Electrical DC Research Articles

Impact of plasma‐treated nano‐alumina on the thermal and electrical properties of epoxy resin at elevated temperatures

AbstractIn this study, to ramp up the thermal stability and insulation characteristics of epoxy resin (EP), the plasma‐treated EP/alumina composites with a mass fraction of 1 wt% were fabricated. The variations of functional groups in the EP composites with/without plasma treatment were characterized by Fourier transform infrared spectroscopy (FTIR), and the glass transition temperature of the specimens was analyzed by differential scanning calorimetry (DSC) analysis. The space charge distributions, the electrical conductivity and DC breakdown strength of the specimens were measured at 90°C. Moreover, the results were further analyzed in depth. The results indicated that the nanocomposites prepared with plasma‐treated nano‐alumina exhibited a higher concentration of OH and CO groups. At 90°C, the plasma‐treated alumina nanoparticles significantly increased the charge injection threshold of EP from about 26 nC (untreated) to 19 nC (treated); reduced the internal electric field distortion, decreased the charge accumulation and dissipation, and increased the breakdown strength from about 104 kV/mm (untreated) to 115 kV/mm (treated), and the conductivity from about 5.1 × 10−14 S/m (untreated) to 3.1 × 10−14 S/m (treated). In summary, it was elucidated that plasma‐treated nano‐alumina particles could effectively reduce deep trap density, trapped charges, charge injection and transportation and reinforce composites' insulation performance at high temperatures.Highlights The DBD plasma treatment is environmentally friendly with high efficiency. The testing adopted advanced characterization and analysis techniques. Plasma treatment of alumina nanoparticles enhanced the thermal stability. The treated nano‐alumina reinforced insulation performance of EP nanocomposites. The plasma treatment raised the space charge injection threshold and barrier.

Optimal Placement and Sizing of Distributed Generation in Electrical DC Distribution Networks Using a Stochastic Mixed-Integer LP Model

AbstractThis paper presents a stochastic mixed-integer linear mathematical model for finding the optimal placement and sizing of distributed generation in a DC distribution network, considering the uncertainty of electrical demand and distributed renewable sources. The proposed model accurately represents the original mixed-integer nonlinear model, obtaining a globally optimal solution in less computational time with low errors. The mathematical model allows for considering constraints related to the maximum limits for the penetration of distributed generation, such as those specified by Resolution CREG 174 of 2021. Furthermore, the uncertainties of the electrical demand, wind energy-based distributed generation (DG), and solar energy-based DG are considered in the mathematical models using a two-stage stochastic programming approach. The accuracy and efficiency of the proposed model were tested and validated on a 21-node DC test system from the specialized literature, and the effectiveness and robustness were assessed on a 69-node DC test system. The obtained results show that the proposed stochastic mixed-integer linear mathematical model performs well.

A peristaltic electromagnetic (EM) micropump with dome-shaped PDMS membranes for biomedical application

A peristaltic electromagnetic (EM) micropump driven by dome-shaped membranes was successfully fabricated and tested. The pump system comprises EM coil components, three magneto-mechanical actuators, and a microfluidic system. The pump system with three actuator membranes/chambers connected in series is intended to replace the conventional valve and pump rollers, enabling the delivery of fluids at a high flowrate. The actuator membrane is made of polydimethylsiloxane (PDMS), measuring 5 mm in diameter and approximately 100 µm thick, and fabricated using soft lithography techniques to form a normally deflected dome-shaped membrane structure. The microfluidic channel is made of PDMS and created using a sacrificial layer-pattern process, allowing straightforward soft-litography process without mold transfer. The fabricated device was tested by applying electrical DC currents ranging from 500 mA to 1000 mA at frequencies up to 10 Hz. This resulted in the depletion of the membrane by up to 2 mm, causing fluid flow through the microchannel at a flow rate of 8 mL per minute. The test results revealed that the peristaltic EM micropump can generate a significant fluid flow rate, making it suitable for pumping controlled fluids within a range of up to 10 mL/minute. This micropump has a wide range of potential applications, including the management of insulin medication for patients with acute diabetes mellitus and the delivery of drugs and dialysate fluid in artificial kidney applications.

