Apparent Charge Research Articles

Influence of Water Ingress on Surface Discharges Occurring on the Silicone Gel Encapsulated Printed Circuit Boards Developed for Deep-Sea Applications

This paper discusses the influence of water ingress on the electrical discharges that arise on the surface of printed circuit boards that are developed for deep sea applications. The primary concern is the electrical discharges arising on the surface of the PCB bridging localized spots/areas between conductive traces, high voltage terminal, mounting hole options, and so on. The current literature focuses on electrical discharges arising on the surface of PCB at low-pressure environments emulating aircraft and space applications. Extending the same approach to deep-sea environments is not feasible since the pressure is very high and the temperatures are very low. In all, a meager attempt has been made to investigate the possible application of such gel-encapsulated PCBs in adverse high-pressure, salt/sea water, low-temperature, deep-sea environments. This experimental study focuses on studying the influence of deionized and sea water on electrical discharges arising on the surface, between conductive tracks of PCB. A group of PCBs with different gaps between the conductive tracks was produced and immersed in deionized and seawater for a specific duration at standard pressure. Afterward, the discharge characteristics were measured the using partial discharge (PD) test method and the respective phase-resolved PD pattern was studied and analyzed. Pertinent experiments revealed that the PD process and eventual failure manifests as a typical and substantial pattern. The apparent charge measured during the PD inception and near-by failure condition, influenced by deionized and seawater, reveals a regular trend. Naturally, a simple observation of the PD pattern might help to identify the intricacy and to initiate a preventive measure well before the complete system suffers a premature failure. Also, based on these results, making slight structural modifications on the PCB at crucial locations might help in retaining the dielectric integrity of the material.

Organic alkalinity dynamics in Irish coastal waters: Case study Rogerstown Estuary

Total alkalinity (TA) is a popularly measured carbonate system parameter and is widely used in calculations of key carbonate system descriptors such as the calcium carbonate saturation state, an important indicator of ocean acidification. Organic alkalinity (OrgAlk) is recognised as a contributor to TA in coastal waters, with this having implications on the use of TA to calculate key carbonate chemistry descriptors. As titratable charge groups of OrgAlk can act as unknown acid-base species, the inclusion of the total concentration and apparent dissociation constants of OrgAlk in carbonate calculations involving TA is required to minimise uncertainty in computed speciation. Here we present an investigation of the prevalence and properties of OrgAlk as well as the impact of OrgAlk on carbonate chemistry calculations in a transitional waterbody. Water samples were collected during low and high tide over a 5-week period in Rogerstown Estuary, Dublin Ireland. TA and OrgAlk were measured using modified Global Ocean Acidification Observing Network (GOA-ON) titration apparatus in conjunction with OrgAlkCalc, an open-source Python based computational programme. pH was measured on the total scale using meta-cresol purple (mCP) as the indicator dye. Dissolved inorganic carbon (DIC), the partial pressure of CO2 (pCO2), in situ pH on the total scale (pHT) and the saturation state of aragonite (∆ΩA) were calculated using pH and both OrgAlk adjusted TA and measured TA as the input parameters. Optical analysis of DOM was conducted to compliment OrgAlk characterisations and to further elucidate OrgAlk sources and dynamics. OrgAlk charge groups concentrations ranged from 35,198 μmol·kg−1, with the highest concentrations observed in more marine waters. Two apparent charge groups were associated with OrgAlk, with pK values of 4.38 ± 0.27 and 6.95 ± 0.43. Differences between calculated carbonate system parameters when using OrgAlk adjusted TA and non-OrgAlk adjusted TA ranged from 88 to 254 μmol·kg−1 DIC, −98–67 μatm pCO2, −0.02–0.12 pHT and 0.02–0.64 ∆ΩA. Variability in the differences in calculated carbonate systems was largely a factor of OrgAlk charge group concentration and pK. This work highlights the importance of considering OrgAlk if using TA as an input parameter in carbonate system investigations of coastal waters.

