Hz AC Research Articles

Influence of electronic scavenger additives on AC breakdown voltage of synthetic ester

This study deals with the influence of two kinds of electronic scavenger additives/compounds, namely methyl iodide (iodomethane), CH3I, and carbon tetrachloride CCl4 on the breakdown voltage (U BDV) of MIDEL 7131 synthetic ester (SE). The tests are conducted under 60 Hz AC voltage according to the IEC 60156 standard, for various concentrations of additives ranging 0–600 ppm. Statistical analysis is performed to check whether the experimental data obey the most used probabilistic distributions for electrical BDVs, namely normal and Weibull laws. The estimation of the BDV with risk probabilities of 1 and 50% are also deduced. It is shown that the average BDV of SE increases with the concentration of both additives up to an optimum value beyond which it decreases; the optimum concentration for both cases is 400 ppm. The improvement of the average U BDV is about 27% with CH3I and 21% with CCl4. The values of U BDV conform to Weibull distribution with CH3I; it is also the case with CCl4, except for 200 ppm.

A heuristic wear model for the contact strip and contact wire in pantograph – Catenary interaction for railway operations under 15 kV 16.67 Hz AC systems

The sliding contact between the pantograph and catenary allows the correct operation of electric trains. However, this contact induces wear on both the components involved in the process, namely the contact strip on the pantograph and the contact wire on the catenary. The influence of operating parameter values (i.e., the fed current intensity, uplift force and train speed) has recently gained attention, with the aim of creating wear models for both parts involved in the contact. In this study, a procedure assessed in the literature is adapted to operating conditions with AC catenary systems at 15kV/16.67 Hz and Cu-impregnated carbon contact strips. The resulting models are suitable for the wear prediction of both the contact wire and the contact strip.

A Novel Active Needle Probe in an Atmospheric Pressure Corona-Based Cold Plasma Reactor With Admixtures of Helium and Dry Air

Corona-based atmospheric pressure cold plasma reactors can be applied to material processing, bacteria inactivation, plasma medicine, etc. Knowledge generated in this article can be used to optimize such reactors when they use electrodes consisting of arrays of needles. The experiment used a gas admixture of helium and dry air and an applied 60-Hz ac voltage of 6.5-kV rms, with an electrode gap of 6 cm. A novel single conducting needle probe was inserted into the corona gap from below the grounded electrode. Two distinct conduction and displacement current signals were captured by a digital oscilloscope: 1) current collected by the probe and 2) current collected by the grounded electrode. Current oscillograms were sorted into several classes, one of which showed evidence that corona pulses launched from the tip of the needle probe acted to shield surrounding portions of the grounded electrode resulting in distinct counter pulses of current (called shielding current pulses) observed at the grounded electrode current sensor. This needle probe has the ability to provide information regarding which electrode launches a corona pulse when both needle arrays (the high-voltage array and the grounded array) are known to be sources of corona discharges.

A kilohertz frequency response pseudocapacitor

Electrochemical supercapacitors have orders of magnitude higher energy density than a dielectric/electrolytic capacitor (EC), but most are unsuitable for applications involving high-frequency signals since their capacitive behavior is limited by the high equivalent series resistance (ESR) to signals of frequencies below 5 Hz. The kHz frequency response supercapacitors are exclusively carbon electrode-based electric double layer capacitor (EDLC). However, an EDLC's areal capacitance is limited by the straight-channel porous morphology of the electrode required for low electrolyte resistance. Moreover, an EDLC's capacitance decays rapidly for frequencies beyond 10 kHz. A pseudocapacitor has a higher specific capacitance than an EDLC, but a kHz pseudocapacitor is not reported. Here we show a titania-based, kHz pseudocapacitor whose ability to retain capacitive behavior at high frequencies (190 μF cm−2 at self resonance frequency (SRF) of 51 kHz) is far superior to the kHz EDLCs (20 μF cm−2 at 80 kHz SRF or 67 μF cm−2 at 20 kHz SRF). The pseudocapacitor could filter a 50 kHz sinusoidal signal to a smooth line with a variance of less than 9×10−4. The variance of 7×10−4 for filtering a 60 Hz AC signal to a smooth line is considerably better than filtering by an EC.