Study on corona discharge on the grounding wire of ±1100 kV transmission line during the downward lightning flash

The atmospheric space electrical field has nonlinear distribution characteristics during thunderstorm activity, which influences the ground surface electric corona of UHV transmission lines. In this paper, the corona discharge model of ground wire of ±1100 kV UHVDC transmission line is established considering the combined effect of ground lightning process and working voltage. With the combined action of thundercloud electrical field and DC voltage, the positive conductor suppresses the electric corona of the upper shied wire, and the negative conductor enhances the discharge of the upper shied wire. The corona current of the right shied wire is 54.7 μA/m larger than that of the left shied wire. When the down leader develops, the leader voltage, the line operating voltage and the thundercloud voltage work together, and the electric corona on the surface of the conductor and shied wire of the transmission line increases rapidly. The corona current increases 102 times on the left shied wire's surface and 103 times on the right shied wire's. Considering the environmental factors and the development of the downgoing leader at the same time, the degree of electric corona on the surface of the shied wire is weakened when the humidity in the space increases, but the overall value of the corona current is much higher than the thundercloud electrical field. When the wind speed increases, the degree of electric corona on the surface of the shied wire is aggravated. The corona current on the surface of the left shied wire is 37.13 μA/m, and the one of the right shied wire is 109.33 μA/m. The corona current value of ground surface increases with the increase of wind direction.

A practicable geophysical resistivity imaging sensing approach for urban geological water disaster detection: A real-world case study

In the urban environment, the transient electromagnetic method often suffers from severe electromagnetic interference because it employs coils to perceive the electromagnetic field. To address this issue, the DC method employs electrodes to shield the electromagnetic noise in the urban environment. In this paper, a new geophysical resistivity imaging sensing approach based on a DC inversion model is proposed to explore and identify the path of underground water to solve the water disaster problem. A real-world case study is carried out in Xinjiang Region. In order to investigate the underground water conducted path, an electrode network is designed and installed for the buildings of interest to collect the DC electrical current and DC electrical potential data. Then, the proposed method establishes a DC resistivity inversion model based on the forward theory and finite-volume technique to extract the geological information from the collected data and visualize the underground water conducted path. Different from existing popular numerical techniques, such as the finite element and finite difference, the finite-volume technique has clear theoretical explanations to make the obtained geological images understandable. As a result, the underground water path can be directly observed from the geological images calculated by the proposed approach to successfully identify and locate the underground water disaster in real-world applications.

Generalized extremal branes in AdS/CMT and holographic superconductors

AdS4 generalized extremal branes are scrutinized in the context of AdS/CFT. Holographic superconductors are studied as dual objects to AdS4 generalized extremal branes, whose coefficients of response and transport in the dual condensed matter theory are calculated and discussed. The holographic Weyl anomaly is also addressed. The holographic superconductor bound current is shown to be enhanced by the parameter controlling the family of AdS4 generalized extremal branes, when compared to the standard AdS4-Reissner–Nordström black brane results. In the probe limit, the electrical DC conductivity for holographic superconductors with AdS4 generalized extremal branedual background is also reported.

