DGA is more sensitive and reliable technique for detecting and evaluating the incipient fault conditions in oil-immersed transformers. The most frequently interpretation technique that used in ...dissolved gas analysis is Duval triangle due to its simplicity and accuracy. Unfortunately the impacts of Ethane (C2H6) and Hydrogen (H2) were not included in Duval triangle in spite of their importance in diagnosing certain faults types. In addition, the problem of no decision associated with some cases that lie out of the specified codes appeared in Doernenburg, Roger's and IEC techniques. Accordingly, this paper presented a new proposed graphical triangle technique using new three gas concentration ratios. These ratios were converted to new three ratio percentages of DGA based on the consideration of all five combustible gases. The aim of that was to overcome the conflict takes place in Duval triangle and other traditional techniques. The accuracy of the proposed triangle technique was evaluated using practical DGA database obtained from different transformers of different ratings life spans reported by Egyptian Electricity Holding Company, IEC TC 10 and related databases surveyed from actual incipient cases. The comparison with Duval and other traditional techniques showed good diagnostic accuracy of the new proposed triangle technique.
Dissolved gas analysis (DGA) of oil is one of the major diagnostic tools that are used to detect the incipient faults of oil-immersed transformers through the correlation between the dissolved gases ...content in transformer oil and a particular malfunction. There are several techniques of DGA to interpret the incipient transformer faults such as Doernenburg ratio, Rogers's ratio, IEC ratio and Duval triangle techniques. This study presents a new proposed technique for transformer fault diagnosis using a new three gas ratios concentration of DGA to overcome the conflict that takes place in the traditional interpretation techniques. The accuracy of the proposed diagnosis technique is verified using practical DGA data obtained from 688 samples that have been collected from different transformers of different rating and different lifespan reported by Egyptian Electricity Holding Company, IEC TC10 and related databases surveyed from actual incident cases. The comparison with traditional DGA techniques showed that the proposed DGA ratio technique has good diagnosis accuracy. It is found that the suggested three ratios technique method has 99.86% accuracy as compared with 85.67% for Duval, 75.08% for Doernenburg, 47.34% for IEC and 39% for Rogers when testing 688 cases.
Dissolved gas analysis (DGA) is one of the most acceptable methods used for detecting and evaluating gases dissolved in mineral oil and also in the solid insulation of internal incipient faults in ...the power and distribution transformers based on the oil samples. DGA has been proved the most accurate method for condition assessment of power and distribution transformers. The fault types depend upon type and concentrations of each gas dissolved in oil. IEC, Rogers, Doernenburg and Duval techniques, in spite of their importance in diagnosing certain types of faults, do not consider the concentrations of carbon monoxide (CO) and carbon dioxide (CO2) to evaluate cellulose insulation degradation. Some of these techniques do not take into account the impact of ethane (C2H6) and hydrogen (H2) for the evaluation of fault types. A new graphical method “Heptagon” based on seven gases produced in faulty transformer oil decomposition is presented. Based on about 452 test samples of transformer oil DGA, the Heptagon figure is drawn and the zones of different fault types are determined. The suggested technique is tested and compared with other techniques.
Keeping the generators operating during transient grid faults becomes an obligation for the bulk wind generation units connected to the transmission network, and it is highly desired for distribution ...wind generators. A proposed scheme is implemented to keep the wind-power DFIG operating during transient grid faults. Challenges imposed on the generator configuration and the control during the fault and recovering periods are presented. A comprehensive time domain model for the DFIG with the decoupled dq controller is implemented using Matlab/Simulink software. Intensive simulation results are discussed to ensure the validity and feasibility of the proposed fault ride through technique. The scheme protects the DFIG components, fulfills the grid code requirements and optimises the hardware added to the generator.
Power variation, voltage fluctuation, and resultant flicker are critical issues related to the integration of directly grid-connected constant-speed wind turbines. This study introduces a methodology ...to enhance the quality of the power and voltage, and minimise the flicker produced from constant-speed direct-connected wind turbines. The method uses an electrolyser/fuel cell combination to be connected to the point of common coupling via limited rating converters. The control scheme is designed to keep the power ramp rate and voltage fluctuation within their limits and minimise the rating of the converters used to interface the electrolyser and the fuel cell. The incorporation of STATCOM and its effect on the generated power and flicker level have been investigated. The simulation results are carried out to demonstrate and validate the proposed technique.
This article is aimed at determining the mutual sequence-impedances between parallel lines and investigating how the sequence networks for single line-to-ground (SLG) and double line-to-ground (DLG) ...faults will be influenced by the mutual coupling effect between the parallel lines. SLG and DLG fault currents with and without mutual effect are calculated when the two lines are fed from one end and when fed from both ends. The fault current calculated taking into account the mutual coupling between parallel lines is always less than the corresponding value without the mutual coupling, whether the lines fed from one end or from both ends.
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