed method and the developed measuring system are based on the use of a capacitive probe, thanks to which the high voltage measurement is safe (galvanic separation from the objects at ahigh potential). It is also flexible because the voltage ratio of this system can be configured in a wide range by changing the probe’s position. The proposed solution makes the portable PD monitoring system fully autonomous and independent of the substation systems and devices. The article presents both the concept of the non-contact HV measurement system and its practical implementation. The procedure for determining the voltage ratio and measurement uncertainty, which is at an acceptable level of 1–5% in laboratory conditions, was discussed in detail. In addition, the article discusses the digital filtering and wavelet de-noising methods implemented in the software of the monitoring system, which makes it possible to measure the voltage in the presence of strong electromagnetic disturbances occurring at the substation. Finally, the results of field tests carried out on a 250 MVA power transformer are presented, which confirmed the high accuracy of the HV measurement using a capacitive probe and the advantages of this technique.

Expert system for predicting the state of transformers based on fuzzy logic

The article examines methods for monitoring the operation of oil-filled transformers and identifies methods for evaluating the state of the transformer using a fuzzy logic device. Solutions for remote analysis of transformer operation have been formed. The methods that were used for diagnostics are presented. Conclusions are drawn on which equipment is more effective for diagnostics of power transformers.

Об эффективности цифровой системы проактивной диагностики силовых трансформаторов

The purpose of the paper is to diagnose the state of a power transformer by determining its equivalent circuit parameters by means of synchronized vector measurements of currents and voltages in the transformer normal operation mode without shutdowns, which makes it possible to increase the reliability of relay protection operation. A cost - effective method for proactive diagnostics of power transformers is proposed. Through monitoring of additional parameters (short circuit resistance, active and inductive resistance of the positive sequence, active and inductive resistance of the negative sequence) it can increase the speed and accuracy of detecting possible internal short circuits arising due to winding damage or high-voltage transformer bushings without diagnosed transformer disconnection from the network. The method allows to estimate the transformer health index and serviceability by the difference between the calculated parameters of the equivalent circuit and the passport values of the parameters. Having conducted the damage causedependent analysis of the number of power transformer damages, the authors determined total economic losses that include the losses caused by equipment damage and losses caused by the interruptions in consumer power supply. The total economic losses for a power transformer with a rated power of 63 MVA amounted to 10687402 rubles. It is shown that the diagnostic system expands the possibilities of analyzing the transformer state in operating modes, allows to pr event the approaching of the damage moment and occurrence of sudden accidents as well as minimizes the expected damage from shutdowns and equipment failure. A hardware and software complex is proposed for the diagnostics of power transformer internal damage. The given main characteristics of the proposed hardware and software complex include the number of measuring channels, accuracy class, sampling frequency, and others. The results of the work expand the possibilities of analyzing the transformer state in the operating mode and can be used in the world practice of creating various monitoring systems designed to identify the defects developing in transformers caused by winding deformation.

Study on the Influence of Measuring AE Sensor Type on the Effectiveness of OLTC Defect Classification.

The principal objective of this study is to improve the diagnostics of power transformers, which are the key element of supplying electricity to consumers. On Load Tap Changer (OLTC), which is the object of research, the results of which are presented in this article, is one of the most important elements of these devices. The applied diagnostic method is the acoustic emission (AE) method, which has the main advantage over others, that it is considered as a non-destructive testing method. At present, there are many measuring devices and sensors used in the AE method, there are also some international standards, according to which, measurements should be performed. In the presented work, AE signals were measured in laboratory conditions with various OLTC defects being simulated. Five types of sensors were used for the measurement. The recorded signals were analyzed in the time and frequency domain and using discrete wavelet transformation. Based on the results obtained, sets of indicators were determined, which were used as features for an autonomous classification of the type of defect. Several types of learning algorithms from the group of supervised machine learning were considered in the research. The performance of individual classifiers was determined by several quality evaluation measures. As a result of the analyses, the type and characteristics of the most optimal algorithm to be used in the process of classification of the OLTC fault type were indicated, depending on the type of sensor with which AE signals were recorded.

Technical and economic efficiency of proactive diagnostic systems for power transformers

The expediency of using systems of proactive diagnostics of power transformers is substantiated. The diagnostic system expands the possibilities of analyzing the transformer condition in operating mode. It allows one to minimize the expected damage from interruptions in power supply and equipment failure. The results can be used in world practice during construction of various control systems to identify developing transformer defects caused by windings deformations.

Frequency Domain Diagnostics of Transformer Insulation

The first part of paper deals with the base information about diagnostics of power transformers. In this part are presented differently insulating methods, for example method of recovery voltage method, method of polarization and depolarization currents and chromatographic analysis.The second part of paper deals use of method of frequency domain spectroscopy for oil power transformers. This method is used in analysis insulating condition of power transformer with system of oil-paper. It was found, that the results of these tests are highly impacted by the operating temperature during the experimental measurement. Moisture and conductivity between insulating paper and oil in an insulating system are highly dependent from temperature.In the other part, the paper presents experimental results of the frequency diagnostic measurement for a real single-phase traction transformer 110/27 kV at different operating temperatures and states (with oil and without).Finally in the last part, the paper presents comparing frequency insulating measurements among several the same single-phase transformers 110/27 kV.

