Impulse Current Generator Research Articles

Energy regulation of impulse current generator modulated DC arc discharge

AbstractThis paper proposes a method of impulse current generator modulated DC arc by combining the advantages of pulse and the RF to solve the low electron energy problem of direct current arc. Through experimental analyzing the electrical, spectral, and optical characteristics of the arc, the effect of impulse current generator (ICG) on improving electron energy is discussed. The results show that the ICG consumes more energy to enhance the strength of arc discharge, and therefore electron energy is increased in a microsecond scale. In addition, it is found that the electron energy of the arc discharge can be adjusted by varying inductance, capacitance, and discharge tube: increasing the inductance or capacitance can increase the electron energy firstly and then decrease it. In adjusting the three adjustable components, adjusting the inductor is the most effective method, followed by adjusting the capacitor, and adjusting the repetition frequency has the least effect. The reason is discussed, and it is believed that the results are related to leakage inductance and distributed capacitance.

Controllable Impulse Current Generator for PHIL Applications in Surge Protection

Controllable Impulse Current Generator for PHIL Applications in Surge Protection

Tortuosity of Lightning Current Arc Channel and the Resultant Distortion of Luminosity Waveform

Light emissions in two optical bands are simultaneously observed from arc discharges produced by three laboratory impulse current generators, representing three current components (return stroke, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$</tex-math> </inline-formula> component, and continuing current) of lightning, applied across an air gap between two round graphite electrodes in a light-tight environment. The results demonstrate that if a tortuosity of the discharge channel did occur, the luminosity waveforms would exhibit distortions. However, these luminosity distortions, often found in naturally-occurred lightning arcs, previously attributed to the spectroscopic wavelength transfer or the increase of neutral spectral lines, are hardly observed in a normal straight laboratory-generated lightning arc, confirming that the distortions in luminosity waveform should be attributed to the tortuosity of lightning channel. The distortions of luminosity waveforms, corresponding to three types of simulated lightning-current components, are featured with various fine structures, which have also been observed in other investigations for electromagnetic fields and acoustic signatures, if a tortuous channel is involved.

An Experimental Study on Novel Gas Discharge Tubes With Graphene as Electron Emission Material

Electrical equipment is subjected to gas discharge tube (GDT) direct current (dc) breakdown voltage dispersion and breakdown voltage drop after a surge. It is noteworthy that GDT damage may even cause the failure of electrical equipment. Accordingly, the chemical vapor deposition (CVD) of graphene was proposed in this study as an electron emission material of the GDT based on the existing electron powder GDT. The GDT exhibiting a voltage class of 470 V was prepared, and its structure and surge characteristics were analyzed. The effects of gas pressure, aging time, and ambient temperature on the breakdown voltage of the graphene GDT were studied. The surge process of the graphene GDT was simulated using the 8/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~\mu \text{s}$ </tex-math></inline-formula> impulse current generator, and the resistance ability of the graphene GDT against the surge was examined. Moreover, it was compared with the same type of commercial electron powder GDT. As indicated by the experimental results, a positive correlation was identified between the gas pressure and the dc breakdown voltage of the graphene GDT under a certain pressure. The effect of aging time and ambient temperature on dc breakdown voltage was limited. The breakdown voltage of the graphene GDT was first increased and then decreased with the increase in the number of surges. After 100 surges, the breakdown voltage of the graphene GDT stabilized at 350 V, whose stability was better than that of the electron powder GDT. The above-described analysis confirmed that graphene GDT exhibits better surge resistance ability.

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.

Investigation of Spherical Electrode Grounding System Under High Impulse Conditions with Different Polarities

There have been many studies in the pasts, which showed that under high impulse conditions, soil ionization process around the electrode would occur, which results in lower resistance and lower transient voltage on the electrode. Several factors have also been found to affect the ionization process in soil such as; soil types and its grain sizes, moisture contents in the soil, earth electrode configurations, impulse polarity, the location of the injection point, the shape of response time, etc. In this paper, spherical electrodes grounding is used to study the ionization process in the grounding system under different impulse polarity of the current. The experiment was done by field measurement using a commercially available impulse current generator. It was found that lower earth resistance was seen to decrease with increasing current magnitudes for both impulse polarities. In addition, it was found that at low impulse current with negative polarity has a higher resistance than that of positive polarity. This paper is, therefore, to investigate towards improvement on grounding electrode’s design, which would consider soil ionization process

On the Characterisations of the Impulse Breakdown in High Resistivity Soils by Field Testing

This paper presents experimental results of high-current impulse tests on six ground electrode configurations. A high impulse current generator is employed to inject different magnitudes of current into these rod electrodes, under both positive and negative impulse polarities. The effect of increasing the number of rod electrodes, hence the resistance at DC or steady-state (RDC), on the impulse response of ground electrodes is analysed. From the analysis of the results, it was found that the larger the size of rod electrodes, the less current-dependent Zimpulse becomes. The percentage of reduction of impulse impedance, Zimpulse from its steady state, and RDC values are found to be independent of impulse polarity. However, as the voltage magnitudes were increased, an occurrence of breakdown was seen, with higher breakdown voltage seen in negative impulse polarity in comparison to positive impulse polarity. Relatively, the higher the breakdown voltage is, seen in the ground electrodes subjected to negative polarity, the faster the time to breakdown is.