In-situ S/TEM DC biasing of p-GaN/AlGaN/GaN heterostructure for E-mode GaN HEMT devices

This work describes an in-situ electrical DC bias study of the E-mode GaN high electron mobility transistor (HEMT) device. A single transistor structure is biased and studied in real-time. The sample was made from an E-mode GaN HEMT device using Focused Ion Beam (FIB) milling and upright lift-off. The device lamella is subjected to forward gate bias to understand the device operation and physical changes under the bias. Active device area and micron level changes due to biasing were studied and identified as crucial factors affecting device reliability during continuous operation. Electric bias-induced physical changes are observed at the p-GaN layer and AlGaN interface on the p-GaN and GaN sides. Localized damage and defect formation, along with elemental diffusion, is observed. The formation of new defects over existing growth defects was seen in the p-GaN/AlGaN/GaN heterostructure. The study helped us identify the exact location of the failure, the region affected under bias, and the occurrence of physical changes due to the electrical bias on the in-situ device. Based on the study, gate breakdown failure and its location at the metal/p-GaN interface are understood to result from physical changes activated by electrical bias.

Tailless Information-Energy Metasurface.

Programmable metasurface technology can achieve flexible manipulations of electromagnetic waves in real time by adjusting the surface structure and material properties and has shown extraordinary potential in many fields such as wireless communications and the Internet of Things. However, most of the programmable metasurfaces have a common feature: a tail (electrical wires and DC powers), which is difficult to supply in some particular application scenarios such as canyons and mountains. To eliminate the limitation of DC power supply, the programmable metasurface and wireless power transfer technology are combined to propose a tailless information-energy metasurface (IEMS). The tailless IEMS platform can dynamically control electromagnetic waves without relying on an external DC power supply; instead, the required DC power is provided internally by the IEMS platform itself. In the tailless IEMS experiments, the concept is demonstrated through the dynamic regulation of wireless channels and the wireless transmission of DC power. This work provides a self-powered method for programmable metasurfaces, expands the application scenarios, facilitates the miniaturization of systems, and makes it easy to integrate with other systems.

An overview of Artificial Intelligence applications to electrical power systems and DC microgrids

An overview of Artificial Intelligence applications to electrical power systems and DC microgrids

Internet of Thing untuk Memantau Sistem Kelistrikkan Pembudidaya Ikan Hias

The Pondakan Alam Sari ornamental fish cultivator group has approximately 50 types of ornamental fish cultivated for domestic and foreign commodities. Market demand for ornamental fish tends to increase yearly, but the market wants stable prices. This price stability is a dilemma for ornamental fish cultivator groups. One of the determinants of the selling price of ornamental fish is operational costs, especially electricity costs. The increase in basic electricity tariffs causes operational costs to increase. Electricity is used to power the circulating water pump 24 hours non-stop daily. This circulating water pump is very important for producing oxygen in the water. If there is no oxygen in the water, ornamental fish will die. To reduce operational electricity costs, the community service team built a DC electricity system sourced from solar energy so that the circulating water pump source no longer uses PLN electricity. This community service program aims to reduce operational electricity costs by building a DC electricity system sourced from solar energy and an IoT-based monitoring process. The implementation method consists of two stages: (1) building physical capital through a solar energy electricity source and DC pump installation and (2) creating a DC electrical parameter monitoring system with the Blynk IoT platform. The evaluation technique was carried out by comparing planning with the progress of implementing activities. The results and implications of activities include the availability of DC electricity sources from renewable energy, namely solar cells with a power of 960 WP, installing 10 DC pumps, and an IoT-based DC electrical parameter monitoring system. Operational costs in managing an ornamental fish business can be reduced by 46% from before using renewable and IoT-based energy. This result will certainly increase the profit margin of ornamental fish farming.

Effect of Deposition Technique of SiNx Passivation Layer on the Electrical DC and RF Properties of AlGaN/GaN HEMTs

Effect of Deposition Technique of SiNx Passivation Layer on the Electrical DC and RF Properties of AlGaN/GaN HEMTs

High-temperature impedance properties of Sr1-xCaxTiO3 ceramics for lead-free capacitor applications

