Non-uniform Voltage Research Articles

Insulation Design of High Voltage and Large Capacity Power Supply Transformer

Abstract At present, the highest voltage level of DC circuit breakers in the world is 535kV. With the construction of 800kV multi-terminal flexible DC project, the demand for DC circuit breaker with higher voltage level is put forward. The voltage level of valve base power supply transformer as the power supply component of the DC circuit breaker is increased to 800kV. Single-section pendulum structure, single-section 100kV and 50kV schemes used at 535kV cannot meet the demand. An 800kV valve base power supply transformer scheme of four 200kV gas-insulated transformers in series is proposed. Its insulation design is also carried out. Firstly, the topology of hybrid DC circuit breaker power supply system and the structure of power supply transformer were described. Secondly, the design of power supply transformer insulation was carried out. Finally, the power supply transformer insulation was tested and verified. The results show that: SF6 power supply transformer internal insulation withstand voltage needs to be multiplied by the multiplication factor. The electric field strength limit of SF6 obtained by experiments is more than 1.5 times of the empirical design value. The internal field strength design of the 200kV power supply transformer takes into account the operating and seismic conditions, and the maximum electric field strength is 15kV/mm and 16.2kV/mm respectively. The curvature radius of the top shielding ring needs to be larger than that of other layers, after optimization, the maximum field strength is 2.68kV /mm when the curvature radius is 300mm. The internal insulation design of 200kV power supply transformer according to lightning impulse. The simulated and measured values of non-uniform voltage coefficient of 800kV power supply transformer under lightning impulse are 1.048 and 1.0488 respectively, in which the voltage equalizing capacitance is 3000pF. The insulation tests of 200kV and 800kV power supply transformer were all passed, and it can be operated safely. Effectively support the development of UHV DC circuit breaker.

Measurement and simulation of voltage differences under ribs and channels and temperature variations within channels in PEMEC

The internal voltage inhomogeneity in a proton exchange membrane electrolyzer cell (PEMEC) is experimentally investigated by using customized gaskets. Three miniature thermocouples are strategically placed inside the channels, specifically in the inlet region, middle region, and outlet region, to monitor temperature variations along the channels. Local voltage measurements are conducted in 13 regions corresponding to the flow channels and 12 regions corresponding to the ribs, under various operating conditions. Additionally, a three-dimensional simulation is performed to analyze the underlying causes of non-uniform voltage distribution and temperature variation. The results reveal contrasting trends in temperature changes along the flow direction, attributable to the varying magnitudes of heat loss and electrochemical heat at different current densities. At low current densities, temperatures increase from the inlet to the outlet along the channels, while at high current densities, temperatures decrease in the same direction. Furthermore, the local voltages of the flow channels (Vchan) and the ribs (Vrib) exhibit different increases along the flow direction at various current densities with the Vchan consistently smaller than Vrib. The inhomogeneity of Vchan is found to be greater than that of Vrib due to bubble disturbances in the channels. The proposed measurement principle for local voltage distribution in PEMECs provides insights into the performance discrepancies between the channel and rib scales in the flow field, thereby enhancing our understanding of electrical property inhomogeneity within the cell.

Predicting Loss Analysis from Luminescence Images in Si Solar Cells with Convolutional Neural Networks

In this work, deep convolutional neural networks (CNNs) are used to speed up the calculation of spatial nonuniform device parameters, voltage and fill factor (FF) losses in crystalline Si solar cells. Luminescence images on finished solar cells, specifically as‐measured electroluminescence (EL) and photoluminescence (PL) images, are used as input features to train the CNN models and losses analysis as output is from a finite‐element modeling program called Griddler. From the analysis of a small dataset of 250 commercial grade solar cells, the CNN models are able to predict the spatially nonuniform distribution of contact resistance and defect parameters of the devices under test and exhibit good performance in the inference of voltage and FF losses. As EL and PL images are widely collected in‐line production data, in the result, the possibility of deploying 2D spatial power loss analysis is implied as a fast, in‐line, and nondestructive analytic tool for solar cells manufacturing.

