High Voltage Gradient Research Articles

Er2O3 doped ZnO–Cr2O3-based varistors with high voltage gradient

ZnO varistors are widely used in modern intelligent electrical equipment, and the preparation of miniaturized varistors with high voltage gradient has become a top priority. This work investigated the preparation of high voltage gradient ZnO–Cr2O3-based varistors doped with Er2O3 and analyzed the relationship between their microstructure and electrical properties. As the doping amount of Er2O3 increases from 0.00 to 0.75 mol%, Er2O3 phase obviously dissolving element Co distributed at the trigeminal grain boundaries increases, leading to the grain size d decreases from 3.16 to 1.70 μm, the nonlinear coefficient α increases from 6.22 to 50.48, the voltage gradient E1mA increases from 428.37 to 1616.76 V/mm, and the leakage current density JL decreases from 375.75 to 0.79 μA/cm2, achieving optimal comprehensive electrical performance of the sample with Er2O3 doping of 0.75 mol%, for which, the residual voltage ratios K reaches the minimum value of 1.14 under the impulse current density Jp of 63.7 A/cm2. When the doping amount of Er2O3 further increases to 1.00 mol%, the excessive Er2O3 phase aggregates at the trigeminal grain boundaries and distributes unevenly, leading to the growth of ZnO grains and performance deterioration of the samples. The ZnO–Cr2O3-based varistors have the advantages of much easier doping, and there is no dopant volatilization during the sintering process. This research provides an important reference for the development of high-performance, miniaturized ZnO–Cr2O3-based varistors.

Inverter-Fed Motor Drive System: A Systematic Analysis of Condition Monitoring and Practical Diagnostic Techniques

Due to their efficiency and control capabilities, induction motors fed with inverters have become prevalent in various industrial applications. However, ensuring the reliable operation of the motor and diagnosing faults on time are crucial for preventing unexpected failures and minimizing downtime. This paper systematically analyzes condition monitoring and practical diagnostic techniques for inverter-fed motor drive systems. This study encompasses a thorough evaluation of different methods used for condition monitoring and diagnostics of induction motors, with the most crucial faults in their stator, rotor, bearings, eccentricity, shaft currents, and partial discharges. It also includes an assessment of their applicability. The presented analysis includes a focus on the challenges associated with inverter-fed systems, such as high-frequency harmonics, common-mode voltages causing the bearing currents, and high voltage gradients (dv/dt) due to fast switching frequency, which can impact the motor operation, as well as its faults analysis. Furthermore, this research explores the usefulness and efficiency of various available diagnostic methods, such as motor current signature analysis and other useful analyses using advanced signal processing techniques. This study aims to present findings that provide valuable insights for developing comprehensive condition monitoring strategies, and practical diagnostic techniques that enable proactive maintenance, enhanced system performance, and improved operational reliability of inverter-fed motor drive systems.

Electric Field Distribution on Zinc Oxide Pills in Gapless Surge Arresters Using Finite Element Method and Evolutionary Optimization Algorithms in HVAC Systems

This article proposes a new method for the optimal design of zinc oxide arresters based on electric field distribution on the zinc oxide column using smart algorithms and finite element analysis. This design prevents premature aging of zinc oxide tablets, especially the initial and final tablets of the column, which have a higher voltage gradient than other parts of the arrester, and subsequently increases the sustainability of the network. The spacer height, fiberglass layer thickness, and grading ring diameter and its location were taken as the problem variables. The surge arrester was designed in AC/DC mode and two-dimensional symmetry using the COMSOL Multiphysics package. For the first time, rational Bezier curves were also used for the arrester design. This paper presents an optimization approach that combines and dynamically links the electrostatic modeling process and the particle swarm optimization (PSO) and differential evolution (DE) algorithms. The proposed approach is a general method that can be used in the design of high-voltage equipment. The results showed that the lifetime and reliability were increased by reducing voltage variations in the ZnO column. Therefore, maintenance cost and implementation of a surge arrester would be reduced. Finally, the external surface of the porcelain housing was placed under the influence of uniform distribution of electric field.

