Lightning Impulse Discharge Research Articles

Breakdown calculation of zoning tests by positive lightnings

To simulate a natural lightning strike, the breakdown should occur within 1–3 μs in an aircraft lightning zoning test. However, the breakdown voltage–time characteristic of the combined gap is hard to derive because of the complex breakdown process. In this paper, a series of positive lightning impulse discharge tests in a rod electrode–floating aircraft model–plate combined gap were conducted. The leader propagation processes in both sub-gaps were observed using a high-speed camera. The potential of the floating aircraft model was analyzed. We propose a potential calculation model for the floating aircraft during the leader propagation phase. After fitting test data, an empirical formula for the connected streamer plasma was given. Taking that model into account, the calculation result of the average breakdown time of the combined gap has an error of <5.7%.

Molecular Mechanism Analysis of Multi-Component Mixed Insulating Oil Improving Lightning Impulse Discharge Characteristics of Oil-Impregnated Paper

Molecular Mechanism Analysis of Multi-Component Mixed Insulating Oil Improving Lightning Impulse Discharge Characteristics of Oil-Impregnated Paper

Atomic scale microparameter analysis of modified natural ester molecules related to impulse discharge characteristics under electric field

Modified natural ester (MNE) has significant potential for application in transformers as an environmentally friendly and renewable energy source. In comparison to natural esters, MNE offers notable advantages in terms of viscosity and power frequency breakdown voltage. However, the lightning impulse breakdown characteristics of MNE and the atomic-scale microscopic mechanisms related to its discharge characteristics remain unclear. Understanding the lightning impulse breakdown characteristics of MNE is crucial for ensuring the safe operation of transformers. In this paper, the density functional theory is used to calculate the change law of the microscopic parameters related to the discharge characteristics of MNE under the electric field under the action of electric field, so as to theoretically evaluate the lightning impulse discharge behavior of MNE. The results reveal that the electronic and geometric structures of MNE molecules are influenced by electric fields, which is the primary factor contributing to the variations in microscopic parameters under different electric field strengths. As the electric field intensity increases, the dipole moment of MNE tends to increase, while the ionization potential and excitation energy of MNE tend to decrease. The decrease of ionization potential, excitation energy and energy gap of MNE molecules is about 6.61%–68.01%, 4.34%–47.66% and 2.01%–69.23%. By comparing the calculated results of mineral oil, natural ester, and MNE microparameters, it can be inferred that the lightning impulse breakdown behavior of MNE is similar to that of natural ester and lightning impulse breakdown voltage of MNE is higher than that of natural ester but still lower than that of mineral oil. The average negative polarity lightning impulse voltages of MNE, natural ester and mineral oil in the 85 mm oil gap are about 245 kV, 199 kV and 304 kV, respectively. The test results confirmed the simulation conclusions. This study provides robust theoretical support for understanding the lightning impulse breakdown characteristics of MNE and ensuring its safe operation in transformers.

Description of the Discharge Process in Long Air Gaps Under Lightning Impulse Voltage

This paper presents high-resolution synchronous, electrical-optical measurements of lightning impulse discharge process in a representative 3 m air gap rod-plane configuration. The observed discharges can be differentiated in multiple sub-processes (streamer, backward wave and leader). We empirically analyze the characteristics and dependencies of these sub-processes and present a physical approach to model the lightning discharge. Reducing the discharge process to the inception and growth of the leader, the presented approach specifically describes the dependence of leader velocity not only on the leader current but also on the electric charge. The leader's required voltage and the conductivity of air gap are investigated as well. As a main contribution, the electrical discharge current can be calculated based on the instantaneous voltage and the determined conductivity of streamer and leader. As of yet, the presented model approach is not generic but limited to standard lightning voltage in rod-plane configurations up to 4 m gap distance.

