High Voltage Gradient Research Articles

Modelling and Analysis of EMI Generated of Power IGBT Modules

Commutations of power IGBT modules used in power converters cause high voltage and current gradients in the collector waveforms, which can generate and irradiate very high electromagnetic noise levels. An innovative experimental - simulative method is presented, which is able to predict irradiated noise levels during converter operation: such method allows power electronics designer to have a proper and simple method to predict spectrum and amplitude of irradiated noise during converter operation, in order to ensure a direct compliance with the enforce normative. The irradiated noise is generated by high frequency conducted current flowing in IGBT module and in the converter. Frequency and amplitude of the internal oscillating currents are simulated by means of a suitable IGBT module model proposed in the past and now optimized for irradiation simulation. The irradiated field during converter operation can be calculated by means of a preliminary static measure executed in anechoic chamber, where the diagram of irradiation of the system is measured at different frequencies, connecting IGBT gate to a radiofrequency generator. Presented results are precise within 3dB limit.

Particularities of Electrochemical Production of Nanocoatings and Nanopowders of Metals, Oxides, and Nitrides by Electrolysis of Acetonitrile at High Voltage Gradient

In this study, nanocoatings and/or nanopowders CdO, Cd3N2, Cu, Cu2O, α-C3N4, α-Si3N4, and β-Si3N4 were produced using an organic solvent (acetonitrile) by activation in an electrochemical cell at a high voltage gradient (400–2000 V/cm) and different modes of non-equilibrium process on the electrodes (cathodes and anodes) in the systems Cd–Ni, Cu–Cu, and Si–Si. To explain the nature of the cathode and anodic reactions with HCOOH formic acid as an electrolyte, the Christiansen–Kramers concept for the Semenov–Hinshelwood classical kinetic theory was used along with results of previous investigations for the appropriate transformation of organics and radicals (using massspectrometry and secondary ion-ion emission). It was established that, in some cases, secondary reactions (parallel to electrolysis reactions) could take place on the corresponding electrodes according to the mechanism of heterogeneous catalysis.

A Novel Method for Improving Water Injectivity in Tight Sandstone Reservoirs

Applicability of electrokinetic effect in improving water injectivity in tight sandstone is studied. DC potential and injection rate are varied for optimization and determination of their individual impact on clay discharge and movement. The liberated clays were characterized through size exclusion microfiltration and ICP-MS analysis. Real time temperature and pH monitoring were also informative. Results showed that severalfold (up to 152%) apparent increase of core permeability could be achieved. Some of the experiments were more efficient in terms of dislodgement of clays and enhanced stimulation which is supported by produced brines analysis with higher concentration of clay element. The results also showed larger quantity of clays in the produced brine in the initial periods of water injection followed by stabilization of differential pressure and electrical current, implying that the stimulation effect stops when the higher voltage gradient and flow rates are no more able to dislodge remaining clays. Additionally, fluid temperature measurement showed an increasing trend with the injection time and direct proportionality with the applied voltage. The basic theory behind this stimulation effect is predicted to be the colloidal movement of pore lining clays that results in widening of pore throats and/or opening new flow paths.

The process of producing tomato paste by ohmic heating method.

In this study, the effect of ohmic heating technique on electrical conductivity, water evaporation rate, heating rate, colour parameters, pH and energy consumption of tomato samples was investigated. Ohmic heating was accomplished till the moisture content of the tomato samples reduced from initial moisture content of as 9.33 (dry basis) to a safer level of 2.2. The results of the nonlinear mathematical model including the effects of voltage gradient level and the temperature on the electrical conductivity changes had good agreement (R ≥ 0.955) with the experimental data. Also, it was observed that the electrical conductivity increased along with concentration of tomato samples. The range of electrical conductivity during ohmic heating was 3.19-8.95 (S/m). It was found that processing time decreased from 28.32 to 4.3min over the voltage gradient range studied (6 to 14V/cm), which resulted in decreased specific energy consumption from 4.63 to 3.05 (MJ/kg water). Due to increasing of heating rate and water evaporation rate at high voltage gradient, the change of the pH was limited. Samples processed in high voltage gradient had higher L*, b* and hue angle (h), lower a* and Chroma (C) values as compared to low voltage gradient. The optimum value of processing time, pH, colour, specific energy consumption was obtained at 14V/cm voltage gradient level.