The Applicability of Very Low Frequency Diagnostic Testing in the Evaluation of Thermally Aged Stator Coil

In this study, stator coils were aged under thermal stress and changes in insulation condition with the aging cycles were evaluated using diagnostic tests. Diagnostic tests such as partial discharge measurement and tan delta and capacitance measurements were performed at 50 Hz, 1 Hz and 0.1 Hz (very low frequency). The results obtained from this study demonstrate the possibility of evaluating the signs of thermal aging in a stator insulation system with very low frequency tests. Partial discharge parameters like peak apparent charge magnitude and integrated charge per cycle along with tan delta and capacitance tip-up values were used to evaluate the stator insulation condition. Diagnostic test results showed an identical trend with aging cycles at all the chosen test frequency, i.e. 50 Hz, 1 Hz and 0.1 Hz, which indicates that testing at 0.1 Hz is suitable for insulation condition evaluation. Further, the tip-up values have shown distinct variations, especially at 0.1 Hz indicating significant thermal degradation in a stator coil.

First-principles study on adsorption of oxygen on H-terminated armchair silicene nanoribbon

This work systematically studies the electronic and optical properties of H-terminated armchair silicene nanoribbon (HASiNR) for oxygen (O2) adsorption using first-principles calculations. The results show that the most stable site for O2 adsorption is the edge of the ribbon, which possesses relatively low adsorption energy of −2.46[Formula: see text]eV, indicating good stability. Particularly, the adsorption energy decreases gradually with the increase of the oxygen concentration. It was also found that the direct bandgap of HASiNR can be effectively tuned by changing the adsorption concentration of O2 gas. Additionally, the analysis of the density of states shows that the adsorption of O2 on HASiNR is chemisorption due to the apparent charge transfer from the ribbon to O2 gas. Besides, the work function, absorption coefficient and refractive index of the HASiNR are sensitive to O2 gas adsorption. Therefore, our studies prove that oxygen gas adsorption allows the HASiNR to modulate its electronic and optical properties.

Investigation of Partial Discharges within Power Oil Transformers by Acoustic Emission

This paper presents the authors’ multi-channel measurement systems designed and built to conduct research on partial discharge phenomena using the acoustic emission method. The systems provide real-time monitoring, recording of signals and analysis of recorded signals. The analysis is carried out in time, frequency, time-frequency and discrimination threshold domains. In particular, a descriptor with the ADC acronym is defined, which ranks the signals according to the so-called degree of advancement. Studies have been carried out, showing that for a single partial discharge source, when tested in parallel, using the electrical and acoustic emission methods, the ranking of the signals using this descriptor is identical to the ranking according to the value of the apparent charge introduced by sources. This paper presents the authors’ patented method of partial discharge location and identification in power oil transformers. The results of tests of power oil transformer at the test station, conducted in parallel with the electric method and the authors’ method, and the results of tests in three selected transformers carried out during ongoing in-situ operation using the authors’ method are presented. Based on these results, the authors make diagnoses of the condition of the insulation systems in the tested transformers. The inspections of these transformers confirm the diagnoses.

Examination of the Partial Discharge Behaviour Within a Spherical Cavity in Insulation Paper of Transformer

This paper investigates the behaviour of partial discharge (PD) in transformer insulation paper based on the Finite Element Method (FEM). The three-dimensional (3D) FEM model consists of conductor and insulation paper, representing part of a transformer’s high voltage winding. The conductor’s width, height, and length used in this study were 2.4 mm, 11.5 mm, and 16 mm. An insulation paper thickness of 1 mm was modelled around the conductor. An internal cavity with a diameter of 0.5 mm cavity was introduced within the insulation paper. This study introduced two locations of the spherical cavities at the centre and left corner of the insulation paper: Location 1 (L1) and Location 2 (L2). An AC voltage of 33 kV, 50 Hz, was applied to the conductor while the bottom of the insulation paper was grounded. The model was used to study the electric field distribution within the insulation paper and its effect on PD current and charge magnitude. The influence of cavity location on the charge magnitude was also examined. It is found that the electric field distribution is influenced by the conductor configuration as well as the location of the cavity. The electric field in the cavity is the highest at L1 compared to L2. The first PD occurs faster for the cavity with a high electric field. Due to the PD occurrence at the same inception field, the real PD current and charge magnitude is similar at different locations. The apparent PD current and charge magnitude induced at the ground electrode is slightly higher at L1 than at L2.

