Search Results (41)

Stray-current and soft-water leaching can induce severe corrosion in reinforced concrete structures and buried metal pipelines within subway environments. The effects of water-to-binder ratio (W/C), modulus of sodium silicate (Ms), and alkali content (AC) on the mechanical properties of fly-ash-based geopolymer (FAG) at various curing ages were investigated. The influence of curing temperature and high-temperature curing duration on the development of mechanical performance were examined, and the optimal curing regime was determined. Furthermore, based on the mix design of FAG resistant to coupled erosion from stray-current and soft-water, the effects of stray-current intensity and erosion duration on the coupled erosion behavior were analyzed. The results indicated that FAG exhibited slow strength development under ambient conditions. However, thermal curing at 80 °C for 24 h markedly improved early-age strength. The compressive strength of FAG exhibited an increase followed by a decrease with increasing W/B, Ms, and AC, with optimal ranges identified as 0.28–0.34, 1.0–1.6, and 4–7%, respectively. Soft-water alone caused limited leaching, while the presence of stray-current significantly accelerated degradation, with corrosion rates increasing by 4.1 and 7.2 times under 20 V and 40 V, respectively. The coupled corrosion effect was found to weaken over time and with increasing current intensity. Under coupled leaching conditions, compressive strength loss of FAG was primarily influenced by AC, with lesser contributions from W/B and Ms. The optimal mix proportion for corrosion resistance was determined to be W/B of 0.30, Ms of 1.2, and AC of 6%, under which the compressive strength after corrosion achieved the highest value, thereby significantly improving the durability of FAG in harsh environments such as stray-current zones in subways. Full article

The application of rebar reinforced ultra-high-performance concrete (R-UHPC) has been increasingly adopted in engineering structures due to its exceptional mechanical performance and durability characteristics. Nevertheless, when subjected to combined saline and stray current conditions, R-UHPC remains vulnerable to severe corrosion degradation. This investigation examined the corrosion performance and tensile behavior evolution of R-UHPC containing 2.0 vol% copper-coated steel fiber content and HRB400 steel rebar with a reinforcement ratio of 3.1%. The accelerated corrosion process was induced through an impressed current method, followed by direct tensile tests at varying exposure periods. The findings revealed that the embedding of rebar in UHPC led to the formation of fiber-to-rebar (F-R) conductive pathways, generating radial cracks besides laminar cracks. The bonding between rebar and UHPC degraded as corrosion progressed, leading to the loss of characteristic multiple-cracking behavior of R-UHPC in tension. Meanwhile, R-UHPC load-bearing capacity, transitioning from gradual to accelerated deterioration phases with prolonged corrosion, aligns with steel fibers temporally. During the initial 4 days of corrosion, the specimens displayed surface-level corrosion features with negligible steel fiber loss, showing less than 4.0% reduction in ultimate bearing capacity. At 8 days of corrosion, the steel fiber decreased by 22.6%, accompanied by an 18.3% reduction in bearing capacity. By 16 days of corrosion, the steel fiber loss reached 41.5%, with a corresponding bearing capacity reduction of 29.1%. During the corrosion process, corrosion cracks and load-bearing degradation in R-UHPC could be indicated by the ultrasonic damage factor. Full article

In this paper, an advanced model of a switched reluctance generator (SRG) with mutual coupling, iron losses, and remanent magnetism is presented. The proposed equivalent circuit for each SRG phase is represented by the winding resistance, phase inductance and electromotive forces (EMFs) induced by mutual flux-linkage and remanent magnetism. In the advanced SRG model, the phase inductance and equivalent iron-loss resistance need not be known, as the components of the phase current flowing through them are determined directly from appropriate look-up tables, making the advanced SRG model simpler. Both the magnitude of the mutual flux-linkage and its time derivative are considered in the advanced model. The proposed model only requires knowledge of data that can be obtained using the DC excitation method and does not require knowledge of the SRG material properties. For the first time, the remanent magnetic flux of the SRG is modeled and the induced EMS caused by it is included in the advanced SRG model. Stray losses within the SRG are considered negligible. Connection to an asymmetric bridge converter is assumed. Magnetization angles of individual SRG phases are provided by the terminal voltage controller. The results obtained with the advanced SRG model are compared with experiments carried out in the steady-state of the 8/6 SRG with a rated power of 1.1 kW SRG over a wide range of load, terminal voltage, turn-on angle, and rotor speed in single-pulse mode suitable for high-speed applications. Full article