Power Converter For 60 Hz-400 Hz Bilateral Power Conversion

A power converter for 60-400 Hz bilateral power conversion (BPC) is proposed in this article. This power converter is composed of three power switch arms, a set of filter inductors, a frequency decoupling circuit, a 60 Hz ac capacitor and a 400 Hz ac capacitor. The proposed BPC has the salient feature that it has the function of 60-400 Hz bilateral power conversion using only one power electronic converter. Hence, the proposed BPC can simplify the power circuit. Both simulation and experimental results verify the performance of the proposed BPC is as expected.

Effects of Frequency and Temperature on Electric Field Mitigation Method via Protruding Substrate Combined with Applying Nonlinear FDC Layer in Wide Bandgap Power Modules

Our previous studies showed that geometrical techniques including (1) metal layer offset, (2) stacked substrate design and (3) protruding substrate, either individually or combined, cannot solve high electric field issues in high voltage high-density wide bandgap (WBG) power modules. Then, for the first time, we showed that a combination of the aforementioned geometrical methods and the application of a nonlinear field-dependent conductivity (FDC) layer could address the issue. Simulations were done under a 50 Hz sinusoidal AC voltage per IEC 61287-1. However, in practice, the insulation materials of the envisaged WBG power modules will be under square wave voltage pulses with a frequency of up to a few tens of kHz and temperatures up to a few hundred degrees. The relative permittivity and electrical conductivity of aluminum nitride (AlN) ceramic, silicone gel, and nonlinear FDC materials that were assumed to be constant in our previous studies, may be frequency- and temperature-dependent, and their dependency should be considered in the model. This is the case for other papers dealing with electric field calculation within power electronics modules, where the permittivity and AC electrical conductivity of the encapsulant and ceramic substrate materials are assumed at room temperature and for a 50 or 60 Hz AC sinusoidal voltage. Thus, the big question that remains unanswered is whether or not electric field simulations are valid for high temperature and high-frequency conditions. In this paper, this technical gap is addressed where a frequency- and temperature-dependent finite element method (FEM) model of the insulation system envisaged for a 6.5 kV high-density WBG power module will be developed in COMSOL Multiphysics, where a protruding substrate combined with the application of a nonlinear FDC layer is considered to address the high field issue. By using this model, the influence of frequency and temperature on the effectiveness of the proposed electric field reduction method is studied.

Characterization of a microsecond pulsed non-equilibrium atmospheric pressure Ar plasma using laser scattering and optical emission spectroscopy

A non-equilibrium atmospheric pressure argon (Ar) plasma excited by microsecond pulse is studied experimentally by laser scattering and optical emission spectroscopy (OES), and theoretically by collisional-radiative (CR) model. More specifically, the electron temperature and electron density of plasma are obtained directly by the laser Thomson scattering, the gas temperature is measured by laser Raman scattering, the optical emissions of excited Ar states of plasma are measured by OES. The laser scattering results show that the electron temperature is about 1 eV which is similar to that excited by 60 Hz AC power, but the gas temperature is as low as 300 K compared to about 700 K excited by 60 Hz AC power. It is shown that the microsecond pulsed power supply, rather than nanosecond ones, is short enough to reduce the gas temperature of atmospheric pressure plasma to near room temperature. The electron temperature and electron density are also obtained by CR model based on OES, and find that the intensities of the optical emission intensity lines of 727.41, 811.73, 841.08, 842.83, 852.44 and 912.86 nm of Ar can be used to characterize the behavior of electron density and electron temperature, it is very useful to quickly estimate the activity of the atmospheric pressure Ar plasma in many applications.

