Search Results (1,163)

Recently, a new stability classification including the frequency, voltage, power angle, and impedance angle stability has been proposed. However, instability coupling among the voltage, power angle, and impedance angle may occur. Previous studies have investigated the coupling between the voltage and power angle. Nevertheless, system instability may also involve the voltage magnitude, power angle, and impedance angle. Dominant instability factor identification remains a research gap. Consequently, this paper proposes an Apparent Power Phasor Trajectory (APPT)-based identification method. Different from coupling analyses that mainly describe interaction relationships or stability boundaries, the APPT constructs comparable trajectory distance indicators in a unified apparent power phasor framework. Based on a two-node equivalent model of a grid-forming inverter, APPT sensitivity relationships and trajectory distance indicators are formulated under a unified metric. Numerical studies show that the proposed method identifies the dominant instability factor in representative scenarios. In the dynamic Kundur case, the overall consistency ratio reaches 95.01%. Simulation-based checks give accuracy values ranging from 97.07% in the reference setting to 90.94% under synchronization mismatch. Together with the IEEE 39 bus case, these results indicate that the APPT provides an interpretable basis for dominant instability factor identification in new power systems. Full article

Powered mobility devices have used lead–acid batteries for decades with some recent designs using lithium-ion batteries. However, both lead–acid and lithium-ion batteries have concerns related to safety and environmental impact. Additionally, powered mobility device users have expressed a desire for new and alternative power sources. Nickel–zinc batteries can charge much faster and are safer and more environmentally friendly. However, nickel–zinc batteries must be discharged at high rates to prevent degradation of the batteries. This project developed a prototype power system using nickel–zinc batteries and supercapacitors to power a scooter. The design uses the nickel–zinc batteries to periodically and quickly charge the supercapacitors which then provide the power the scooter. Testing confirmed that the power system maintained appropriate voltage and current during use and that the scooter was able to perform with the same range, speed, and power as a current commercially available scooter. Full article

As power grids transition towards highly renewable generation on a global scale, maintaining dynamic stability is becoming a major challenge. Replacing traditional synchronous generators with inverter-based renewables strips the grid of rotational inertia, leaving active distribution networks highly vulnerable to frequency deviations and voltage spikes. To avoid expensive poles and wires upgrades, Battery Energy Storage Systems (BESS) are increasingly being deployed as Non-Network Solutions (NNS). However, the current literature reveals a distinct gap between the macro-scale economic planning of these storage assets and the micro-scale dynamic control actually required to keep the grid resilient. To address this gap, this review proposes a multi-layer deterministic synthesis framework that links physical renewable modelling, degradation-aware techno-economic planning, deterministic forecasting, and EMS dispatch through offline time-domain control validation for AC-microgrid energy storage integration. The research examines how advanced central control units within battery management systems can rigorously and jointly estimate State of Charge (SoC) and State of Energy (SoE) to ensure accurate grid-aware dispatch. Furthermore, the study explores the integration of degradation-aware economic modelling in HOMER Pro with dynamic transient control in MATLAB/Simulink R2025b, driven by hybrid metaheuristic optimization algorithms like Grey Wolf Optimizer (GWO) and Particle Swarm Optimization (PSO). This analysis demonstrates that integrating energy storage must be treated as a tightly coupled multidimensional optimization problem to successfully deliver the secure and sustainable infrastructure needed to solve the modern energy trilemma. Full article

In this paper, the influence of voltage change rate on the process of steep pulse air discharge is studied under an environment of 7000 m atmospheric pressure. Six sets of nanosecond pulses with different voltage change rates are used, and the initial and breakdown gaps of the streamer are analyzed by numerical simulation and ICCD imaging. The results show that when the voltage change rate is large, the electric field develops rapidly, which can promote the early formation of the streamer. However, if the effective duration of the pulse is too short and the voltage duration is insufficient, the streamer cannot develop further, and partial breakdown occurs. As the voltage change rate decreases and the pulse width increases, the streamer is more likely to form a through channel, and the discharge penetration time decreases first and then increases. The experimental and simulation results are consistent. In the low-pressure environment, the pulse leading edge variation characteristics are more sensitive to the formation of streamers, which has a reference value for the gap insulation and pulse withstand voltage design of high-altitude electrical equipment. Full article