Multi-Stroke Lightning Interaction with Wiring Harness: Experimental Tests and Modelling

This paper presents the obtained results of experimental tests and modelling of lightning disturbances that were propagated in a model of aircraft cable bundle and caused by multiple lightning return-strokes interactions. The work is a continuation of previous research, which was concerned mainly with the interaction of lightning discharge with a single return-stroke. The section of the cable harness arranged above the metal plate was investigated. In one of its wires, a multiple-stroke current representing indirect lightning effects was injected from an impulse current generator dedicated to avionics immunity tests. Overvoltages induced at the ends of other wires surrounded by a braided shield, as well as the influence of line parameters and shield grounding condition on the shape and level of observed transients, were examined. The computer simulation results match the measurement data with satisfactory accuracy, and therefore, the presented model can be used to estimate indirect lightning effects in the wiring harness of avionics.

Simulation of impulse current generator for testing surge arresters using frequency-dependent models

The object of research is the equivalent circuit of an impulse current generator designed for testing surge arresters. Calculation of the impulse current generator parameters when discharging a capacitor bank to a complex nonlinear load is a difficult task for an analytical solution. Until now, the application of surge arrester frequency-dependent models was limited to the problems of overvoltage computation. Surge arrester frequency-dependent models can predict the residual voltage with high accuracy. This is the reason to consider that surge arrester frequency-dependent models can be used for calculating the main parameters of impulse current generators designed for physical testing of surge arresters.&#x0D; The task of determining the equivalent circuit parameters required for getting a discharge current of a given waveform and amplitude in an impulse current generator scheme with a nonlinear load was solved using circuit simulation.&#x0D; This article presents the results of studying the processes in impulse current generator equivalent circuit. In the circuit a dynamic model of a surge arrester is used as the load model. For this, an equivalent circuit for the discharge path of the impulse current generator was drawn up. The parameters of the circuit elements (including the required number of capacitors and their charging voltage) are determined, which are necessary for getting a discharge current of a given standardized waveform and amplitude. The parameters of the discharge path are determined for surge arresters of three different voltage classes. It was found that the relative error when determining the residual voltage between the terminals of the surge arrester model does not exceed 3 %.&#x0D; The work contributes to the further development of circuit simulation of surge arresters and the expansion of the scope of surge arrester dynamic models. As a result of the research performed, the possibility of using surge arrester frequency-dependent models for determining the discharge current waveform in impulse current generators is shown. The research performed is relevant due to the fact that surge arresters have become a main tool for protecting the insulation of electrical network equipment against external and internal overvoltages

Design of 4-stage Marx generator using gas discharge tube

In this paper, a Marx generator voltage multiplier as an impulse generator made of multi-stage resistors and capacitors to generate a high voltage is proposed. In order to generate a high voltage pulse, a number of capacitors are connected in parallel to charge up during on time and then in series to generate higher voltage during off period. In this research, a 6kV Marx generator voltage multiplier is designed using gas discharge tube (GDT) as an electronic switch to breakdown voltage. The Marx generator circuit is designed to charge the storage capacitor for high impulse voltage and current generator applications. According to IEC 61000-4-5 class 4 standards, the storage capacitor must be charged up to 4 kV. The results show that the proposed Marx generator can produce voltages up to 6.8 kV. However, the storage capacitor could be charged up to 1 kV, instead of 4 kV in the standard. That is because the output impulse voltage has narrow time period.

Experimental study on artificial lightning ignition phenomenon and model of the fuel bed

As global warming continues, wildland lightning fires have exhibited an increasing trend. The phenomenon of lightning ignition and a model are urgent research fields. In this study, an impulse current generator was used to study artificial lightning ignition. Ignition phenomena for several fuel beds were compared. Flames in the grass bed existed in the form of particles, but these particle flames had a short duration and were extinguished by the shock waves from the artificial lightning. It is noteworthy that a 10/350 μs impulse current could ignite a cotton fibre bed and produce sustained and stable combustion. An artificial lightning ignition model for the fuel bed was established. The model was verified by artificial lightning ignition experiments. The results show that the model could be applied to grass and needle fuel beds and waveforms of 10/350 μs impulse current and short continuing current. The findings of this study provide valuable information for understanding the mechanism of lightning ignition.