Energetics and Ionic–Electronic and Geometric Variabilities of Hydroxylammonium-Based Salts

In the present work, we study the formation energy of energetic ionic salts (EISs), as well as the volumetric and electric variabilities of ions involved in EISs, by employing 25 hydroxylammonium cations (HA+) in 22 salts as examples. We identify the viability of a dispersion-corrected density functional theory method, PBE-D3(BJ), to describe the lattice parameters, with a mean relative deviation of 1.26% and a maximal relative deviation of 2.5%. Thereby, the ionization energy, formation energy, and lattice energy are predicted. The variability of volume (VHA+) is confirmed in different HA+-based salts, as well as between two HA+ of the same lattice with Z′ > 1. The largest difference of VHA+ among the 25 HA+ reaches ∼9%. This variability of VHA+ is originated from the difference in crystal field effects, or intermolecular interactions. That is, the stronger intermolecular hydrogen bond tends to exhibit a stronger drag and pull effect on HA+ and leads to a larger VHA+. In comparison, it exhibits a more significant variability of electricity, as the maximal total Mulliken charge of HA+ (QHA+) is >1.67 times the minimal one. Moreover, the observed QHA+ varying from 0.164 to 0.438 e is much less than the apparent charge of 1 e, suggesting the highly insufficient charge of HA+ in EISs. This means that the ionic bonding does not necessarily govern the intermolecular interactions in common EISs. Besides, an electrostatic potential (ESP) minimum-oxygen balance (OB) correlation is found in the anions countering HA+, as the more negative OB tends to cause a more negative ESP minimum. All of these findings are expected to richen the insight into the nature of EISs as a special group of EMs.

NIR-II Perylene Monoimide-Based Photothermal Agent with Strengthened Donor-Acceptor Conjugation for Deep Orthotopic Glioblastoma Phototheranostics.

Extensive efforts have been devoted to the design of organic photothermal agents (PTAs) that absorb in the second near-infrared (NIR-II) bio-window, which can provide deeper tissue penetration that is significant for phototheranostics of lethal brain tumors. Herein, the first example of NIR-II-absorbing small organic molecule (N1) derived from perylene monoamide (PMI) and its bio-application after nano-encapsulation of N1 to function as a nano-agent for phototheranostics of deep orthotopic glioblastoma (GBM) is reported. By adopting a dual modification strategy of introducing a donor-acceptor unit and extending π-conjugation, the obtained N1 can absorb in 1000-1400nm region and exhibit high photothermal conversation due to the apparent intramolecular charge transfer (ICT). A choline analogue, 2-methacryloyloxyethyl phosphorylcholine, capable of interacting specifically with receptors on the surface of the blood-brain barrier (BBB), is used to fabricate the amphiphilic copolymer for the nano-encapsulation of N1. The obtained nanoparticles demonstrate efficient BBB-crossing due to the receptor-mediated transcytosis as well as the small nanoparticle size of approximately 26nm. The prepared nanoparticles exhibit excellent photoacoustic imaging and significant growth inhibition of deep orthotopic GBM. The current study demonstrates the enormous potential of PMI-based NIR-II PTAs and provides an efficient phototheranostic paradigm for deep orthotopic GBM.

Structures and electron states of (4,4)CNT-graphene hybrid system through DFTB investigation

Self-consistent density functional tight binding (SCC-DFTB) algorithm is performed to investigate the connection of a (4,4) carbon nanotube and graphene having topological defects. The examined seamless coupling CNT-graphene configurations are characterized by packing geometries, bond length, bonding energy, chemical potential, HOMO-LUMO energy gap, Mulliken populations on atoms, charge density differences, and molecular orbitals on HOMO and LUMO energy levels. Simulation results show that coupling models among the bottom atoms of the tube and the graphene atoms around the defect as well as defect patterns greatly affect configurations and electrical structures of coupled systems. Graphene having some defective patterns improves high possibility for strongly bonding the tubes. Apparent charge transfer occurs among the atoms in the tubes and graphene, and differences of transferred charges can be also found in the coupling modes. In addition, for the atoms at the connecting knots, their s and p orbitals present significant differences in the abilities of losing and gaining charge. Charge density differences as well as molecular orbitals on the HOMO and LUMO energy levels indicate the bonding between the tube and graphene as well as electron’s distribution in space.