The focus of this paper is to seek means of increasing induction motor efficiency to a comparable level to a permanent magnet motor. Harmonic and high-frequency losses increase the rotor core and copper loss, often limiting IM efficiency. The research in this study focuses on reducing rotor core and copper losses for this purpose. An accurate finite element model of a prototype motor is developed. The accuracy of this model in predicting the performance and losses of the prototype motor is verified with experiments over a 32 Hz–125 Hz supply frequency range. The verified model of the motor is used to identify the causes of the rotor core and copper losses of the motor. It is found that the air gap flux density of the motor contains many harmonics, and the slot harmonics are dominant. The distribution of the core loss and the copper loss is investigated on the rotor side. It is discovered that up to 35% of the rotor copper losses and 90% rotor core losses occur in the regions up to 4 mm from the airgap where the harmonics penetrate. To reduce these losses, one solution is to reduce the magnitude of the air gap flux density harmonics. For this purpose, placing a sleeve to cover the slot openings is investigated. The FEA indicates that this measure reduces the harmonic magnitudes and reduces the core and bar losses. However, its effect on efficiency is observed to be limited. This is attributed to the penetration depth of flux density harmonics inside the rotor conductors. To remedy this problem, several FEA-based modifications to the rotor slot shape are investigated to place rotor bars deeper than the harmonic penetration. It is found that placing the bars further away from the rotor surface is very effective. Using a 1 mm sleeve across the stator’s open slots combined with a rotor tapered slot lip positions the bars slightly deeper than the major harmonic penetration depth, making it the optimal solution. This reduces the bar loss by 70% and increases the motor efficiency by 1%. Similar loss reduction is observed over the tested supply frequency range. Full article

Solid-State Transformers (SSTs) enable significant improvements in size and functionality compared to conventional power transformers. However, one of the key challenges in Solid-State Transformer design is achieving reliable insulation between the high-voltage and low-voltage sections. This proposal presents the design and optimization of a high-insulation Medium-Frequency Transformer (MFT) for 66 kV grids operating at 50 kHz and delivering up to 75 kW for SST applications using Inductive Power Transfer (IPT) technology. A fixed 50 mm gap between the primary and secondary windings is filled with dielectric oil to enhance insulation. The proposed IPT system employs a double-D coil design developed through iterative 2D and 3D finite element method simulations to optimize the magnetic circuit, thereby significantly reducing stray flux and losses. Notably, the double-D configuration reduces enclosure losses from 269.6 W, observed in a rectangular coil design, to 4.38 W, resulting in an overall system loss reduction of 42.4% while maintaining the electrical parameters required for zero-voltage switching operation. These advancements address the critical limitations in conventional Medium-Frequency Transformers by providing enhanced insulation and improved thermal management. The proposed IPT-based design offers a low-loss solution with easy thermal management for solid-state transformer applications in high-voltage grids. Full article

