Apparent Charge Research Articles

Apparent and True Charges in the Partial Discharge Model at Different Defective Domain Sizes

A model of the partial discharges in a sample of solid insulation with air cavity is presented. The material of the insulation is cross-linked polyethylene. The model is based on an active-capacitive equivalent circuit, in which the resistance of the air cavity at the instant of a partial discharge ignition is shunted by the active resistance of the spark. The model takes into consideration the delay of the discharge development. The evaluation of the diagnostic value of the apparent and true charges is carried out. The results of the apparent and true charges relationship with the dimensions and proportions of the air cavity are presented. It is shown that the same magnitude of both true and apparent charges can correspond to the different volumes and shapes of the air cavities in the insulation.

Monolayer Janus Te2Se-based gas sensor to detect SO2 and NOx: a first-principles study.

In this study, the adsorption of gas molecules, such as O2, NH3, CO, CO2, H2O, NOx (x = 1, 2) and SO2, on Janus Te2Se monolayer has been investigated by means of density functional theory (DFT) calculations. We show that Janus Te2Se monolayer is preferable for SO2 and NOx molecules with suitable adsorption strength and apparent charge transfers. We further calculated the current-voltage (I-V) curves using the nonequilibrium Green's function (NEGF) method. The transport feature exhibits distinct responses with a dramatic change of I-V curves before and after NOx (SO2) adsorption on Janus Te2Se. Thus, we predict that Janus Te2Se could be a promising candidate for SO2 and NOx sensors with high selectivity and sensitivity. Moreover, the effect of strain on the gas/substrate adsorption systems was also studied, implying that the strained Janus Te2Se monolayer could enhance the sensitivity and selectivity to SO2 and NO2. The adsorbed SO2 and NO2 on Janus Te2Se could escape by releasing the applied strain, which indicates that the capture process is reversible. Our study widens the application of Janus Te2Se not only as piezoelectric materials, but also as a potential gas sensor or capturer of SO2 and NOx with high sensitivity and selectivity.

Исследование характеристик частичных разрядов в СПЭ-изоляции кабеля с множественными дефектами

The paper simulates the electric field intensity picture in the cable with one and several defects. Modeling has shown that the presence of several closely spaced defects does not lead to an increase in the electric field intensity in comparison with one defect. On the basis of experimental studies, an analysis of defects' number influence on various parameters of partial discharges (PD) is performed. Artificial defects are created in the area of the XLPE-insulated cable termination. The following parameters of PD are measured: the magnitude of the apparent charge, the power (intensity) of partial discharges, the phase-resolved partial discharge (PRPD) patterns, the shape of PD signals. The analysis shows an increase in the number of defects does not affect the characteristics of partial discharges, despite the fact the defects are located in different sections of the cable with distributed parameters. Thus, it can be difficult to quantify defects during cable partial discharge measurements.

GW/BSE nonadiabatic dynamics simulations on excited-state relaxation processes of zinc phthalocyanine-fullerene dyads: Roles of bridging chemical bonds

In this work, we employ electronic structure calculations and nonadiabatic dynamics simulations based on many-body Green function and Bethe-Salpeter equation (GW/BSE) methods to study excited-state properties of a zinc phthalocyanine-fullerene (ZnPc-C60) dyad with 6-6 and 5-6 configurations. In the former, the initially populated locally excited (LE) state of ZnPc is the lowest S1 state and thus, its subsequent charge separation is relatively slow. In contrast, in the latter, the S1 state is the LE state of C60 while the LE state of ZnPc is much higher in energy. There also exist several charge-transfer (CT) states between the LE states of ZnPc and C60. Thus, one can see apparent charge separation dynamics during excited-state relaxation dynamics from the LE state of ZnPc to that of C60. These points are verified in dynamics simulations. In the first 200 fs, there is a rapid excitation energy transfer from ZnPc to C60, followed by an ultrafast charge separation to form a CT intermediate state. This process is mainly driven by hole transfer from C60 to ZnPc. The present work demonstrates that different bonding patterns (i.e. 5-6 and 6-6) of the C−N linker can be used to tune excited-state properties and thereto optoelectronic properties of covalently bonded ZnPc-C60 dyads. Methodologically, it is proven that combined GW/BSE nonadiabatic dynamics method is a practical and reliable tool for exploring photoinduced dynamics of nonperiodic dyads, organometallic molecules, quantum dots, nanoclusters, etc.