Experimental analysis of artificial lightning breakdown and ignition characteristics in grassland

Lightning fire is an important influencing factor of grassland ecology. It is one of the important ignition sources of grassland fire. The previous researches on lightning fires were mainly focused on forests, but researches on grassland were insufficient. In this paper, the impulse voltage generator was used to evaluate the breakdown characteristics of grass bed. The relationship of breakdown voltage to moisture content and bulk density was obtained. Based on the impulse current generator, an artificial lightning ignition prediction model of impulse current was derived. Results show that the breakdown voltage of grass bed decreases rapidly with the increase of moisture content. With the increase of peak current, the total lightning energy increases, while the heating efficiency decreases.

Studies on ablation failure on pipeline related to lightning strikes

The phenomena lightning causes failure of buried pipelines, in the form of ablation pits on pipe wall, have been reported several times in the past, and there are only few studies focusing on the formation of such failure and the impact to structural integrity in service. To study factors causing the formation of ablation pits on pipelines, lightning strike simulation experiments were conducted on pipeline steel specimens by means of an impulse current generator facility. With the obtained steel specimens from the simulation experiments, combined with the failure samples obtained in the field, metallographic examination and mechanical property tests were carried out for further fitness-for-service analysis. The results showed that the field failure samples had consistent properties with the laboratory specimens. The microstructure of the damage part transitioned in the order of, from the ablation zone inward to the matrix, a remelting zone, an HAZ surface layer, an HAZ subsurface layer, an HAZ innermost layer, and the matrix. The field and laboratory ablation failure samples showed similar changing trend of hardness, i.e., gradually decreasing from the remelting zone to the matrix. These observations demonstrate that the damage parts have distinct mechanical properties from the normal matrix. In conclusion, the ablation failure caused by lightning strike had severe impacts to the pipeline material itself, which necessitated thorough repair of the HAZ by grinding or other measures.

Получение соединений разнородных материалов электроимпульсной сваркой – прессованием

A study of the process of high-speed consolidation of powder materials with the simultaneous formation of a welded joint with the surface of the metal base is presented. Thermal and power effects are used as a result of passing the current pulse through the powder composition and the inductor. The electric circuit of the gradual connection of the processing zone and the magnetic hammer, consisting of a flat inductor and a pusher, is proposed. The electric impulse welding-pressing device (EIWP) is connected to a impulse current generator (ICG) with a capacitive energy storage. Impulse currents of 200 - 300 kA allow to obtain Joule heat, warming up the composition to pre-melting temperatures (0,6-0,8) T m , and magnetic pressure of 500∙10 6 N/mm 2 during the process (100-200)∙10 -6 s. The equipment with energy consumption up to 10 kJ with a discharge frequency of 5 kHz is used. The study of the connection zone showed that the welding of the composition with monolithic materials occurs in the solid phase, new structures are not formed. The implemention of a monolithic material in the form of a wire into the pressing zone allows to obtain a connection of dissimilar materials keeping the original structure. In this case, the powder composition is a connecting element. Thus, copper compounds with steel, aluminum, brass and other materials are obtained. The dependences of the strength of compounds on the discharge energy of ICG are obtained

Investigation of lightning ignition characteristics based on an impulse current generator.

Lightning strike is an important ignition source of forest fires. Artificial lightning discharge is a method for studying lightning fires. However, there is not enough data on the ignition of combustible materials caused by artificial lightning discharge. Previous studies on lightning ignition have focused on the heating and ignition effects of long continuing current (LCC), but the function of the impulse current that occurs before the LCC has not been taken into account. In this paper, an impulse current generator of 8/20 μs was used to simulate the ignition effect of impulse current on conifer needle beds. Different current waveforms have different ignition characteristics. We compared five kinds of conifer needle beds. The average of the current needed to ignite the needle bed of Larix gmelinii (Ruprecht) Kuzeneva was the smallest, and the average of the breakdown voltage was the smallest for the needle bed of Pinus massoniana Lamb. The total energy input to the conifer needle beds was fitted as a multiple log‐linear regression model. The heating energy proportion value varies with different bulk densities, current amplitudes, and moisture contents. Based on this data, the heating energy of the impulse current transferred to the needles can be predicted. This information in conjunction with previous research on LCC was used to derive a lightning ignition prediction model of the full waveform for conifer needle beds.

