Ground Electrode Research Articles

Characteristics of three-electrode pulsed surface dielectric barrier discharge: streamer-to-spark transition and hydrodynamic expansion

Streamer-to-spark transition and hydrodynamic expansion in a three-electrode pulsed surface dielectric barrier discharge are studied under atmospheric-pressure air. Three sequential discharge processes of the primary streamer, transitional streamer and spark phase during a single pulse are observed from the time-resolved plasma morphologies. The primary streamer and transitional streamer phases, with a rising voltage and low current, followed by a spark phase with a rapidly falling pulse and ascending current are characterized. Images of the discharge development show that the transitional streamer is maintained in the ionization channel after the primary streamer bridges the high-voltage electrode and the second grounded electrode. When the transitional streamer develops to a certain level, the streamer discharge transfers into the spark discharge. As a result, two shock waves are induced in the two exposed electrode domains, and then merge into a single ellipse during the process of hydrodynamic expansion. Boltzmann plots indicate that the electron temperature is 4.815 eV in the initial phase of spark discharge and gradually decreases in the spark phase. Stark broadening of the O atomic line shows that the electron density is 7.06 × 1017 cm−3 during the spark phase.

Characteristic studies on positive and negative streamers of double-sided pulsed surface dielectric barrier discharge

The mechanisms of streamer generation and propagation in double-sided pulsed surface dielectric barrier discharge (SDBD) on both sides have been analyzed and investigated by experiment and numerical simulation. The fully exposed asymmetric SDBD has two discharge processes located on the high voltage electrode (HVE) side and the ground electrode (GE) side. Discharge images of the HVE side and GE side are taken by a digital camera under continuous pulse and ICCD (Intensified Charge Coupled Device) is utilized to diagnose the generation and propagation of streamers in single pulse discharge. In order to understand the physical mechanisms of streamer evolution more deeply, we establish a 2D simulation model and analyze it from the aspects of electron density, ion density, reduced electric field and electron impact ionization source term. The results show that the primary and secondary discharges on the HVE side and the GE side of the double-sided SDBD are composed of positive streamer and negative streamer, respectively. On the HVE side, the accumulation of positive charges on the dielectric surface causes the direction of the electric field to reverse, which is the principal factor for the polarity reversal of the streamer. On the GE side, both the negative charges accumulated on the dielectric surface and the falling voltage are the key factors for the streamer polarity switch.

Transmission Line Dynamic Circuit Model for Effective Length of Ground Electrode Under Lightning Transients

The effective length of the ground electrode is one of the primary research interests of lightning grounding system design. In this article, using a practical numerical analysis, a new expression for estimating the effective length of the simple ground electrode is proposed. A new dynamic circuit model based on the transmission line is developed to derive the expression. The model considers the soil ionization, frequency-dependent soil parameters, mutual reactance, and skin effect. Several rigorous impulse test simulations are performed on different electrode lengths, soil properties, and lightning currents to estimate the effective length of ground electrode numerically. A new expression is arrived at using the curve-fitting and optimization technique from the relationships of the effective length with soil resistivity, impulse rise time, and current. The proposed dynamic model and the expression to obtain the effective length are validated by published results.

The position of ground electrode affects electrocardiographic parameters in horses.

