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1
Huang, Bin, Le-qin Wang e Jia Guo. "Performance comparison of circular, two-lobe and elliptical journal bearings based on TEHD analysis". Industrial Lubrication and Tribology 66, n. 2 (4 marzo 2014): 184–93. http://dx.doi.org/10.1108/ilt-11-2011-0086.
Testo completoAbstract (sommario):
Purpose – The purpose of this paper is to study the different performance of circular, two-lobe and elliptical journal bearings by TEHD analysis. Design/methodology/approach – A complete 3D TEHD model of journal bearings is set up and applied to the lubricant performance calculation of the conventional circular, two-lobe and elliptical journal bearings. The finite difference method is employed to solve the THD model, and the thermo-elasto deformations on the pad are obtained by the finite element software ANSYS11.0. The data transfer between the THD model and ANSYS11.0 is carried out automatically by Interface Program. Findings – It is found that under the identical geometric parameters and operating condition, the circular journal bearing possesses the greatest magnitude of the maximum oil film pressure, the two-lobe one takes the second place and the elliptical one possesses the smallest magnitude. The thermo-elasto deformations on the pad is the same order of magnitude with the minimum film thickness. Practical implications – A complete 3D TEHD model made up of the THD model and ANSYS11.0 can be applied on journal bearings in practice applications. Originality/value – This paper set up a complete 3D TEHD model that is in common use for the lubricant performance analysis of circular and non-circular journal bearings.
2
Anang, Nurhazwani, e Wan Mariam Wan Muda. "Analysis of total harmonic distortion in single-phase single-stage grid-connected photovoltaic system". International Journal of Power Electronics and Drive Systems (IJPEDS) 14, n. 1 (1 marzo 2023): 471. http://dx.doi.org/10.11591/ijpeds.v14.i1.pp471-479.
Testo completoAbstract (sommario):
<p>This study presents the power quality issue mainly focus the effect of total harmonic distortion (THD) on a grid-connected PV system. Firstly, a grid-connected PV system with a single-phase single-stage has been developed to monitor the output values of voltage and current and also its harmonic distortion behaviours. Maximum power point tracking (MPPT) was implemented since it is proven as the first step for THD reduction because MPPT will extract maximum output power, voltage, and current of the PV system without fluctuation which leads to a low THD level. Furthermore, the employment of a good filter also reduces the THD level in a PV system. Thus, this study will focus on the THD analysis to resolve the power quality problems in the grid-connected PV system. The result shows that the THD value for current, <em>I<sub>THD</sub></em> analysis is more significant than the THD value for voltage, <em>V<sub>THD</sub></em> analysis in the case of grid-connected PV systems operating under different solar irradiances. In a conclusion, the increase in solar irradiance will increase the rated values of generated power and current thus, increasing the performance of THD values.</p>
3
Muzakki, Rizdam Firly, e Chairul Gagarin Irianto. "Voltage THD Analysis on the Use of DC Motors in Steel Milling Process". Jurnal Edukasi Elektro 7, n. 1 (30 maggio 2023): 1–11. http://dx.doi.org/10.21831/jee.v7i1.59289.
Testo completoAbstract (sommario):
A milling process utilize DC motors and rectifier circuits. Semiconductor components in the rectifier circuit could cause harmonic distortion. At PT X, the voltage THD generated at the 6KV feeder panel has exceeded the standards set by the IEEE. This study aims to analyze the voltage THD caused by a controlled rectifier circuit and DC motors, and to design a filter to mitigate it. MATLAB software is used to analyze the THD voltage. From the simulation results, it is known that the 400KW, 450KW, and 600KW DC motors produce voltage THD values of 9.35%, 14.23%, and 12.28% respectively which exceed the set standards of 8%. A single-tuned passive filter is designed to reduce the THD voltage value on each motor. The installation of the filter effectively reduces the THD voltage value in the 400KW, 450KW, and 600KW DC motors to 4.34%, 5.38%, and 6.35% respectively.
4
Glavatskih, S. B., e Michel Fillon. "TEHD Analysis of Thrust Bearings With PTFE-Faced Pads". Journal of Tribology 128, n. 1 (14 dicembre 2005): 49–58. http://dx.doi.org/10.1115/1.1843833.
Testo completoAbstract (sommario):
Results of a combined theoretical and experimental investigation into the operation of thrust bearings with polytetrafluoroethylene (PTFE)-faced pads are reported. Bearing performance is analyzed in terms of temperature, power loss, oil film thickness and pressure. These parameters are first calculated using a THD model. The effect of PTFE facing on bearing thermal performance is then presented and discussed. A TEHD model is subsequently employed. Obtained TEHD results show that oil film thickness and temperature are strongly affected by the PTFE layer. Theoretical results are compared with measured temperature, oil film thickness, and pressure.
5
Kienker, Paul K., Zhengyan Wu e Alan Finkelstein. "Mapping the membrane topography of the TH6–TH7 segment of the diphtheria toxin T-domain channel". Journal of General Physiology 145, n. 2 (12 gennaio 2015): 107–25. http://dx.doi.org/10.1085/jgp.201411326.
Testo completoAbstract (sommario):
Low pH triggers the translocation domain of diphtheria toxin (T-domain), which contains 10 α helices, to insert into a planar lipid bilayer membrane, form a transmembrane channel, and translocate the attached catalytic domain across the membrane. Three T-domain helices, corresponding to TH5, TH8, and TH9 in the aqueous crystal structure, form transmembrane segments in the open-channel state; the amino-terminal region, TH1–TH4, translocates across the membrane to the trans side. Residues near either end of the TH6–TH7 segment are not translocated, remaining on the cis side of the membrane; because the intervening 25-residue sequence is too short to form a transmembrane α-helical hairpin, it was concluded that the TH6–TH7 segment resides at the cis interface. Now we have examined this segment further, using the substituted-cysteine accessibility method. We constructed a series of 18 mutant T-domains with single cysteine residues at positions in TH6–TH7, monitored their channel formation in planar lipid bilayers, and probed for an effect of thiol-specific reagents on the channel conductance. For 10 of the mutants, the reagent caused a change in the single-channel conductance, indicating that the introduced cysteine residue was exposed within the channel lumen. For several of these mutants, we verified that the reactions occurred primarily in the open state, rather than in the flicker-closed state. We also established that blocking of the channel by an amino-terminal hexahistidine tag could protect mutants from reaction. Finally, we compared the reaction rates of reagent added to the cis and trans sides to quantify the residue’s accessibility from either side. This analysis revealed abrupt changes in cis- versus trans-side accessibility, suggesting that the TH6–TH7 segment forms a constriction that occupies a small portion of the total channel length. We also determined that this constriction is located near the middle of the TH8 helix.
6
Nakaiwa, Koichi, Hiroyuki Wakiwaka e Kunihisa Tashiro. "Analysis of Three Phase Linear Synchronous Motor Distortion Factor". Materials Science Forum 792 (agosto 2014): 239–44. http://dx.doi.org/10.4028/www.scientific.net/msf.792.239.
Testo completoAbstract (sommario):
The relation between the Electro Motive Force (EMF) and Total Harmonic Distortion (THD) was compared and verified by magnet arrangement. Using Halbach array, thrust was more increase by change of magnet arrangement. Moreover, the variable trend of cogging and THD by magnet ratio and magnet form change was checked.
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Khristiana, Harrij Mukti, Sudjito Soeparman, Slamet Wahyudi e Rini Nur Hasanah. "Analysis of loss on single-phase dry transformers with non-linear load". Eastern-European Journal of Enterprise Technologies 5, n. 8 (113) (31 ottobre 2021): 17–22. http://dx.doi.org/10.15587/1729-4061.2021.240233.