Treatment of Pb-contaminated soil by electrokinetics: Enhancements by varying voltage, chelant, and electrode material

This work examines the removal of lead (Pb) from artificially contaminated soils (1000 mg/kg Pb) using the Electrokinetic Remediation (EKR) technique. Operating parameters, including periodic voltage gradient, electrolyte amendments with ethylenediaminetetraacetic acid (EDTA) and a non-ionic surfactant (Tween 80), and type of electrode material were investigated. Results indicated that a high voltage gradient (2.5 V/cm), in conjunction with EDTA as electrolyte, and stainless-steel electrodes favored the overall removal process. Pb removal by selected electrolytes was in order EDTA (65 %) > Distilled water (64.1 %) > Tween 80 (6.2 %). Visual Minteq v.3.1 software was employed to predict the chemical equilibrium of different chemical species of Pb against pH. Results confirmed that when EDTA was used as an electrolyte, the [Pb-EDTA]2− complex predominated over the Pb(OH)2 complex at an alkaline pH, resulting in more removal. Findings suggested that stainless steel was a better alternative to graphite with respect to removal efficiency and corrosion effect at the anode. Considering the maximum Pb removal with EDTA at higher voltage, the energy consumption was also maximum (78.3KWh/m3). Nevertheless, the economic evaluation suggested that the cost per gram removal of Pb was lowest in this experiment (8 US$/g Pb) and, thus, can be considered for practical applications to treat the Pb-contaminated soils.

Combined effects of high voltage gradient and electrolyte conditioning on electrokinetic remediation for chromium (VI)-contaminated soils

Combined effects of high voltage gradient and electrolyte conditioning on electrokinetic remediation for chromium (VI)-contaminated soils

Electrical parameters of ohmically heated cow’s milk

Science and industry are very interested in alternative pasteurization and sterilizing methods, like the direct electrical effect. An experimental batch ohmic heating unit was built and manufactured for this study. Our goal is to design and build batch Ohmic heating equipment that ensures adequate pasteurization of whole cow’s milk while also looking into the electrical phenomena that occur throughout the process. Ohmic and conventional heating technology were used to heat cow’s milk from 15 to 72°C. The temperature increased when ohmic heating was applied with varying voltage gradients (6.08, 9.56, and 19.13 V/cm), resulting in a substantial decrease (p≤ 0.05) in the heating time for milk pasteurization. The current that flows through the sample was higher at higher voltage gradients, which led to a quicker accumulation of heat. The change in electric current during ohmic heating of the milk is only dependent on the electrical conductivity when the voltage is constant. Ohmic heating induced a significant (p≤0.05) increase in system performance coefficient (SPC) values with increasing voltage gradients, resulting in heating rates (°C/minute).
 

Electrohydrodynamic air amplifier for low-energy airflow generation—An experimental proof-of-concept

With electrohydrodynamics (EHD), we can propel air in a low-energy fashion. EHD airflow, or ionic wind, arises when a high voltage gradient is applied to a set of electrodes. The air ionizes between electrodes via corona discharge and accelerates in an electric field, exchanging momentum with the surrounding air. While the ionization process is energy-efficient, reaching competitive flow rates remains challenging from a high-voltage engineering perspective. To increase EHD-generated flow rates, this study experimentally investigates a novel concept called EHD air amplification. The concept uses ionic wind as bleed flow to induce a more significant bulk flow by the air-amplifying Coanda effect. Due to the complex interactions between EHD and dielectric structures for air amplification, the conceptual EHD air amplifier device is designed stage-wise, starting with a simple emitter-collector electrode configuration. First, regular EHD flow was studied in a 150 × 150 × 500 mm3 channel. Then, a dielectric material was added to determine its influence on the electric field. The impact of a converging nozzle on the EHD-generated airflow was subsequently studied. Lastly, the converged nozzle airflow was used to create a bleed flow on a plate to facilitate air amplification of the surrounding air. We show the proof-of-concept for an EHD air amplification system. After a voltage threshold of 14 kV, amplified airstreams up to an amplification factor of 3 were measured. Maximum airflow rates of about 15 m3 h−1 were obtained shortly before electric breakdown at 22 kV. Compared to regular EHD, we achieved a higher aerodynamic performance for the same electric energy invested. The flow rate to electric power ratio increased to 66% in EHD air amplification compared to regular EHD. The proposed EHD air amplifier operates at atmospheric pressure. It lays the groundwork for further optimization studies to position EHD air amplification as a low-energy, low-maintenance, motor- and noiseless airflow generation technology.

Effects of Sb doping on the electrical characteristics of Ta-doped SnO2 varistors

This article describes the combined mixture of antimony and tantalum in SnO2 varistors. The results show that a moderate level of antimony can reduce the grain resistivity and maintain a high voltage gradient while providing good nonlinearity. The best electrical properties were obtained by doping 0.5 mol% antimony pentoxide and 0.003 mol% tantalum pentoxide. The nonlinear coefficient of 51, the leakage current of 5.7 μA/cm2, the voltage gradient of 480 V/mm and the grain resistance of 5.0 Ω.

