Earth Electrode Research Articles

Determination of Threshold Electric Field of Practical Earthing Systems by FEM and Experimental Work

In this paper, the results of an experimental study and finite-element method (FEM) of the impulse characteristics of simply built practical earthing systems consisting of 2, 3, and 4 rods are reported. These electrodes are installed at three outdoor test sites having nonuniform soil and different soil profiles to provide variation in the result analysis. The tests on these electrodes were intended to determine the nonlinear characteristics of earthing systems which can be seen from their voltage and current traces and reduction of their impulse resistance values. Two-rod electrodes in the highest soil resistivity profile showed the largest reductions in impulse resistance due to soil ionization compared with other earth electrodes. Computer simulations of all the nine earthing systems using the FEM are also conducted, which showed good agreement with the measured results. It was also found from FEM that threshold electric field Ec is dependent on the earthing systems configurations, soil profile, and impulse resistances.

The Analysis of Transient Grounding Resistance of Portable Horizontal Grid Earth Electrodes

Based on current situation of mobile equipments earth devices, a new type of portable horizontal grid earth electrode has been designed. With the impulse ground measurement system, different number of earth electrodes responses to double exponential pulse current have been tested on cement grounds. Impulse waves of voltage and current have been gotten by experiments, and the curve of Transient Grounding Resistance (TGR) can be calculated. The analysis of discharging capacity of horizontal grid earth electrodes in time domain has great significance in the design of mobile equipments earth devices.

Design and performance of a high pressure, flowing liquid dielectric peaking switch

A repetitive, high-voltage liquid dielectric switch for high-power microwave (HPM) applications is currently being developed and investigated at the French-German Research Institute of Saint-Louis (ISL). The switch was designed to be implemented in existing coaxial pulse line structures and is being driven by compact modular Marx generators at rise times of about 7 ns and output voltages up to 400 kV. A pumping system consisting of a gear pump and a piston diaphragm pump was installed, which allowed the operation of the switch at flow rates up to 100 ml/s and pressures up to 1800 kPa. Galden, a perfluoropolyether, was chosen as the liquid dielectric. Computational fluid dynamics (CFD) simulations of liquid flow through the switch were carried out. The results led to optimized electrode geometry with an asymmetric radial inward flow between the concave copper-tungsten electrodes and an axial outward flow through a bore hole inside the earth electrode, in order to minimize the risk of a turbulent flow through the switch. The measurements of the achievable breakdown field strength showed a significant dependency on the pressure and on the type of the Galden fluid used. A Galden fluid with a high boiling temperature is to be preferred, as it has the least tendency to contain micro gas bubbles. Maximum breakdown field strength of 10.1 MV/cm at a pressure of 2050 kPa and at a gap distance of 0.28 mm is reported using Galden HT270. This represents an increase of 270% in comparison to the breakdown field strength of 3.8 MV/cm at atmospheric pressure. The typical switch rise time was 0.49 ns; the achieved voltage rise time was 5.6×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> V/s. Initial two-pulse experiments were carried out to investigate the achievable pulse repetition rate by charging the switch directly with a high voltage capacitor charger at a charging voltage of 50 kV and a charging time of 210 μs. The measured 90% recovery time of 4.0 ms at a pressure of 320 kPa shows the potential of the liquid dielectric switch to operate at frequencies above 200 Hz.