Enhancement of Terahertz radiation due to excitation of SPW on graphene strip coated on GaAs structure

The present study proposes a methodology for improving terahertz (THz) radiation through the utilisation of a laser directed towards a graphene strip that has been coated onto a GaAs structure. The presence of a non-uniform voltage results in the production of a transient current when the laser interacts with GaAs material. The generation of THz radiation is attributed to the current that is produced along the length of GaAs structures. Concurrently, a portion of the laser beam interacts with the graphene strip, inducing a surface plasma wave (SPW) that propagates along the surface of the graphene. The amplitude of the SPW experiences an exponential decay as it travels away from the interface in both the media. The impact of the transverse electric field of surface plasmon waves in graphene on the transient current in GaAs material has been observed to enhance THz radiation. The frequency of the SPW increases in a parabolic manner as the graphene strip increases with rises with rise in propagation vector. The plasmonics (Graphene plasmons: GPs) approach used for the proposed model enables us to making the emitted radiation suitable for Terahertz spectroscopy, imaging and non-destructive testing, Highspeed data transfer, Terahertz microscopy, Terahertz microscopy, Terahertz microscopy, Quantum technology.

Localized Average Voltage Distribution on the Surface of NMC622 Electrode Measured Using Integrated Al-Voltage Probes during the Cell Cycling at Different C-Rates

Studying localized voltage distribution of electrode surfaces in Li-ion batteries (LIBs) during cell cycling at constant current enables better understanding of the cell degradation phenomenon and prediction of the state of the health. In many studies, individual electrode potentials are analyzed during cell cycling at different C-rates using a reference electrode integrated into the cell, studying the electrochemical reaction mechanism of single electrodes [1,2]. However, for long length electrodes in pouch cells, nonuniform voltage distributions are developed on the electrode surfaces due to inhomogeneous lithiation and de-lithiation during cell cycling. This voltage distribution can cause a variety of issues including loss of energy, accelerated cell degradation, and overcharge or over-discharge of the cell at specific points on the electrodes. For example, recent literature shows that the region of the electrode closest to the current collector tab in pouch cells has the highest state of charge [3].Usually, pouch cells are constructed with different dimensions, depending on the application. However, there is a lack of information on the local voltages at electrode surfaces during charge and discharge at different C-rates. To understand the degradation mechanisms of active electrode materials in the pouch cell application, it is therefore important to spatially quantify the voltage distribution on the electrode surfaces at different C-rates.In this study, two pairs of thin film Al voltage probes were placed carefully onto the surface of NMC622 rectangular cathode to monitor the voltage distribution between equidistant points parallel and perpendicular to the tab direction along the electrode. Following this, a pouch cell was constructed with the cathode (2 mAhcm-2) sandwiched between two graphite-based anodes with an areal charge density of 2.4 mAhcm-2. The surface electrode potentials were measured individually against a standard reference Li/Li+ electrode in-operando during the formation cycle as well as during charge and discharge at rates of C/10, C/5, and C/3.The results show that the electrochemical potential close to the tab is always higher than that further away. A potential gradient exists perpendicular to the tab direction, which increases and decreases continuously during charging and discharging respectively. The potential difference between two lateral points parallel to the tab direction is significantly lower than the difference between two points perpendicular to the tab direction. This voltage distribution across the electrode usually manifests due to the inhomogeneous lithium diffusion along the plane of the electrode. This can be influenced by the electronic and ionic conductivity of the electrode along its plane. Therefore, in addition, Electrochemical Impedance Spectroscopy (EIS) measurements were performed, both perpendicular and parallel to the tab directions at different states of charge (SOC) of the cell. The EIS measurements confirm that the resistance perpendicular to the tab directions is higher than that parallel to the tab direction. Therefore, our results show that it is highly recommended to place voltage and temperature sensors closer to the tabs to monitor the state of health of the cell.[1] Sols L and Engineering A 1995 Current and Potential Distribution in Parallel Electrodes 244 236–44[2] Raccichini R, Amores M and Hinds G 2019 Critical review of the use of reference electrodes in li-ion batteries: A diagnostic perspective Batteries 5 1–24[3] Liu J, Kunz M, Chen K, Tamura N and Richardson T J 2010 Visualization of charge distribution in a lithium battery electrode J. Phys. Chem. Lett. 1 2120–3