ABSTRACT Lead-free Sr0.6Ca0.4TiO3 ceramic was prepared by solid-state reaction route. X-ray diffraction technique showed the phase purity and identified the orthorhombic perovskite structure. Scanning Electronic Microscopy observation evidenced homogeneous morphology and dense microstructure. Electrical conduction and dielectric relaxation mechanisms at high temperature have been studied by complex impedance measurement techniques over a wide range of frequencies and temperatures, from 100 Hz to 1 MHz and from 573 K to 783 K. Fitting of impedance measurements allowed us to study grains and grain boundaries electrical characteristics and their contribution to the conduction and dielectric relaxation processes in the ceramic. Electrical conduction in grains is due to oxygen vacancy jumps for temperatures below 733 K and to polarons above 763 K. Electrical DC conductivity in grains and grain boundaries is mainly due to oxygen vacancies. Impedance measurements and relaxation time distribution function calculations show non-Debye-type relaxation effects for both grains and grain boundaries.

Determination of the Magnetic Intermediate Permeability of Special Materials Based on FEM-Simulation and Hall-Sensor Measurement

This document presents the process flow and the experimental conditions for calculating the static magnetic intermediate permeability of a specimen with a dedicated geometrical contour and surface for simulation parameter of metal detection systems. In this case, intermediate is explained and defined as probes with a magnetic permeability between 10 and 1000. An analysis of recent and current measurement standards as well as similar simulation principles leads to the contribution value of this new hybrid process flow. To calculate the permeability value in a first step, an electromagnetic circuit was constructed and excited with a defined electrical DC current with a dedicated tolerance for generating a static approximated homogenic magnetic field in a defined air gap space sector. Additionally, to the H-field generation part double copper coil, two magnetic ferrite cylinders with known permeability were used. The electrical and magnetic circuit has been modeled by an Ansys FEM Electronic Desktop software; the solver is magnetic static. Specifically, the simulated magnetic field distribution of the airgap was evaluated by using different Hall sensor elements with different tolerances. Subsequently, the electromagnetic circuit was expanded by implementing different cylindrical and cube shaped probes on a defined position inside the air gap sector with homogenic magnetization. Moreover, based on the analysis of the air gap structure without the probes, a detailed 3D-FEM model of the air gap magnetic field with special probes was established, which provides the environmental field distribution of the probes. The simulation models were compared with the corresponding Hall sensor measurements, which proved the high accuracy experimental validity of the models established in this paper. Finally, some key features related to parameter variations in the electromagnetic circuit were extracted, which can significantly reflect the characteristics of the robustness of the measurement principle. The main findings reported in this paper will be beneficial for magnetic parameter settings in electromagnetic simulation.

Dynamic memory tuned by frequency in a homologous thermotropic liquid crystal.

With scaling of dynamic RAM and NAND memory technologies reaching a limit, there is a need for dynamic memory with high density. In this work, an investigation on existence of dynamic memory feature in a frequency tuned homologous series of thermotropic liquid crystals has been carried out. A homologues series of five thermotropic liquid crystalline compounds comprising of 4-butyl benzoic acid and various alkyloxy benzoic acids are prepared, and all these mesogens exhibit only nematic phase. Liquid crystal dynamic memory storage setup consists of a conducting transparent glass cell with two indium tin oxide coated transparent glass plates acting as electrical electrodes in which the selected thermotropic liquid crystal is filled by capillary action. The temperature dependent dielectric relaxation studies enable to elucidate the relaxation frequency of each of these mesogens in nematic phase. The liquid crystal at different temperatures is excited with the relaxation frequency at various chosen fields, and the dielectric hysteresis is recorded. The magnitude of the hysteresis loop is directly proportional to the memory storage capacity. The main objective of this work is observation of dynamic memory storage in liquid crystals exhibiting nematic phase, at different frequencies in a thermotropic liquid crystal as the ingredient in a conducting polyamide buffed glass cell excited by an external electrical dc stimulus. The variation of the hysteresis loop with varying field; temperature and frequency are also studied and reported in this work.

