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Power Transformer Diagnostics, Monitoring and Design Features

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A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (15 February 2016) | Viewed by 106477

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Prof. Dr. Issouf Fofana

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Aging of Oil-Filled Equipment on High Voltage Lines (ViAHT), Department of Applied Sciences, Université du Québec à Chicoutimi (UQAC), Chicoutimi, QC G7H 2B1, Canada
Interests: electromagnetic compatibility; electrical engineering; electrical insulation; dielectric materials; problems associated with the transport and distribution of electrical energy
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Dear Colleagues,

Transformers are key components in electric power distribution and transmission systems and it is essential that they function properly for many years. With increasing age, there are potential risks of extremely high monetary losses due to unexpected failures and outages. The fundamental objective is to promote the longest possible service life, to minimize lifetime operating costs, and to predict the time ripped to remove the transformer, on a planned basis, for revision or replacement. For these reasons, transformer life management gained the past decades an ever-increasing interest due to economic and technical reasons. The greatest challenges are related to the need for methods to assess the condition and life expectancy along with the improvement of transformers efficiency by noble designs and or application of new materials. The Special Issue will cover theoretical and practical developments with special emphasis on new R&D trends in transformer designs and transformer diagnostic and maintenance recent challenges. Topics of interest for publication include, but are not limited to:

new or emerging diagnostic/monitoring technologies
mineral oils of improved characteristics, additives
nanofluids and synthetic/vegetable dielectric liquids
new materials for transformers
transformer life management

Prof. Dr. Ing. Issouf Fofana
Guest Editor

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Keywords

power transformers
insulating liquids
insulating solids
transformer design
aging
diagnostic and monitoring
life management
transformer components

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Published Papers (13 papers)

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Editorial

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5 pages, 174 KiB

Open AccessEditorial

Power Transformer Diagnostics, Monitoring and Design Features

by Issouf Fofana and Yazid Hadjadj

Energies 2018, 11(12), 3248; https://doi.org/10.3390/en11123248 - 22 Nov 2018

Cited by 7 | Viewed by 3192

Abstract

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

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

Research

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3460 KiB

Open AccessArticle

Moisture Migration in an Oil-Paper Insulation System in Relation to Online Partial Discharge Monitoring of Power Transformers

by Wojciech Sikorski, Krzysztof Walczak and Piotr Przybylek

Energies 2016, 9(12), 1082; https://doi.org/10.3390/en9121082 - 17 Dec 2016

Cited by 42 | Viewed by 9114

Abstract

Most power transformers operating in a power system possess oil-paper insulation. A serious defect of this type of insulation, which is associated with long operation time, is an increase in the moisture content. Moisture introduces a number of threats to proper operation of the transformer, e.g., ignition of partial discharges (PDs). Due to the varying temperature of the insulation system during the unit’s normal operation, a dynamic change (migration of water) takes place, precipitating the oil-paper system from a state of hydrodynamic equilibrium. This causes the PDs to be variable in time, and they may intensify or extinguish. Studies on model objects have been conducted to determine the conditions (temperature, humidity, time) that will have an impact on the ignition and intensity of the observed phenomenon of PDs. The conclusions of this study will have a practical application in the evaluation of measurements conducted in the field, especially in relation to the registration of an online PD monitoring system. Full article

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

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4986 KiB

Open AccessArticle

Raman Spectral Characteristics of Oil-Paper Insulation and Its Application to Ageing Stage Assessment of Oil-Immersed Transformers

by Jingxin Zou, Weigen Chen, Fu Wan, Zhou Fan and Lingling Du

Energies 2016, 9(11), 946; https://doi.org/10.3390/en9110946 - 12 Nov 2016

Cited by 37 | Viewed by 5902

Abstract

The aging of oil-paper insulation in power transformers may cause serious power failures. Thus, effective monitoring of the condition of the transformer insulation is the key to prevent major accidents. The purpose of this study was to explore the feasibility of confocal laser Raman spectroscopy (CLRS) for assessing the aging condition of oil-paper insulation. Oil-paper insulation samples were subjected to thermal accelerated ageing at 120 °C for up to 160 days according to the procedure described in the IEEE Guide. Meanwhile, the dimension of the Raman spectrum of the insulation oil was reduced by principal component analysis (PCA). The 160 oil-paper insulation samples were divided into five aging stages as training samples by clustering analysis and with the use of the degree of polymerization of the insulating papers. In addition, the features of the Raman spectrum were used as the inputs of a multi-classification support vector machine. Finally, 105 oil-paper insulation testing samples aged at a temperature of 130 °C were used to further test the diagnostic capability and universality of the established algorithm. Results demonstrated that CLRS in conjunction with the PCA-SVM technique provides a new way for aging stage assessment of oil-paper insulation equipment in the field. Full article

