Actual Lightning Research Articles

Simulation of Cloud-to-Ground Lightning Strikes to Wind Turbines Considering Polarity Effect Based on an Improved Stochastic Lightning Model

The accurate determination of the annual lightning flash number to a wind turbine is essential for designing proper lightning protection measures. However, the method to assess the lightning risk of wind turbines recommended by the IEC is not associated with the actual lightning attachment process. Additionally, there is little research on positive cloud-to-ground (+CG) lightning. In this study, a lightning risk assessment method correlated with wind turbines on the basis of an improved stochastic lightning model is proposed. Based on the model, the influence of the lightning current amplitude, wind turbine heights and blade rotations on lightning strike risk are quantitatively analyzed. Moreover, the development and distribution characteristics of negative cloud-to-ground (−CG) lightning and +CG lightning are discussed. Finally, a more accurate calculation method of lightning strike risk is proposed considering the polarity effect. The results show that the effect of blade rotations on lightning risk cannot be ignored when the lightning current is large or when the wind turbine is tall. The −CG lightning has more bifurcation, but the dispersity of its development path and the lightning strike point are both small. The +CG lightning has scattered lightning strike points, and the development paths are tortuous, and. According to the verification calculation, the results calculated in this paper are in better agreement with the observation data than the results calculated by the IEC (International Electrotechnical Commission) recommended method.

Research on overvoltage protection of adjacent distribution network by lightning striking plant grounding network dissipation

In order to study the lightning strike plant grounding network scattered flow on the adjacent distribution network overvoltage protection, the establishment of the installation of extended lead, the laying of vertical grounding body and the installation of isolation belt three plant and adjacent distribution line overvoltage protection model, analysis of the 10 kV distribution line and the adjacent plant grounding network spacing, soil resistivity and lightning current amplitude on the adjacent plant line lightning overvoltage impact, and compared the diversion method and insulation spacing method protection effect. The research results show that: the installation of extended lead, the laying of vertical grounding body and the installation of isolation belt can effectively reduce the distribution line overvoltage, the installation of extended lead voltage reduction effect is the best, voltage reduction efficiency is stable in more than 20%; distribution line and the adjacent plant grounding network spacing and soil resistivity has a great impact on the voltage reduction efficiency after protection, but the lightning current amplitude has little impact on the voltage reduction efficiency after protection. The research results can provide reference for the overvoltage protection of distribution lines when the actual lightning strikes the plant.

Lightning monitoring method based on distributed traveling wave and lightning location system

In order to improve the accuracy of lightning strike fault location and identification based on the distributed traveling wave monitoring system and lightning location system, the location algorithm and recognition algorithm are improved and integrated. The distributed traveling wave monitoring device is regarded as the lightning detection sub-station, and the calculation results of the lightning location system are corrected to get the accurate lightning flashover tower position. The lightning flashover voltage of the positioning tower is calculated based on the lightning current amplitude and the procedure method. After the lightning fault type is predetermined, the recognition calculation based on waveform feature extraction can be carried out. The actual lightning tripping fault and waveform were used to verify, the results show that the proposed method can effectively improve the accuracy of lightning strike fault location and identification.

Conceptual Design and Feasibility Study of Flexible Gas-Insulated Transmission Line Using CF3I Gas Mixture

SF6 is widely used in high voltage equipment because of its outstanding characteristics as insulation medium. However, SF6 is a potent greenhouse gas, so its use and emission are regulated. CF3I has been investigated as a candidate for SF6 alternative gas, whose environmental impact is much less than that of SF6 and other fluorocarbon-based gases. In addition, a flexible gas-insulated transmission line (FGIL) is expected to be used for power transmission from offshore wind farms due to its high flexibility and low capacitance. In this paper, the feasibility of 22 kV class FGIL utilizing atmospheric pressure CF3I gas is evaluated from the viewpoint of withstand voltage with actual lightning impulse tests. The cross-sectional size of FGIL is determined by considering insulation condition, heat transfer condition, sheath electric field condition and spacer stress condition. The impulse tests for FGIL are conducted in straight and bent states, and it is revealed that the 50% breakdown voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> of straight state exceeded lightning impulse withstand voltage (LIWV) for 22 kV class, and that V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> of bent state falls below LIWV.