Study on Resonance Phenomenon Caused by Voltage Fluctuation of Power Supply in JT-60SA EF Coil

For the large research Tokamak JT-60SA, evaluating the withstand voltage between conductors is one of the most critical factors for the coil design. The power supply feeding the coil injects a wide spectrum of frequency components. The transient response and resonance phenomena induce a non-uniform voltage distribution in the coil. The transiently concentrated voltage can cause the insulation breakdown between conductors, and JT-60SA may not be able to operate safely. This study conducted an impulse test to evaluate the withstand voltage between adjacent conductors for an equilibrium field (EF) coil. The actual power supply voltage for the EF coil was measured to investigate the ramp rate (dv/dt) and frequency spectrum. In addition, based on the results of a resonance test of the EF dummy coil, a circuit simulation model for the EF coil was developed to evaluate the effect of the transient response and resonance phenomenon on the voltage in the coil. The results of this study provide fundamental data that can be used to ensure that the EF coil does not cause insulation breakdown.

A new method for assessment of electro-osmotic permeability through the integration of theoretical and experimental ion flux in electrokinetic processes

Electrokinetic (EK) technology is promising for removing heavy metals from contaminated unsaturated soils. It is crucial to accurately determine the unsaturated electro-osmotic permeability for predicting the efficiency of EK treatment, optimizing treatment strategies, and accurately predicting the distribution of contaminant concentrations. However, the current approach of estimating unsaturated electro-osmotic permeability, which involves measuring effective voltage, drainage volume, and performing exponential fitting, fails to address the issue of uneven voltage gradient distribution during EK treatment. Herein, a novel method was presented for estimating the electro-osmotic permeability of unsaturated porous media. This method quantifies the electro-osmotic flow in an unsaturated porous medium by considering the difference in mass-transfer efficiency (MTE) between real (with electro-osmotic flow) and hypothetical cases (without electro-osmotic flow). This difference serves as a metric for estimating the electro-osmotic permeability. Results revealed a linear relationship between the electro-osmotic permeability and the product of volumetric moisture content and tortuosity, with the slope related to the ionic mobility of target ions, hypothetical and actual MTE. To validate this method, hexavalent Cr (Cr(VI)) was selected as the target contaminant and six EK experiments were conducted with varying initial volumetric moisture content. The feasibility of the method was evaluated by fitting the results of these experiments to obtain the specific slope of the porous medium used. Compared to the existing effective voltage–drainage volume–exponential fitting method, the proposed method offers several advantages. First, it effectively addressed the issue of nonuniform voltage distribution during EK treatment in the unsaturated porous medium. Second, it overcame the problem of a nonzero electro-osmotic permeability at zero volumetric moisture content in the exponential empirical formula. Third, the proposed method was based on theoretical derivations instead of relying solely on empirical fitting. Finally, the proposed method does not require a prior estimate of the saturated electro-osmotic permeability of the porous medium.

Electromagnetic force distribution computations due to switching surge in disc-type winding

This manuscript discusses the computation of electromagnetic forces on a disc-type winding due to a standard switching impulse (SSI). First, the resistances, inductances and capacitances (RLC) of a 30 MVA, 33/11 kV disc-type distribution transformer were estimated to obtain the winding equivalent circuit. The transient voltage waveforms for each of the disc layers and corresponding resonances of the windings under the SSI were then obtained in time domains. Next, the axial and radial force distributions in the disc winding due to the SSI were computed. The forces on each disc layer and along the disc windings due to the SSI were computed based on the analytical and numerical methods via the finite element method (FEM) respectively. The non-uniform switching impulse voltage distribution results in non-uniform force distribution along the disc winding. The magnitude of the axially directed force on the disc winding is found to be higher as compared to the radially directed force.

