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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 (LN2) 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.

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 (O 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.

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.

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.

The diploma thesis deals with the experimental construction of a non-contact high-voltage voltmeter for measuring potentials on the basis of generally known and available data. The aim of this work is clear description of the production procedure, functional measuring device, comparison of the influence of material and shape of electrodes on the measurement itself. Another goal of the work is also a general direction to reusing unnecessary or non-functional parts and materials, usually intended for disposal, in various structures.

International audience; A simple method is proposed to calibrate the energy of an electron beam. An electrical floating metal foil is irradiated by the incident electrons. The electron energy is deduced from the magnitude of the surface potential developed on the irradiated conductor surface. The measurement of the surface potential is made outside the vacuum chamber on a metallic slab connected through a coaxial feedthrough to the electron irradiated sample. The energy calibration obtained by this method is compared to the conventional method based on measuring the energy position of the backscattered electron elastic peak.

This paper presents a non-contact approach to obtain simultaneous current-voltage (I-V) curves of photovoltaic (PV) substrings and modules in a string without the need of disconnecting the individual modules from the string. There are two types of I-V curve tracers currently available in the marketplace, capacitor-based and electronic load-based. The primary requirement of these conventional I-V tracers is the disconnection of individual modules in the string so that the individual modules can be connected through the connectors of the individual modules. These conventional contact-tracers have three major limitations in the utility scale power plants: safety during disconnecting and reconnecting field-aged module connectors, extensive time and hardship of test personnel and limited availability of clear sunny hours/days to obtain I-V curves of 1000s of modules in the field. To mitigate all these three limitations, we experimented with a non-contact I-V (NCIV) tracer approach. In this approach, we utilized an electrostatic voltmeter (ESV) in combination with a voltage probe and a hall sensor to obtain I-V curves. A major application of the NCIV tracer is that it can instantaneously identify the underperforming modules in a string without the need of disconnecting the individual modules and translating the measured I-V curves to standard reporting conditions such as STC (standard testing conditions) because all the modules in the string are simultaneously measured at a single prevailing weather condition of irradiance, temperature, wind speed and wind direction.

Surface charge accumulation on polymer insulating material has been recognized as an important factor for electric field distortion that results in reduction of surface flashover voltage. This paper reports on the charge accumulation behavior between a pair of finger-shaped electrodes on epoxy/Al2O3 nanocomposites under dc voltage superimposed by repetitive pulses. The charge distribution was measured by means of an electrostatic voltmeter, from which the average charge density could be calculated. Effects of dc voltage, nanofiller content, and pulse voltage on charge accumulation behavior were investigated. Obtained results showed that with the increase in the filler content from 0 wt% to 5 wt%, the average charge density increased initially then appeared to decrease. The superposition of repetitive pulses on dc voltage led to a remarkable growth in charge accumulation as compared with that when only dc voltage was applied. It is suggested that the charges are originated from local gaseous ionization and/or electrode injection, which is determined by the combined voltage. The charge density is dependent upon the surface trap, which is affected by nanofiller content. The superposition of repetitive pulse is considered as a possible reason to encourage local gaseous ionization that results in enhanced accumulation of surface charge.

Surface charge accumulation on epoxy based nanocomposites under DC stress with and without the presence of a magnetic field was investigated in this work. Two mm-thick sheet samples were prepared by adding 60 nm-Al 2 O 3 particles into epoxy with filler content of 1 to 5 wt%. A pair of finger-shaped electrodes was employed to introduce electric charges onto the sample surface under DC stress of ±5 and ±10 kV. The magnetic field was established by using a pair of permanent magnets, by which a magnetic flux density of 100 and 180 mT was achieved. Surface charge between the electrodes was measured by means of a Kelvin type electrostatic voltmeter, and the influence of nano-filler content and magnetic flux density on charge distribution as well as charge density was estimated. The results indicate that increasing nano-filler content from 0 to 5 wt%, the average charge density increased initially then decreased. The presence of a magnetic field results in a deflection of charge profile as compared with that formed without a magnetic field. The charge density increased as the magnetic flux density increased from 0 to 180 mT. It is suggested that the charge trajectory close to high voltage electrode varies by the combined electric-magnetic force, by which electric field recovery in such a region is facilitated thus more charges are encouraged to accumulate on the surface.