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

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787 KiB

Open AccessArticle

An Integrated Decision-Making Model for Transformer Condition Assessment Using Game Theory and Modified Evidence Combination Extended by D Numbers

by Lingjie Sun, Yingyi Liu, Boyang Zhang, Yuwei Shang, Haiwen Yuan and Zhao Ma

Energies 2016, 9(9), 697; https://doi.org/10.3390/en9090697 - 31 Aug 2016

Cited by 47 | Viewed by 6835

Abstract

The power transformer is one of the most critical and expensive components for the stable operation of the power system. Hence, how to obtain the health condition of transformer is of great importance for power utilities. Multi-attribute decision-making (MADM), due to its ability of solving multi-source information problems, has become a quite effective tool to evaluate the health condition of transformers. Currently, the analytic hierarchy process (AHP) and Dempster–Shafer theory are two popular methods to solve MADM problems; however, these techniques rarely consider one-sidedness of the single weighting method and the exclusiveness hypothesis of the Dempster–Shafer theory. To overcome these limitations, this paper introduces a novel decision-making model, which integrates the merits of fuzzy set theory, game theory and modified evidence combination extended by D numbers, to evaluate the health condition of transformers. A four-level framework, which includes three factors and seventeen sub-factors, is put forward to facilitate the evaluation model. The model points out the following: First, the fuzzy set theory is employed to obtain the original basic probability assignments for all indices. Second, the subjective and objective weights of indices, which are calculated by fuzzy AHP and entropy weight, respectively, are integrated to generate the comprehensive weights based on game theory. Finally, based on the above two steps, the modified evidence combination extended by D numbers, which avoids the limitation of the exclusiveness hypothesis in the application of Dempster–Shafer theory, is proposed to obtain the final assessment results of transformers. Case studies are given to demonstrate the proposed modeling process. The results show the effectiveness and engineering practicability of the model in transformer condition assessment. Full article

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

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3143 KiB

Open AccessArticle

Streamer Propagation and Breakdown in a Very Small Point-Insulating Plate Gap in Mineral Oil and Ester Liquids at Positive Lightning Impulse Voltage

by Pawel Rozga

Energies 2016, 9(6), 467; https://doi.org/10.3390/en9060467 - 17 Jun 2016

Cited by 21 | Viewed by 6415

Abstract

This article presents the results of comparative studies on streamer propagation and breakdown in a point-insulating plate electrode system in mineral oil and two ester liquids. The studies were performed for a 10-mm gap and a positive standard lightning impulse. The work was focused on the comparison of light waveforms registered using the photomultiplier technique. The results indicated that both esters demonstrate a lower resistance against the appearance of fast energetic streamers than mineral oil. The reason for such a conclusion is that the number of lightning impulses supplied to the electrode system for which the above-mentioned fast streamers appeared at a given voltage level was always higher in the case of ester liquids than mineral oil. In terms of breakdown, the esters tested were assessed as more susceptible to the appearance of breakdown in the investigated electrode system. The number of breakdowns recorded in the case of esters was always greater than the corresponding number of breakdowns in mineral oil. This may be supposed on the basis of the obtained results that imply that, in both synthetic and natural ester, the formed breakdown channel, which bridged the gap through the surface of pressboard plate, is characterized by higher energy than in the case of mineral oil. Full article

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

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3719 KiB

Open AccessArticle

An Intelligent Sensor for the Ultra-High-Frequency Partial Discharge Online Monitoring of Power Transformers

by Jian Li, Xudong Li, Lin Du, Min Cao and Guochao Qian

Energies 2016, 9(5), 383; https://doi.org/10.3390/en9050383 - 19 May 2016

Cited by 22 | Viewed by 7502

Abstract

Ultra-high-frequency (UHF) partial discharge (PD) online monitoring is an effective way to inspect potential faults and insulation defects in power transformers. The construction of UHF PD online monitoring system is a challenge because of the high-frequency and wide-frequency band of the UHF PD signal. This paper presents a novel, intelligent sensor for UHF PD online monitoring based on a new method, namely a level scanning method. The intelligent sensor can directly acquire the statistical characteristic quantities and is characterized by low cost, few data to output and transmit, Ethernet functionality, and small size for easy installation. The prototype of an intelligent sensor was made. Actual UHF PD experiments with three typical artificial defect models of power transformers were carried out in a laboratory, and the waveform recording method and intelligent sensor proposed were simultaneously used for UHF PD measurement for comparison. The results show that the proposed intelligent sensor is qualified for the UHF PD online monitoring of power transformers. Additionally, three methods to improve the performance of intelligent sensors were proposed according to the principle of the level scanning method. Full article

