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The groundings of the power distribution, signaling, and power systems of a railway system are individually performed to realize fail safe, and the groundings are often installed in close proximity. Thus, when a grounding electrode is invaded by a lightning current, its ground potential rises together with the potential of the adjacent grounding electrodes; hence, there is a possibility of a large overvoltage being applied to the connected devices. In this paper, we have investigated the potential spread between two rod-shaped electrodes widely used in the grounding of the power, signal, and distribution systems of a railway system using the finite-difference time-domain method. The results of this paper are organized in such a way that the extent of the potential spread to the neighboring grounding electrodes can be understood from information such as the grounding resistivity at the installation location of the ground electrode and the wavefront duration of the lightning current, and these findings will be useful for grounding design. We also investigate the effect of the insulator between two neighboring electrodes to prevent the potential spread. [ABSTRACT FROM AUTHOR]

This paper embodies the results of experimental studies of a dielectric barrier discharge low-temperature nonequilibrium plasma reactor that runs in air and nitrogen at atmospheric-pressure conceived for surface treatment applications. A homemade reactor, of typical plane-to-plane geometry with the dielectric covering the upper electrode which is stressed by a high voltage (40 kV, 3–20 kHz) is used. Electrical signals (current and voltage), optical emission spectroscopy records, and total light emission measured by photomultiplier have been analyzed and used to distinguish different plasma regimes which are studied for the treatment of a lignocellulosic material (sugarcane bagasse). In the filamentary discharge regime, the gas temperature of few tens of degree Celsius above the ambient one was determined, the electronic temperature of some electronvolts and electron density in the range of 1012–1013 cm−3 were estimated. Plasma treated pellets of sugarcane bagasse were analyzed by diffuse reflectance infrared Fourier transform spectrometry and the relative results obtained under filamentary discharge regime have shown significant degradation of the lignin macromolecule. It has been shown important modifications on the lignocellulosic material, namely, the plasma attacks drastically the lignin bonds. Strong modification of lignin was observed near wavenumber of 3400 cm−1, due to stretching vibrations of OH, and for the band 1114 cm−1 which is related to C=C and C=O stretching. Severe decrease of the band intensity 1596 cm−1, which due to C=C stretching and C=O, is also a result of the treatments done in this paper. [ABSTRACT FROM AUTHOR]

The design and development of a new nonintrusive-type true-rms ac voltage measurement probe are presented in this paper. The measurement circuit of the capacitively coupled nonintrusive voltage sensor is designed to provide an output that is directly proportional to the rms value of unknown ac voltage $\text{V}_{\mathrm {X}}$ , which contains the power frequency (50 or 60 Hz) component along with the typical harmonic frequency components due to nonlinear loads. This is accomplished by a specially designed autobalancing signal conditioning circuit. The existing noncontact probes are designed for a set frequency and will not provide accurate rms value of a signal that has multiple frequency components. The output is independent of the coupling capacitance between the probe electrode and the insulated wire/cable under measurement. Thus, the sensor has low sensitivity to the variation due to the probe-to-wire capacitance, good linearity (0.95%), and accuracy (0.88%) over a range of voltages (0–1000 V) tested. Various parameters that affect the performance of the probe are analyzed, quantified, and discussed in this paper. A prototype of the probe along with the proposed autobalancing circuit has been designed and developed. The prototype has been tested in detail to evaluate the accuracy, linearity, and repeatability. The results obtained established the practicality of the proposed scheme. [ABSTRACT FROM AUTHOR]

This paper suggests an advanced approach in the verification of the adequacy of a grounding system (GS) located in a common zone of influence with other GSs, taking into account the mutual interferences between the GSs. In fact, the presence of other GSs can transfer inadmissible touch and step voltages on the testing GS, particularly sensitive for critical power systems as data centers and hospitals. The safety of a local GS or of a global GS (GGS) does not admit uncontrolled interferences. Simulation programs assume a relevant importance, because they allow analyzing the interferences of GSs, particularly in operational difficulties for the tests. GSs have to maintain within the installation lifetime their characteristics of integrity and continuity and their safety performances; hence, they require a management program. This paper highlights the relevance of intrinsically safe GSs that guarantee safe touch/step voltages lower than permissible permanent voltages such as GGSs. GSs in city centers and urban and industrial areas evolve in time. Each installation of a new GS can influence the performance of the GSs existent in the area. Inspections and measurements are also necessary, following variations that can influence essential requirements. [ABSTRACT FROM AUTHOR]

Due to its low-loss and high dielectric strength, polypropylene is widely used as electrical insulation material in pulse capacitors. In order to study its breakdown characteristics for nanosecond voltage pulses, an experimental setup was designed to generate voltage pulses with a 10%–90% rise time of 38 ns and a full width at half maximum of about 90 ns. Tests of the three polypropylene films with thicknesses of 12, 15, and $18~\mu \text{m}$ were performed. In addition, hundreds of nanoseconds pulse and dc voltage were also applied for comparison. The experimental results reveal that most of the breakdown occurs during the front edge of the pulse for tens of nanoseconds pulse, and the breakdown strengths of the three kinds of polypropylene films are almost identical for different applied voltages, which show a weak correlation between the thickness of the dielectric and the breakdown field. The expected breakdown strength of tens of nanoseconds pulse defined in this paper is not significantly higher than the mean value of the hundreds of nanoseconds pulse and the dc condition, suggesting that the breakdown of a thin polypropylene film is mainly determined by the electrical field but not the voltage-time cumulative effect. All these observations strengthen the conclusion that the breakdown of a thin polypropylene film is an intrinsic phenomenon. [ABSTRACT FROM AUTHOR]