Lightning strike-induced dynamic conduction characteristics and damage behavior of carbon fiber-reinforced polymer composites

This study aimed to reveal the lightning-induced conduction characteristics and improve the lightning damage simulation of carbon fiber-reinforced polymer (CFRP) composites. The real-time conductivity of CFRPs under lightning impulses was investigated. A potential barrier model of “fiber-resin-fiber” units was established based on the electron hopping and tunneling effect to clarify the nonlinear conduction mechanism. An impulse equivalent circuit model of CFRPs was constructed and experimentally verified. The effective resistance was proposed and incorporated into the coupled thermoelectrical damage analysis of CFRPs under lightning component A. The simulated damage based on different conductivity models was compared with the experimental results, indicating that the adoption of effective resistance can advance the simulation study of lightning-induced damage in actual lightning environments. This adoption can decrease the maximum deviation in simulated in-plane damage from −42.8% to −8.86% and decrease the deviation in the predicted through-thickness damage from 2 to 3 layers to within 1 layer.

Design and Experimental Study of Traveling Wave Signal Generator for Distribution Network

Aiming at the problem of operation safety and stability of electrical equipment in distribution network caused by impulse voltage, this paper will study and analyze the traveling wave signal generator. Through the study of the standard lightning wave shape characteristics and the mechanism and characteristics of the existing lightning impulse voltage signal generator equipment, the working principle of the corresponding traveling wave signal generator was designed and the relevant parameters were calculated. Finally, the results of the research and analysis were simulated and analyzed with the Multisim simulation software. Test results show that the impulse voltage generated by the full wave form basic satisfy the provisions of this design is expected waveform, and consistent with the actual lightning wave shape, therefore, this thesis studies the traveling wave signal generator unit can meet the normal travelling wave signal of traveling wave positioning system requirements, verify the real effectiveness and practicability of this thesis research.

Investigation of composite material destruction under lightning stroke effect

Destruction processes of composite materials under lightning stroke effect have been studied. The results of characteristic damages of samples have been presented upon a series of tests conducted with standard lightning currents and those ones whose shape is close to actual lightning stroke. There have been exhibited distinctions between the levels of sample damages: in the second case significant damages of composite matrix external layers have been shown, among which multiple destructions of bundles of carbon fibers at a depth of several layers, layer delamination and cavities formed inside sample. There have been described the results of generalized analysis of damages obtained by applying nondestructive inspection methods: stereoscopic microscope investigation and X-ray microtomography. The mechanism of damages has been presented on the basis of obtained data. The results of testing electrical, mechanical, thermal properties of composite samples have been given upon a set of experiments for lightning current resistance.

Study on the Image Observation Method and Characteristics of Soil Discharge Process Under Multiple Impulse Currents

There are multiple discharges in one breakdown during a lightning incident. A lightning incident usually contains 3–5 return strokes. In this case, the lightning incident will not be well simulated by the first stroke. To date, a single impulse current waveform has been used to simulate the lightning impulse incident in research on the lightning impulse characteristics of soils, leading to some differences with observations of actual lightning discharges. In this paper, a time-delayed control technique and a controlled gaps-group isolation technique were used to produce the multiple high-impulse currents discharge to a soil sample, while nonintrusive X-ray imaging technology was used to obtain images of the discharge channel in the soil. The impulse characteristics of the soil under multiple impulse currents are studied. The differences between the discharge characteristics of the soil under multiple impulse currents and a single pulse are compared. It can be found that there has been a reduction in the effective soil resistivity under multiple impulse currents, and this reduction will be recovered over time. At the same time, a brief analysis of the discharge mechanism of the soil under multiple impulse currents is proposed, based on analysis of X-ray images of discharge channels.