Effect of Molecular Structure on the Difference of Lightning Impulse Discharge Between Mineral Oil and Natural Ester Using DFT Calculation

The lighting impulse breakdown performance of natural ester (NE) is lower than that of the traditional mineral oil, which is a key point that needs to be considered in high-voltage level and large capacity transformers. The micromolecular structures of NE and mineral oil are quite different, which leads to significant differences in macroperformance. Therefore, molecular models of two types of oil were constructed in this article, and density functional theory (DFT) was used to calculate molecular microscopic parameters, such as ionization potential (IP) and polarization properties under the action of electric fields (EFs) with different directions. The results show that the IP of the NE is smaller than mineral oil, and the IP of the two oils continues to decrease with the increasing EFs, which is mainly because the highest occupied molecular orbital (HOMO) energy level of NE is significantly higher than that of mineral oil under EFs. Therefore, the lightning impulse breakdown voltage of NE will be lower than that of mineral oil, and the electron density difference (EDD) and atomic force of NE are greater than mineral oil under the EF; thus, the electronic structure of NE is more susceptible to EF. The differences of electronic structure between NE and mineral oil cause the discharge threshold of NE lower than that of mineral oil, which makes the discharge streamers in NE tend to develop along the axial direction of the electrode.

Micro-physical parameter dynamic evolution behaviour of a natural ester molecular chain under a changing electric field and its correlation mechanism with lightning impulse discharge: theoretical analysis

The lightning impulse breakdown properties of natural esters are very important for their further applications. This paper focuses on the discharge mechanism investigation of a natural ester insulating liquid under a lightning impulse electric field. Based on density functional theory (DFT), the configuration, electron structure, ionization and electron affinity process, excitation process and molecular orbital of natural ester molecules were calculated under different electric field strengths. A correlation mechanism between the micro-physical parameters of ester insulating liquid molecules and discharge was proposed. The molecular electrostatic potential was used to predict the active point of discharge. The results show that the molecular structure of triglycerides shows yield behaviour under electric field action. The electrons are redistributed in the direction of the source of the electric field. Among the four triglycerides, the ionization and electron affinity process, excitation process and molecular orbital of glycerol tripalmitate were least affected by the electric field. The microscopic properties of other triglycerides were significantly affected by the electric field. According to the electrostatic potential (ESP) result of natural ester molecules, it can be predicted in the experiment that the surface of H atoms of the triglyceride ester group easily forms electron traps to bind electrons, while the surface of an O atom at the ester of a triglyceride undergoes electron collisions resulting in an electrical discharge. The proportion of palmitic acid in natural esters could be increased or pure glycerol tripalmitate could be used as an insulating oil to solve the problem of the low lightning impulse breakdown voltage of natural esters.

Optical Emission Spectroscopy of Lightning Impulse Discharges in Long Air Gaps with and without Water Mist

This work aims to study the various parameters of LI (lightning impulse) discharge channels in an air gap, i.e., the reactive radicals, electron density and channel temperature, and the influence of water mist on the reactive radicals, electron density and channel temperature of the discharge using optical emission spectroscopy. During a LI discharge in air, the gas in the air becomes highly ionized, and the spectra of which are similar to reference spectra of natural lightning. The electron density and channel temperature of the discharges in air under a LI voltage is ca. 3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">23</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and ca. 13,000 K, respectively, both of which are lower than those of natural lightning. Compared with LI discharges in air, more OH and OH <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> radicals are detected when the discharge takes place in a water mist-air mixture, indicating the partial decomposition of water molecules on the surface of water droplets during the LI discharge. The addition of water mist results in an 8.8-10.7% lower electron density than during LI discharges in air. However, the addition of water mist does not obviously influence the channel temperature of the air discharge.

Lightning protection of multi‐fracture arc‐quenching lightning protection gap for 35 kV distribution lines

Owing to the low insulation level of 35 kV distribution lines, lightning outage accidents and huge economic losses occur frequently. Therefore, a multi-fracture arc-quenching lightning protection gap (MFALPG) for 35 kV distribution lines is developed to ensure the safety and stability of power supply. Here, the principle of MFALPG is presented through the electromagnetic self-contraction effect and qualitative modelling theory. In order to investigate the coupling effect between high-energy compressional waves and arcs, a mathematical model of airflow coupled arc was developed to simulate and analyse the arc-quenching process. Theoretical analysis and simulation results show that the high-energy compressional wave is triggered by the impulse arc rapidly, and the arc conductivity drops abruptly in a short time. Finally, a lightning impulse discharge test and the power frequency withstand voltage test are performed to determine the 35 kV power frequency continuous current interruption test parameters. Under the action of the MFAPLG, the entire time of arc duration is less than 3 ms, and reignition phenomenon of the arc is not found after the subsequent power frequency voltage is restored.

