Energies

Research

7 pages, 5333 KiB

Open AccessArticle

Identification of Stray Gassing of Dodecylbenzene in Bushings

by Michel Duval and Constantin Ene

Energies 2021, 14(9), 2350; https://doi.org/10.3390/en14092350 - 21 Apr 2021

Viewed by 1645

Several high voltage condenser type OIP (oil impregnated paper) bushings used in the electrical industry are filled with dodecylbenzene, because of its ability to absorb hydrogen formed by corona partial discharges in the thick paper insulation of these pieces of equipment. Some of [...] Read more.

Several high voltage condenser type OIP (oil impregnated paper) bushings used in the electrical industry are filled with dodecylbenzene, because of its ability to absorb hydrogen formed by corona partial discharges in the thick paper insulation of these pieces of equipment. Some of them form large quantities of ethane, raising the concern of overheating faults in their paper insulation, which may be risky for their safe operation in service. The article presents dissolved gas analysis results of oil samples taken from the bushings with high ethane formation, together with results of laboratory tests of stray gassing of dodecylbenzene performed according to CIGRE procedure. By using Duval Pentagon 2 it is possible to compare patterns in the laboratory and in bushings and evaluate the temperature range of possible defects. Stray gassing/overheating of dodecylbenzene in bushings within the stray gassing temperature range and whatever the possible other causes, is not a concern for their safe operation according to observations published by CIGRE. Full article

(This article belongs to the Special Issue Dissolved Gas Analysis (DGA) and Its Applications in Condition Monitoring of Power Equipments)

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22 pages, 5356 KiB

Open AccessArticle

Complementary Analysis for DGA Based on Duval Methods and Furan Compounds Using Artificial Neural Networks

by Ancuța-Mihaela Aciu, Claudiu-Ionel Nicola, Marcel Nicola and Maria-Cristina Nițu

Energies 2021, 14(3), 588; https://doi.org/10.3390/en14030588 - 24 Jan 2021

Cited by 23 | Viewed by 2602

Abstract

Power transformers play an important role in electrical systems; being considered the core of electric power transmissions and distribution networks, the owners and users of these assets are increasingly concerned with adopting reliable, automated, and non-invasive techniques to monitor and diagnose their operating [...] Read more.

Power transformers play an important role in electrical systems; being considered the core of electric power transmissions and distribution networks, the owners and users of these assets are increasingly concerned with adopting reliable, automated, and non-invasive techniques to monitor and diagnose their operating conditions. Thus, monitoring the conditions of power transformers has evolved, in the sense that a complete characterization of the conditions of oil–paper insulation can be achieved through dissolved gas analysis (DGA) and furan compounds analysis, since these analyses provide a lot of information about the phenomena that occur in power transformers. The Duval triangles and pentagons methods can be used with a high percentage of correct predictions compared to the known classical methods (key gases, International Electrotechnical Commission (IEC), Rogers, Doernenburg ratios), because, in addition to the six types of basic faults, they also identify four sub-types of thermal faults that provide important additional information for the appropriate corrective actions to be applied to the transformers. A new approach is presented based on the complementarity between the analysis of the gases dissolved in the transformer oil and the analysis of furan compounds, for the identification of the different faults, especially when there are multiple faults, by extending the diagnosis of the operating conditions of the power transformers, in terms of paper degradation. The implemented software system based on artificial neural networks was tested and validated in practice, with good results. Full article

(This article belongs to the Special Issue Dissolved Gas Analysis (DGA) and Its Applications in Condition Monitoring of Power Equipments)

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12 pages, 2550 KiB

Open AccessArticle

Using the Analysis of the Gases Dissolved in Oil in Diagnosis of Transformer Bushings with Paper-Oil Insulation—A Case Study

by Tomasz Piotrowski, Pawel Rozga, Ryszard Kozak and Zbigniew Szymanski

Energies 2020, 13(24), 6713; https://doi.org/10.3390/en13246713 - 19 Dec 2020

Cited by 8 | Viewed by 2150

Abstract

The article describes a case study when the voltage collapse during lightning impulse tests of new power transformers was noticed and when the repeated tests finished with a positive result. The step-by-step process of reaching the conclusion on the basis of dissolved gas [...] Read more.

The article describes a case study when the voltage collapse during lightning impulse tests of new power transformers was noticed and when the repeated tests finished with a positive result. The step-by-step process of reaching the conclusion on the basis of dissolved gas analysis (DGA) as a key method of the investigations was presented. The considerations on the possible source of the analysis showed that the Duval triangle method, used in the analysis of the concentration of gases dissolved in oil samples taken from bushings, more reliably and unambiguously than the ratio method recommended in the IEC 60599 Standard, indicated a phenomenon which was identified in the insulation structure of bushings analyzed. Additionally, the results from DGA were found to be consistent with an internal inspection of bushings, which showed a visible trace of discharge on the inside part of the epoxy housing, as a result of the lightning induced breakdown. Full article

(This article belongs to the Special Issue Dissolved Gas Analysis (DGA) and Its Applications in Condition Monitoring of Power Equipments)

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16 pages, 1967 KiB

Open AccessArticle

Diagnostic Simplexes for Dissolved-Gas Analysis

by James Dukarm, Zachary Draper and Tomasz Piotrowski

Energies 2020, 13(23), 6459; https://doi.org/10.3390/en13236459 - 7 Dec 2020

Cited by 10 | Viewed by 3137

Abstract

A Duval triangle is a diagram used for fault type identification in dissolved-gas analysis of oil-filled high-voltage transformers and other electrical apparatus. The proportional concentrations of three fault gases (such as methane, ethylene, and acetylene) are used as coordinates to plot a point [...] Read more.

