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Developing a fluidic platform that combines high-throughput with reconfigurability is essential for a wide range of cutting-edge applications, but achieving both capabilities simultaneously remains a significant challenge. Herein, we propose a novel and unique method for droplet manipulation via drawing surface charge graphics on electrode-free papers in a contactless way. We find that opposite charge graphics can be written and retained on the surface layer of porous insulating paper by a controlled charge depositing method. The retained charge graphics result in high-resolution patterning of electrostatic potential wells (EPWs) on the hydrophobic porous surface, allowing for digital and high-throughput droplet handling. Since the charge graphics can be written/projected dynamically and simultaneously in large areas, allowing for on-demand and real-time reconfiguration of EPWs, we are able to develop a charge-graphic fluidic platform with both high reconfigurability and high throughput. The advantages and application potential of the platform have been demonstrated in chemical detection and dynamically controllable fluidic networks. [ABSTRACT FROM AUTHOR]

In this work, we describe the synthesis of novel electrically and magnetically dual-driven Janus particles for a handwriting-enabled twisting ball display via the microfluidic technique. One hemisphere of the Janus particles contains a charge control agent, which allows the display color to be controlled by applying a voltage and superparamagnetic nanoparticles, allows handwriting by applying a magnetic field to the display. We fabricated a twisting ball display utilizing these Janus particles and tested the electric color control and handwriting using a magnet. As a result, the display was capable of permitting handwriting with a small magnet in addition to conventional color control using an applied voltage (80 V). Handwriting performance was improved by increasing the concentration of superparamagnetic nanoparticles and was determined to be possible even when 80V was applied across the electrodes for 4 wt.% superparamagnetic nanoparticles in one hemisphere. This improvement was impossible when the concentration was reduced to 2 wt.% superparamagnetic nanoparticles. The technology presented in our work can be applied to low-cost, lightweight, highly visible, and energy-saving electronic message boards and large whiteboards because the large-size display can be fabricated easily due to its simple structure. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of the underlying mechanism behind the interface charge barrier between oil and oil immersed paper. Two types of oils and two types of cellulose papers are selected in the study. The interface charges of the samples are measured by the pulsed electro-acoustic (PEA) method and the zeta potentials of different oil-paper combinations are also measured. The results show that the amount of interface charge changes with the type of oils and papers, and is much larger than the Maxwell-Wagner-Sillars (MWS) polarization charge. The difference in the amount of interface charges cannot be attributed to the difference in the conductivity and permittivity of the materials. It is suggested that the barrier for charge transport across the interface, which is formed due to the electric double layer, should be taken into consideration to explain the interface charge behavior in oil-paper insulation. [ABSTRACT FROM AUTHOR]

Breakdown strength is an important electrical property of insulating paper. Oil-impregnated paper of various aging states was prepared. Its breakdown voltage was then measured at pulsating direct current (DC) voltage with various ripple factors, and alternating current (AC) and DC voltage for comparison, respectively. The AC breakdown voltage is the smallest, and pulsating DC (r = 1/5) breakdown voltage is the greatest before the paper reaches its end of life. A dielectric model was adopted to investigate the difference in magnitude of breakdown voltage at different voltage waveforms. Meanwhile, it was found that breakdown voltage fluctuated and even increased occasionally during the thermal aging process, and a somewhat opposite changing tendency versus aging time was observed for breakdown voltage at DC voltage and pulsating DC voltage with small ripple factors (r = 1/5 and 1/3), compared with AC voltage. The degree of polymerization (DP) and moisture content of the paper were measured, and the characteristics of the pores and cracks of the paper were obtained to investigate the possible influencing factors of breakdown voltage at different aging states. The results showed that the moisture content, oil absorption ability associated with pores and cracks of paper, and the damage to paper structure all contributed to the variation of the breakdown voltage versus aging time, while the importance of their influence differed as the aging state of paper varied. [ABSTRACT FROM AUTHOR]

The in situ and direct extraction, desorption and ionization of in-gel intact proteins after electrophoresis has been achieved by carbon nanotubes (CNTs)-modified paper spray mass spectrometry at ambient conditions. Characteristics of CNTs (including larger surface area, smaller pore diameter and enhanced conductivity) were endowed to the porous filter paper substrate by uniformly dispersing the CNTs on the filter paper. Upon applying electric potential to the CNTs-modified paper, the in-gel proteins were extracted from the gel and subsequently migrated to the tip of the filter paper by electrophoresis-like behavior for paper spray ionization, which was monitored by extracted ion chronograms. The characterizations of modified filter papers and CNTs nanoparticles further confirmed the role of CNTs in in-gel protein extraction, protein migration as well as spray ionization at the paper tip. Under optimized conditions, a mixture of cytochrome c, lysozyme and myoglobin was successfully separated by native electrophoresis and subsequently analysed by the present method, showing a limit of detection of 10 ng per gel band. The present strategy offers a new pathway for the direct detection of in-gel intact proteins at ambient conditions without any pre-treatment (e.g. digestion, chemical extraction and desalting), which exhibits potential applications in top-down proteomics. [ABSTRACT FROM AUTHOR]

