Electrostatic Voltmeter Research Articles

Complex characterisation of Cr-doped α-Al 2O3 for DBD applications

Al2O3 samples doped with Cr2O3 up to 10vol.%(12.7wt%) were investigated with respect to their electrical, structural and morphological properties relevant to their use as a dielectric barrier in dielectric barrier discharges (DBDs). The surface properties were analysed using atomic force microscopy and a scanning electron microscope. The structural properties were investigated using x-ray diffraction (XRD) analysis. Regarding electrical properties, we measured the dielectric constant of the material, the discharge ignition voltage in a coplanar configuration in the air as well as in nitrogen, and the working domains (WDs) of atmospheric pressure Townsend discharge (APTD). The charge-trapping properties of the studied samples were measured by an electrostatic voltmeter. There was observed a significant ignition voltage decrease with maximal decrease for sample doped with 1vol.%Cr2O3 . For the samples doped with 10vol.% of Cr2O3 a rapid surface potential decay was observed that is important from the viewpoint of DBDs plasma filamentation due to the so-called surface memory effect. The WDs of the APTD showed variations, and it has been significantly extended for the 5Cr sample up to at least 24 kHz compared to other samples. Thus, the results presented in this paper show the potential of Cr-doped dielectric barriers and point towards future research directions.

Do Surface Charges on Polymeric Filters and Airborne Particles Control the Removal of Nanoscale Aerosols by Polymeric Facial Masks?

The emergence of facial masks as a critical health intervention to prevent the spread of airborne disease and protect from occupational nanomaterial exposure highlights the need for fundamental insights into the interaction of nanoparticles (<200 nm) with modern polymeric mask filter materials. While most research focuses on the filtration efficiency of airborne particles by facial masks based on pore sizes, pressure drop, or humidity, only a few studies focus on the importance of aerosol surface charge versus filter surface charge and their role in the net particle filtration efficiency of mask filters. In this study, experiments were conducted to assess mask filter filtration efficiency using positively and negatively charged polystyrene particles (150 nm) as challenge aerosols at varying humidity levels. Commercial masks with surface potential (Ψf) in the range of -10 V to -800 V were measured by an electrostatic voltmeter and used for testing. Results show that the mask filtration efficiency is highly dependent on the mask surface potential as well as the charge on the challenge aerosol, ranging from 60% to 98%. Eliminating the surface charge results in a maximum 43% decrease in filtration efficiency, emphasizing the importance of electrostatic charge interactions during the particle capture process. Moreover, increased humidity can decrease the surface charge on filters, thereby decreasing the mask filtration efficiency. The knowledge gained from this study provides insight into the critical role of electrostatic attraction in nanoparticle capture mechanisms and benefits future occupational and environmental health studies.

Voltage mapping and local defects identification in solar cells using non-contact method

Electroluminescence, infrared imaging, and current–voltage curve techniques are used to detect and map underperforming cells in a photovoltaic module or the modules in a photovoltaic string. In this work, we present a non-contact electrostatic voltmeter technique to detect and map the underperforming spots in a cell and the cells in a module. This non-contact technique directly maps the charged surface voltage (671 mV) of the superstrate glass, and it had an 11-mV difference with the voltmeter values (660 mV). Another data set of voltage values obtained by electroluminescence images conversion into a voltage map showed a difference of 7 mV with the non-contact voltmeter values. The direct voltage values obtained at various good and poor-performing spots of the cells using this technique are 3.69 V and 3.79 V and are validated using the voltage values obtained in electroluminescence analysis and the difference in voltage obtained by the two techniques is determined to be less than 2%. In this work, we combine the strengths of two complementary techniques of the electrostatic voltmeter (strength: quantitative) and electroluminescence (strength: spatial mapping) to obtain a quantitative spatial mapping of defects. Furthermore, this work is extendable to detect the poor-performing modules in solar PV power plants.