Synchronous Switch Energy Extraction Circuit for Motor Regenerative Braking Enhancement

The synchronous switch technique has been utilized as a promising solution to enhance the energy harvesting capabilities of piezoelectric devices. It utilizes a switched inductive branch to compensate for the capacitive source and increase the real power. The synchronous switch technique was also extended to enhance energy harvesting from electromagnetic (EM) sources. This paper introduces a synchronous switch energy extraction (SSEE) circuit and examinates its performance in motor regenerative braking (RB) enhancement. In the SSEE scheme, a switched capacitive branch is connected to compensate for the inductive source of an electromagnetic motor. The output current from a coil is made in phase with the induced voltage source. The braking power is significantly improved. Therefore, the kinetic energy is extracted much faster to brake the motor quickly, while a portion of the extracted energy is harvested into storable electrical dc energy. This paper comprehensively evaluates the SSEE performances, in terms of energy harvesting and motor braking, respectively. Experimental results show that, given a flywheel released from the same speed, the SSEE can recover 182.5% more energy than the diode-bridge rectifier. For the braking performance, the SSEE can reduce the braking time by 35.1%, compared with the short-circuit braking (SCB) case.

Frequency response analysis of a toroidal field coil of the divertor tokamak test facility

The magnet system of the Divertor Tokamak Test (DTT) facility is mainly made up with superconducting coils. During the operation of the DTT machine, high voltages will appear across each Toroidal Field Coil (TFC) when fast current will ramp down; the reason why, a reliable electrical insulation is required for the operation of the TFC system. With the aim of checking the correct sizing and implementation of the electrical insulation, different DC and AC electrical tests will be performed during all the coil manufacturing process. Among these, the impedance spectrum test, or rather the complex impedance measurement over several decades of frequency range, can be used to analyze the frequency response of the coil. The variations of the resonance frequency (f0), during its electrical acceptance test, can be useful to make predictions about the detectability of internal failure conditions in a coil. This paper focuses on analysis of the frequency response of a TFC, using a numerical simulation approach. The goal is to assess the impedance spectrum of a TFC within a fixed frequency band by a frequency-dependent lumped network. Starting from the TFC layout, a WP with the casing has been modeled by a complex network of lumped parameters in Ansys 2021/R2 environment. The data (amplitude and phase angle vs frequency) obtained have been used to study the f0 variation during the different manufacturing stage of the WP. This model will be able to make predictions about the detectability of internal short-circuit in a TFC.

A Modeling Toolkit for Comparing AC and DC Electrical Distribution Efficiency in Buildings

Recently, there has been considerable research interest in the potential for DC distribution systems in buildings instead of the traditional AC distribution systems. Due to the need for performing power conversions between DC and AC electricity, DC distribution may provide electrical efficiency advantages in some systems. To support comparative evaluations of AC-only, DC-only, and hybrid AC/DC distribution systems in buildings, a new modeling toolkit called the Building Electrical Efficiency Analysis Model (BEEAM) was developed and is described in this paper. To account for harmonics in currents or voltages arising from nonlinear devices, the toolkit implements harmonic power flow, along with nonlinear device behavioral descriptions derived from empirical measurements. This paper describes the framework, network equations, device representations, and an implementation of the toolkit in an open source software package, including a component library and graphical interface for creating circuits. Simulations of electrical behavior and device and system efficiencies using the toolkit are compared with experimental measurements of a small office environment in a variety of operating and load configurations. A detailed analysis of uncertainty estimation is also provided. Key findings were that a comparison of predicted versus measured efficiencies and power losses in the validation testbed using the initial toolkit implementation predicted device- and system-level efficiencies with reasonably good accuracy under both balanced and unbalanced AC scenarios. An uncertainty analysis also revealed that the maximum estimated error for system efficiency across all scenarios was 3%, and measured and modeled system efficiency agreed within the experimental uncertainty in approximately half of the scenarios. Based on the correspondence between simulation and measurement, the toolkit is proposed by the authors as a potentially useful tool for comparing efficiency in AC, DC, and hybrid AC/DC distribution systems in buildings.

