Person: İSPİRLİ, MEHMET MURAT
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İSPİRLİ
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MEHMET MURAT
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Publication Open 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, OzcanInsulators 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.Publication Open 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, BulentThe 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.Publication Open Access Recurrence Plot Analysis of Unsatured Polyester Samples Subjected to Contamination(ISTANBUL UNIV-CERRAHPASA, 2018) İSPİRLİ, MEHMET MURAT; Yilmaz, Aysel Ersoy; Ispirli, Mehmet MuratPolymer materials that are used in outdoor enviroments are exposed to humidity and polution. In addition, some insulation materials installed in water or embeded to slush containing serious pollutants for a long time. These conditions adversely affect the dielectric properties of insulating materials. In this study, the prepared unsaturated polyester (UPE) samples are stored in an ionized water solution for 8, 24, and 168 hours. This ionized water solution is considered to represent the polluted water in the outdoor environments. Further, the dielectric behaviors of the prepared polyester samples are investigated using the inclined plane test (IPT) method, whereas the leakage current data that are recorded during the experiment are analyzed using the recurrence plot (RP) method. The results of applying the inclined plane test on the unsaturated polyester samples depict that the lifetime of the samples decreased with an increase in the period of storage in the ionized water solution. Further, the results of the recurrence plot analysis reveal that the recurrence plot point density also depicted a decrease with an increase in the period of storage in the ionized water solution.Publication Open 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.Publication Open Access The effect of water on tracking failure of epoxy/MgO samples(2022-12-01) İSPİRLİ, MEHMET MURAT; Kirkagac K., İSPİRLİ M. M., Ersoy A.In this study, the change in the electrical performance of epoxy/MgO, which is one of the materials used to increase the performance of epoxy resin, was evaluated under the effect of water. Accordingly, comparative tracking index (CTI) experiments, which are one of the effective methods used to model electricity\"s effect on surface properties, were used. To measure the performance of epoxy resins without additions, 1%, 3% and 5% nanosized MgO-added samples were prepared. Prepared samples were stored 24 h, 48 h, 72 h, 96 h and 120 h in pure water. Then, the samples were subjected to CTI test in a laboratory environment. Recorded leakage current from experiments was analyzed using harmonic analysis. While the experimental results obtained have resulted in improvements like those of MgO/epoxy additions previously reported in the literature, the resistance of the observed samples after their exposure to pure water has been reported, in the opposite direction. Thus, with this experimental study, it has been demonstrated that it is necessary to add some hydrophobic compounds to show the desired performance in the external environment with MgO-doped epoxy resins. It should be supported by extra protection in such dense liquid environments.Publication Open Access The application of recurrence plot in tracking characteristics of PU-Based insulation material(2022-11-01) İSPİRLİ, MEHMET MURAT; İSPİRLİ M. M., ERSOY A.Cable joints are the weakest part of underground energy transmission systems due to the presence at the interface between the insulation material and the cable conductor. Underground cables serve under heavy service conditions (dust, dirt, humidity, etc.). So, the tracking resistance of polymers used in joint points of underground cables needs to be determined. In the first section of the study, equivalent samples were prepared under vacuum conditions in laboratory conditions from PU-based filling material used as filler material in low voltage underground cable joints. Prepared samples were tested in an established CTI test setup according to ASTM D5288. Samples were tested in prepared test setup under 600 V, 500 V, 400 V, and 300 V voltages. In the second section of the study, leakage currents were analyzed with the recurrence plot method, which is frequently used in nonlinear times series analysis. Later, recurrence quantification analysis was made by Recurrence Rate (RR) and Determinism (DET) parameters. The behavior of the system occurs less linear with decreased Recurrence Rate in Recurrence Quantification Analysis (RQA). RR and DET parameters increased with the decrease in voltage levels. As a result of, it is revealed that the tracking formation behavior of the PU cable joint becomes more unstable with increasing voltage. Thus, the CTI and RQA are shown to be also available to determine the tracking resistance of cable joints.Publication Open 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.