Plastic has significant negative consequences for the environment and human health, demanding greener alternatives. Lignocellulose is a sustainable biomass material, and its paper has been considered as a potential material to replace plastics. Micro-nano lignocellulose, derived from natural plants, possesses a small size and abundant hydrogen bonding capacity. However, there is no clear explanation for the interactions between lignin and micro-nano cellulose, and little understanding of how the interaction can affect the papers' structure and optical properties. Electrostatic potential calculation is a reliable tool to explain non-covalent interactions, and can explore the binding between lignin and micro-nano cellulose. In this paper, kenaf – a non-wood fiber raw material – was employed to prepare micro-nano lignocellulose. The resulting slurry facilitated the production of transparent paper via a simple casting method. The prepared transparent micro-nano paper exhibited high transparency (~90 %), UVA resistance (~80 %), and hydrophobicity (~114°). More importantly, the electrostatic potential calculation demonstrates the inherent relationship between structure and performance, providing practical knowledge for constructing film materials. [Display omitted] [ABSTRACT FROM AUTHOR]

In accordance with environmental sustainability and in order to optimize the recycling process of prints from indirect electrophotography with liquid toner the results of investigating the effects of changes in printing conditions on the characteristics of recycled fibres is presented. Changing of printing machine conditions, respecting of voltage variations, comprises of the reverse rollers and intermediate cylinder. Based on the results it can be concluded that the change in the voltage of the reverse rollers more affect the recycling efficiency with respect to the voltage change of the intermediate cylinder. Brightness gain is higher when the print for recycling is made on uncoated paper compared to coated, and dependent on the voltage changes. Effective residual ink concentration decreases far more on handsheets obtained from recycled samples on uncoated paper in relation to both sides coated paper. Increasing the positive voltage of intermediate cylinder and increasing the negative charge of reverse rollers increases the 3 D gamut CIE L*a*b* color cubic units. Guidelines for the size of the voltage in order to obtain optimal print reproduction are provided. The further research will include the development in area of clean technologies, advanced materials, closed loop systems; therefore the significant terms in the area of environmental sustainability. [ABSTRACT FROM AUTHOR]

Oil-paper insulation of higher voltage winding and traction winding in on-board traction transformers frequently withstand large AC fluctuation voltages mainly combined with AC and inter-harmonic components. This paper presents the characteristics of partial discharge (PD) of oil-paper insulation under superimposed inter-harmonic AC voltages. The experimental results show that the addition of the inter-harmonic to the fundamental sinusoidal component results in variation of peak voltage and dv/dt along the phase. This superimposed inter-harmonic AC voltages has a significant impact on PD including partial discharge inception voltage (PDIV), breakdown voltage, PD repetition rate, and phase resolved partial discharge (PRPD). In addition, a dynamic characterization method of PD statistical parameters is proposed to determine the developing trend. The critical values and inflection points of PD are obtained. Besides, the theoretical mechanism is expounded to better interpret and understand the influence of inter-harmonic component on PD properties. These methods will provide the dynamic datasets and more information for insulation condition assessment of on-board traction transformer. [ABSTRACT FROM AUTHOR]

E‐paper is an important candidate for ultra‐low‐power display of IoT environments. However, the switching speed and driving voltage are factors hindering E‐paper's prevailing. Here, we demonstrated using LC and viscosity modifier to simultaneously double the switching speed and cut down the driving voltage to half; meanwhile, the e‐paper still sustained the same contrast and bistability. This concept may pave a new route for future E‐ink research and production. [ABSTRACT FROM AUTHOR]

In this paper, the temporal space charge dynamics under both temperature and voltage polarity reversal of an epoxy resin impregnated crepe paper are characterized by pulsed electroacoustic method. It is found that the space charge injection and the interfacial traps located between the epoxy and paper plays an important role in determining the space charge dynamics. The results reveal that below 353 K, the calculated interfacial charge density is consistent with the Maxwell-Wagner (MW) model, while above 353 K, it is smaller than the measured value. The time constant during charging is much smaller than that predicted by the MW model and the space charge injection showed polarity effect, which leads to the interfacial charge densities under polarity poling voltage not being equal. It is proposed that the interfacial traps and space charge injection should be responsible for the observed space charge dynamics. [ABSTRACT FROM AUTHOR]