A brief study on the kinetic of the voltammetric behavior of the modified carbon paste electrode with NiO nanoparticles towards loratadine as a carboxylate-amidic drug compound

A carbon paste electrode (CPE) was modified by NiO nanoparticles (NPs). NiO NPs were synthesized by the sol-gel method and characterized by XRD and SEM-EDX techniques. The non-calcined NiO NPs and the calcined one at 200 °C showed an amorphous phase. The calcined sample’s grain size was estimated at 36 and 42 nm by applying the Scherer and Williamson-Hall equations, respectively. Cyclic voltammogram (CV) of the NiO-CPE showed an irreversible response with a peak separation of 320 mV in 0.1 M NaOH. The peak current was improved by the addition of loratadine (Lor). The apparent charge transfer coefficients of αa and αc were 0.56 and 0.32, and the rate-constant values (ks) were 0.068 and 0.01 s−1 for the anodic and cathodic directions from the CV results, respectively. The diffusion coefficient (D) was estimated 1.48 × 10−8 cm2 s−1 for the Lor analyte. The modified electrode had a geometric surface area of about 0.0314 cm2 and the effective one of about 0.2 cm2.

Electrostatically mediated layer-by-layer assembly of a bioinspired thymine polycation and gold nanoparticles

In this work, we built self-assembled structures of gold nanoparticles (AuNPs) using a new polyelectrolyte formed by copolymerization of the monomers 4-vinylbenzyl thymine (VBT) and 4-vinylbenzyl triethylammonium chloride (VBA). For the synthesis, a monomer ratio of 1 mol of VBT to 16 mol of VBA was used to obtain the polycation [(VBT)1:(VBA)16]16+ with a charge density suitable for the electrostatic adsorption of citrate stabilized AuNPs. The objective of this work was to explore the optical and electrochemical properties of the structure built on gold and quartz substrates with a view to its potential application as a (bio)sensor for optical and electrochemical detection. The polycation adsorption process was studied by surface plasmon resonance, which allowed us to select the appropriate concentration and adsorption time for the polymer and verify the formation of the self-assembly. Characterization of the system by atomic force microscopy allowed determining that AuNPs are distributed in isolation, such as dimers, trimers, tetramers, or bigger aggregates. The analysis of the resonance of the localized surface plasmons (LSPR) of the AuNPs, as well as the increase in the intensity of the polycation Raman signals revealed the electromagnetic coupling between close nanoparticles. In addition, the electrochemical impedance spectroscopy study of gold electrodes modified with the ([(VBT)1:(VBA)16]16+/AuNPs)n multilayer showed that incorporation of the AuNPs in the structure produced an increase in the apparent heterogeneous charge transfer constant. This fact indicates that the structure of the film and the nanoparticles distribution favor the electronic conduction mediated by AuNPs. The observed properties indicate that this multilayer represents a very interesting platform for the development of (bio)sensors based on optical or electrochemical detection.

3D Model of partial discharge in defects with different sizes and positions in power cable for distribution and transmission networks

The knowledge of partial discharge (PD) phenomena inside electrical insulation of power cables is an important issue for assessing the insulation condition and its degradation state, obtaining information about the likelihood of failure. PDs cause signals to propagate along the cable, as noise phenomena, and contribute to the insulation degradation, culminating in a disruptive fault with the interruption of power supply. Therefore, PDs are considered the best ‘early warning’ indicators of insulation degradation and their modelling, with the development of on-line PDs location methods, are important topics to increase the networks’ electricity security. In this study, a three-dimensional (3D) model of PD events using the CST STUDIO® Dassault software is proposed. PDs inside air inclusions in epoxy-resin are analysed with different shapes, positions and sizes of the defect. The electric-field distribution is evaluated with the conduction current inside the void and the apparent charges induced on the electrode. The effectiveness of the model is validated by comparing the simulation results with other published experimental results. Finally, a description of a 3D–1D hybrid model useful to describe the propagation of PD signals in power networks is given.

