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The main results of two reliability surveys are presented. The surveys were conducted to assemble objective data on the performance of transformers in service. The surveys provide useful information on the causes of transformer failures, the most likely affected components, and the related outage times. The most important methods actually in use fo...
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... the first component involved (Fig. 1) it may be noted that about 33% of failures are due to the windings. The failures were also subdivided as a function of downtime (Fig. 2) into three classes (not more than one day; from 1 to 30 days; and more than 30 days) in order, however roughly, to be able to correlate downtime with the components involved in the failures. From ...
Citations
... The power transformer is a multifaceted entity that is susceptible to encountering diverse anomalies, which can be classified as either endogenous or exogenous faults. As depicted in Figure 1, various types of faults may arise in distinct regions, including on the winding, tank, insulating oil, core, terminal, cooling system, and tap changer, as highlighted in reference [15]. The external faults commonly manifest as a result of external short circuits within the power system, over-flux phenomena, or overloading. ...
... Instances of anomalies in these latter regions are infrequent during regular operational states. [15]. ...
... Globally, Figure 1. Power transformer failure classification [15]. ...
The detection of partial discharge (PD) activities in high-voltage equipment can be conducted according to several mechanisms of signal detection, including electromagnetic wave signal detection, acoustic signal detection, chemical reactions, electrical signal detection, and optical emission detection. Recently, multiple methods of detection and localization of partial discharge activities, which occurred in power transformers and gas-insulated switchgear (GIS), have been proposed to monitor the health condition of high-voltage equipment, especially when the awareness regarding preventive maintenance has been emphasized at the industrial level and among electrical providers. In aligning the needs of the industrial sector and the improvement of PD-detection methods, this manuscript focuses on reviewing the current practice methods for the detection and localization of PD signals in high-voltage equipment, comparing their efficacy, and summarizing the future direction of research work-related methods of PD detection. The comparative reviews are discussed in terms of the mechanism of PD signal detection, indication parameters, calibration techniques, and the advantages and limitations of each method of PD measurement in detail.
... The ratio of certain gases' concentrations allows one to detect the type of equipment damage and its location [9][10][11][12][13]; 2. Power factor analysis. Power factor measurements and a power transformer's capacitance are analyzed based on retrospective changes in these values for the particular unit under consideration [14]; 3. Winding resistance and transformation ratio assessment allows one to identify turn-toturn short circuits and power transformer insulation and winding damages [14,15]; 4. Transformer no-load losses assessment, the changes in which indicate probable power transformer magnetic core damage [16,17]; 5. Thermographic transformer inspection, which allows one to identify the frame's hot spots, indicating deviations in the cooling system operation and short circuits [15][16][17][18]; 6. Detection of partial discharges. ...
... The ratio of certain gases' concentrations allows one to detect the type of equipment damage and its location [9][10][11][12][13]; 2. Power factor analysis. Power factor measurements and a power transformer's capacitance are analyzed based on retrospective changes in these values for the particular unit under consideration [14]; 3. Winding resistance and transformation ratio assessment allows one to identify turn-toturn short circuits and power transformer insulation and winding damages [14,15]; 4. Transformer no-load losses assessment, the changes in which indicate probable power transformer magnetic core damage [16,17]; 5. Thermographic transformer inspection, which allows one to identify the frame's hot spots, indicating deviations in the cooling system operation and short circuits [15][16][17][18]; 6. Detection of partial discharges. ...
This manuscript addresses the problem of technical state assessment of power transformers based on data preprocessing and machine learning. The initial dataset contains diagnostics results of the power transformers, which were collected from a variety of different data sources. It leads to dramatic degradation of the quality of the initial dataset, due to a substantial number of missing values. The problems of such real-life datasets are considered together with the performed efforts to find a balance between data quality and quantity. A data preprocessing method is proposed as a two-iteration data mining technology with simultaneous visualization of objects’ observability in a form of an image of the dataset represented by a data area diagram. The visualization improves the decision-making quality in the course of the data preprocessing procedure. On the dataset collected by the authors, the two-iteration data preprocessing technology increased the dataset filling degree from 75% to 94%, thus the number of gaps that had to be filled in with the synthetic values was reduced by 2.5 times. The processed dataset was used to build machine-learning models for power transformers’ technical state classification. A comparative analysis of different machine learning models was carried out. The outperforming efficiency of ensembles of decision trees was validated for the fleet of high-voltage power equipment taken under consideration. The resulting classification-quality metric, namely, F1-score, was estimated to be 83%.
... The power transformer is a complex structure experiencing faults, which are categorized into internal and external faults. Fig. 1 shows the classification of fault in the power transformer [8]. Global statistics show that 70% -80% of transformer's faults are internal faults [9]. ...