A piezoelectric based touch sensitive device has been successfully fabricated by screen printing silver (Ag) and polyvinylidene fluoride (PVDF) inks as conductive and piezoelectric materials, respectively, on paper substrate. X-ray diffraction (XRD) analysis was performed to verify the formation of β-phase crystals in the PVDF layer during the curing process. Voltages, as high as 0.22 V, were observed for human finger touch tests and a sensitivity of 0.3 V/N was obtained when varying forces ranging from 0.2 N to 1.4 N, in steps of 0.2 N, were applied on the printed device. The piezoelectric-voltage analysis demonstrated that the printed device can be used for both touch and force sensing applications. [ABSTRACT FROM AUTHOR]

This paper presents a novel coupling between a four-phase electroextraction (EE) system and paper spray mass spectrometry (PS-MS) for the extraction, pre-concentration, and direct analysis of target compounds in different samples. The approach, EE-PS-MS, is based on the sorption of analytes directly on the tip of a triangular-shaped chromatographic paper, with subsequent prompt analysis by PS-MS. Thus, no off-line extraction step is required before the PS analysis, improving the protocol efficiency and reducing the analysis time. In addition to functioning as a porous material to absorb the target compounds, the chromatographic paper also served as the support for one of the aqueous phases of the optimized four-phase electroextraction system. Extraction conditions, such as the composition of the donor and organic phases, applied electric potential, and extraction time, were optimized. Three different applications, involving biofluid, food, and water quality analysis, were evaluated as a proof-of-concept. These applications involved the determination of (i) cocaine and lidocaine in saliva, (ii) malachite green in tap water, and (iii) bisphenol A (BPA) in red wine. When compared with direct PS-MS, the novel EE-PS-MS protocol improved the sensitivities by factors ranging from 14 to 110, depending on the analyte and the sample. The electroextraction procedures were performed on a laboratory-built 66-well plate, which offered the functionality of simultaneous sample handling and, most importantly, improved analytical throughput. [ABSTRACT FROM AUTHOR]

Beeswax, a natural nontoxic biological material, is used as the gate dielectric of flexible low-voltage indium–zinc-oxide (IZO)-based homojunction thin-film transistors (TFTs) on paper substrates. A high specific capacitance of 5 \mu \textF /cm2 is measured at 1 Hz in the beeswax film due to the electric-double-layer effect. The current ON/OFF ratio, subthreshold swing, and field-effect mobility of the IZO-based TFTs on paper substrate are estimated to be 7.6\times 10 ^6 , 86 mV/decade, and 14.6 cm2 /Vs, respectively. In addition, our results demonstrate that the flexible oxide-based TFTs on paper substrate show a good stability after 3000 times bending and 30 days aging testing. Such flexible low-voltage oxide-based homojunction TFTs have potential applications in portable paper electronics. [ABSTRACT FROM PUBLISHER]

Transformer oil, insulating paper, high voltage direct current (HVDC) bushings and on-load tap changer (OLTC) are essential parts of converter transformers. When the power flow of the HVDC system is reversed or a sudden outrage occurs, the charge field will deform the dielectric internal electric field, thus easily leading to the occurrence of discharge or insulation damage. In this case, it is necessary to carry out the characterization of the oil?paper interface to avoid these consequences. This paper analyses the interface charge accumulation and dissipation characteristics of an oil?paper insulation system under DC and polarity reversal voltages. In this paper, induced electrification was used to charge the composite oil?paper insulation. The amplitude of DC and polarity reversal voltages applied in this paper was 4 kV, and paper with thicknesses of 0.08 and 0.13 mm was used. This research offers a theoretical exploration to optimize the transformer oil? paper insulation structure and prevent damage to its insulation systems. From the research on different layers and thicknesses of paper, it can be concluded that the decay is fast in the initial period and then becomes slower with the lapse of time until finally the decay curve tends to become flat. With an increase in the number of the paper layers, the interface charge density decreases. So in real life multilayer paper is used to avoid failures owing to its structural weakness. Regarding the DC polarity reversal effect, increasing the thickness of the paper is equivalent to adding paper layers. The dissipation rate of the positive interface charge is quicker than that of the negative one. In the polarity reversal test, the dissipation rate becomes smaller as the reversal time gets longer. [ABSTRACT FROM AUTHOR]

Electro thermal papers have been widely applied in people's daily life. Compared to traditional metal alloy resistance heaters, three dimensional graphene/carbonized-PAN composite freestanding paper with lightweight, good flexibility and excellent electrothermal performance is presented. It retains intrinsic properties of graphene sheets in the bulk state, and exhibits fast electrothermal response under low operation voltage with robust mechanical property. The fastest specific heating rate could be up to 213 °C s−1 V−1, and the highest T s is 235 °C at low driving voltage just of 1.75 V, which far surpasses those of previous carbon-based film heaters, commercial nichrome wire, and Kanthal wire. These outstanding properties together with the advantage of facile and large-scale fabrication, make the composite paper with great potential applications in flexible electronics. Image 1 [ABSTRACT FROM AUTHOR]