AC Loss Analysis on Coated Conductors at different Sinusoidal Frequencies for Electric Propulsion Applications

Superconducting magnets are one of the superior contenders in achieving the targets of electric aircraft industry successfully as they have very high power densities compared to other battery storage systems. Many aviation research agencies are looking at superconducting magnets as one of the alternate in replacing the conventional jet engines completely (electric aircrafts) or partially (hybrid aircrafts). National Aeronautics and Space Administration (NASA) and Air Force Research Laboratory (AFRL), USA has reported that high temperature superconducting magnets possesses higher specific energies (Wh/kg) and have infinite number of recharge cycles compared to other storage technologies employed for energy requirements. The other advantage of using such magnets is that there will be no hazardous disposals like batteries which lower the overall pollution. Superconducting magnets are DC operated systems however during charging or discharging transient behaviour of current results in the losses which would further ends up with heat generation. Heat generation during charging or discharging period would cause quenching of the superconductor due to sudden temperature rise.In this work, electromagnetic analysis on superconducting magnet having capacity of 1 MJ has been performed where a 2D numerical model is developed using H-formulations in order to estimate the AC losses for a high temperature superconducting tape manufactured by SuperPower (SCS 12050) having 330 A critical current at 77 K. AC current having different load factors has been fed through the stacked tapes at 50 Hz, 60 Hz and 70 Hz frequency and AC losses have been evaluated. It has been found that at higher frequencies the AC losses are found to be larger than lower frequencies. Overcritical currents have been found in the current density distribution due to the application of E-J relationship for the homogeneous 2D numerical model.

The incorporation of particles suspended in the electrolyte into plasma electrolytic oxidation coatings on Ti and Al substrates

This investigation concerns the mechanisms by which (fine) particles become incorporated into plasma electrolytic oxidation (PEO) coatings when added to the electrolyte. Three different types of particle have been used, covering a wide size range, and processing has been carried out with both Al and Ti substrates. For some of these combinations, the particulate was chemically similar to the expected PEO product, while for others it was different. The power supply was 50 Hz AC, with a pre-selected current density. It has been established that, where such reactions are chemically favoured, phase changes can occur that must have involved the particulate reaching very high temperatures. From this and other evidence, it is concluded that the main incorporation mechanism involved is that of (fine) particulate being swept into the pores associated with active discharge sites, while they are being refilled with electrolyte immediately after collapse of the plasma. They are then likely to become entrapped, and in many cases to be strongly heated as the plasma is created during the next discharge cycle. Typical pore sizes are such that particles (or particulate clusters) above about 10 μm in size would be unlikely to enter them. While particles a few microns in diameter can become incorporated, it takes place more readily with sub-micron particles. It is also concluded that electrophoretic forces are unlikely to play any significant role in the incorporation process.

Cold Plasma Processing of Biochar Using Corona Discharge in Atmospheric Pressure Dry Air and Helium

Cold plasma generated from a gas admixture of helium and dry air with 60-Hz ac voltage at 6.50-kV rms was utilized to process biochar. Reactive oxygen and nitrogen species (RONS) were generated in the cold plasma and these chemical radicals modified the biochar. Plasma-processed biochar samples were immersed in distilled water after which the pH of the solid/water mixture was measured. This pH test provided a quick and reliable indication that the plasma-processing modified the biochar, after which more thorough tests were applied. The pH data showed that plasma-processed biochar/water admixtures have lower pH, indicating plasma processing introduced more acidic groups onto the biochar. After pH analysis the solid biochar granules were reclaimed from solution and the leachate was evaluated for carbon content resulting from material leaching into the distilled water. Fourier-transform infrared spectroscopy (FTIR) spectra were measured for dry samples of biochar before and after immersion in the distilled water. Cold plasma processing converted recalcitrant biochar mass into labile biochar mass, resulting in an enhanced amount of water-extractable carbon. FTIR spectra showed that new oxygen- and nitrogen-containing functional groups were introduced into the labile portion of the biochar and that functionalized material leached into solution.