The International Electrotechnical Commission Standard 61936-1 “Power installations exceeding 1 kV a.c.” defines the “global grounding system” (GGS) as an equivalent grounding system that ensures “no dangerous touch voltages.” This paper deals with an analysis of the parameters that characterize the behavior of grounding systems (GSs) operating in the same zone of influence (ZOI) and proposes to recognize four levels of “globality.” With this aim, the geometric criterion and the safety criterion are introduced to identify the ZOI. The safety criterion allows for identifying a GGS and characterizing the global ZOI of a GGS. This paper highlights the relevance of recognizing what is intrinsically safe for a GS that guarantees safe touch/step voltages lower than permissible permanent voltages. An integration of many coexisting GSs for constitution and extension, naturally, can reach the level of an intrinsically safe GS and, hence, of a GGS. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel conductance parallel-wire array probe (CPAP) to measure the interface characteristics of segregated horizontal oil–water two-phase flows. A measurement system of CPAP is designed to make it work in a cyclic excitation mode and detect the interfacial heights at different locations of a pipe cross section. A finite-element analysis and a static calibration experiment are conducted to access the relationship between the interfacial height and the dimension conductance detected by the CPAP. Through carrying out a dynamic experiment of horizontal oil–water flows, the 3-D oil–water interfaces are reconstructed using the CPAP responses to study the interfacial evolution and its effect on the droplet detachment. Finally, the average fluctuations of the oil–water interfaces are extracted based on the reconstructed 3-D oil–water interface. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of charge redistribution on supercapacitor charge capacity by experimentally estimating the charge capacity bounds. An analysis of a physics-based $RC$ ladder circuit model for supercapacitors reveals the theoretical bounds and provides guidelines for designing experiments to estimate the bounds. The upper bound corresponds to a long time constant voltage charging process and the lower bound is established using a charging process with the largest possible current. Bounds of two types of supercapacitor charge capacity are estimated: the total charge stored in the supercapacitor that can be released during multiple discharging processes and the utilized charge delivered during one discharging action. The relationship between the utilized charge capacity and the discharge current is examined and different patterns are observed depending on the supercapacitor state of charge. For a fully charged supercapacitor, the utilized capacity increases when the discharge current decreases. For a supercapaictor partially charged by a relatively large current, the utilized capacity is dependent on both the discharge current and the supercapacitor operation voltage range. The difference between the bounds is significant for both types of charge capacity. These observations provide guidelines for optimizing the supercapacitor charging and discharging policies for different applications. [ABSTRACT FROM AUTHOR]

This paper presents the results of field measurements of touch voltages occurring in buildings under ground-fault conditions, as well as resistance-to-ground of edifices of different nature (i.e., masonry, reinforced concrete, etc.). The goal of this experimental study was to confirm that ground-fault potential profiles and touch voltages in buildings do depend on the make-up of the structure, the floor material, the configuration and location of the grounding electrodes with respect to the point of touch, and the presence of metalwork (e.g., metal pipes) bonded to the ground system. The results of the above measurements, involving buildings of different construction type, are herein presented and discussed, and were obtained following the analytical models illustrated in Part I of this paper. [ABSTRACT FROM AUTHOR]

Global earthing systems (GESs), which are created by the interconnection of local earthing systems, should guarantee the absence of dangerous touch voltages. According to international standards, one of the reasons for this safety characteristic of GESs is that medium-voltage and low-voltage grounding systems form a quasi-equipotential area. Typical examples of GESs are in city centers due to the high number of interconnected grounding systems in the area. For this reason, in addition to ground grids, other metallic parts with different primary functions shall be also considered, e.g., water and gas pipes, tramway tracks, and building foundations can modify the electric potential distribution in the area. In this paper, a model based on the Maxwell's subareas method (MaSM) is used to evaluate how buried metallic parts, which are not intentionally connected to ground grids, modify the electric potential on the soil surface. First, the MaSM model is validated with experimental measurements on a simple electrode configuration. The measured voltages are compared with the MaSM results and with the results obtained with a finite-element method model simulated with COMSOL Multiphysics. Then, the simulations are carried out on a realistic urban test case. [ABSTRACT FROM AUTHOR]

The adequacy of grounding systems has to be periodically verified in operational time. With urban development and building growth adjacent to power systems as high-voltage/medium-voltage substations, it is very rare to have an area around with sufficient accessibility for installing potential and current electrodes. This paper discusses a safety criterion to verify the effectiveness of a grounding system. This criterion suggests conservative tests for both ground potential rise and touch and step voltages that allow to verify the grounding systems' effectiveness in areas with reduced accessibility and to monitor its evolution in time. [ABSTRACT FROM AUTHOR]

Grounding resistance is an important basic index used to ensure the safety and reliability of grounding systems. In this paper, a method for grounding resistance measurement based on the fall of potential curve is proposed that can be performed using a 2–2.5D lead wire length. In this method, the potential distribution near the auxiliary current electrode is tested and is used as the main analysis and measurement parameter. Based on the relationship between the potential distribution generated by the grounding grid and the current electrode, the grounding resistance of the grounding grid can be deduced. First, the voltages between the grounding grid and the earth surface potential near the current electrode are measured; then, the ground potential rise (GPR) of the grounding grid is calculated through theoretical analysis and numerical calculation; and finally, the grounding resistance is calculated by dividing the potential by the test current. This method avoids the complex task of accurate compensation point location required for traditional measurement methods, and can be performed easily and quickly using a short lead wire. Measurement results from spot testing show that the proposed method can meet the accuracy requirements of engineering testing. [ABSTRACT FROM AUTHOR]