Background and Aim:Improper attachment of the grounding lead is one of the artifacts and causes difficulty in interpretation of ECG. This study aimed to examine the effects of the position of a ground electrode on electrocardiographic (ECG) parameters in horses.Materials and Methods:Sixteen Arabian horses without any cardiac problems were included in this study. The animals were divided into two groups, the base-apex lead method 1 (BA1 method) and the base-apex lead method 2 (BA2 method) with the reposition of the ground limb electrode to the xiphoid. ECG recordings (paper speed=25 mm/s and calibration=10 mm/mV) were performed to obtain six limb leads (leads I, II, III, aVR, aVL, and aVF). The amplitude and duration of P waves and QRS complexes, PR interval, QT interval, and T duration were analyzed. T wave morphology was observed. Heart rate was evaluated by using R-R interval in each recording.Results:Heart rate, P duration and amplitude, PR interval and T duration, and QRS duration and amplitude were not significantly different between the BA1 and the BA2 method, except that the BA2 method had a significantly higher QT interval than did the BA1 method (p<0.05). A higher significance of the percentage of coefficient of variation was seen on the P wave amplitude and the ORS amplitude in the BA1 method when compared to BA2 method (p<0.05).Conclusion:These data indicated that base-apex lead method with reposition of the ground limb electrode to the xiphoid can decrease variation of ECG configuration and might be useful for routine ECG evaluation and monitoring in horses. The limitation of this study was the evaluation of cardiac morphology and function by echocardiography to exclude cardiac problems. In further, the studies should examine the effect of breed, age, body weight, and sex on electrocardiography parameters in horses.

Current Density Limit of DC Grounding Facilities Considering Impact on Zebrafish (Brachydanio rerio)

Grounding facilities, including high-voltage DC grounding electrodes and auxiliary anodes in impressed current cathodic protection systems, inject current into the ground. This study developed an experimental platform to determine the safe limit of current density for such facilities through an analysis of fish behavior on the platform. Zebrafish (Brachydanio rerio) were selected for the experiment and placed in a tank; two rod electrodes were used to inject direct current into the water. A wireless camera was focused on the water tank to video record possible changes in fish behavior. The output voltage of the DC power source was varied, and the trajectories of the fish under various direct current fields were recorded. A tracking program was developed to analyze the trajectories and quantify the behavior of the fish. A new method combining the trajectories of fish samples with the results of current density calculations for analysis was proposed. Results demonstrated that the zebrafish could sense current in the water and turn when exposed to certain current densities. The intensity of the current at the turning points was statistically analyzed, and the threshold of current density at which the fish could no longer tolerate the current and turned was 0.4231 A/m2.

The Effect of Discharge Mode on the Distribution of Myocardial Pulsed Electric Field-A Simulation Study for Pulsed Field Ablation of Atrial Fibrillation.

Background: At present, the effects of discharge modes of multielectrode catheters on the distribution of pulsed electric fields have not been completely clarified. Therefore, the control of the distribution of the pulsed electric field by selecting the discharge mode remains one of the key technical problems to be solved. Methods: We constructed a model including myocardium, blood, and a flower catheter. Subsequently, by setting different positive and ground electrodes, we simulated the electric field distribution in the myocardium of four discharge modes (A, B, C, and D) before and after the catheter rotation and analyzed their mechanisms. Results: Modes B, C, and D formed a continuous circumferential ablation lesion without the rotation of the catheter, with depths of 1.6 mm, 2.7 mm, and 0.7 mm, respectively. After the catheter rotation, the four modes could form a continuous circumferential ablation lesion with widths of 10.8 mm, 10.6 mm, 11.8 mm, and 11.5 mm, respectively, and depths of 5.2 mm, 2.7 mm, 4.7 mm, and 4.0 mm, respectively. Conclusions: The discharge mode directly affects the electric field distribution in the myocardium. Our results can help improve PFA procedures and provide enlightenment for the design of the discharge mode with multielectrode catheters.

Reactive species production and toluene degradation in an expanded streamer discharge plasma induced by a floating plate electrode