Superconducting magnet is an important portion in international thermonuclear experimental reactor (ITER). The reliability of superconducting magnet is of great significance for the stable operation of ITER. Due to its excellent cryogenic electrical properties, low thermal shrinkage stress and strong radiation resistance, polyimide (PI) is often used as the insulating material for superconducting magnet. Since a pulse power is used to drive ITER device, PI faces the dual challenge of low temperature and pulse voltage. It is easy to cause charge accumulation and lead to insulation breakdown. This article studied the surface charge and discharge features of PI irradiated by electron beam of various doses under repetitive pulse voltage. The irradiation doses are 0, 300, 500 and 700 kGy. The surface charging was finished with a 40% relative humidity under pulse voltage. The electrostatic voltmeter was employed to collect surface potential data. The results show that moderate irradiation can promote the surface charge decay, reduce the charge accumulation, and make the trap level of PI shallower. Nevertheless, excessive irradiation can weaken the effect.

Previous studies had shown that the distribution of charges generated by corona discharge is controlled by several factors such as the geometry of the electrode system and the level of the applied voltage. The aim of this paper was to evaluate the uniformity of charge distribution at the surface of dielectric materials (PVC plates and PP films) exposed to a corona discharge generated by a tri-needle-type electrode at rest or in motion. The surface electric potential mapping performed with a non-contact electrostatic voltmeter shown that the non-uniformity of the corona charge is related to the geometry of the electrode employed in the experiments and can be reduced to less than 5%, when choosing the appropriate values for the distance between needles and for their height above the samples. It was also found that exceeding a certain value of applied voltage accelerated the surface potential decay, a phenomenon that explains the deterioration of charge uniformity.

Surface potential decay on negative corona charged epoxy/Al2O3 nanocomposites irradiated with high-energy electron beam has been investigated in this paper. 2-mm-thick laminate nanocomposite samples were irradiated with electron beam at an average energy of 7.5 MeV, and the total accumulated dose was up to 500 kGy. After the irradiation, the nanocomposites were corona charged with dc voltage at −10 kV through a pair of needle to plate electrode. Surface potential of the sample was then measured by means of an electrostatic voltmeter through which trap distribution and carrier mobility were calculated. Differential scanning calorimetry curve for the each sample was measured to understand the change in chemical and physical structures induced by the irradiation. Results obtained indicated that the presence of nanofiller in the nanocomposites played a role in limiting the charge transportation both before and after the irradiation, and the charge transportation behavior was remarkably dependent upon the total irradiation dose. It is found that when irradiated with a certain total dose of electron beam, electron migration within epoxy and its nanocomposites is restricted, which should be attributed to the high-energy irradiation-induced structural change of the material.

The ability of polymers to acquire and retain electrostatic charges is valued in designing new equipment like electrostatic separators, electret filters, and powder coating devices. Several recent studies have pointed out the beneficial effect of electric charges on the lubricated contacts. The aim of this paper is to compare two physical mechanisms of electric charging of polymers: 1) triboelectric effect; and 2) corona discharge. The experiments are performed with 5-mm-thick samples of Acrylonitrile-butadiene-styrene, poly-vinyl-chloride, and polypropylene. The cartography of the electric potential is made using the induction probe of an electrostatic voltmeter. The tribocharging is done by back and forth movement of two polymer plates in conformal contact with each other (speed: 7 to 30 mm/s; constant normal force: 10 N). Uniform corona charging is performed by moving the sample in the space charge zone generated by a wire-type high-voltage electrode used in a triode configuration with the potential of the grid electrode set at 1 and 2 kV. The electric potential at the surface of tribocharged polymers is less uniform, but decays slower than that of corona-charged samples.