Each grounding system (GS) needs periodical measurements to control its adequacy to the safety conditions. The tests of step and touch voltages are the sole measurements available in urban or industrial areas with reduced accessibility. In fact, in these areas, the classic measurements used to verify the electrical characteristics of the GS generally present some operational difficulties. The auxiliary current electrodes can only be located at short distances, and thus, the test methods and techniques result in conservative values in comparison with the prospected true values measurable by adopting a remote auxiliary electrode. The locations of auxiliary current electrodes at short distance make it easier to keep them permanently installed and to permit the monitoring of the adequacy of GS. This paper presents the measuring touch/step voltages procedure that provides conservative results showing some case studies done in GS of high voltage/medium voltage substations. It is essential to have the map of the constitution and configuration of the GS to know its data and the location of the various equipment and buildings, the presence of extraneous conductive parts inside, and in proximity of the substation, such as other GS. The field measurements require a good experience of the operator that can be learned by carrying out measurements in cases of GS with influence zone accessible, so that it is possible to compare the traditional method with a remote electrode and the method at short distance. [ABSTRACT FROM PUBLISHER]

The three-electrode plasma reactor for the treatment of polluted gases combines a dielectric-barrier discharge with a remote third electrode, designed to enhance streamer propagation in a relatively large region. In this paper, experimental studies of the electrical magnitudes of the discharge for different electrode bias voltage configurations are presented. Also, the Laplacian electric field distribution in the interelectrode gap is calculated for each configuration. The degradation efficiency of NO in an N2 atmosphere for the different configurations is also reported. It is found that the discharge is generated only for that electrode bias configuration for which the external electric field promotes the streamer propagation across the electrode gap. Also, for a triggered discharge, the reactor efficiency for the removal of NO changes with the different electrode bias configurations. This result can be explained in terms of the electric field intensity. The configuration with higher external electric field improves the number of streamers propagating in the interelectrode gap so that more reactive species generated in the streamers are effectively entrained in the gas flow to be treated. [ABSTRACT FROM AUTHOR]

The audible noise (AN) production mechanism caused by corona discharge in ultrahigh voltage transmission lines is less understood. The study on sound pressure characteristic is necessary to obtain the inherent relation between AN and corona discharge. In this paper, the experimental research on single-point direct current (dc) corona discharge was evolved and the time-domain sound pressure waveform was obtained using capacitor microphone. The experiment results show that the dc corona discharge comprises multiple subsequent discharge pulses. The discharge voltage and the electrode polarity have a direct effect on the rising time and pulsed width of the single current pulse. The waveform of sound pressure produced by single discharge is a bipolar microsecond pulse, which lags behind the current pulse in time domain. The time delay is propagation time of sound signal from the discharge spot to the measurement spot. Based on the corona discharge characteristic in dc voltage, the experiment platform for nanosecond pulsed discharge was built to obtain the relation between discharge parameter and sound parameter. The characteristics of sound pressure in different discharge conditions were analyzed. The study results indicate that the sound pressure produced by pulsed discharge is similar with that produced by corona discharge. The experiment platform for pulsed discharge can be used to research the AN production mechanism by dc corona discharge. [ABSTRACT FROM AUTHOR]

Potential drop (PD) measurements are well established for use in materials testing and are commonly used for crack growth and strain monitoring. Traditionally, the experimenter has a choice between employing direct current (dc) or alternating current (ac), both of which have strengths and limitations. The dc measurements are afflicted by competing spurious dc signals and, therefore, require large measurement currents (tens or hundreds of amperes) to improve the signal-to-noise ratio, which in turn leads to the significant resistive Joule heating. The ac measurements have superior noise performance due to the utilization of phase-sensitive detection and a lower spectral noise density but are subject to the skin effect and are, therefore, not well suited to high-accuracy scientific studies of ferromagnetic materials. In this paper, a quasi-dc monitoring system is presented which uses very low-frequency (0.3–30-Hz) current which combines the positive attributes of both dc and ac while mitigating the negatives. Bespoke equipment has been developed that is capable of low-noise measurements in the demanding quasi-dc regime. A creep crack growth test and fatigue test are used to compare noise performance and measurement power against alternative DCPD equipment. The combination of the quasi-dc methodology and the specially designed electronics yields exceptionally low-noise measurements using typically 100–400 mA; at 400 mA, the quasi-dc system achieves a 13-fold improvement in signal-to-noise ratio compared to a 25-A dc system. The reduction in measurement current from 25 A to 400 mA represents a ~3900-fold reduction in measurement power, effectively eliminating resistive heating and enabling much simpler experimental arrangements. [ABSTRACT FROM AUTHOR]

The ability to monitor neurochemical dynamics in target brain regions with a high degree of temporal resolution has assisted researchers in investigating the pathogenesis, and pathophysiology of a variety of neurological and psychiatric disorders. Current systems for neurochemical monitoring are bulky or expensive, limiting widespread exploration of this research field and preventing large-scale parallel experimentation. In this paper, we present a new miniaturized research platform, the TinyFSCV system, which can be used to monitor dynamic changes in neurochemicals through Fast-Scan Cyclic Voltammetry (FSCV). This system contains a precision voltage output circuit that can accurately output potentials between −0.55 to 2 V and scan a connected electrochemical cell at up to 400 V/s, the required speed to sense most neurochemicals with FSCV. In addition, the device includes precision current measurement circuity with a measurement range of −115 to $115~\mu \text{A}$ capable of taking measurements at up to 56 KS/s. Four experiments are conducted to demonstrate the capability of the system. These consisted of: static bench tests, static ferrocene tests, and static and dynamic dopamine tests. These experiments demonstrate the ability of the miniaturized platform to accurately sense and measure neurochemicals. Ultimately, the TinyFSCV system is a platform that can enable large-scale, low-cost parallel experimentation to take place in the field of neurochemical monitoring. In addition, this device will increase the accessibility of neurochemical sensing, providing advanced tools and techniques to more researchers, and facilitating widespread exploration of the field of neurodynamics. [ABSTRACT FROM AUTHOR]