ELECTRICAL CONDUCTIVITY APPLICATION IN OHMIC PASTEURIZATION OF ORANGE JUICE

The conversion of electrical energy into heat energy, which results in internal energy generation, is the underlying premise of Ohmic heating. An experimental batch Ohmic heating unit was built and manufactured for this study. The effect of voltage gradient of alternating current during batch Ohmic heating on orange juice was investigated. Parameters such as temperature, electrical current, time consumption, system performance coefficient, and heating rate of orange juice under Ohmic heating process were studied. The time consumption such as (23.02, 11.25, and 2.19 minutes) to reach the Ohmic pasteurization temperature (95 °C) was decreased as the voltage gradients (9.20 V/cm, 12.64 V/cm, and 25.28 V/cm) increased respectively. The electrical current was rapidly increased (4.46 Amp.) in accordance with the higher voltage gradient (25.28 V/cm) to attain the pasteurization temperature. With rising voltage gradients, Ohmic heating resulted in greater system performance coefficient values. The heating rate appears to have grown dramatically as the voltage gradients increased.

Multi-Criteria based Steady-State and Dynamic Reactive Power Planning for Transmission Systems

Planning of reactive power compensation devices as part of the grid planning process is becoming increasingly important due to decreasing reactive power reserves from conventional power plants. Planning such devices requires the consideration of the reactive power demand both during steady-state operation and disturbances as well as gradual power-flow shifts. To control the voltage in these scenarios, a portfolio comprising location, rated power and technology of reactive power compensation devices must be identified. In this paper, a planning approach with a coupled determination of steady-state and dynamic reactive power demand is applied to a generic transmission system. Different characteristic grid use cases are analysed for the identification of the steady-state reactive power demand. The determination of the dynamic demand involves the analysis of critical power-flow shifts within an hourly generation time series. Shifts leading to insufficient voltage stability reserves and high voltage gradients are considered in the planning approach. Furthermore, critical line-outage and short-circuit scenarios are analysed in connection with an increasing demand for dynamic reactive power compensation. Results emphasise that the coupled determination of steady-state and dynamic reactive power demand identifies suitable portfolios of different compensation devices using synergies for voltage control during steady-state operation, disturbances and power-flow shifts.

Fabrication of high voltage gradient ZnO nanoparticle-Bi2O3-Mn2O3-based thick film varistors at various sintering temperature

In this research, 20 nm zinc oxide nanoparticles were utilized to fabricate significant voltage gradient zinc oxide nanoparticle-Bi2O3-Mn2O3-based thick film varistors (TFVs) by applying screen printing method. Different low temperatures during the sintering process had a considerable effect on the zinc oxide nanoparticle-based TFVs. In particular, the low temperatures improved the growth of ZnO grains, which was obvious even at 550 °C. The huge surface area of the 20 nm zinc oxide encouraged an intense surface interaction even at minimal sintering temperatures. The sintering technique also enhanced the internal structure of the crystal. Minimizing the fundamental compressive stress depended on the XRD lattice constant and the FWHM analysis. The variable temperatures of the sintering process considerably impacted the electrical behaviours of the samples. A remarkable increase in the voltage gradient of the varistor sintered up to 5732.5 V/mm at 700 °C was observed. The electrical resistivity dropped dramatically from 621.8 kΩ.cm (varistor at 550 °C) to 147.3 kΩ.cm at 800 °C sintering temperature. The small size of grains with perfect boundaries was the main reason for the enhancement of the voltage gradient. The optimal electrical characteristics with a 63 nonlinearity coefficient and 103 μA leakage current were achieved in the varistor sintered at 700 °C. Moreover, maximum permittivity and minimum dissipation factor were attained through the minimal frequency range. Therefore, the sintering process could be applied as a novel technical approach for the dominant voltage gradient of zinc oxide nanoparticle-based TFVs with enhanced microstructural and electrical behavior and good nonlinearity.

