Residual Flux Research Articles

Eliminating Inrush Current in Transformers using a Residual Flux Control Algorithm

Eliminating Inrush Current in Transformers using a Residual Flux Control Algorithm

Point on Wave Energization Strategy and Sequential Phase Shifting for Sympathetic Inrush Current Mitigation in Three-Phase Transformer - Measurement

Inrush currents generated when an electrical transformer is energized can achieve great values and cause abnormal difficulties in the power grid. The sympathetic inrush current phenomenon is resulted in the power system when a transformer is energized with the existence of other transformer already energized. The main objective of this article is the attenuation of sympathetic inrush current in a three-phase transformer. The control technique is carried out by the consideration of the residual flux value when de-energizing the transformer as well as respecting the three-phase shifting. Moreover, an experimental setup to measure the inrush current will be presented. Furthermore, a technique for controlling the circuit breaker to energize a 2 kVA three-phase transformer which allows the sympathetic inrush current to be attenuated was also applied and tested in the experimental. The contribution of this paper is that this technique is applied in measurements with an in-depth estimation of the residual flux. The proposed technique made it possible to completely eliminate the sympathetic inrush current.

Residual Flux Measurement of Single-phase Transformers based on Equivalent Resistance

Due to the presence of transformer residual flux, the magnetic flux of the core rapidly reaches saturation, thus causing an inrush current when the no-load transformer is directly connected to the grid, which affects the safe operation of the grid. Therefore, it is necessary to study the residual flux in the core to reduce the inrush current. However, the residual flux estimation has a large error. In this paper, a method is proposed to measure the residual flux of the transformer core by solving equivalent resistance and determining the direction of residual flux by the difference between the forward and reverse transient currents. In addition, the relationship between residual flux and equivalent resistance is established, and the empirical formula is obtained for calculating the residual flux. To evaluate the effectiveness of the proposed method, the residual flux of the square core is measured on the constructed experimental platform. Compared with the experimental results, the relative error of the residual flux of the core calculated by the proposed method is within 6%, which has higher accuracy and provides a reference for residual flux estimation.

Research on Residual Flux Measurement Method for Power Transformers

The residual flux of power transformers is an important factor affecting the inrush current. In order to solve the problem of residual flux measurement of power transformers, this paper proposes an indirect measuring method of residual flux based on the first peak value of inrush current. Through the investigation of the relationship between the inrush current, closing angle and residual flux, the value of residual flux can be measured by measuring the inrush current with controlled closing angle of different conditions, and the accuracy and validity of the residual flux measurement method is verified by experiment.

Effect of defects on flux expulsion of pure niobium superconducting radio frequency cavities via spatial temperature gradient

Since flux vortices are easily pinned by defects in superconducting radio frequency (SRF) cavities, trapped magnetic flux increases the surface resistance of the SRF cavity. It has been experimentally demonstrated that trapped magnetic flux can be expelled by cooling down a superconducting cavity under a large spatial temperature gradient. In this paper, we use the time-dependent Ginzburg–Landau (TDGL) theory to theoretically investigate the effect of defects on the flux expulsion ability of pure niobium superconducting cavities with an applied spatial temperature gradient. It is shown that the residual flux vortex density displays a notable stepwise decreasing trend with increasing temperature gradient at smaller residual fields, while it shows a stepwise rising with increasing defect size. Both larger defect number and size make vortices difficult to be expelled. Moreover, long cooling time is beneficial for vortices to be expelled, and the cooling time has nearly no significant effect on flux expulsion under conditions of large cooling times. The results in this paper provide some theoretical guidelines for improving the performance of superconducting cavities in practical situations.

Highly Sensitive and Quantitative Magnetic Nanoparticle-Based Lateral Flow Immunoassay with an Atomic Magnetometer.

Lateral flow immunoassay (LFIA) is a simple point-of-care method for detecting various analytes. However, the lack of test result precision and poor quantification are the main bottlenecks of LFIA. Although magnetic nanoparticles (MNPs) have gained prominence as potent labels in LIFA, the quantitative detection method for trace biomarkers remains to be improved. Here, we propose a promising real-time biosensing platform based on a highly sensitive atomic magnetometer to fulfill the quantitative detection of MNP-based lateral flow immunochromatographic assays. The strategy entails obtaining the residual flux density component spectrum by continuously and linearly scanning the trace MNP label and then resolving the magnetization and quantity from the spectrum. Moreover, we exploit the theoretical model of the magnetic dipole to verify the method's reliability. Regarding carcinoembryonic antigen detection, the atomic magnetometer exhibits a low detection limit of ∼0.01 ng mL-1 with a 100-fold enhancement factor compared to optical detection methods and a more straightforward mechanism than other magnetic detection approaches. Together, these results provide valuable insight for the potential application of atomic magnetometer quantum measurement techniques in intelligent diagnosis and treatment.