In order to study the effect of glaze erosion on the performance of porcelain post insulator, an inclined plane (IP) test similar to IEC 60587 standard was conducted on a cylindrical insulator sample under laboratory conditions for ac voltage, and a new test method, called graphite-layer-based glaze erosion test was proposed in this paper and performed on the sheds of a 40.5 kV post insulator. The experimental details of the graphite-layerbased glaze erosion test was introduced, the technical points of which are coating a graphite layer on the surface of the shed using a brush mold which contains multiple hollowed-out rhombic grids, and arranging high voltage electrode at shed root and grounded electrode at shed edge respectively at both ends of the graphite layer, so as to form continuous and stable surface arcing under ac voltage and therefore achieve desired glaze electrical erosion effect. The graphite layer is a uniform viscous mixture made up with flake graphite and liquid glue according to a quality ratio of 1:1.2. The arcing process, arc current characteristics, surface temperature, and glaze erosion appearance were analyzed. Leakage current under power frequency voltage and flashover voltage of the eroded cylindrical insulator by IP test were measured, while porosity test and scanning electron microscopy (SEM) tests were conducted on samples taken from the sheds after graphite-layer-based glaze erosion test. The results indicate that glaze erosion will decrease both electrical and mechanical performance of the porcelain post insulator. The new test method proposed in this paper has been proved to be effective for glaze erosion test and consumes much less time compared with IP test, which provides a new idea for accelerated tracking and erosion test of glaze and porcelain materials so as to study the aging characteristics of porcelain insulators. [ABSTRACT FROM AUTHOR]

To study the dc insulation design of gas insulated switchgear (GIS), the insulation characteristics under lightning impulse (LI) voltage with a superimposed dc voltage (superimposed voltage) must be clarified. The paper experimentally examined the GIS breakdown characteristics under this superimposed voltage. The test models simulating an insulator creepage surface were used for which consideration of the influence of dc voltage among various other GIS insulating elements is particularly important. To be specific, a cylindrical model made of epoxy resin or fiber-reinforced plastic (FRP) as the material and a conical epoxy spacer model were tested. For the cylindrical model, a cap-shaped electrode was placed on the insulator and a small gap was established between the end of the electrode and the insulator. When the dc breakdown voltages were measured using these samples, they were higher for the applied voltage of positive polarity than that of negative polarity for all samples. The post-test observation of the electrification condition revealed greater electrification on the insulator surface for the applied voltage of positive polarity. The electrification charges are considered to have relaxed the electric field and increased the breakdown voltage. Subsequently, the breakdown test was conducted using a superimposed voltage, whereby a foregoing dc voltage was applied to samples for a certain period, whereupon a LI voltage was applied with the dc voltage continually applied. The breakdown voltage when the LI voltage and dc voltage had equivalent polarity was approximately same to the LI alone breakdown voltage. Conversely, when they were opposite in polarity, the breakdown voltage under the superimposed voltage obviously tended to decrease from the LI alone breakdown voltage. It is considered attributable to the fact that the insulator surface was electrified by the foregoing dc voltage and applying LI voltage opposite in polarity to this electrification intensified the electric field where the breakdown started to occur. Accordingly, it emerged that the GIS breakdown characteristics changed significantly depending on the polarity combinations of LI and dc voltages. The influence of these polarities must be taken into consideration when studying the GIS dc insulation design. [ABSTRACT FROM AUTHOR]

Grounding systems (GSs) must be tested periodically in order to maintain the touch voltage (TV) and step voltage (SV) below a safe value in all of the zones of the installation. Measurements of the ground resistance and of the TV and SV are typically done by the fall-of-potential (FoP) method, locating the auxiliary current electrode at remote distance to test the effective behavior of the GS. In urban areas, it could be very complicated or impossible to install the auxiliary current electrode as required, not having area around with sufficient accessibility. At this aim, this paper describes a methodology of using multiple current electrodes at short distances, modifying the classic FoP practice, so that the measurements of TV and SV are always conservative. The adequacy of a GS is verified if the values of the TV and SV, tested inside and in the vicinity of the GS, are below the permissible limits, regardless if they are true or conservatively increased. Thus, the measured TV and SV by the suggested method, always conservative, allow verifying the adequacy of GSs, in the cases where it is impossible to locate the remote auxiliary electrode. [ABSTRACT FROM AUTHOR]

The ionic wind technology produced by corona discharge has drawn massive attention as a new driving force, especially in flow control applications. This paper introduces a non-friction test platform with air track in order to gauge the thrust produced by a 19 points-to-grid and a 31 points-to-grid EHD gas pump. Five major parameters of the EHD gas pump are focused, which includes the electrode gap, the spacing of point electrode, the curvature of point tips, the applied voltage and the discharge current. Through experimental study, the relationships between the performance of thrust of EHD gas pump and its major parameters are clarified. Eventually, a method of achieving high thrust with a low power consumption is brought up. [ABSTRACT FROM PUBLISHER]

In this paper, power frequency breakdown tests as well as positive and negative lightning impulse breakdown tests have been performed. The breakdown voltages of CF3I/CO2/N2, c-C4F8/CO2/N2, CF3I/c-C4F8/CO2 gas mixtures have been measured in different gas pressures, mixing ratios and electrodes distances in slightly non-uniform electric fields. In addition, the breakdown voltages of CF3I/c-C4F8/CO2 gas mixtures have been comparatively analyzed with SF6/CO2, CF3I/CO2, c-C4F8/CO2 gas mixtures. The results show that CO2 is excellent buffer gas to CF3I and c-C4F8 as it has synergistic effect. The power frequency breakdown voltages of CF3I/c-C4F8/CO2 gas mixtures are basically the same as that of c-C4F8/CO2 gas mixtures, which are higher than that of CF3I/CO2 gas mixtures. Besides, the 50% breakdown voltage of c- C4F8/CF3I/CO2 gas mixtures under lightning impulse are higher than that of CF3I/CO2. Compared with SF6/CO2 gas mixtures, CF3I/c-C4F8/CO2 gas mixtures have the same insulating performance in short electrode distance, and show more excellent insulating ability at an electrode distance more than 20mm. [ABSTRACT FROM AUTHOR]