Influence of surface resistivity of insulation films on penetration phenomenon by negative lightning impulse discharge

AbstractA method is needed to prevent damage of wind power generators from lightning strikes even if lightning strikes the blades. In our experiment, the discharge progressing to the film was hard to penetrate the low surface resistivity polyethylene terephthalate (PET) films with conductive coating on one side, although the discharge always penetrated the uncoated PET film. This result was confirmed when the coated surface of the film was directed to either the high voltage rod electrode side or the ground plate electrode side. It was also confirmed that the progress of negative leader generated from the high voltage rod electrode side was hindered by the film from the photograph with the high speed camera. The time constant was calculated from the product of the surface resistance and the capacitance between the film and the plate electrode. As a result, it was suggested that the propagation of electric potential might be fast because time constant is smaller in the case of the low surface resistivity PET films.

Influence of Surface Resistivity of Insulation Films on Penetration Phenomenon by Negative Lightning Impulse Discharge

Influence of Surface Resistivity of Insulation Films on Penetration Phenomenon by Negative Lightning Impulse Discharge

Proposed Scheme of Pliable Gas Insulated Transmission Line and Its Comparative Appraisal Regarding Electrostatic and Dielectric Aspects

Gas insulated transmission lines (GILs) are being used in electrical systems regarding power transmission and substation interconnection. However, operational complexities of conventional schemes, such as structural rigidity, corrosion protection, gas leakage in case of seismic vibrations, larger bending radius and jointing complexities which restrain their application perspectives, could be curtailed by developing a flexible GIL. In this research paper, a new pliable scheme of gas insulated transmission line is proposed. Further, COMSOL Multiphysics® (version 5.1, COMSOL Inc., Stockholm, Sweden) based electrostatic assay and practically performed high voltage tests-based dielectric analysis is performed for the proposed scheme. Electrostatic appraisal is comprised of field utilization based electrostatic stress analysis. In addition, dimensional optimization of pliable GIL regarding enclosure and pitch sizes in relation to electrostatic stresses and field utilization is also performed. Regarding dielectric perusal, experimental setup has been developed for standard lightning impulse and disruptive discharge tests in order to investigate the synergistic dielectric characteristics of proposed flexible post insulators for pliable GIL. Experimental and simulation appraisal unveil that the proposed scheme exhibits almost analogous electrostatic and dielectric behavior in comparison to the conventional GIL scheme and could simplify the operational intricacies associated with conventional scheme. The proposed modifications could eliminate the requirement of trench development, corrosion protection and acceleration dampers, along with a significant reduction in required land area at bends, due to a smaller bending radius which will ultimately result in substantial cost reduction.

Insulation Reconstruction for OPGW DC De-Icing and Its Influence on Lightning Protection and Energy Conservation

In order to satisfy demands for DC de-icing of optical fiber composite overhead ground wire (OPGW) and solve questions such as those relating to circulating current loss and liability of suffering from lightning strike, the grounding method of OPGW must be changed from the current commonly used method of being grounded at every tower to being grounded at one tower. The OPGW would be connected to the tower by an insulator, which is often shunt connected with a protective discharge clearance. The recommended value of the discharge clearance is from 70 to 80 mm. The lightning impulse discharge voltage of such a clearance is generally not more than 100 kV. However, as the transmission line is struck by lightning, over-voltage on the clearance is 885 kV at least, even up to a few MV. The clearance can be broken down reliably. The influence of insulation reconstruction for OPGW on the induced current and the power loss of the AC transmission line was studied by means of theoretical analysis and simulation calculations. Results indicate that change of the OPGW grounding mode could reduce the induced current of the ground wire to below 1 A and reduce the power loss of the line to below 1 W/km. Power loss could be reduced by over 99%. Adoption of a suitable grounding mode for OPGW is of great significance for DC de-icing, lightning protection safety, and energy savings for UHV projects.

