High Impulse Currents Research Articles

Effect of high resistivity soil under high impulse currents

In this paper, experimental test results of several ground electrodes surrounded with gravelly soil medium subjected to high impulse currents were studied, to investigate the effect of confined soil surround electrodes. Ground resistance measurements were performed at low magnitude of voltage and current, where the results are compared to the impulse characteristics of ground electrodes. This paper shows a significant difference in the RDC values and impulse characteristics of ground electrodes when gravelly soil medium surrounded the ground electrode in comparison to the electrodes installed in natural soil. This indicates that the confined soil around the electrode has a major effect on the performance of ground electrodes, whether at steady state or under high impulse conditions. Equivalent circuit for each tested electrode was developed with personal simulation program with integrated circuit emphasis (PSPICE), where the effect of inductance was seen in the electrodes surrounded with gravelly soil.

Magnetohydrodynamic simulation and test of compression arc-extinguishing device under icing condition

When the weather is cold and wet, the insulator and the transmission line components often undergo icing. In order to study the inhibition effect of the compression arc-extinguishing device with icing on the recovery of arc plasma conductivity and air disruptive strength, this paper will verify it through simulation and test. In the simulation part, a two-dimensional geometric model is established, and the magnetohydrodynamic equation group is used as the control equation group. The breakdown characteristics of the device with and without icing are compared, and the dynamic characteristics of the arc are studied in terms of temperature and conductivity. The results show that the temperature of the arc plasma can be reduced to 3000 K within 1 ms, and the conductivity can be reduced to 0 within 250 µs. In the test part, the suppression effect on arc current amplitude after the device with icing is subjected to high current impact is verified, and the coupling triggering method of impulse voltage and power frequency voltage is adopted to further verify the arc extinguishing condition of the device when the power frequency current continues. The results show that the amplitude of the arc produced by high current impulse decreases from 67 to 35 kA and to 0 within 1 ms after passing through the device with icing, and the current amplitude can still drop to 0 at 2.5 ms after adding the power frequency voltage. It is proved that the device with icing can inhibit the recovery of arc plasma conductivity and air disruptive strength.

Magnetic Properties of Lightning‐Induced Glass Produced From Five Mineral Phases

AbstractThe physical properties of minerals are modified by the high temperatures of volcanic lightning during explosive eruptions. Alteration involves rapid heating and volatilization, melting, and fusion of ash grains within the discharge channel, followed by rapid quenching into new glassy textures. High current impulse experiments reveal that lightning alters not only the morphology and mineralogy of volcanic ash but also its magnetic properties. We investigate lightning‐induced magnetic changes in five igneous minerals (<32 μm powders of albite, labradorite, augite, hornblende, and magnetite) by comparing hysteresis parameters before and after impulse experiments conducted at peak currents of 25 and 40 kA. Both the paramagnetic and ferrimagnetic behaviors of the samples were altered, which we interpret as a superposition of two processes. (a) Rapid melting allows iron contained within inclusions of Fe‐oxides and Fe‐bearing silicates to diffuse into the newly formed melt, thereby increasing the paramagnetism of the resulting glass. (b) Nucleation and growth of magnetite from the newly formed melt increases the ferrimagnetic behavior of the post‐experimental samples. Nominally non‐Fe‐bearing silicates like albite and labradorite have significantly increased paramagnetism and ferrimagnetism. Fe‐bearing silicates like augite and hornblende contain higher concentrations of ferrimagnetic inclusions, from which Fe diffuses into the newly formed melt, thereby increasing paramagnetism while decreasing ferrimagnetism. Experiments conducted on magnetite produced new magnetite crystals with dendritic habits. Although specific to volcanic ash, these results provide important insights into the magnetism of other materials affected by lightning on Earth, the Moon, and throughout the solar system.

Review: Factors Affecting the Performance of Ground Electrodes under High Impulse Currents

Most studies have observed that the impedance values of ground electrodes under high impulse conditions (Zimp) are lower than the resistance values under steady-state conditions (RDC). It has been suggested that this is due to the ionisation process in soil, where streamers will propagate away from the electrodes, causing an increase in the ionisation zone, thus reducing the Zimp values. The percentage difference between Zimp and RDC is found to be dependent on several factors. This paper aims to review and present the findings of previously published work on the percentage difference between Zimp and RDC in relation to various factors.