A Duval triangle is a diagram used for fault type identification in dissolved-gas analysis of oil-filled high-voltage transformers and other electrical apparatus. The proportional concentrations of three fault gases (such as methane, ethylene, and acetylene) are used as coordinates to plot a point in an equilateral triangle and identify the fault zone in which it is located. Each point in the triangle corresponds to a unique combination of gas proportions. Diagnostic pentagons published by Duval and others seek to emulate the triangles while incorporating five fault gases instead of three. Unfortunately the mapping of five gas proportions to a point inside a two-dimensional pentagon is many-to-one; consequently, dissimilar combinations of gas proportions are mapped to the same point in the pentagon, resulting in mis-diagnosis. One solution is to replace the pentagon with a four-dimensional simplex, a direct generalization of the Duval triangle. In a comparison using cases confirmed by inspection, the simplex outperformed three ratio methods, Duval triangle 1, and two pentagons. Full article

(This article belongs to the Special Issue Dissolved Gas Analysis (DGA) and Its Applications in Condition Monitoring of Power Equipments)

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18 pages, 414 KiB

Open AccessArticle

A Methodology for the Calculation of Typical Gas Concentration Values and Sampling Intervals in the Power Transformers of a Distribution System Operator

by Sergio Bustamante, Mario Manana, Alberto Arroyo, Raquel Martinez and Alberto Laso

Energies 2020, 13(22), 5891; https://doi.org/10.3390/en13225891 - 12 Nov 2020

Cited by 2 | Viewed by 2735

Abstract

Predictive maintenance strategies in power transformers aim to assess the risk through the calculation and monitoring of the health index of the power transformers. The parameter most used in predictive maintenance and to calculate the health index of power transformers is the dissolved [...] Read more.

Predictive maintenance strategies in power transformers aim to assess the risk through the calculation and monitoring of the health index of the power transformers. The parameter most used in predictive maintenance and to calculate the health index of power transformers is the dissolved gas analysis (DGA). The current tendency is the use of online DGA monitoring equipment while continuing to perform analyses in the laboratory. Although the DGA is well known, there is a lack of published experimental data beyond that in the guides. This study used the nearest-rank method for obtaining the typical gas concentration values and the typical rates of gas increase from a transformer population to establish the optimal sampling interval and alarm thresholds of the continuous monitoring devices for each power transformer. The percentiles calculated by the nearest-rank method were within the ranges of the percentiles obtained using the R software, so this simple method was validated for this study. The results obtained show that the calculated concentration limits are within the range of or very close to those proposed in IEEE C57.104-2019 and IEC 60599:2015. The sampling intervals calculated for each transformer were not correct in all cases since the trend of the historical DGA samples modified the severity of the calculated intervals. Full article

(This article belongs to the Special Issue Dissolved Gas Analysis (DGA) and Its Applications in Condition Monitoring of Power Equipments)

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9 pages, 3149 KiB

Open AccessArticle

Identification of Stray Gassing of Inhibited and Uninhibited Mineral Oils in Transformers

by Michel Duval and Thomas Heizmann

Energies 2020, 13(15), 3886; https://doi.org/10.3390/en13153886 - 30 Jul 2020

Cited by 8 | Viewed by 3187

Abstract

The aim and contribution of this paper is to identify with Duval Pentagon 2 the stray gassing (SG) patterns of inhibited and uninhibited mineral oils in transformers in service and in the well-established laboratory SG tests of CIGRE and ASTM, so that SG [...] Read more.

The aim and contribution of this paper is to identify with Duval Pentagon 2 the stray gassing (SG) patterns of inhibited and uninhibited mineral oils in transformers in service and in the well-established laboratory SG tests of CIGRE and ASTM, so that SG in transformers can be easily distinguished from the other types of faults occurring in them. The SG test of IEC 60296-2020 is inadequate or much less effective for that purpose. Full article

(This article belongs to the Special Issue Dissolved Gas Analysis (DGA) and Its Applications in Condition Monitoring of Power Equipments)

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12 pages, 5552 KiB

Open AccessArticle

Combined Duval Pentagons: A Simplified Approach

by Luiz Cheim, Michel Duval and Saad Haider

Energies 2020, 13(11), 2859; https://doi.org/10.3390/en13112859 - 3 Jun 2020

Cited by 34 | Viewed by 5839

Abstract

The paper describes a newly proposed combination of the two existing Duval Pentagons method utilized for the identification of mineral oil-insulated transformers. The aim of the combination is to facilitate automatic fault identification through computer programs, and at the same time, apply the [...] Read more.