Testo completoAbstract (sommario):
The paper studies power losses in transformers due to non-linear loads. The research aims to analyze the power loss in a single-phase dry transformer under a non-linear load. The research uses an SW43W Power supply type, FlukeView Power Quality Analyzer as a DC or AC power supply on the primary side of the transformer. The non-linear load is connected to the secondary side. The loading test of the dry transformer was carried out at non-linear loads. The load variations used 0 %; 12.5 %; 25 %; 37.5 %; 50 %; 62.5 %; 75 %; 87.5 % and 100 %, as well as variations in the THD value by adjusting the ignition angle (α). The non-linear loads used are Half-Wave Rectifier and Controlled Half-Wave Rectifier with resistive loads with variations in THD values. The results showed that the transformer losses comprised Pno load and Pload. The operation of the transformer with constant input voltage and frequency with THDv<5 % resulted in a constant Pno load value at all load values. The greater the percentage of the load, the higher the load. The increase in THD because of non-linear load will increase the load on the transformer. The value of the derating factor is obtained by connecting the increase in losses (∆PLosses), which is influenced by THD and the increase in temperature T(°C) in dry transformers. When the transformer is loaded with a non-linear load, the derating factor<1. THD and derating factor form a linear relationship, when THD increases, the derating factor value decreases. Linear load on the transformer causes a decrease in its capacity, but if it gets a non-linear load with THD=39.1 %, it can withstand a load of 84.294 %, besides the increase in total harmonic distortion will increase losses and reduce transformer capacity
8
Salman, Layth S., e Harith Al-Badrani. "Design and performance analysis of asymmetric multilevel inverter with reduced switches based on SPWM". International Journal of Power Electronics and Drive Systems (IJPEDS) 14, n. 1 (1 marzo 2023): 320. http://dx.doi.org/10.11591/ijpeds.v14.i1.pp320-326.
Testo completoAbstract (sommario):
<span lang="EN-US">Multilevel inverters have the benefit of producing high output voltage values with little distortion. This paper deals with decreasing total harmonic distortion (THD) and providing an output voltage with various step levels switching devices. In this study, a 27-level inverter with three asymmetric H-Bridge was designed and simulated based on level shift sinusoidal pulse-width modulation and phase shift sinusoidal pulse-width modulation methods. MATLAB/Simulink has been used to create this model and test it at different types of loads. The results showed that a multilevel inverter with (PS-PWM) produces less (THD) than a multilevel with (LS-PWM), when the resistive load was used, the produced voltage and current THD in (PS-PWM) and (LS-PWM) are 3.02% and 4.30% respectively, that has resulted from the linearity between voltage and current in the resistive load. While in the case of applying an inductive load, the THD in the voltage is constant in both (PS-PWM) and (LS-PWM) methods and has the same values as the THD in a resistive load. However, the THD in the current with inductive load decreased to 2.79% in (PS-PWM) and 4.04% in (LS-PWM). Finally, these results show that the performance of the proposed power circuit with PS-PWM is better than (LS-PWM).</span>
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Goncharevskyi, S., M. Makarchuk e V. Martynyuk. "Temperature of representative areas of the breast department of the vegetative nervous system as the index of human organism functional state". Bulletin of Taras Shevchenko National University of Kyiv. Series: Problems of Physiological Functions Regulation 23, n. 2 (2017): 27–33. http://dx.doi.org/10.17721/2616_6410.2017.23.27-33.
Testo completoAbstract (sommario):
Almost all processes in the human body in one way or another connected with the autonomic nervous system. That's why it is real to evaluate the functional state of the person by temperature characteristics of representative points of the autonomic nervous system. Location and information of these points are confirmed by fundamental research. However, simply measuring the temperature at some points may not be sufficient to establish any systematic changes in the human body. The establishment of such changes requires systematic assessment of interdependent significant relationships between these parameters.The main aim of our research was to study effects of myocardial infarction in the thoracic region of the autonomic nervous system. The temperature of representative areas of the thoracic autonomic nervous system we measured by infrared thermometer (Medisana FTO D-53340 , with an accuracy of 0.1 degree Celsius). Statistical analysis was conducted in the packet Statistics 10. The presence of a difference in the temperature coefficients of representative areas (p<0,05). For the left side of the spine characterized by a difference in Th1–Th5 segments, which confirms their diagnosis: Th1 – 0,931,12 (control) and -0,797,49 (experiment), Th2 – 1,571,12 and -0,486,70, Th3 – 1,582611,12325 and -0,663,36, Th4 – 0,85913 0,92611 and -1,74,64, Th5 – 0,923480,75469 and-1,615,73 respectively. For the right side of the thoracic spines: Th6 – 0,850,73 (control) and -0,797,49 (experiment), Th7 – -1,000,79 and -1,370,69, Th8 – -0,960,73 and -0,990,68, Th9 – -0,120,64 and -0,380,83, Th10 – -0,921,14 and -1,031,00, Th11 – -1,691,05 and -1,861,06, Th12- -1,651,15 and -1,961,12 respectively. We found that myocardial infarction is manifested in the thoracic spine. In an experimental group there is significant difference of temperature in all segments. We can also notice asymmetry of temperatue between the right and left side of the spine. In the test group there are a deviation from the normal temperature in the first five thoracic segments on the left side, which confirms their diagnosis. On the right side of the spine there are a deviation in the last seven segments, which may indicate the compensatory mechanisms of regulation of the system. We can observe the temperature asymmetry, which in long-term exposure can negatively affect to the body.
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Yaqoob, Salam J., Jawad K. Raham e Hassan A. Sadiq. "Analysis and Simulation of Current-source Flyback Inverter with Efficient BCM Control Strategy". WSEAS TRANSACTIONS ON ELECTRONICS 12 (8 novembre 2021): 132–40. http://dx.doi.org/10.37394/232017.2021.12.18.
Testo completoAbstract (sommario):
The Flyback inverter is a single-stage power inverter which represent an attractive solution for photovoltaic (PV) grid-tied inverter application. The main advantages of a current-source flyback inverter are high power density and high efficiency due to its small, as well as low total harmonic distortion (THD) operation. However, a flyback topology works with Discontinuous Conduction Mode (DCM) control strategy has lower efficiency and poor THD values. In this paper, an efficient current-source flyback inverter topology works with Boundary Conduction Mode (BCM) control strategy is presented. Besides, an efficient incremental conductance (IC) maximum power point tracking (MPPT) is used to extract the maximum power from the PV module. To verify the proposed control a power simulator (PSIM) software is used. As a result, the simulation results indicates that the BCM control is more efficient than the DCM method for various weather conditions. Finally, the proposed BCM strategy is compared with DCM control in terms of THD and thus it is achieved lower THD contain in the injection current of grid.
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Wang, Nenzi, e Chih-Ming Tsai. "Assessment of artificial neural network for thermohydrodynamic lubrication analysis". Industrial Lubrication and Tribology 72, n. 10 (4 giugno 2020): 1233–38. http://dx.doi.org/10.1108/ilt-03-2020-0109.
Testo completoAbstract (sommario):
Purpose In this study, artificial neural networks (ANNs) are constructed and validated by using the bearing data generated numerically from a thermohydrodynamic (THD) lubrication model. In many tribological simulations, a surrogate model (meta-model) for obtaining a fast solution with sufficient accuracy is highly desired. Design/methodology/approach The THD model is represented by two coupled partial differential equations, a simplified generalized Reynolds equation, considering the viscosity variation across the film thickness direction and a transient energy equation for the 3-D film temperature distribution. The ANNs tested are having a single- or dual-hidden-layer with two inputs and one output. The root-mean-square error and maximum/minimum absolute errors of validation points, when comparing with the THD solutions, were used to evaluate the prediction accuracy of the ANNs. Findings It is demonstrated that a properly constructed ANN surrogate model can predict the THD lubrication performance almost instantly with accuracy adequately retained. Originality/value This study extends the use of ANNs to the applications other than the analyses dealing with experimental data. A similar procedure can be used to build a surrogate model for computationally intensive tribological models to have fast results. One of such applications is conducting extensive optimum design of tribological components or systems. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2020-0109/
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Gupta, Ranitesh, e Kuldeep Sahay. "Comparative analysis of THD for square-wave inverter at different conduction modes". International Journal of Applied Power Engineering (IJAPE) 12, n. 3 (25 luglio 2023): 312. http://dx.doi.org/10.11591/ijape.v12.i3.pp312-320.
