Windage Research Articles

A Bi-Level Optimized Dispatching Method for Grids with High Penetration of New Energy Considering Ancillary Service Costs

To address the issue of high auxiliary service costs caused by the grid connection of new energy generation, a dual layer optimization scheduling method for high penetration new energy power grids is proposed, taking into account the auxiliary service costs of grid connection. The correlation between the output fluctuations and load fluctuations of new energy generation is analyzed, and a calculation model for auxiliary service costs caused by grid connection of new energy generation is established. Taking into account the timescale division requirements for grid energy trading and auxiliary service market transactions, a new high penetration energy grid two-level optimization scheduling model is established. The upper level scheduling model aims to minimize the sum of grid energy procurement costs and auxiliary service costs caused by new energy generation and completes the optimization scheduling of the grid for several hours. The lower level scheduling model aims to closely follow the upper level scheduling plan for new energy power plants/groups. Optimization and scheduling of the power grid for tens of minutes is completed, taking into account the balanced allocation of wind and solar losses among various power plants within the new energy power plant group. The simulation results show that the method proposed in this paper can reduce the energy transaction costs and auxiliary service transaction costs of the power grid during low and peak load periods.

Wellbeing, quality of life and satisfaction of patients with hard-to-heal wounds: a descriptive study.

A hard-to-heal wound is defined as a wound that failed to proceed through the normal phases of wound healing in an orderly and timely manner. The purpose of this article is to describe the impact of hard-to-heal wounds on the wellbeing, quality of life (QoL) and satisfaction with QoL of patients in Oman with hard-to-heal wounds. A descriptive cross-sectional study of patients with hard-to-heal wounds attending three tertiary care hospitals using a self-reported questionnaire was conducted. A total of 275 patients took part in the study. Patients reported a low wellbeing score (67.06±19.72), moderate QoL score (52.18±25.07) and moderate satisfaction scores (68.91±23.88). Significant mean differences were reported with age, sex, educational level, monthly income and type of wound all at p<0.05. The findings of this study demonstrated that hard-to-heal wounds could influence the wellbeing, QoL and overall satisfaction with QoL of patients. Funding was received through an internal grant of the Sultan Qaboos University to conduct the research conducting the research (IG/CON/FACN/20/01). The authors have no conflicts of interest to declare.

Performance of a gelling fibre dressing in management of wounds in a community setting: a sub-analysis of the VIPES study.

To evaluate the use and performance of a gelling fibre dressing (Biatain Fiber; Coloplast A/S, Denmark) in the management of wounds in community nursing practice. A sub-analysis of the prospective, observational, real-world VIPES (Observatoire en Ville des Plaies ExSudatives) study was conducted. Patients with exuding wounds, for which nurses chose to apply the gelling fibre as a primary dressing, were included. Outcomes included assessments of wound condition and patient/nurse opinion. Overall, 149 patients with acute (n=52; 34.9%) or hard-to-heal (chronic) (n=97; 65.1%) wounds were included. At baseline, mean±standard deviation wound age was 351.5±998.2 days, 108 (72.5%) wounds were moderately-to-highly exuding, and 126 (84.6%) showed exudate pooling in the wound bed. At the last follow-up visit, 29 (19.5%) wounds had healed, within a median of 36 days, and 64 (43.0%) were progressing towards healing. From baseline to the last follow-up visit, significant reductions in wound surface area (p<0.05), depth (p<0.01), exudate level (p<0.0001), and in the proportion of wounds with sloughy tissue (p<0.0001) were observed. Most wounds had no (n=86; 58.5% (two missing values)) or low exudate pooling (n=45; 30.6% (two missing values)) at the last visit and proportions of patients with healthy wound edges/periwound skin increased from baseline. At the last visit, wounds were considered improved by nurses in 71.4% (n=105) of cases, and by patients in 66.7% (n=98) of cases (two patients missing). Patients who received treatment with the gelling fibre experienced improvements in the condition of a range of complex wounds. This analysis highlights the importance of adequate exudate management, and indicates how the selection of an appropriate wound dressing can encourage healing progression. This study was financially supported by Laboratoires Coloplast SAS, Paris, France. Coloplast A/S funded the writing and editing of the article and contributed to its content. Coloplast A/S and Laboratoires Coloplast SAS reviewed the article for scientific accuracy. Nurses received financial compensation for their participation in the study. NA is a full-time employee of Coloplast A/S. APJ was an employee of Coloplast A/S when this article was written. FA was a full-time employee of Laboratoires Coloplast SAS at the time of publication development. RS and CJ are full-time employees of CEN Biotech. AK received an educational grant from Coloplast A/S to provide scientific input to the publication. The authors have no other conflicts of interest to declare.