This paper presents an experimental work investigating the failure data of oil-impregnated paper under pulsating DC voltage. The failure data of the oil-impregnated paper specimens were obtained through constant voltage stress tests; the Weibull distribution was used to estimate the statistical distribution of failure data. The exponential function (EF) and the inverse power function (IPF) were used to modify the Weibull distribution of failure data, so as to obtain two dual-variable Weibull failure distributions (WFDs), which were used to analyze failure data of oil-paper specimens obtained under pulsating DC and individual DC and AC voltages. Their adequacies were evaluated by using failure data obtained through the constant stress tests under various voltages. Both EF-modified and IPF-modified WFDs show more adequacy for failure data of oil-paper insulation under DC and pulsating DC voltages than AC voltages. The EF-modified WFD was more adequate than IPF-modified WFD in estimating the statistical distribution of failure data. [ABSTRACT FROM PUBLISHER]

The oil-paper insulation of valve-side windings in a high voltage direct current (HVDC) converter transformer is subjected to both complicated voltage and severe thermal stresses. Partial discharge (PD) occurring in oil-paper bounded cavities is influenced by voltage stress type as well as temperature. This paper presents PD behaviors in an oil-paper bounded gas cavity under pulsating DC voltages. The voltage across the gas cavity and PD inception voltages at different test conditions are analyzed. Influences of temperature on statistical PD distributions and parameters are also presented. A numerical model is used to interpret PD behaviors under pulsating DC voltages and various temperatures. Experimental results and theoretical statements show that the temperature exhibits a great influence on the behaviors of cavity discharge under pulsating DC voltages. Volume resistivity, gas pressure, charge decay time constant, and electron generation rate are the primary parameters influencing PD behaviors at different temperatures. [ABSTRACT FROM PUBLISHER]

The paper presents a technique for determining the time index of growth of the slope of reverse voltage for double insulated cables, based on the body of the theory of series. It is proved that in the vicinity of the extremum point (maximum) the function of the reverse voltage is approximated by polynomials of the nth power. It is proposed to use second-degree polynomials for practical calculations. The method for calculating relevant indicators is illustrated using real data. Analysis of deviations made it possible to conclude that the calculation method proposed in the paper is far more accurate. In the final part of the study, it was concluded that there is a promising outlook for further development of methodological guidelines for determining complex indices of the remaining life of the cable, including but not limited to the use of various mathematical methods. [ABSTRACT FROM AUTHOR]

Surface light-emitting transparent nanocellulose papers operating by alternating current voltages were demonstrated, where phosphors were embedded in the paper and silver nanowire electrodes were formed on both side of the paper. Silver nanowire electrodes were first coated on membrane filter with vacuum filtration using wet wiper tissues and then successfully transferred to the paper surface by a mechanical compression. The power consumption of a light-emitting paper was small in less than 0.36 W/cm². We could control the luminescent color and intensity from light-emitting papers by adjusting electrical frequency and the applied voltage level. White light emission was also demonstrated by using phosphors with a broad luminescence spectrum. The results develop into a versatile approach for commercializing the nanofibrillated cellulose and pave the way towards the realization of commercially viable, flexible and transparent light-emitting papers. [ABSTRACT FROM AUTHOR]

The oil-impregnated paper, as a vital part in the oil-paper insulation system, serves as the main insulation medium in converter transformer suffering various electric fields. However, the accumulated surface charge on the paper would accelerate the degradation of insulation system and may lead to surface flashover. Direct-fluorination is a method to change the chemical components of polymer matrix thus could affect the surface property of the dielectric material without the alternation of bulk property. This paper presents a method to modify the surface structure of the paper applied in transformers. The paper used in the experiment was treated using the F2/N2 mixture with a volume fraction of 10% for the F2 gas at a pressure of 0.05 MPa in a reaction vessel for 2, 5, 10 and 15 min, respectively. The chemical elements, functional group and physical morphology of the paper before and after modification were measured with energy dispersive X-ray spectroscopy (EDAX), attenuated total reflection infrared (ATR-IR) and scanning electron micrographs (SEM), respectively. Surface and volume resistivity of the fluorinated paper were measured. Furthermore, the surface charge property of the oil-impregnated paper was measured under various positive and negative voltages. Obtained results showed that the fluorination had an obvious influence on the chemical property and surface structure of the paper leading to the reduction of surface and volume resistivity. The treatment was shown to reduce the initial potential and cause acceleration in charge decay process. The trap distribution of the paper surface presented alternation as well. [ABSTRACT FROM PUBLISHER]