Development of ionization chamber for in-line intensity monitoring of large profile parametric X-ray beam

An in-line ionization chamber has been developed for the real-time measurement of the absolute intensity of the pulsed parametric X-ray (PXR) beam during irradiation experiments. The quasi-monochromatic PXR generating system was developed at the Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University. In contrast to typical narrow X-ray beams in synchrotron radiation facilities, the PXR beam profile is as large as approximately 100 mm in diameter with rather uniform flux distribution at the X-ray output port in the experimental hall. The energy of the PXR beam ranges from 5 to 34 keV, which is specified by the PXR target crystal plane and its geometrical condition. The ionization chamber is of a plane parallel type employing 6-μm thick double-sided aluminum vapor-deposited polyester films for the plane electrodes through which the X-ray beam passes. The plane bias electrode has been placed at an equal distance of 25 mm from the two plane earth electrodes that act as the beam windows with an aperture diameter of 120 mm. Due to the pulsed property of the PXR beam and the geometrical configuration of the ionization chamber, the charge-sensitive preamplifier output pulse height represents an integral of the fast electron current, corresponding to a half of the total ionization charge produced by the beam. The intensity of the PXR beam has been measured for various X-ray energies by using nitrogen and argon, respectively, as the filling gas.

Variations of Absorbance, TOC and pH in Humate Solution by Water Surface Pulsed Discharge

Investigation on removal of persistent substances in water is performed by surface pulse discharge spreaded on the water utilizing pulsed power source. Humate, the target in this study, is one of the persistent substances. A Blumlein type pulse forming network (B-PFN) is provided in the work. The discharge gap in atmosphere that is a main part of the reactor is constructed by multi-needles and surface of the humate solution filled in a bath with mesh sheet as the earth electrode. In this study, temporal variations of the absorbance, pH and total organic carbon concentration (TOC) in the humate solution are investigated with observations by a spectrophotometer, an EC/pH meter and a total organic carbon analyzer. From the results, the decrease of absorbance in the humate solution is observed together with pH and total organic carbon concentration. We consider that the decreases of these quantities on humate solution are attributed by ultraviolet rays emitted from the surface discharge as well as the pulsed discharge in bubbles.

The application of a novel Ti/SnO2–Sb2O3/PTFE-La-Ce-β-PbO2 anode on the degradation of cationic gold yellow X-GL in sono-electrochemical oxidation system

In this study, the novel PbO2 electrodes co-doped with rare earth (La and Ce) were prepared by electrodeposition technique. The rare earth co-doped electrode applied as an anode was carefully studied for the degradation of cationic gold yellow X-GL, in sono-electrochemical oxidation system. Optimal degradation conditions were achieved by investigating the effects of different parameters, such as initial concentrations, pH levels, electrolyte concentrations, current densities, on the constant frequency and power of ultrasound. Under the optimal conditions, removal rates of cationic gold yellow X-GL and COD were about 99.95% and 74.03%, respectively, after 2h degradation. Moreover, the synergistic effect in sono-electrochemical oxidation system was also certificated and discussed. In addition, SEM images indicated that the surface of Ti/SnO2–Sb2O3/PTFE-La-Ce-β-PbO2 electrode had the dense structure and the preferred crystalline orientation, which could be helpful to improve the mass transportation and mineralization of cationic gold yellow X-GL.

EMI Analysis in Electrical Drives Under Lightning Surge Conditions

In this paper, a complete model of a power drive system including the earth electrodes is proposed to evaluate electromagnetic conducted interference due to lightning pulses. Circuit model of a power drive system is joined with a full-wave approach for the simulation of the time behavior of the grounding system. The proposed model enables to predict the electromagnetic conducted interference generated in the power drive system when lightning conditions involve the earth electrodes.

Technique to increase the effective length of practical earth electrodes: Simulation and field test results

Field experiments and computer simulations of two sectionalized horizontal earth electrodes are presented. The electrodes were energized using various voltage sources (dc, and transients of different shapes), and measurements of current and voltage magnitudes along the length of the electrode were examined. Furthermore, by incrementally increasing the length of the test electrodes, the effective length of the earth electrodes was determined experimentally. The experimental and simulation results show reasonably close agreement which gives confidence in predicting the effective length. A new method is proposed to increase the effective length of the horizontal earth electrode by installing an additional insulated parallel conductor which is bonded to the horizontal electrode at points along its length. Such insulated conductor allows current to be distributed further away from the injection point without high leakage as would occur with standard horizontal electrodes buried in the ground. The results show that the current and voltage distributions are modified such that a greater length of buried conductor is utilized and that this contributes to an additional reduction in the earth impedance, and hence the earth potential rise at the point of current injection. The effect of the proposed technique is simulated on a practical wind turbine earthing design, and shows significant gains.