Analysis of Parasitic Parameters and Winding Loss Characteristics of High-Frequency Transformer under Different Winding Structures

Abstract With the development of the smart grid and the increasing access of renewable energy to the distribution grid, the traditional AC power grid puts forward an urgent demand for power electronic transformer (PET). The high-frequency transformer (HFT) serves as the core equipment of PET, and its electromagnetic structure and parasitic parameters are the hot spot of study in the field of power electronics. In this paper, the parasitic parameters, winding loss, and leakage magnetic field characteristics of the 20 kHz, 20 kVA HFT are investigated under different winding structures. The results show that the higher the degree of crossover of HFT winding, the lower the leakage magnetic field. The cross winding reduces winding loss and leakage inductance, and also attenuates the impact of frequency variations. The higher the winding height, the lower the leakage inductance. As the insulation thickness increases, the leakage inductance rises. The distribution capacitance varies opposite to the leakage inductance. Based on the analysis of winding loss and parasitic parameters, as well as the consideration of insulation, the final winding layout, the height of winding and the thickness of insulation of the HFT are determined.

Simulation of temperature rise in low voltage winding of natural oil circulation transformer and analysis of oil flow heat dissipation

Abstract The heat dissipation performance of an oil-immersed transformer is the key to its stable operation. Winding loss is a crucial part of transformer heat loss, and winding heat dissipation greatly influences the rise in transformer temperature. In this paper, depending on the finite element method, the magnetic field distribution of a 66 MVA (225/26.4 kV) natural oil circulation transformer is analyzed, and the DC and eddy current losses of the low voltage winding are calculated. Based on the finite volume method, the temperature field distribution of the low-voltage winding is calculated, and the heat flux distribution of the contact surface between the disc insulation paper and the oil flow is obtained. It is found that there are transition points and extreme points between the upper and lower surface of the disc and the inner and outer surface of the disc, and the heat flux on the upper and lower surface of the disc conductor has obvious alternating oscillation. This study provides direction for further analysis and understanding of the heat dissipation mechanism and structural design of natural oil circulation transformers.

Wind Roche-lobe Overflow in Low-mass Binaries: Exploring the Origin of Rapidly Rotating Blue Lurkers

Wind Roche-lobe overflow (WRLOF) is a mass-transfer mechanism proposed by Mohamed and Podsiadlowski for stellar binaries wherein the wind acceleration zone of the donor star exceeds its Roche-lobe radius, allowing stellar wind material to be transferred to the accretor at enhanced rates. WRLOF may explain characteristics observed in blue lurkers and blue stragglers. While WRLOF has been implemented in rapid population synthesis codes, it has yet to be explored thoroughly in detailed binary models such as MESA (a 1D stellar evolution code), and over a wide range of initial binary configurations. We incorporate WRLOF accretion in MESA to investigate wide low-mass binaries at solar metallicity. We perform a parameter study over the initial orbital periods and stellar masses. In most of the models where we consider angular momentum transfer during accretion, the accretor is spun up to the critical (or breakup) rotation rate. Then we assume the star develops a boosted wind to efficiently reduce the angular momentum so that it could maintain subcritical rotation. Balanced by boosted wind loss, the accretor only gains ∼2% of its total mass, but can maintain a near-critical rotation rate during WRLOF. Notably, the mass-transfer efficiency is significantly smaller than in previous studies in which the rotation of the accretor is ignored. We compare our results to observational data of blue lurkers in M67 and find that the WRLOF mechanism can qualitatively explain the origin of their rapid rotation, their location on the H-R diagram, and their orbital periods.

Interleaved ZVS DC‐DC converter with ultrahigh step‐down and flexible gain

AbstractThis paper proposes a novel non‐isolated ultrahigh step‐down interleaved DC‐DC converter with an extremely extended duty cycle based on the series capacitor and coupled‐inductor techniques. The proposed converter utilizes a three‐winding coupled inductor (TWCI) to enhance the step‐down conversion ratio. In contrast to conventional coupled inductor‐based step‐down converters, its voltage gain improves as the turn ratio approaches unity. Consequently, coupled inductors have significantly lower winding losses. Furthermore, there is no extra constraint on the turn ratio of the TWCI. It results in a highly flexible voltage gain and more design freedom. Other advantages of the employed series capacitor and coupled inductor techniques can be listed as, zero voltage switching (ZVS) condition for all switches, significant reduction of the total switching device power (SDP) and recovery of the energy of leakage inductors. They all reduce power losses and costs. Steady‐state analysis, derivation of voltage gain and design considerations are discussed in detail. Finally, a 200 W, 400‐to‐12 V experimental prototype is implemented to verify the effectiveness and feasibility of the proposed converter.

