Search Results (99)

The 4-aminobutyrate (GABA) shunt bypasses 2-oxoglutarate dehydrogenase and succinyl-CoA synthetase in the tricarboxylic acid cycle (TCAC) by diverting 2-oxoglutarate to glutamate and generating GABA via glutamate decarboxylase (GAD), whereas polyamine oxidation generates GABA directly from 4-aminobutanal. During salinity stress, the TCAC switches from a cyclic to a non-cyclic mode of operation probably due to the inhibition of two thiamine pyrophosphate-dependent enzymes, 2-oxoglutarate dehydrogenase and pyruvate dehydrogenase, and increases GAD activity via both transcriptional and post-transcriptional (i.e., elevated cytosolic Ca²⁺/calmodulin, H⁺ or glutamate) processes. Diversion of 2-oxoglutarate may occur via an increase in aminating glutamate dehydrogenase activity, due at least in part to the accumulation of ammonium, resulting from changes in protein synthesis and degradation. Inhibition of diamine oxidase activity by aminoguanidine suggests that polyamine oxidation contributes up to one-third of the salinity-regulated GABA level; however, Arabidopsis thaliana (L.) Heynh. GAD loss-of-function mutants suggest that polyamines account for less. The use of aminoguanidine and/or the GAD inhibitor, 3-mercaptopropionic acid, in combination with GAD or 4-aminobutanal dehydrogenase loss-of-function mutants, offers additional opportunities to understand if both GABA sources give rise to succinate, which can function to restore or partially restore TCAC activity during salinity stress. Full article

During the switch-off process, the contact erosion generated by the AC contactor will seriously affect its performance, thereby directly influencing the normal operation of the power equipment. Therefore, aiming at the problem of contact erosion caused by contact bounce during the switch-on and switch-off period of AC contactors, this paper designed the driving circuits during the switch-on, holding, and switch-off processes. During the switch-on process, DC excitation was used instead of AC excitation to eliminate or reduce the contact bounce. During the holding process, low-voltage DC was used instead of high-voltage AC to save energy and reduce coil losses. During the switch-off process, the contact current was used as the control factor, and the scheme of shunting control was employed to achieve the goal of few or even no arcs. In addition, in order to detect the high voltage and large current signals in the main circuit, the three-phase voltage acquisition circuit and three-phase current acquisition circuit were designed. Therefore, a whole process dynamic control which included the switch-on, holding, and switch-off was formed. Through simulation testing and relevant experimental testing, the results demonstrated the correctness and effectiveness of the designed circuit. Full article

Vacuum circuit breakers (VCBs) have been extensively employed in switching shunt capacitor banks. However, research on the prestrike characteristics of double-break VCBs in making power frequency voltage remains limited. This study aims to investigate the influence of different closing time differences on the prestrike characteristics of double-break VCBs in making power frequency voltage, and to compare these influences with those of single-break VCBs. Experiments were conducted using vacuum interrupters rated at 24 kV, with contacts made of CuCr40 alloy doped with 1 wt% graphene. Taking the closing time of the high-voltage break as the time zero point, three closing time differences (0 ms, 0.727 ms, and −0.347 ms) were set, and experiments were carried out at six closing phase angles (from 0° to 150° in 30° increments) for each condition. The experimental results demonstrate that when the closing of the high-voltage break lags behind that of the low-voltage break by 0.347 ms, the double-break VCB exhibits optimal prestrike performance, where prestrike is almost entirely suppressed except at the 90° phase angle. Furthermore, the prestrike performance during the closing of the double-break VCB is significantly superior to that of the single-break VCB, characterized by a steeper RDDS curve. These findings provide a theoretical basis for the design of control-switching double-break VCBs. Full article

Distribution networks (DNs) now operate under tighter conditions due to rising penetration of renewables, active prosumers, and exposure to transmission-level contingencies. Distribution Network Reconfiguration (DNR) has proven effective for reducing losses, improving voltage profiles, and enhancing the resiliency of the grid. This paper introduces a three-stage optimization strategy for DNR, combining topological reconfiguration with reactive power support. The first stage, Reconfiguration of Tie-Line Switches (RTLS), utilizes a Particle Swarm Optimization (PSO) algorithm augmented with a Depth-First Search (DFS) mechanism to identify optimal radial structures that minimize active power losses. Once a viable configuration is established, the process proceeds to the second stage, Shunt Capacitor Sizing (SCS), wherein PSO is again employed to determine optimal capacitor sizing across predefined bus locations. The third stage reexecutes the RTLS process using the updated reactive power profile to assess whether further improvements in loss reduction can be achieved. If a superior topology is discovered, it is adopted as the final configuration; otherwise, the SCS solution is retained. This iterative and feedback-based architecture ensures an effective balance between network efficiency and voltage stability using a heuristic approach. The proposed methodology is validated on the IEEE 33-bus and IEEE 123-bus benchmark systems, as well as a custom 7-bus test case. Comprehensive scenario-based analysis, including normal, heavily, and lightly loaded conditions and varying power factor (PF) cases (good and poor PF), confirms the robustness and effectiveness of the approach in achieving considerable loss minimization and voltage profile improvement. For instance, in heavy-load conditions, active-power losses dropped by 39% and 70% for 33-bus and 123-bus cases, respectively. Full article