Freezing is an important technique for preserving muscle foods (encompassing mammalian meat, poultry, and seafood). However, traditional thawing methods have several drawbacks, including excessive drip loss, nutrient leaching, and overall quality degradation. To address these issues, emerging technologies such as high-voltage electric field, ohmic, microwave, ultrasound-assisted, low-temperature combined with high-humidity (LHT), radiofrequency (RF), and vacuum thawing have been developed. Despite their potential, existing literature frequently focuses on standalone methods or isolated engineering parameters, leaving a critical knowledge gap regarding their comparative industrial viability and combined synergistic effects. Based on a comprehensive literature search across major scientific databases, the changes in meat product quality during the thawing process were systematically discussed, followed by an exploration of the principles and applications of these innovative methods. Crucially, comparative findings indicate that LHT thawing most effectively preserves water-holding capacity (WHC) and minimizes lipid oxidation. In contrast, RF thawing provides the optimal balance between rapid thawing rates and uniform quality retention for large-scale operations, while hybrid approaches (e.g., microwave combined with ultrasound) successfully balance high-speed processing with the prevention of structural degradation. Furthermore, the practical applications of these technologies in the food industry were presented, emphasizing the growing trend of combining multiple techniques. The advantages and disadvantages of the thawing process are analyzed to provide theoretical references and practical insights for enhancing the quality of commercial meat products. Full article

On-site withstand voltage testing is essential for evaluating insulation performance and detecting defects in UHV AC equipment; however, existing safety distance criteria are mainly based on empirical experience or extrapolated from low-altitude and lower-voltage conditions, limiting their applicability. To address this issue, a systematic framework for safety distance calculation and altitude correction is developed. The selection principles and circuit configuration of the test system are analyzed to clarify the constraints between power capacity and tuning under high-voltage, large-capacity conditions. Based on air-gap discharge characteristics, a minimum safety distance model is established for the 1000 kV main transformer with respect to grounded structures and personnel. Meteorological factors and proximity effects are further incorporated to propose correction methods and on-site zoning strategies. Results indicate that a baseline safety distance of approximately 10 m is appropriate at altitudes up to 1000 m, and the model captures the nonlinear degradation of insulation strength in long air gaps at higher altitudes. A case study at 3620 m yields a minimum safety distance of 16.4 m, providing a quantitative basis for safe UHV AC on-site testing under varying altitude conditions. Full article

Van der Waals (vdW) multiferroic tunnel junctions (MFTJs) based on two-dimensional layered materials have emerged as a promising platform for next-generation non-volatile memory devices. In this work, we propose and theoretically investigate a high-performance all-vdW MFTJ consisting of a sliding ferroelectric bilayer GeC barrier sandwiched between asymmetric ferromagnetic metallic electrodes, Fe₃GaTe₂ and Fe₃GeTe₂. Using first-principles calculations combined with the non-equilibrium Green’s function (NEGF) method, we demonstrate that the bilayer GeC possesses robust vertical ferroelectricity switchable by interlayer sliding. By incorporating monolayer graphene as protective layers to mitigate metal-induced gap states, the device preserves the intrinsic ferroelectric polarization of the barrier. Our results reveal that four distinct non-volatile resistance states can be realized by independently manipulating the ferroelectric polarization and magnetization configurations. Remarkably, the device exhibits a giant Tunneling Magnetoresistance (TMR) ratio of up to 750.95% and a large Tunneling Electroresistance (TER) ratio of 322.97%. Furthermore, we observe perfect spin-filtering efficiency and a significant negative differential resistance (NDR) effect under finite bias voltage. These findings suggest that the Fe₃GaTe₂/graphene/bilayer-GeC/graphene/Fe₃GeTe₂ heterostructure is a compelling candidate for multifunctional spintronic applications in the post-Moore era. Full article