In this work, a novel positive pulsed wire-plate-wire (w-p-w) streamer discharge reactor is developed by introducing a floating plate electrode based on the previous wire-wire (w-w) reactor to attain a larger plasma propagation and improve the toluene degradation performance. The streamer propagation characteristics, distribution of·OH, toluene degradation efficiency, and process efficiency of reactive species production of the w-p-w reactor were studied and found to be highly related to the position of the floating plate electrode. ICCD images show that an intensive negative streamer can be generated from the ground electrode in the w-p-w reactor, which differs from the corona-like negative discharge in the w-w reactor. The position of the floating electrode decides the distance of the positive discharge (d+) and the negative discharge (d-), subsequently affecting the reactive species production and toluene degradation of the w-p-w reactor. When the d+ /d- reaches 1:1 where a relatively symmetrical and even distribution of·OH is achieved over the discharge gap, the toluene degradation efficiency and CO2 selectivity is 17% and 14% respectively higher than that of the w-w reactor at 230 J/L. According to a kinetic model including competition by the reaction intermediates, the highest process efficiency of reactive species production is obtained when d+ /d-= 1:1 in the w-p-w reactor, consistent with its superior toluene degradation performance. FTIR results indicate that the types of toluene degradation byproducts are not affected by the insertion of the floating electrode, however, a more thorough toluene degradation can be achieved in the w-p-w reactor.

Rio Madeira HVDC System: Commissioning of the Ground Electrode for Bipole 2 at Porto Velho

The original ground electrode of the Madeira River HVDC transmission system, bipole 2, was discarded due to the risk of saturation of the transformers in the Converter Substation of Porto Velho, located 15 km away, during the monopolar operation with ground return. After an extensive geophysical survey, a new site was selected, 40 km from the converter substation. For the confirmation of the new site, it was built in the central area of the site, a single-well 47 m deep test electrode, interconnected to the original 15 km electrode line by an additional 40 km long temporary line. A new electrode was then designed. This paper summarizes the test electrode procedure and the activities developed for the new electrode commissioning after its construction, which can be divided into two phases–pre-commissioning and commissioning. The electrode pre-commissioning was performed before its energization for the evaluation of the integrity of its components. The commissioning tests started with electrode energization, employing the electrode line, and an unbalanced bipole operation, which allowed the evaluation of its electrical performance. However, the main objective of the paper is the evaluation of the electrode resistance, which is an essential HVDC electrode parameter.

Simulation Study on Lightning Impulse Characteristics of Flexible Graphite Composite Grounding Materials Applied to Grounding Grid of Power System

The flexible graphite composite grounding electrode is a non-metallic grounding electrode with good electrical conductivity, corrosion resistance and non-ferromagnetic properties. In order to analyze the impulse characteristics of the graphite composite grounding electrode, this paper builds a frequency domain electrical network model and an equivalent radius iterative algorithm, considering skin effect, inductance effect, capacitance effect and spark discharge effect. The impulse characteristics of typical metal grounding electrodes and graphite composite grounding electrodes are analyzed by simulation. The research results show that: Compared with the traditional metal grounding electrode, the graphite composite grounding electrode has a smaller skin and inductance effect under the action of the impulse current, and a better current flowing capability; as the soil resistivity increases, the inductance effect and the skin effect are weakened, while the spark discharge effect is gradually enhanced and dominates. The spark discharge effect can effectively decrease the grounding resistance. The obtained critical value of the normalized parameter of 412 kA Ω, can be taken as the threshold to discriminate the conditions with dominate inductance effect from the conditions with dominant spark discharge effect.

Analytical Solution for the Transient Current Induced along the Vertical Grounding Electrode

The paper deals with the analysis of the Pocklington integro-differential equation in the time domain and its analytical solution for the transient current induced along the vertical grounding electrode and, as such, represents a continuation of the research pertaining to the horizontal grounding electrode previously reported by one of the authors. The electrode is excited by a current source impressed at one end of the electrode, representing the model of the lightning strike current. A novel analytical solution is derived using the Laplace transform. Results obtained with this time domain solution are compared with the results obtained via analytical solution of the corresponding Pocklington equation in the frequency domain in conjunction with inverse fast Fourier transform (IFFT). The results obtained via different methods are shown to be in a very good agreement. The results of the time domain analytical solution for the vertical electrode are also compared with the results of the time domain analytical solution for the horizontal electrode, where greater influence of earth-air interface on an induced current is observed. These procedures can be implemented as benchmarking techniques as well as tools for rapid estimation of the observed phenomena.