The increasing penetration of wind energy into modern power grids introduces new challenges, particularly regarding fault current levels and voltage stability during disturbances. This study proposes and evaluates a new Solid State Fault Current Limiter (SSFCL) topology for mitigating the adverse effects of faults in wind-integrated power systems. The proposed SSFCL consists of a bridge section and a shunt branch, designed to limit fault current while maintaining power quality. Unlike conventional SSFCLs, the proposed topology incorporates both DC and AC reactors with an Integrated Gate-Commutated Thyristor (IGCT) switch, to provide current limiting and voltage stabilization, effectively mitigating the negative impacts of faults. A comprehensive MATLAB/Simulink-based simulation is conducted on a realistic grid model. First, appropriate AC and DC reactor impedances are selected to balance fault current suppression, cost, and dynamic response. Then, three fault scenarios, transmission line, distribution grid, and domestic network, are analyzed to assess the fault current limiting performance and voltage sag mitigation of the SSFCL. In the simulation analysis, the DC reactor current and the voltage across the SSFCL device are continuously monitored to evaluate its dynamic response and effectiveness during fault and normal operating conditions. In addition, the fault current contribution from the wind farm is assessed with and without the integration of the SSFCL, along with the voltage profile at the Point of Common Coupling (PCC), to determine the limiter’s impact on system stability and power quality. Finally, the performance of the proposed SSFCL is compared to that of the resistive-type superconducting fault current limiter (R-SFCL) under identical fault scenarios to assess the technical and economic standpoints of the proposed SSFCL. Simulation results show that the SSFCL reduces the peak fault current by up to 29% and improves the voltage profile at the PCC by up to 42%, providing comparable performance to the R-SFCL while avoiding the need for cryogenic systems. Full article

In this work, we investigate the electrical properties of a metal–insulator–semiconductor (MIS) heterojunction based on porous silicon dioxide (Ag/pSiO₂/Si). The porous silicon (PS) films were elaborated by electrochemical anodization under specific experimental conditions to obtain a porosity of about 55%. Porous silicon (PS) was oxidized by IR-RTP at different oxidation temperatures (Tox) ranging from 200 to 950 °C under an oxygen atmosphere. The morphology of the samples was analyzed using a scanning electron microscope (SEM). Ag/Al and Ag contacts were screen printed on the back and front sides of the heterojunction, respectively. Both the series and shunt resistances were derived from dark current–voltage (I–V) characteristics related to the various Ag/pSiO₂/Si heterojunctions. In this context, the reflectance was also measured at different oxidation temperatures to investigate its correlation with the series resistance (Rs) and shunt resistance (Rsh). The optimum electrical performance was obtained for an oxidation temperature close to 400 °C. Depending on the pSiO₂ thickness, two conduction mechanisms were highlighted within the devices. For a Tox below 200 °C, as well as for the non-oxidized devices, the conduction mechanism is governed by the tunneling current through the pSiO₂ film. However, when the Tox increases and exceeds 200 °C, the pSiO₂ thickness increases, leading to the switching of the conduction mechanism to a thermionic instead of a tunneling effect mechanism. Full article

The controlled switching of capacitor banks when properly parameterized brings significant benefits to the bank, circuit breaker, and adjacent equipment by significantly reducing the levels of inrush currents. This article explores and analyzes the waveforms from a circuit breaker equipped with both preinsertion resistors (PIR) and a controlled switching device (CSD), proposing a dynamic approach to determine the better closing times for both the PIR and the main contact of the circuit breaker, thereby reducing inrush current levels and improving system performance and reliability. The study employs a computational tool to identify the circuit breaker’s contacts insertion points, presenting important information such as the best closing instant for the main contact, the determination of preinsertion time, and maximum inrush current peak. The waveforms used in the study originate from both a real power shunt capacitor bank from a Brazilian substation and simulations modeled using the Alternative Transient Program (ATP). This dynamic approach not only reduces inrush current levels, but also contributes to increasing the useful life of the capacitor bank elements, the circuit breaker itself, and neighboring equipment. Full article

