A Detection System of Gas Concentration Based on Low-Loss Fiber Loop Ring-Down Spectroscopy
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In the engineering application of power transformers, due to phenomena such as overheating and partial discharge, the transformer may have a fault. Acetylene is one of the important characteristic components when the transformer is failure. The acetylene detection is significant to the diagnosis and evaluation of transformer operational condition. Therefore, a fiber loop ring-down system is built to detect acetylene in this paper. The fiber collimators at both ends of the gas cell are adjusted to reduce the loss of the gas cell system. The absorption line at 1531.6nm of the acetylene molecule was selected and the response characteristics of the system to the concentration of trace acetylene gas were studied through experiment. The ring-down waveforms at different concentrations of acetylene are measured. After fitting the peak value of waveforms, the corresponding ring-down time can be calculated and the quantitative relationship between ring-down time and concentration is also studied based on the least square method. The results show that there is a good linear dependence between the ring-down time and the concentration. The research results provide a new method for the online detection of dissolved gases in the transformer oil.Keywords:
Acetylene
Dissolved Gas Analysis
Condition Monitoring
Dissolved gas analysis (DGA) is widely accepted as an effective technique to detect incipient faults within power transformers. Gases such as hydrogen, methane, acetylene, ethylene and ethane are generated as a result of insulation oil decomposition, while carbon monoxide and carbon dioxide are generated as a result of insulation paper decomposition. Laboratory-based gas chromatography (GC) in accordance to ASTM D3612 standard is globally accepted as a reliable technique to quantify dissolved gases in transformer oil samples. However, this technique incurs running cost and requires an expert to conduct the test. Furthermore, due to the complexity of the equipment, measurement is only performed in a laboratory environment and takes long time to get the results since the extraction of the oil sample from the transformer. To overcome these issues, various online DGA techniques have been developed and currently used by industry. However, these techniques are still considered in development stage with some limitations that have to be addressed to fully accept its results. This paper proposes a new method to estimate the concentration of various dissolved gases in transformer oil using near infrared-to-infrared (NIR-IR) spectroscopy that can be conducted instantly onsite with relatively inexpensive equipment. The proposed measuring technique does not call for expert person to conduct the measurements and has the potential to be implemented online. Results show a good correlation between oil spectral response and the concentration of each dissolved gas in the oil at particular wavelength range. Fuzzy logic model approach is employed to model this correlation and estimate the concentration of each dissolved gas.
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The transformer is a vital constituent of the electricity network. Trouble-free operation of the transformer is very essential to maintaining a reliable and uninterrupted power supply. Several electrical and physicochemical diagnostic methods are in practice for condition monitoring of power transformers to keep them in service. Dissolved Gas Analysis (DGA) is considered as the paramount tool for assessing emerging faults in oil-filled transformers. Numerous established methods like Key Gas, Doernenburg Ratio, Rogers Ratio, Nomograph, IEC Ratio, Duval Triangle, Pentagon etc. are available for analyzing and interpreting the gas content of oil to predict the type of plausible fault. Accurate and interference-free measurement of dissolved hydrocarbon gases is essential for application of these interpretation methods. The chemical behavior of oil differs based on the source, refining process, additives, contamination, service condition, service period, and so on. As a result, it is critical to look at the impact of these changes in oil on the formation of dissolved gases. Samples of almost the same age with varying chemical status are selected for the study. The trends in the formation of dissolved gases in transformers under service for a studied period are presented. The accelerated ageing study at 120°C of oil samples in the laboratory with copper and kraft paper is also conducted for comparison with field data. Despite a substantial variation in gas content among field and laboratory aged samples, no significant effect on the interpretation of the incipient fault is observed.
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Abstract This paper investigates the applications of photoacoustic spectrometry (PAS) to analyze dissolved gases in transformer oil. An inexpensive experimental device with an electric pulse infrared light and six filters has been developed to detect six main fault gases in transformer oil, namely, CH 4 , C 2 H 6 , C 2 H 4 , C 2 H 2 , CO, and CO 2 . The method of choosing the characteristic wavelengths for the above six fault gases is discussed in detail. A weighted least‐square error method is proposed to analyze the measured data and to determine the component concentrations of dissolved gas in oil. Two sample sets of gas mixtures are analyzed by the experimental device for the purpose of verification. The PAS measurements are compared with the true values and the values measured by a conventional gas chromatograph (GC) method. The comparison results show that PAS is an effective way of analyzing dissolved gases in transformer oil, which exhibits some advantages in the gas detection such as consuming no gas, separating no gas, high accuracy, high stability, and rapid measurements. Copyright © 2007 John Wiley & Sons, Ltd.
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Abstract Measuring the content of dissolved gas components in transformer insulating oil by gas chromatography is an important means to judge the internal potential faults of oil filled electrical equipment in the process of operation supervision. The necessary work skills of power grid operators include the ability to detect the content of dissolved gas in transformer oil and judge the operation state of transformer. This paper introduces a preparation method and equipment of transformer standard oil. It can quickly prepare standard oils with various gas component contents. The standard oil quantity value is accurate, the data stability period is greater than 90 days, and the uncertainty is less than 5%. The equipment can be used for training and evaluation of transformer oil gas chromatographic analysis practitioners and calibration of transformer oil on-line gas chromatograph.