How does sequence influence charge regulation of disordered proteins?

Charge regulation, defined as the regulation of charge states of ionizable residues through the uptake or release of protons, can influence the conformational ensembles and distributions of charge states that are accessible to intrinsically disordered proteins. These influences are exerted through sequence- and conformational-context dependent pKa values. We recently developed and deployed a q-canonical ensemble that allows for the linked analyses of separate measurements, of charge and conformation as a function of pH. When combined with atomistic, q-canonical Monte Carlo simulations based on the ABSINTH implicit solvation model, we were able to uncover the pH-dependent interplay of charge state and conformational heterogeneity. However, the combinatorial increase in the number of charge states to consider has remained a persistent challenge. Here, we introduce a breakthrough that allows us to predict the extent of charge regulation to be expected for IDPs arbitrary numbers of ionizable residues. The algorithm leverages prior information regarding the effects of local sequence contexts on charge regulation. Longer sequences with arbitrary numbers of ionizable residues are built up using a chain-growth Monte Carlo procedure, each step building on extant information for peptide fragments. We have deployed the new methodology in a high-throughput investigation of sequences drawn from the IDRome, which is the sub-proteome of intrinsically disordered regions (IDRs). We find that the apparent charge, obtained by assuming model compound pKa values, is rarely the same as the real charge that one predicts based on an accounting of charge regulation effects. This work paves the way to understanding the sequence features that result in charge regulation effects, and their importance to biomolecular processes.

Wide-Frequency Finite Element Based Model for Partial Discharge Pulse Propagation in Stator Winding of Generators

Condition monitoring of generators is one of the main keys to reduce outages and keep the system stable during disturbances. The partial discharge (PD) test is among the most reliable tools for diagnosing generator insulation defects in the early stages. However, various studies show that it is impossible to correlate the measurement results with the apparent charge of the occurred PD in the generator winding. Therefore, no specific threshold can be set for the harmful PD activities in the generator stator windings. Modeling the stator winding for PD pulse propagation helps to interpret the PD test results properly. In this regard, this paper presents a finite element method (FEM)-based model with acceptable accuracy in a wide frequency range. Practical laboratory tests performed on stator bars are used to validate the model. The results and findings of the proposed model are fully matched with practical tests. Also, the proposed model covers the features obtained for PD pulse propagation in previous experimental studies. The proposed model can be employed to investigate the PD pulse propagations at both low and high frequencies, which is an important tool to analyze the results of a PD test correctly.

Partial Discharge Activity in Rotating Machine Type II Insulation Systems as a Function of Temperature and AC Supply Frequency

The main purpose of this study was to investigate if the application of very low frequencies for PD measurements in type II generator bar insulation is relevant when compared to applying power line frequency at different test temperatures. Laboratory experiments were performed on two stator bar types rated 6.4 kV and 7.4 kV, labeled as Group A and Group B. The stator bars were taken from service and spare part storage (pristine). The samples were preconditioned at the maximum test voltage of 1.5 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> before sweeping the AC high voltage supply from 0.1 Hz and 50 Hz. The test temperature was varied between 20 °C and 155 °C. Investigation of cross sections of the generator bars was done to qualitatively describe the voids. The main results showed that the partial discharge inception voltage (PDIV) for Group A was temperature independent at 50 Hz and decreased by 40 % at 0.1 Hz with increased temperatures, whereas the PDIV for Group B was frequency independent and increased by 70 % with temperature. Similarly, the PD magnitude and total apparent charge decreased by 90 % for Group B with increased temperature, whereas it more than doubled for Group A with temperature. The tested bars from Group A showed significantly larger voids, located close to the copper conductors, compared to Group B, where voids were mainly located within the mainwall insulation. Results indicated that tests performed at 0.1 Hz cannot directly represent results obtained at 50 Hz. Using a wide range of frequencies and test temperatures broadens the understanding of the behavior of the voids inside the mainwall insulation.

Molybdenum Oxycarbide Supported Rh-Clusters with Modulated Interstitial C-O Microenvironments for Promoting Hydrogen Evolution.

