Search

Accurate calculation of the electromagnetic force distribution of transformer windings under different loads and fault conditions is of great significance for transformer maintenance, condition evaluation and life prediction. Due to the influence of offshore wind power systems, offshore wind power transformers have high harmonic content and large changes in load rates, which can easily cause the coil destabilization, winding deformation or even damage because of the uneven distribution of the electromagnetic force. To improve the accuracy of electromagnetic force calculation, this paper proposes a fractional order numerical method. First, a three-dimensional axisymmetric transformer model and a symmetrical lumped parameter equivalent circuit model are established, respectively, based on field-circuit coupling. Second, the fractional order approximation of circuit components is realized by using the improved Oustaloup filter. In the fractional order model, the transformer is replaced by the lumped parameter equivalent circuit model. Third, as in the calculation process for integer order electromagnetic force, the integer order current has a large error, and the current waveform does not match the actual power frequency. The fractional order current and electromagnetic force at the 0.9 order are closer to the rated value. Finally, the effects of different load rates, three-phase short circuits and harmonic conditions are studied with the fractional order model. Compared with the traditional integer order finite element electromagnetic model, the fractional order equivalent circuit model established in this paper is more accurate and suitable for electromagnetic force calculation. The proposed method is significant for the structural design and state detection of transformers and also could be applied in the analysis of other dry-type transformers. [ABSTRACT FROM AUTHOR]

Experimentation is a common method to reveal the stick–slip vibration characteristics of horizontal well drill string system. Three different diameters of mini bits and an experimental bench of horizontal well drillstring system are innovatively designed to simulate the interaction between the bit and rock and the interaction between the drill pipe and well wall, which are the two boundary conditions that generate stick–slip vibration. The effects of bit type, drill pipe stiffness, rotational speed, and (ROP) Rate of Penetration on stick–slip vibration are investigated using rock-breaking experiments. The experimental results show that as the rotational speed increases from 9 to 45 r/min, (SSVI) stick–slip vibration intensity decreases. When the rotational speed is 9 r/min, the SSVI of the bit with higher cutter density drilling rock is lower than that of the bit with lower cutter density drilling rock. When the rotation speed is 45 r/min, the SSVI of the three bits is equal. The SSVI of drill pipe with smaller stiffness is greater than that of drill pipe with larger stiffness. The SSVI increases as the ROP increase from 0.36 to 1.26 m/h. The experimental findings aid in our understanding of the causes of stick–slip vibration. It lays the groundwork for the next step in reducing the harm caused by stick–slip vibration. [ABSTRACT FROM AUTHOR]

Aqueous Zn/MnO2 batteries with mildly acidic electrolytes are promising candidates for low cost, high safety electrochemical energy storage for grid-scale applications. However, the complexity of the chemistry results in conflicting reports of operation principles, making rational improvements challenging. In this work, operando synchrotron X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) as well as ex situ Raman spectroscopy, XRD, and XAS characterization were used to probe the mechanism of aqueous Zn/α-MnO2 batteries with ZnSO4 electrolyte. A multi-stage Mn dissolution–conversion charge storage mechanism was revealed, which consists of reversible solid-aqueous phase transformation via Mn dissolution–deposition reactions and a solid redox mechanism via Zn-ion insertion. This mechanism is supported by thermodynamic calculations paired with in situ electrolyte pH measurements to provide further mechanistic insights. The findings establish a detailed charge storage mechanism for aqueous Zn/α-MnO2 batteries with a well resolved reversible layered charge product structure, that can serve as a reference for future studies on advancing the reversibility and stability of aqueous Zn/α-MnO2 batteries. [ABSTRACT FROM AUTHOR]

An azobenzenediamide bridged bis (β-cyclodextrin) chiral stationary phase (AZCDP) was prepared, and its high-performance liquid chromatography performance in reversed-phase and polar organic modes was evaluated by chiral probes, including triazoles, flavanones, amino acids and β-blockers. The results showed that AZCDP had strong chiral separation ability and the 40 chiral compounds were successfully resolved, of which 32 were completely separated (R s ≥ 1.5) and the best enantioresolution was up to 3.93 within 20 min under a wide range of pH value and temperature. The separation ability of AZCDP with double cavities was significantly better than common CD-CSPs with single cavity, which was related to the synergistic inclusion effect. Compared with the previously reported stilbene (C=C)-bridged CSP, AZCDP with azobenzene (N=N)-bridged had a wider resolution range. For example, it could resolve myclobutanil, pindolol, carteolol, betaxolol, bevanolol and bitertanol, which could not be resolved before, and should be related to the fact that the flexible N=N was more compatible with the synergistic inclusion between cavities than the rigid C=C bridge group. The azobenzenediamide bridging group could also provide hydrogen bond, π–π and other sites, which was conducive to chiral separations. [ABSTRACT FROM AUTHOR]

Particle-attached (PA) and free-living (FL) bacterial communities play essential roles in the biogeochemical cycling of essential nutrients in aquatic environments. However, little is known about the factors that drive the differentiation of bacterial lifestyles, especially in flooding lake systems. Here we assessed the compositional and functional similarities between the FL and PA bacterial fractions in a typical flooding lake—the Poyang Lake (PYL) of China. The results revealed that PA communities had significantly different compositions and functions from FL communities in every hydrological period, and the diversity of both PA and FL communities was affected mainly by the water regime rather than bacterial lifestyles. PA communities were more diverse and enriched with Proteobacteria and Bacteroidetes, while FL communities had more Actinobacteria. There was a higher abundance of photosynthetic and nitrogen-cycling bacterial groups in PA communities, but a higher abundance of members involved in hydrocarbon degradation, aromatic hydrocarbon degradation, and methylotrophy in FL communities. Water properties (e.g., temperature, pH, total phosphorus) significantly regulated the lifestyle variations of PA and FL bacteria in PYL. Collectively, our results have demonstrated a clear ecological differentiation of PA and FL bacterial communities in flooding lakes, suggesting that the connectivity between FL and PA bacterial fractions is water property-related rather than water regime-related. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)