Blocking Or Guiding Upstream-migrating Fish:A Commentary On The Success Of The GraduatedField Electric Fish Barrier

Fisheries managers have been interested in the control of fish movement for a variety of reasons and for a considerable period of time. The most common reasons are the containment of invasive species and the protection of all or selected fish species at industrial installations such as hydroelectric stations and the cooling water systems of thermal power stations. The use of electricity has proven to be most popular in the prevention of upstream passage at hydropower tailrace sites and also at river and canal sites selected as the last line of defence against the spread of invasive species. At other locations electric barriers are deployed to block and guide upstream migrants towards census facilities. In the past the reliability and operational safety of electric fish barriers has been an issue but these concerns have been overcome by advances in fisheries technology associated with the demands of large installations. A significant number of graduated field electric fish barriers have been installed in the USA and other parts of Europe where electrode arrays are deployed on or in the river bed. They present upstream migrants with higher voltage gradients as fish progress into the field, eventually causing their downstream drift to safety. This paper reviews the performance of several electric fish barriers in the USA and Europe. Monitoring has shown that the graduated field fish barrier is effective in

Temperature dependent electrical conductivities of ginger paste during ohmic heating

Ohmic heating is now regarded as highly attractive advanced technique for food processing wherein electric current is passed through the liquid particulates foods with primary purpose of heating them. The success of ohmic heating depends on the rate of heat generation in the system, the electrical conductivity of the food, method by which the food flows through the system and composition of the food. In this study, the ginger paste at different salt treatment (0–2% w/w) was heated in a laboratory scale ohmic heater by applying voltage gradients (5–13 V/cm). The temperature dependent electrical conductivity was obtained at different time interval of 0, 5 and 10 minute at different temperatures (30–60°C). Bubbling was observed above 70°C especially at high voltage gradients. The electrical conductivity measured in terms of point and bulk electrical conductivity. Point electrical conductivity was greater than bulk electrical conductivity. The point and bulk electrical conductivity values were in the range of 4.41 to 6.63 and 3.75 to 5.87 mS/cm respectively.

중금속으로 오염된 해양퇴적토의 전기동력학적 정화

퇴적토는 미사 및 점토와 같은 미세토의 함량이 높으며, 유기물질이 많으며, 완충능이 크기 때문에 퇴적토로부터 중금속을 제거하는 것은 매우 어렵다. 본 연구에서는, 중금속으로 오염된 퇴적토에서 중금속을 제거하기 위해 2 V/cm의 일정한 전압경사를 적용한 실험실 규모의 전기동력학적 (EK) 정화공법을 사용하였다. 실험을 위해 적용한 음극 전해질로는 0.1 M의 ethylenediaminetetraacetic acid (EDTA), citric acid (CA), <TEX>$HNO_3$</TEX>, HCl, 그리고 수돗물을 사용하였으며, 양극 전해질로는 수돗물을 사용하여 순환시켜 주었다. 음극 전해질로 CA를 사용한 실험군에서 Ni, Cu, Zn, Pb는 각각 초기와 비교하여 92.4, 96.1, 97.1, 88.1%의 중금속 제거효율을 보였다. 높은 전압경사를 적용하게 되면, 음극 전해질내에 citrate 및 EDTA가 퇴적토로 이동이 용이하게 되며, 그로 인해 중금속-킬레이트 화합물을 형성하여 중금속의 추출률을 높일 수 있었다. 이러한 결과를 바탕으로, 높은 전압경사를 적용한 EK 실험에서 음극 전해질로 EDTA 혹은 CA를 사용하면 퇴적토로부터 중금속을 효과적으로 추출할 수 있다고 판단된다. Sediment contains a high fraction of organic matter, high buffering capacity, and a large portion of fine grained particles such as silt and clay, which are major barriers to remove heavy metals from sediments. In this study, a lab-scale electrokinetic (EK) technique was applied to remove heavy metals effectively from marine sediment at a constant voltage gradient of 2 V/cm. A concentration of 0.1 M of ethylenediaminetetraacetic acid (EDTA), citric acid (CA), <TEX>$HNO_3$</TEX>, and HCl were circulated in the cathode, and tap water was circulated in the anode. CA extracted 92.4% of Ni, 96.1% of Cu, 97.1% of Zn, and 88.1% of Pb from marine sediment. A higher voltage gradient enhanced the transport of citrate and EDTA into the sediment and, therefore, increased metal extraction from the marine sediment through a complexation reaction between metals and the chelates. Based on these results, the electrokinetic process using a high voltage gradient with EDTA and CA might be useful to extract heavy metals from marine sediment.