Soybean (Glycine max L.) is a globally strategic crop valued for its high-quality protein and oil, yet its yield potential is frequently constrained by inconsistent seed germination and a heavy reliance on chemical treatments that carry environmental and health risks. Physical pre-sowing stimulation has emerged as an eco-friendly alternative, but the comparative efficacy of direct current (DC) versus alternating current (AC) high-voltage electric fields—and the mechanistic basis for their differential effects—has remained poorly understood. Here, we systematically compared DC and AC pre-sowing treatments across a comprehensive matrix of field intensities (0.5, 1.0, and 1.5 kV/cm) and exposure durations (30, 60, and 120 s) at a fixed electrode gap of 10 cm, using soybean seeds of the Volgogradka 1 cultivar. Germination energy (day 3) and total germination (day 7) were assessed under standardized laboratory conditions in triplicate, followed by a replicated field trial to evaluate plant height, bean yield, and disease incidence. DC treatment significantly outperformed both the untreated control and AC treatment: germination energy increased by up to 60%, and total germination reached 100% compared with 85% in the control. The optimal DC window was identified at 0.8–1.5 kV/cm with a 30 s exposure. In stark contrast, AC treatment at industrial frequency not only failed to enhance germination but also frequently suppressed it and markedly increased susceptibility to fungal crown rot. Field results corroborated these findings: DC-treated seeds produced the highest bean mass (85 g per five plants vs. 80 g in the control), while AC-treated seeds yielded the lowest (72 g). Backward elimination regression analysis revealed that field intensity alone was the sole significant predictor of treatment outcomes, whereas exposure time and interaction effects were non-significant. We conclude that short-duration DC pre-sowing stimulation (1.0 kV/cm, 30–60 s) is a robust, chemically safe, and readily scalable technique for enhancing soybean establishment and yield. Conversely, AC treatment at power frequency is not recommended due to its deleterious effects on plant health and productivity. These findings establish a clear, evidence-based framework for the rational design of electrical seed treatment protocols. Full article

To address the limited spatial localization accuracy of partial discharge (PD) in high-voltage cable terminations and the difficulty in accurately determining the trigger time in traditional ultrasonic detection, this paper proposes an electro-acoustic synergistic localization technology based on a high-frequency current transformer (HFCT) and a Sagnac optical fiber interferometer. A high-sensitivity Sagnac acoustic sensor based on a 3D-printed photosensitive resin mandrel was developed. Through structural design and 0–50 kHz amplitude–frequency testing, the sensor exhibits a dominant resonant response at 33.2 kHz. This narrow-band, high-sensitivity characteristic effectively enhances the perception capability for weak PD ultrasonic signals. An electro-acoustic synergistic detection system was constructed, in which the high-frequency PD current signal captured by the HFCT was used as the electrical time reference, and a dual-channel Sagnac sensor array was used to extract the arrival times of ultrasonic waves. In a 12 kV laboratory cable-termination PD experiment, the proposed system identified the representative built-in air-gap PD source with an absolute localization error of 5 mm under the tested laboratory configuration. This value should be interpreted as the localization result for the tested representative defect, rather than as a generally validated accuracy specification of the system. This study provides a proof-of-concept laboratory demonstration of an electro-acoustic localization strategy that combines the fast electrical response of HFCT detection with the electromagnetic-interference immunity and acoustic sensitivity of Sagnac fiber-optic sensing. Full article

Accurate harmonic measurement is required for power quality (PQ) compliance in South Africa’s inverter-based renewable grids. The frequency response of the current transformer (CT) has been characterised through structured testing, while voltage transformers (VTs) remain untested under harmonic excitation in local conditions. This paper proposes a method for evaluating single-phase VT frequency response by adapting CT test strategies to voltage excitation. MATLAB R2025b Simulink models support interpreting measured data. The framework measures ratio and phase errors up to the 60th harmonic (3 kHz) and detects resonances important for PQ assessment. The study addresses a methodological gap in South African PQ measurement and supports the development of standardised procedures for evaluating VT frequency response in renewable power systems. Full article

High levels of photovoltaic penetration and synchronous generator decommissioning are weakening grid strength and increasing voltage support requirements, yet most studies still assess support technologies primarily based on technical performance rather than full lifecycle utility value. The key gap is the absence of a consistent framework that links technical performance to lifecycle cost, tariff impact and investment outcomes across competing technologies. This study addresses that gap by developing a transparent utility-oriented assessment framework to compare Static Var Compensator (SVC), Static Synchronous Compensator (STATCOM), Synchronous Condenser (SC) and grid-forming BESS (BESS-GFM) options in a weak high-PV penetration network. Quasi-dynamic simulations on an IEEE 9-bus system were used to quantify technical benefits, which were then converted into lifecycle financial metrics within a total expenditure (TOTEX)-based model and combined with practical decision criteria through multi-criteria decision analysis (MCDA). The results show that while all four technologies improve system performance, their overall value differs once cost, tariff impact, risk and flexibility are considered. Under the adopted assumptions, STATCOM provides the best overall balance and ranks highest. Full article