A Single Stage Common Ground Three-Level PV Inverter With Integrated Power Decoupling

In this paper, a T-type common ground transformer-less single phase inverter with dynamic swing of the dc-link voltage is presented for photovoltaic (PV) application. The topology is a combination of a bi-directional, partial-power-processing boost stage and an asymmetric half-bridge inverter stage along with a T-branch. It takes advantage of the three-level switching states with reduced voltage stress on the main switches to achieve lower switching loss and almost one-half the inductor current ripple w.r.t. two level implementation. The double line frequency power decoupling is addressed by a dynamic dc-link approach, which allows a large swing of the dc-link to reduce the decoupling capacitor requirement, enabling an all-film capacitor implementation. This topology also significantly reduces the high-frequency capacitive coupled ground current by directly connecting the PV negative terminal to the grid neutral. Moreover, an adaptive dc-link voltage control scheme that optimally changes the average value of the dc-link voltage as the operating conditions (load and power factor) vary, has been proposed and thoroughly investigated from the perspective of better utilization of passive components and further reduction of switching losses. A SiC MOSFETs-based 1 kVA laboratory prototype has been built to validate the converter's operation at 200 V dc nominal input and 120 V/60 Hz ac nominal output with a wide range of power factor and load operations. Extensive experimental results validate the superior performance of the topology with the adaptive dc-link voltage control implementation showing a peak efficiency of 98.22% and a CEC efficiency of 98.03% at 50 kHz switching frequency.

Об оценке коммутационной способности тяговых двигателей грузовых электровозов

An important direction in the development of JSC Railways is increasing the volume of freight traffic over the railway network. A number of measures are being taken to achieve the predicted strategic indicators in the locomotive complex. The most large-scale activities include research and experimental works aimed at improving the traction properties of electric locomotives in the Eastern polygon, which is one of the most heavily loaded sections of the Russian railway network. This is an important link connecting Southeast Asia and Europe. The conditions under which the railway transport operates require, among the priority tasks, efficient use of the locomotive fleet with high operational reliability to ensure safe train traffic. The Eastern polygon uses a system of electric traction powered by the 25 kV, 50 Hz AC voltage. Freight trains are driven by 2ES5K and 3ES5K electric locomotives equipped with pulsating current commutator traction machines. In implementing the required traction forces, the traction electric drive of such locomotives has a number of limitations. One of them is the quality of switching on the traction motor commutator. Achieving better reliability of traction motors, which are regarded as the weak link of electric locomotives, is a topical problem. The number of their failures due to faults of direct and pulsating current traction motors is at the level of 20--22%. The greatest difficulty is to increase the switching reliability. A switching quality criterion for traction electric motors of electric locomotives is proposed, which takes into account the degree to which the armature reaction magnetomotive force is compensated in the switching zone. The width of the sparkless operation region cannot fully characterize the traction electric motor switching capacity. Its calculation takes into account the spark voltage under the brush, the effect of electromagnetic factors on the switching, the design of additional poles, and the kind of load current. The accomplished calculations have shown that the proposed switching reliability quality criterion objectively characterizes the switching quality in the limiting mode and is consistent with the long-term experience of their operation in AC electric locomotives.

Plasma diagnostic of gliding arc discharge at atmospheric pressure

A gliding arc discharge (GAD) with a water spray system was constructed. A non-thermal plasma, generated between two V shaped electrodes in an ambient argon driven by 100 Hz AC voltage, was investigated using optical emission spectroscopy (OES) with different gas flow rates (0.5, 1, 1.5, 2 , 2.5 , 3 1/min). Boltzmann plot method was used to calculate electron temperature (Te) and electron density (ne). The electrodes design was spectrally recognized and its Te value was about 0.588-0.863 eV, while the ne value of 6.875×1017-10.938×1017 cm-3. The results of the plasma diagnostics generated by gliding arc showed that increasing gas flow rates was associated with decreased electron temperature (Te), Debye length, and Debye Number, along with decreased electron density (ne) and plasma frequency.