Testo completoAbstract (sommario):
This paper proposes conduction schemes for the most common six-switch voltage sources inverter. Also, a comparative study of the output THD for different conduction modes of switches for a three-phase square wave inverter is done, as the harmonic content of any electrical system is important to analyze its performance. The harmonic distortion of the load voltage and load current is taken as the main constraint to evaluate the performance of the three-phase inverter. So, control strategies for various loads are executed for different modulation schemes of inverter switches using MATLAB/Simulink software. Obtained results show that 150° conduction gives the least THD for output current, and 170° conduction gives the least THD for output voltage for three-phase inverters. Also, harmonic contents are reduced using a passive LC filter at the output of the inverter.
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Choi, Sugy, Megan A. O’Grady, Charles M. Cleland, Elizabeth Knopf, Sueun Hong, Thomas D’Aunno, Yuhua Bao, Kelly S. Ramsey e Charles J. Neighbors. "Clinics Optimizing MEthadone Take-homes for opioid use disorder (COMET): Protocol for a stepped-wedge randomized trial to facilitate clinic level changes". PLOS ONE 18, n. 6 (9 giugno 2023): e0286859. http://dx.doi.org/10.1371/journal.pone.0286859.
Testo completoAbstract (sommario):
Introduction Regulatory changes made during the COVID-19 public health emergency (PHE) that relaxed criteria for take-home dosing (THD) of methadone offer an opportunity to improve quality of care with a lifesaving treatment. There is a pressing need for research to study the long-term effects of the new PHE THD rules and to test data-driven interventions to promote more effective adoption by opioid treatment programs (OTPs). We propose a two-phase project to develop and test a multidimensional intervention for OTPs that leverages information from large State administrative data. Methods and analysis We propose a two-phased project to develop then test a multidimensional OTP intervention to address clinical decision making, regulatory confusion, legal liability concerns, capacity for clinical practice change, and financial barriers to THD. The intervention will include OTP THD specific dashboards drawn from multiple State databases. The approach will be informed by the Health Equity Implementation Framework (HEIF). In phase 1, we will employ an explanatory sequential mixed methods design to combine analysis of large state administrative databases—Medicaid, treatment registry, THD reporting—with qualitative interviews to develop and refine the intervention. In phase 2, we will conduct a stepped-wedge trial over three years with 36 OTPs randomized to 6 cohorts of a six-month clinic-level intervention. The trial will test intervention effects on OTP-level implementation outcomes and patient outcomes (1) THD use; 2) retention in care; and 3) adverse healthcare events). We will specifically examine intervention effects for Black and Latinx clients. A concurrent triangulation mixed methods design will be used: quantitative and qualitative data collection will occur concurrently and results will be integrated after analysis of each. We will employ generalized linear mixed models (GLMMs) in the analysis of stepped-wedge trials. The primary outcome will be weekly or greater THD. The semi-structured interviews will be transcribed and analyzed with Dedoose to identify key facilitators, barriers, and experiences according to HEIF constructs using directed content analysis. Discussion This multi-phase, embedded mixed methods project addresses a critical need to support long-term practice changes in methadone treatment for opioid use disorder following systemic changes emerging from the PHE—particularly for Black and Latinx individuals with opioid use disorder. By combining findings from analyses of large administrative data with lessons gleaned from qualitative interviews of OTPs that were flexible with THD and those that were not, we will build and test the intervention to coach clinics to increase flexibility with THD. The findings will inform policy at the local and national level.
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Tediosi, F., G. Bertolini, F. Parazzini, G. Mecca e L. Garattini. "Cost Analysis of Dialysis Modalities in Italy". Health Services Management Research 14, n. 1 (febbraio 2001): 9–17. http://dx.doi.org/10.1177/095148480101400102.
Testo completoAbstract (sommario):
This study analyses management and costs of dialysis in the Italian National Health Service (NHS). Information on efficacy and health-related quality of life (HRQOL) based on the existing literature also is presented. The clinical differences between the dialysis modalities seem to be related to their appropriateness to specific patient groups. Efficacy rates are similar and the only differences are in complications and HRQOL. Traditional haemodialysis (THD) can be done by Italian patients in dialysis centres or in hospital. High-flux haemodialysis (HFHD) is generally only done in hospital. Peritoneal dialysis (PD) is usually done at home. The cost analysis was performed on a sample of Italian dialysis centres and hospitals, according to the full cost method. As expected, HFHD was more expensive than THD and PD, but no marked differences emerged among the different HFHD modalities. THD modalities in dialysis centres were less costly than in hospitals. Automated PD (APD) was much more expensive (almost twice) than continuous ambulatory PD (CAPD), the cheapest method in absolute terms. This study confirms that dialysis is costly and that it is very difficult to assess the cost-effectiveness of the different approaches. Although this study has limits, it should provide sufficient analytical information to local healthcare managers for more rational allocation of financial resources to dialysis services.
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Tediosi, F., G. Bertolini, F. Parazzini, G. Mecca e L. Garattini. "Cost analysis of dialysis modalities in Italy". Health Services Management Research 14, n. 1 (1 febbraio 2001): 9–17. http://dx.doi.org/10.1258/0951484011912483.
Testo completoAbstract (sommario):
This study analyses management and costs of dialysis in the Italian National Health Service (NHS). Information on efficacy and health-related quality of life (HRQOL) based on the existing literature also is presented. The clinical differences between the dialysis modalities seem to be related to their appropriateness to specific patient groups. Efficacy rates are similar and the only differences are in complications and HRQOL. Traditional haemodialysis (THD) can be done by Italian patients in dialysis centres or in hospital. High-flux haemodialysis (HFHD) is generally only done in hospital. Peritoneal dialysis (PD) is usually done at home. The cost analysis was performed on a sample of Italian dialysis centres and hospitals, according to the full cost method. As expected, HFHD was more expensive than THD and PD, but no marked differences emerged among the different HFHD modalities. THD modalities in dialysis centres were less costly than in hospitals. Automated PD (APD) was much more expensive (almost twice) than continuous ambulatory PD (CAPD), the cheapest method in absolute terms. This study confirms that dialysis is costly and that it is very difficult to assess the cost-effectiveness of the different approaches. Although this study has limits, it should provide sufficient analytical information to local healthcare managers for more rational allocation of financial resources to dialysis services.
16
Chien, Siong Kai, Sy Yi Sim, Wahyu Mulyo Utomo, Sie Long Kek, Farahiyah Mustafa, Nor Aira Zambri, Alvin John Lim Meng Siang e Gia Yi Sim. "Enhanced DTC induction motor drives for THD minimization performance improvement with multilevel inverter". International Journal of Power Electronics and Drive Systems (IJPEDS) 13, n. 1 (1 marzo 2022): 93. http://dx.doi.org/10.11591/ijpeds.v13.i1.pp93-101.
Testo completoAbstract (sommario):
Direct torque control (DTC) is a method applied in induction motor (IM) drives to control the speed and torque of IM accurately and independently without feedback signal. However, in fast fourier transform (FFT) analysis, the total harmonic distortion (THD) of the IM drives is high in DTC method with conventional inverter (CI). Therefore, the purpose of this study is to minimize the THD without affecting the drive’s performance. A DTC IM drive with multilevel inverter (MLI) is proposed in this study to reduce THD and preserve good speed and torque response of IM simultaneously. DTC IM drive with proposed MLI based THD minimization has several advantages over the DTC IM drive with CI, including higher generated output voltage with low distortion, operate under low switching frequency, and work with renewable energy. In order to prove the effectiveness of the proposed MLI based THD minimization in DTC IM drive, MATLAB Simulink is used to investigate the response of the IM drive and THD under different operating condition. From this study, proposed MLI based THD minimization DTC IM drive is able to reduce THD with a maximum of 13% in low speed operation as compared to DTC IM drive with CI.
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Perreault, Maxime, Sina Hamzehlouia e Kamran Behdinan. "Application of computational fluid dynamics for thermohydrodynamic analysis of high-speed squeeze-film dampers". Transactions of the Canadian Society for Mechanical Engineering 43, n. 3 (1 settembre 2019): 306–21. http://dx.doi.org/10.1139/tcsme-2018-0060.