High-accuracy characterization of pyroelectric materials: A noncontact method based on surface potential measurements

The characterization of pyroelectric materials is essential for the design of pyroelectric-based devices. Pyroelectric current measurement is the commonly employed method, but can be complex and requires surface electrodes. Here, we present noncontact electrostatic voltmeter measurements as a simple but highly accurate alternative, by assessing thermally-induced pyroelectric surface potential variations. We introduce a refined model that relates the surface potential variations to both the pyroelectric coefficient and the characteristic figure of merit (FOM) and test the model with square-shaped samples made from PVDF, LiNbO3 and LiTaO3. The characteristic pyroelectric coefficient for PVDF, LiNbO3 and LiTaO3 was found to be 33.4, 59.9 and 208.4 [Formula: see text]C m[Formula: see text]K[Formula: see text], respectively. These values are in perfect agreement with literature values, and they differ by less than 2.5% from values that we have obtained with standard pyroelectric current measurements for comparison.

Insights into the charge transfer during water-jet charging process of meltblown nonwoven fabrics

Water-jet charging is one of the effectively methods to improve the filtration efficiency of polypropylene meltblown nonwoven fabric (PMNF) which is the core layer of face masks while its charging mechanism is still unclear. In this work, we directly investigate the charge transfer during the water-jet charging process by measuring charges carried by the water and PMNF in real time by using an electrostatic voltmeter and a portable petrol powered sprayer as the simulating water-jet charging equipment. Our work provides experimental evidences for understanding the charge transfer process during the water-jet charging treatment of PMNF and uncover the water-jet charging mechanism.

Application of non-contact electrostatic voltmeter to identify underperforming modules in grid-connected photovoltaic systems

This paper presents a technique that uses maximum power point voltage (Vmpp) to quantitatively identify the underperformance photovoltaic (PV) modules in grid-connected PV systems using a non-contact Electrostatic Voltmeter (ESV). Unlike the other existing techniques, this technique doesn't require the module's disconnection from the grid or other modules in a string. First, in this work, the ESV was tested for the application of thin film modules (off-grid and on-grid), and a comparison of the ESV sensed voltages with the voltmeter voltage values indicated a difference of less than 2%. Second, the least power-producing module was identified by the IV curves analysis and the Vmpp technique, and the results were compared. The comparison of both characterization tools quantitatively pointed out to the same module as the lowest performance module. It is a contactless, time and cost-saving method and is useful for quantitatively determining defective and poor-performing PV modules in large power plants where continuity of the energy production is preferred during the testing.

Use of non-contact voltmeter to quantify potential induced degradation in CdTe modules

Potential induced degradation (PID) is a significant reliability issue for photovoltaic modules in the field. Conventionally, to detect the PID-affected modules, all the modules in a string are individually disconnected and measured using I-V (current–voltage) tracers. It is extremely time-consuming, expensive and unsafe (if the module connectors are field aged) approach. In our approach, we aim detecting the PID-affected modules quickly, inexpensively and safely without disconnecting individual modules in the string. In this study, contactless electrostatic voltmeter’s (ESV) strength was explored to detect the PID-affected cadmium telluride (CdTe) modules in a string. These contactless measurements on high-voltage PV strings could make this technique unique and preferable to detect PID-affected modules in a string compared to the I-V curve method. In this work, a CdTe module was stressed for PID using the Aluminum (Al) foil method in a walk-in environmental chamber, which resulted in a reduction of module's peak current (Imax), peak voltage (Vmax), and fill factor (FF), and hence power (Pmax). Outdoor light I-V, EL, and ESV measurements were performed pre- and post-PID to determine the effectiveness of the non-contact ESV technique. The ESV technique successfully detected the change in Vmax, and hence Pmax, compared to the pre-and post-PID conditions. A difference of less than 2% was observed in the results of the non-contact and non-interruptive method compared to the conventionally used interruptive voltmeter or I-V tracer method. This technique and the test results demonstrate a significant promise to identify poor-performing modules in PV string without disconnection of individual modules in the string.