Design and Implementation of 150 W AC/DC LED Driver with Unity Power Factor, Low THD, and Dimming Capability

This paper presents the implementation of a two-stage light-emitting diode (LED) driver based on commercial integrated circuits (IC). The presented LED driver circuit topology, which is designed to drive a 150 W LED module, consists of two stages: AC-DC power factor correction (PFC) stage and DC/DC power converter stage. The implementation of the PFC stage uses IC NCP1608, which uses the critical conduction mode to guarantee a unity input power factor with a wide range of input voltages. The DC/DC power converter with soft-switching characteristics for the entire load range uses IC FLS2100XS. Furthermore, the design of an electromagnetic interference (EMI) filter for the LED driver and the dimming control circuit are discussed in detail. The hardware prototype, an LED lighting system, with a rated power of 150 W/32 V from a nominal 220 V/50 Hz AC voltage supply was tested to show the effectiveness of the design. The presented LED driver was tested for street lighting, and the experimental results show that the power factor (PF) was higher than 0.97, the total harmonics distortion (THD) was lower than 7%, and the efficiency was 91.7% at full load. The results prove that the performance of the presented LED driver complies with the standards: IEC61000-3-2 and CIRSP 15:2009.

Psychological Correlates of Nonspecific Electrodermal Responses.

Spontaneous fluctuations in electrodermal responses are known as nonspecific electrodermal responses (NS.EDRs). The use of NS.EDRs as a tool in applied psychophysiological research has resulted in a variety of publications. NS.EDRs are examined separately as associated with the (as a biomarker of) levels of anxiety. The aim of this study was to compare changes (in terms of amplitude, frequency and time components) in NS.EDRs at two different (pre and post of an external stimulus) resting phases. NS.EDRs (nonspecific skin conductance responses (NS.SCRs), nonspecific skin potential responses (NS.SPRs), and nonspecific skin susceptance responses (NS.SSRs)) were recorded from 50 apparently healthy volunteers simultaneously at the same skin area. They were scored as NS.SCRs and NS.SSRs for changes greater than 0.02 μS and NS.SPRs greater than 0.02 mV. It was found that NS.EDRs, in particular NS.SCRs and NS.SPRs, were significantly changed in the second resting period, following the specific stimulus. More specifically, the amplitude of NS.EDRs were significantly decreased for NS.SCRs (p<0.001) and for NS.SPRs (p<0.005), but NS.SSRs remained stable. Moreover, the rise time of NS.SCRs was decreased in the second resting time. Furthermore, the frequency of responses was also changed. The computed NS.EDRs, in particular NS.SCRs and NS.SPRs could be of psychological interest and be used to study the electrodermal responses in detail. NS.SSRs were found to be robust with respect to nonspecific stimuli at various relaxation periods and their role was found to be less important in analysis of NS.EDRs in comparison to NS.SCRs and NS.SPRs at low frequency (20 Hz AC current). This should be considered in analysis of NS.EDRs. The computed NS.EDRs, especially NS.SCRs and NS.SPRs may be used as a useful measure of arousal due to their fast response and sensitivity to nonspecific stimuli and may also be used in assessment of individual differences.

Application of AC and DC magnetic field for surface wave excitation to enhance mass transfer

Abstract Refining the metallic melts and removal of contaminants from the free surface may be sped up by increasing the surface area of mass exchange interface. It is relevant to both the case of volatile impurity evaporation in a vacuum as well as the case of chemical reactions when the continuous crust of reaction products should be interrupted. Previously proposed low-frequency AC magnetic field excitation of intense surface waves is limited by skin-effect. The induced sign-alternating forcing at high dimensionless frequency values becomes dominantly pulsing at considerably higher than unity values, delivering time-averaged stirring without intense surface waves. Superimposing DC magnetic field over AC one produces stronger alternating forcing with the frequency of the AC field. We are reporting an experimental setup which incorporates very high Ampere-winding 50 Hz AC Bitter coil surrounded by a powerful permanent magnet system. Experiments demonstrating surface waves were done at room temperature with liquid Galinstan alloy in two crucibles, corresponding to the cases of relatively high and low skin-effect. In the following work proposed method will be tested in liquid silicon refining process from phosphorus and boron.