Background: As a ubiquitous apicomplexan parasite, Toxoplasma gondii causes huge economic losses and poses a great threat to the health of animals, including humans, worldwide. In some kangaroo species, T. gondii can be fatal. To date, little information is available on T. gondii infection in the red kangaroos in east China. At a zoo in east China, thirteen red kangaroos consecutively developed clinical signs from July to November 2016, resulting in the deaths of seven, three of which were analyzed in this study. Methods: In the present study, ascitic fluid, blood and samples from the brain, heart, liver, spleen, lung, kidney, and mesenteric lymph nodes of three dead red kangaroos were collected. The pathogen was explored through microscopic observation, nested PCR, immunofluorescence antibody test (IFAT), hematoxylin–eosin (HE) staining, and immunohistochemistry (IHC) staining, respectively. Meanwhile, the potential source of the infection was also investigated by testing the blood of stray cats in the zoo for T. gondii using nested PCR. Results: Three dead red kangaroos were subjected to a necropsy, and organisms resembling T. gondii were detected in their ascitic fluids under microscope. This infection was further confirmed by a nested PCR assay, which resulted in a successful amplification and sequencing of the 433 bp fragment of the T. gondii 5.8S rRNA gene in all the dissected tissues, including heart, liver, spleen, lung, kidney, lymph nodes, cecum, and brain, as well as in body fluids (blood and ascitic fluid). Furthermore, the tachyzoites were observed in the heart, liver, spleen, lymph nodes, cecum, and brain through IFAT and HE staining. Administration of classic drugs (sulfadiazine and pyrimethamine) against T. gondii significantly alleviated the clinical signs of the sick kangaroos. The possible source of this infection was traced to a native stray cat, as T. gondii DNA was detected in its blood. Conclusions: In the present study, lethal T. gondii infection in red kangaroos has been described for the first time in east China, highlighting the necessity and urgency for close and long-term surveillance of this parasite infection in captive animals. The same strain of T. gondii detected in kangaroos as that found in stray cats wandering in the same area emphasizes the importance of controlling stray cat populations to mitigate the risk of Toxoplasma transmission to other animals. Full article

An efficient numerical calculation method of stray-field loss is investigated for typical magnetic load components (grain-oriented silicon steel sheets (GO), magnetic steel plate, and combined components of both materials) under non-sinusoidal excitations (NSE) containing symmetrical harmonic and DC to avoid the local overheating caused by high stray-field loss density. The paper investigates the stray-field loss with different types of load components and working conditions based on the leakage flux complementary-based measurement method, derives an analytical formulation calculating the energetic hysteresis model parameters under different magnetic flux densities to reduce the dependence on measurement data, establishes a loss calculation method considering the influence of non-sinusoidal magnetization on magnetic loss, and discusses the advantages and limitations of existing numerical approaches of additional loss to establish an effective computational strategy of stray-field loss. Finally, the effectiveness of the proposed method is verified by simulations and experiments. Full article

One of the most important issues that can significantly affect the electric power network’s ability to operate sustainably is the optimal power flow (OPF) problem. It involves reaching the most efficient operating conditions for the electrical networks while maintaining reliability and systems constraints. Solving the OPF problem in transmission networks lowers three critical expenses: operation costs, transmission losses, and voltage drops. The OPF is characterized by the nonlinearity and nonconvexity behavior due to the power flow equations, which define the relationship between power generation, load demand, and network component physical constraints. The solution space for OPF is massive and multimodal, making optimization a challenging concern that calls for advanced mathematics and computational methods. This paper introduces an innovative metaheuristic algorithm, the Egyptian Stray Dog Optimization (ESDO), inspired by the behavior of Egyptian stray dogs and used for solving both single and multi-objective optimal power flow problems concerning the transmission networks. The proposed technique is compared with the particle swarm optimization (PSO), multi-verse optimization (MVO), grasshopper optimization (GOA), and Harris hawk optimization (HHO) and hippopotamus optimization (HO) algorithms through MATLAB simulations by applying them to the IEEE 30-bus system under various operational circumstances. The results obtained indicate that, in comparison to other used algorithms, the suggested technique gives a significantly enhanced performance in solving the OPF problem. Full article

Brushed DC motors and generators (DCMs) are extensively used in various industrial applications, including the automotive industry, where they are critical for electric vehicles (EVs) due to their high torque, power, and efficiency. Despite their advantages, DCMs are prone to premature failure due to sparking between brushes and commutators, which can lead to significant economic losses. This study proposes two approaches for determining the temporal and frequency evolution of Shannon entropy in armature current and stray flux signals. One approach indirectly achieves this through prior analysis using the Short-Time Fourier Transform (STFT), while the other applies the Stockwell Transform (S-Transform) directly. Experimental results show that increased sparking activity generates significant low-frequency harmonics, which are more pronounced compared to mid and high-frequency ranges, leading to a substantial rise in system entropy. This finding enables the introduction of fault-severity indicators or Key Performance Indicators (KPIs) that relate the current condition of commutation quality to a baseline established under healthy conditions. The proposed technique can be used as a predictive maintenance tool to detect and assess sparking phenomena in DCMs, providing early warnings of component failure and performance degradation, thereby enhancing the reliability and availability of these machines. Full article