The high voltage power transformer is the critical element of the power system, which requires continuous monitoring to prevent sudden catastrophic failures and to ensure an uninterrupted power supply. The most common failures in the transformer are due to partial discharge (PD) in electrical insulations which are the results of the insulation degradation over time. Different approaches have been proposed to monitor, detect, and locate the partial discharge in power transformers. This paper reviews and evaluates the current state-of-the-art methods for PD detection and localization techniques, and methodologies in power transformers. Detailed comparisons of PD detection techniques have been identified and discussed in this paper. The drawbacks and challenges of different partial discharge measurement techniques have been elaborated. Finally, brief reviews of PD denoising signals, feature extraction of PD signals, and classification of partial discharge sources have been addressed.
... Con el tiempo estas imperfecciones pueden terminar deteriorando todo el sistema de aislación del transformador de potencia (Wang et al., 2002). Hay dos métodos utilizados para la detección de PDs: La detección de las señales acústicas y la medición de las señales eléctricas (Cardoso y Oliveira, 1999). Las PDs pueden ser medidas a través de sensores piezoeléctricos, fibra óptica y sensores de extra-alta frecuencia (Zargari y Blackburn, 1996). ...
Resumen Este artículo presenta una revisión general del marco conceptual relacionado con la gestión activos para transformadores de potencia y la evaluación del riesgo asociado a sus fallas. El índice de riesgo es una herramienta esencial para realizar la gestión de activos, especialmente porque apoya al gestor en el proceso de toma de decisiones. El índice de riesgo está compuesto por dos factores: i) el factor de consecuencia, que valora los impactos que se podrían presentar en caso de falla del equipo; y ii) la probabilidad de falla que se determina a partir de los resultados de las pruebas de funcionamiento, de la historia de la operación y del historial de fallas, entre otros aspectos. Se presentan aspectos generales relacionados con la gestión de activos según las normas internacionales, para luego tratar con mayor detalle aspectos específicos relacionados con la evaluación del índice de riesgo del transformador, encontrados en la literatura. Palabras clave: transformador de potencia, gestión de activos, índice de riesgo, ensayos de campo Abstract This article presents an overview of the conceptual framework related to the asset management of power transformers, and to the assessment of risks associated with transformer failures. The risk index is an essential tool for developing the management of this asset, especially because it supports the asset manager in the decision-making process. The risk index is composed by two indicators: i) consequence factor, which assesses the impacts that could arise in the event of equipment failure, and ii) the probability of failure, which is determined from the results of tests for transformer functioning, operating history, and failure history, among others. General aspects of asset management according to international standards are presented, to then deal with specific aspects related to evaluation of the transformer risk index, found in the literature.
... One of the common conclusions of these surveys is the increasing need for the development of new diagnostic techniques, which can be applied without taking transformers out of service, and which can also provide a fault severity criteria, in particular for determining transformers winding insulation faults. In fact, winding defects are the most significant failure type that occurs in power transformers and they are also the ones with an associated longer downtime [4], [9], [12]- [13]. ...
... Previous research, concerning the use of the Park's Vector Approach, has demonstrated the effectiveness of this non-invasive technique for diagnosing malfunctions in operating three-phase induction motors, power electronics and adjustable speed drives [24]. Preliminary experimental results, presented in [9], concerning the use of the supply current Park's Vector Approach, have also demonstrated the effectiveness of this technique for diagnosing the occurrence of inter-turn insulation faults in the windings of operating three-phase transformers. The on-line diagnosis is based on identifying the appearance of an elliptic pattern, corresponding to the transformer supply current Park's Vector representation, whose ellipticity increases with the severity of the fault and whose major axis orientation is associated to the faulty phase. ...
This paper presents the application of the on-load exciting current Extended Park's Vector Approach to diagnose incipient turn-to-turn winding faults in operating power transformers. Experimental and simulation test results demonstrate the effectiveness of the proposed technique, which is based on the spectral analysis of the AC component of the on-load exciting current Park's Vector modulus.
... Therefore, it is quite obvious the need for the development of on-line diagnostic techniques that would aid in transformer maintenance. A survey of the most important methods, actually in use, for condition monitoring and diagnostics of power and distribution transformers, presented in [3], stresses the need for the development of new diagnostic techniques, which can be applied A. J. M. Cardoso is with the Department of Electrical and Computer Engineering, Faculty of Sciences and Technology, University of Coimbra, P-3030-290 Coimbra, Portugal and also with the Instituto de Telecomunicações (e-mail: ajmcardoso@ieee.org). ...
... Previous research, concerning the use of the Park's Vector Approach, has demonstrated the effectiveness of this non-invasive technique for diagnosing malfunctions in operating three-phase induction motors, power electronics and adjustable speed drives [12]. Preliminary experimental results, presented in [3], concerning the use of the supply current Park's Vector Approach, have also demonstrated the effectiveness of this technique for diagnosing the occurrence of inter--turn insulation faults in the windings of operating three-phase transformers. The on-line diagnosis is based on identifying the appearance of an elliptic pattern, corresponding to the transformer supply current Park's Vector representation, whose ellipticity increases with the severity of the fault and whose major axis orientation is associated with the faulty phase. ...