Study on Impulse Breakdown Characteristics of Internal-Gap Lightning Protection Device Applied to 35 kV Distribution Line

External environmental factors have no effect on the breakdown performance of the internal gap, leading to the anti-icing and anti-storm features of the internal-gap lightning protection device (ILPD). In this paper, a test platform is created to study the impulse discharge and arc erosion characteristics of the ILPD applied to a 35 kV distribution line. The 50% lightning impulse voltage and discharge stability of the ILPD are experimentally analysed. The results show that the ILPD has good discharge voltage repeatability under multiple impulses. Under a positive lightning impulse, the 50% breakdown voltage of the ILPD is 3.8–11.4% higher than that of the outer-gap lightning protection device (OLPD). A finite element simulation model is created for electric field analysis. The maximum electric field strength of the ILPD is 4.68% lower than that of the OLPD, leading to a higher lightning breakdown voltage. High-speed camera shooting shows that the discharge arc may lead to the erosion of the discharge tube, reducing its insulation performance. A large current impulse test platform is set up for arc energy analysis, which indicates that more than 90% of the energy is absorbed by the varistor during lightning stroke. The quality and leakage current of the discharge tube did not change significantly after testing. Given the current design of varistors, the per unit length energy of arc is less than 4.5 J/mm due to the numerical calculation, which is far less than the experimental arc energy (25.0 J/mm). Therefore, arc erosion will not cause the insulation performance of discharge tube to decrease when using the current varistor design.

Study on the lightning strike discharge characteristics of switchgear air gap at low air pressure condition

The usage of medium-voltage switchgear is more and more common in high altitude areas. Few relative standards about the selection of switchgear air gap in low air pressure conditions are currently available for referring. In this study, four different types of switchgear air gaps, as well as a typical rod-plane gap, are taken as the samples, and their positive and negative lightning strike discharge characteristics under low air pressure are tested in the artificial climate chamber. The effects of the electrode structure, polarity, air pressure, humidity, and gap distance on the discharge performances are analysed as well. Research results indicate that the four switchgear air gaps and typical rod-plane gap differs greatly in lightning impulse discharge performances and polarity effects. In low air pressure conditions, the lightning impulse breakdown voltage of either positive or negative polarity can be corrected by U 50 = U 50,0 × (P/P 0) n . The discharge voltage under positive lightning impulse is more easily affected by air pressure than that under negative lightning impulse. Atmosphere humidity will cause dispersiveness of air-gap lightning impulse discharge voltage, which performs to be non-linear with a gap distance lower under 400 mm. Research results are referable for the design, selection and installation of medium-voltage switchgear in high altitude areas.

Study on operating properties of ceramic long rod insulator for transmission line

The material prescription, potential distribution, contamination trend and surface insulating properties under contamination and lightning conditions for the ceramic long rod insulator are investigated. The surface contamination trend of the ceramic long rod insulator can be fitted to an exponential function in a low rainfall area. Potential distribution calculation by three-dimensional finite element method shows that over 50% operating voltage concentrates on the single unit of high-voltage polarity for the long rod insulator string, which is more uneven in comparison with the disc ceramic insulator string. Five-hundred kilovolt full-scale artificial pollution test demonstrates that the contamination flashover voltage of the ceramic long rod insulator has a negative exponential relationship with equivalent salt deposit density and a linear relation with string length. A lightning impulse discharge test confirmed that the relation between 50% lightning impulse discharge voltage and dry arcing distance was also linear for a ceramic long rod insulator string.

Study on arc temperature calculation model for air gap discharge

Summary A model to calculate arc temperature of air gaps discharge is presented in this article. Based on the energy balance equation, we obtained the mathematical method to evaluate the arc temperature. According to the model, arc temperature was calculated for two air gaps with different distance, respectively. The results showed that the peak arc temperature of 16.7 m air gap is 36 368°K, and the peak arc temperature of 10 m air gap is 34 277°K, which are in good agreement with the experiment results. The model built in this article can be used for lightning and switching impulse discharges in air gaps. Copyright © 2013 John Wiley & Sons, Ltd.