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Abstract NOTE: The first page of text has been automatically extracted and included below in lieu of an abstract Session 1559 A QUADRUPOLE MASS SPECTROMETER BASED GAS ANALYZER FOR POWER TRANSFORMER FAULT ASSESSMENT Saleh M. Sbenaty Department of Engineering Technology and Industrial Studies Middle Tennessee State University ABSTRACT This paper describes the feasibility of using a quadrupole mass spectrometer-based gas analyzer to predict malfunctions in high-voltage oil-filled power transformers using the analysis of dissolved gases in oil technique. A vacuum system for the quadrupole analyzer and the gas introduction system is designed and built for this purpose. A method for the extraction of the dissolved gases in oil is developed and the gas introduction system is described. The spectra of the thirteen gas species of interest are obtained and the sensitivity factors for each gas are calculated. The spectra of a standard gas mixture and the dissolved gases in oil from a faulty transformer oil specimen are obtained. The data reduction procedure is described and is used to reduce these spectra to the partial pressures of the 13 gas species. Finally, the concentration of each gas is calculated and methods for fault assessments are presented. INTRODUCTION Gas analysis is one of the best available techniques for transformer fault prediction and diagnosis. Scientists have found several decades ago that a loaded power transformer tends to evolve gases1, 2. These gases, the result of normal aging processes of the insulating materials, dissolve in the transformer’s oil. The concentrations of these gases are usually small in normal operation and depend upon the solubility of each gas in oil and the transformer’s type. When a fault or a combination of faults exists in a power transformer, however, the concentrations of the evolved gases are comparatively large3. It was also realized that the amount of evolved gases and gas species depend on the nature of the fault. For example, hydrogen (H2) and acetylene (C2H2) are the main gaseous constituents when arcing in oil occurs. Hot spots mostly evolve carbon oxides (CO2 + CO) and light hydrocarbon gases. On the other hand, partial discharges (corona) produce hydrogen and other light hydrocarbon gases. In addition, slowly developing faults were found to produce decomposition gases4. By analyzing these dissolved gases, therefore, one can detect an incipient fault and reveal the operating condition of a power transformer before a costly and/or catastrophic accident occurs such as interruption of service and explosion. FAULT DIAGNOSTIC TECHNIQUES Several diagnostic methods using gas analysis can be used to predict faults in a power transformer5, 6. x The Dornenburg Ratio Method uses the following four gas ratios: methane/hydrogen (CH4/H2), acetylene/ethylene (C2H2/C2H4), ethane/acetylene (C2H6/C2H2), and acetylene/methane (C2H2/CH4). These ratios are calculated from the measured concentrations
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Dissolved Gas Analysis (DGA) is a common tool used to understand the condition and processes ongoing inside the transformer. Increased levels of certain gasses in the transformer oil can be measured and interpreted according to guidelines. By the analysis of amounts of hydrogen, volatile hydrocarbons and carbon oxides dissolved in the insulating oil dielectric and thermal faults can be detected at an early stage.
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Dissolved gas analysis (DGA) is routinely used to determine the concentrations of gases dissolved in the insulating oil of transformers. These concentrations are used to investigate and diagnose electrical or thermal faults [1]. Such faults cause the transformer oil, pressboard, and other insulating materials to de compose and generate gases, some of which dissolve in the oil. The results of DGA must be accurate if faults are to be diag nosed reliably. Commercial testing laboratories understandably prefer measurements that can be made easily and quickly. In this paper, DGA results from five independent testing lab oratories are compared and discussed. A dissolved gas-in-oil standard with known dissolved gas concentrations was used as the basis of comparison.
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The condition evaluation of insulating oil of power transformer is performed by oil contamination test and the dissolved gas analysis method. The first technique comprises of dielectric strength, interfacial tension, acidity, water content, color, and power factor. The limit value is assigned to each diagnostic test result in order to classify the condition of insulating oil as good, suspect, and poor. The second technique is based on the key gases and the Duval triangle to distinguish the possible fault types by analyzing the amount of gases dissolved in the insulating oil. Two transformer models rated 115/22 kV, 25 MVA and 230/69/22 kV, 200 MVA are selected in the analysis because of their available historical test data. The problems such as overheated cellulose, corona in oil, and thermal fault are finally recognized.
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Dielectric withstand test
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Fault diagnosis methods of transformer based on dissolved gas detection in oil by gas chromatography
Large transformer is the core equipment in power system, the diagnosis and prevention of equipment fault is very important to the safe operation of power system. At high temperature and high voltage, dissolved gas produced by the decomposition of transformer oil is an important indicator of transformer operation status. However, due to the low content of dissolved gas and the complexity of the measurement processes, it is easy to produce errors, which brings great challenges to the accurate detection of dissolved gas. In addition, how to establish the correct relationship between the content of dissolved gas components with the types and degrees of transformer fault also needs to be studied. Therefore, this paper first clarified the measurement processes of dissolved gas in transformer oil, then analysed the possible error sources of each link, then introduced common error assessment methods and proposed feasible methods to reduce dissolved gas test errors, and finally introduced the application of artificial intelligence to fault diagnosis of transformers based on dissolved gas content. This paper will provide some feasible theoretical support for reducing the measurement error of dissolved gas in transformer oil and accurately diagnosing transformer faults.
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Analysis of gases dissolved in insulating oil offers the most promising diagnostic method for the faults in oil-filled transformers. This diagnostic method is based on the decomposed gas products for example H2, CH4, C2H2 etc., from insulating oil due to faults, overheat and discharge, in transformer. In case of fault in the oil-filled transformer decomposed products are almost generated from insulating solid-materials without insulating oil. Therefore, it is useful for diagnostic of transformer that the decomposed products from insulating sol id-materials in insulating oil are analyzed. An experimental survey over the decomposed products generated by overheat and discharge in oil-filled transformers was carried out through simplified model tests. Gas chromatography-mass spectrometer and purge/trap extraction were employed in analyses of decomposed products from insulating solid-materials in insulating oil. Decomposed products characteristic to each solid-materials were identified by the experiment. Above diagnostic method is useful early detection and location of faults in oil-filled transformers.
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Oil analysis
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