The estimation of pH is vital to assess the biochemical and biological processes in a wide variety of applications ranging from water to soil, health, and environment monitoring. This work reports a screen-printed flexible and disposable pH sensor using the impedimetric method. The pH sensor was fabricated by screen printing graphene-carbon (G-C) modified zinc oxide (ZnO)-based active layer on a paper substrate and shows nearly three orders of change in impedance magnitude in the pH range of 2–9. The sensor was carefully designed using COMSOL Multiphysics software to understand the influence of electrode geometry and the electrical potential developed across the structure. The developed sensor was used for pH monitoring of soil and exhibited high sensitivity of 5.27 $\text{k}\Omega $ /pH 2–8 with a correlation coefficient (${R}^{{2}}$) of 0.99. Finally, an IoT-enabled smart pH detection system was implemented for continuous pH monitoring for potential application in digital agriculture. The outcome demonstrates that the presented flexible and disposable pH sensor could open new opportunities for monitoring of water, product process, human health, and chemical (or bio) reactions even by using small volumes of samples. [ABSTRACT FROM AUTHOR]

To investigate the characteristics of micro bridges and their interactions with partial discharge (PD) in oil-paper insulation under DC voltage, an experimental platform with two-copper-electrode models is established. Generation and growth of micro bridge impurities are observed. PDs in experimental process are detected and analyzed. The result shows that the generation and growth of micro bridges have three stages based on their quantity and shape. At first stage PD accelerates the generation of micro bridges. At second stage the grown bridges trigger stronger discharges. At the last stage a so-called "hazardous bridge" that triggers highly intensive PDs emerges, through which breakdown happens. Therefore, bridges and PDs promote each other to cause insulation failure. In addition, impurities at the second stage are observed to transform into pile-like, bridge-like or particle-like shapes. The transformation process is considered to relate with the change of composition force on fiber bundles. Besides, a "cluster discharging" phenomenon is observed at the second stage, which is associated with the generation and disappearance of micro bridge impurities. [ABSTRACT FROM AUTHOR]

The voltage on the valve side windings of the converter transformer is non-sinusoidal, which contains many high-order harmonic components. To calculate the nonlinear electric field distribution under the non-sinusoidal voltage, the harmonic-balanced decomposition finite element method (HBDFEM) is proposed in this paper. By using the fixed-point method, the finite element stiffness matrix of each iteration is decomposed according to the harmonic order, by which the memory consumption can be remarkably reduced. To verify the effectiveness of the proposed algorithm, a typical model of the oil-paper insulation structure is taken for instance, and the results obtained by the HBDFEM is compared with two algorithms, the traditional HBFEM and the time step method. The calculation results show that the HBDFEM can effectively reduce the computation cost for the nonlinear electric field problems with the non-sinusoidal periodic voltage. And it can be applied to analyze the compound electric field problems of the actual converter transformer. The electric field distribution of a ±500 kV converter transformer is calculated and analyzed considering the nonlinear relationship between the electric field and the medium conductivity. [ABSTRACT FROM AUTHOR]

Rationale: Paper spray (PS) has been developed as a method of choice for point‐of‐care analysis in many real cases, where its applications can be further expanded with delicate high‐throughput design. To achieve this goal, we developed a new PS regime, with the assembly of an induced high voltage into the ion source. Compared with regular DC high voltage, the newly developed setup is capable of high‐throughput, simple configuration and rapid switching between individual papers without complicated electric/mechanic design. Methods: A device of high‐throughput induced PS (IPS) was designed by using a two‐dimensional (2D) rotating platform equipped with a circular glass plate. The paper substrate was placed on the circular glass plate and separated from the electrode. The method avoids physical contact between the electrode and the sample. Charged droplets were generated at the paper tip once an induced high voltage was applied to a wet paper. Results: A relatively rapid analytical speed of 2.6 s per sample was achieved via IPS‐MS. Rapid quantification of amitriptyline (AMT) in complicated matrices was obtained within 1 min using an isotope internal standard method. Limits of detection for AMt in urine, FBS and blood were calculated to be 1.04, 0.84 and 1.33 ng/mL, respectively. In addition, high‐throughput IPS‐MS can be used for chemical reaction monitoring. Conclusions: We have demonstrated the versatility of high‐throughput IPS‐MS in ambient ionization, which successfully simplified the experimental installation and facilitated the experimental operation. Therefore, we believe that high‐throughput IPS‐MS analysis will be widely used for discovering drugs and screening reactions, and the present design has the potential for applications in paper chip‐MS analysis. [ABSTRACT FROM AUTHOR]