MMC-HVDC line fault identification scheme based on single-ended transient voltage information entropy

High resistance faults are the main cause of protection refusal action in high voltage direct current transmission line protection based on modular multilevel converters (MMC-HVDC). Furthermore, noise can affect the protection method. It is imperative to mitigate the High resistance faults and the influence of noise on the protection method. This paper analyzes the reasons for the difference in the initial voltage slopes of the internal and external faults under the traveling wave level. Subsequently, it analyzes the reasons for the difference in the complexity of the internal and external fault waveforms. Based on these analyses, a complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) information entropy method for line fault identification in the presence of white noise is proposed in this paper. The fault identification criteria are subsequently used to identify the internal and external faults. The transmission model of 77 level bipolar MMC-HVDC system grounded via a grounding electrode lead is simulated in the RTDS. The results show that the proposed method can enhance the anti-interference ability of the signal, identify the high resistance fault effectively and reliably, and avoid the error problem caused by a synchronous clock.

Analysis of soil impulse discharge characteristics based on optical‐electrical synchronous observation

The impulse performance of grounding electrodes highly depends on soil impulse discharge characteristics. The analysis of soil discharge dynamic process images is helpful to understand the impulse discharge mechanism of grounding electrodes. This paper designed an optical-electrical synchronous observation platform for simulate soil (SiO2 crystal) discharge, and discharge dynamic process images is obtained by high-speed camera. Through analysing breakdown delay time and thermal power before breakdown, it is found that soil impulse discharge is mainly an electrical breakdown process, and soil ionization intensity is positively correlated with the light intensity emitted by whole soil sample in breakdown channel development stage. The time from voltage application to the occurrence of ionization is defined as initial ionization delay time (IIDT). Using image processing technology, the change curve of optical image average grayscale value with time in the process of soil discharge is obtained, and a calculation method of IIDT is proposed by comparing the difference between average grayscale value curve and background image average grayscale value. Experiment results show that IIDT is negatively correlated with impulse voltage, particle size and water content, but not with salt content.

Stimulating the Cochlear Apex Without Longer Electrodes: Preliminary Results With a New Approach.

To investigate a new surgical and signal processing technique that provides apical stimulation of the cochlea using a cochlear implant without extending the length of the electrode array. Three adult patients who underwent cochlear implantation using this new technique. The patients received a cochlear implant. The surgery differed from the standard approach in that a ground electrode was placed in the cochlear helicotrema via an apical cochleostomy rather than in its typical location underneath the temporalis muscle. Clinical fitting was modified such that low frequencies were represented using the apically placed electrode as a ground. Pitch scaling and speech recognition. All surgeries were successful with no complications. Pitch scaling demonstrated that use of the apically placed electrode as a ground lowered the perceived pitch of electric stimulation relative to monopolar stimulation. Speech understanding was improved compared with preoperative scores. The new surgical approach and clinical fitting are feasible. A lower pitch is perceived when using the apically placed electrode as a ground relative to stimulation using an extracochlear ground (i.e., monopolar mode), suggesting that stimulation can be provided more apically without the use of a longer electrode array. Further work is required to determine potential improvements in outcomes and optimal signal processing for the new approach.

