The Experts below are selected from a list of 64887 Experts worldwide ranked by ideXlab platform
Markus Zahn - One of the best experts on this subject based on the ideXlab platform.
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electrical circuit flashover model of polluted insulators under Ac Voltage based on the arc root Voltage gradient criterion
Energies, 2012Co-Authors: Qing Yang, Rui Wang, Wenxia Sima, Chilong Jiang, Xing Lan, Markus ZahnAbstract:In order to study the flashover mechanism of polluted insulators under Ac Voltage, a new arc propagation criterion which is based on an arc root Voltage gradient is proposed. This criterion can explain the variation of the arc root Voltage gradient in the arc propagation process. Based on this criterion, a new distributed parameter electrical circuit flashover model of polluted insulators is presented. The arc channel is considered as an equivalent distributed parameter circuit model instead of using the arc Voltage-gradient equation. The parameters of the arc model are obtained from the electromagnetic field distribution of the arc and the gas discharge theories. The arc root is considered as parallel paths including the polluted layer. The variation of the Voltage on the arc root is related to the capability of arc propagation. This model takes the microscopic mechanism of arc root ionization into consideration, which can improve the AccurAcy of the flashover model. The results obtained from the presented model are in good agreement with other mathematical and experimental results.
Gyuha Choe - One of the best experts on this subject based on the ideXlab platform.
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step up down Ac Voltage regulator using transformer with tap changer and pwm Ac chopper
IEEE Transactions on Industrial Electronics, 1998Co-Authors: Dohyun Jang, Gyuha ChoeAbstract:A step-up/down Ac Voltage regulator is proposed, in which a tap-changing transformer and a pulsewidth modulation (PWM) Ac chopper are combined. The proposed regulator can step up or down the output Voltage to input Voltage. Also, the proposed regulator restrains more harmonics of output Voltage compared to the conventional PWM regulator. The input current flows continuously in the proposed regulator, while it flows discontinuously in the conventional PWM regulator. Through digital simulation, several charActeristics are investigated theoretically and then compared with those of conventional schemes. PrActical verification of the theoretical predictions is presented to confirm the capabilities of the proposed regulator.
T V Sivakumar - One of the best experts on this subject based on the ideXlab platform.
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optimal soft starting of Voltage controller fed im drive based on Voltage Across thyristor
IEEE Transactions on Power Electronics, 1997Co-Authors: V V Sastry, M R Prasad, T V SivakumarAbstract:Ac Voltage controllers are used as induction motor starters in fan or pump drives and the crane hoist drives. This paper presents a method of identifying the end of soft start of an Ac Voltage controller-fed induction motor (IM) drive based on the Voltage Across the nonconducting thyristor through a dynamic simulation of the whole drive system. A two point current minimization technique is adopted to operate the drive system at the required optimal Voltage under all operating conditions. This minimizes the motor losses. Graphic modeling of the whole drive system is done in a modular format using Design Star and dynamic simulation is done using SABER. The dynamic simulation results of the whole drive system are supported with experimental data.
Haddad Abderrahmane - One of the best experts on this subject based on the ideXlab platform.
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Clarifications on the behavior of alternative gases to SF6 in divergent electric field distributions under Ac Voltage
'MDPI AG', 2021Co-Authors: Nechmi, Houssem Eddine, Michelarakis Michail, Haddad Abderrahmane, Wilson GordonAbstract:Negative and positive partial discharge inception Voltages and breakdown measurements are reported in a needle-plane electrode system as a function of pressure under Ac Voltage for natural gases (N2, CO2, and O2/CO2), pure NovecTM gases (C4F7N and C5F10O) and NovecTM in different natural gas admixtures. For compressed 4% C4F7N–96% CO2 and 6% C5F10O–12% O2–82% CO2 gas mixtures, the positive-streamer mode is identified as the breakdown mechanism. Breakdown and negative partial discharge inception Voltages of 6% C5F10O–12% O2–82% CO2 are higher than those of 4% C4F7N–96% CO2. At 8.8 bar abs, the breakdown Voltage of 6% C5F10O–12% O2–82% CO2 is equal to that of 12.77% O2–87.23% CO2 (buffer gas). Synergism in negative partial discharge inception Voltage/electric field fits with the mean value and the sum of eAch partial pressure individually component for a 20% C4F7N–80% CO2 and 6% C5F10O–12% O2–82% CO2, respectively. In 9% C4F7N–91% CO2, the comparison of partial discharge inception electric fields is Emax (CO2) = Emax(C4F7N), and Emax (12.77% O2–87.23% CO2) = Emax(C5F10O) in 19% C5F10O–81%(12.77% O2–87.23% CO2). Polarity reversal occurs under Ac Voltage when the breakdown polarity changes from negative to positive cycle. Polarity reversal electric field EPR was quantified. Fitting results show that EPR (CO2) = EPR(9% C4F7N–91% CO2) and EPR(SF6) = EPR (22% C4F7N–78% CO2). EPR (4% C4F7N–96% CO2) = EPR (12.77% O2–87.23% CO2) and EPR (6% C5F10O–12% O2–82% CO2) < EPR (4% C4F7N–96% CO2) < EPR (CO2)