Numerical study of a 20-cell tubular segmented-in-series solid oxide fuel cell

Tubular segmented-in-series solid oxide fuel cells (SIS–SOFCs) have the advantages of good thermal shock resistance, mechanical strength, and easy sealing because of their tubular structures, and they gain a high operating voltage due to their series configuration. Previous studies have mainly focused on the optimization of a single cell segment while ignoring the flow and heat transfer between series cells. In this study, a 20-cell in-series SOFC model is developed by coupling the electrochemical reactions and mass, momentum, and heat transfer processes. The temperature and composition have a striped distribution because of the noncontinuous electrochemical reaction area. The discontinuity of the heat generation and the intrinsic limit of the access air cooling lead to temperature nonuniformity, while the uneven temperature and component consumption result in the nonuniform voltage of each series cell. For the problems of nonuniform temperature and voltage distributions in the SIS–SOFC, two effective solutions are proposed and evaluated. By introducing a heat pipe as a fuel inlet tube and increasing the length of the downstream cell in turn, the temperature difference is reduced from 111 K to 25 K, and the voltage difference is decreased from 120 mV to 7 mV at an operating current of 3 A.

Investigation on the Negative Capacitance Field Effect Transistor with Dual Ferroelectric Region

This paper proposes a new structure of the negative capacitance field effect transistor (NCFET), which features of the dual ferroelectric region (DFR) when compared to the conventional NCFET. The dual ferroelectric region with FE1 region and FE2 region forms a non-uniform voltage amplification effect, leads to the significantly improvement of the gate control ability and modulates the electric characteristics of the NCFET. The mechanism of the voltage amplification effect, polarization reversal, channel surface electric field, and ferroelectric polarization intensity distributions are investigated. The influences of the ferroelectric parameters α and β on the electric characteristics are discussed. The results show that the DFR-NCFET is able to obtain a subthreshold swing (SS) below the Boltzmann limit (60 mV/dec) by increasing the ferroelectric parameter α of the FE2 region.

Polarization Gradient Effect of Negative Capacitance LTFET.

In this paper, an L-shaped tunneling field effect transistor (LTFET) with ferroelectric gate oxide layer (Si: HfO2) is proposed. The electric characteristic of NC-LTFET is analyzed using Synopsys Sentaurus TCAD. Compared with the conventional LTFET, a steeper subthreshold swing (SS = 18.4 mV/dec) of NC-LTFET is obtained by the mechanism of line tunneling at low gate voltage instead of diagonal tunneling, which is caused by the non-uniform voltage across the gate oxide layer. In addition, we report the polarization gradient effect in a negative capacitance TFET for the first time. It is noted that the polarization gradient effect should not be ignored in TFET. When the polarization gradient parameter g grows larger, the dominant tunneling mechanism that affects the SS is the diagonal tunneling. The on-state current (Ion) and SS of NC-LTFET become worse.

Global Modeling of Millimeter-Wave Transistors: Analysis of Electromagnetic-Wave Propagation Effects

In this study, the transmission line concept and the electron transport theory are consolidated in a global modeling approach, the wave-electron-transport (WET) model, to account for the physical phenomena in millimeter-wave devices. No equivalent circuit model is required to represent the innate properties of the device. Hence, the model is reliable for both small- and large-signal analyses. The electrodes of a transistor act as coupled multi-conductor transmission lines at millimeter-wave bands. The WET model consists of a device solver to obtain solutions for carrier-transport equations of the intrinsic device, and an electromagnetic solver (EM solver) to provide solutions for the governing transmission lines equations. As it is crucial to transfer data between these two solvers, an interface scheme is also developed and included in the WET model. The extrinsic parameters of the device are extracted using a novel systematic technique merely based on the physical structure of the transistor. In this paper, the modeling procedure is applied to a fabricated GaN-HEMT device. Power sweep analysis has verified the accuracy of the proposed model under both linear and non-linear operations. Non-uniform voltage distribution caused by traveling waves over the electrodes is elaborately discussed to demonstrate the necessity of incorporating distributed effects.