Epoxy resin is widely used in disc-type spacers of gas insulated switchgear (GIS). Surface flashover related to the existence of surface charge often occurs on the spacer, which is a great threat to the application of HVDC GIS and the safety of entire grid. Moreover, the influence on surface charge dynamic behavior under pulse voltage produced by switch overvoltage, accompanying with the DC voltage, is still unclear. In order to research the comprehensive effect of DC and pulse voltage on surface charge behavior, in this paper, epoxy resin sample was charged by a corona discharge system and the charge distribution was measured by an electrostatic voltmeter. The results are obtained from the research of different pulse amplitudes and pulse polarities. When DC and pulse voltage with the same polarity are applied, smaller pulse voltage would push the original charges away, resulting in the decrease of initial surface potential. But a big pulse voltage could increase the surface potential. The speed of surface charge dissipation has an opposite tendency. When the pulse polarity becomes the opposite of DC voltage, surface potential at the sample center will be a heteropolar value at the beginning and then it gradually becomes consistent with the initial polarity. In addition, the surface charge change rate will rise with the increase of heteropolar pulse voltage. The Trap energy distributions were used to analyze charge decay process in the last section.

Silicon strip sensors as used for tracking detectors in high-energy physics experiments are bare large-area silicon devices without any packaging. To protect them from environmental influences like humidity and mechanical damage, a passivation is deposited as the uppermost layer. The passivation can consist of different materials like silicon oxide, silicon nitride, polyimides or doped glasses. In this study we first demonstrate the impact of static surface charge on the sensor characteristics. This is followed by investigations on how sensitive different passivation layers of silicon strip sensors are against charge-up and how these charges retain. For such purpose, a corona charge-up device has been built and used to charge up the detectors. The surface potential distribution caused by the charge was mapped using an electrostatic voltmeter. The self-discharge of sensors with different passivation layers was investigated by long-term studies.

Reducing the unwanted electrostatic charge to a safe level is the goal of any charge neutralization device. The aim of the present work is to study the influence of the voltage waveform and frequency on the efficiency of charge elimination by using a wire-to-grid dielectric barrier discharge (DBD). The DBD electrode was subjected to high voltages of various waveforms, amplitudes and frequencies. Three voltage waveforms, namely sinusoidal, square and triangular signals, were studied in neutralization of positively charged polyethylene (PE) granules. The resultant surface potential distribution, before and after neutralization, was measured using an electrostatic voltmeter. The obtained neutralization rates of the three voltage waveforms were compared in view to recommend the most efficient high voltage signal. The DBD currents, transferred charge and consumed power, corresponding to the three signals forms, were measured and compared. The obtained results show that the efficiency of the neutralization using the DBD electrode depends on both amplitude and frequency of applied voltage as well as the signal waveform. The square waveform was the more convenient signal leading to best neutralization results in comparison to the sinusoidal and triangular signals.

The dielectric barrier discharge (DBD) is a convenient way to modify the surface properties of polymers. The aim of this study is to evaluate the effect of atmospheric DBD treatment on the triboelectric properties of polymers in sliding contact. The experiments were carried out on two polymers that were rubbed against each other: PP and PE. The pairs of samples were exposed to the DBD, and then taken to a triboelectric test bench for friction charging. The distribution of electric potential at the surface of the tribocharged samples was measured by an electrostatic voltmeter. The triboelectric behavior of the considered polymers depends on the conditions of DBD treatment: thickness of the dielectric barrier and duration of the exposure to the non-thermal plasma.

A system for the measurement of surface potential on epoxy insulator within a direct-current (DC) gas-insulated system (GIS) of 320 kV nominal voltage is presented. Challenges encountered were the operating conditions: applied voltages up to 250 kV -and hence elevated electric field stress-, elevated temperature generated by the full load conductor current of 4600 A, pressurized gas atmosphere, and continuous operation for periods up to 6 months. Furthermore, a positioning system integrated within the GIS enables sequential scanning of two insulator surfaces while minimally disturbing the original system geometrical and electrical configuration. The sensor itself is modified non-contact voltmeter, using a miniature electrostatic field chopper probe. We demonstrate the capability of the system by following the time evolution of the surface potential on DC epoxy partition insulators, as well as recording its spatial distribution in the final resistive state.