Breakdown voltage in long tubes: the effect of surface charge

The study focuses on ignition processes in long discharge tubes (the length of which is large compared to the diameter) in rare gases Ne, Ar, and their mixture at a low pressure (∼1 Torr). Gas breakdown was caused by ramp voltage pulses of positive or negative polarity applied to the active electrode. The breakdown voltage was determined by the voltage drop at breakdown. The emission of the ionization wave (IW) preceding the breakdown was explored. The discharge tubes were exposed to two types of external influences. The first was illumination of the tube cathode with visible spectrum light, while the second was the constant or pulsed bias of the cathode potential by a value lower than that of maintaining discharge. In both cases the breakdown voltage increased up to doubling under some conditions. The observation of the IW revealed the presence of extra waves preceding the regular pre-breakdown IW. The extra wave velocity and emission intensity differed from those of the regular waves. Their main feature is that they do not overcome the entire inter-electrode gap, but weaken and disappear in between. It is assumed that the extra waves deposit the wall surface charge, which in turn affects the breakdown voltage. The increased breakdown voltage value remains for tens of minutes, which could indicate the surface charge lifetime of the same order. This was confirmed by direct wall-potential measurements using an electrostatic voltmeter.

Experimental and theoretical investigation of water-jet triboelectric charging of meltblown nonwoven fabrics

The water-jet triboelectric charging technique has been widely used in China to improve the filtration efficiency of meltblown nonwoven fabric. However, there are few reports on research about water-jet triboelectric charging in the literature. In this paper, influences of the conductivity and pH of water on the filtration efficiency of meltblown nonwoven fabrics were investigated. The surface charge potential and its distribution of water-jet triboelectric charged meltblown nonwoven fabrics were characterized from microscopic and macroscopic aspects by using a bio atomic force microscope and electrostatic voltmeter. The charge stability was analyzed by using the thermally stimulated discharge technique. Meltblown nonwoven fabrics were water-jet triboelectric charged repeatedly in order to explore the charging mechanism. It is found that meltblown nonwoven fabrics with high filtration efficiency were developed by water-jet triboelectric charging treatment and the electrical conductivity of water had more influence than the pH on the filtration efficiency of triboelectric charged meltblown nonwoven fabrics. In addition, a possible mechanism of water-jet triboelectric charging is proposed based on experiments and characterizations.

Triboelectric charging of melt-blown nonwoven filters with high filtration efficiency

As a novel technology to convert low-frequency energy into electric power, the triboelectric nanogenerator is a hot research topic recently. However, the nature of charge carriers and their transfer mechanisms still remain poorly understood, especially for the cases of liquid–solid triboelectric nanogenerator. In this paper, charges produced by a triboelectric charging process were designed to provide melt-blown nonwoven fabrics with high filtration efficiency by making full use of the electrostatic attraction filtration mechanism. Influences of water conductivity and drying temperature on the filtration efficiency of melt-blown nonwoven fabrics were investigated. And the corresponding properties such as the surface charge potential and charge stability were analyzed by using the electrostatic voltmeter, bio atomic force microscope and thermally stimulated discharge technique. In addition, metal and inorganic elements in the masterbatch and water before and after triboelectric charging were measured in order to uncover the charge transfer mechanism. Melt-blown nonwoven fabrics with filtration efficiency as high as 96.8% was obtained through the triboelectric charging treatment by using water with the conductivity as low as 1.1 μS/cm for the first time. Negative and positive surface charge density appeared randomly on both sides of melt-blown nonwoven fabrics after the triboelectric charging treatment from the bio atomic force microscope measurement while only one kind of surface charge density can be achieved in the research of TENG, that is, negative or positive. It seems there are both electron and ion transfers during the triboelectric charging process and electron transfer seems to have more important contribution for the generation of charges.

