Negative Voltage Polarity Research Articles

Asymmetrical AC field emission current characteristics of vacuum interrupters subjected to inrush current

According to the IEC standards, test objects in back-to-back capacitor bank switching tests are subjected to inrush currents of 20 kA peak and 4250 Hz frequency during making operations. For vacuum interrupters (VIs), the contact surfaces may be seriously damaged by the high-energy arc of the inrush current. The field emission current characteristics reflect the surface microscopic conditions after undergoing the inrush current. The objective of this paper is to investigate the impact of the inrush current during back-to-back capacitor bank making operations on the field emission current characteristics of vacuum interrupters under AC power frequency voltage. The amplitudes of the inrush current were set as 10 and 20 kA, respectively. The sample VIs underwent the inrush current at each amplitude twice. After each inrush current, the field emission current of the VI was measured by applying a power frequency voltage upon the contacts with a fixed gap of 1 mm. By applying an AC power frequency voltage, an unsymmetrical field emission current was measured. In addition, according to the Fowler-Nordheim (F-N) theory, the field enhancement factor β and the effective emission area Ae were calculated. The experimental results show that there is a significant unsymmetrical field emission current at each polarity of the power frequency voltage. Moreover, during the voltage rising phase, the field enhancement factor β is higher and the effective emission area Ae is smaller than that during the voltage falling phase for both positive and negative voltage polarities. A heating-cooling hysteresis effect of the emission sites could explain the phenomena.

Experimental Study of EDM-Drilling and Shaping of SiSiC and SiC

A growing interest in the machining of Silicon carbide (SiC) is caused by its excellent properties. This makes SiC and Siliconized Silicon carbide (SiSiC) suitable for a variety of applications, like cutting tools, electric systems, electric circuit elements, structural materials, etc. However, the material properties create difficulties in SiSiC processing. For this reason electrical discharge machining (EDM) was utilized to process it. The influence of EDM drilling process parameters such as pulse duration, polarity and ignition voltage on material removal rate (MRR), electrode wear, machining time and hole diameter are studied in the present work. All drilling and shaping experiments were performed using standard brass multi-hole electrodes with internal flushing. The highest impact to the material removal rate was reached with electrode negative polarity and ignition voltage of 120V. Experiments showed almost linear dependence between ignition voltage and MRR in the range from 60V to 120V. The highest reduction of the electrode wear was reached with positive electrode polarity and pulse duration of 5μs. Experiments showed a square law dependence between pulse duration and electrode wear in the range from 0.6μs to 5μs. This is due to the fact that the thermal conductivity and melting point of brass is lower than that of SiSiC. The material removal process can be caused by thermal stress and cracking as well as melting and evaporation. The increase of impulse frequency creates cracking and spalling effect that can be the reason why the short impulses bring higher material removal.

Impact of Thermoelectric Effects on Phase Change Memory Characteristics

Joule heating in phase change memory (PCM) controls programming characteristics, read disturb, and programming disturb. To optimize the energy consumption and reliability of PCM, a thorough understanding of Joule heating as a function of the electrical operation of the device is thus strongly required. This paper presents a comprehensive characterization of thermoelectric (TE) effects in PCM operated at positive and negative voltage polarity. The impact of polarity was studied for all major temperature-dependent properties of the PCM device, namely, melting, crystallization, ion migration, threshold switching, and holding. It was demonstrated that heating is less efficient under negative voltage, compared with positive voltage. It was also shown that the positive and negative voltages needed to induce all above phenomena display a universal correlation. We propose a unified finite-element model for the PCM, which correctly accounts for the observed polarity-dependent heating and the universal voltage characteristics. The impact of isotropic scaling on TE is finally addressed.

Ignition of hydrocarbon : air mixtures by a nanosecond surface dielectric barrier discharge

Ignition of stoichiometric hydrocarbon : air mixtures by a nanosecond surface dielectric barrier discharge has been experimentally studied at room temperature and atmospheric and subatmospheric pressures. Observations were made for different voltage polarities and shapes of the high-voltage electrode. The ignition delay time and the velocity of the combustion wave were measured in a C2H2 : air mixture versus applied voltage by processing discharge gap images. It was concluded that the mixtures are ignited easier by the discharge for a negative voltage polarity and when it develops from a gear-like electrode. A 2D simulation of the discharge was performed to calculate the temporal and spatial distributions of generated active species and gas temperature during the discharge and in its afterglow for both electrode polarities. It was shown that the voltage threshold for ignition by a negative-polarity discharge is lower than that for a positive-polarity discharge, in qualitative agreement with observations. This is due to the formation of a region with efficient active species production and fast gas heating in the immediate vicinity of the high-voltage electrode when a voltage of negative polarity is applied to it.