Lightning Impulse Discharge Behaviour in Tap-Water Gap

When the soil invaded by water as the grounding medium in green power generation sites near river basins, on the coast, is dominantly characterized in terms of its resistivity, the characteristics of the voltage and current waveforms on transient discharges such as the soil can be experimentally investigated using the liquid gap, reproducing the resistivity of the soil. The transient discharge characteristics is available information on the surge withstand rating of surge protective devices used in the green power generation sites. Experimental results on the behaviour of lightning impulse discharges in a tap-water gap are reported; these results show that the resistivity of tap water is nearly equal to those of a river and cultivated and marshy land. Further, (1) the discharge voltage and current waveforms indicate the periodic attenuated waveforms for one period, and the voltage waveforms indicate amplitude distortions; (2) the discharge impedance obtained using the fitting curves to the discharge waveforms ranges from 1 to 2.5 times that of the tap-water resistance, i.e., 80Ω, and from 8 to 3.2 times that for positive and negative rod discharges.

Positive lightning impulse discharges along cylindrical insulating surfaces bridging a short rod-plane gap

The salient characteristics of the predischarge phenomena and flashover along cylindrical insulating surfaces bridging a short rod-plane gap under positive lightning impulse voltages were measured in a wide range of applied peak voltages. Materials used in the investigation were polytetrafluoroethylene (PTFE), silicone-rubber, nylon and glazed porcelain; the case of air alone was regarded as reference. Corona inception is favoured by the presence of an insulating surface, this being more evident for materials of high permittivity and for initial than secondary corona. At relatively high applied voltages, the initial corona characteristics are directly related to the field enhancement at the tip of the stressed electrode. However, near threshold inception conditions there is a marked reduction of the inception field with material permittivity; an assisting mechanism of initiatory electron production was put forward to explain this behaviour. Initial corona streamers require higher applied voltages to arrive at the earthed plane when propagating along an insulating surface than in air alone. Flashover, closely related to secondary corona characteristics, is always preceded by continuous corona growth, occurring mainly in free air away from the insulating surface because of possible positive surface charge deposition by the initial corona; the latter is characteristic for polymeric insulating surfaces. There is a reduction of the dielectric strength of the gap in the presence of an insulating surface, more pronounced for higher material permittivity, related to the facilitating action of the field enhancement close to the rod tip on continuous corona growth preceding flashover.

Investigation of diagnostic techniques for metal oxide surge arresters

Gapless metal oxide surge arresters (MOSA) have been available in the market for many years since they were first introduced in the 1970's. The aim of this study is to investigate some reliable diagnostic techniques to assess the condition of a metal oxide surge arrester when subjected to severe lightning strikes in the field. A number of nondestructive and destructive diagnostic techniques for metal oxide surge arrester (MOSA) are discussed in this paper. The nondestructive techniques include the standard 1 mA reference voltage, lightning impulse discharge residual voltage and a number of modern diagnostics based on polarization methods: Return voltage and polarization/depolarization current measurements. In order to observe, analyze and correctly explain the degradation phenomena, a number of destructive techniques based on microstructure observation are also conducted. The techniques include optical microscopy, scanning electron microscopy, X-Ray diffraction and energy dispersive spectrometry. The single and multipulse currents of 8/20 mus wave shape were used to artificially degrade the MOSA. The before and after diagnostic results of the nondestructive and destructive techniques are presented and interpreted to understand the aging mechanism in MOSA. The importance of modern nondestructive electrical diagnostics based on polarization methods is validated by test results and is highlighted in detail in this paper. Finally the correlation of the results of different diagnostic techniques with each other and with the results of standard techniques is discussed

Lightning overvoltage protection of AC railroad vehicles by polymeric arresters

In order to improve the operational reliability of AC railroad vehicles, ZnO surge arresters are used to protect them against overvoltages. The most serious threat to arresters installed on the roof of an AC railroad vehicle is the lightning overvoltage. When lightning strikes the mast or conductors, the distribution system can be treated as a system of multiple conductors including feeders, messenger wires, contact wires, protective wires and two tracks. The lightning impulse discharge current through the arrester and the absorbed impulse discharging energy by arrester in the actual field operation and the protective effect of arrester were analyzed by EMTP and discussed when lightning strikes the mast or distribution lines. When the arrester Is installed on the roof of a railroad vehicle, the potential difference on the primary side of high voltage transformer inside the vehicle is suppressed below 150 kV under very serious condition.