The impulse dielectric behavior of N2 gas in sphere-plane gap

The focus of this work has been on the pre-breakdown phenomena and the breakdown characteristics of N2 gas in a sphere-plane gap under various impulse voltages. Both electrical and optical experimental investigation methods were used. Following parameters were considered: gas pressure range from 0.2 to 0.6 MPa, electric field utilization factor of the electrode configuration 71%, positive and negative impulse waveforms with the rise time of 500 ns, 1.2 μs and 180 μs. The observed discharge processes before the breakdown through the light emission images by the ICCD camera are in good agreement with the streamer mechanism. Under both polarity stresses, discharges are initially concentrated around the tip of the sphere and later pointing towards the earth electrode. However, negative streamers are thinner and more diffuse. As expected, the breakdown voltages for negative polarity are lower than those for positive polarity regardless of the gas pressure and shape of the applied impulse voltage. The breakdown voltage is increased with shortening the rise time of pulse waveforms. As a substitute for SF6, N2 gas under pressures above 0.3 MPa can reach the standard rated withstand voltage for 24 kV C-GIS.

Effect of the shape of earth electrode and the earth system of the ground potential distribution

Effect of the shape of earth electrode and the earth system of the ground potential distribution

Lightning Protection and Grounding of Building in the First Phase in Handan-Xingtai Section of the Middle Route of South-to-North Water Diversion Project

Based on the condition of the South-to-North Water Diversion Project,this paper introduces the lightning protection principles of hydrostructure and electrical equipments according to the reasons of lightning from three aspects,namely using air-termination and earth-termination system to discharge lightning current,protecting against lightning surging on incoming services and limiting over-voltage on equipments.There are five primary protection measures:distributaries,voltage sharing,shield,grounding and clamp protection.In the design of lightning protection,natural earth electrode is adopted with priority supplemented by artificial earth electrode in order to reduce the cost.Double or treble-deck grounding grid is designed for flumes,hoist chambers,transformer substations and other buildings so as to protect the equipments and discharge lightning current through grounding.

Computer Simulation of Lightning Strikes to a Horizontally Buried Earth-Electrode: A Parametric Analysis

Earthing systems made basically from earth electrodes need to be effectively designed to meet the increasing demand on safety. The aim of this paper is to use computer simulation to analyze the transient response of a horizontally buried earth electrode and how this response is influenced by factors like the energization type, the soil parameters, the depth of burial and the earth electrode geometry. The model used is the transmission line theory with a general application of the telegraphy equations which are solved numerically using the finite difference time domain scheme while the per unit length parameters were computed from a well known integral expression using the moment’s method. The results of the parametric analysis are validated by comparison with those found in literature.

Recommendations for grounding systems in lightning protection systems

This paper presents some practical recommendations for designing grounding systems as part of an integral protection system against lightning strikes. These recommendations are made taking into account the results of academic software whose development was based on hybrid electromagnetic method and the method of moments. This paper presents the results of impedance and transient voltage for triangle, wye, counterpoises and mesh configurations. Some recommendation are made concerning the use and characteristics of earth electrodes, for example effective counterpoise length, where to locate grounding rods, where to connect down conductors in a mesh and the potential difference between points on the same grounding electrodes. These recommendations guide a systems' designer to ensure greater benefit from grounding setups without wasting money.