Enhancement of COD-Nutrients Removals and Filterability of Secondary Clarifier Municipal Wastewater Influent Using Electrocoagulation Technique

The present work studied experimentally the variations of some characteristics of the mixed liquor solution in wastewater treatment plants (WWTPs) under the effect of electrocoagulation (EC) technique. Unlike conventional methods, electrocoagulation was performed using cylindrical perforated iron electrodes to achieve a good distribution of the applied DC field onto the municipal wastewater. Effects of electrocoagulation time, applied voltage gradient, and aeration on the mixed liquor characteristics were considered. The study figured out the dependency of the local pH and oxidation potential reduction (OPR) values, near anode and cathode on these operational conditions. It was found that electrocoagulation process reached steady state conditions in no more than 60 minutes. At high voltage gradient (6 V/cm), the steady removal efficiencies of COD and nutrients exceeded 89%. While aeration showed moderate influence on removal efficiencies and wastewater sludge filterability, it significantly affected the pH and ORP near the electrodes especially at the low voltage gradient. Results also indicated that the sludge filterability was improved notably by increasing the voltage gradient to have minimal levels of specific-resistance to filtration (SRF).

Ohmic heating of pomegranate juice: Electrical conductivity and pH change

Ohmic heating is an alternative fast heating method for food products. In this study, the effect of ohmic heating technique on electrical conductivity, heating rate, system performance and pH of pomegranate juice was investigated. Ohmic heating rate, electrical conductivity, and pH are dependent on the voltage gradient used (30–55V/cm). As the voltage gradient increased, time, system performance and pH decreased. The electrical conductivity of the sample increased with temperature rise (20–85°C). The range of electrical conductivity during ohmic heating was 0.209–1.013 (S/m). Among the two models tested to fit the electrical conductivity of pomegranate juice, the linear model gave the best fit for all the data points. Bubbling was observed above 81°C especially at high voltage gradients. The system performance coefficients for pomegranate juice samples were in the range of 0.764–0.939.

Electrode Configuration for Electrokinetic Restoration of Greenhouse Saline Soil

Electrokinetic restoration (EKR) of saline soil has been achieved successfully on a laboratory scale. In this study, the effectiveness of an electrokinetic system with one anode in the center of the electrokinetic cell and two cathodes at the end of the cell was investigated to simulate the EKR system, with electrodes installed in the ridge and furrow pattern of a field. Anions were transported toward the anode centered in the cell, and cations were moved toward both cathodes. Chloride and nitrate were almost completely removed from the soil; however, a certain amount of sulfate accumulated in the anode region. Although the voltage influenced the transport of salts in the soil, there was no significant increase in the reduction of electrical conductivity at a higher voltage gradient. The pattern of salt removal was symmetric around the center anode, and energy consumption was less than that of a normal system. This means that the system can be used effectively to remove salts from saline greenhouse soil.