Study of Temperature Rise Characteristics and Voltammetry Characteristics of ZnO Varistor under 10/350μs Pulse Current

To study the effect of 10/350μs pulse current on the electrical performance of ZnO varistor, a high-current impulse experimental study was conducted in this paper. Firstly, the varistor was subjected to different amplitude impulse discharge experiments, and the temperature change of the varistor after the impulse was recorded. Then, the temperature of the varistor at the moment of 1 second after the pulse impulse was suffered by the Asymptotic function, and the Levenberg-Marquardt optimization algorithm was calculated to compare the temperature rise of the varistor under different current amplitudes. Finally, the upward shift of voltammetry characteristics in the high-current region after the impulse was explained according to the double Schottky barrier model and the linear chain aging theory. The results show that the higher the pulse current amplitude is, the higher the temperature rise of the varistor is at the 1s moment. The highest voltammetry characteristic upshift is caused by the 6.4kA pulse current. The temperature rise and the voltammetry characteristic drift in the high-current region are positively correlated. The results of the study can provide a reference for manufacturers to produce ZnO varistors for direct lightning protection of buildings.

Lightning Impulse Current Tests on some Electroconductive Fabrics

On the search of lightweight lightning protection materials that can be used as part of Lightning Protection Systems (LPS), we investigate some types of electroconductive fabrics by applying several high lightning impulse currents in laboratory. Samples of four commercially available electroconductive textiles were analyzed: two rip-stop, a plain-weave, a non-woven, and additionally a carbon-impregnated polymeric film. Under laboratory conditions, each sample was subject to several subsequent lightning-like currents, recording both voltage and current signals. Optical and scanning electron microscope observations were performed after tests, revealing some patterns or morphological changes on the fabric surface. Despite these changes, the investigated conductive textiles withstand the several lightning impulse currents applied. Results suggest that some conductive fabrics could be used in personal mobile shelters, to protect human beings against the earth potential rise caused by a close lightning discharge.

Impulse Characteristics of Ground Electrodes in Low Resistivity Soil

Soil properties have been known to be the factors that influence the ionization process in soil, which cause the impulse impedance, Zimpulse to be lower than that at steady state resistance, RDC. Many studies have established the relationship between the percentage reduction of Zimpulse from RDC in such that the percentage reduction is more pronounced in high resistivity soil, or in high RDC, than that at low resistivity soils. Nevertheless, Zimpulse is not the only parameter in representing the characteristics of soil under high impulse conditions, where from the voltage and current waveforms, the current rise and discharged times can also be established, where more accurate and extensive analysis of the electrical characteristics of ground electrodes subjected to high impulse currents can be achieved. This paper presents the experimental results of four ground electrodes, installed in agricultural land, with soil resistivity, of below 3 Ωm, subjected to high impulse currents, where the parameters of current rise times, Zimpulse and current discharged times were investigated. Two of these ground electrodes are having close RDC values, despite having different electrode's configurations, were also investigated. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Development and Traceability Method of a 100 kA Reference Impulse Current Measuring System

In order to improve the measurement accuracy of high impulse current, this paper presents the system composition, performance improvement and, traceability method of a 100 kA impulse current measuring system. Since the scale factor of the measuring system can be determined by the product of the scale factor of the components such as the shunt and the digital recorder, a method of component quantity traceability is proposed. Based on a shunt with rated current of 100 kA, a stable measuring system is developed. In addition, a reference impulse current calibrator and a step current generator for traceability are developed, so that the impulse scale factor of the shunt considering skin effect can be accurately calibrated. A single influence quantity independent quantification method was proposed. The influence of measurement error of 100 kA impulse current measuring system is analyzed quantitatively. Based on the high current test results and theoretical analysis, the measurement uncertainty components of peak current and time parameters are evaluated. The expanded uncertainty of the scale factor and time parameters were 0.4% ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> = 2) and 0.8% ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> = 2) respectively. Evaluation results demonstrate that the developed measuring system can accurately reproduce and measure the high exponential lightning impulse current.