The Shunt Active Filter (SAF) is an effective solution for mitigating electrical perturbations in power networks. SAFs usually consist of a voltage source inverter (VSI) with lossy transistors and bulky inductors. In this context, this article proposes analytical models to evaluate the losses and efficiency of a SAF. The models include conduction and switching losses in the transistors and diodes and are valid for both IGBT and SiC MOSFET transistors. The methodology consists of analysing the current waveform to separate the portion flowing through the transistor or diode. IGBT and SiC MOSFET are compared in two cases: firstly, the classic SAF operation with harmonic and reactive power compensation and, secondly, in the case of power injection by a photovoltaic panel or batteries, in addition to the classic SAF operation. The results are validated with real manufacturer data. A step-by-step comparison shows a good accuracy of the model. Therefore, the developed methodology is useful for a SAF designer to select relevant components for the converter and to estimate the efficiency of the system accurately and quickly. Full article

In this study, a single-pole double-throw (SPDT) switch for Sub-6 GHz application is designed. In particular, a shunt inductor is connected to the antenna port of the switch for ESD (electrostatic discharge) protection in RF (radio frequency) front end module. The shunt inductor not only serves as an ESD protection device, but also serves as a component of a parallel resonance circuit to suppress insertion loss of the switch. In addition, in order to secure the power handling capability, transistors turned off in the transmit (Tx) mode are implemented as quadruple-gate transistors. An SPDT switch is fabricated using GaAs pHEMT provided in the 500 nm GaAs BiFET process to verify the feasibility of the proposed switch structure. The operating frequency is set from 3 GHz to 5 GHz. The insertion loss and isolation measured in the Tx mode are lower than 0.35 dB and higher than 31.6 dB, respectively. The insertion loss and isolation measured in the Rx mode are lower than 0.32 dB and higher than 33.9 dB, respectively. The chip size including test pads is 0.890 × 0.875 mm². Full article

Shunt active power filters (SAPFs) have been around for a long time. They improve the quality of a current drawn from the grid when feeding non-linear loads formed by old-fashioned power electronic converters such as uncontrolled and controlled rectifiers. Most SAPFs are implemented using the well-known six-switch three-phase inverter (SSTPI) topology. This paper investigates the capability of adopting the four-switch three-phase inverter (FSTPI) scheme to develop low-cost SAPFs, mainly for low-power ranges. The performance of the proposed SAPF using the FSTPI topology is compared with the conventional scheme of an SAPF formed by the six-switch three-phase inverter (SSTPI) topology. Qualitative and quantitative analyses are conducted. The performance of the proposed FSTPI-based SAPF is investigated under different loading conditions. The obtained results indicate the validity and effectiveness of the FSTPI scheme in improving the quality of currents drawn from the AC grid. The SAPF scheme investigated is also feasible and results in cost reduction when the SAPF power circuit is constructed with modern WBG devices, such as SiC-based MOSFETs, which are relatively expensive (approximately three times the price of the equivalent Si IGBTs). Full article

Energy storage systems (ESSs) and active power filters (APFs) are key power electronic technologies for FACTS (Flexible AC Transmission Lines). Battery energy storage has a structure similar to a shunt active power filter, i.e., a storage element and a voltage source inverter (VSI) connected to the grid using a PWM filter and/or transformer. This similarity allows for the design of an ESS with the ability to operate as a shunt APF. One of the key milestones in ESS or APF development is the DC-link design. The proper choice of the capacitance of the DC-link capacitors and their equivalent resistance ensures the proper operation of the whole power electronic system. In this article, it is proposed to estimate the required minimum DC-link capacitance using a spectral analysis of the DC-link current for different operating modes, battery charge mode and harmonic compensation mode, for a nonlinear load. It was found that the AC component of the DC-link current is shared between the DC-link capacitors and the rest of the DC stage, including the battery. This relation is described analytically. The main advantage of the proposed approach is its universality, as it only requires calculating the harmonic spectrum using the switching functions. This approach is demonstrated for DC-link capacitor estimation in two-level and three-level NPC inverter topologies. Moreover, an analysis of the AC current component distribution between the DC-link capacitors and the other elements of the DC-link stage was carried out. This part of the analysis is especially important for battery energy storage systems. The obtained results were verified using a simulation model. Full article