This paper describes a device that emulates propagation of action potentials along a peripheral nerve, suitable for reproducible testing of bio-potential recording systems using nerve cuff electrodes. The system is a microcontroller-based stand-alone instrument which uses established nerve and electrode models to represent neural activity of real nerves recorded with a nerve cuff interface, taking into consideration electrode impedance, voltages picked up by the electrodes, and action potential propagation characteristics. The system emulates different scenarios including compound action potentials with selectable propagation velocities and naturally occurring nerve traffic from different velocity fiber populations. Measured results from a prototype implementation are reported and compared with in vitro recordings from Xenopus Laevis frog sciatic nerve, demonstrating that the electrophysiological setting is represented to a satisfactory degree, useful for the development, optimization and characterization of future recording systems. [ABSTRACT FROM AUTHOR]

In contrast to extensive publication on the behavior of space charge in polymeric insulation materials subject to individual dc or ac voltages, space charge in the situation of composite voltages has not yet been reported. In this paper, the dynamics of space charge in polyethylene subjected to combined ac and dc voltages have been experimentally investigated using the pulsed electroacoustic technique. Results show that combined voltages could significantly enhance the space charge accumulation. The dc component voltage determines the charge accumulation in the bulk of polyethylene while ac component influences the charge density on the electrodes. The amount of charge in the bulk depends on the ratio between ac and dc voltage components. This result is important to understand the electrical performance of high voltage equipment where insulation may experience the combined ac and dc voltages. [ABSTRACT FROM AUTHOR]

In this paper, a device for accurate electrical measurements for nanosecond repetitive pulsed discharges (NRPDs) is presented. The experimental setup developed is based on an interelectrode system integrated in a transverse electromagnetic cell. This setup allows synchronizing the voltage and current measurements with a 4-GHz frequency bandwidth, corresponding to 250-ps pulse duration. A coaxial-shaped sharp metallic needle serves as a probe for current measurements. The needle probe is also the point electrode of a point-to-plane system used to generate discharges. The experimental setup was used to electrically characterize NRP corona and diffuse discharges, in negative polarity. Discharge current pulses with rise times less than 1 ns and amplitudes up to 120 mA were measured. The energy deposited by discharges was also determined. [ABSTRACT FROM PUBLISHER]

Pulsed electro-acoustic measurement system is one of the versatile systems for measurement of charges accumulated in dielectric materials. The charge is measured as a voltage signal observed at an amplifier output which gets input from an acoustic sensor. Because of limited frequency bandwidth of the acoustic sensor and amplifier, all experimentally acquired signals require processing technique like deconvolution to estimate original signal (charge). Due to presence of noise in all experimental signals, deconvolution turns out to be an optimization problem. The optimum deconvolution involves estimation of optimum value of a deconvolution parameter, also known as regularization parameter. This parameter controls the tradeoff between signal distortion and noise minimization. In literature, several methods were suggested for estimation of optimum value of regularization parameter. However, each method yields a different estimate for the parameter. In this paper, the suitability of these conventional methods is investigated for estimation of space charge. Also a simple, yet, better estimation method, specific to space charge estimation, is presented. Interesting results and discussion on efficacy of these methods against, simple spectral division followed by Gaussian filtering, is also presented. [ABSTRACT FROM PUBLISHER]

The uneven distribution of voltage along the composite insulator strings harmed their electrical and mechanical properties heavily, which threatened the safety of power system. Inserting metal electrodes in the silicone rubber sheds of composite insulator helps increase their self-capacitance, thereby ameliorating the voltage distribution along the string. In this paper, a new structure of weather sheds with metal electrodes inserted has been designed. Tests on composite insulators with different metal electrodes setup were conducted to examine their voltage distribution performance. Corona inception voltage of the mentioned composite insulators was obtained by a remote monitoring system as a criterion of the voltage distribution performance. Simulation model of the insulators were set up and calculation of their voltage and electric field distribution were carried out by finite element method (FEM). The calculation result was in good compliance with the experiment result. The applied voltage at the live end of composite insulator decreased by 4% when inserting electrodes in the weather sheds, which was verified by both experiment and simulation results. [ABSTRACT FROM AUTHOR]

As one of the most commonly used insulating mediums, in electrical discharge, sulfur hexafluoride (SF6) will decompose in the presence of water vapor and oxygen, producing various gaseous by-products. It is shown that the concentrations and production rates of SF6 gaseous decomposition by-products heavily depend on electrical field to gas density ratio (E/N) under corona discharge. Regarding the difficulty in measuring E and N, applied voltage and the SF6 pressure, are proposed in this paper to describe E and N, respectively. Several experiments of 50-Hz AC discharges were carried out under different applied voltages and different SF6 pressures using point-to-plane electrodes. The concentrations of SF6 gaseous by-products were measured by a gas chromatograph-mass spectrometer system (GS/MS). Experimental data show that the concentrations of SF6 gaseous by-products increase while the ratio (SOF2+SO2)/SO2F2 decreases, with increasing applied voltage. The concentrations decrease with increasing pressure of SF6. The formation mechanisms of SF6 gaseous by-products with the variations of applied voltage and the SF6 pressure are discussed, such as SO2F2, SOF2+SO2, CF4, and CO2 and so on. An experimental expression is derived which connects the SF6 pressure with the concentration of the decomposition by-products. [ABSTRACT FROM AUTHOR]

The paper reviews previous work on the DC inclined plane test and suggests equivalent DC voltage levels in parallel to AC voltage in the ASTM inclined plane tracking and erosion test. The aim of this work is to provide a basis for standardizing the inclined plane test for DC voltage. Round robin tests done in five laboratories on five specimens of a silicone rubber material were done with the purpose of establishing appropriate ratios by which the equivalent DC voltages can be determined with respect to the corresponding AC voltages. These levels were determined as 67% and 87%, for +DC and ?DC respectively, of the AC initial tracking voltage, and for practical purposes, these levels are rounded to 70 and 90%. [ABSTRACT FROM AUTHOR]