Testo completoAbstract (sommario):
In high-speed turbomachinery, the presence of rotor vibrations, which produce undesirable noise or shaft deflection and losses in performance, has brought up the need for the application of a proper mechanism to attenuate the vibration amplitudes. Squeeze-film dampers (SFDs) are a widely employed solution to the steady-state vibrations in high-speed turbomachinery. SFDs contain a thin film of lubricant that is susceptible to changes in temperature. For this reason, the analysis of thermohydrodynamic (THD) effects on the SFD damping properties is essential. This paper develops a computational fluid dynamics (CFD) model to analyze the THD effects in SFDs, and enabling the application of CFD analysis to be a base-line for validating the accuracy of analytical THD SFD models. Specifically, the CFD results are compared against numerical simulations at different operating conditions, including eccentricity ratios and journal whirl speeds. The comparisons demonstrate the effective application of CFD for THD analysis of SFDs. Additionally, the effect of the lubricant THDs on the viscosity, maximum and mass-averaged temperature, as well as heat generation rates inside the SFD lubricant are analyzed. The temperature of the lubricant is seen to rise with increasing whirl speed, eccentricity ratios, damper radial clearance, and shaft radii.
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Zhao, Wenyong, Jie Jiang, Yawen Luo, Jiahao Li e Yuqiang Ding. "Atomic Layer Deposition of La2O3 Film with Precursor La(thd)3-DMEA". Coatings 13, n. 5 (5 maggio 2023): 870. http://dx.doi.org/10.3390/coatings13050870.
Testo completoAbstract (sommario):
In this paper, a new precursor La(thd)3-DMEA (thd = 2,2,6,6-tetramethyl-3,5-heptanedione, DMEA = N,N′-dimethylethylenediamine) was synthesized and characterized with 1H-NMR and X-ray single crystal diffraction. The thermal properties of La(thd)3-DMEA were checked by thermogravimetric analysis (TGA), which confirmed that the volatility and suitability of La(thd)3-DMEA are suitable for atomic layer deposition (ALD). We studied the atomic layer deposition of La2O3 films on a SiO2 surface with La(thd)3-DMEA and O3 as precursors. Self-limiting deposition behaviors were found for the prepared films. The purity and surface morphology of the as-grown La2O3 films, which possessed a constant growth rate of ~0.4 Å/cycle at 250–280 °C, were confirmed by XPS, SEM, and AFM. The results show that La(thd)3-DMEA is a suitable precursor for the atomic layer deposition of La2O3 film.
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Paranjpe, R. S. "Analysis of Non-Newtonian Effects in Dynamically Loaded Finite Journal Bearings Including Mass Conserving Cavitation". Journal of Tribology 114, n. 4 (1 ottobre 1992): 736–44. http://dx.doi.org/10.1115/1.2920943.
Testo completoAbstract (sommario):
Non-Newtonian effects of multigrade engine oils in dynamically loaded crankshaft bearings are analyzed. The main focus of this work is on the shear-thinning effect. Viscoelastic effects are also considered over a limited range of the relaxation time. It has been shown that the same generalized Reynolds equation used in the Thermohydrodynamic (THD) analysis can be used for analyzing the shear-thinning effects as well. Consequently the shear thinning effect and the THD effect can be treated together. A mass conserving cavitation algorithm developed earlier for doing the THD analysis is used to solve the generalized Reynolds equation. Non-Newtonian shear-thinning significantly affects the power loss, film thickness, and oil flow of a multigrade oil as compared with a Newtonian oil. Over the range of relaxation times considered, no viscoelastic effects were discernible for crankshaft bearings lubricated with multigrade oils.
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Janardana, I. G. N., I. W. Arta Wijaya e I. N. Karnata Mataram. "Effect Of Value Of Resistance Announcement To Thd In Electrical System Faculty Of Engineering University Udayana Denpasar". Journal of Electrical, Electronics and Informatics 2, n. 1 (10 febbraio 2018): 21. http://dx.doi.org/10.24843/jeei.2018.v02.i01.p05.
Testo completoAbstract (sommario):
AC (Air Conditioner), TV, lamp, LCD and others are categorized as nonlinear load generating harmonics. The high content of harmonics has a negative impact on the quality of electrical power. The result of measurement of THD (Total Harmonic Distortion) current at 9 ohm ground resistance value at phase R = 9,8%, phase S = 11,0%, phase T = 7,5% exceed from standard value IEEE 519 Year 2014 equal to ? 5 , 0%, THD measurement of phase voltage R = 1.4%, phase S = 1.2%, phase T = 1.3%, meet the maximum THDv standard of ? 5%. To overcome this problem, it was observed the effect of the value of ground resistance to THDi and THDv on the electrical system of the College of Engineering Faculty of Denpasar. This method of analysis with ETAP software simulation. With grounding system ? 3 ohm only effect on current THD only with decreasing value of THDi become: phasa R = 4,2%, phase S = 5% and phase T = 4,3%, meaning with grounding system ? 3 ohm THD current fulfill IEEE 519 - 2014 standard <5%. while THD voltage has no effect (THD value of fixed voltage). Several studies have suggested that THD repair can be done by filter installation. However in this study the installation of grounding system ? 3 ohms can reduce the value of current THD.
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Sambhi, Shilpa, Ankit Mittal e Aviral Srivastava Ayan Mondal Nitin Varshney. "THD Analysis of Cascaded Multi-level Inverters using different PWM Techniques". International Journal of Trend in Scientific Research and Development Volume-3, Issue-4 (30 giugno 2019): 1082–85. http://dx.doi.org/10.31142/ijtsrd23984.
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Rani, R. A., Shakir Saat, Yusmarnita Yusop, Huzaimah Husin, F. K. Abdul Rahman e A. A. Isa. "The Effects of Total Harmonics Distortion for Power Factor Correction at Non-Linear Load". International Journal of Power Electronics and Drive Systems (IJPEDS) 7, n. 2 (1 giugno 2016): 551. http://dx.doi.org/10.11591/ijpeds.v7.i2.pp551-560.
Testo completoAbstract (sommario):
This paper presents the effect of total harmonic distortion (THD) in power factor correction (PFC) at non-linear load. This study focuses on the relationship between THD and PFC. This is beacuse,the power factor affects THD. This occurs in power system as we have variety of loads, i. e linear load or non-linear load. The variety of loads will influence the sinusoidal waveform, which comes out from harmonic distortion. Thus, based on this study, we can compare the effective method in improving the power factor as it will not disturb the performance of THD. The focus of study is on the single phase load, where the voltage restriction is 240 V. The analysis will only focus on the consumer, which depends on the variety of non-linear load. Besides, the parameters for analysis are based on the percentage of THD and the value of power factor. The instrument for measuring the parameter is based on power factor correction device or technique. On the other hand, the method that was used for this study is based on simulation which incorporated the Multisim software. At the end of ths study, we can choose the most effective method that can be used to improve the power factor correction without disturbing the THD.
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Braide, S. L. "Evaluation and Analysis of Harmonic Distortion on 330kV Network Case Study Selected Sub-Region Nigerian Power System for Improve Power Quality". Journal of Progress in Engineering and Physical Science 1, n. 1 (novembre 2022): 13–22. http://dx.doi.org/10.56397/jpeps.2022.11.03.
Testo completoAbstract (sommario):
This paper presented fundamental characteristics of harmonic studies and its related work. The total harmonic distortion (THD) of the transmission line were computed using harmonics contents parameters of the waveform (harmonic voltage and impedance magnitude values). Results of THD for the 330kV transmission line are presented using harmonic load flow analysis in ETAP—domain on the view to measure the level of distortion in the network. Figure 2 shows the section of the harmonic load flow simulation in order to check for degree of harmonic distortion in the system under investigation. The provision of the harmonic frequency with greater magnitude exceeding THD and IHD limits are violated in accordance to IEC 61000-3-6:2008 (European Standards) are used as benchmark for measurement. That is the distortion for current and voltage (THDi% and THD%) are 0.5 and 1.5 respectively particularly harmonic order (h) ≤ 13. Consequently, the harmonic frequency violations with greater magnitude of 5th, 7th, 11th, and 13th order in the network are mitigated with 3-unit of single tuned filter to the affected buses for improved power quality.
