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ORAL, BÜLENT

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Start date: 2010 × Has files: true ×

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Now showing 1 - 10 of 11
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    PublicationOpen Access
    Electric field analysis of 66 kV and 110 kV SiR insulators under combined AC-DC voltages
    (ELSEVIER, 2022-04) ORAL, BÜLENT; Ispirli, Mehmet Murat; Oral, Bulent; Kalenderli, Ozcan
    Insulators are the most crucial part of power systems. The insulation performance of insulators is vital for the sustainability of power systems. Recently, silicone rubber (SiR) insulators are used frequently in all sections of the power systems. In this paper, a SiR insulator currently used in power transmission systems has been analyzed under combined AC-DC voltage using the finite element method. In the analysis, positive and negative DC voltages in different amplitude ratios were superimposed over the phase-earth operating voltage of the insulator. Analyses in the study were made in time-dependent. Only DC voltage was applied to the insulator for the first 60 s, AC + DC voltage was applied between 60 to 120 s. Thus, the electric field behavior of the SiR insulator under combined AC-DC voltage has been obtained. The change of electric field based on positive and negative DC components was investigated. As a result of the study, the effect of the polarity of the DC component in the combined voltage was observed. As a result, effect of the polarity of the DC component in the combined voltage on the maximum electric field intensity was observed. (C) 2021 The Author(s). Published by Elsevier Ltd.
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    PublicationOpen Access
    Investigation of impact of DC component on breakdown characteristics for different electric fields under composite AC & DC voltage
    (WILEY, 2022-01-13) ORAL, BÜLENT; Ispirli, Mehmet Murat; Kalenderli, Ozcan; Seifert, Florian; Rock, Michael; Oral, Bulent
    The valve side of the converter in the high-voltage direct current is subjected to mixed voltages such as composite AC & DC voltage. In this study, the effects of the homogeneity of electric field on breakdown voltage were investigated for different +/- DC component amplitudes of the composite voltage. The field efficiency factor was calculated using mean and maximum field strengths for all of them. Variation of breakdown voltage of air was examined under the composite AC & DC voltage for different ratios +/- DC. As one result of the study, the breakdown occurs at the positive half-wave of the AC voltage despite - DC voltage being applied due to positive corona discharge pulses. This breakdown point is named as the polarity change point. The breakdown voltage increases with the decrease of DC voltage component up to polarity change point in nonuniform electric field. In less uniform electric field, the AC breakdown voltage was measured slightly higher than the DC breakdown voltage. In less uniform electric field, as the ratio of the applied AC voltage to DC voltage increases, the breakdown voltage gradually approaches the AC breakdown voltage. This result is similar to the result obtained for the +DC component in non-uniform electric field experiments.
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    PublicationOpen Access
    Challenges during commissioning and operation in photovoltaic power plants by electrical faults
    (2023-05-01) SAĞLAM, ŞAFAK; ORAL, BÜLENT; Gökgöz M., SAĞLAM Ş., ORAL B.
    Problems such as increasing environmental pollution and global warming due to fossil fuels used in energy production have revealed the requirement for renewable energy sources. In addition to this situation, the decreasing fossil fuel reserves, and the need to diversify energy production resources to ensure energy supply security for countries have made the use of renewable energy sources a necessity. Therefore, demand for solar energy will continue to increase, considering the increasing renewable energy need. To increase energy efficiency, the uninterrupted production of photovoltaic power plants during production hours is important to reduce the consumption of fossil fuels. For this reason, situations and malfunctions that prevent uninterrupted operations should be detected. Fault classification contributes to the rapid identification of problems by providing fast diagnostics for possible faults. When the previous studies in this field are examined, there are publications about general faults in photovoltaic power plants and publications about electrical faults separately. However, there are limitations in academic studies that deal with the difficulties encountered in the commissioning and operation of photovoltaic power plants in detail and examine electrical faults. In this context, there is a need for relevant studies. In this study, the possible failures that may occur during the commissioning and operation of photovoltaic power plants will be categorized and this study is intended to be a resource for studies on this subject. It is aimed to create a resource for academic studies and to contribute to field applications to companies in the sector.
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    PublicationOpen Access
    Application and comparative analysis of fuzzy inference system for transformer fault diagnosis with dissolved gases in oil
    (2021-10-28) ORAL, BÜLENT; İSPİRLİ, MEHMET MURAT; İSPİRLİ M. M., Adalı H., KALENDERLİ Ö., Çelik M. Z., ORAL B.
    Oils are used for cooling and insulation in transformers. The fault currents occurred on transformers can damage windings and insulation. As a result of this incoming fault current, gas emission occurs in materials such as oil and pressboard. The type of these gases released gives information about the fault of the transformer. In this study, it has been studied on the determination of the fault by analyzing the gases released as a result of the failure in 63 transformers using FIS. As a result of the analysis, the results obtained with FIS were compared with analyzed results with IEC 60599 and fault reports from the corporation, which these values obtained. When 63.5% true results were obtained compared to IEC 60599, 97.6% correct results were obtained compared to fault reports of the corporation because 22 of 63 transformer gas values were not actually suitable for applying the IEC Ratio method.
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    PublicationOpen Access
    The importance of in-service training in restructuring sectors
    (ELSEVIER SCIENCE BV, 2010) ORAL, BÜLENT; Oral, Bulent; Saglam, Safak; Uzunboylu, H
    Reduction or abolishment operation of government's intervention to economy, accelerating since the beginning of 1980s, is adopted by many governments as governance policy. This policy, being widely used in manufacturing industry and service sector at the beginning, has been used subsequently in electricity, natural gas, water ... etc industry as natural monopoly. The employee needs to know position at institution organization, individual value and expectations. It is effective on the employee performance. In this context, the employees can take in-service education their institutions and regulatory authorities, which regulate and supervise the sectors. The in-service education plan is supported the program content and process by academic circles. In this study, it is emphasized process and content of scheduled in-service education program.