This paper considers the possibility of numerical generation of pulse breakdown voltage random variable in SF6 gas. A theoretically constructed model was tested at low, medium, and high values of \(pd\) product (pressure \(\times \) interelectrode distance), ranging from 0.1 mbar mm to 50 bar mm. Numerical generation of the statistic sample of the pulse breakdown voltage random variable was performed in homogenous and nonhomogenous fields. Variable experiment parameters were the pulse rise rates (from 1 to 400 kV/ \(\mu \) s). Obtained results indicate that the proposed theoretical–numerical model is absolutely satisfactory at high values of \(pd\) product (10–50 bar mm), which is the very region of SF6 gas application. At lower values of \(pd\) product (less than 10 bar mm), there are certain deviations between a numerically generated statistic sample of the pulse breakdown voltage random variable and the one obtained experimentally. However, this deviation is not relevant from the aspect of engineering practice. [ABSTRACT FROM PUBLISHER]

Charge accumulation on an insulator surface under AC electric field is uncertain and is different from DC. In this paper, a method of extracting the phase of voltage truncation time is proposed. The characteristics of charge distribution on an insulator surface under AC voltage is obtained, and the relationship between the voltage phase and the surface charge distribution is investigated. The measurement results of charge distribution and the microscopic discharge process are compared and analyzed which can overcome the deficiency of the traditional off-line measuring method. In addition, the effect of voltage amplitude and insulator material characteristics on the surface charge are studied. It is shown that the charge distribution on an insulator surface shows a three-tier concentric circular structure, and the distribution characteristic of the charge is closely related to the phase of the AC voltage truncation time and the insulation material. The charge density is also affected by the voltage amplitude. [ABSTRACT FROM AUTHOR]

The primary mode of the pulsed positive streamer discharge in water has been studied by the shadowgraph imaging techniques utilizing an ultrahigh speed frame camera system. The propagation speed and the flare angle of the fan-shaped primary streamer were measured and their dependence on the water conductivity and the applied voltage were investigated. The initial propagation speed of the primary streamer is about 4–6 km/s and rapidly decreases to about 1.5 km/s. The water conductivity and the applied voltage have no significant influence on the propagation speed of the primary streamer. The flare angle of fan-shaped structure of the primary streamer ranges from 150° to 210°, and increases with increasing the applied voltage. In the voltage range 15 to 17 kV, the water conductivity has no significant influence on the flare angle of the fan-shaped structure, but as the applied voltage increases beyond 18 kV, the flare angle of the fan-shaped structure decreases with increasing the water conductivity. Based on the plasma discharge in a bubble and the fact that the radius of primary streamer is about 200–400 $\mu \text{m}$ , the primary streamer in water seems to be incepted by the positive ions at the head of the discharge filament generated in the microbubble, which penetrates into the water through spattering process and forms a gaseous trajectory in the bulk water. [ABSTRACT FROM AUTHOR]

DC switchgear using gas circuit breakers (CBs) in parallel to a LC-resonant path is used for decades already. This “passive oscillation” topology relies on negative damping of the oscillating current made possible by the fact that the voltage drop over the CB decreases with increasing current. This concept is cheap and reliable since it does not require any active components besides the mechanical breaker. However, the achievable breaking times and maximum interruptable current amplitude highly depend on the $u(i)$ characteristic of the axially blown arc inside the breaker. Improvements to the breaking chamber could move the maximal breakable current to higher values and reduce the time to current zero. Analyzing which parameters influence the arc voltage is crucial for this optimization. Knowing which axial segments contribute how much to the total arc voltage enables a deeper understanding and possibilities to improve performance. Direct measurements of voltages inside the nozzle of a CB are not feasible; therefore, an indirect method was developed. The contact positions in a model CB were varied systematically, and by evaluating the $u$ ($i$) curves of 13 different configurations, the voltage drop of eight segments of 2 cm length was calculated. It is shown that most of the voltage drops over the converging nozzle part, where gas density and acceleration is high. These segments also exhibit beneficial behavior with $\text{d}u/\text{d}i$ being negative. The method was validated by comparing the extracted results with suitable direct measurements. [ABSTRACT FROM AUTHOR]

An experiment was performed to study the effect of a magnetic field on the initial radius of a metallic gas-puff Z-pinch with a power-law density profile. The IMRI-5 generator (450 kA and 450 ns) was used as a driver. The preembedded axial magnetic field $B_{z0}$ was varied from 0 to 1.5 T. To determine the initial pinch radius $r_{0}$ , the function $r(t)$ was used that was derived from the time dependence of the pinch inductance $L(t)$. The time-dependent inductance $L(t)$ , in turn, was determined as a function of load voltage $V_{\mathrm{ load}}(t)$ and pinch current $I(t)$. The function $r(t)$ was verified using time-gated optical imaging. Measurements have shown that the initial radius of the metallic gas-puff Z-pinch decreased from 7 to 8 cm at $B_{z0} = 0$ to 2.1–1.7 cm at $B_{z0} = 1.5$ T. The decrease in initial radius $r_{0}$ was accounted for by the effect of the magnetic field on the ion gyroradius. [ABSTRACT FROM AUTHOR]