When a 35 kV distribution network has the problem of insufficient reactive power, the input of a shunt reactor is a common compensation method. Vacuum circuit breakers are widely used in 35 kV distribution networks because of their superior arc extinguishing performance and convenient maintenance. However, in recent years, accidents involving vacuum circuit breakers breaking shunt reactors have occurred more frequently in China, such as high-frequency phase-to-phase short circuits, inter-turn burning losses, bus outlet short circuits, etc., which can cause serious damage and pose a greater threat to the safety of the power system. This paper focuses on the switching overvoltage generated by the vacuum circuit breaker cutting off the shunt reactor. Firstly, the mechanism of overvoltage generation is analyzed theoretically. It is concluded that the equivalent chopping current of the other two phases caused by the continuous reignition of the first open phase is the root cause of the high-amplitude interphase overvoltage. Based on the MODELS custom programming module in EMTP/ATP, according to the process of breaking and reigniting the circuit breaker, this paper uses Fortran language to compile the program and establishes a model of a vacuum circuit breaker, including power frequency current interception, high-frequency current, zero-crossing, breaking, and arc reignition modules. The vacuum circuit breaker is simulated for hundreds of continuous reignitions in milliseconds. Finally, a simulation study on the overvoltage suppression measures of a 35 kV shunt reactor is carried out. The comprehensive comparison of various suppression measures provides a reference for the reasonable selection of actual engineering conditions. Full article

The observed development of offshore wind farms has resulted in an increasing presence of long extra-high voltage cables, with lengths ranging from 10 to 200 km. These cable lines are compensated for by a shunt reactor(s). The transient states that accompany switching operations, in this type of line, cause a number of challenges. There are slightly different and more dangerous phenomena than in classic uncompensated lines. One such phenomenon is the zero-missing phenomenon. The most effective methods for mitigating these phenomena are still under investigation and comparison to identify the optimal countermeasures. Applying a single minimization countermeasure often leads to avoiding one phenomenon (e.g., zero-missing phenomenon) while enhancing another (e.g., switching overvoltages). This can challenge designers, as they must consider the trade-offs between these competing objectives. The added value of this article is an analysis of the impact of the compensation level and its distribution (shunt reactor(s) location) in the offshore wind farm power export systems on zero-missing phenomenon and switching overvoltages. These analyses are supported by simulation cases mapping the case of the Polish power system. The results of the presented analysis are very important in light of a dynamic development of offshore wind farms and may be utilized by designers of power export systems, and can mitigate the significant risks occurring in such systems during energization cable lines. Full article

Glutamate is an essential amino acid in both the energy and biosynthetic processes in plant cells. The aim of this work was to study changes in glutamate metabolism upon irradiation of maize (Zea mays L.) leaves with light of different spectral compositions, as well as to identify mechanisms regulating the work of enzymes involved in the studied process. A study was conducted of light-induced changes in glutamate metabolism in maize leaves, mediated by redirecting the glutamate flow to the γ-aminobutyric acid (GABA) shunt. Glutamate dehydrogenase (GDH) was more active in darkness, and the irradiation by red light inhibited the expression of both the Gdh1 and Gdh2 genes. EGTA and ruthenium red abolished the effects of light, indicating the participation of Ca²⁺ ions in phytochrome signal transduction. Contrary to GDH, glutamate decarboxylase (GAD) activity was moderately higher in the light, stimulated by red light, while far-red light reversed the effect. The effect of light on Gad expression was more pronounced than on GAD activity. Irradiation by red light also resulted in the increase in activity of GABA transaminase (GTA), which was abolished by far-red light. The third enzyme of the GABA shunt, succinic semialdehyde dehydrogenase (SSADH), was also activated by light. The effect of light on the expression of Ssadh1, but not on Ssadh2, was phytochrome-dependent. It is concluded that irradiation by light shifts glutamate metabolism from GDH to GAD with the activation of GABA transaminase and SSADH. This suggests that the GABA pathway plays a role in the maintenance of the tricarboxylic acid cycle in the light via bypassing its reactions when the 2-oxoglutarate dehydrogenase complex is inhibited and the cycle switches to the open mode. Full article

The high-thrust linear motor used for the electromagnetic launch is switched by switches composed of anti-shunt thyristors. During the switching process, different current path states will appear, which will lead to changes in motor parameters and current fluctuation. Focusing on the air-core synchronous linear motor with parallel and series power supply, this paper analyzes the change in current path caused by the change in the trigger signal of anti-parallel thyristors in the process of sectionalized stator switching. The motor circuit model of the switching process is derived. A new sectionalized stators switching method is proposed to realize the smooth switching of the sectionalized stators linear motor. Finally, the correctness of the analysis and modeling is verified by simulation, and the effectiveness of the sectionalized stators switching method is tested by using the test prototype. Full article