The paper describes a newly proposed combination of the two existing Duval Pentagons method utilized for the identification of mineral oil-insulated transformers. The aim of the combination is to facilitate automatic fault identification through computer programs, and at the same time, apply the full capability of both original Pentagons, now reduced to a single geometry. The thorough classification of a given fault (say, of the electrical or thermal kind), employing individual Pentagons 1 and 2, as originally defined, involves a complex geometrical problem that requires the build-up of a convoluted geometry (a regular Pentagon whose axes represent each of five possible combustible gases) to be constructed using computer language code and programming, followed by the logical localization of the geometrical centroid of an irregular pentagon, formed by the partial contribution of individual combustibles, inside two similar structures (Pentagons 1 and 2) that, nonetheless, have different classification zones and boundaries, as more thoroughly explained and exemplified in the main body of this article. The proposed combined approach results in a lower number of total fault zones (10 in the combined Pentagons against 14 when considering Pentagons 1 and 2 separately, although zones PD, S, D1 and D2 are common to both Pentagons 1 and 2), and therefore eliminates the need to solve for two separate Pentagons. Full article

(This article belongs to the Special Issue Dissolved Gas Analysis (DGA) and Its Applications in Condition Monitoring of Power Equipments)

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28 pages, 2362 KiB

Open AccessArticle

An Interval Forecasting Model Based on Phase Space Reconstruction and Weighted Least Squares Support Vector Machine for Time Series of Dissolved Gas Content in Transformer Oil

by Fang Yuan, Jiang Guo, Zhihuai Xiao, Bing Zeng, Wenqiang Zhu and Sixu Huang

Energies 2020, 13(7), 1687; https://doi.org/10.3390/en13071687 - 3 Apr 2020

Cited by 6 | Viewed by 2197

Abstract

Transformer state forecasting and fault forecasting are important for the stable operation of power equipment and the normal operation of power systems. Forecasting of the dissolved gas content in oil is widely conducted for transformer faults, but its accuracy is affected by data [...] Read more.

Transformer state forecasting and fault forecasting are important for the stable operation of power equipment and the normal operation of power systems. Forecasting of the dissolved gas content in oil is widely conducted for transformer faults, but its accuracy is affected by data scale and data characteristics. Based on phase space reconstruction (PSR) and weighted least squares support vector machine (WLSSVM), a forecasting model of time series of dissolved gas content in transformer oil is proposed in this paper. The phase spaces of time series of the dissolved gas content sequence are reconstructed by chaos theory, and the delay time and dimension are obtained by the C-C method. The WLSSVM model is used to forecast time series of dissolved gas content, the chemical reaction optimization (CRO) algorithm is used to optimize training parameters, the bootstrap method is used to build forecasting intervals. Finally, the accuracy and generalization ability of the forecasting model are verified by the analysis of actual case and the comparison of different models. Full article

(This article belongs to the Special Issue Dissolved Gas Analysis (DGA) and Its Applications in Condition Monitoring of Power Equipments)

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12 pages, 4539 KiB

Open AccessArticle

Influence of Aging on Oil Degradation and Gassing Tendency for Mineral oil and Synthetic Ester under Low Energy Discharge Electrical Faults

by L. Loiselle, U. Mohan Rao and I. Fofana

Energies 2020, 13(3), 595; https://doi.org/10.3390/en13030595 - 29 Jan 2020

Cited by 14 | Viewed by 3145

Abstract

The intent of this work is to understand the influence of low energy discharge electric faults in mineral oil and synthetic esters on liquid degradation and gassing tendency at different aging conditions (based on acidity values). A low energy discharge electric fault has [...] Read more.

The intent of this work is to understand the influence of low energy discharge electric faults in mineral oil and synthetic esters on liquid degradation and gassing tendency at different aging conditions (based on acidity values). A low energy discharge electric fault has been created by continuous discharge of 9 kV for five hours on the liquid surface using a suitable laboratory setup. Liquid degradation is reported by adopting UV spectroscopy, turbidity, and particle counter measurements. The gassing tendency is understood by dissolved gas analysis using Duval’s triangle and Duval’s pentagon methods for mineral oil and non-mineral oils accordingly. It is observed that the influence of low energy discharges on liquid degradation is higher in mineral oils than synthetic esters. The fault gasses in mineral oil are involved with electrical and thermal faults accompanied by stray gassing whereas only partial discharge activity is noticed for synthetic esters. Importantly, the existence of low energy discharge faults like corona discharges will involve a generation of excess high molecular weight products as compared to low molecular weight products that are soluble in liquid volume. Full article

(This article belongs to the Special Issue Dissolved Gas Analysis (DGA) and Its Applications in Condition Monitoring of Power Equipments)

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