Anode dependence of set voltage in resistive switching of metal/HfO2/metal resistors

The anode dependence of set voltage in resistive switching behaviors of metal/HfO2/metal resistors is investigated by applying positive and negative voltage polarity, and by changing the location of the electrodes made of various metals including Al, Pt, Mo, and Ru. When the same anode is applied to resistors whatever cathodes are, their set voltages in high resistance state are very similar. The strong anode dependence on set voltage is related to the potential near the anode domain owing to the partial rupture of the conducting filament. This rupture of filaments makes the thick insulator film thinner with a small potential barrier.

English

This paper proposes a double input dc-dc converter based on integration of CUK and Zeta converter suitable for telecom power supplies. In the proposed converter, the input dc voltage can be either bucked or boosted and also input dc sources can deliver power to the load individually or simultaneously. The combination results in an output voltage of negative polarity, but by introducing a diode, capacitor cross-bridge, the polarity is reversed to positive voltage at the output terminals. The converter is capable of providing both the step-up and step-down conversion at reasonable duty ratios. The converter is analyzed for steady state behaviour and presented in this paper.

Ignition dynamics of dry-etched vertical cavity single-hole microdischarge reactors in ac regime operating in noble gases

Silicon-based multi-cavity microdischarge reactors allow the generation of large-area uniform glow discharges over a wide pressure range up to atmospheric pressure. These devices, fabricated using micro electro-mechanical system technology, have shown complex interactions between the individual cavities. To discriminate these interactions, devices with only one shallow vertical cavity are studied here. Operation characteristics are investigated using electrical and optical analysing techniques. The spatial and temporal dynamics of the discharge are investigated for positive and negative voltage polarity of the applied ac voltage ramp by phase-resolved imaging. Within each voltage half-period, emission from the single cavity shows repetitive pulsing features and distinct spatial distributions. In the positive half-period, ring-shaped structures develop, while the negative half-period is distinguished by a bell-shaped intensity distribution. Effects of pressure and operation frequency on the spatial and temporal intensity profiles are discussed.

Electrical properties of atomic layer deposited Al2O3 with anneal temperature for surface passivation

The electrical characteristics of Al2O3 layers prepared by the atomic layer deposition technique using O3, H2O, and plasma O2, as oxidants are investigated through capacitance–voltage measurements of metal–insulator–semiconductor capacitors. Particular emphasis is placed on the properties of thermal annealed Al2O3 for surface passivation. Capacitance measurements at flatband voltage before and after the application of constant voltage stress in the inversion regime indicate that the charge trapping and hysteresis behavior of the capacitors are more dominant at low temperature annealing. Positive flatband voltage shifts due to negative charge tunneling are also observed under both negative and positive bias voltage polarities. The interface trap densities of O3 and plasma O2-based Al2O3 samples at 450°C decrease by an order of magnitude with increasing annealing temperature, approaching the interface trap density levels in the 1011eV−1cm−2 range. However, H2O-based Al2O3 doesn't change considerably. The interface trap density distribution shows that H2O-based Al2O3/Si annealed over 400°C has depassivated defects, similar to those observed in SiO2/Si interfaces. A comparison of the emitter saturation current density and the interface defect density shows that the interface density at the midgap is not so useful in predicting interface recombination after corona charging.

Streak Observation of Dc Pre-breakdown Phenomenon in Silicone Oil/Low Density Polyethylene (LDPE) with Different Viscosities

We observe streak images of dc pre-breakdown in silicone-oil (10 cSt, 100 cSt and 10000 cSt) / low density polyethylene (30 μm in thickness) composite insulation under needle / sphere electrode by using the 20 meter long image guide scope and a streak camera. In the case of composite insulation with 10 cSt of silicone-oil, breakdown light propagates from the needle side under both voltage polarity. However, in the 10000 cSt case, breakdown light propagates from the film side under the negative voltage polarity. The mechanism of these transient phenomena are discussed in this paper.