Research on large-capacity impulse test technology for distribution transformer based on energy storage intelligent power

Large-capacity impulse test of distribution transformer requires a large amount of instantaneous energy, while the impulse mode of conventional dedicated high-voltage line and generator requires synchronous switch, adjusted impedance, generator, etc., which has low operability and the risk of affecting system stability. To solve the problems in the large-capacity impulse test of distribution transformers, this paper proposes a high-current impulse test method based on energy storage technology, power electronics technology and intelligent control technology. The stepless continuous adjustable voltage of large capacity short circuit test, precise control of test current peak factor and stable output are realized, and the corresponding smart energy storage power supply for the large capacity test of a distribution transformer is developed. Through simulation and live test, the design of the energy storage intelligent power supply proposed in this paper greatly reduces the power supply side capacity requirements of large capacity impulse test of power distribution, and has excellent operability in field test.

Study on the Measurement of the On-Site Overvoltage and Internal Temperature Rise Simulation of the EMU Arrester

In order to analyze the explosion accidents of the CRH5 EMU roof arrester in recent years, an internal temperature measuring platform based on fluorescence fiber was established, and the temperature distribution characteristics under the continuous operating voltage and high-current impulse were analyzed. The test results show that passing section overvoltage and steep impulse overvoltage have higher amplitudes, while high-harmonic overvoltage has a lower amplitude but a longer duration. The maximum temperature rise of the arrester was 5.2 °C under 34 kV for 3 h. The surface temperature of the valve plate column was high in the middle and low on both sides; the maximum temperature difference at different positions was only 2.2 °C. The maximum temperature of the valve plate column rose to 97.6 °C under 105 times of the high-current impulse, and the maximum temperature difference at different positions reached 33.8 °C. Then, the actual overvoltage of the arrester in operation was measured and analyzed statistically, and the arrester simulation model was established. The temperature characteristics of the normal arrester and the arrester with the electric tree were studied under the actual typical overvoltage, and the influence of air velocity on the internal temperature rise was analyzed. The simulation results show that, due to the low amplitude and small current of high-harmonic overvoltage, the internal temperature rise of the normal and defective arresters was very small. Under the effects of passing section overvoltage and steep impulse overvoltage, the internal temperature of the normal arrester can reach 36.57 °C and 241 °C, and the arrester with the electric tree defect can reach 44.75 °C and 536 °C, respectively. The air velocity has little effect on the internal temperature rise of the arrester. Passing section overvoltage and steep impulse overvoltage occur frequently and have an obvious influence on the internal temperature rise of the arrester, so the roof overvoltage of the EMU is an important reason for the arrester burst.

Corrosion resistance of AZ31 alloy after treatment with high current density impulse or/and laser irradiation in Hank’s solution

In this article, we have introduced a new method that can improve the corrosion resistance of AZ31 alloy. We compared the biodegradation of AZ31 alloy foil treated with a high current density impulse (HCDI), laser irradiation (LI) and HCDI-LI with that of the untreated one. The rate of the biodegradation of AZ31 alloy treated with HCDI-LI was lower than those of the untreated one, the alloy treated with HCDI or LI. Thus, the improved corrosion resistance of the AZ31 alloy treated with HCDI-LI allows its use for medical purposes.

The electrical model and harmonic characteristics of ZnO varistor considering unipoilar impulse aging polarity effect

The frequent and high amplitude unipolar impulse currents during the process of switching-on AC filter banks can accelerate the aging of arresters in some ultrahigh-voltage direct-current (UHVDC) and HVDC transmission systems, and result in polarity effect of zinc-oxide (ZnO) varistors. Hence, an improved ZnO varistor electrical model considering the polarity effect caused by unipolar impulse aging was proposed under power frequency voltage. Accelerated aging test under a negative polarity 15/35 µs impulse current was conducted on ZnO varistor samples to validate the proposed model. Furthermore, the current waveform and harmonic characteristics of the leakage current and its resistive component were simulated. Comparative analysis revealed that the simulation results were generally consistent with the test results. Based on the results, it's inferred that the variation of even-order harmonics are attributed to the polarity effect, and can be considered as one of the aging criterion of arresters.