This paper investigates the behavior of power transformers under the occurrence of permanent or intermittent winding insulation faults. For the study of these phenomena, a simple and efficient permeance-based electromagnetic transformer model is proposed, which is based on the simultaneous consideration of magnetic and electric equivalent circuits. To incorporate the internal faults in this model, a suitable equivalent circuit of the faulty winding is described. With the aid of this transformer model, the onload exciting current Park's Vector Approach will be applied for diagnosing the occurrence of permanent and intermittent winding faults. Experimental and simulation tests results are presented in this paper, which demonstrate not only the adequacy of the digital transformer model for winding fault studies, but also the effectiveness of the proposed technique for detecting winding interturn insulation faults in operating three-phase transformers.
... But this method is not sensitive. 2) In-service partial discharge testing [1,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. PD in transformers degrades the properties of the insulating materials and can result in eventual failures. ...
The power transformers are the key equipments in the power system. To keep the stable operation of the transformers, it's necessary to get their state information on a real-time basis. Therefore, the efficient online monitoring system is developed which obtain the state of the transformers by the accelerometers attached on the tank. The locations of these accelerometers can be determined by the method of varying current with constant frequency. The vibration intensity change is used to initially detect the windings' state by online monitoring the vibration signal of the shocks. Then the time-frequency analysis further processes these signals in order to detect the fault information contained. The short-circuit experiments have been done on the large power transformer of 50000KVA, which finds that the time-frequency analysis can be used to more precisely detect the fault characteristics of windings. Compared with traditional off line short circuit reactance method, the time-frequency analysis is more effective.
... As a result, it is quite obvious the need for the development of on--line diagnostic techniques that would aid in transformers maintenance. A survey of the most important methods, actually in use, for condition monitoring and diagnostics of power and distribution transformers, presented in [2], stresses the need for the development of new diagnostic techniques, which can be applied without taking transformers out of service, and which can also provide a fault severity criteria, in particular for determining transformers winding insulation faults. ...
... Previous research, concerning the use of the Park's Vector Approach, has demonstrated the effectiveness of this non invasive technique for diagnosing malfunctions in operating three--phase induction motors, power electronics and adjustable speed drives [10]. Preliminary experimental results, presented in [2], concerning the use of the supply current Park's Vector Approach, have also demonstrated the effectiveness of this technique for diagnosing the occurrence of inter-turn insulation faults in the windings of operating three-phase transformers. The on-line diagnosis is based on identifying the appearance of an elliptic pattern, corresponding to the transformer supply current Park's Vector representation, whose ellipticity increases with the severity of the fault and whose major axis orientation is associated to the faulty phase. ...
This paper presents the application of the on-load exciting current Park's vector approach for diagnosing permanent and intermittent turn-to-turn winding faults in operating power transformers. A digital model for the simulation of the behavior of three-phase transformers affected by the presence of winding faults is also proposed. Experimental and simulated results demonstrate the effectiveness of the proposed diagnostic technique, which is based on the on-line monitoring of the .on-load exciting current Park's Vector patterns.
... Previous research, concerning the use of the Park's Vector Approach, has demonstrated the effectiveness of this non-invasive technique for diagnosing malfunctions in operating three-phase induction motors, power electronics and adjustable speed drives [9]. Preliminary experimental results, presented in [10], concerning the use of the supply current Park's Vector Approach, have also demonstrated the effectiveness of this technique for diagnosing the occurrence of inter-turn insulation faults in the windings of operating three-phase transformers. The on-line diagnosis is based on identifying the appearance of an elliptic pattern, corresponding to the transformer supply current Park's Vector representation, whose ellipticity increases with the severity of the fault and whose major axis orientation is associated to the faulty phase. ...
... The second step is to determine the type of fault. Two methods most commonly used are the key gases and gas ratios [17,18,21,22,23,27,29,30,36,39,45,56,58,60,76]. The first involves plotting all the total dissolved combustible gas (TDCG) as a percent of their total in a histogram. ...
... An excitation current test provides the no load losses of the transformer. It is done routinely only in a factory setting [22,27,39,45,60]. Excitation current is measured by applying a rated voltage to the primary winding with the secondary winding open-circuited. ...
... Partial discharge (PD) in transformers degrades the properties of the insulating materials and can lead to eventual failures [23]. There are two commonly used PD detection methods: detection of the acoustic signals and measurement of the electrical signals produced by the PD [27]. PD can also be detected indirectly using chemical techniques such as measuring the degradation products produced by the PD. ...
As transformers age, their internal condition degrades, which increases the risk of failure. To prevent these failures and to maintain transformers in good operating condition is a very important issue for utilities. Traditionally, routine preventative maintenance programs combined with regular testing were used. The change to condition-based maintenance has resulted in the reduction, or even elimination, of routine time-based maintenance. Instead of doing maintenance at a regular interval, maintenance is only carried out if the condition of the equipment requires it. Hence, there is an increasing need for better nonintrusive diagnostic and monitoring tools to assess the internal condition of the transformers. If there is a problem, the transformer can then be repaired or replaced before it fails. An extensive review is given of diagnostic and monitoring tests, and equipment available that assess the condition of power transformers and provide an early warning of potential failure.