Modernization of acoustic method for the diagnostics of power transformers based on digital signal processing

The technology of modernization of acoustic diagnostics of oil-filled transformers is described by connecting an additional diagnostic unit for analyzing the temporal and statistical characteristics of the measuring signal. The algorithm of the block functioning is based on the application of identification measurements technologies and digital processing of diagnostic signals, classification of parameters according to designated signal classes and conclusion of the object state with the name. The results of studies of measuring signal images of transformer diagnostics operated on the basis of «SEVKAZENERGO» JSC are presented.

Analysis of insulation properties of transformer materials at different ambient temperatures

Abstract The first part of paper deals with the base information about diagnostics of power transformers. The second part of paper deals use of method of frequency domain spectroscopy (FDS) for traction transformer. This method is used in analysis insulating condition and its solution has scientific importance for analysis of power transformer with system of oil-paper. It was found, that the results of these tests are highly impacted by the operating temperature during the experimental measurement. Finally, the paper presents experimental results of this diagnostic measurement for a real traction transformer at different operating temperatures and states (with oil and without). It has been found, that moisture and conductivity between paper and oil in an insulating system are highly dependent from temperature.

Analysis of Gas Generated in Mineral Oil, Synthetic Ester, and Natural Ester as a Consequence of Thermal Faults

The gases generated by electrical and thermal faults are similar in the case of mineral oil, synthetic ester, and natural ester. However, there are considerable differences in the amount of the generated gases and their solubility in these liquids, what should be taken into account during power transformer diagnostics by means of dissolved gas analysis (DGA) method. The aim of the research was to compare the gases generated as a result of thermal faults (250°C, 350°C, and 450°C) in mineral oil and both esters. The following gases were analyzed: hydrogen, methane, ethane, ethylene, acetylene, propane, propylene, carbon oxide, and carbon dioxide. A qualitative and quantitative analysis of these gases was carried out by means of gas chromatography. A large share of propane in the sum of the gases generated in the esters, mainly in the synthetic ester, was found. Propane and propylene in most of the gas interpretation approaches are omitted. The authors proved that in the case of synthetic ester, using propane as the key gas for thermal faults detection is justified. The obtained results can be used to improve the interpretation of the DGA results, in the case of ester liquids used in power transformers.

Vibro-Acoustic Methods in the Condition Assessment of Power Transformers: A Survey

It has been over two decades since the publication of pioneer works about the power transformer diagnostics based on monitoring of their acoustic fingerprints. Since then, there has been great progress in this field and the methods used are as complex as ever. Any unnecessary intervention on a power transformer implies its temporary disconnection from the power grid. The inability to supply electricity to the customer means not only financial loss for the utility but also generates a non-material loss, e.g., the loss of reputation to the customer. Faster, more accurate, more reliable, and less invasive diagnosis is the main reason behind development and improvement in this field. The main goal of this paper is to categorize and review state-of-the art of vibro-acoustic diagnostic methods for power transformers. This paper opens with a brief note about continuous condition monitoring, after which we overview the causes of transformer vibrations as well as the collection and preprocessing of diagnostic data. Then, we review and categorize works related to the acoustic condition assessment of power transformers considering both: feature extraction in the time, frequency, time-frequency domain, and mathematical modeling and system identification of dynamic systems.

Power Transformer Diagnostics, Monitoring and Design Features

The reliability of the power grid system directly contributes to the economic well-being and the quality of life of citizens in any country. [...]

АНАЛИЗ ПРИЧИН ВЫХОДА ИЗ СТРОЯ ТРАНСФОРМАТОРОВ 110 кВ И МЕТОДЫ ИХ ДИАГНОСТИРОВАНИЯ

The article deals with the diagnostics of power transformers by different methods. Particular attention is paid to modern methods and diagnostic tools that maximally allow to determine the state of the transformer. Based on the statistical processing of the results of the research, the authors indicate that the most common failures are: damage to the windings of transformers with the possibility of regulation under load, without disconnecting power and leaving consumers without power supply (RPN) for any period of operation. The greatest number of damages for transformers with on-load tap-changers with a service life of 10-30 years, for high-voltage bushings after 10 years of operation. The most severe damage to the transformer is an internal short circuit (short circuit). These types of overvoltage cause damage to the windings in 80% of the total number of damage, high-voltage bushings - 89%, RPN - 25% and other elements - 36%. It is indicated that a serious consequence occurs when such defects develop, as: the reduction of the electrical strength of the oil channel of high-voltage hermetic bushings due to deposition of sediment on the inner surface of porcelain and on the surface of internal insulation; reduction of the electrical strength of paper-oil insulation of high-voltage leaky inlets due to moisture and pollution; humidification, contamination and wear (aging) of the insulation of the windings; burn-out of the coil insulation and windings of the windings because of the long non-operation of the through-current fault on the low-voltage side of the transformer; errors in installation, repair and operation. In the conclusions it is recommended to supply the manufacturers of power transformers with means for diagnosing the main elements of power transformers, which should be built-in. Particular mention was made of the need to focus in the future on improving existing and creating new methods for monitoring equipment of power transformers.