This study examined a newly developed environmentally friendly plant-based corrosion inhibitor (Xanthium sibiricum). The natural potential method, linear polarization method, steel weight loss method, and corrosion area method were employed to verify the inhibitor’s effectiveness in chloride-containing concrete. The results indicated that Xanthium sibiricum elevated the natural potential of reinforcing steel in concrete, increased its self-corrosion potential, and reduced the self-corrosion current. After three months of curing, the corrosion rate of steel without an inhibitor was approximately 47.5% faster than the experimental group, with the steel loss rate about 40% more severe. The effectiveness of the inhibitor was influenced by increased chloride content in concrete. A two-dimensional multiphase ion transport model of reinforced concrete with realistic aggregate distribution was established using the finite element method (FEM). This model simulated chloride ion transport under typical civil engineering service environments—the coupled effects of a stray current and chloride environment. A predictive formula for the residual compressive strength of reinforced concrete was derived after corrosion under various voltages and chloride ion concentrations for a specific duration. In conjunction with a pump station project operating in a similar environment, the optimal dosage of the Xanthium sibiricum inhibitor for practical engineering was determined to be 2 g/L. At this dosage, the strength of reinforced concrete specimens increased by approximately 31.1%. Finally, a predictive formula for the residual compressive strength of reinforced concrete with an added inhibitor was obtained after corrosion under various voltages and chloride ion concentrations for a specific duration. The conclusions can enhance the durability and safety of concrete structures in similar projects, showing promising application prospects. Full article

Magnetic shunts efficiently mitigate losses caused by leakage currents in the tank walls of power transformers. Transformer manufacturers frequently utilize vertical magnetic shunts positioned on the inside surfaces of the transformer tank walls. This study investigated the optimum use of horizontal shunts in a power transformer. A 50 MVA power transformer, manufactured on a commercial scale and featuring optimized vertical magnetic shunts integrated into the wall structure, was analyzed using the 3D finite element method for 100 ms at full load. Simulations for analyses were performed using a commercial ANSYS Electronics Desktop 2021 R1 FEM software program. The model’s validity was demonstrated by verifying the analysis results with experimental tank loss values. Tank loss samples were obtained by analyzing the transformer tank for two milliseconds with vertical magnetic shunts only on the long front wall and the short side wall. Using these loss samples as a reference, parametric analyses were performed for two milliseconds with horizontal magnetic shunts only on the short side wall and only on the long front wall of the tank. A tank model with horizontal magnetic shunts of an appropriate location and size was obtained via the parametric analyses. This model was analyzed for 100 milliseconds at full load and compared with the experimental results of the transformer manufacturer’s vertical magnetic shunt transformer. According to the results, a saving of 25.83% was achieved in the horizontal magnetic shunt volume compared with the vertical magnetic shunt volume. The maximum magnetic flux density was lower in the horizontal magnetic shunts, and the maximum current density was lower in the transformer tank with horizontal magnetic shunts. Full article

A two-year-old female crossbreed dog, previously a stray with no known owner, was adopted and subsequently spayed. The dog exhibited weight loss over a period of two months and died suddenly during a leashed walk. Upon necropsy, enlargement of the submandibular, prescapular, and popliteal lymph nodes was noted. The intrathoracic cavity contained a substantial volume of yellowish-white fluid. Lymph nodes in the mediastinal and ventral thoracic centers were also enlarged, hemorrhagic, and friable. Microscopic examination revealed significant architectural changes in the lymph nodes, characterized by a pronounced cellular infiltrate consisting of lymphocytes and histiocytes, along with macrophages containing intracytoplasmic Leishmania amastigotes. Immunohistochemical analysis of the lymph nodes confirmed positive staining for Leishmania amastigotes. This case represents the first report of canine leishmaniasis associated with acute pleural effusion and sudden death. Full article