Electrohydrodynamic flow patterns and collection efficiency in narrow wire-cylinder type electrostatic precipitator

Recently, narrow electrostatic precipitators (ESPs) have become a subject of interest because of their possible application for the cleaning of the exhaust gases emitted by diesel engines. Diesel engines emit fine particles, which are harmful to human and animal health. There are several methods for decrease particulate emission from a diesel engines, but up to now, these methods are not enough effective or very expensive. Therefore, an electrostatic precipitation was proposed as an alternative method for control of a diesel particulate emission. In this work, results of electrohydrodynamic (EHD) secondary flow and particle collection efficiency measurements in a narrow wire-cylinder type ESP are presented. The ESP was a glass cylinder (300 mm × 29 mm) equipped with a wire discharge electrode and two collecting cylinder-electrodes. A 0.23 mm in diameter and 100 mm long stainless-steel discharge wire electrode was mounted in the center of the cylinder, parallel to the main flow direction. The collecting electrodes were made of stainless steel cylinders, each with a length of 100 mm and inner diameter of 25.5 mm. An air flow seeded with a cigarette smoke was blown along the ESP duct with an average velocity of 0.9 m/s. The EHD secondary flow was measured using 2-dimensional particle image velocimetry (PIV) method. The PIV measurements were carried out in the wire electrode mid-plane, perpendicularly to the wire and the collecting electrodes. The results show similarities and differences of the particle flow in the wire-cylinder type ESP for a negative and a positive DC voltage polarity. The collection efficiency was calculated from the fractional particle concentration. The fractional particle concentration was measured using the optical aerosol spectrometer. The results of the fractional collection efficiency confirmed the common view that the collection efficiency of fine particles in the ESP increases with increasing voltage and it is higher for negative voltage polarity and decreases when decreasing particle diameter.

Electrohydrodynamic secondary flow and particle collection efficiency in a one-sided spike-plate type electrostatic precipitator

In this work, results of electrohydrodynamic secondary flow and particle collection efficiency measurements in an electrostatic precipitator under positive and negative voltage polarity are presented. The electrostatic precipitator had two plate collecting electrodes and a single spike discharge electrode. The spike tips were only on one side of the discharge electrode, therefore called a one-sided spike electrode. The electrohydrodynamic secondary flow pattern and collection efficiency measurements were carried out for two one-sided spike electrode positions: with the spike tips directed either upstream or downstream the primary flow. The results of the flow pattern measurement showed different flow patterns for different spike tips positions in respect to the primary flow direction. The electrostatic precipitator collection efficiency measurements clearly showed difference in the particle collection for both spike tips positions. Since the other electrostatic precipitator working parameters were the same, it can be concluded that the observed change of the electrohydrodynamic secondary flow was the main reason of the difference in the electrostatic precipitator collection efficiency.

Collection efficiency in narrow electrostatic precipitators with a longitudinal or transverse wire electrode

Recently narrow electrostatic precipitators (ESPs) have become a subject of interest because of their possible application in diesel engine exhaust systems. In this work, results of particle collection efficiency measurements in narrow electrostatic precipitators for negative and positive dc voltage polarity are presented. The ESP used in this work was a parallelepiped equipped with wire discharge electrode and two collecting plate-electrodes. The experiments were carried out for two discharge electrode positions: longitudinally or transversely to the main flow direction. The obtained results showed that the collection efficiency strongly depends on the discharge electrode position. It is higher in the ESP with longitudinally-to-flow placed discharge electrode. The collection efficiency is also influenced by the EHD secondary flow generated in the ESP. The EHD secondary flow with high migration velocity (y-component of the particle velocity) and low turbulence intensity increase the chance of the particle deposition on the collecting electrodes.