Nondestructive and electromagnetic evaluations of stealth structures damaged by lightning strike

Stealth technology is very important for the survival of military aircraft. A stealth aircraft structure has both electromagnetic and mechanical functions. Lightning can cause failure on both the points. In this study, we claim that the stealth structure should be evaluated nondestructively and electromagnetically, and we propose a method for full-field evaluations of both the functions. First, a radar absorbing structure was designed and fabricated with stealth capability in the X-band. The radar absorbing structure consisted of a carbon nanotube layer (glass/epoxy dispersed with multiwalled carbon nanotubes), a spacer layer (glass/epoxy) and a perfect electrical conductor layer. A lightning test was performed using an impulse current generator according to standard regulations. Then, nondestructive damage and electromagnetic performance evaluations were performed using a pulse-echo laser ultrasonic propagation imager and a scanning free-space measurement system, respectively. The results showed that neither structural damage nor changes in the electromagnetic properties were observed during the two evaluations. In general, the composites were severely damaged by lightning. However, it turned out that the radar absorbing structure with the carbon nanotube layer could prevent serious damage to stealth function as well as material damage owing to the high conductivity of the carbon nanotubes dispersed in its surface layer.

Damage Characteristics and Microstructure Response of Steel Alloy Q235B Subjected to Simulated Lightning Currents

This paper elucidates the damage characteristics, microstructure response and temperature rise of steel alloy Q235B suffered from lightning currents, which is the basis for lightning protection of oil tanks. Damage is inflicted in the designed Q235B specimens by using the multi-waveform multi-pulse impulse current generator to characterize the damage response induced by four typical lightning current components. The changes in the element composition and micro-hardness of Q235B are documented in the experiment. The microstructure changes in response to the temperature rise are analyzed by the proposed lightning-metal temperature rise model. The results reveal that, first, return stroke current with an amplitude of 201.2 kA leads to the largest damaged area of 3523.8 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Continuing current in the stroke intervals with a charge transfer of 12.1 C results in the damaged area of 12.6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and the damaged depth of 0.5 mm. Long continuing current after stroke with a charge transfer of 210.1 C leads to the deepest damaged depth of 3.0 mm. The demixing phenomenon occurs on the cross-section, forming the damage zone, transition zone, and origin zone. The damage zone mainly consists of martensite transferred from pearlite and ferrite at temperature 990 °C. The transition zone is mainly martensite and ferrite forming at temperature 900 °C. The hardness of the three zones is 450, 310, and 180, respectively. The damaged depth is only 0.001 mm caused by the subsequent return stroke current with an amplitude of 102.2 kA.

Influence of slit alignment and slit width on the luminosity measurement of arc discharge channel

The luminosity of lightning channel is closely related to the lightning current. In the present paper, a lightning channel luminosity detection system (LCLDS), comprising of an avalanche photodiode module, a neutral density filter, an extension tube and an adjustable horizontal slit, is assembled. By using the impulse current generator, lightning impulse currents with different amplitudes and also different waveforms were produced in a 15-mm open-air gap between two graphite-rod electrodes. The luminosity and the current of discharge channel were measured synchronously. The experiments looking into the influencing factors of luminosity measurement, including the alignment of the silt and the slit width, were carried out. Obtained results show that the slit opening center of LCLDS should be aligned to the center of the discharge gap. Otherwise, in the case of improper alignment, the measured luminosity waveforms associated with the same injected current might be quite different in the amplitudes as well as in the waveforms. Moreover, the peak luminosity increases linearly with increasing slit width, whereas the luminosity waveforms are practically unaffected, implying that, in the practical application, the slit width can be adjusted to alter the luminosity signal output according to the actual need. Obtained results here can establish the foundation to develop the correlation between the current and the corresponding luminosity in the future.

Applications of impulse current and voltage generators dedicated to lightning tests of avionics

Applications of impulse current and voltage generators dedicated to lightning tests of avionics

An improved Current Voltage Transferring Device for high current high frequency measurement

This paper represents the characteristics of the improved Current Voltage Transferring Device (CVTD) for high current measurement including lightning impulse currents. The improved CVTD has been developed from the prototype CVTD to provide exceptional characteristics for high current with high frequency measurement. The improved CVTD in h-shaped configuration is made of copper and aluminium. The relationship between input current and output voltages of the new CVTD was investigated with short and long duration lightning impulse currents to establish the empirical formulas. The typical impulse current generator was used to generate 8/20μs lightning impulse current with the amplitude of 940A while the impulse generator with crowbar elements was utilized to generate 10/350μs lightning impulse current with magnitude of 30.2kA for the experiment. The lightning impulse current measurement characteristics of the CVTD and Rogowski coil were examined. From the experiments, the new improved CVTD shows the superior characteristics to measure the impulse currents with very fast rise time. Besides, nanosecond pulses superimposed on the lightning impulse currents were detected by only the improved CVTD. According to the experiments, there is no doubt that the new improved CVTD is a superior one for high current with high frequency measurement especially lightning impulse currents.