Experimental characterization of electric potential uniformity at the surface of polymer plates corona charged by multiple-row needle-type electrodes

Diverse configurations of needle-type electrodes are commonly used to generate DC or AC corona discharges in various industrial applications. Previous studies confirm that the amount of charges generated by corona discharge is controlled by several factors such as the level of applied voltage, the ambient conditions, as well as the geometry of the electrode system. This paper aimed to evaluate the distribution uniformity of the charges generated by multiple-row needle-type electrodes and deposited on the Polyvinyl Chloride (PVC) plate surface, either at rest (“static” regime) or in motion (“dynamic” regime) under the corona electrode. The potential at the PVC plate surface was measured by a non-contact electrostatic voltmeter. The electric potential maps resulting from the experiments carried out in “static” regime, point out that the uniformity of the corona charging effect generated by the electrodes is related to their geometry and the level of the applied voltage. In the “dynamic” regime experiments, the surface potential profiles show that the distribution of electric potential on corona-charged polymer plates depends on the number of needles and the direction of movement under corona electrode system. Comparing the results obtained in this paper with the results obtained in previous studies, lead us to a general conclusion that the uniformity can be improved, to attain values higher than 95%, and this depends on the geometry of the electrode system and on the direction of the movement of the polymer plates in the electric field.

Effects of Irradiation on Surface Charge and Discharge Behaviors of PI Film Under Pulse Voltage

The superconducting magnet, as a main component of the international thermonuclear experimental reactor (ITER), is critical to the ITER's long-term stability. Polyimide (PI) not only has excellent electrical properties at cryogenic temperature, but also has strong irradiation resistance, which has become the common choice of insulating materials for the superconducting magnet. Due to the pulsed power supply used in the ITER, PI is facing the dual challenges of cryogenic temperature and pulsed voltage. The surface charge characteristics of irradiated PI film by different doses of electron beam were studied in this paper. The surface charging is completed under the pulse voltage with 40% relative humidity. The partial discharge initial voltage (PDIV) and breakdown voltage in liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) were measured by electrostatic voltmeter. The findings indicate that proper irradiation can help to minimize charge accumulation and decrease the trap level. At the same time, the PDIV and breakdown voltage can be increased by irradiation. However, too much irradiation can weaken this influence.

Study of the Influence of the Different Parameters of the Atmospheric DBD Treatment on the Surface Roughness and the Electric Potential Distribution Generated After the Tribocharging of Polypropylene

Square plates of polypropylene (PP), dimensions 100 mm × 100 mm × 4.5 mm, were treated by atmospheric dielectric barrier discharge (DBD) generated between two disk-type electrodes (Ø 75 mm), energized from an ac amplifier 30 kV, 20 mA. The study aimed at evaluating the factors that affect the roughness and the triboelectric behavior of the plasma-treated samples. The alteration of surface aspect after each treatment was clearly visible with the naked eye and the changes were confirmed by measurements carried out with a portable roughness meter (Surftest SJ-210) and a digital microscope (Keyence VHX-7000). The roughness of the PP samples increased from an initial arithmetic mean Ra = 0.06 μm (±0.01 μm) and standard deviation Rq = 0.08 μm (±0.01 μm) to Ra = 0.22 μm (±0.03 μm) and Rq = 0.25 μm (±0.03 μm), respectively. These increases were highly dependent on the air gap distance (10.5-13.5 mm), the treatment time (5-20 min), and the configuration of the DBD cell, i.e., the number (one or two) and the thickness (4-5 mm) of the glass dielectric barriers. Untreated and DBD-treated samples were tribocharged in a linear tribometer, to evaluate the effect of the cold plasma treatment on the electric potential generated on the polymer surface by the triboelectric effect. The electric potential measured by a noncontact electrostatic voltmeter (Trek, 341B) was higher and better distributed over the surface of the plasma-treated samples.