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Naida, S. A., Y. O. Onykienko, O. I. Drozdenko, O. I. Smolenska, V. S. Baran e N. O. Iakunina. "Analysis of the influence of load inductance on nonlinear distortions of a class D amplifier caused by «dead time»". Electrical Engineering & Electromechanics, n. 3 (23 giugno 2021): 32–37. http://dx.doi.org/10.20998/2074-272x.2021.3.05.
Testo completoAbstract (sommario):
Goal. Analysis of the effect of load inductance at the output of the class D amplifier for different values of the duration of «dead time» and assessment of the adequacy of existing mathematical models for calculating the THD at the output of the amplifier depending on the duration of «dead time». Methodology. The study of the effect of «dead time» on the THD was performed using a computer model of the half-bridge converter board EPC9035 from Efficient Power Conversion. This board contains GaN transistors EPC2022 eGaN®, the corresponding control driver and other necessary elements for operation. The use of GaN transistors has made it possible to investigate the operation in a wide range of frequent switching, both to control the motor and to amplify the audio signal. Results. It is established that the value of load inductance affects the level of nonlinear distortions caused by «dead time». At inductance values that provide a constant sign of the output current, a difference arises between the duration of the input and output pulses, which increases the THD. At inductance values, when the choke current changes sign during a pulse, there is no error between the duration of the input and output pulses. Changing the inductance changes the relationship between the error signal and the non-error signal. THD changes accordingly. At high conversion frequencies, the voltage spikes caused by the choke current through the built-in diodes during the dead time are partially compensated by overcharging the output capacitance of the transistors, which also reduces harmonic distortion. Originality. For the first time, the value of the THD at the outlets in the fallowness of the different indices of the inductance of the choke and the theoretical calculation of the value in the results of the computer model was obtained. Practical significance. The dependence of the THD values on the inductance of the choke for converters with a switching frequency range from 1 kHz to 400 kHz, which allows them to be used both to control the motor and to amplify the audio signal.
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Jeong, Y. H., e T. J. Park. "THD Analysis of a Hydraulic Servo Valve Using CFD". Journal of The Korean Society for Fluid Power & Construction Equipments 11, n. 1 (1 marzo 2014): 8–13. http://dx.doi.org/10.7839/ksfc.2014.11.1.008.
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Kuznetsov, Evgeny, Sergei Glavatskih e Michel Fillon. "THD analysis of compliant journal bearings considering liner deformation". Tribology International 44, n. 12 (novembre 2011): 1629–41. http://dx.doi.org/10.1016/j.triboint.2011.05.013.
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Dheeraj, K. L., M. Diwakar, M. Durga Raj, M. Eswar e K. Naga Venkatesh. "THD Analysis of Cascaded Mli for Various PWM Techniques". International Journal of Engineering Trends and Technology 11, n. 3 (25 maggio 2014): 146–49. http://dx.doi.org/10.14445/22315381/ijett-v11p228.
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Kumar, Abhimanyu, e Dr Sanjay Jain. "Multilevel Inverter with Predictive Control for Renewable Energy Smart Grid Applications". International Journal of Electrical and Electronics Research 10, n. 3 (30 settembre 2022): 501–7. http://dx.doi.org/10.37391/ijeer.100317.
Testo completoAbstract (sommario):
In a world where climate changes and power management are becoming increasingly important, research work focuses on renewable energy based smart grid to meet adequate demands of energy. The smart grid is a modernized autonomous power network that can transmit electricity effectively, conserve resources and costs, and increase the local grid's stability. As a result, a smart grid connected multilevel inverter is presented in this work. The inverter is controlled using a model predictive control algorithm with increased levels with the primary goal of controlling the injected power generated by the renewable source, improving the quality of the current waveform, lowering THD, and eliminating the shift phase among the injected current and the grid voltage in effort to match the smart grid network's requirements. Therefore, this paper aims to show the performance analysis of multilevel inverters with predictive control for renewable energy smart grids application. The major concern was observed with most of the multi-level inverters are that with increased level total harmonic distortion (THD) is increased if switching control is not designed properly. Therefore, in this case predictive control is implemented on renewable energy based smart grid inverters to increase level with minimum voltage THD and current THD. The case analyzed voltage and current THD in the different levels of multilevel inverter. The result analysis was performed on 7, 11, 17, 21, 27, 31, 37 and 41 respectively. From result analysis it was observed that minimum THD was observed with level 31, i.e., 0.35% and at level 41 it was increased up to 0.55% which is still not high as compared to other existing MLI architectures. The result findings of proposed approach decreased THD with varying levels and outperforms better as compared to other works.
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Zygarlicki, Jarosław, e Janusz Mroczka. "Method of testing and correcting signal amplifiers’ transfer function using prony analysis". Metrology and Measurement Systems 19, n. 3 (1 ottobre 2012): 489–98. http://dx.doi.org/10.2478/v10178-012-0042-7.
Testo completoAbstract (sommario):
Abstract This article presents a way of analyzing the transfer function of electronic signal amplifiers. It also describes the possibility of using signal precorrection which improves the parasitic harmonics in the THD (Total Harmonic Distortion) of the amplified signal by correcting linearity of the tested amplifier’s transfer function. The proposed method of analyzing and presenting the transfer function allows to diagnose the causes of generating parasitic harmonics, what makes it a useful tool when designing low distortion amplifier systems, such as e.g. amplifiers in measurement systems. The presented THD correction can be used in e.g. amplifier systems that cooperate with arbitrary generators.
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Adjie, Alfin Prima, e Muhammad Imran Hamid. "Harmonics Analysis of Input Current of 3-Phase PWM Rectifier". Andalas Journal of Electrical and Electronic Engineering Technology 1, n. 1 (7 maggio 2021): 31–40. http://dx.doi.org/10.25077/ajeeet.v1i1.6.
Testo completoAbstract (sommario):
Rectifier is a non-linier load that causes harmonic distortion in the power system. Pulse-width modulation (PWM) method is an effective method in pressing the magnitude of harmonics in a rectifier application, it provides an almost sinusoidal input current. However, the variation of loads that supplied by a rectifier cause the harmonics that arise can still beyond the applicable standard. The amount of harmonics in the operating range of a rectifier need to be identified to determine the filter on the input side. In this research article, 3-phase PWM rectifier was designed with hysteresis current control technique using PSCAD software simulation. Harmonic compensation was carried out by applying an active filter based on P-Q theory to reduce the harmonic distortion that occurs in the input current, thus giving a low total harmonic distortion (THD) value. Based on the simulation, 3-phase PWM rectifier operation starting at a power level of 150 kW, giving a THD value above 5-10% by the increasing the amount of load supplied by the rectifier. The application of active filter based on the P-Q theory is able to compensate harmonics in the input current wave with a THD value below 5% in the rectifier operating range.
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Ha, Eunyoung, Mikyung Kim, Jaemoo Chun, Chang-Seob Seo, YouMee Ahn e Jeeyoun Jung. "Tongqiaohuoxue Hinders Development and Progression of Atherosclerosis: A Possible Role in Alzheimer’s Disease". Biology 9, n. 11 (27 ottobre 2020): 363. http://dx.doi.org/10.3390/biology9110363.
Testo completoAbstract (sommario):
Atherosclerosis is closely associated with Alzheimer’s disease (AD). Tongqiaohuoxue decoction (THD) is a classical herbal prescription in traditional Chinese medicine widely used for the prevention and treatment of cerebrovascular disease. This study aimed to explore the therapeutic effects of THD on atherosclerosis and AD. Eight-week-old C57BL6/J wild-type and ApoE-deficient (ApoE-/-) mice were fed a high-fat and high-cholesterol diet for eight weeks, followed by oral phosphate-buffered saline vehicle or THD treatment for eight weeks further. In ApoE-/- mice, THD attenuated lipid deposition in the aorta and the brain, and abrogated atherosclerotic changes without affecting serum lipid profiles while decreasing amyloid plaque formation. In vitro assays undertaken to understand THD’s effects on lipid clearance in the aorta and brain vessels revealed that THD treatment inhibited the lipid uptake, stimulated by oxidized low-density lipoprotein, resulted in decreased endothelial cell activation through reduction in intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and monocyte chemoattractant protein-1 levels. Serum analysis revealed inhibitory effects of THD on resistin production, which has important roles in the development of both atherosclerosis and AD. In conclusion, the current study demonstrates beneficial effects of THD on the development and progression of atherosclerosis, and a possible protective role against AD.