Correlation of powers of Hüsler–Reiss vectors and Brown–Resnick fields, and application to insured wind losses

Hüsler–Reiss vectors and Brown–Resnick fields are popular models in multivariate and spatial extreme-value theory, respectively, and are widely used in applications. We provide analytical formulas for the correlation between powers of the components of the bivariate Hüsler–Reiss vector, extend these to the case of the Brown–Resnick field, and thoroughly study the properties of the resulting dependence measure. The use of correlation is justified by spatial risk theory, while power transforms are insightful when taking correlation as dependence measure, and are moreover very suited damage functions for weather events such as wind extremes or floods. This makes our theoretical results worthwhile for, e.g., actuarial applications. We finally perform a case study involving insured losses from extreme wind speeds in Germany, and obtain valuable conclusions for the insurance industry.

A calculation method of winding loss of high frequency transformer based on finite element method

In this paper, a winding loss calculation method used in the field of converter transformers is introduced into the realm of high-frequency transformers for the first time. In addition, the impact of winding structure on the calculation accuracy of the method is considered for the first time. Comparing the calculation results of this method with those of the formula method, based on the results of finite element simulation. The feasibility of using this method to calculate the winding loss of a high-frequency transformer is verified. First, the winding loss of rectangular wire commonly used in small-capacity high-frequency transformers is analyzed. Based on the finite element simulation results, the accuracy of the hybrid method is compared with the formula calculation method to demonstrate the feasibility of the hybrid method. Then, using the same method, the accuracy of the hybrid method in calculating the winding loss of the circular wire, which is also used in small-capacity high-frequency transformers, is compared with the formula method. The maximum number of continuous winding layers has been modified, and the outcomes for various layers are being computed. Finally, the cross-transposition winding structure is also calculated, demonstrating that the hybrid method is not only applicable to wires of various shapes but also compatible with different winding structures. The results show that the hybrid method has good calculation accuracy and applicability. It can provide more precise calculation results for the winding loss of high-frequency transformers with various winding shapes.

AC Loss Estimation Method for REBCO Superconducting Tapes in AC+DC Fields for Field Windings in Fully Superconducting Synchronous Machine for Electric Aircraft

Abstract The estimation of AC loss in REBa2Cu3O y (REBCO; RE = rare earth, such as Y, Eu, and Gd) superconducting tapes within superconducting synchronous motors and generators for electric aircraft is imperative during the design stage phase to optimize efficiency and cooling considerations. Our previous studies clarified the AC loss characteristics, focusing on estimating the AC loss in armature windings. While the magnetic field applied to the armature windings is exclusively as an AC field, the field windings are subject to a composite field comprising both AC and DC components. Notably, the amplitude of the AC component is markedly smaller than the magnitude of DC component. This study experimentally investigated to consider the AC loss properties in field windings. The experimental results were as follows: When subjected to operational conditions of field windings within synchronous motor and generator, the AC loss increased with the DC field strength. This property is attributed to a reduction in the critical current induced by the external field. Hence, we modified the method for estimating AC loss. Subsequently, we validated the effectiveness of the modified method.

Polymeric Nanoparticles for Wound Healing.

Skin injury is one of the most prevalent lesions in humans, and many such wounds, including deep burns and chronic skin wounds, are notoriously difficult to heal. It has been established by medical practitioners that current wound therapies are not perfectly effective and are far from satisfactory. Meanwhile, nanotechnologies have made it possible to develop pharmaceutical formulations that can elevate the effectiveness of conventional pharmacotherapies to entirely new heights. Most nanostructured biomaterials used to treat wounds, including those that have helped establish this fascinating subject, have been polymeric. The bibliographic analysis presented here shows a steady growth in the research output of studies on the use of polymeric nanoparticles in wound healing therapies. This article provides an overview of polymeric nanoparticles for the treatment of wounds with an emphasis on different chemistries and polymer-drug combinations that have been proven the most effective. The wound age, pathophysiology, wound healing treatments of the present and past, as well as the physicochemical nature and methods for the synthesis of polymeric nanoparticles, are all covered in the opening parts of the review. The existing polymeric nano-drug delivery systems with the greatest promise for wound healing and skin regeneration are subsequently addressed and their potentials summarized.