Effect of (Sm, In) Doping on the Electrical and Thermal Properties of Sb2Te3 Microstructures.

Doped Sb2Te3 narrow-band-gap semiconductors have been attracting considerable attention for different electronic and thermoelectric applications. Trivalent samarium (Sm)- and indium (In)-doped Sb2Te3 microstructures have been synthesized by the economical solvothermal method. Powder X-ray diffraction (PXRD) was used to verify the synthesis of single-phase doped and undoped Sb2Te3 and doping of Sm and In within the crystal lattice of Sb2Te3. Further, the morphology, structure elucidation, and stability have been investigated systematically by scanning electron microscopy (SEM), Raman analysis, and thermogravimetric analysis (TGA). These analyses verified the successful synthesis of hexagonal undoped Sb2Te3 (AT) and (Sm, In)-doped Sb2Te3 (SAT, IAT) microstructures. Moreover, the comparison of dielectric parameters, including dielectric constant, dielectric loss, and tan loss of AT, SAT, and IAT, was done in detail. An increment in the electrical conductivities, both AC and DC, from 1.92 × 10-4 to 4.9 × 10-3 Ω-1 m-1 and a decrease in thermal conductivity (0.68-0.60 W m-1 K-1) were observed due to the doping by trivalent (Sm, In) dopants. According to our best knowledge, the synthesis and dielectric properties of (Sm, In)-doped and undoped Sb2Te3 in comparison with their electrical properties and thermal conductivity have not been reported earlier. This implies that appropriate doping with (Sm, In) in Sb2Te3 is promising to enhance the electronic and thermoelectric behavior.

Effect of Electric-Field Components on the Flashover Characteristics of Oil-Paper Insulation Under Combined AC-DC Voltage

Flashover characteristics are closely related to the electrical field distribution on the surface of oil-paper insulation. In this study, the effects of electrical field and DC voltage components on the creepage flashover characteristics of oil-paper insulation under combined AC-DC voltage (CADV) are investigated using two electrode models. The results demonstrate that when the DC voltage component is large, the flashover voltage under the influence of strong parallel electric field component is approximately 1.2 times higher than that under the influence of strong normal electric field component. When the DC voltage component value increases under the influence of strong normal electric field component, the value of corresponding AC voltage component of the creepage flashover voltage exhibits a decreasing trend. It is believed that due to the strong normal electric field component, the electrons intensify the collision on the surface of the insulating pressboard. Under the influence of the DC voltage component and due to the presence of space charge on the insulating pressboard, the distribution shape of carbonized particles on the surface of the insulating pressboard after creepage flashover is different. Furthermore, the instantaneous energy release during creepage flashover under CADV is higher than that under AC voltage, and the greater the DC voltage component value, more severe is the damage to the fibers on the insulating pressboard surface.

Droop control for district heating networks: Solution for temperature control of multi-energy system with renewable power supply

In a district heating system, the flow of heated water transfers enthalpy from the generation side to the load side. It is thus critical to maintain the supply temperature at a desired level. However, with the rise of renewable energy sources in the district heating network, the temperature of the heated water tends to be disturbed. This calls for a deployment of thermal energy storage. To effectively exploit the flexibility of thermal energy storage, the relationship between the temperature of the district heating water and the power sharing with other thermal energy resources is considered in this paper. Based on this relationship, the concept and realization of a droop control for the district heating network is proposed. It is shown how the droop characteristic between the temperature of the heated water and the power sharing of the thermal energy storage for the district heating network is developed in analogy to the droop control used in an electrical dc network. The droop characteristic so supports the control of a district heating network. The theoretical considerations are complemented by application to a residential district heating network model to illustrate the functionality of the control. The studies are conducted with the program PSCAD, which is otherwise typically used for simulating electromagnetic transients.