On the crosslinking temperature dependence of charge transport behavior in XLPE film deduced from surface potential decay measurements

The effect of crosslinking temperature on charge transport behavior in crosslinked polyethylene (XLPE) film has been investigated by means of surface potential decay measurements. 200 μm-thick XLPE specimens were prepared by hot-molding low density polyethylene (LDPE) by adding dicumyl peroxide (DCP) as crosslinking agent and phenolic antioxidant with temperatures ranging from 150 to 180 °C. Surface potentials on corona-charged samples were monitored by using a Kelvin type probe equipped with an electrostatic voltmeter, based on which trap distribution, effective charge mobility and field dependent conductivity were estimated. Fourier Transform Infrared (FTIR) spectrum and Differential Scanning Calorimeter (DSC) analysis were employed to examine the change in chemical structure and crystal morphology of test samples. Results obtained show that the charge transport dynamics is cross-linking temperature and polarity dependent. With the rise of the crosslinking temperature, the mobility of positive charge increases monotonously from 1.05 × 10−16 m2V−1s−1 to 5.42 × 10−15 m2V−1s−1, whereas the mobility of negative charge shows a fall-and-rise tendency that a minimum value of 1 × 10−16 m2V−1s−1 appears at 160 °C. A single trap center for electron is observed at any test sample. However, as regards to hole, a double-trap-center feature tends to appear as the temperature exceeds 160 °C. Moreover, with the increase of the crosslinking temperature, the conductivity of sample becomes field dependent. It is suggested that the variation of charge transport behavior should be ascribed to the presence of by-products as well as the crystallinity change caused by the temperature.

Investigation of surface strain by digital image correlation and charge trap characteristics of epoxy alumina nanocomposites

Epoxy alumina nanocomposites were fabricated through shear mixing of alumina nanoparticles in to epoxy resin under optimum process conditions for its potential application as insulator in transformer. The fundamental insight in to the influence of ageing of nanocomposite insulator due to its continuous exposure to UV irradiation and water in terms of their charge trap characteristics was explored. The surface potential decay and strain variation of nanocomposite samples were measured by using Electrostatic voltmeter and Digital Image Correlation technique (DIC), respectively. Diffusion of water into epoxy alumina nanocomposite is less compared with pure epoxy resin. It has been observed that surface potential decay rate and trap depth have shown increasing and decreasing trend, respectively, with the addition of alumina nanoparticles in to epoxy resin. The UV and water aged nanocomposites exhibited a decreasing trend of surface potential decay rate and the governing reasons could be due to surface damage causing increase in deep trap formation. The tensile strength and stiffness of the samples have increased with the addition of alumina nanoparticles in to the epoxy resin. It could be due to the better bonding of alumina particles with epoxy resin. The surface strain induced in to the sample during tensile loading and the surface potential decay rate of nanocomposite has shown a direct correlation, as observed in the present work.

Electrostatic Properties of Clothing Fabrics Suitable for Different End-Uses

The static electricity properties of textile products are very important, especially when clothing comfort is the main subject. In this study, four sets of clothing fabrics containing 33 systematic and 18 non-systematic woven fabrics in total were used in order to examine the electrostatic charging properties. A testing mechanism which provides static electricity by the triboelectrification method was manufactured, and electrostatic voltage values occurring on the fabric samples were measured by an electrostatic voltmeter simultaneously with the testing mechanism. The repeatability of the results was checked by using polyester and cotton systematic woven fabrics. After this stage, the effects of fabric structural parameters and the rubbing period on electrostatic charging properties were evaluated. Moreover, non-systematic commercial woven fabrics were also tested in the study. In the last section of the experimental part, the best clothing and lining fabric combinations were revealed according to the lowest static electricity results.