Identification of Mechanistic Subtleties that Apply to Voltammetric Studies at Boron-Doped Diamond Electrodes

The α-[S2W18O62]4–/5– and α-[S2W18O62]5–/6– polyoxometalate (POM) reduction processes at boron-doped diamond (BDD) disk electrodes in acetonitrile (0.50 M [n-Bu4N][PF6]) have been investigated using large-amplitude Fourier transformed alternating current (FTAC) voltammetry. The origins of subtle differences in experimental data and simulated data modeled assuming the Butler–Volmer relationship with ion-paring implicitly included, planar diffusion and a uniform surface are considered. Parameters estimated are the apparent heterogeneous electron-transfer kinetics (kapp0′), apparent formal reversible potential (Eapp0′), and apparent charge transfer coefficient (αapp′). The electrode kinetic parameters, in contrast to theoretical predictions of the model employed, are dependent on frequency, POM concentration, and the data analysis method. Reasons for nonconformance to the model include the adsorption of POM on graphite-like sp2-bonded carbon impurities, limitations in the availability of charge carriers in BDD, and the method of incorporating ion pairing when slow electrode kinetics apply. Masking of the sp2 carbon-rich (edge) region of the BDD disk provided FTAC voltammetric data that complied much more closely with the simulated data. Nevertheless, data analysis still produces a concentration dependence in the estimated kapp0′ values, which is considered in terms of the assumption of an infinite number of charge carriers. Conclusions derived from this study are likely to be generally applicable to electrode kinetic investigations at BDD electrodes.

Carrier concentration variety over multisectoral boron-doped HPHT diamond

A set of multisectoral boron-doped diamond plates cut from a 10-ct high pressure high temperature single crystal was thoroughly studied. The plates’ morphologies were examined by atomic-force microscopy, it showed the average roughness of 5–10 nm. For electrical measurements, ohmic and rectifying platinum contacts were deposited by magnetron sputtering. Schottky diodes arrays were investigated by admittance spectroscopy; current-voltage (I–V) and capacitance-voltage (C–V) characteristics were obtained and analysed. Frequency dispersion of C–V characteristics was registered. Blue (111) and white (100) faces of samples showed a drastic difference in I–V and C–V behaviour. Mathematical processing of the obtained data was performed and the depth distributions of apparent charge carriers were obtained for all diodes. The registered concentration for the white sector is in the range (1–3)·1017 cm−3, and for the blue sector it is one order more. Charge carrier distribution over the sample surface was obtained and it showed a fine correlation with sectors’ colour and growth direction with appropriate discussion.

Gas-Sensing Properties of the SiC Monolayer and Bilayer: A Density Functional Theory Study.

Using density functional theory calculations, the adsorption of gaseous molecules (NO, NO2, NH3, SO2, CO, HCN, O2, H2, N2, CO2, and H2O) on the graphitic SiC monolayer and bilayer has been investigated to explore the possibilities in gas sensors for NO, NO2, and NH3 detection. The strong adsorption of NO2 and SO2 on the SiC monolayer precludes its applications in nitride gas sensors. The nitride gases (NO, NO2, and NH3) are chemisorbed on the SiC bilayer with moderate adsorption energies and apparent charge transfer, while the other molecules are all physisorbed. Further, the bilayer can effectively weaken the adsorption strength of NO2 and SO2 molecules, that is, NO2 molecules are only weakly chemisorbed on the SiC bilayer with an Eads of −0.62 eV, while SO2 are physisorbed on the bilayer. These results indicate that the SiC bilayer can serve as a gas sensor to detect NO, NO2, and NH3 gases with excellent performance (high sensitivity, high selectivity, and rapid recovery time). Moreover, compared with other molecular adsorptions, the adsorption of NH3 molecules significantly changes the work function of the SiC monolayer and bilayer, indicating that they can be used as optical gas sensors for NH3 detection.