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

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11635 KiB

Open AccessArticle

Comparison of Dissolved Gases in Mineral and Vegetable Insulating Oils under Typical Electrical and Thermal Faults

by Chenmeng Xiang, Quan Zhou, Jian Li, Qingdan Huang, Haoyong Song and Zhaotao Zhang

Energies 2016, 9(5), 312; https://doi.org/10.3390/en9050312 - 25 Apr 2016

Cited by 43 | Viewed by 10065

Abstract

Dissolved gas analysis (DGA) is attracting greater and greater interest from researchers as a fault diagnostic tool for power transformers filled with vegetable insulating oils. This paper presents experimental results of dissolved gases in insulating oils under typical electrical and thermal faults in transformers. The tests covered three types of insulating oils, including two types of vegetable oil, which are camellia insulating oil, Envirotemp FR3, and a type of mineral insulating oil, to simulate thermal faults in oils from 90 °C to 800 °C and electrical faults including breakdown and partial discharges in oils. The experimental results reveal that the content and proportion of dissolved gases in different types of insulating oils under the same fault condition are different, especially under thermal faults due to the obvious differences of their chemical compositions. Four different classic diagnosis methods were applied: ratio method, graphic method, and Duval’s triangle and Duval’s pentagon method. These confirmed that the diagnosis methods developed for mineral oil were not fully appropriate for diagnosis of electrical and thermal faults in vegetable insulating oils and needs some modification. Therefore, some modification aiming at different types of vegetable oils based on Duval Triangle 3 were proposed in this paper and obtained a good diagnostic result. Furthermore, gas formation mechanisms of different types of vegetable insulating oils under thermal stress are interpreted by means of unimolecular pyrolysis simulation and reaction enthalpies calculation. Full article

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

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3682 KiB

Open AccessFeature PaperArticle

Performance of Natural Ester as a Transformer Oil in Moisture-Rich Environments

by Kapila Bandara, Chandima Ekanayake, Tapan Saha and Hui Ma

Energies 2016, 9(4), 258; https://doi.org/10.3390/en9040258 - 31 Mar 2016

Cited by 45 | Viewed by 11773

Abstract

Interest has risen among utilities in using natural ester (NE) insulating oils in transformers as a substitute for conventional mineral oil. However, present understanding on aging behaviour of NE-paper composite insulation system and knowledge on application of existing condition monitoring tools for NE-based insulation are inadequate. This limits the cost effective and reliable field applications of NE insulating oil. To pave the way the application of NE-based insulation in transformers, a systematic study has been performed to compare the aging behaviour of transformer grade pressboard (PB) impregnated in NE and conventional mineral oil. Applicability of a number of chemical and physical parameters, including acidity value, dielectric dissipation factor (DDF), viscosity, and colour for assessing the quality of NE insulating oil is also discussed in this paper. Comparisons are made based on the limiting values provided in the related IEEE Standard and properties of mineral oil under similar aging conditions. Full article

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

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1957 KiB

Open AccessArticle

Reliability Analysis and Overload Capability Assessment of Oil-Immersed Power Transformers

by Chen Wang, Jie Wu, Jianzhou Wang and Weigang Zhao

Energies 2016, 9(1), 43; https://doi.org/10.3390/en9010043 - 14 Jan 2016

Cited by 16 | Viewed by 6178

Abstract

Smart grids have been constructed so as to guarantee the security and stability of the power grid in recent years. Power transformers are a most vital component in the complicated smart grid network. Any transformer failure can cause damage of the whole power system, within which the failures caused by overloading cannot be ignored. This research gives a new insight into overload capability assessment of transformers. The hot-spot temperature of the winding is the most critical factor in measuring the overload capacity of power transformers. Thus, the hot-spot temperature is calculated to obtain the duration running time of the power transformers under overloading conditions. Then the overloading probability is fitted with the mature and widely accepted Weibull probability density function. To guarantee the accuracy of this fitting, a new objective function is proposed to obtain the desired parameters in the Weibull distributions. In addition, ten different mutation scenarios are adopted in the differential evolutionary algorithm to optimize the parameter in the Weibull distribution. The final comprehensive overload capability of the power transformer is assessed by the duration running time as well as the overloading probability. Compared with the previous studies that take no account of the overloading probability, the assessment results obtained in this research are much more reliable. Full article

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

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1965 KiB

Open AccessArticle

Study of the Impact of Initial Moisture Content in Oil Impregnated Insulation Paper on Thermal Aging Rate of Condenser Bushing

by Youyuan Wang, Kun Xiao, Bijun Chen and Yuanlong Li

Energies 2015, 8(12), 14298-14310; https://doi.org/10.3390/en81212429 - 18 Dec 2015