Ohmic heating: A post production technology applied to tomato puree

In this study, ohmic heating treatment was applied to different volume by volume concentrations (100, 90, 80, 70 and 60%) of tomato puree. The puree was ohmically heated from 30 to 70°C at four different voltage gradients of 8, 6, 4 and 2V/cm for different concentrations. Measurements had been made on electrical conductivity, ohmic heating rate, pH and TSS. The voltage gradient and concentration had significant effect on electrical conductivity of tomato puree. Electrical conductivity and ohmic heating rate increased linearly with temperature, concentration and voltage gradient. The pH and TSS were also noted before and after heating. The treatment had no significant effect on pH and TSS values. With respect to system performance coefficient, as the concentration of tomato puree decreased the efficiency of ohmic heating apparatus shifted towards higher voltage gradient in the prescribed voltage range.

Modeling the Inactivation of <i>Byssochlamys fulva</i> During Ohmic Heating of Lime Juice

This study was carried out to reduce <i>Byssochlamys fulva</i> PTCC 5062 in lime juice. The main and interaction effects of pH (3.5 and 4.5) and voltage gradient (15 and 20 V/cm) were investigated on mold inactivation during ohmic heating at 88, 93, and 98°C. The results showed that pH and voltage gradient had significant effects on D_value and Z_value (p<0.01). In order to model the survival behavior of <i>Byssochlamys fulva PTCC 5062</i>, due to the nonlinearity of the curves, Weibull model was found to give more accurate estimation compared to classical first-order model. The results of D_value showed that like conventional method, the temperature is the most influential factor affecting the reduction of this heat-resistant mold. It has also been demonstrated that at lower pH and higher voltage gradient, <i>Byssochlamys fulva</i> PTCC 5062 is more sensitive to temperature. This study showed that the highest inactivation rate of this mold was achieved at 98°C, 20 V/cm and pH=3.5.

High‐performance ZnO varistor ceramics prepared by arc‐induced flash sintering with low energy consumption at room temperature

The development of ultra-high voltage transmission lines requires a ZnO arrester with excellent electrical response and high voltage gradient. Compared with conventional preparation methods, flash sintering allows fast production of novel high-performance ZnO varistor ceramics with low energy consumption and controlled grain growth. Herein, ZnO varistor ceramics were prepared using the flash sintering method at an air pressure of 21 kPa for 60 s at 25°C. The results showed that the flash-sintered samples had fine grains and reduced loss of volatile elements. Moreover, the voltage gradient, leakage current density, and non-linear coefficient of the flash-sintered varistor ceramics were significantly improved compared with those of conventionally sintered samples. Owing to the short preparation time and absence of a heating process, the energy consumption of the proposed flash sintering method was significantly reduced to 10% of that by conventional sintering. The proposed method is a promising approach for the preparation of ZnO arresters with excellent electrical properties and serves as an effective method that realises energy saving and emission reduction.

In situ removal of cadmium by short-distance migration under the action of a low-voltage electric field and granular activated carbon

Cd pollution in soil is a global environmental issue of great concern. The secondary release and low removal rate of Cd are obstacles to the use of adsorption techniques. To develop a sustainable and effective remediation technique, low-voltage direct current (DC) and granular activated carbon (GAC) were applied for in situ Cd removal. The results showed that a low-voltage gradient was more favourable than a high-voltage gradient for Cd removal. A voltage gradient of 0.2 V cm−1 acted as a driving force for Cd migration while limiting the side effects caused by DC. As an auxiliary enhancement measure, polarity exchange was effective in maintaining uniform distributions of soil moisture and temperature as well as a stable pH while improving Cd removal by weakening inhibition caused by OH− generated at the cathodes. The average removal rates of total and bioavailable Cd were 61.05% and 76.96%, respectively. The potential mobility of Cd in soil was assessed by the mobility factor (MF). The MF was lowered from 42.66% to 8.96%, indicating that the risks of Cd mobility were reduced to low levels. The energy consumption and utilization efficiency of the method were 5.65 KWh m−3 and 11.25, respectively. The energy utilization efficiency was significantly higher than the efficiencies of other methods that use DC to improve Cd removal. The results suggested that the in situ removal of Cd by low-voltage DC and GAC was efficient and avoided the secondary release of Cd.

Flashover on H.V. Insulators Coated with a Non-Linear Conductive Film.(Dept.E)

Aiming to improving the insulator resistance in the polluted media, a new proposed model consisting of an insulating surface coated by a non-linear conductive film has been studied. There are two important roles of the non-linear film. At low voltage gradient, a very small current passes. This low leakage current tends to raise the surface temperatures slightly above the ambient and retards dew deposition, which contributes to many flashovers. At high voltage gradient, i.e. the condition of dry zones formation; the leakage current increases sharply under the discharge across the dry zones, so this discharge diminishes. To investigate the effect of this non-linear film on the surface diacharge and flashover, the electrical characteristics of non-linear film has been studied, and both theoretical model and experimental work, which has been carried out with simple model are discussed. It has been found that the chance of the formation of local surface discharges, and the critical flashover voltage has increased due to the existence of this non linear film. The mathematical expressions of the electric field in the discharge column and pollution layer were deduced for computing the critical flashover voltage.