Anions Enhance Rare Earth Adsorption at Negatively Charged Surfaces.

Anions are expected to be repelled from negatively charged surfaces. At aqueous interfaces, however, ion-specific effects can dominate over direct electrostatic interactions. Using multiple in situ surface sensitive experimental techniques, we show that surface affinities of SCN- anions are so strong that they can adsorb at a negatively charged floating monolayer at the air-aqueous interface. This extreme example of ion-specific effects may be very important for understanding complex processes at aqueous interfaces, such as chemical separations of rare earth metals. Adsorbed SCN- ions at the floating monolayer increase the overall negative charge density, leading to enhanced trivalent rare earth adsorption. Surface sensitive X-ray fluorescence measurements show that the surface coverage of Lu3+ ions can be triple the apparent surface charge of the floating monolayer in the presence of SCN-. Comparison to NO3- samples shows that the effects are strongly dependent on the character of the anion, providing further evidence of ion-specific effects dominating over electrostatics.

Adsorption behaviour of Si anchored on g-C3N4/graphene van der Waals heterostructure for selective sensing of toxic gases: Insights from a first-principles study

Monitoring the levels of toxic gas molecules could efficiently ensure the safety of human health and the environment. Herein, the adsorption behaviour, geometries, energies and electronic properties of H2S, CO, NO2, NH3 and CO2 gas molecules on the Si-doped g-C3N4/graphene surface were systematically investigated using density functional theory calculations. Based on the study of adsorption and desorption behaviour, we indicate that Si-doped g-C3N4/graphene was a suitable sensing material for H2S, CO and CO2, while being a disposable gas sensor for the detection of NH3 and NO2 due to their greater adsorption energy. The electronic properties of Si-doped g-C3N4/graphene heterostructure showed strong hybridisation between the adsorbate orbitals and interacting surfaces, as well as the remarkable presence of NH3 and NO2 orbitals around the Fermi level. The Si-doped g-C3N4/graphene were potentially good H2S, CO and CO2 sensors because of the short recovery time, shift in electrical conductivity, apparent charge transfer and reasonable adsorption energies. To sum up, the results obtained in this study could provide details about the process of gas sensing mechanism.

Green bio-synthesis of Ni/montmorillonite nanocomposite using extract of Allium jesdianum as the nano-catalyst for electrocatalytic oxidation of methanol

In this work, synthesis of Ni nanoparticles was carried out successfully by water extract of Allium jesdianum as a biochemical reducing agent in the presence of montmorillonite clay (MMT) as a natural solid support for the first time. Then the electrochemical activity of the synthesized nanocomposite was investigated in methanol electrocatalytic oxidation. MMT with high cation exchange capacity and nano layer structure was exposed to ion exchange conditions in nickel solution. Then Ni 2+ ion exchanged form was used in this process as a source of ions and also capping agent. Water extract of Allium jesdianum used as a reducing agent due to abundant availability of phenolic and flavonoid contents. The synthesized Ni/MMT nanocomposite was characterized using UV–Vis spectroscopy (UV–Vis), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM) and Energy-dispersive X-ray spectroscopy (EDX). The surface of prepared modified electrode has been characterized using SEM to evaluate the morphology, showing uniform dispersion of Ni nanoparticles with mean diameter of 12 to 20 nm. The modified carbon paste electrode was then used in methanol electrocatalytic oxidation reaction. Methanol oxidation on the proposed modified electrode surface occurs at 0.6 V and 0.3 V in alkaline and acidic medium respectively. Also, the results showed the better performance of modified electrode toward methanol electrocatalytic oxidation in comparison with carbon paste electrode that is modified by ion exchanged MMT. Charge transfer coefficients and apparent charge transfer rate constant for the modified electrode in the absence of methanol in alkaline medium were respectively found as: α a = 0.53, α c = 0.37 and k s = 1.6 × 10 −1 s −1 . Also, the average value of catalytic rate constant for the electrocatalytic oxidation of methanol by the prepared nano-catalyst was estimated to be about 0.9 L·mol -1 ·s -1 by chronoamperometry technique. The prepared electrode was also effective for electrocatalytic oxidation of ethanol and formaldehyde in alkaline medium. Ni/MMT nanocomposite which was synthesized by green method has the suitable electrocatalytic activity to methanol electrocatalytic oxidation. • Ni/MMT nanocomposite was synthesized by green method using Allium jesdianum water extract. • Ni/MMT nanocomposite was characterized by UV–Vis, XRD, SEM, TEM and EDX techniques. • The particles size of Ni/MMT was in the range of 12–20 nm. • Ni/MMT nanocomposite has electrochemical activity for oxidation of methanol in alkaline and acidic medium.