Cited by 15 | Viewed by 6089

Abstract

This paper studied the impact of moisture on the correlated characteristics of the condenser bushings oil-paper insulation system. The oil-impregnated paper samples underwent accelerated thermal aging at 130 °C after preparation at different initial moisture contents (1%, 3%, 5% and 7%). All the samples were extracted periodically for the measurement of the moisture content, the degree of polymerization (DP) and frequency domain dielectric spectroscopy (FDS). Next, the measurement results of samples were compared to the related research results of transformer oil-paper insulation, offering a theoretical basis of the parameter analysis. The obtained results show that the moisture fluctuation amplitude can reflect the different initial moisture contents of insulating paper and the mass ratio of oil and paper has little impact on the moisture content fluctuation pattern in oil-paper but has a great impact on moisture fluctuation amplitude; reduction of DP presents an accelerating trend with the increase of initial moisture content, and the aging rate of test samples is higher under low moisture content but lower under high moisture content compared to the insulation paper in transformers. Two obvious “deceleration zones” appeared in the dielectric spectrum with the decrease of frequency, and not only does the integral value of dielectric dissipation factor (tan δ) reflect the aging degree, but it reflects the moisture content in solid insulation. These types of research in this paper can be applied to evaluate the condition of humidified insulation and the aging state of solid insulation for condenser bushings. Full article

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

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Review

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1955 KiB

Open AccessReview

Electrical-Based Diagnostic Techniques for Assessing Insulation Condition in Aged Transformers

by Issouf Fofana and Yazid Hadjadj

Energies 2016, 9(9), 679; https://doi.org/10.3390/en9090679 - 26 Aug 2016

Cited by 84 | Viewed by 9904

Abstract

The condition of the internal cellulosic paper and oil insulation are of concern for the performance of power transformers. Over the years, a number of methods have been developed to diagnose and monitor the degradation/aging of the transformer internal insulation system. Some of this degradation/aging can be assessed from electrical responses. Currently there are a variety of electrical-based diagnostic techniques available for insulation condition monitoring of power transformers. In most cases, the electrical signals being monitored are due to mechanical or electric changes caused by physical changes in resistivity, inductance or capacitance, moisture, contamination or aging by-products in the insulation. This paper presents a description of commonly used and modern electrical-based diagnostic techniques along with their interpretation schemes. Full article

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

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864 KiB

Open AccessEditor’s ChoiceReview

Review of Physicochemical-Based Diagnostic Techniques for Assessing Insulation Condition in Aged Transformers

by Janvier Sylvestre N’cho, Issouf Fofana, Yazid Hadjadj and Abderrahmane Beroual

Energies 2016, 9(5), 367; https://doi.org/10.3390/en9050367 - 13 May 2016

Cited by 188 | Viewed by 11818

Abstract

A power transformer outage has a dramatic financial consequence not only for electric power systems utilities but also for interconnected customers. The service reliability of this important asset largely depends upon the condition of the oil-paper insulation. Therefore, by keeping the qualities of oil-paper insulation system in pristine condition, the maintenance planners can reduce the decline rate of internal faults. Accurate diagnostic methods for analyzing the condition of transformers are therefore essential. Currently, there are various electrical and physicochemical diagnostic techniques available for insulation condition monitoring of power transformers. This paper is aimed at the description, analysis and interpretation of modern physicochemical diagnostics techniques for assessing insulation condition in aged transformers. Since fields and laboratory experiences have shown that transformer oil contains about 70% of diagnostic information, the physicochemical analyses of oil samples can therefore be extremely useful in monitoring the condition of power transformers. Full article

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

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10893 KiB

Open AccessReview

Progress of Space Charge Research on Oil-Paper Insulation Using Pulsed Electroacoustic Techniques

by Chao Tang, Bo Huang, Miao Hao, Zhiqiang Xu, Jian Hao and George Chen

Energies 2016, 9(1), 53; https://doi.org/10.3390/en9010053 - 18 Jan 2016

Cited by 30 | Viewed by 7915

Abstract

This paper focuses on the space charge behavior in oil-paper insulation systems used in power transformers. It begins with the importance of understanding the space charge behavior in oil-paper insulation systems, followed by the introduction of the pulsed electrostatic technique (PEA). After that, the research progress on the space charge behavior of oil-paper insulation during the recent twenty years is critically reviewed. Some important aspects such as the environmental conditions and the acoustic wave recovery need to be addressed to acquire more accurate space charge measurement results. Some breakthroughs on the space charge behavior of oil-paper insulation materials by the research team at the University of Southampton are presented. Finally, future work on space charge measurement of oil-paper insulation materials is proposed. Full article

(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)

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