고온초전도 DC 케이블 시스템용 PPLP 및 GFRP의 절연 특성

DC high-temperature superconducting(HTS) cable system has attracted a great deal of interest from the view point of low loss, dense structure and large capacity. A HTS cable system is made of cable and termination. The insulating materials and insulation technology must be solved for the long life, reliability and compact of cable system. In this paper, we will report on the dielectric breakdown characteristics of insulating materials for HTS cable and termination. The AC, DC and lightning impulse breakdown strength of laminated polypropylene paper(PPLP) and glass fiber reinforced plastic(GFRP) have been measured under nitrogen pressures in the range of 0.l-0.4MPa. PPLP and GFRP are found to have a significantly higher DC breakdown strength. Also, DC surface flashover voltage of negative polarity is slightly higher than that of positive polarity in GFRP.

Energy transfer efficiency of nano-seconds pulsed power generator for nonthermal plasma processing technique

Development of a high voltage nano-seconds pulsed power generator (NS-PG) is attracting attentions from plant manufacturing makers since it enables higher energy efficiencies of plasma processing: such as pollution control, ozone generation and so on. The pulsed power system developed in this study consisted of a pulsed charging circuit, the NS-PG, and a load. The NS-PG consisted of a high-pressure spark gap switch (SGS) as a low inductance self-closing switch, a triaxial Blumlein line as a pulse-forming line, and a voltage transmission line from the Blumlein line to load. The SGS was filled with SF6 gas, and the output voltage of the generator is regulated by varying the pressure of SF6. The pulse duration of output voltage is 5 ns. In this study, energy transfer efficiency from NS-PG to load is investigated for both positive and negative voltage polarities. In addition, experiments were carried out using a low inductance resistor and a discharge reactor as connected load. The results showed maximum energy transfer efficiency was 85.2% in case of a low inductance resistive load, and 56.7% in case of a discharge reactor. Further efficiency can be achieved by impedance matching the discharge reactor to the NS-PG.

In‐channel amperometric detection for microchip electrophoresis using a wireless isolated potentiostat

The combination of microchip electrophoresis with amperometric detection leads to a number of analytical challenges that are associated with isolating the detector from the high voltages used for the separation. While methods such as end-channel alignment and the use of decouplers have been employed, they have limitations. A less common method has been to utilize an electrically isolated potentiostat. This approach allows placement of the working electrode directly in the separation channel without using a decoupler. This paper explores the use of microchip electrophoresis and electrochemical detection with an electrically isolated potentiostat for the separation and in-channel detection of several biologically important anions. The separation employed negative polarity voltages and tetradecyltrimethylammonium bromide (as a buffer modifier) for the separation of nitrite (NO₂⁻), glutathione, ascorbic acid, and tyrosine. A half-wave potential shift of approximately negative 500 mV was observed for NO₂⁻ and H₂O₂ standards in the in-channel configuration compared to end-channel. Higher separation efficiencies were observed for both NO₂⁻ and H₂O₂ with the in-channel detection configuration. The limits of detection were approximately two-fold lower and the sensitivity was approximately two-fold higher for in-channel detection of nitrite when compared to end-channel. The application of this microfluidic device for the separation and detection of biomarkers related to oxidative stress is described.

Transport Mechanism of Chemical Species in a Pin-water Atmospheric Discharge driven by Negative Voltage

Atmospheric plasma discharges at a gas-liquid interface have recently paid great attention because of many possible applications. Although chemically reactive species, e.g., OH, O, O3, H2O2, play an important role in many applications, their transport mechanism has not yet been clarified. In this study, flow fields in air and water were observed to elucidate the mechanism of chemical species transport. We used a dielectric barrier discharge ignited between a metal pin electrode and the surface of water by applying high AC voltage of negative polarity to the metal pin electrode. To visualize the chemical species distribution in the water, methyl red solution was used and color change was observed. In addition, the relationship between the flow field and the color change of methyl red solution was examined. Furthermore, a computational study was conducted to understand the effect of the flow on the chemical species transport. The results show that the chemical species in the water were transported mainly by the circulating flow induced by the discharge.