Influence of metal particle contamination on surface charging behaviors as well as flashover characteristics for PTFE insulators in vacuum was experimentally investigated under impulse voltage under a planar electrodesample structure. The surface charge was measured by a vibrating Kelvin probe used in conjunction with an electrostatic voltmeter. The effects of metal particle positioned on insulator, e.g., near cathode, at the middle of cathode-anode surface and near anode, on surface charging and flashover voltage were discussed. It is confirmed that the secondary electron emission process governs surface charge accumulation behaviors under impulse excitation, which initiates from cathode triple junction (CTJ) and develops towards anode. Surface charging is much more severe with metal particle contamination, and flashover voltage decreases as the size of metal particle increases due to the enhanced electric field at CTJ. This study is helpful to make a better understanding of the mechanism of surface flashover for insulators with metal particle contamination.

The surface charge and space charge accumulation in paper used in oil&ndash, paper insulation system may distort electric field distribution and lead to the flashover and breakdown of insulation system. In this paper, the effect of gas-phase fluorination on the surface charge and space charge characteristics of oil-impregnated Nomex paper was investigated. Nomex T410 was fluorinated at 25 &deg, C using F2/N2 mixtures with 20% F2 in volume at 0.05 MPa for 15, 30 and 45 min. Fourier Transform Infrared Spectroscopy (FTIR) proved that the molecular chain scission and cleavage occurred during gas-phase fluorination. Furthermore, the surface charge and space charge characteristic of the original and fluorinated oil-impregnated paper were measured using an electrostatic voltmeter and Pulsed Electroacoustic (PEA) equipment respectively. Furthermore, the hole and electron trap distribution of the samples were obtained by Isothermal Surface Potential Decay (ISPD) model. The results showed that both the positive and negative charge decay rates were accelerated by gas-phase fluorination and the hole, electron trap energy and density of the fluorinated samples were reduced by fluorination. It is suggested that the space charge dissipation was also accelerated by fluorination, indicating that gas-phase fluorination is an effective approach to modify the charge dynamics of oil-impregnated Nomex paper.

International audience; Triboelectric charging is used in many applications including electricity nanogeneration, safety or electrostatic separation of insulating materials. Insulating granules charge must be the highest in electrostatic separators so that the electric field forces allow their separation. Dielectric barrier discharge (DBD), used for ozone production, depollution or surface treatment, is able to change the triboelectric properties of insulating materials. The aim of this study is to improve the triboelectric charging of polyethylene particles by exposing them to an atmospheric DBD. Signal shape, exposure duration, voltage amplitude, and frequency, which rule the DBD, are studied. After exposing the particles to DBD, they are charged in a vibratory device during 5 min. Then, particles are put in a Faraday pail connected to an electrostatic voltmeter to measure the acquired charge. Results show that the square waveform has the best effect and that the duration of the DBD treatment should not exceed 10 s, for the amplitude of the applied voltage of 21 kV.

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.

With the emergence of superconductor technology, high-temperature superconducting (HTS) cable is receiving considerable attention for application in power systems. Polypropylene laminated paper (PPLP) and liquid nitrogen (LN 2 ) have been widely used as insulation and coolant, respectively, in HTS cable systems, where the insulation is threatened by surface charge and quench. Direct fluorination is an effective method to improve the electrical properties on the material surface. To restrain the surface charge accumulation and prolong the insulation life, the surface potential behaviors of fluorinated PPLP under the quench condition has been studied to clarify the effects of fluorination time and low temperature. PPLP specimens were fluorinated in a reaction kettle using a F 2 /N 2 blend with an 80% volume fraction of nitrogen and pressure of 0.1 MPa for respectively 5, 10, and 15 min. Corona charging was performed with dc voltage at a relative humidity of ~15% in atmospheric air on room temperature specimens and after the specimens had been cooled by LN 2 for 20 s before the corona charging. Then, the surface potential was measured with an electrostatic voltmeter. The results indicate that the accumulation and decay behaviors of the surface potential for PPLP are affected by the charge polarity, specimen temperature, and fluorination time.