Study of vitamin C degradation in acerola pulp during ohmic and conventional heat treatment

Vitamin C degradation in acerola pulp during thermal treatment by ohmic and conventional heating was evaluated. The ohmic heating technology was studied using a Central Composite Rotatable Design, and two variables were evaluated: the solids content of the pulp (2–8 g/100 g) and the heating voltage (120–200 V). The results indicate that ascorbic acid degradation was significantly influenced by both of the aforementioned variables. The total vitamin C degradation was influenced by the linear and the quadratic effects of the voltage. A comparative evaluation of the conventional and the ohmic heating processes showed that ohmic heating, when performed with low voltage gradients, promoted degradation of both the ascorbic acid and the total vitamin C in a manner similar to conventional heating. However, high voltage gradients induced greater ascorbic acid degradation because of electrochemical reactions. These reactions increased when high electric fields were applied, producing compounds that catalyzed the degradation pathways of ascorbic acid in the presence of oxygen.

Effect of Sintering Temperature on Electrical Properties of ZnO Varistor Ceramics

To obtain ZnO varistors with high voltage gradient, ZnO varistors were fabricated by traditional ceramic sintering technique, the effect of different sintering temperature (1135～1155 °C) on electrical properties of ZnO varistors were investigated. The experimental results show that with increasement of sintering temperature, the grain size of ZnO varistor ceramic becomes bigger, the voltage gradient of varistor decreases and the density is improved. When the sintering temperature is at 1135 °C, the voltage gradient of varistor is up to 329V/mm, the leakage current is 8μA and the density is 96.4%. When the sintering temperature is at 1140 °C, the voltage gradient of varistor is 301V/mm, the leakage current is 4μA and the density is 96.6%. Compared the results at 1135 °C with 1140 °C , it is found that the comprehensive electrical properties of ZnO varistors reach maximum at 1140 °C.

Fast mechanical shutter for pulsed ion beam generation

A pneumatically actuated mechanical shutter has been developed for pulsed ion beam operation. The mechanical shutter provides vacuum isolation between the gas filled ion source (nominally at ∼10mTorr) and the high vacuum accelerator chamber (nominally <μTorr), which is essential for applications involving high voltage gradients. In the present design, the FWHM pulse length of the ion beam was measured to be approximately 1.5ms with rise and decay times of ∼1ms. Steady-state pressure measurements show an order of magnitude decrease in the main chamber pressure by incorporating the shutter.

Study on Microstructure of ZnO Lighting Arrester with High Voltage Gradient

To obtain ZnO arrester with high voltage gradient and small size, through the optimizing foundamental formula of arrester and changing sintering temperature and holding time, the electrical properties and microstructure of varistors were studied. The density of varistors was determined by using the mass - volume method , voltage gradient and leakage current of ZnO arrester were measured with Ⅱ Surge Arrester Tester DC parameters, microstructure of varistor ceramics were studied by means XRD and SEM. The experimental results show that with increasement of the sintering temperature, the density of varistors increases, and the voltage gradient continues to decrease and leakage current almost keeps unchangable. As the holding time increases, while as the voltage gradient continues to decrease, and leakage current almost unchanges.

Study on Microstructure and Electrical Properties of ZnO Varistor Ceramics

To obtain ZnO varistors with high voltage gradient, ZnO varistors were fabricated by traditional ceramic sintering technique, which were sintered from 1135 to 1155 °C, the microstructure and properties of varistors were characterized by SEM, X-rays diffraction and DC parameter instrument for varistors. The experimental results show that the spinel phase Zn7Sb2O12 generated during sintering process, very thin amorphous Bi rich films are formed between the ZnO/ZnO grain boundaries, with increasement of sintering temperature, the grain size of ZnO varistor ceramic becomes bigger, the voltage gradient of varistor decreases and the density is improved. The optimized parameters are that when the sintering temperature is at 1140 °C, the voltage gradient of varistor is 301V/mm, the leakage current is 4μA and the density is 96.6%, the comprehensive electrical properties of ZnO varistors reach maximum.

Research on the Impact of Different VG on Electrokinetic Removal of Heavy Metal Wastes

This paper aims to investigate the effects of different VG (voltage gradient) on electrokinetic removal technology, and examine electrode pH, electric conductivity, voltage drop in the sample, electric current, and the electroosmotic flow. It is indicated that with the increase of VG, the electrolytic reaction rate accelerates during the electric removal experiment, which has affected both system current and the pH value &amp; electric conductivity of electrolyte solutions. The higher VG is, the faster the electrolyte solution pH varies；the higher VG is, the faster the electric conductivity changes. Meanwhile the magnitude of electroosmotic flow increases with the increase of the VG.