A novel method for Lorentz force detuning compensation in multi-cell superconducting RF cavity and its validation at room temperature.

A tuner is an important element of a superconducting radio frequency (SCRF) cavity, which is used to tune the cavity at resonance frequency. The measurement and control of the pulsed detuning phenomenon is very challenging and can be measured in the superconducting state of the cavity at a high voltage gradient. This paper describes an innovative method and unique approach for the measurement of dynamic changes in resonance frequency of the SCRF cavity even at room temperature. For this purpose, a 1.3GHz nine-cell prototype dressed cavity with RRCAT's designed X-link tuning device is used. A test setup for measurements of dynamic changes in resonance frequency of the RF cavity has been designed and developed. The cavity response for piezo-excitation at various pulse widths has been determined. In order to simulate the Lorentz force detuning (LFD) effect, the source frequency has been modulated similar to the superconducting scenario in the SCRF cavity. To compensate the simulated detuning, a fast tuner is operated with half sinusoidal pulses at various combinations of pulse width and time advance to find out an optimum waveform. This optimized waveform will be used with a fast tuning control system to control LFD under actual operation conditions of the SCRF cavity.

Investigation of Electrical Conductivity Value and Cooking Homogeneity During Ohmic Cooking of Turkish Sausage

Turkish Sausage (Sucuk) is an important traditional meat product for Turkish society and is used in breakfast, grill, daily meals, and toast. Sucuk samples were cooked by heating up to 80 °C with ohmic heating using eight different voltage gradients. The cooking process has shortened due to the increase in the voltage during ohmic cooking. It was determined that the electrical conductivity value increased as the temperature increased during ohmic cooking, and the electrical conductivity value varied between 0.51-3.38 S m-1. At the end of the ohmic cooking process, the temperature homogeneity of the samples was examined with the help of a thermal camera and it was determined that homogeneous cooking could not be provided in low voltage gradients. As a result, it was determined that the sucuk sample could be cooked with ohmic cooking and that homogeneous cooking in a high voltage gradient can be provided.

Electrical Modelling of Switching Arcs in a Low Voltage Relay at Low Currents

The arc behaviour of short, low current switching arcs is not well understood and lacks a reliable model. In this work, the behaviour of an arc in the air is studied during contact separation at low DC currents (0.5 A to 20 A) and for small gap lengths (0 mm to 6 mm). The experiments are performed on a low voltage relay with two different electrode configurations. The arc voltage is measured during the opening of the contacts at constant current. The arc length is determined optically by tracing the mean path of the arc over time from a series of high-speed images. From the synchronised data of voltage vs. distance, first a sudden jump of the voltage at the start of contact opening is observed. Secondly, a sudden change in the voltage gradient occurs as the arc is elongated. Short arcs with a length up to approximately 1.25 mm show an intense radiation in the overall gap region and high voltage gradients. An unexpected behaviour never reported before was observed for longer arcs at low current: Two characteristic regions occur, a region in front of the cathode, with a length of approximately 1.25 mm, having an intense radiation and a high voltage gradient as well as a region of much lower radiation intensity and a comparatively lower voltage gradient in the remaining gap area despite a small anode spot region. The characteristic border of approximately 1.25 mm is almost independent of the current. A generalised arc voltage model is proposed based on the assumption that a constant sheath voltage and two discrete field regions exist, which are modelled as two independent linear functions of voltage vs. length. The data for various currents is combined to yield a general non-linear function for predicting the arc voltage vs. arc length and current.

High nonlinearity and low leakage current SnO2 varistor ceramics by co-doping with yttrium and tantalum

We report on co-doping of tantalum and yttrium into SnO2 varistors. The electrical parameters of the prepared devices show that a moderate tantalum doping level reduces the leakage current while maintaining a high voltage gradient and excellent nonlinearity. Yttrium and tantalum doping levels of 0.05 mol% and 0.003 mol%, respectively, gave the best electrical performance, including a nonlinear coefficient of 54, leakage current of 3.2 μA/cm2 and voltage gradient of 485 V/mm.