Epoxy resin is widely used in disc-type spacers of gas insulated switchgear (GIS). Surface flashover related to the existence of surface charge often occurs on the spacer, which is a great threat to the application of GIS and the safety of entire grid. Moreover, the influences on surface charge under pulse voltage produced by switch overvoltage, accompanying with the AC voltage, are still unclear. In order to research the comprehensive effect of AC and pulse voltage on surface charge, in this paper, epoxy resin sample was charged by a corona discharge system and the charge distribution was measured by an electrostatic voltmeter. The results are obtained from the research of different pulse amplitudes, pulse numbers and pulse polarities. The surface potential is a negative value after AC voltage applied for a period of time. When AC and negative pulse voltage are applied, smaller pulse voltage would push the original negative charges away. As a result, initial negative surface potential decreases. But bigger pulse voltage could increase the charge accumulation. When the pulse polarity becomes positive, surface potential at the sample center will be positive value at the beginning and then it gradually changes from positive to negative potential. In addition, the influence on surface charge decay rate will be enhanced with the increase of pulse number under the same pulse voltage. Trap energy distributions were used to analyze charge decay process in the last section.

Non-contact measurements performed with the auto-compensated electrostatic induction probe of an electrostatic voltmeter are often employed to characterize the charging state of insulating materials, such as films or non-woven media. The aim of the paper is double: (i) describe a simple method for assessing the resolution of such a probe; (ii) discuss the significance that can be attributed to the value displayed by the electrostatic voltmeter when the charge is non-uniformly distributed at the surface of the bodies examined by the probe and no constant surface potential can be defined. The measurements were performed for some simple experimental models that simulate surface potential non-uniformity of constant-charge insulating bodies. By examining the different surface potential distribution curves that were obtained for each of the situations under study, it is possible to estimate the resolution of the probe. A commercial computer program based on the superficial charge simulation method was employed for the numerical analysis of the electric field in a simplified 2-D representation of the geometric system formed by the probe, the experimental model, and the grounded plate. The potential that anneals the electric field at the surface of the probe (to simulate its principle of operation) was calculated by an iterative method. A good agreement was found between the results of the numerical simulations and the experimental data. The errors that can be made in the interpretation of the results of surface potential measurements are illustrated by the case of a non-uniformly-charged non-woven polypropylene fabric.

Electrostatically induced voltage generated on printed circuit boards in a grounded metal box occasionally causes a malfunction and failure of the electronic equipment. A person who walks into a room that has an air conditioner can be electrified up to −10 kV or more. However, a microelectronics device malfunctions by an occurrence of induced voltage of less than 10 V. In the present paper, the induced voltages on an ungrounded one of two conductors that are contained in the metal box are measured and calculated when a charged body moves away from a partially opened metal box. The induced voltages are measured by the use of a spark gap and an electromagnetic wave sensor and are compared with the results from an electrostatic voltmeter. The induced voltages are calculated, moreover, by the use of q=cv, with the capacitances and charges. The results show that the induced voltages of −42% of the voltages of the charged body are generated in the metal box when a charged body moves away from the metal box. The results will be helpful in considering preventive measures of the malfunction and failure of electronic equipment.

The surface potential behaviors of fluorinated polyimide films under low temperature were studied to clarify the effects of fluorination time and low temperature. Polyimide specimens were fluorinated in a reaction kettle at 55 °C using a F2/N2 blend with volume fraction of 80% nitrogen and 0.05 MPa for respectively 15, 30, 45 and 60 min. The specimens without fluorination were also prepared for reference. Corona charging was performed with pulse voltage at a relative humidity of ∼ 11% in atmospheric air. Then the specimens were cooled by liquid nitrogen in 10 s before or after corona charging. The surface potential was measured by the device of an electrostatic voltmeter. The experimental results indicate that the accumulation and decay behaviors of surface potential in the surface of polyimide films are affected by the charge polarity, specimen temperature and fluorination time.

This paper reports a feasibility study of the ion balance measurement by the partial surfaces. The partial surfaces were exposed under the dc corona ionizer which could be varied ion balance. The appearance of electrostatic potential, which is caused by the imbalance of positive and negative ions, was measured by the high impedance electrostatic voltmeter. The result from these partial surfaces was compared with the standard test method which is using the 6″×6″ charged plate. The average voltages of all segments of the partial surfaces are correlated to the electrostatic potential values which were measured by the standard 6″×6″ charged plate. Moreover, the partial surfaces offer the fine-grained level of results. It validates that the precision of the ion balance measurement can be improved by the partial surfaces.