In order to improve the friction and wear properties of the paper-based friction materials, SiC particles (SiCp) were uniformly deposited onto the paper-based friction material via electrophoretic deposition with 300 V, 400 V and 500 V deposition voltages, obtaining the SiCp-content of 10.8, 15.9 and 22.9 wt%. The microstructure and thermal stability of the paper-based friction materials were characterized by scanning electron microscope (SEM) and thermogravimetry (TG). And the porosity, mechanical and tribological properties of samples were tested by mercury injection apparatus, electromechanical universal testing machine and friction tester. The results show that the uniform distribution of SiCp in the paper-based friction materials decreases the porosity and obviously improves the thermal stability and mechanical properties. Meanwhile, the incorporation of SiCp increases the stability of friction coefficient and the wear resistance of paper-based friction materials. Especially, the wear rate of paper-based friction material with 400 V deposition voltage treatment (CP400) for optimal SiCp-content of 15.9% decreases by 51.2% from 5.8 × 10 −14 to 2.8 × 10 −14 m 3 /(N·m) compared with that of the bare paper-based friction material (CP0). The electrophoretic deposition techniques provide the possibility of uniform addition of micro-nano particles to the paper-based friction material, which is beneficial to improve the friction and wear properties. [ABSTRACT FROM AUTHOR]

The article presents the results of comparative investigations of partial discharges in two insulation systems; aramid-enhanced cellulose paper-mineral oil, and pure cellulose paper-mineral oil. Partial discharges were investigated in a diagonal electric field with vertical and horizontal components. This field is treated as the most dangerous for insulation. The research was carried out on Nomex® 910 paper and cellulose paper samples, each paper being 0.25 mm thick. Samples of the two materials were tested at four levels of moisture. The inception voltage of partial discharges of all samples tested decreased as their moisture content increases. It was also proved that Nomex® 910 has a significantly higher partial discharge inception voltage than the cellulose paper, although this difference decreased with increasing moisture content. [ABSTRACT FROM AUTHOR]

Heretofore, unlike HVAC transformers, there is not much experience in both insulation design guides and test methods for ultra HV converter transformers. This special insulation phenomenon is very prominent due to the complication of voltage applied on valve-side windings of converter transformers. There is a severe lack of empirical research on partial discharge in oil-paper insulation under the combined ACDC voltage. The study in this paper provides a timely research into the issues. Nine possible configurations, which intent to simulate different defects in the transformer, have been investigated. The PD inception voltages varied ratios of combined AC-DC voltages were conducted. The discharge magnitude and its relation with the applied voltage for selected four common configurations were obtained during voltage increasing and decreasing respectively, which presented the PD initiating process and also reflected the insulation behavior of dielectrics. Besides, the Finite Element Analysis Soft was used to propose the effect of morphology of electrode surface (3 dimensional roughness is approximately 0.03 mm) on PD characteristics, which is very lacking in the previous references. The roles of DC and AC component in PD characteristics were discussed in the context of the relevant work in literatures. [ABSTRACT FROM AUTHOR]

To facilitate better interpretation of dielectric response measurements--thereby directing numerical evidence for condition assessments of oil-paper-insulated equipment in high-voltage alternating current (HVAC) transmission systems--a novel approach is presented to estimate the parameters in the extended Debye model (EDM) using wideband frequency domain spectroscopy (FDS). A syncretic algorithm that integrates a genetic algorithm (GA) and the Levenberg-Marquardt (L-M) algorithm is introduced in the present study to parameterize EDM using the FDS measurements of a real-life 126 kV oil-impregnated paper (OIP) bushing under different controlled temperatures. As for the uncertainty of the EDM structure due to variable branch quantity, Akaike's information criterion (AIC) is employed to determine the model orders. For verification, comparative analysis of FDS reconstruction and results of FDS transformation to polarization--depolarization current (PDC)/return voltage measurement (RVM) are presented. The comparison demonstrates good agreement between the measured and reconstructed spectroscopies of complex capacitance and tan δover the full tested frequency band (10-4 Hz-10³ Hz) with goodness of fit over 0.99. Deviations between the tested and modelled PDC/RVM from FDS are then discussed. Compared with the previous studies to parameterize the model using time domain dielectric responses, the proposed method solves the problematic matching between EDM and FDS especially in a wide frequency band, and therefore assures a basis for quantitative insulation condition assessment of OIP-insulated apparatus in energy systems. [ABSTRACT FROM AUTHOR]

A novel paper-based biofuel cell with a series/parallel array structure has been fabricated, in which the cell voltage and output power can easily be adjusted as required by printing. The output of the fabricated 4-series/4-parallel biofuel cell reached 0.97±0.02 mW at 1.4 V, which is the highest output power reported to date for a paper-based biofuel cell. This work contributes to the development of flexible, wearable energy storage device. [ABSTRACT FROM AUTHOR]