An Ultraviolet Photon Counting Imaging System Based on a SiC SPAD Array

This letter presents a novel ultraviolet photon counting system based on a SiC SPAD array. The detector is made of 4H-SiC with a fairly low dark current in pA level and the array size is $1\times 128$ . In order to reduce the influence of dark count on image quality, this letter proposes an adaptive sampling readout circuit system, which can automatically adjust the SPAD hold-off time according to the photon density of the applications. Aiming at the nonuniform breakdown voltage of SPADs in a linear array, an adjustable bias voltage circuit is adopted to realize the accurate adjustment of pixel SPAD’s bias voltage. The ROIC is taped out in TSMC 0.18 $\mu {\mathrm{ m}}$ standard CMOS process and connected to the SPAD array by a gold bonding package. Based on the self-developed imaging system, UV photon counting imaging and deep violet- visible light fusion imaging are realized for the first time.

A Nonuniform Reference Voltage Optimization Based on Relative-Precision-Loss Ratios in MLC NAND Flash Memory

In Multi-Level-Cell (MLC) NAND flash memory, cell-to-cell interference (CCI) and retention time have become the main noise that degrades the data storage reliability. To mitigate such noise, a relative precision loss (RPL) nonuniform reference voltage sensing strategy is proposed in this paper. First, based on the NAND flash channel model with CCI and retention noise, we simulate the data storage process of MLC NAND flash by Monte Carlo method, and find that the threshold-voltage of each disturbed storage state shows approximately to be Gaussian distributed. Then, by Gaussian approximation, the distribution of threshold voltage can be estimated easily in mathematics with a little loss. Second, we introduce a concept of log-likelihood ratio (LLR)-based RPL ratio to determine the dominating overlap regions, and then propose a new nonuniform reference voltage sensing strategy. This strategy does not only reduce the memory sensing precision (i.e., the number of reference voltages), but also maintains the reliability of the soft information of NAND flash memory channel output for soft decoding. Third, we implement extensive simulations to verify the performance of the new nonuniform sensing strategy. The BER performances of LDPC codes for different sensing strategies are provided to show that the proposed LLR-based RPL-nonuniform sensing strategy can make a good compromise between memory sensing latency and error-correction performance.

Distributed robust secondary voltage control for islanded microgrid with nonuniform time delays

This paper proposes a nonuniform delay-dependent robust secondary voltage control strategy with a finite-time voltage reference observer for an islanded microgrid. A discrete-time consensus algorithm is introduced to track the output voltage. By model transformation, a closed-loop microgrid control system is obtained. And then, the corresponding global stability and robust performance analysis theorems are derived. After implementing a series of trial studies, the impacts of secondary voltage control gains, sampling time on energy-to-peak robust performance are obtained. And the feasible optimal voltage control gains can be derived. Besides, a distributed cooperative secondary frequency control is introduced. Simulations of a four inverter-based microgrid test system are presented to verify the control performance. The simulation results indicate that our proposed method can maintain accurate voltage/frequency restoration and active power sharing. In addition, the voltage control gain parameters, arbitrary nonuniform time delays, and especially sampling time effects on the secondary voltage control performance are also verified.

Comparison of conventional and new cascaded multilevel inverter topologies based on novel indices

This paper proposes new indices of cascaded multilevel inverters (MLIs) in order to compare the conventional topology with 10-existed new topologies. Reduction in the number of power switches is the main target of these new topologies. This aim is to reduce the total cost of designed inverters, though the mentioned aim is not enough to design new inverters. Thus, in this study, four comparative indices including sources power uniform distribution index (SPUDI), switches current uniform distribution index (SCUDI), switches loss uniform distribution index (SLUDI), and switches voltage uniform distribution index (SVUDI), are proposed. In addition, it is shown that in most of the new topologies, reducing the number of switches can lead to lowered values of the proposed indices, after which non-uniform power, current, loss, and voltage pattern are obtained. The results prove that mere emphasis on the number of switches, along with the exclusion of either of the proposed indices will cause significant problems, where cost reduction may be underachieved. Based on new indices, the advantages of conventional topology over new ones are presented in this study.