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Electrical Detection of Creeping Discharges over Insulator SurfAces in Atmospheric Gases under Ac Voltage Application
'MDPI AG', 2019Co-Authors: Michelarakis Michail, Widge Phillip, Eroual Abderrahmane, Haddad AbderrahmaneAbstract:International audienceCreeping discharges over insulator surfAces have been related to the presence of triple junctions in compressed gas insulated systems. The performance of dielectric materials frequently utilised in gaseous insulating high Voltage applications, stressed under triple junction conditions, has been an interesting topic approAched through many different physical perspectives. Presented research outcomes have contributed to the understanding of the mechanisms behind the related phenomena, mAcroscopically and microscopically. This paper deals with the electrical detection of creeping discharges over disc-shaped insulator samples of different dielectric materials (polytetrafluoroethylene (PTFE), epoxy resin and silicone rubber) using atmospheric gases (dry air, N2 and CO2) as insulation medium in a point-plane electrode arrangement and under Ac Voltage application. The entire approAch implementation is described in detail, from the initial numerical field simulations of the electrode configuration to the sensing and recording devices specifications and applications. The obtained results demonstrate the dependence of the generated discharge Activity on the geometrical and material properties of the dielectric and the solid/atmospheric gas interfAce. The current work will be further extended as part of a future extensive research programme
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Electrical detection of creeping discharges over insulator surfAces in atmospheric gases under Ac Voltage application
MDPI, 2019Co-Authors: Michelarakis Michail, Eroual Abderrahmane, Lugg-widge Phillip, Haddad AbderrahmaneAbstract:Creeping discharges over insulator surfAces have been related to the presence of triple junctions in compressed gas insulated systems. The performance of dielectric materials frequently utilised in gaseous insulating high Voltage applications, stressed under triple junction conditions, has been an interesting topic approAched through many different physical perspectives. Presented research outcomes have contributed to the understanding of the mechanisms behind the related phenomena, mAcroscopically and microscopically. This paper deals with the electrical detection of creeping discharges over disc-shaped insulator samples of different dielectric materials (polytetrafluoroethylene (PTFE), epoxy resin and silicone rubber) using atmospheric gases (dry air, N2 and CO2) as insulation medium in a point-plane electrode arrangement and under Ac Voltage application. The entire approAch implementation is described in detail, from the initial numerical field simulations of the electrode configuration to the sensing and recording devices specifications and applications. The obtained results demonstrate the dependence of the generated discharge Activity on the geometrical and material properties of the dielectric and the solid/atmospheric gas interfAce. The current work will be further extended as part of a future extensive research programm
Hanan A Almekhaizim - One of the best experts on this subject based on the ideXlab platform.
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a hybrid real coded genetic algorithm pattern search approAch for selective harmonic elimination of pwm Ac Ac Voltage controller
International Journal of Electrical Power & Energy Systems, 2013Co-Authors: A K Alothman, Nabil A Ahmed, M E Alsharidah, Hanan A AlmekhaizimAbstract:AbstrAct Selective harmonic elimination-pulse width modulation techniques offer a tight control of the harmonic spectrum of a given Voltage waveform generated by a power electronic converter along with a low number of switching transitions. Traditional optimization methods suffer from various drawbAcks, such as prolonged and tedious computational steps and convergence to local optima; thus, the more the number of harmonics to be eliminated, the larger the computational complexity and time. This paper presents a novel method for output Voltage harmonic elimination and Voltage control of PWM Ac/Ac Voltage converters using the principle of hybrid Real-Coded Genetic Algorithm-Pattern Search (RGA-PS) method. RGA is the primary optimizer exploiting its global search capabilities, PS is then employed to fine tune the best solution provided by RGA in eAch evolution. The proposed method enables linear control of the fundamental component of the output Voltage and complete elimination of its harmonic contents up to a specified order. Theoretical studies have been carried out to show the effectiveness and robustness of the proposed method of selective harmonic elimination. Theoretical results are validated through simulation studies using PSIM software pAckage. Finally, these results are verified by means of an experimental prototype.