In this paper, the rapid aging due to Partial Discharge (PD) activity was investigated in unaged and thermally aged oil-impregnated paper with a disk-shaped cavity between the sheets of paper. The PD inception voltage and the voltage for instantaneous breakdown were measured, and the time to breakdown was measured by applying voltages less than the instantaneous breakdown voltage. A comparison between time to breakdown of unaged and thermally aged paper shows no significant difference between thermally aged and unaged paper at sustaining PD activity. The time to breakdown as a function of applied electric field was plotted and compared for both cases showing points scattered around a line in log-log scale. Changes of the PD parameters, such as PD magnitude and PD repetition rate were analyzed from the beginning of PD activity up to the moment of breakdown. The results show that the number and magnitude of PD increase at the beginning of aging until they reach to a maximum value, then both quantities decrease slowly over time until the final puncture breakdown occurs. The results emphasize the importance of PD monitoring on real equipment with oil-impregnated paper as insulation system, such as power transformers, since a focus on the number and magnitude of PD at just the present time may mislead the interpretation. Dielectric spectroscopy measurements performed on unaged and thermally aged paper showed an increasing trend of ε" after the sheets of paper were exposed to thermal aging for longer time. Dielectric spectroscopy measurements performed on samples before and after exposure to PD activity showed a big change of ε", This change can be attributed to byproducts and ions produced by PD activity. [ABSTRACT FROM AUTHOR]

Water (H2O) microdroplets are sprayed onto a magnetic iron oxide (Fe3O4) and Nafion-coated graphite mesh using compressed N2 or air as the nebulizing gas. The resulting splash of microdroplets enters a mass spectrometer and is found to contain ammonia (NH3). This gas–liquid–solid heterogeneous catalytic system synthesizes ammonia in 0.2 ms. The conversion rate reaches 32.9 ± 1.38 nmol s−1 cm−2 at room temperature without application of an external electric potential and without irradiation. Water microdroplets are the hydrogen source for N2 in contact with Fe3O4. Hydrazine (H2NNH2) is also observed as a by-product and is suspected to be an intermediate in the formation of ammonia. This one-step nitrogen-fixation strategy to produce ammonia is eco-friendly and low cost, which converts widely available starting materials into a value-added product. [ABSTRACT FROM AUTHOR]

The effect of HV impulses on surface and cavity partial discharges (PD) of oil-impregnated paper (OIP) is investigated in this work, by subjecting specimens to impulse voltages superimposed on a continuous AC voltage. The superposition of transient and AC voltage is relevant to insulation systems in power-system equipment, which is exposed to transients such as lightning and switching impulses during its operation. For several different PD-generating defects in oil-impregnated paper, the PD behaviors before and after the impulse are compared. The influence of moisture content is studied by using OIP with moisture content <0.5%, 3.0% and 5.5%. The results show a distinctive behavior of PD due to the impulse for each defect and insulation condition, either by change in the PD rate and magnitude or by causing PD inception or extinction. Recordings of the voltage signals and associated PD measurements during and after the incidence of a high voltage transient are of potential use for condition assessment of the insulation of power transformers and their bushings, as a form of online diagnostics. [ABSTRACT FROM AUTHOR]

In comparison with the AC and DC working voltages, the effect of switching impulse voltage on insulation is very different because of its fast-rising rate and large amplitude. This paper mainly focuses on the characteristics of PD in oil-impregnated paper insulation under switching impulse voltage. First, a robust experimental platform was set up including the impulse power source, test samples with uniform gas and oil gap, and the signal acquisition and processing system. PD characteristics in the air and oil gap are analyzed and compared involving the time-domain waveforms, the variation tendency of the average amplitude and numbers of PD pulses, the occurrence time and the instantaneous value of impulse corresponding to the first PD. Based on the dielectric barrier discharge (filament) theory, a parallel microcircuit model was established to explain the similarities and dissimilarities, and to evaluate the gap discharge intensity. The occurrence and development of PD under switching impulse voltage of typical oil-impregnated paper defect were studied systematically with simulation, experiments, and modeling. [ABSTRACT FROM AUTHOR]

A new concept for reusable eco-friendly hydrogel electrolytes based on cellulose is introduced. The reported electrolytes are designed and engineered through a simple, fast, low-cost, and eco-friendly dissolution method of microcrystalline cellulose at low temperature using an aqueous LiOH/urea solvent system. The cellulose solution is combined with carboxymethyl cellulose, followed by the regeneration and simultaneous ion incorporation. The produced free standing cellulose-based electrolyte films exhibit interesting properties for application in flexible electrochemical devices, such as biosensors or electrolyte-gated transistors (EGTs), because of their high specific capacitances (4-5 µF cm−2), transparency, and flexibility. Indium-gallium-zinc-oxide EGTs on glass with laminated cellulose-based hydrogel electrolytes (CHEs) as the gate dielectric are produced presenting a low working voltage (<2 V), showing an on-off current ratio ( Ion/off) of 106, a subthreshold swing lower than 0.2 V dec−1, and saturation mobility (μSat) reaching 26 cm2 V−1 s−1. The flexible CHE-gated transistors on paper are also demonstrated, which operate at switching frequencies up to 100 Hz. Combining the flexibility of the EGTs on paper with the reusability of the developed CHEs is a breakthrough toward biodegradable advanced functional materials allied with disposable/recyclable and low-cost electronic devices. [ABSTRACT FROM AUTHOR]