Procedure to carry out quality checks in photovoltaic grid-connected systems: Six cases of study

Assessing the correct operation of PV grid-connected systems (PVGCS) is paramount not only for mere energy and profitability concerns but also for safety reasons. Intended to this purpose, the IEC 62446 standard is open to some tests to be required in some circumstances, in addition to those stated in this document. Our work proposes a procedure to carry out quality checks in PVGCS complying with this standard and dealing with some tests not mentioned in it – namely, PV generator peak power measurement, inverter response and earth electrode measurement – so that the verification of the system gets more comprehensive. This procedure was carried out in six PV plants sited in different locations with a Mediterranean climate in Spain. The most remarkable results of this experimental campaign may be summarized as follows: an excellent on-site behavior of the inverters, in general very good figures for the isolation and earth electrode resistance and a scarcely relevant existence of hot spots. On the down side, some figures for the peak power of the tested PV generators well below their nominal value were found. The procedure described in this paper has proved to be a useful tool to assist in the verification of a PVGCS after installation and for subsequent re-inspection or maintenance.

Comparison of Degradation Phenomena on Silicone Rubbers Eroded by DC and AC Discharges

The salt fog tests for silicone rubbers (SiR) were performed under DC or AC voltage application. During a test, intensive discharges occurred around an earth electrode when positive DC voltage was applied. In the case of negative DC voltage application, intensive discharges occurred around an electrode which the voltage was applied. In other words, the intensive discharge concentrated around a cathode electrode, which caused heavy erosion around the electrode. In contrast, for the case of AC voltage application, the intensive discharge and heavy erosion did not occur.

Electromagnetic Calculation of Combined Earthing System with Ring Earth Electrode and Vertical Rods for Wind Turbine

Electromagnetic Calculation of Combined Earthing System with Ring Earth Electrode and Vertical Rods for Wind Turbine

Evaluation Of Four Local Materials As Backfill To Achieve A Low Earth Electrode Resistance

In this study, the efficiency of materials available for free, namely palm kernel oil cake, tyre ash, wood ash and powdered cocoa shell, as conductive backfill for reducing earth electrode resistance was evaluated. Earth rod of 30-cm length and 14-mm diameter was installed for each backfilling material at a site and their performance compared with that of a reference earth rod also installed at the same site. The results show that tyre ash provides a stable earth electrode resistance in both dry and wet weather conditions and improves it to about 16%.

Correlation Between Steady State and Impulse Earth Resistance Values

This study presented experimental results of earthing systems under low-magnitude currents and under high impulse currents. The details of the measuring circuit involved for both types of testing were described. Three field sites were selected. At each site, three earth electrodes configurations were used. This makes up to nine earthing systems. From both low magnitude and impulse tests, the correlation between the steady state earth resistance value and the earth resistance under fast impulse currents can be observed. The relation between the calculated and measured steady state earth resistance is also shown in this study.

SOIL IONIZATION DUE TO HIGH PULSE TRANSIENT CURRENTS LEAKED BY EARTH ELECTRODES

This paper proposes a numerical model of the soil ionization phenomena that can occur when earth electrodes are injected by high pulse transient currents, as the one associated with a direct lightning stroke. Based on finite difference time domain numerical scheme, this model ascribes the electrical breakdown in the soil to the process of discharge in the air. In fact, as soon as the local electric field overcomes the electrical strength, the air in the voids trapped among soil particles is ionized, and the current is conducted by ionized plasma paths locally grown. The dimension of these ionized air channels is strictly dependent upon the local temperature. Thus, a local heat balance is enforced in order to obtain the time variable conductivity profile of the medium. This model can be implemented both for concentrated and extended electrodes, since no hypothesis has to be enforced about the geometric shape of the ionized region. Validation of the proposed model is obtained by comparing simulation results with experimental data found in technical literature.

Circumstances affecting the protection against electrode potential rise (EPR)

In this paper the grid resistance of substations with different earth electrode and soil structures is investigated by simulation studies with the use of CDEGS (Current Distribution, Electromagnetic Fields, Grounding and Soil Structure Analysis) software code. The paper presents the effect of grid geometry, soil characteristics, the effectiveness of the vertical earth rods and the conductor diameter.