Experimental validation of piezoelectric shunt tuning with residual mode correction: Damping of plate-like structures

The effective vibration mitigation properties of piezoceramic patches with inductive-resistive shunts are investigated experimentally. A shunt tuning method is proposed, in which a consistent correction for the influence from residual vibration modes is included by an effective modal capacitance, evaluated from measured charge and voltage amplitudes in short- and open-circuit conditions, respectively. The robustness of the proposed method is verified experimentally for both a free beam and a free plate structure with four shunted piezoceramic patch pairs. A stable and fully passive inductor is produced by winding a copper wire around a magnetic core, which requires precise inductance tuning to determine the final number of turns. It is demonstrated that the effective modal capacitance interpolates consistently between the blocked and static capacitances, commonly used for single-mode tuning of piezoelectric inductive-resistive shunts. By imposing pseudo-random vibrations, the piezoelectric current and voltage signals are measured and evaluated by their frequency response functions. Spectrum peak values determine the apparent short-circuit charge to open-circuit voltage ratio for each shunt, which directly determines the shunt components by explicit tuning formulas. Good correlation between numerical and experimental results are obtained for the free beam, while for the free plate experiment effective multi-mode shunt tuning is obtained by a modified effective electromechanical coupling coefficient.

Precise partial discharge localization in axisymmetric geometries

A predictive diagnosis of the health of insulating electrical components subjected to partial discharges seems still hard to achieve. Especially the determination of the residual life is, in many cases, very uncertain. In highly valuable components, such as cables and joints, the precise localization of partial discharge events may provide a valuable tool to estimate the progression of degeneration phenomena such as the electrical treeing. In this work we introduce a novel technique used to locate the position of moving charges that exploits the induced current on a set of properly placed electrodes. This technique has been previously developed in the framework of radiation detectors. In particular, we develop and analyze the performances of a localization method based on the measurement and analysis of induced currents and especially tailored to locate the internal discharges in axis symmetric components. The method is also capable to determine the real dipole moment produced by a discharge. This provides a measurement of the discharge strength that is more physically relevant than the commonly used apparent charge mentioned by international standards. The evaluation of the performances of the method is performed by building a proper test bed with a known defect.

Thermal properties and space charge behavior of thermally aged polypropylene/elastomer blends nanocomposite

Polypropylene (PP)-based composites including PP/thermoplastic polyolefin (TPO) elastomer blends and PP/TPO-based nanocomposite are rather promising insulation materials for HVDC cables. Aging is an inevitable issue in practical operation and needs to be investigated thoroughly. In this paper, PP/TPO blends and PP/TPO/ZnO nanocomposite were prepared and thermally aged at 130 °C for various periods (28 days at longest). The micro-morphology, thermal properties and high-temperature space charge behavior were investigated. The results show that PP and TPO still exhibited excellent compatibility without phase separation after thermally aging. The crystallinity was not influenced after thermally aging, but a new endothermic peak at about 140 °C appeared in the melting process of thermally aged composites. Space charges accumulated in the two thermally aged composites, but dissipated slowly in PP/TPO, while dissipated rapidly first and then reduced in PP/TPO/ZnO nanocomposite. The calculated apparent charge mobility and trap level distribution based on space charge dissipation show that deep traps increased in aged PP/TPO, but decreased in aged PP/TPO/ZnO nanocomposite, which may be correlated with the chemical variation of thermally aged polymer matrix. The work may give a reference on the aging research of PP-based composite material for recyclable HVDC cable insulation.