DC and AC electric field analysis and experimental verification of a silicone rubber insulator

This paper presents the electric field analysis as well as the experimental verifications of a silicone rubber insulator by considering DC and AC voltage conditions. As a first step, a 3D electric field simulation of the insulator was performed by using a commercially available software based on finite element method. DC voltage and 50 Hz power–frequency voltage simulations were conducted for the given insulator. Low frequency field distribution along the insulator has been investigated to find threshold frequency values for resistive and capacitive field regions. The effect of the conductivity of air surrounding the insulating system on the electric field was evaluated. For each condition, electric potential and field distribution along the creepage path of the insulator was obtained. In addition to the simulation studies, voltage measurements under AC and DC conditions utilizing a different approach for the silicone rubber insulators were conducted on the insulator by using a non-contact type electrostatic voltmeter to validate the simulation results.

Determination of the spatial impulse response of compensating electrostatic voltmeters

The accumulation of surface charges is a crucial challenge, especially for HVDC components. Accumulated surface charges can change the electric field distribution and generate weak points, especially in case of superimposed transient voltages and, therefore lower the performance e.g. of insulators. Hence, an accurate measurement of the surface potential and so the surface charges is necessary to optimize these components. Commonly, the surface potential is measured with an electrostatic voltmeter. In this study a procedure for determining the spatial impulse response of a compensating electrostatic voltmeter depending on only the surface to probe distance is presented. Based on the performed measurements a mathematical model is developed to describe the capacitive influence and significance of the local surface potential on the measurement result. The actual measurement value is a weighted and averaged value given by the actual position and its surrounding, which is also confirmed by numerical simulations. The performed procedure enables high accuracy of the measurement of surface potentials and so of surface charges using different types of electrostatic voltmeters and shows the limitation of the measurement procedure. This knowledge increases the possibility to design optimized components for HVDC systems.

Non-contact measurement of electric charges on water surface supplied with plasma

Transferred charges in water associated with discharges are measured using an electrostatic voltmeter, without any physical contact between the electrode and water. Unlike the method that uses a voltage probe, this method allows for the estimation of charges in water under an electrically floating state. In this paper we introduce a needle-water discharge system which uses the needle electrode over the ultrapure water surface. First, we evaluated our needle-water discharge system with various applied voltages by analysing the current waveforms. Thereafter, by synchronising an oscilloscope and a data logger, the surface potential and discharge waveforms were obtained simultaneously at different time scales. It was found that the measured surface potential of water is proportional to the transferred charges. Two types of materials, namely, glass and polystyrene, were used as the water container material, and it was observed that when the glass container is used, the characteristic decay time of the potential is 2.02 s, which is much shorter than in the case of a polystyrene container. This is due to a much lower surface resistivity of polystyrene. This finding is important because when a DC voltage is applied to the needle electrode, discharging is terminated due to the charges accumulated in water. The termination tendency is, however, varies based on the container material used, even when the same voltage conditions are applied.

Experimental study of controlled active neutralization of polypropylene films

AC corona discharge is widely employed for neutralizing the electric charges at the surface of insulating bodies: films, plates, granules, etc. If uncontrolled, this active neutralization process is accompanied by the persistence of a residual charge at the surface of the treated bodies. The aim of this present work is to demonstrate experimentally the efficiency of the controlled active neutralization using AC corona generated in a triode-type electrode configuration, with the grid connected to the ground. The experimental study was carried out on DC corona charged polypropylene films that were neutralized by a sinusoidal corona discharge at industrial frequency (50 Hz). The distribution of the electric potential at the surface of the charged and neutralized samples were measured by a non-contact electrostatic voltmeter. The factors under study were: the amplitude of the AC voltage applied to the corona electrode of the triode system, the duration of exposure to the corona discharge, the scanning speed, and the spacing between the grid and sample. The experimental results obtained show that the neutralization rate is close to 100%, i.e. the electric potential profiles obtained at the surface exposed to AC corona discharge show the absence of the residual charge. The results show that the efficiency of the controlled active neutralization depends on the energy that the AC corona discharge imparts to the charged samples, and that affects the trapped bulk charge.