Tuning the microenvironment and electronic structure of support materials is essential strategy to induce electron transfer between supports and active centers, which is of great importance in optimizing catalytic kinetics. In this study, the molybdenum oxycarbide supported Rh-clusters are synthesized with modulated interstitial C-O microenvironments (Rh/MoOC) for promoting efficient hydrogen evolution in water splitting. Both electronic structure characterizations and theoretical calculations uncover the apparent charge transfer from Rh to MoOC, which optimizes the d-band center, H2 O adsorption energy, and hydrogen binding energy, thus enhancing its intrinsic hydrogen-evolving activities. In addition, the co-occurrence of interstitial C and O atoms in MoOC supports plays a vital role in the dissociation reaction of water during the hydrogen-evolving process. Impressively, the Rh/MoOC exhibits excellent hydrogen-evolving activities in terms of exceptional turnover frequency values (11.4 and 39.41 H2 s-1 in alkaline and acidic media) and mass activities (21.3 and 73.87 A mg-1 in alkaline and acidic media) at an overpotential of 100mV, which is more than 40 times higher than that of the benchmark commercial Rh/C catalysts. This work sheds new light on designing water dissociation materials that surpasses most of the reported catalysts.

High Q‐factor anapole mode based on localized spoof surface plasmon polaritons

AbstractRecently, localized spoof surface plasmon polaritons (LSSPPs) have emerged as a new research frontier due to their unique properties and potential applications in integrated circuits. The toroidal dipole is a localized electromagnetic response different from electric and magnetic dipoles. Anapole is the nonradiating source produced by the interference between identical radiation patterns of toroidal and electric dipoles in the far field. This paper proposes a novel high Q‐factor compact planar resonator consisting of split‐ring resonators to support the LSSPPs anapole at microwave frequency, which shows an apparent nonradiating charge–current configuration. In simulation and measurement, we observe the nonradiating property of the anapole mode. Further, we demonstrate that the LSSPPs anapole resonance has the tunable property, which is very sensitive to structural changes. These might lead to potential applications in the design of plasmonic deformation sensors, cloaking, and absorbers.

An Error Correction Method for PD Apparent Charge Measurement in Power Transformers

When partial discharge (PD) measurement is performed on power transformers under the IEC60270 standard, a large error will occur in apparent charge estimation due to the winding distributive longitudinal capacitances and unknown location of the PD source. A frequency-spectrum-based PD localization and an apparent charge error correction method are proposed based on winding RLC ladder network gray-box modeling with FRA results and intelligent algorithm. An experiment on a 220 kV inhomogeneous model winding is carried out and the proposed method is applied. The results show that the maximum error of apparent charge has reduced from 37.7 dB to less than 3 dB which shows an error decrease of 70%, verifying the feasibility of this method on real windings. The proposed method requires only single-end PD measurement and follows strictly the IEC60270 standard, which is hopefully to be extended to more complex transformer windings in future research.

Long-Term Partial Discharge Behavior of Protrusion Defect in HVDC GIS

This article investigates the partial discharge (PD) behavior of protrusion defects in real-size high-voltage direct current gas insulated switchgear (HVDC GIS) for SF6 and SF6 alternative gases including fluoronitrile–CO2 mixture (10%) and fluoroketone–dry air mixture (6.6%). The evolution of PD apparent charge and PD repetition rate for all investigated gases is presented and discussed. The measurement results indicate that PD behavior changes as a function of time. The PD apparent charge increases and the PD repetition rate decreases with the increase of voltage application time. This evolution can be related to the change in protrusion tip radius due to electrochemical etching: radius of the protrusion’s tip being enlarged. In addition, the pulse sequence analysis (PSA) plots of the PDs caused by this defect are presented. It is observed that the PSA plots change over time. Therefore, for the development of a robust PD monitoring and defect-recognition tool, as well as for the assessment of risks in the operation of HVDC GIS, it is crucial to take these changes into account.