This study assesses the possibility of identifying non-through defects in dielectric coatings, specifically interfacial defects located at the metal–coating boundary, by means of high-voltage non-destructive testing. It is demonstrated that partial discharges causing characteristic distortions of the applied test-voltage pulse can be used as a reliable diagnostic feature of such defects. Using an equivalent capacitive representation of a defective coating, a relationship is established between the apparent charge and the geometry of the air-filled gap. The proposed approach is supported by COMSOL simulations of the electric-field distribution and by experiments performed on Plexiglas specimens containing blind holes of different depths. In addition, a method is developed for isolating the partial-discharge signal based on a weighted sum of increments in the root-mean-square deviations of the second derivative of the voltage waveform. The resulting relationships enable estimation of the residual coating thickness in the defect region. Full article

Grain-oriented (GO) silicon steel cores in low-voltage current transformers suffer magnetic degradation from residual stress and increased dislocation density during slitting and winding. This study addresses the gap in systematic optimization of secondary annealing on assembled toroidal cores using a 3² full-factorial design varying temperature (650, 850, 1050 °C) and holding time (60, 90, 120 min) on M4 grade cores. Results showed temperature is the dominant factor, while holding time exhibits a synergistic non-linear effect. The optimal condition (850 °C, 90 min) reduced specific losses from 0.85 W/kg to 0.43 W/kg (49% reduction). Mechanistic analysis confirmed this improvement is driven by complete primary recrystallization (equiaxed grains ~50–60 µm), dislocation annihilation (~10 HV hardness reduction), and reinforcement of the Goss texture ({110} <001>). SEM, EDS, and ICP-OES demonstrated that the Carlite coating remained dimensionally (1.67–1.83 µm) and chemically stable, with beneficial decarburization. Temperatures above 850 °C caused magnetic deterioration due to excessive grain growth. These results provide a validated, industrial framework for recovering magnetic efficiency in wound toroidal cores without compromising coating integrity. Full article

A Wedge Shaped T–Type magnetic flux concentrator (MFC) is proposed to improve the magnetic detection capability of tunneling magnetoresistance (TMR) sensors. The TMR chip used in this work integrates a CoFeSiB soft magnetic thin film on-chip and exhibits a sensitivity of 251 mV/Oe with a magnetic noise of 65.3 pT/sqrt(Hz). Based on magnetic circuit analysis and finite-element simulations, the key structural parameters of the Wedge Shaped T–Type MFC were optimized, including the air-gap distance, aspect ratio, and input–output cross-sectional ratio. The optimal parameters were determined as an air gap of 200 μm, an aspect ratio of 2, and a cross-sectional compression ratio exceeding 100. Sixteen MFC structures with different sizes were fabricated and integrated with the TMR sensors for experimental evaluation. The results show that the external flux concentrator does not introduce additional voltage noise while significantly improving the sensor response. With optimized structures, the sensor sensitivity increases from 251 mV/Oe to 17,812 mV/Oe, and the magnetic noise is reduced from 65.3 pT/sqrt(Hz) to 0.92 pT/sqrt(Hz) at 1 Hz. The experimental results demonstrate that the Wedge Shaped T–Type MFC effectively enhances the magnetic field gain and significantly improves the detection limit of TMR sensors. Full article

Railway traction power supply systems (TPSSs) are evolving from passive grid-fed infrastructures into active energy systems with local photovoltaic (PV) generation capacity, energy storage systems (ESSs), and converter-based regulation. Unlike conventional microgrids, TPSSs feature single-phase, highly dynamic traction loads; short-duration regenerative braking bursts; and strict constraints on voltage quality, stability, and protection. These characteristics make the energy management of distributed PV-storage-integrated TPSSs a distinct research problem. This review examines the field from three coupled perspectives: supply architecture, power electronic interfaces, and energy management strategies. First, representative integration architectures are classified into substation-side, wayside-distributed, and hybrid multi-port schemes. Second, converter interfaces and flexible traction substations are analyzed as the enabling layer for coordinated control of PV, ESS, the utility grid, and traction feeders. Third, major energy management strategies, including rule-based, optimization-based, hierarchical multi-timescale, and uncertainty-aware methods, are compared. The review further discusses power quality, stability, protection, and battery degradation constraints that shape practical deployments. Finally, research gaps and future directions are identified to further the development of more robust, railway-specific, and implementation-oriented PV-storage energy management. Full article