Drug-binding albumins forming stabilized nanoparticles for co-delivery of paclitaxel and resveratrol: In vitro/in vivo evaluation and binding properties investigation

Albumin has been regarded as the ideal drug carrier for delivering hydrophobic agents into cancer cells over decades. Combination therapy of paclitaxel (PTX) with resveratrol (RES) could enhance the sensitivity of multidrug resistance (MDR) cancer cell lines to PTX. In this study, novel paclitaxel/resveratrol co-loaded albumin nanoparticles (PTX/RES NPs) were developed to achieve synergistic anticancer efficacy and conquer paclitaxel resistance. The hybrid NPs had an average diameter of about 150 nm and an apparent negative surface charge of about −33 mV. PTX/RES NPs could be efficiently internalized by cells and exert synergistic combination efficacy of the two drugs, thus resulting in dramatically in vitro cytotoxicity even against MDR cancer cells. In vivo antitumor assay demonstrated that the antitumor effect of the hybrid NPs was superior to that of single drug-loaded NPs or free drug combination. Molecular docking analysis disclosed that the binding of PTX and RES to bovine serum albumin (BSA) was noncompetitive but the binding free energy of BSA/PTX dockings was significantly lower than BSA/RES dockings, which resulted in high encapsulation efficiency and sustained drug release profiles of PTX. In summary, the PTX/RES co-delivery system might be a promising strategy for combined anticancer therapy to overcome tumor drug resistance.

Charge transfer as a ubiquitous mechanism in determining the negative charge at hydrophobic interfaces

The origin of the apparent negative charge at hydrophobic–water interfaces has fueled debates in the physical chemistry community for decades. The most common interpretation given to explain this observation is that negatively charged hydroxide ions (OH–) bind strongly to the interfaces. Using first principles calculations of extended air–water and oil–water interfaces, we unravel a mechanism that does not require the presence of OH–. Small amounts of charge transfer along hydrogen bonds and asymmetries in the hydrogen bond network due to topological defects can lead to the accumulation of negative surface charge at both interfaces. For water near oil, some spillage of electron density into the oil phase is also observed. The computed surface charge densities at both interfaces is approximately -0.015 {rm{e}}/{{rm{nm}}}^{2} in agreement with electrophoretic experiments. We also show, using an energy decomposition analysis, that the electronic origin of this phenomena is rooted in a collective polarization/charge transfer effect.

Phase-space joint resolved PD characteristics of defects on insulator surface in GIS

Partial discharges (PDs) initiated by conductive particles attached to the insulator surface in gas-insulated metal-enclosed switchgear (GIS) may occur at different particle tips with varying spatial information. PD modes also differ depending on the spatial position and voltage phase. In this study, PDs were investigated as per phase-space joint resolved characteristics using two photomultiplier tubes and phase-resolved discharge images. PDs were observed to occur mainly at the negative particle tip regardless of the half-cycle. A sudden increase in apparent PD charge is attributed to the corona-creepage transition. The PD mode transition mechanism and effectiveness of the on-site dielectric test for defect detection were also determined. The results presented here may provide theoretical support for GIS defect identification and threat assessment.

Green gas for grid as an eco-friendly alternative insulation gas to SF6: From the perspective of PD initiated by metallic particles under DC

Abstract This paper dealt with characteristics of partial discharge (PD) initiated by metallic particles under DC voltage in green gas for grid (g3), which is an emerging and promising eco-friendly alternative insulation gas to SF6. Experimental setup was configured to simulate PD under DC in gas-insulated power facilities. Two types of particle, namely rectangle particle and sphere particle were used. The results indicated that the discharge inception voltages in g3 gas were 90.1-92.5% of that in SF6. In two particles, PD occurred with higher average apparent charge and discharge repetition rate in g3 compared with those in SF 6 gas. The time-resolved partial discharge presented similar characteristics in g3 and SF6 gas. The time interval between two successive discharge pulses were 0.1 ms-10 ms and 5 ms-15 ms in the rectangle particle and sphere particle, respectively. Results from this paper are expected to provide fundamental material for the development of SF 6 -free gas-insulated power apparatus.