In pulse-modulated (PM) radio frequency (RF) atmospheric pressure glow discharges (APGDs), the alpha–gamma mode transition is analyzed and confirmed with I – V characteristic curve. The behaviors of alpha–gamma mode transition in PM RF APGDs are more complicated than that in continuous wave (CW) RF APGDs. In terms of amplitude of applied RF voltage just before a pulse falling edge ( V\mathrm {appls} ), the critical V\mathrm {appls} at the alpha–gamma mode transition in a PM RF APGD increases with the decreasing duty ratio and is higher than that of a CW RF APGD. The feature of the alpha–gamma mode transition in a PM RF APGD is attributed to the gas temperature rise depending on both the RF voltage and duty ratio. The alpha–gamma mode transition is verified to occur at the initial phase of a PM RF APGD and the onset is earlier at a higher transient RF voltage. As the mode transition occurs, a RF voltage spike is formed in the pulse waveform. [ABSTRACT FROM AUTHOR]

To date, there has not been a completely satisfactory comparison between theory and experiment for a ground system that is excited by a current with a submicrosecond rise time. This requires careful definitions of both the measured and calculated voltages because the electric field is no longer conservative and voltages become path dependent. An experiment performed by EdF in the late 1970s has been carefully analyzed and compared with a simulation using full-wave theory. The comparison is excellent, and this example can now be used as a “gold standard” to which approximate grounding theories can be compared. [ABSTRACT FROM AUTHOR]

Electrical impedance tomography is a functional reconstruction technique for detection inside the human body. Considering the anisotropic physiological characteristics, we apply a generalized back projection algorithm to a 2-D simulation model. To solve the anisotropic inverse problem, we design an excitation calibration configuration to amend voltage data. The imaging results reconstructed by the new method in 2-D model show good quality assessed by several quantitative metrics. [ABSTRACT FROM PUBLISHER]

To analyze the electric field around bipolar resectoscopes, used in urology, in terms of reasons for late complications after a surgical treatment a flexible multielectrode system was developed to measure the 3-D potential distribution. A high spatial resolution is achieved with the least possible individual measurements under the conditions of a quasi-static electric field. A flexible arrangement and positioning of the measuring points in the vertical direction of the experimental environment enable an adjustable spatial resolution and the selection of the region of interest. The existing influence of the multielectrode system on the measuring results is described and a correction method is presented to achieve significant results. Thus, the multielectrode system is usable for a comparative study of bipolar resectoscopes varying in the arrangement of resection and return electrode. [ABSTRACT FROM PUBLISHER]

Two-phase flow is widely encountered in process engineering and related scientific research. Understanding flow patterns and their transitions is important to discover the fluid mechanics of two-phase flow. In order to investigate the complexity of horizontal gas–water two-phase flow and accurately identify the flow pattern, a 16-electrode electrical resistance tomography was used to collect the spatial distribution of phase fraction. The experimental data are compressed and treated as a 16-D time series corresponding to the average response of the phase distribution in the field of each exciting electrode, which can be studied with graph-based techniques. Three connectivity metrics—correlation, coherence, and the phase-lag index are extracted from the multivariate time series, which correspond to the amplitude, power, and phase-based connectivity among signals, respectively. Together, these connectivity metrics make a comprehensive description of the characteristics of each flow pattern and reveal the transition process of flow patterns. The dynamic characteristics of typical flow patterns are then analyzed using the method of graph-variate signal analysis named graph-variate dynamic connectivity. [ABSTRACT FROM AUTHOR]

The determination and optimization of the rated capacitance of a capacitor voltage transformer (CVT) is very valuable for the optimal design of a CVT since it is a fundamental parameter for solving many problems such as minimizing the effect of stray capacitance (SC), ensuring a high accuracy of voltage measurement, and fast transient response. SC is known to seriously affect the capacitance of an ultra-high-voltage (UHV) CVT resulting in a larger additional measurement error and a higher false operation rate of relay protection; it is usually unknown or poorly quantified and cannot be measured directly. A new effective and reliable method for rated capacitance design of a new UHV equipotential shielding CVT under the interference of SCs is proposed and successfully demonstrated in this work. An equivalent mathematical model is established to derive the CVT rated capacitance and the SCs are extracted using a finite element method. The performance of this method is verified in the experiment to demonstrate the effectiveness of the method. [ABSTRACT FROM AUTHOR]

In general, a polymer insulator to which high voltage is applied reaches a complete volume breakdown state through a propagation of electrical trees. A flame retardant such as metal hydroxide has an endothermic reaction and releases water at high temperature. If the energy of the partial discharge is consumed by a dehydration reaction, the growth length of electrical tree will be restrained and the polymer's insulator lifetime will improve. Therefore, we studied the effects of metal hydroxide on treeing under high electric fields and confirmed that the voltage lifetime of the epoxy resin with 30 phr of magnesium hydroxide was approximately 100 times longer than the neat epoxy resin. We also detected magnesium oxide by electron beam diffraction analysis of the fillers located contiguous to the electrical trees. The dehydration reaction of magnesium hydroxide took place. The suppression of tree growth by fillers is generally explained by a barrier effect, but such fillers as metal hydroxide that generated the dehydration reaction provide another mechanism for the restraint of tree growth. [ABSTRACT FROM AUTHOR]

In the present contribution, we analyze and quantify micro-discharge currents originating from rough electrode surfaces in HVDC gas insulated switchgear (GIS) applications. These currents can be significantly larger than those in the gas phase caused by natural ionization or those from bulk conduction in the solid insulators. They may thus dominate the charging of the insulator surface and are thus a key dimensioning criterion. Five different electrode systems with different, but clearly defined, roughness were designed. To quantify the amplitude of the micro discharge current as a function of the electrical field strength on the electrode surface, the consequence of these discharges in the form of accumulated charges on the surface of a PTFE sample was measured. The measurements were compared to simulation results from a model that uses the Townsend approximation for unipolar saturation ionic current, which is a widely used approximation in many areas of applications. As a main finding of our investigations, to avoid micro discharges, electrical field strengths of 7.1 kV/mm should not be exceeded in HVDC GIS design using typical industrial electrode roughness around 2 ?m and 0.5 MPa SF6. [ABSTRACT FROM AUTHOR]