Optimization of conductors arrangement in slot for alternating current winding losses reduction

PurposeThe purpose of this study is to evaluate and minimize the losses of alternating current (AC) in the winding of electrical machines. AC winding losses are frequently disregarded at low frequencies, but they become a significant concern at high frequencies. This is the situation where applications require a high speed. The most significant applications in this category are electrical propulsion and drive systems.Design/methodology/approachAn analytical model is used to predict the AC losses in the winding of electrical machines. The process involves dividing the slot into separate layers and then calculating the AC loss factor for each layer. The model aims to calculate AC losses for two different winding arrangements involving circular conductors. This application focuses on the stator winding of a permanent magnet synchronous motor that is specifically designed for electric vehicles. The model is integrated into an optimization process that makes use of the genetic algorithm method to minimize AC losses resulting from the arrangement of conductors within the slot.FindingsThis study and its findings demonstrate that the arrangement of the conductors within the slot has a comparable effect on the AC losses in the winding as the machine's geometric and physical properties. The effectiveness of electrical machines depends heavily on optimizing the arrangement of conductors in the slot to minimize AC winding losses.Originality/valueThe proposed strategy seeks to minimize AC winding losses in high-speed electric machines by providing a cost-effective and precise solution to improve energy efficiency.

Influence of Scallops on Windage Loss and Flow Characteristics in Disk-Type Gap

Abstract Windage loss and flow characteristics in a disk-type gap featuring scalloped structures are investigated in this paper. Special attention is paid to the size of the scallops and the associated loss models. The respective losses and scallop effects in the gap are explored with various combinations of depths, quantities, and rotating speeds. The results indicate that scallop structures positively contribute to increased windage losses, accounting for more than 60% of the overall losses. An internal spiral vortex band is formed along the scallop wall, with the scallop depth ratio exerting influences on loss, reaching a maximum of 8.1%. The current scallop loss model overlooks the consideration of the total arc length ratio of scallops to the circumference, presenting a limitation, and the maximum relative deviation from numerical simulation results is observed to be 111.4%. An increase in arc length ratio results in a higher total loss, although the loss per individual scallop is diminished, manifesting in reduced vortices and pressure differences. Furthermore, a modified model is proposed to increase the precision of the current loss model. The maximal relative deviations of 13.8% confirm that the modified model is accepted to predict the windage loss in disk-type gaps with scallops. The conclusions offer valuable insights into the structural design of impellers and high-speed electrical machines with superior efficiency.

Design of coils for high-power medium-frequency transformers using Grain-Oriented hot cores

This article proposes a design of windings for medium-frequency transformers (MFTs) at the heart of high-power Solid-State Transformers (SSTs). With aluminum interleaved foils of the correct thicknesses, it is possible to obtain low winding losses and a very low leakage inductance well adapted to high-power SSTs able to operate in the medium-voltage grid (5–20 kV). The MFT equivalent resistance and leakage inductance are determined using an analytical model based on Dowell’s hypotheses. Several interleaved winding configurations are analyzed and compared to the standard structure made of two concentric foil coils. The experimental validation is made with short-circuit tests of an MFT fed by a low-level square voltage source at several kHz, which can provide the necessary high current.

Correlation of wind and precipitation annual aggregate severity of European cyclones

AbstractThis study has investigated the correlation between wind gust and precipitation annual aggregate severity arising from extratropical cyclones over the Europe‐Atlantic region. Annual aggregate severity indices have been constructed by summing exceedances above chosen damage thresholds of wind gust and precipitation accumulation for all storms. A strong positive correlation between wind and precipitation aggregate severity exists at low thresholds. At higher thresholds where severity indices are a better reflection of wind and flood losses, negative correlations occur over Western Europe. These aggregates should therefore not be assumed to be either independent or positively correlated.