DFTB investigations of structures and electron states for a decahedron Ti7 cluster on graphene on electrical level

We performed self-consistent charge density functional tight binding simulations to investigate the interactions between a decahedron Ti 7 cluster and graphene. Different adsorption behaviors of the cluster on perfect and defective graphene are characterized by adsorption energy, chemical potential, HOMO-LUMO energy gap, charge density differences, Mulliken populations on atoms, and molecular orbitals on HOMO and LUMO energy levels. Simulation results show that relatively contacting orientations of the cluster and graphene as well as adsorption positions greatly affect adsorption's packing configurations. The defective graphene improves high possibility for strongly binding the metal cluster. Apparent charge transfer occurs from the cluster to graphene for the adsorption on defective graphene. The molecular orbitals on the HOMO and LUMO energy levels present differences for different adsorption configurations. • A decahedron Ti 7 cluster and graphene • Different adsorption behaviors of the cluster on perfect and defective graphene • Adsorption energy, chemical potential, HOMO-LUMO energy gap • Charge density differences, Mulliken populations on atoms, and molecular orbitals on HOMO and LUMO energy levels

Decrypting the Influence of Axial Coordination on the Electronic Microenvironment of Co-N 5 Site for Enhanced Electrocatalytic Reaction

Decrypting the Influence of Axial Coordination on the Electronic Microenvironment of Co-N ₅ Site for Enhanced Electrocatalytic Reaction

Investigation of Surface Adsorption and Electrode Passivation during Electrochemical Oxidation of Redox-Active Organics

Redox-active organic molecules (ROMs) have gained interest as electroactive materials for redox flow batteries (RFBs). Electrochemical properties of ROMs, i.e., their solubility and redox potential, can be tuned through molecular engineering of the base molecule. Previously, we reported values of the apparent anodic charge transfer coefficient α (values approaching 1) associated with the electrochemical oxidation of a model ROM, 4-hydroxy-TEMPO.1 Also, we have proposed an adsorption-mediated mechanism to explain this unusual value of α, and have presented evidence to support the occurrence of adsorbed intermediates. Here, we extend this investigation to gain further insights using techniques of slow-scan voltammetry and electrode cycling, and apply them to other ROMs. We will discuss results of spectroscopic and micro-gravimetric studies, which provide further insights into the physicochemical properties of the adsorbed surface-passivating films. Ramifications of these to implementation of ROMs in flow batteries will be discussed too.[1] N. A. Shaheen, M. Ijjada, M. B. Vukmirovic, R. Akolkar. J. Electrochem. Soc., 167 (2020) 143505. Acknowledgements: Investigation of the model ROM was supported by Breakthrough Electrolytes for Energy Storage (BEES)—an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award #DE-SC0019409. Work completed at Argonne was supported by the Joint Center for Energy Storage Research (JCESR), a U.S. Department of Energy, Energy Innovation Hub, and by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education (ORISE) for the DOE. ORISE is managed by ORAU under contract #DE‐SC0014664. All opinions expressed in this paper are the author’s and do not necessarily reflect the policies and views of DOE, ORAU, or ORISE.

Influence of Voltage Harmonics on Partial Discharge Diagnostics in Electric Motors Fed by Variable-Frequency Drives

Typically, in partial discharges (PD) diagnostics tests carried out in a laboratory, harmonic content in a voltage waveform is ignored. However, during the operation of variable-frequency drives (VFD)-fed electric motors, the distorted voltage waveform is produced due to the addition of harmonics components in the sinusoidal voltage waveform. The distortion level increases when the VFD is operated at a lower speed ratio. The additional spectral components in the applied voltage waveform can have a significant impact on the PD behavior in the insulation of the electric motor. Therefore, during online PD monitoring, overlooking the harmonic regime in the applied voltage may lead to a false interpretation of PD data. This article investigates the influence of voltage harmonics distortion produced during the variable-speed operation of VFD on PD characteristics. For this purpose, online PD measurements have been carried out by performing a series of experiments on eight VFD-fed motors under variable operating conditions. The PD severity at different harmonic compositions is experimentally investigated by determining various PD characteristic parameters including PD inception voltage, accumulated apparent charge, average discharge current, discharge power, and quadratic rate. Also, two terms Gaussian models have been mathematically developed using 288 data samples to quantify the variations in PD characteristic parameters against distortion parameters. The article proposes a framework for properly evaluating harmonics impact in PD for electric motors and correctly estimating stator insulation degradation.