This paper presents a design study focusing on the thermal safety of an induction motor integrated with a pump unit, which operates submerged in liquefied natural gas (LNG) in the LNG tanks of LNG carrier ships ranging from 150 K to 200 K cubic meters (CBM). In this study, we carried out the electromagnetic design of the induction motor and verified the thermal safety against a temperature increase due to losses during the motor operation through thermal fluid analysis, taking into account the discharge flow of the emergency pump and the air gap of the motor. In the electromagnetic design, the resistivity of the stator winding copper conductors and the rotor aluminum bars, which act as important design constants for the rated operating and starting characteristics of the induction motor in cryogenic temperature environments, reflects the characteristic of linearly changing with the temperature. In cryogenic environments, the reduction in the resistance of the rotor bars of the induction motor leads to a decrease in the starting torque characteristics. Therefore, the shape optimization design of the rotor bar was performed to improve the starting torque characteristics, and 2D electromagnetic analysis was performed on the magnetic flux density distribution and magnetic saturation using Ansys Electromagnetics 16.0. After the electromagnetic design, a 3D thermal flow analysis was conducted using Ansys Fluent 17.0, considering the stator iron losses, rotor bar losses, stator and rotor iron losses, and stray load losses as heat sources. The flow analysis aimed to analytically verify the thermal safety concerning the vaporization of the LNG flowing through the emergency pump’s discharge flow path and the motor’s internal air gap. The motor was manufactured, and the rated and starting operating characteristics of the motor were measured under LN2 submerged conditions according to the IEEE 112 F1 method, to validate whether the performance characteristics met the specifications’ requirements. Subsequently, the thermal safety of the motor was finally verified through a temperature increase test under LNG submerged conditions after assembling it with the emergency pump. Full article

Designing and manufacturing transformers often involves variations in heights and thicknesses of windings. However, such geometric asymmetry introduces a significant impact on the magnitude of stray transformer losses. This study examines the effects of asymmetric coils on the generation of stray losses within core clamps and transformer tank walls. A model has been introduced to ascertain the dispersion magnetic field’s value at a specific distance from the coil. The analysis extends to characterising the dispersion magnetic field reaching the tank walls by using electromagnetic simulation by a finite element method. It explores strategies to diminish stray losses, including the placement of magnetic shunts as protective shields for the tank walls. It delves into the efficacy of employing a transformer shell-type configuration to mitigate the magnetic dispersion field. The findings revealed that achieving greater symmetry in transformer coils can minimise stray losses. Specifically, the incorporation of magnetic shunts has the potential to reduce additional losses by 40%, while the adoption of a shell-type configuration alone can lead to a 14% reduction. This work provides valuable insights into optimising transformer designs, contributes a user-friendly tool for estimating additional tank losses, thereby enhancing the knowledge base for transformer manufacturers. Full article

A multi-step approach for the fast calculation of the magnetic field inside transformer tank shields, based on the 2D FEM, is presented in the paper. Due to the limitations of the 2D FEM, the proposed approach utilizes several 2D FEM models and calculates the magnetic field in multiple steps to account for the 3D geometry of the problem. In the first step, a distribution of the magnetic flux density that enters the tank shields is calculated using the quasi-3D model of the transformer. This quasi-3D model is obtained by superimposing the solution of multiple axisymmetric 2D FEM models, and assumes a considerably simplified transformer geometry. To account for the tank shield geometry that is neglected in the quasi-3D FEM model, an additional 2D FEM model with tank shields is introduced. After the distribution of the magnetic flux density that enters the tank shields is calculated, it is imposed in the final 2D FEM model with a non-linear tank shield which is used to calculate the magnetic flux density distribution inside the tank shields. The proposed approach enables a fast calculation of magnetic field distributions, both in the vertical and horizontal directions. The results of the proposed approach are compared against the 3D FEM. The relative error of the maximum magnetic flux density is under 2%, while the NRMSE of the magnetic flux density distribution within the tank shields is under 10%. The key contribution of the proposed approach is a low computation time. In the presented case study, the total computation time of the proposed approach is ~30 s, while the computation time of the 3D FEM is ~1 h. As the computation time is significantly reduced, while the accuracy is acceptable, the proposed approach can be a good alternative to the 3D FEM for design purposes. Therefore, it has industrial value. Full article