The oil-impregnated paper, which is the major section in converter transformer, plays a considerable role in the reliability and safety of power grid. However, the insulation degradation will be accelerated by the accumulation of charges that are on the surface of oil-impregnated paper. Therefore, the operating overvoltage occurs and irremediable damage will appear. Direct fluorination is an effective method of modifying the chemical components of polymer matrix so as to have effects on the surface characteristic of the insulating material without reforming the bulk properties. In this research, for studying effects of fluorination on charge behavior on the surface of oil-impregnated paper under the application of DC and impulse voltage, the F2/N2 compound, which the volume fraction for the F2 gas occupied 10 % and the pressure was 0.05 MPa in a reaction kettle for 5, 30 and 60 min respectively, was applied. Meanwhile, the chemical bond groups and the surface morphology of the fluorinated specimen were tested. Besides, the DC voltage amplitude was 4 kV and the applied time was 4 min. The impulse frequency was 500 Hz and the impulse voltage amplitude was 1, 2, 3 and 4 kV, respectively. The charge properties under various situations were investigated. From the research under the application of different fluorination time, impulse voltage amplitudes and polarities, conclusions can be drawn that, fluorination has significant effects on the chemical structure properties and surface characteristic of oil-impregnated paper. Furthermore, the initial potential can be reduced and the decay process of surface charge can be accelerated with different fluorination time increasing from 0 to 30 min. Nevertheless, the tendency is the opposite when the fluorination time continuously extends from 30 to 60 min. The trap distribution also exhibits alternation through the fluorination. [ABSTRACT FROM PUBLISHER]

Due to its excellent performance, oil-paper insulation has been widely used in many power apparatuses including converter transformer of high voltage direct current (HVDC) system. Space charge accumulation phenomena may significantly distort local electric field inside transformer and cause oil-paper insulation overstressing. As a result of long term operation, oil-paper gradually degrades. In most severe cases, the breakdown of insulation system may occur. In this work, the effect of space charge on breakdown characteristics of aged oil-paper insulation is investigated. Oil-paper samples with different aging states are obtained by thermally accelerated aging for various periods of time, categorized by the degree of polymerization (DP) of 1107 (new), 725, 504, 376 and 241, respectively. Experimental results show that the breakdown voltage of oil-paper samples without pre-stressing remains almost constant with thermal degradation. After the homo-polarity pre-stress, when the DP value is higher than ∼300 (from 1107 to 376), the breakdown voltage has an increasing tendency with an increase in thermal degradation. On the contrary, the breakdown voltage presents a decreasing tendency after the hetero-polarity pre-stress. When the DP is lower than ∼300 (DP241), the changes of breakdown voltage does not remain the same trend as previous samples after pre-stressing. Meanwhile, space charge distributions in different aged samples are measured by the pulsed electro-acoustic (PEA) method, and the trap parameters are correspondingly evaluated. It has been experimentally demonstrated that special attention should be paid to space charge accumulation and aging state of oil-paper insulation, which may lead to severe insulation accidents. [ABSTRACT FROM AUTHOR]

Oil-paper insulation system is an extraordinarily essential system of converter transformers as well as HVDC bushings. When the system changes its state, such as switching the thyristors, operating over-voltage appears, and the charge will deform the dielectric internal electric field, thus easily leading to the occurrence of discharge or insulation failure, so charge accumulation and dissipation on oil-paper insulation under pulse voltage need more investigation. This paper studies the surface charge behavior on double-layer oil-paper insulation under pulse voltage and inducing electrification was used to charge the oil-paper composite. Studies of various voltage amplitudes, pulse frequencies, numbers and polarities showed that the decay is fast initially, and then becomes slower with the time. Eventually the dissipation of charge behaviors tends to be flat. With the increase of voltage amplitudes, the surface potential rises, and less positive charges are accumulated on the surface than negative charges. The increase of the pulse frequency causes the initial values of surface potential a little smaller and the charge to dissipate more quickly. Also, with the increase of pulse numbers, the initial value gets bigger and the surface charge would be slowly dissipated. From the tdV/dt and decay time curves, the figures of positive voltage usually have two peaks, while there is only one peak in most of the curves under the negative one. With the increase of voltage amplitudes, the charge will dissipate more quickly. Additionally, the peak value and the characteristic time increase with the reduction of pulse frequency and the addition of numbers. [ABSTRACT FROM PUBLISHER]