A new method to electrical parameters identification of carbon fiber reinforced composites using lightning disturbances corresponding to subsequent return strokes

Carbon fiber reinforced polymers (CFRPs) are modern materials increasingly used in the aerospace industry due to its excellent mechanical properties but there is still a lot to do to improve their electrical capabilities. The paper presents a new prototype measurement system and method for identifying electrical parameters of conductive composites using both: low DC electrical signals and high-current impulses of lightning nature. Detail presentation of the measurement setup and used techniques was made on prepared three types of CFRP laminate samples consisting of five carbon fabric layers each with different contents of flame retardant and carbon black conductive additives. The 4-electrode and Van der Pauw methods were used for low voltage measurements of volume and surface resistivity. 15 kA high-current pulses have been applied to determine composite sample parameters such as equivalent volume and surface resistivity, surge impedance, current distribution and damage immunity to the effects of the lightning-type currents.

On the Use of High-Power Diodes as Crowbar Switch for Capacitive High-Current Generators

A technically easy way to reproduce lightning current pulses is to use a capacitive high-current impulse generator with a crowbar switch. For the crowbar switch, commonly spark-gaps are used which can withstand the mechanical and thermal stress due to the high current pulses. The spark-gap is triggered by an external high voltage trigger-device when the oscillating current attains the maximum. For extremely high currents, it is a common method to combine two of such generators to a tandem generator. In this case, it is necessary that the crowbar switches of both generators are triggered time-synchronized and decoupled by the use of an inductance. In order to avoid the triggering and the decoupling of the crowbar switches, we replaced the spark-gaps of both crowbar switches of our tandem generator by two diode-stacks, each consisting of 25 high-power diodes. After this modification, the tandem generator is able to reproduce even extremely high lightning currents as the 10/350 μs current pulse up to a level of more than 300 kA. The use of the diode-stacks also allows to combine the high-current generator with other current generators as a long duration current generator used for the experimental simulation of the continuing currents. Because no decoupling inductance is needed and the arc of the spark gap is avoided, the tandem generator is now able to test equipment with higher inductance and resistance compared to the generator with spark-gap based crowbar switch.

Arc-extinguishing characteristics of semi-enclosed structures based on theory of positive shock wave reflection

Lightning current in the process of discharge can cause the potential differences between insulators to rise, hindering the normal operation of the equipment. To reduce the potential difference between insulators during a lightning strike, this study proposes a semi-enclosed structure to limit the rise of potential between insulators. Lightning-induced overvoltage causes the semi-enclosed structure to discharge, forming an arc channel. Because the arc is compressed by the structure, an overpressure-induced shock wave is generated. Positive reflection occurs when the shock wave hits the wall that damages the development of the arc through superposition. By using the theory of positive reflection of shock waves, the overpressure due to a positively reflected wave, generated by an impulse current of 8/20 µs with a peak value of 10 kA, was as high as 4.8 MPa, 48 times the initial pressure. Moreover, a 3D high-current impulse discharge model was established in COMSOL to simulate the process of shock discharge of the structure in the case of a large current. Finally, current-induced shock tests were carried out in the semi-enclosed structure. The results show that the maximum pressure in the semi-enclosed structure was 4.38 MPa at 10 µs and conductivity dropped to zero at 80 µs. In experiments, the amplitude of the impulse current decreased from 9.54 to 5.72 kA, and the current dropped to zero at about 65 µs. The results show that the semi-enclosed structure can extinguish the arc and limit the rise of potential between insulators.

Testing of Conductive Carbon Fiber Reinforced Polymer Composites Using Current Impulses Simulating Lightning Effects

Carbon fiber reinforced polymer (CFRP) composites are lightweight and an increasingly used material with good mechanical properties. In the aviation industry, they are also required to have specific electrical properties that guarantee resistance to the direct and indirect lightning effects. The paper is focused on the description of a test stand and development of a method used to determine the electrical characteristics of conductive CFRP laminate samples with the use of high current impulses of lightning nature. Samples of three laminates (square format with side 30 × 30 cm) with a different composition were tested on the constructed stand, confirming the possibility of characterizing this type of laminate sample in terms of electrical conductivity and resistance to the effects of lightning current. It was possible to observe the impulse current flow (with a peak value up to 15 kA and a rise time above 6 µs) from the high voltage electrode placed in the center of the sample in all directions towards the edge. The optical fiber measuring system was used to record the voltage and current time waveforms. The energy stored in the impulse current generator was sufficient to simulate the mechanical damage, such as burnout and delamination, that accompanies the direct lightning strike to structural elements made of CFRP. The influence of the matrix composition used for laminate fabrication on the test results describing the electrical properties of the tested CFRP samples was noted. The experimental setup allows the testing of specimens with a maximum width and length of 50 × 50 cm and any thickness with a peak current of up to 50 kA.