As one kind of the basic insulating materials, polyimide has been widely used in turn to turn insulation and turn to ground insulation in inverter-fed motors. However, the pulse voltage from the converter often causes overvoltage and localized high electrical field in the insulation system. During applying the pulse voltage, charges accumulate on the surface of the insulator, which could affect the dielectric property and cause the breakdown of insulation. Direct fluorination is a method to modify the surface layer of the polymers without changing the bulk properties. As a result of the fluorination, hydrogen atoms are replaced by the fluorine atoms and the component of the polymer surface is changed, which can influence the surface charge accumulation and affect the electrical properties. The experiment in this paper was focused on the effect of pulse duration and pulse number on surface charge of the polyimide films. The polyimide films with the fluorination time of 0, 15, 45 and 60 min were prepared. Surface charging was performed by corona discharging using repetitive pulse power at the temperature of 20 °C with the relative humidity of ~15%. The repetition frequency was 1 kHz and the pulse duration was 50, 110 and 210 μs, respectively. The surface charge decay was measured using a specific probe coupled with an electrostatic voltmeter. The results showed that the surface charge increases with increasing the pulse number and the duration of the microsecond pulse.

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.

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.

International audience; 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.

This paper deals with the design and development of an electrostatic voltmeter based on surface potential sensor. For the realization of the device, constructed by us, a surface potential measuring sensor EFS-22D has been used, consisting of a measuring probe and an electronic converter for measuring voltages in the range from 0V to 900V at a distance between the sample and the surface of the probe within 1 – 3.5mm. The measuring probe is composed of an oscillating mechanism (of the type of a tonometer), with metal electrodes attached to it, which block the electric field. The movement of these electrodes is accomplished by means of a piezo-electric element. The chopper is tuning fork oscillator type shutter. The surface potential, measured by the probe of the sensor, is converted into analogue voltage, varying from 0 to 4.5V, which is then converted into a digital value by a 15-bit sigma-delta analogueto-digital converter, connected to a microcontroller. The data from the measurements are transmitted from the microcontroller to a personal computer through a Bluetooth module. User software has been developed, allowing for: recording the obtained values from the measurements; their visualization both in digital and analogue form; digital filtration of the noise from the sensor; and statistical analysis of the obtained data

Surface flashover across solid insulators in vacuum-dielectric system greatly weakens the overall performance of pulsed power equipment. It is reported that flashover is crucial in relation to surface charging behaviors on insulator surface. Therefore, it is of great significance to study mechanism of surface charge accumulation in vacuum. In this paper, surface charging behaviors on alumina ceramics insulators were experimentally investigated under negative impulse voltage. Surface potential distribution were measured by an electrostatic voltmeter with a vibrating Kelvin probe utilizing field nullifying technique. Surface charging behaviors for different amplitudes and number of negative impulse voltage were both studied, and the metal granule was introduced to research the development of surface charge accumulation. For impulse voltage, Schottky injection of homo-charges from electrode into sample surface layer has little influence on surface charging as the voltage duration is too short for charge injection and migration on surface layer. Surface charging is mainly caused by the secondary electron emission (SEE) process on sample surface due to its extremely fast establishment process. The insulator surface is merely positively charged. Surface charges gradually expand from cathode toward anode with the application of impulses, which needs ∼10 impulses to reach a saturated charged surface. A linear relationship is obtained between saturated surface potential and applied voltage.

International audience; Electrostatic charge generated by friction is well known but poorly understood. The aim of this study is to evaluate the effects of various factors involved in the frictional conformal-contact. The study focused on the tribocharging process between two polymer slabs. As it is a multi-factorial process with several interacting variables, the experimental design methodology was employed for its modeling. Three factors were taken into consideration and their domains of variation established as follows; contact force, from 2 to 10 N; charging time, from 10 to 290 s and the frequency of back-and-forth sliding motion, from 0.5 to 1.5 Hz. The distribution of the electric charge at the surface of polymers was measured by the auto-compensated inductive probe connected to an electrostatic voltmeter. A mathematical model allowing the evaluation of the effects of the various factors and of their interactions was obtained. A comparison between the triboelectic behavior of PTFE, PVC and ABS was made. It was found that electric potential increases with the contact force and the charging time, but decreases with the frequency of the back-and-forth sliding motion.