Smart Switching in Single-Phase Grid-Connected Photovoltaic Power Systems for Inrush Current Elimination

Grid-connected photovoltaic (PV) power systems are one of the most promising technologies to address growing energy demand and ecological challenges. This paper proposes smart switching to mitigate inrush currents during the connection of single-phase transformers used in PV systems. An effective inrush current mitigation contributes to the reliability of PV systems. The inrush current severity is influenced by the pseudorandom residual flux at the transformer core and the energization point-on-wave. The most common approach to avoid inrush currents is controlled connection, which requires prior knowledge of the residual flux. However, the residual flux can differ in each case, and its measurement or estimation can be impractical. The proposed smart switching is based on a comprehensive analysis of the residual flux and the de-energization trajectories, and only requires two pieces of data (ϕRM and ϕ0, flux values of the static and dynamic loops when the respective currents are null), calculated from two simple no-load tests. It has a clear advantage over common approaches: no need to estimate or measure the residual flux before each connection, avoiding the need for expensive equipment or complex setups. Smart switching can be easily implemented in practical settings, as it considers different circuit breakers with distinctive aperture features, making it cost-effective for PV systems.

Sustainable recycling of aerospace-grade ultra-clean 7050 aluminum alloy melts through argon refining without secondary aluminum dross generation

The refining of aluminum scraps commonly employs nitrogen-fluxes to eliminate impurities. However, the aluminum nitride (AlN) generated by the reaction between nitrogen and the aluminum melt, along with residual fluxes, contribute to low cleanliness of the recycled aluminum melt and pose difficulties for the disposal of secondary aluminum dross (SAD). Our innovative research has resulted in the recycling of aerospace-grade clean aluminum alloy melts. The results indicate that the argon bubble floating process adsorbs inclusions and hydrogen, achieving an aerospace-grade ultra-clean melt. The solid-liquid interface between the tube wall and the melt provides a diffusion channel for hydrogen atoms, and the bubbles rising up along the wall lead to a higher hydrogen content in the melt. The argon refining dross is primarily composed of Al and Al2O3, which can be recycled as a raw material for aluminum electrolysis. Argon refining can decrease the hydrogen content and the number of inclusions with particle size ≥40 μm in the recycled aluminum melt to the level of aerospace aluminum alloy melt. Nonetheless, the particle size ≥20 μm remains 1.5–2.5 times that of primary aluminum.

Improving Efficiency of a Pole-Changing Vernier Machine Considering Residual Magnetic Flux Density

This paper presents the efficiency improvement of a pole-changing vernier machine (PCVM) by considering the residual magnetic flux density (Br) of low coercivity force (LCF) permanent magnets (PMs). The PCVM operates in two modes: vernier machine (VM) mode and permanent magnet synchronous machine (PMSM) mode, achieved through pole-changing. Pole-changing involves reversing the magnetic flux direction of LCF PM to alter the number of rotor pole pairs. By changing the number of rotor pole pairs, the PCVM operates as a VM mode at low speeds, providing high torque, and as a PMSM mode at high speeds, offering high efficiency. To achieve this, a combination of high coercivity force (HCF) PM and LCF PM is utilized in a single structure. The magnetic flux direction in the LCF PM is determined by Br, and the highest efficiency is achieved when Br reaches its maximum value |Brm|. This paper focuses on improving efficiency by obtaining Brm in VM mode and −Brm in PMSM mode through the design process. Additionally, finite element analysis (FEA) is employed to compare the performance of the improved model, which considers Br, with that of the conventional model, designed without considering Br. The improved model achieves higher Br values in each mode compared to the conventional model, resulting in increased torque density. Consequently, this leads to improved efficiency.