Breakdown measurements are carried out in liquids under point-sphere and pointplane electrode geometries, over a large range of gap distances up to 35 cm. Non-polar hydrocarbon liquids with different chemical structures are studied: saturated, aromatic, polyaromatic, mineral oils, and ester. Two high voltage impulse shapes are used: the standard lightning impulse (LI), and a specific ?step? impulse (ST). Step impulses are favorable to interpret breakdown measurements since the applied voltage remains constant while prebreakdown streamers propagate. Conversely, with lightning impulse and long gaps the propagation of streamers with a low propagation velocity (a few km/s) is quenched due to the rapidly decaying voltage. In this case, breakdown can result only from the propagation of faster streamers, which appear in very different conditions according to the liquid nature. The results obtained allow us to interpret the large variations of breakdown voltage observed in large gaps, when either the high voltage impulse shape or the liquid nature is changed. These results also help to define proper conditions for testing and comparing liquids. Testing with lightning impulse in short gaps, such as in standard tests, does not provides data relevant for very high voltage applications. [ABSTRACT FROM AUTHOR]

Electrical impedance tomography (EIT) is used to image the electrical property distribution of a tissue under test. An EIT system comprises complex hardware and software modules, which are typically designed for a specific application. Upgrading these modules is a time-consuming process, and requires rigorous testing to ensure proper functioning of new modules with the existing ones. To this end, we developed a modular and reconfigurable data acquisition (DAQ) system using National Instruments' (NI) hardware and software modules, which offer inherent compatibility over generations of hardware and software revisions. The system can be configured to use up to 32-channels. This EIT system can be used to interchangeably apply current or voltage signal, and measure the tissue response in a semi-parallel fashion. A novel signal averaging algorithm, and 512-point fast Fourier transform (FFT) computation block was implemented on the FPGA. FFT output bins were classified as signal or noise. Signal bins constitute a tissue's response to a pure or mixed tone signal. Signal bins' data can be used for traditional applications, as well as synchronous frequency-difference imaging. Noise bins were used to compute noise power on the FPGA. Noise power represents a metric of signal quality, and can be used to ensure proper tissue-electrode contact. Allocation of these computationally expensive tasks to the FPGA reduced the required bandwidth between PC, and the FPGA for high frame rate EIT. In 16-channel configuration, with a signal-averaging factor of 8, the DAQ frame rate at 100 kHz exceeded 110 frames s ^-1, and signal-to-noise ratio exceeded 90 dB across the spectrum. Reciprocity error was found to be < 1\% for frequencies up to 1 MHz. Static imaging experiments were performed on a high-conductivity inclusion placed in a saline filled tank; the inclusion was clearly localized in the reconstructions obtained for both absolute current and voltage mode data. [ABSTRACT FROM PUBLISHER]

Platinum (Pt) is the most commonly used metal for stimulating electrodes. This study aims to determine the amount of charge that can be delivered without causing irreversible electrochemical reactions (charge injection capacity, Q inj) of Pt macroelectrodes (geometric surface area >0.001 cm2) in vitro and in vivo using voltage transient measurements. Pt macroelectrodes were stimulated with biphasic charge-balanced cathodic-first constant-current pulses in phosphate buffered saline. Potential excursions were measured (versus Ag/AgCl electrode) and used to determine Qinj. The in vitro Qinj were compared to those measured in vivo following: acute and chronic implantation close to the retina; chronic intracochlear implantation; and acute subdural implantation, in the cat. Qinj increased with pulsewidth from 35 to 54 μC/cm2 for respective pulse widths of 100 to 3200 μs per phase in vitro. Qinj was significantly less in vivo. There was no significant difference in Qinj between acutely (3.84 to 16.6 μC/cm2 with pulsewidths of 100 to 3200 μs) and chronically (6.99 to 15.8 μC/cm2 with pulsewidths of 200 to 3200 μs) implanted suprachoroidal electrodes. Intracochlear Qinj was not different to suprachoroidal Qinj, while subdural Qinj was significantly less than the suprachoroidal Q inj (p < 0.05). These results have important implications in providing guidelines on Qinj for the safe use of Pt stimulating macroelectrodes and question the relevance of measuring Qinj in vivo using voltage transients. [ABSTRACT FROM PUBLISHER]

Capacitive electrodes are a promising alternative to the conventional adhesive electrodes for ECG measurements. They provide more comfort to the patient when integrated in everyday objects (e.g., beds or seats) for long-term monitoring. However, the application of capacitive sensors is limited by their high sensitivity to motion artifacts. For example, motion at the body–electrode interface causes variations of the coupling capacitance which, in the presence of a dc voltage across the coupling capacitor, create strong artifacts in the measurements. The origin, relevance, and reduction of this specific and important type of artifacts are studied here. An injection signal is exploited to track the variations of the coupling capacitance in real time. This information is then used by an identification scheme to estimate the artifacts and subtract them from the measurements. The method was evaluated in simulations, lab environments, and in a real-life recording on an adult's chest. For the type of artifact under study, a strong artifact reduction ranging from 40 dB for simulated data to 9 dB for a given real-life recording was achieved. The proposed method is automated, does not require any knowledge about the measurement system parameters, and provides an online estimate for the dc voltage across the coupling capacitor. [ABSTRACT FROM PUBLISHER]

We have used a pulsed power generator based on stacking MOSFET switches to create breakdown in water and generate shock waves. The pulses with an exponential decay have a maximum voltage of 4 kV. With the pulse application of approximately \(50~\mu \) s, the breakdown voltage is approximately 3 kV. Postbreakdown events, such as shock wave emission and bubble expansion and collapse were recorded by a fast camera. The shock speed was recorded as 1.5 km/s and the maximum bubble diameter is 2.3 mm. This shock wave generator can be used on the microscope and provides a means of studying the shock impact on biological cells. [ABSTRACT FROM PUBLISHER]