Electromagnetic design and tuning of the four-vane radio frequency quadrupole with nonuniform intervane voltage profile

Equipartitioning is an efficient beam-dynamics design scheme also for radio frequency quadrupole (RFQ). To realize an equipartitioned RFQ, it is essential to reproduce the nonuniform intervane voltage profile required from the beam dynamics. We developed a cavity design and tuning method to this end. The dimensions of a voltage-ramped four-vane cavity were determined by a three-dimensional rf simulation. To produce the desired vane voltage profile, the longitudinal variation of the cross-sectional shape was adjusted using the least-squares method based on the simulated responses of the vane-base width to the quadrupole-mode field. In the low-level tuning, slug-tuner positions were determined based also on the least-squares solutions obtained from the simulated tuner responses to the field profile. Finally, the deviation of the quadrupole-mode field was within 1.5% from the design profile, and the mixed dipole modes were 1% of the quadrupole-mode field after only two iterations of tuner adjustment; they are sufficiently smaller than the requirement of 2%.

Новое устройство для контроля качества высоковольтной электрической изоляции

The article examines different physical values that are connected with the absorption phenomenon and their use for condition assessment of non-uniform high voltage isolation. The device has been developed for condition monitoring of non-uniform high voltage isolation and determination of its remaining lifespan using isolation condition evaluation based on absorption phenomenon.

A finite element method for electrowetting on dielectric

We consider the problem of electrowetting on dielectric. The system involves the dynamics of a conducting droplet, which is immersed in another dielectric fluid, on a dielectric substrate under an applied voltage. The fluid dynamics is modeled by the two-phase incompressible Navier-Stokes equations with the standard interface conditions, the Navier slip condition on the substrate and a contact angle condition which relates the dynamic contact angle and the contact line velocity, as well as the kinematic condition for the evolution of the interface. The electric force acting on the fluid interface is modeled by the Maxwell's equations in the domain occupied by the dielectric fluid and the dielectric substrate. We develop a numerical method for the model based on its weak form. This method combines the finite element method for the Navier-Stokes equations on a fixed bulk mesh with a parametric finite element method for the dynamics of the fluid interface, and the boundary integral method for the electric force along the fluid interface. Numerical examples are presented to demonstrate the accuracy and convergence of the numerical method, the effect of various physical parameters on the interface profile and other interesting phenomena such as the transportation of droplet driven by applied non-uniform voltage.

Development of High Gradient ZnO Arrester Material for High Voltage Applications

The presence of stray capacitance in ZnO (Zinc Oxide) surge arresters causes hurdles in arrester operation and non-uniform voltage distribution along the arrester column, especially for High Voltage (HV) and Extra high voltage (EHV) applications. Since the magnitude of stray capacitance is directly proportional to the arrester height; the shortening of surge arresters is a preeminent method to enhance the arrester performance and voltage distribution. Particularly, this stray capacitive effect delays the arrester operation from in-action to action mode, especially against very fast surges. Moreover, the shortening of the arrester column improves the voltage distribution and hence the electric field varies between the stacks. Therefore, this research work focuses on the preparation of two new high gradient arrester materials doping with rare earth oxides. The microstructures of the newly developed materials are analyzed. It is found that there is a reduction of grain sizes and an increase of voltage gradients in the newly developed arrester materials. From this, the height requirement per unit is estimated and compared with the conventional ZnO arrester. Using these high gradient materials, the reduction of height and compactness of the arrester assembly may be achieved greatly. Thus, the developed ZnO surge arrester with high gradient materials enhances the arrester behavior with the attendant improvement of voltage distribution due to its reduced height and stray effect.