CO2 dissociation in a packed bed DBD reactor: effect of streamer discharge

Non-thermal plasma catalysis, as a special heterogeneous catalytic reaction, needs to consider both gas discharge and catalytic reaction. Packed bed dielectric barrier discharge (PB-DBD) is widely used in non-thermal plasma catalysis, but the exact control principle of gas discharge, especially streamer discharge, is not clear. In this study, therefore, the orderly arranged dielectric rods were packed in the discharge gap of PB-DBD, and the streamer discharge behaviors were controlled by adjusting their diameter(s), quantity(ies), location(s) and dielectric constant(s). Al2O3 and ZrO2 dielectric rods with dielectric constants of about 9 and 25 were used as packing material. Pure CO2 was used as reaction gas and discharge gas. Discharge images showed that stable and controllable streamer discharges can be formed between the dielectric rod and ground electrode. The intensity, width and length of the streamer discharge can be significantly changed by optimizing the dielectric constant, diameter, packing number and position of the dielectric rod, thereby affecting the CO2 conversion efficiency. Increasing dielectric constant and the distance between the dielectric rod and ground electrode can increase the intensity of streamer discharge, thus promoting the CO2 conversion efficiency. Compared with an empty reactor, after packing 24 ZrO2 dielectric rods with a diameter of 1 mm, the CO2 conversion and energy efficiency increased from 9.58% to 20.1% and from 1.67% to 2.89%, respectively. In short, this research has important implications for plasma catalysis. This study not only reveals the synergistic characteristics between streamer discharge and CO2 dissociation, but also provides an important idea for structural optimization of PB-DBD catalyst.

Ionic Wind Simulation of Wire-Aluminum Foil Electrode Structure Lifter in 2-D Space

The electrohydrodynamic (EHD)-driven lifter is an electrostatic levitation device, which can generate a driving force without any mechanical rotating component. Due to the consistency of its driving condition with the Biefeld–Brown (BB) effect, it is used for ionic air propulsion. Nowadays, various methods have been used to study the thrust generating mechanism of the lifter. However, those methods cannot concentrate on its physical changing procedure. Given this, the finite-element simulation method is used to investigate the ionic wind in a two-dimensional asymmetric electrode system of the lifter model. In this work, the physical process of corona discharge in the electrode system is simulated and analyzed. First, some empirical relationships are used to introduce a mathematical model, including the ionic wind. Second, the model is adjusted for simulation in Comsol. Finally, it can be concluded from the analysis and comparison of the results that the ionic wind’s numerical value can be affected by some structural parameters of the electrode system. Furthermore, the ionic wind’s maximum value is observed on both sides of the grounding electrode, not between the two electrodes, which is not compatible with ionic wind formation. Besides, it can be speculated that positive ions might have a force on the grounding electrode. This work provides a valuable reference to the microphysical phenomenon for the lifter.

A newly designed ignition method for miniature radio frequency ion thruster

The ignition methods used by micro-radio frequency (RF) ion thrusters have a disadvantage, that is, the starting voltage and flow rate are obviously higher than the rated value, which will easily damage the grid after long-term use. To decrease the starting voltage and flow and reduce the damage to the grid, a new ignition system is proposed in this paper. This system uses an intake pipe as the ground electrode, has an inductance coil and a pre-ionization chamber, and enables the miniature RF ion thruster (Harbin Institute of Technology's RF Ion Thruster 4, HRIT-4) to ignite at the rated voltage and flow by means of strong electric field breakdown and electromagnetic coupling. The experimental results show that when the flow rate is 1.0 SCCM, the ignition voltage is lower than 1900 V, and when the flow rate is 1.5 SCCM, the ignition voltage is lower than 1400 V.

Airborne Transient Electromagnetic Simulation: Detecting geoelectric structures for HVdc monopole operation

Geoelectric structures have great influence on the earth surface potential (ESP) induced by ground return currents (GRCs) in high-voltage dc (HVdc) monopolar operations. Traditional ground-detection methods are cumbersome due to the long distances between the grounding electrodes of substations. The airborne transient electromagnetic (ATEM) method has become a popular technique for exploring large-scale geoelectric structures. First, we analyze the influences of different 3D geoelectric models on the fluctuation in GRCs and propose a 3D model to evaluate ATEM simulations. Second, we present an efficient ATEM simulation method based on a finite-element (FE) algorithm to obtain the 3D geoelectric structure used to calculate the ESP. The stability and convergence rate of solving FE systems are improved by using an induced dimension reduction (IDR) solution algorithm. The detectability of the ATEM method is validated by an inversion case based on the Occam algorithm. The numerical results demonstrate that our robust ATEM simulation method is useful for detecting the 3D geoelectric structure used in ESP analysis.