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John Adrian F. De Guzman, Kimberly Mae L. Leyson, Bernard Gabriel C. Mendoza, Gio Paulo R. Quezada e Charles G. Juarizo. "IoT-based monitoring, analysis and supervisory control of voltage harmonics in a three-phase system using four singles tuned lowpass filter". World Journal of Advanced Research and Reviews 19, n. 1 (30 luglio 2023): 600–609. http://dx.doi.org/10.30574/wjarr.2023.19.1.1400.
Testo completoAbstract (sommario):
Total Harmonic Distortion is a vital part of communications, power distribution, and audio. In power distribution, it must be kept as low as possible. Voltage pollution occurs at the point of common coupling, which leads to a higher THD. Higher THD ensues thermal stress to the system where issues in the power system arise. Odd harmonic frequencies, specifically, the 5th, 7th, 11th, and 13th are the primary cause of the increase in THD. Several ways to reduce harmonics are the use of reactors, passive filters, and active front end solutions. This study is focused on minimizing the voltage harmonics by monitoring the voltage coming from a three-phase system by using four single-tuned filters that will tune out the unwanted harmful frequencies. The data will send through the IoT analytics platform which can then be viewed from ThingView, and the filters can be controlled through Arest.io. The system was compared to an oscilloscope then used Root-Mean-Square Error for system reliability test and yielded 0.097696 for data without filter and 0.048485 for data with a filter. Lastly, the system effectively decreased the THD by 32% compared to an unfiltered source.
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Mohamed Ahmed, Penrose Cofie, John Fuller e Charlie Tolliver. "THD analysis and cost comparison for an N-level H-bridge inverter incorporating passive and active filters". World Journal of Advanced Engineering Technology and Sciences 5, n. 2 (30 marzo 2022): 045–53. http://dx.doi.org/10.30574/wjaets.2022.5.2.0043.
Testo completoAbstract (sommario):
Multilevel H-bridge inverters have grown in popularity in electronic direct current (DC) to alternating current (AC) power conversion. In the renewable energy field, H-bridge inverters are used for converting DC voltage obtained from solar panels to AC voltage. However, H-bridge inverters produce undesirable odd harmonics in their output. Several H-bridges are, therefore, usually cascaded to reduce the total harmonic distortion (THD) in their output, but the results aren’t satisfactory in most cases. In this paper, both active and passive filters are incorporated in a cascaded H-bridge inverter to reduce the THD further. Then cost comparison is made of cascaded H-bridge inverters (3, 5, 7, 9, and 11-levels) without a filter and multilevel cascaded H-bridge inverters (3, 5, 7, 9, and 11-levels) with a passive filter or active filter. Powersim (PSIM) platform is used to perform the THD analysis.
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Harish, S. P., S. Sridhar, Omsekhar Indela, Kumaran G. Kodeeswara e P. Parthiban. "Analysis of Five Leg Voltage Source Inverter Fed Dual Motor Drive System". E3S Web of Conferences 309 (2021): 01142. http://dx.doi.org/10.1051/e3sconf/202130901142.
Testo completoAbstract (sommario):
With the advent of electric vehicle multi-machine drives are attaining overwhelming responses from the researchers and industries in recent years, as compared to their counterpart of single machine drive. In this regard, the industries are looking for multi motor control with single inverter system with precise speed control. The solution of aforesaid problem lies with multi-leg inverter fed dual induction motor drives that are capable for high power ratings and other specific applications. Any faults in the system leads to the failure of the operation of the entire drive system. Hence condition monitoring of the entire drive system becomes of paramount significance. Considering the aforementioned points, this paper focuses on the fault analysis of five leg voltage source inverter feeding dual induction motors. The drive system is simulated using MATLAB/ SIMULINK for different pulse width modulation techniques like SPWM, SVPWM and Two Arm Modulation (TAM) Techniques. The effect on fault in the inverter like opening of the switch and shorting the switch, on the performance of the induction motors are analysed. Total Harmonic Distortion (THD) of the stator current for different modulation techniques are compared for the analysis purpose. From the results it is observed that the THD is less for SVPWM techniques as compared with SPWM and TAM method. But independent control of both the machine cannot be attained by SPWM and SVPWM method. For independent speed control TAM method is used. So a trade-off has to be done considering the requirement and THD. It is finally concluded that independent speed control is achieved at the cost of higher THD.
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Saurabh Kumar, Adeeb Uddin Ahmad, Neevatika Verma,, Vikas Verma and Shweta Singh. "Implementation Analysis of Solar PV Based SEPIC Inverter System". International Journal for Modern Trends in Science and Technology 7, n. 10 (31 ottobre 2021): 8–16. http://dx.doi.org/10.46501/ijmtst0710002.
Testo completoAbstract (sommario):
For welfare of environment, world needs to use more and more renewable energy system not only at the level of industrial but also for domestic load system. Due to much installation cost involving in a solar PV cell/panel based system there is a need of better mechanisms to get maximum utilization and benefits from the system with reliable operation, especially in the case of microgeneration power plant to full fill the minimum desired requirements of domestic appliances to achieved reliable operation. Mostly available PV based inverter system having problem of low output voltage generation and THD producing issue, which needs to a requirements of extra circuit to the control THD and boost up the level of output voltage. In this paper, solar PV based closed loop SEPIC converter by PWM technique to maintain a step up constant dc output voltage with no polarity reversal, low ripple in output and minimizing the requirement of additional filter circuit and fed to single phase inverter. This paper has been focused for the overall single phase PV based SEPIC inverter system implementation, performances and simulated on MATLAB/SPS software to provide low losses, 2% minimum THD and reliable operation in compare with single phase PV based Cuk inverter is used for DC-AC conversion system to compatible with domestic load appliances.
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Ramadhani, Ummi Khofifah Qodariah, Asmar Asmar e Wahri Sunanda. "Pengaruh Total Harmonic Distortion Terhadap Power Factor Pelanggan Rumah Tangga 900 – 2200 VA Dusun Tujuh Bubung Kepulauan Bangka Belitung". AVITEC 4, n. 2 (2 agosto 2022): 177. http://dx.doi.org/10.28989/avitec.v4i2.1290.
Testo completoAbstract (sommario):
The high content of harmonics in an electric power system can cause several disturbances to the system, such as increasing power losses in the system, causing various damage to electrical equipment, and causing the use of electrical energy to be ineffective. Harmonics is caused by the operation of non-linear electrical loads. The interacting harmonic currents with the supply system impedance distorts the supplier's output current and voltage which in turn adversely affects the loads connected to the system and the supply itself. This study aims to analyze the quality of THD in Bubung Tujuh Hamlet, Sangku Village. In this study, THD measurements were carried out and analyzed the effect of harmonics on the power factor using a linear regression test. The results of the measurement and analysis of THDV ranged from 1.0% - 6.8%, with the final analysis of THDV still meeting the set standard of 5%. THDI ranged from 2.3% - 66.7% with the final analysis THDI did not meet the standard. THD of the village's electrical system is still at the standard limits set and THD(V) effect on PF.
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Budi Aryawan, I. Putu, Antonius Ibi Weking e I. Wayan Rinas. "ANALISIS PEMASANGAN FILTER PASIF DAN AKTIF TERHADAP KANDUNGAN HARMONISA DAN RUGI-RUGI DAYA GARDU DISTRIBUSI KA 2085 DI PT. PLN (Persero) DISTRIBUSI BALI RAYON MENGWI". Jurnal SPEKTRUM 5, n. 1 (25 giugno 2018): 41. http://dx.doi.org/10.24843/spektrum.2018.v05.i01.p06.