Tunable anti-plane wave bandgaps in 2D periodic hard-magnetic soft composites

In this paper, we present a theoretical model for the analysis of large magneto-deformation and the anti-plane shear wave bandgaps in 2D periodic two-phase hard magnetic soft composite structures subjected to magnetic stimuli. The constitutive behavior of the phases in the hard-magnetic soft composite is described using the incompressible Gent model. To solve the incremental anti-plane wave equations, the finite element method and the Floquet–Bloch theorem for periodic media are utilized. Using the developed framework, we numerically study the dependency of the bandgap width and their location on the direction and magnitude of the applied magnetic flux density vector, material parameter contrasts, and geometry and volume fraction of the inclusion phase. The numerical results reveal that significant tunability of the bandgap is achieved when the applied magnetic flux density direction is along the residual magnetic flux density direction. Also, it is seen that the geometry of the inclusion has significant effect on the bandgap width. The crucial inferences from the present investigation can find their potential use in the design and manufacturing of futuristic smart soft wave devices with tunable band structures.

Reliable detection of stick welds at resistance spot welding

Resistance spot welding (RSW) of galvanized steel sheets brings a risk of faulty welds in the form of stick-welds. These differ from high-quality spot welds in the way that only the coatings are joined with a material bond, but the base materials are not fused together. Stick-welds can occur, among other things, in critical material combinations with greatly differing sheet thicknesses or with increased wear of the welding electrodes. Due to the significantly different material-specific strengths of zinc and steel, stick-welds do not meet the required weld strengths. Therefore, it is important to reliably prevent or detect the stick-welds. However, the established and most frequently used non-destructive (NDT) method for spot welds by manual ultrasonic testing reaches its limits in this respect, as the fused zinc layers are almost as sound-conductive as proper spot welds. A promising alternative is the method of passive magnetic flux density testing (pMFT) developed at the Technische Universität Dresden, Chair of Joining Technology and Assembly. With this NDT method, the spot welds are first magnetized and their residual flux density on the surface is measured. Due to the different magnetic properties of the used steel alloys and their zinc-coating, clear differences can be measured between correct and stick-welds. This paper shows the experimental design and the developed procedure for evaluating the spot welds on different galvanized steel sheet alloys. In addition, the high potential of integrating this NDT method into fully automated production lines is shown in order to bridge the gap between the highly automated RSW process and NDT, which can only be carried out manually up to now.

Interpreting the Si ii and C ii Line Spectra from the COS Legacy Archive Spectroscopic SurveY Using a Virtual Galaxy from a High-resolution Radiation-hydrodynamic Simulation

Observations of low-ionization state metal lines provide crucial insights into the interstellar medium (ISM) of galaxies, yet, disentangling the physical processes responsible for the emerging line profiles is difficult. This work investigates how mock spectra generated using a single galaxy in a radiation-hydrodynamical simulation can help us interpret observations of a real galaxy. We create 22,500 C ii and Si ii spectra from the virtual galaxy at different times and through multiple lines of sight and compare them with the 45 observations of low-redshift star-forming galaxies from the COS Legacy Spectroscopic SurveY (classy). We find that the mock profiles provide accurate replicates of the observations of 38 galaxies with a broad range of stellar masses (106–109 M ⊙) and metallicities (0.02–0.55 Z ⊙). Additionally, we highlight that aperture losses explain the weakness of the fluorescent emission in several classy spectra and must be accounted for when comparing simulations to observations. Overall, we show that the evolution of a single simulated galaxy can produce a large diversity of spectra whose properties are representative of galaxies of comparable or smaller masses. Building upon these results, we explore the origin of the continuum, residual flux, and fluorescent emission in the simulation. We find that these different spectral features all emerge from distinct regions in the galaxy’s ISM, and their characteristics can vary as a function of the viewing angle. While these outcomes challenge simplified interpretations of down-the-barrel spectra, our results indicate that high-resolution simulations provide an optimal framework to interpret these observations.

Multiple load operation of indirect matrix converter for different frequencies using symmetrical space vector modulation

AbstractThis study describes an indirect matrix converter (IMC) that uses symmetrical space vector pulse width modulation (SSVPWM) to feed two loads from a single DC link at a variable frequency. Output stage‐I is connected to the static load, while output stage‐II is connected to the PMSM for speed control. It is appropriate for drive systems with variable frequency, such as those seen in wind power generation and aviation. In recent years, significant studies on AC‐AC converters have been conducted due to the rising interest in electric cars and renewable energy. The performance of permanent magnet motors is better than that of other types of AC motors due to their superior performance and residual flux permanent magnets. Contrary to normal back‐to‐back power conversion systems, IMC does not necessitate the use of capacitors in the DC‐link, decoupled control between the two‐stages, a simple clamping circuit or zero current switching in the rectifier stage, allowing the system's volume to be reduced. It is investigated how well the two output stages of the proposed IMC perform. To illustrate the benefits of the suggested IMC design, an improved SSVPWM is employed, and MATLAB/SIMULINK‐based simulations were performed to validate the efficacy of the modulation mechanism. In addition, the real‐time implementation of the work was validated using a real‐time simulator, OPAL‐RT (OP4510).