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    PublicationOpen Access
    Transformation of technical education faculties in Turkey in the process of European Union: Faculty of applied sciences
    (ELSEVIER SCIENCE BV, 2010) ORAL, BÜLENT; Saglam, Safak; Oral, Bulent; Uzunboylu, H
    Countries education systems unavoidably changes to adapt themselves to innovations because of developing technology and globalization. This perspective technical education faculty position is queried which are established with the aim of educate technical teachers for vocational high schools in Turkey. Faculty of applied sciences model can replace with the technical education faculty that has completed its mission. It is possible to educate engineers with the faculty of applied sciences who has qualified, keep up the technology and has the characteristics necessary for the working life. (C) 2010 Elsevier Ltd. All rights reserved.
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    PublicationOpen Access
    The effect of dc voltage pre-stress on the breakdown voltage of air under composite dc and li voltage and test circuit: Design and application
    (2022-02-01) İSPİRLİ, MEHMET MURAT; ORAL, BÜLENT; İSPİRLİ M. M., Kalenderli Ö., Seifert F., Rock M., ORAL B.
    © 2022 by the authors. Licensee MDPI, Basel, Switzerland.The use of HVDC systems is increasing in number due to technological innovations, increasing power capacity and increasing customer demand. The characteristics of insulation systems under composite DC and LI voltage must be examined and clarified. In this study, firstly, experimental circuits were designed to generate and measure composite DC and LI high voltage using a simulation program. The coupling elements used were chosen according to simulation results. Afterward, experimental circuits were established in the laboratory according to the simulation results of the designed experimental circuit. Then, breakdown voltages under composite DC and LI voltage for less uniform and non-uniform electric fields were measured with four different electrode systems for positive and negative DC voltage pre-stresses with different amplitudes. The 50% breakdown voltage was calculated using the least-squares method. Finally, 3D models were created for the electrode systems used in the experiments using the finite element method. The efficiency factors of electrode systems calculated with the FEM results were correlated with the experimental breakdown voltage results. Thus, the breakdown behavior of air under bipolar and unipolar composite voltages (CV) was investigated. In conclusion, the experimental results showed that very fast polarity change in bipolar CV causes higher electrical stress compared to unipolar CV.
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    PublicationOpen Access
    Investigation of Failures during Commissioning and Operation in Photovoltaic Power Systems
    (2024-03-01) SAĞLAM, ŞAFAK; ORAL, BÜLENT; Gökgöz M., Sağlam Ş., Oral B.
    Considering global warming and environmental problems, the importance of renewable energy sources is increasing day by day. In particular, the effects of wind and solar power, which are variable renewable power sources, on the power system necessitate their evaluation in terms of the reliability of the power system. Photovoltaic panels, which enable the conversion of solar power into electrical power with semiconductors, have started to take an important place in global energy investments today. Photovoltaic power plants increase the demand for this energy source with continuous energy conversion depending on sunshine duration and radiation intensity. Among the renewable energy sources, the most easily utilized energy source, regardless of geographical conditions, is the sun. To prevent the energy production of PV power plants from being interrupted, it is necessary to address and analyze all kinds of faults that will affect power production in order to increase the reliability of the system. Academic studies in this field are generally grouped under two topics: classification of faults or modeling of electrical faults. Based on this, in this study, the problems that occur during the installation and operation of photovoltaic systems are classified, and the relevant faults are modeled and simulated in MATLAB Simulink version 23.2 (R2023b). Thus, a scientific approach to the problems of photovoltaic power plant operating conditions has been gained, which will be the basis for academic studies.
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    PublicationOpen Access
    A review of short-term wind power generation forecasting methods in recent technological trends
    (2024-12-01) SAĞLAM, ŞAFAK; ORAL, BÜLENT; Arslan Tuncar E., Sağlam Ş., Oral B.
    Climate change and the escalating demand for energy are among the most pressing global challenges of our era. Renewable energy sources, such as wind energy, are considered a viable solution to these issues. However, the integration of renewable energy sources into electric power systems also presents operational challenges, particularly in terms of uncertainty. In order to mitigate this uncertainty, it is crucial to improve the accuracy of generation forecasting methods for wind energy. This review explores various wind power forecasting methods, categorizing them by factors such as time frame, and model structure. Special attention is given to short-term forecasting, crucial for the day-ahead electricity market. This study traces the evolution of wind power forecasting, from early statistical approaches to the integration of numerical weather prediction, machine learning, neural networks, and advanced techniques. Its aim is to provide valuable insights into wind power forecasting methods for stakeholders, including grid operators, traders, and wind farm operators. This review serves as a vital resource for researchers and industry professionals navigating the dynamic field of wind power forecasting, contributing to effective renewable energy resource management in a rapidly evolving energy sector.
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    PublicationOpen Access
    Challenges of renewable energy penetration on power system flexibility: A survey
    (ELSEVIER, 2020-09) ORAL, BÜLENT; Impram, Semich; Nese, Secil Varbak; Oral, Bulent
    Flexibility in power systems is ability to provide supply-demand balance, maintain continuity in unexpected situations, and cope with uncertainty on supply-demand sides. The new method and management requirements to provide flexibility have emerged from the trend towards power systems increasing renewable energy penetration with generation uncertainty and availability. In this study, the historical development of power system flexibility concept, the flexible power system characteristics, flexibility sources, and evaluation parameters are presented as part of international literature. The impact of variable renewable energy sources penetration on power system transient stability, small-signal stability, and frequency stability are discussed