Testo completoAbstract (sommario):
Operation of nonlinear loads can cause harmonic distortion in the voltage and current waveforms that result in abnormal electrical system condition. Content THD (Total Harmonics Distortion) an excess flow can cause power quality systems become worse, thus causing the system power factor is lower. Active filter and Passive filter which aims to reduce harmonics that arise. Analysis THD simulation and measurement results in accordance with IEEE 519-2014 and analysis designing of a passive filter and active filter is right to suppress harmonic distortion. The analysis shows that the installation of active filters causes the current and voltage THD contents to comply with the standard IEEE 519-2014 standards is ?12% and 5%. The use of passive and active filters can reduce THDi content to 8.45% and 3.07%, respectively. While for THDv decreased respectively to 3.68% and 3.45% which already meet the IEEE 519-2014 standards. Power losses decreased respectively to 4.36 kW and 3.86 kW. Installation of active filters is better for reducing THD (Total Harmonics Distortion) and power losses in KA 2085 transformers.
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Han, T., e R. S. Paranjpe. "A Finite Volume Analysis of the Thermohydrodynamic Performance of Finite Journal Bearings". Journal of Tribology 112, n. 3 (1 luglio 1990): 557–65. http://dx.doi.org/10.1115/1.2920293.
Testo completoAbstract (sommario):
A rigorous thermohydrodynamic (THD) analysis of finite journal bearings has been developed. THD analysis not only allows a more accurate prediction of the bearing performance characteristics, but it also provides the temperature distribution in the bearing. It involves the simultaneous solution of the Reynolds and energy equations and can handle a wide variety of flow situations, including reverse flow, recirculating flow, and cavitation. The overall numerical scheme is based on a fully conservative finite-volume formulation. The calculated results are compared with the published literature. The qualitative agreement is good. Sample calculations for a typical automotive bearing show that the oil supply pressure and supply configuration significantly affect the bearing performance.
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Yang, Zhou, L. San Andres e D. W. Childs. "Thermohydrodynamic Analysis of Process-Liquid Hydrostatic Journal Bearings in Turbulent Regime, Part II: Numerical Solution and Results". Journal of Applied Mechanics 62, n. 3 (1 settembre 1995): 679–84. http://dx.doi.org/10.1115/1.2896000.
Testo completoAbstract (sommario):
A finite difference scheme is implemented to solve the nonlinear differential equations describing the turbulent bulk-flow on the film lands of a hydrostatic journal bearing (HJB). A Newton-Raphson scheme is used to update the recess pressures and to satisfy the mass continuity requirement at each bearing recess. Comparisons of numerical predictions from the thermohydrodynamic (THD) model with experimental measurements of mass flow rate, fluid temperature, and static stiffness coefficient from a LH2 test HJB article show very good agreement. In particular, the exit temperature of the bearing is lower than the supply temperature; i.e., the liquid temperature decreases along the bearing length. Similar values of direct stiffness and damping coefficients are predicted by the adiabatic THD model and other considering isothermal flow characteristics. However, the THD model predicts lower cross-coupled stiffness and whirl frequency ratio (WFR < 0.5). The results show that for the application presented, the LH2 hydrostatic bearing is more stable than previously thought.
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Savitha, M., e S. Nagaraja Rao. "Switching angle optimization and fault analysis of a multistring-multilevel inverter for renewable-energy-source applications". Clean Energy 6, n. 6 (1 dicembre 2022): 907–30. http://dx.doi.org/10.1093/ce/zkac055.
Testo completoAbstract (sommario):
Abstract In this paper, a multistring-multilevel inverter (M-MLI) for renewable-energy-source applications has been proposed with reduced switch count and harmonics along with single-switch fault analysis for various levels. It requires only ‘m+1’ power switches for ‘m’ voltage levels. The proposed work achieves the fine-tuning of switching angles using a metaheuristic technique, i.e. the teaching–learning-based optimization algorithm (TLBOA), to mitigate the total harmonic distortion (THD) of the M-MLI. Furthermore, the proposed TLBOA has been compared with conventional modulation techniques such as equal phase (EP), half-equal phase (HEP), near-level control (NLC) and Newton–Raphson (NR) to verify the effectiveness of TLBOA for various voltage levels in terms of % voltage-THD (%V-THD), computational time and methodology. By fine-tuning the switching angles, the %V-THD is improved significantly when compared with EP, HEP, NLC and NR modulation techniques. For an 11-level single-phase M-MLI, the %V-THD using TLBOA at 0.91 modulation index (MI) is 5.051%. The lower-order harmonics, i.e. 5, 7, 11 and 13, are eliminated to improve the power quality. Furthermore, MLIs are often prone to failure, resulting in waveform distortion. The extreme reduction in power quality impacts the load and significant damage is likely. The location of the open-circuit fault to be identified becomes more tedious under the faulty conditions with increased switch counts and voltage levels since the mathematical modelling fails to address the scenario in less computational time. Hence, the machine-learning approach, i.e. support vector machine (SVM) with Bayesian optimization, has been discussed to locate the faulty switch. Finally, the proposed M-MLI configuration has been modelled, simulated and validated using MATLAB® and Simulink®. The results of the M-MLI configuration have been verified for 7, 9 and 11 levels using TLBOA along with fault analysis using the SVM approach.
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Larkin, D. J., L. V. Interrante e A. Bose. "Application of chemical vapor deposited yttria for the protection of silicon carbide fibers in a SiC/Ni3Al composite". Journal of Materials Research 5, n. 11 (novembre 1990): 2706–17. http://dx.doi.org/10.1557/jmr.1990.2706.
Testo completoAbstract (sommario):
A CVD process has been developed for coating Textron-Avco SCS-6 SiC fiber with yttria. Both Y(fod)3·H2O and Y(thd)3 (fod = 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedionato; thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) were examined as potential Y2O3 CVD precursors. Analysis of the deposits by Auger spectroscopy indicated significant F and C'incorporation in the case of Y(fod)3 · H2O whereas, under appropriate conditions, Y(thd)3 gave a deposit which was essentially free of C and other impurities. GCFTIR analysis of the volatile products of the CVD process indicated isobutylene, tetrafluoroethylene, 1,1-difluoroethylene, fluoroform, and fluoroethylene for Y(fod)3 · H2O and mainly isobutylene and propylene for Y(thd)3. The precursor Y(thd)3 was chosen to deposit 1–2 μm of yttria on short lengths of silicon carbide fibers. The coated fibers were then incorporated into a nickel aluminide (Ni3Al) matrix by reactive sintering, with yttria affording protection from the known SiC + 2Ni ⇉ Ni2Si + C degradation process. The SiC/Ni3Al composites, before and after annealing at 1000 °C for up to 100 h, were studied by using SEM and EMPA to determine the extent of reaction. With the exception of certain portions of the fibers that were inadequately coated with yttria, complete protection of the fibers was indicated.
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Hariton, Anamaria, Cristian Zet e Cristian Foșalǎu. "Distortion Analysis for Programmable Analog Signals Generated Using FPGA". Bulletin of the Polytechnic Institute of Iași. Electrical Engineering, Power Engineering, Electronics Section 68, n. 1 (1 marzo 2022): 49–65. http://dx.doi.org/10.2478/bipie-2022-0003.
Testo completoAbstract (sommario):
Abstract Practical applications in electrical engineering often deal with analog signals, but there are employed also digital circuits and microcontrollers. Sometimes it is easier or cheaper to improvise DA and AD converters instead of using dedicated ones. This paper is a comparative analysis of how accurate the analog signals can be generated from digital systems, like Field Programmable Gate Arrays (FPGAs) using only additional passive circuits. For this analysis, different FPGAs families were tested. Two alternatives of generating analog signals were considered in this study: PWM and R2R network. The analysis has been performed for a common frequency band, from 100 Hz to 30 kHz, using a virtual instrument for building an automated test system. At 10 kHz the PWM module obtains better THD values, reaching even 0.013% and at 30 kHz the R2R module obtains better THD values, reaching even 0.222%.