System peaks in capillary zone electrophoresis of anions with negative voltage polarity and counter‐electroosmotic flow

The system peaks that often appear on electropherograms in anion separation by CE with indirect spectrophotometric detection, negative voltage polarity and cathodic EOF are studied. The system peaks are shown to correspond to the zones with the changed concentration of the BGE constituents; they appear while the zone of each analyte anion passes through the outlet end of the capillary and are transported to the detector by EOF. An equation is suggested for predicting migration times of the system peaks with an error of 1%. The ratios of the system peak area to the analyte peak area are found to amount to 20%. It is shown that it is possible to avoid overlapping of the system peaks and analyte peaks by controlling the EOF velocity owing to hydrodynamic pressure. Using the mathematical simulation of CE shows that the system peaks and baseline shift can result from changing the transference numbers of the BGE ions and analyte ions at the capillary edge. The cases when the system peak may be incorrectly identified as the peak of analyte ion are considered. In order to avoid such errors, some practical recommendations are given.

An Area-Efficient Fully R-DAC-Based TFT-LCD Column Driver

This paper proposes an area-efficient fully resistor-string digital-to-analog-converter (R-DAC)-based thin-film transistor liquid crystal display (TFT-LCD) column driver in which DACs supply only negative-polarity voltages, while polarity inverters generate positive-polarity voltages from negative-polarity voltages. An offset cancellation technique is employed in negative-polarity buffers and polarity inverters. An experimental prototype 8-bit column driver was implemented using 0.35-m CMOS technology to verify the proposed driving scheme. The settling time is within 5 s, and the maximum deviation is 0.68 LSB. The average area per channel is 0.04 mm2. Compared with a conventional fully R-DAC-based TFT-LCD column driver, the proposed driving scheme has a DAC area saving of 41%.

Pulsed Discharge Induced by Nanosecond Pulsed Power in Atmospheric Air

Nonthermal plasmas have been widely used for various applications. Observation of a discharge plasma is an essential aspect for understanding the plasma physics of this growing field. In this paper, the propagation of a general pulsed discharge having a 100-ns pulse duration is observed by taking framing and streak images and spectroscopic measurement. The results showed that two discharge phases exist in the general pulsed discharge, namely, a streamer discharge and the following glowlike discharge. Between these two phases, the electrode gap impedance changed dramatically which could cause impedance mismatching between the power generator and the electrode. In addition, the gas temperature increased about 150 K during the glowlike discharge, which causes further energy loss in plasma-enhanced chemical reactions. Consequently, it was decided to remove the glowlike discharge phase and to only have the streamer discharge. A nanosecond pulsed power generator having a pulse duration of 5 ns was developed, and the observed discharge propagation ended before it shifts to the glowlike discharge. The streamer propagation velocity with the nanosecond pulsed discharge was 6.0-8.0 mm/ns, which is much faster than that of a general pulsed discharge, and showed little difference between positive and negative voltage polarities.

TH‐D‐BRB‐04: Ion Chamber Dosimetry Modification under Strong Magnetic Field Conditions

Purpose: To examine the dose response of an ion chamber in an external magnetic field and to simulate the energy deposition using the Monte Carlo technique. Method and Materials: This work investigates the response of a 0.6cm3 Farmer chamber to an 11.17 mCi 137Cs source under the influence of a 1.5 T magnetic field on a GE MRI scanner. A wooden frame was designed that allowed varying field direction measurements while keeping the source to chamber axis distance constant. Monte Carlo simulations were conducted using FLUKA a particle physics transport package to score the energy deposition and the average electron track length inside the cavity. Results: Higher chamber current readings were obtained when a transverse (to chamber central axis) magnetic field was applied compared to zero B field conditions. Lower readings were obtained when a longitudinal field was present. A 4.8% increase was observed for the transverse field measurements and negative voltage polarity while a 3.5% decrease was measured for the longitudinal case. The positive polarity measurements showed a 3.7% increase and an 11.5% decrease in transverse and longitudinal fields vs. a 4.0% increase and a 6.0% decrease found through Monte Carlo simulations. The average track length increased by 11.0% and decreased by 6.8% in transverse and the longitudinal fields.Varying the electric field applied to the electrodes showed no significant changes in chamber response. Conclusion: The dose response of a Farmer chamber in an external magnetic field varies with the average charged particle trajectory length. The average trajectory depends on the B field magnitude and direction and on the energy spectrum of the primary photon beam. Thus an alignment with the B field direction would be essential. Smaller cavity chambers are expected to be affected less under B field conditions and should be investigated in the future.