AC ageing characteristics of Y2O3-doped ZnO varistors with high voltage gradient

In this paper, AC ageing characteristics of high voltage gradient ZnO varistors doped with different Y 2 O 3 concentration were investigated. The voltage gradient of these samples is markedly improved by increasing Y 2 O 3 content, however, the nonlinear coefficient decreases and the leakage current increases at the same time. Y 2 O 3-doped ZnO samples exhibit lower stability under accelerated AC ageing stress of 0.85 V 1mA/135 °C/168 h, compared with samples without Y 2 O 3. Double-Schottky barrier(DSB) parameters before and after ageing tests indicate that the decrease of barrier height for traditional sample is less than that for high voltage gradient sample, which should be ascribed to its slight variation in the interface state density.

Admittance Spectroscopy of Y&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-Doped ZnO Varistors Sintered at Different Temperature

ZnO varistors are multicomponent polycrystalline ceramics with highly nonlinear current-voltage characteristics and surge energy absorption capabilities. The voltage gradient of the ZnO varistor is inversely proportional to its average grain size. Recently, the rare-earth oxides have been reported as growth inhibitor of ZnO grains to obtain high voltage gradient. Although the dopant of rare-earth oxides can remarkably enhance the voltage gradients of varistor samples, their leakage currents and nonlinear coefficients deteriorate at the same time. In this paper, the sintering effects on electrical characteristics and admittance spectroscopies of ZnO varistor samples doped with yttrium oxides were investigated. Samples were fabricated under different sintering temperatures, including 1000 °C, 1100 °C, 1200 °C and 1300 °C. Then, the electrical characteristics and admittance spectroscopies of these varistor samples were measured. The measured current-voltage results behave special U-type curves related to sintering temperature. Furthermore, the admittance spectroscopy of these samples revealed the sintering effects on the intrinsic defects of ZnO varistors.

Conductive Anodic Filament (CAF) Formation Part I: the Influence of Water-Soluble Flux on Its Formation

Conductive anodic filament (CAF) is a failure mode in printed wiring boards (PWBs) which occurs under high humidity and high voltage gradient conditions. The filament, a copper salt, grows from anode to cathode along the epoxy–glass interface. Ready and Turbini identified this copper salt as Cu2(OH)3Cl, atacamite. In the present work polyethylene glycol (PEG) and polyethylene propylene glycol (PEPG) fluxes were used to process hole-to-hole test coupons. The coupons were exposed to temperature, humidity, and bias testing of 85°C, 85% relative humidity (RH), and 200 V bias for 28 days. The aged coupons were then cross-sectioned, and scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) revealed that, in addition to CAF formation at the epoxy–glass interface, a copper-chloride-containing compound was present in the polymer matrix for coupons processed with PEPG. This compound was characterized using x-ray photoelectron spectroscopy (XPS) as CuCl. Coupons processed with PEG created CAF only at the epoxy–glass interface. Based on previous publications on copper electrodeposition in the presence of PEG, it appears that a PEG-Cu-Cl complex forms, binding the available Cu and acting as a barrier to the formation of CuCl in the polymer matrix.

High-Throughput Capillary-Electrophoresis Analysis of the Contents of a Single Mitochondria

We present a technique for labeling the contents of acidic organelles and rapidly releasing, separating, and detecting their labeled contents with laser-induced fluorescence. We have performed solution-phase separation of the contents of single mitochondria and single 100 nm vesicles, which represents a demonstration of an analyzed volume of approximately 1 aL. Our strategy to label the acidic contents of the mitochondrion relies on the use of the membrane-permeable dye, Oregon Green diacetate succinimidyl ester, and a membrane-permeable base to raise intramitochondrial pH. In order to measure the contents, we utilized a glass microfluidic chip and high voltage gradient for millisecond capillary electrophoresis separation after single-mitochondrion photolysis. We observed heterogeneity among a population of mitochondria with respect to a constituent chemical component.