Accurate transformer inrush current analysis by controlling closing instant and residual flux

This paper proposes a comprehensive process for analyzing accurate transformer inrush current by elaborately controlling the closing instant of a circuit breaker and the level of residual flux in the iron core. The effectiveness of the proposed analyzing process is verified with a laboratory-scaled test system consisting of a 100 kVA 380/320 V Dyn11 three-phase dry-type transformer and a thyristor-based point-on-wave device. Moreover, the measured inrush currents by the proposed process are compared with those calculated by widely accepted inrush current equations. The proposed analyzing process is highly effective to demonstrate the inrush current under the specified energizing condition concerning the closing instant of the voltage and the residual flux in the iron core. The results show that there is a big difference between the measured and calculated inrush currents under the identical energizing condition of the voltage angle with 0° and the residual flux density with approximately 70%.

A comparative study between three of the physical antifouling techniques for oily wastewater filtration using ceramic membranes: Namely; the novel periodic transmembrane pressure technique, pulsatile flow, and backflushing

In this study, we evaluate the performance of the newly developed periodic transmembrane pressure technique (PTMP) in relation to two conventional physical antifouling techniques, namely, backwashing and backpulsing in the context of the filtration of oily water systems using ceramic membranes. The results demonstrate that the novel PTMP established higher performance than the other two techniques. Values of the overall permeate volume, steady-state permeate flux, residual flux, and fouling reversibility using the PTMP were shown to be higher than those of the other two techniques. In addition, visual inspection of the internal surface of membrane channels post-filtration shows that the PTMP achieved a clean as-new surface compared to the other two techniques. Resistances-in-series model analysis was employed to inspect and analyze the development of fouling upon using the three techniques. PTMP presented a negligible internal resistance and a small cake layer resistance compared to backwashing, pulsatile flow, and regular crossflow filtration. The PTMP is therefore a promising physical antifouling method that can be implemented in an existing crossflow filtration system with basic modification, in addition to the ease of use and energy efficiency.

COSMOS2020: Exploring the Dawn of Quenching for Massive Galaxies at 3 < z < 5 with a New Color-selection Method

We select and characterize a sample of massive (log(M */M ⊙) > 10.6) quiescent galaxies (QGs) at 3 < z < 5 in the latest Cosmological Evolution Survey catalog (COSMOS2020). QGs are selected using a new rest-frame color-selection method, based on their probability of belonging to the quiescent group defined by a Gaussian mixture model (GMM) trained on rest-frame colors (NUV − U, U − V, V − J) of similarly massive galaxies at 2 < z < 3. We calculate the quiescent probability threshold above which a galaxy is classified as quiescent using simulated galaxies from the shark semi-analytical model. We find that, at z ≥ 3 in shark, the GMM/NUVU − VJ method outperforms classical rest-frame UVJ selection and is a viable alternative. We select galaxies as quiescent based on their probability in COSMOS2020 at 3 < z < 5, and compare the selected sample to both UVJ- and NUVrJ-selected samples. We find that, although the new selection matches UVJ and NUVrJ in number, the overlap between color selections is only ∼50%–80%, implying that rest-frame color commonly used at lower-redshift selections cannot be equivalently used at z > 3. We compute median rest-frame spectral energy distributions for our sample and find the median QG at 3 < z < 5 has a strong Balmer/4000 Å break, and residual NUV flux indicating recent quenching. We find the number densities of the entire quiescent population (including post-starbursts) more than doubles from 3.5 ± 2.2 × 10−6 Mpc−3 at 4 < z < 5 to 1.4 ± 0.4 × 10−5 Mpc−3 at 3 < z < 4, confirming that the onset of massive galaxy quenching occurs as early as 3 < z < 5.