Hum Noise Reduction using Novel Complementary Pair VSSLMS Algorithm

This paper presents a novel Complementary Pair Variable Step-size (CPVSS) Least Mean Square Algorithm which is implemented for active noise cancellation application. The result presents the effect of filtration to remove the 50 Hz ac hum noise from the 500 Hz audio tone. Discrete Fourier Transform, Short Time Fourier Transform, and Welch Periodogram of the noisy signal and filtered signal have been presented which shows effective improvement in SNR. The simulation study has shown the superiority of this algorithm over other algorithms under consideration.

A Hybrid Predictive Control for a Current Source Converter in an Aircraft DC Microgrid

A current source converter (CSC) is a promising topology for interfacing aircraft generators with the onboard DC microgrid. In this paper, a hybrid predictive control is proposed for the CSC with an output LC filter in such application. Deadbeat predictive control with larger sampling time is applied to the output circuit, generating reference source currents. Finite-set model predictive control with smaller sampling time is applied to the input circuit to achieve sinusoidal source currents, which is simplified by saving the source current predictions. The proposed scheme eliminates both the proportional-integral controller and the weighting factor, which are required in the existing studies. Besides, it has lower control complexity. A SiC-MOSFET-based prototype is used to verify the validity of the proposed scheme. Experimental results under 150 V/350–800 Hz AC input and 270 V DC output demonstrate the superior control performance.

Study on corona discharge spatial structure and stages division based on visible digital image colorimetry information

Due to the progress in photoelectric detection techniques, visible light images provide more abundant spatial structure information, which facilitates the detection of the colorimetry distribution in discharge images. In this study, the 50Hz AC high voltage power source was applied to the 15 mm needle-plane gap under room temperature and atmospheric pressure. The discharge images in the time scale of seconds were obtained by a high resolution digital camera. Two kinds of colorimetry indicators based on RGB model and HSI model were used to reflect the spatial structure and the colorimetry variation of discharge areas. Our experimental results demonstrated the growth, suppression, and penetration of the filamentary discharge and reflected that the relative intensity of characteristic color varies with different voltages. According to the variation of colorimetry information, we divided the AC corona stages, and the stage division results of two models are well correlated. Oscilloscope electrical signals verify the reliability of the colorimetry result, and colorimetry information shows the advantage of overcoming the randomness of one single discharge pulse amplitude. The colorimetry information extracted from images can represent the statistical characteristics of a large number of discharges, helping to characterize the spatial structure of corona discharges and evaluate its status.

Limitations Regarding Use of the ABC-Model for Interpretation of Partial Discharge Measurements

The main purpose of the work presented here is to facilitate use of partial discharge (PD) measurements as a diagnostic tool for condition assessment of hydropower generator bars. The main aim of the work is to clarify how measured inception and extinction voltage, detected number and magnitude of PDs relate to the void size and the physical discharge mechanisms in the voids. The laboratory tests were performed on 3 mm thick samples, consisting of three 1 mm thick layers containing a cylindrical disc shaped void in the center of the middle layer. The void diameters varied from 3 to 20 mm. Insulation discs of polycarbonate and generator insulation based on mica and glass fiber reinforced epoxy tape were examined. In case of the polycarbonate samples comparable tests were performed on objects with either conductive or insulting void surfaces. During application of a stepwise increasing/decreasing 50 Hz AC voltage, the partial discharge activity was detected using a conventional PRPDA detection system.The inception voltage was found to decrease with increasing void diameter, in accordance with results from electric field calculations showing increased field enhancement in the larger voids. In all cases the apparent discharge magnitude increased with increasing diameter. In case of conducting void surfaces this discharge magnitude and number of PDs per period were, in accordance with the theory, found to be proportional to the total surface area of the void. In case of voids with insulating surfaces, this proportionality was valid up to a void diameter of 10 mm. Larger voids resulted in higher number of PD each at lower apparent charge magnitude than expected, indicating several parallel discharges, during which a section of the void surface is discharged only. In contradiction to the assumptions of the abc-model nearly no difference was observed between the PD inception and extinction voltage, indicating a high and rapidly decaying remanent charge.Thus, the abc-model assumption of each PD causing a complete void discharging is only fulfilled if the surfaces are conducting, or the voids are small. The results indicate that changes of internal conditions of the void during the period of PD measurements