Estimation of Amount of the Evaporated OPGW Strand Struck by a High-current Impulse Arc

Estimation of Amount of the Evaporated OPGW Strand Struck by a High-current Impulse Arc

Alteration of volcanic ash glass chemistry due to lightning

Volcanic lightning generates high temperatures (>1500 °C) that melt volcanic ash particles, which re-solidify into lightning-induced volcanic spherules (LIVS). These LIVS have been documented within several ashfall deposits from multiple explosive volcanic eruptions. While several studies have analyzed the morphology and formation processes of LIVS, there is limited research on the chemical composition of these glassy particles. High-current (7 and 25 kA) impulse experiments were performed on very fine volcanic ash (<32 μm) produced from andesitic pyroclasts to create lightning-induced volcanic particles. The pre- and post-experimental ash was analyzed using a combination of wavelength and energy dispersive spectroscopy. The unaltered post-experimental particles, in addition to the pre-experimental samples, are characterized by angular grain shapes and euhedral mineral microlites within a glass matrix. Conversely, the 29 analyzed lightning-induced particles have a rounded morphology and are composed of chemically distinct and highly variable glass with no preserved microlites. Observed within the post-experimental particles are chemically diverse flow structures that are compositionally different than the surrounding glass, indicating mingling between molten components derived from the initial mineral and glass. Transformation of volcanic ash particles into LIVS will provide evidence of lightning during explosive eruptions and may increase the leaching rate of elements into the environment following ash deposition.

Research Progress in Silver Zinc Oxide Electrical Contact Material

Since the performance of silver metal oxide (Ag/MeO) electrical contact materials directly affects the reliability and service life of switching apparatus, the related research on high-performance Ag/MeO electrical contact materials has not stopped. And with the rapid development of switching apparatus, higher and higher requirements are put forward for the performance of Ag/MeO electrical contact materials. Thanks to low and stable contact resistance, short arc burning time, good resistance to high current impulse (3000-5000 A) and good anti-arc erosion, silver zinc oxide (Ag/ZnO) more than just serves as an indispensable environmentally friendly alternative to silver cadmium oxide (Ag/CdO) electrical contact material, and has become one of the important research hotspots of Ag/MeO in recent years. Nevertheless, Ag/ZnO is suffering the increasingly serious challenges, especially the poor processability and electrical properties due to the easy segregation of zinc oxide (ZnO) during the process of preparation, which urge scholars at home and abroad to seek favorable methods to optimize the Ag/ZnO. As yet, impressive strides have been made in optimization the preparation process, nano-technology and additive modification of materials, and research on the failure mechanism of materials. Aiming to provide reference for optimizing Ag/ZnO electrical contact material, this review retrospects the research progress in Ag/ZnO electrical contact materials in recent years, and expounds the preparation methods, processing technology, modification research and failure mechanism of Ag/ZnO, and points out the future development directions of Ag/ZnO.

Investigative Study of Vertical Electrodes Encased in Concrete/Mortar with Various Sizes of Air Voids

Ionisation can occur in the soil when high impulse currents are subjected to grounding systems. This occurrence is generated by a difference in the dielectric strength value between the soil and air voids. Several published works investigating the ionisation process in soil have seen that the degree of ionisation is dependent on several factors, among them soil resistivity, ground electrode size and impulse polarity. The effects on soil resistivity, such as the moisture content in soil, soil grain size, type of soil and its temperature, have been studied; however, the effect of the size of air voids in soil has not been extensively presented. This study considered four rod electrodes—a conventional rod electrode, conventional electrode with porous concrete (PC), conventional electrode with concrete mixed with a foaming agent (FC) and conventional electrode with concrete (NC)—to provide variations in the size of air voids. Resistance values, RDC, were measured for all these electrodes, and we found that the conventional rod electrode had the lowest value. A detailed evaluation of these rod electrodes under high impulse conditions revealed that similar current rise and discharge times were seen in all electrodes; however, PC, with the largest size of air voids, had the lowest impulse impedance (Zimp value) for the current magnitudes below 2 kA.