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Maklakov, Alexander S., Tao Jing e Alexander A. Nikolaev. "Comparative Analysis of Current and Voltage THD at Different Grid Powers for Powerful Active Front-End Rectifiers with Preprogrammed PWM". Machines 10, n. 12 (1 dicembre 2022): 1139. http://dx.doi.org/10.3390/machines10121139.
Testo completoAbstract (sommario):
Preprogrammed pulse width modulation (PPWM) techniques are drawing a great deal of interest due to their strong harmonic performance. However, there have not yet been any systematic studies or elaboration of the influence of different grid powers on current and voltage THD using PPWM. Therefore, this article focuses on a comparative analysis of current and voltage THD in a system with a three-phase, three-level active front-end (AFE) at different grid powers by applying PPWM. A six-pulse electric drive power circuit and one laboratory measurement platform were designed and set up to achieve the above goals. The comparative results were calculated up to the 50th (THD50) and 100th (THD100) harmonics against the frequency of the PPWM, ranging between 150 Hz and 750 Hz. The grid power and AFE power ratio was between 30 and 230 under three different AFE-consumed currents. The experimental results were analyzed and compared, and they demonstrated for the first time how the grid power and AFE power ratio with different PPWM patterns can influence current and voltage THD. The research results suggest that it is necessary to review the existing calculation methods for current and voltage THD using modern electric power quality standards. The results presented in this article also provide a reference point for researchers and engineers when considering the electromagnetic compatibility (EMC) of nonlinear consumers in the design of similar circuits.
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Khamis, Aziah, Yan Xu e Azah Mohamed. "Comparative Study in Determining Features Extraction for Islanding Detection using Data Mining Technique: Correlation and Coefficient Analysis". International Journal of Electrical and Computer Engineering (IJECE) 7, n. 3 (1 giugno 2017): 1112. http://dx.doi.org/10.11591/ijece.v7i3.pp1112-1124.
Testo completoAbstract (sommario):
A comprehensive comparison study on the datamining based approaches for detecting islanding events in a power distribution system with inverter-based distributed generations is presented. The important features for each phase in the island detection scheme are investigated in detail. These features are extracted from the time-varying measurements of voltage, frequency and total harmonic distortion (THD) of current and voltage at the point of common coupling. Numerical studies were conducted on the IEEE 34-bus system considering various scenarios of islanding and non-islanding conditions. The features obtained are then used to train several data mining techniques such as decision tree, support vector machine, neural network, bagging and random forest (RF). The simulation results showed that the important feature parameters can be evaluated based on the correlation between the extracted features. From the results, the four important features that give accurate islanding detection are the fundamental voltage THD, fundamental current THD, rate of change of voltage magnitude and voltage deviation. Comparison studies demonstrated the effectiveness of the RF method in achieving high accuracy for islanding detection.
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Vinothini, K., e P. Maruthupandi. "Performance Analysis of Isolated Bridgeless SEPIC Converter for EV Battery Charging". March 2022 4, n. 1 (9 maggio 2022): 28–39. http://dx.doi.org/10.36548/jucct.2022.1.004.
Testo completoAbstract (sommario):
The conventional Electric Vehicle(EV) battery charging systems with power factor correction circuits have limitations due to conduction losses present in the input side bridge rectifiers. This paper presents a Bridgeless Isolated Single-Ended Primary Inductance Converter (SEPIC) with improved power factor and reduced THD to increase performance. Throughout the charging time of the Electrical Vehicle, the input side maintains a near-unity power factor. Because the DBR is eliminated, the current is conducted through a smaller number of devices, resulting in considerable reductions in conduction losses. This optimizes the charging system's efficiency in alternative to the existing BL SEPIC converter. A constant current/constant voltage controlling mode is used to charge the EV battery, which delivers good results in terms of intrinsic PFC and decreased THD, hence increasing the charging performance of this system.
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Mahabharathi, S., e S. Sowkarthika. "A Performance Analysis of Switched Capacitor Based Multilevel Inverter". March 2022 4, n. 1 (26 aprile 2022): 19–31. http://dx.doi.org/10.36548/jeea.2022.1.003.
Testo completoAbstract (sommario):
A multilayer inverter based on Switched Capacitors (SC) using the Nearest Level Modulation (NLM) technique has been presented. To generate five levels, this multilevel inverter employs eight switches and two capacitors. The technique of nearest level modulation is used to provide a high-quality output voltage with low harmonic content. According to the simulation results, the expected inverter has lower Total Harmonic Distortion (THD) than a conventional inverter, using a voltage balancing control mechanism. The voltage on the DC-link capacitor is balanced using the NLM method. Through a SC-based inverter in the NLM approach, different voltage levels can be produced with a high voltage gain, resulting in less power outages, less turning stress, and better converter efficiency. As a result, no further devices are required to balance the voltage of both capacitors. The proposed system is simulated with MATLAB/SIMULINK, and its THD performance is tracked.
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Mahabharathi, S., e S. Sowkarthika. "A Performance Analysis of Switched Capacitor Based Multilevel Inverter". March 2022 4, n. 1 (26 aprile 2022): 19–31. http://dx.doi.org/10.36548/jeea.2022.1.003.
Testo completoAbstract (sommario):
A multilayer inverter based on Switched Capacitors (SC) using the Nearest Level Modulation (NLM) technique has been presented. To generate five levels, this multilevel inverter employs eight switches and two capacitors. The technique of nearest level modulation is used to provide a high-quality output voltage with low harmonic content. According to the simulation results, the expected inverter has lower Total Harmonic Distortion (THD) than a conventional inverter, using a voltage balancing control mechanism. The voltage on the DC-link capacitor is balanced using the NLM method. Through a SC-based inverter in the NLM approach, different voltage levels can be produced with a high voltage gain, resulting in less power outages, less turning stress, and better converter efficiency. As a result, no further devices are required to balance the voltage of both capacitors. The proposed system is simulated with MATLAB/SIMULINK, and its THD performance is tracked.
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Siddiqui, Umar Farooq, e Pallavi Bondriya. "THD Analysis of Induction Motor Using Solid State Switching Devices". International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering 04, n. 01 (20 gennaio 2015): 347–56. http://dx.doi.org/10.15662/ijareeie.2015.0401041.
Testo completo
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Saxena, Snigdha, Peeyush Chandra e Prawal Sinha. "THD Analysis of Non-Constant Gap, Externally Pressurized Conical Bearings". Tribology Transactions 38, n. 2 (gennaio 1995): 438–44. http://dx.doi.org/10.1080/10402009508983426.
Testo completo
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Kumar, Mahender, M. A. Uqaili, Z. A. Memon e Bhagwan Das. "Mathematical Modeling of THD Mitigation Using HAPF for UPS System with Experimental Analysis via Hybrid Interface of Optical USB and Power Quality Meter". Mathematical Problems in Engineering 2021 (29 settembre 2021): 1–15. http://dx.doi.org/10.1155/2021/3981287.
Testo completoAbstract (sommario):
This paper discusses a novel analysis scheme based on the hybrid interface of Optical USB and Power Quality Meter for measuring Total Harmonic Distortion (THD) that exists in the Uninterruptable Power Supply (UPS) system and connected load. The designed hybrid interface experimentally analyzes the power quality and harmonics of the Uninterrupted Power Supply (UPS) system, and mitigation is proposed with the proposed Single-Phase Hybrid Active Power Filter (HAPF) based on instantaneous Power Theory (PQ) with hysteresis control technique and synchronous frame reference (DQ) with hysteresis control techniques at nonlinear load. This study authenticates and gives appropriate measurements in analyzing the harmonics and voltage distortion during conversion of power. The designed work offers the compensation and elimination of harmonic currents using PQ and DQ theory at different nonlinear loads. The proposed HAPF for the UPS system has demonstrated the significant reduction in THD using proposed Power Theory (PQ) with hysteresis control technique from 46.58% to 1.51% and by using DQ theory with hysteresis control technique has reduced THD from 46.58% to 1.38%. Finally, the results are compared between PQ and DQ. It is validated via results that DQ theory eliminated harmonics and also having less THD as compared to PQ-theory. Furthermore, one of the key aspects of the work is the analysis of power quality using Optical USB Interface (OC4USB) and FLUKE series power quality analyzer.