Dynamic signatures of microplastic distribution across the water column of Yangtze River Estuary: Complicated implication of tidal effects

Riverine microplastic (MP) discharge into the ocean contributes greatly to global MP contamination, yet our understanding of this process remains primitive. To deepen our interpretation of the dynamic MP variation throughout the estuarine water columns, we sampled at Xuliujing, the saltwater intrusion node of the Yangtze River Estuary, over the course of ebb and flood tides in four seasons (July and October 2017, January and May 2018 respectively). We observed that the collision of downstream and upstream currents contributed to the high MP concentration and that the mean MP abundance fluctuated with the tide. A model of microplastics residual net flux (MPRF-MODEL), taking the seasonal abundance and vertical distribution of MP along with current velocity into consideration, was developed to predict the net flux of MP throughout the full water columns. 2154 ± 359.7 t/year of MP was estimated to flow into the East China Sea via the River in 2017–2018. Our study suggests that riverine MP flux can be overestimated due to reciprocating current carried MP from the estuary. Using the tidal and seasonal variation in MP distribution, we calculated the tide impact factor index (TIFI) for the Yangtze River Estuary to be between 38.11% and 58.05%. In summary, this study provides a baseline of MP flux research in the Yangtze River for similar tidal-controlled rivers and a contextual understanding of how to appropriately sample and accurately estimate in a dynamic estuary system. The redistribution of microplastics may be impacted by complex tide processes. Although not observed in this study, it may merit investigation.

A sharp interface immersed edge-based smoothed finite element method with extended fictitious domain scheme

This paper proposes a versatile and robust immersed edge-based smoothed finite element method with the mass conservation algorithm (IESFEM/Mass) to solve partitioned fluid–structure interaction (FSI). A gradient smoothing technique was used to solve the system governing equations, which can improve the calculated capability of the linear triangular elements in two phases. Based on the quadratic sharp interface representation of immersed boundary, an extended fictitious domain constructed by a least squares method approximately corrected the residual flux error. The compatibility for boundary conditions on moving interfaces was satisfied, thus eliminating spurious oscillations. The results from all numerical examples were consistent with those from the existing experiments and published numerical solutions. Furthermore, the present divergence-free vector field had a faster-converged rate in the flow velocity, pressure, and FSI force. Even if in distorted meshes, the proposed algorithm maintained a stable accuracy improvement. The aerodynamics of one- and two-winged flapping motions in insect flight has been investigated through the IESFEM/Mass. It can be seen that the wing–wake interaction mechanism is a vital factor affecting the lift. The applicability of the present method in the biological FSI scenario was also well-demonstrated.

Optimization of Mold Slag for Continuous Casting of Peritectic Steel

To reduce the occurrence of stickers and longitudinal cracks during continuous casting (CC) of peritectic steel, herein, the use of a mold slag with high basicity and adequate lubrication is proposed. Laboratory results indicate that the mold slag with a basicity of 1.75 and 2.3 wt% Li2O content exhibits a lower break and melting temperatures and relatively fast crystallization rate. The proposed mold slag can rapidly induce crystallization to control the heat flux, and the residual flux after crystallization and formation of the solid slag still exhibits excellent lubrication on the initial shell. Thus, coordination control of heat transfer and lubrication during CC of peritectic steel can be achieved. Industrial trials obtain satisfactory results, the application of the designed mold slag reduces the occurrence of stickers, and longitudinal cracks are reduced at the initial stage of one sequence casting.

Research on the torque performance for two multi-pole bilayer magnetorheological fluid couplings

This paper studies on the permanent magnets configuration on the transmission torque of the multi-pole bilayer magnetorheological (MR) coupling. Based on the electromagnetic field theory, the magnetic circuit models of traditional permanent magnet array (TPMA) and Halbach permanent magnet array (HPMA) are established, and the magnetic flux density within the MR fluid working gaps has been derived in order to evaluate the merits of the designed MR coupling. A 3D FE magnetic-fluid analysis has been necessary following the initial conceptual analysis, in order to study the influence of key parameters on the transmission torque. The results show that the transmission torque of the MR coupling with Halbach permanent magnet array is 33.45% higher than that of the ordinary permanent magnet array, with a same structure size. For the MR coupling with Halbach permanent magnet array, the unilateral magnetic focusing effect is better with the increase of the residual flux density of the secondary magnetic pole as well as the radial length of magnetic pole. And the single side magnetic focusing effect is the best when the main magnetic pole is 15°. The influence of the magnetic pole angle on the transmission torque has been further studied.