A Novel Planar Grounded Capacitively Coupled Contactless Conductivity Detector for Microchip Electrophoresis.

In the microchip electrophoresis with capacitively coupled contactless conductivity detection, the stray capacitance of the detector causes high background noise, which seriously affects the sensitivity and stability of the detection system. To reduce the effect, a novel design of planar grounded capacitively coupled contactless conductivity detector (PG-C4D) based on printed circuit board (PCB) is proposed. The entire circuit plane except the sensing electrodes is covered by the ground electrode, greatly reducing the stray capacitance. The efficacy of the design has been verified by the electrical field simulation and the electrophoresis detection experiments of inorganic ions. The baseline intensity of the PG-C4D was less than 1/6 of that of the traditional C4D. The PG-C4D with the new design also demonstrated a good repeatability of migration time, peak area, and peak height (n = 5, relative standard deviation, RSD ≤ 0.3%, 3%, and 4%, respectively), and good linear coefficients within the range of 0.05–0.75 mM (R2 ≥ 0.986). The detection sensitivity of K+, Na+, and Li+ reached 0.05, 0.1, and 0.1 mM respectively. Those results prove that the new design is an effective and economical approach which can improve sensitivity and repeatability of a PCB based PG-C4D, which indicate a great application potential in agricultural and environmental monitoring.

Calculation of DC current distribution in AC power system near HVDC grounding electrode in subregional layered soil

The DC current from the grounding electrode of a HVDC system may result in great ground potential differences in a large area, and may flow into the widely distributed systems with dispersed grounding points such as AC power grid which may disturb the systems. Soil resistivity is the most important factor that affects the current distribution. The heterogeneous soil has a subregional layered structure on the whole. In this paper, a numerical approach coupling the boundary element method with complex image method is developed to calculate the current fields in the subregional layered soil. By using indirect boundary element method, the subregional layered soil is turned into a uniformly layered soil in which the electric field is calculated with the help of complex image method. The calculation scale is much smaller than that just using the boundary element method, and the complex image method can be extended to calculate the electric field in soil with complex structure. Then, an equivalent circuit network in the complex soil is extracted and is coupled with the equivalent circuit of AC power grid, with which the DC current distribution in an AC power grid around a HVDC grounding electrode is analyzed. The results show that even in the area where the ground electrode is located, the ground potential gradient in the subregional layered soil is different from the result in the uniformly layered soil, which leads to a difference in the current flowing through the neutral point of the substation. The closer the DC grounding electrode or the substation is to the interface of the subregional layered soil, the greater the effect on the ground potential around the DC grounding electrode and the DC current flowing through the substation.

Effectiveness of Large Soil Grain Sizes in Studying Impulse Characteristics of Soil

There have been many published studies analysing the impulse characteristics of soil and various soil properties. Some of these published results are found to be largely different and inconsistent from one study to another. Soil properties may be complex in nature, and its characteristics under high impulse conditions are influenced by many factors, which result in inconsistency in the results. Nevertheless, it has been known that under high impulse conditions, ionisation in the soil would occur due to air discharges in the air voids within the soil, and interfaces between the soil and the ground electrodes. It is also possible that the expansion of the ionisation zone, leading to the occurrence of breakdown in soil, gives better conduction in soil, producing longer streamers and higher magnitudes of current. However, limited study on the impulse breakdown characteristics of soil is found, which was believed to have been due to voltage/current magnitudes that are not high enough to cause the occurrence of soil breakdown. It is important to determine the factors that will cause breakdown to occur in soil when subjected under high impulse conditions since this will give more effective grounding systems when subjected to high impulse conditions. This paper shows that the soil grain size contributes to the most pronounced factor in influencing the soil characteristics under high impulse conditions, in comparison to any other factors. This paper considers thirty-two soil samples containing various percentages of water contents, subjected to high impulse conditions. The soil samples are housed in a hemispherical environment with two different active electrodes, and pre-breakdown and breakdown characteristics of various soils, configurations and percentage of water content are studied.