Study on windage loss characteristics of supercritical CO2 Taylor-Couette-Poiseuille flows

Taylor-Couette-Poiseuille (TCP) flow is prevalent in rotating machinery, occurring extensively between a high-speed rotating shaft and its static case. This study employed a numerical simulation method to investigate the flow characteristics and windage loss in supercritical carbon dioxide (sCO2) TCP flow. The findings revealed that increasing the rotational Reynolds number and aspect ratio and decreasing the axial Reynolds number and radius ratio reduced the friction coefficient (Cf). Ultimately, a Cf correlation for sCO2 TCP flow was derived through fitting simulation results, exhibiting an average relative error within ± 2 %. These results established a theoretical foundation for the structural design of sCO2 rotating machinery.

AC loss study on a 3-phase HTS 1 MVA transformer coupled with a three-limb iron core

High-temperature superconducting (HTS) technology provides an alternative approach to achieve compact transformers. Addressing AC loss in the HTS winding is crucial for HTS transformer applications. Most numerical AC loss studies on HTS transformers have neglected the influence of iron cores. This work carries out an AC loss study to explore the impact of an iron core on the HTS windings in a 3-phase HTS 1 MVA transformer coupled with it. AC loss simulations for the transformer winding both with and without the iron core are conducted by adopting the three-dimensional (3D) T-A homogenization method. When the iron core is incorporated, the saturation magnetic fields of iron materials, flux diverters (FDs) with different geometries, and variations in turn spacings in the LV winding composed of Roebel cables are considered to investigate their influence on the AC loss of the transformer winding. The inclusion of the iron core leads to a 1.2% increase in AC loss for the transformer winding while simulating at the rated current. We attribute this slight difference to the non-inductive winding structure of the transformer winding, where a strong magnetic field generated in the space between the LV and HV windings effectively shields the influence of the iron core.

Transmission Expansion Planning Considering Storage, Flexible AC Transmission System, Losses, and Contingencies to Integrate Wind Power

To meet future load projection with the integration of renewable sources, the transmission system must be planned optimally. Thus, this paper introduces a comparative analysis and comprehensive methodology for transmission expansion planning (TEP), incorporating the combined effects of wind power, losses, N-1 contingency, a FACTS, and storage in a flexible environment. Specifically, the optimal placement of the FACTS, known as series capacitive compensation (SCC) devices, is used. The intraday constraints associated with wind power and energy storage are represented by the methodology of typical days jointly with the load scenarios light, heavy, and medium. The TEP problem is formulated as a mixed-integer nonlinear programming (MINLP) problem through a DC model and is solved using a specialized genetic algorithm. This algorithm is also used to determine the optimal placement of SCC devices and storage systems in expansion planning. The proposed methodology is then used to perform a comparison of the effect of the different technologies on the robustness and cost of the final solution of the TEP problem. Three test systems were used to perform the comparative analyses, namely the Garver system, the IEEE-24 system, and a real-world Colombian power system of 93 buses. The results indicate that energy storage and SCC devices lead to a decrease in transmission requirements and overall investment, enabling the effective integration of wind farms.

Litz-Wire Winding Loss Calculation Method for Optimal Design of High-Frequency Transformers

Litz-Wire Winding Loss Calculation Method for Optimal Design of High-Frequency Transformers

Development of a screening system of gene sets for estimating the time of early skeletal muscle injury based on second-generation sequencing technology.

The present study is aimed to address the challenge of wound age estimation in forensic science by identifying reliable genetic markers using low-cost and high-precision second-generation sequencing technology. A total of 54 Sprague-Dawley rats were randomly assigned to a control group or injury groups, with injury groups being further divided into time points (4h, 8h, 12h, 16h, 20h, 24h, 28h, and 32h after injury, n = 6) to establish rat skeletal muscle contusion models. Gene expression data were obtained using second-generation sequencing technology, and differential gene expression analysis, weighted gene co-expression network analysis (WGCNA) and time-dependent expression trend analysis were performed. A total of six sets of biomarkers were obtained: differentially expressed genes at adjacent time points (127 genes), co-expressed genes most associated with wound age (213 genes), hub genes exhibiting time-dependent expression (264 genes), and sets of transcription factors (TF) corresponding to the above sets of genes (74, 87, and 99 genes, respectively). Then, random forest (RF), support vector machine (SVM) and multilayer perceptron (MLP), were constructed for wound age estimation from the above gene sets. The results estimated by transcription factors were all superior to the corresponding hub genes, with the transcription factor group of WGCNA performed the best, with average accuracy rates of 96% for three models' internal testing, and 91.7% for the highest external validation. This study demonstrates the advantages of the indicator screening system based on second-generation sequencing technology and transcription factor level for wound age estimation.