Artificial lightning strike tests on PRSEUS panels

The lightning damage resistance of Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) panels was characterized experimentally. Two unprotected PRSEUS panels were subjected to standard impulse current waveforms (consistent with actual lightning strikes) with 50, 125, and 200 kA nominal peak currents at a variety of panel locations. Lightning-induced damage to the PRSEUS panels was a strong function of (1) the peak current, (2) the lightning attachment location (mid-bay, stringer, frame, etc.) that involved different through-thickness Vectran™ stitching, and (3) the presence of a surface finish paint.The sizes of the damaged regions increased as the peak current increased, since greater peak current leads to more Joule heating. The lightning-damaged PRSEUS panels exhibited unique damage features due to the presence of through-thickness Vectran™ stitches and warp-knitted fabrics. Through-thickness Vectran™ stitches constrained the development and spread of intense local damage in the vicinity of the lightning attachment point. The polyester warp-knit threads used to stitch the warp-knitted laminates together appeared to influence the development of widespread small-scale fiber damage in the region surrounding the strike. Consequently, the Vectran™ structural stitches, as well as the polyester knit threads holding the tows together, have a significant beneficial effect on both the size of the impingement region and the subsequent damage propagation within the laminate. In addition, damage to the painted panel was greater for each current level than for the sanded (unpainted) panel.

Practical Application of In-door Tested Scaled Models on Real Building structures

Lightning indoor testing got a very low attention of the researchers. Although lightning is impossible to create inside the laboratory however it can be presented using high voltage impulse. High voltage impulse was generated in this paper which presents the actual lightning. Selected building structures were tested under the high voltage condition. This idea was implemented practically by applying it on different real building structures. Different building with different roof tops were observed practically and it was found that this research work has a good agreement of the lightning strike points observe during the indoor activities in high voltage lab and out door activity during the field study.

Design of conception on lightning monitoring system for strikes to structures

The object of research is the monitoring system (MS) for lightning, which strikes specific objects or happening nearby. It is based on the use of regular (not high-speed) video cameras. Among drawbacks of some existing MS having video capturing of strike position, one can indicate that in automatic setting modes they are able to record comparatively reliably only discharges including continuous current component. Also, the triggering to start saving of video fragment with lightning into memory and transmission to server is provided usually by optical sensor only. Other sensors are used rarely or their characteristics are not well substantiated. High-speed cameras are also utilized sometime, but this is expensive and usually related to research projects. Two variants of MS conception were worked out during the study – complex and simplified. It is suggested to use additional sensors (electric and magnetic field, acoustic) for reliable triggering of MS and also several video cameras. In both variants of MS, for extraction of only frames containing captured lightning strikes from the whole recorded video row, it is suggested to use software based on computer vision library (Open CV). Characteristics of all sensors are substantiated and recommended, in particular: – video cameras – IP-type, 25…50 fps, 1080р or better; – optical sensor – sensitivity range 0.4…1 μm, time resolution – 1 μs, distance – up to 500 m; – «slow» electric field antenna – electronic type, 0.1…10 Hz; – «fast» electric field antenna – rode or plate type, 1 kHz…5(20) MHz; – magnetic field registration – compact ferrite antenna, 3…30(100) kHz; – thunder recording – capacitor microphones at 0 to 1…2 kHz. Experimental laboratory tests are carried out regarding designed optical sensor performance by using impulse current, which have parameters corresponding to actual lightning.

Breakdown characteristics of oil-impregnated paper and influential factors for damped alternating oscillation waveforms

As striking lightning impulse waveforms in power transformers are quite different from the standard lightning impulse waveform (SLIW) used in the withstand voltage tests, it is essential to identify the breakdown characteristics of oil-impregnated paper (OIP) under non-SLIW and to quantitatively compare them with those under SLIW. On that basis, the impulse insulation levels of power transformers can be rationally determined and then the insulation specifications can be evaluated to maintain high equipment reliability. In this paper, with damped alternating oscillation waveform as a representative basis, the breakdown characteristics of oil-impregnated paper were experimentally obtained by changing the frequency and damping rate of the applied voltage. All experiments were conducted using a column-column electrode model. In addition to the 50% breakdown voltages (U50), Minimum breakdown voltage Umin and V-t characteristics under different circumstances, the influence of various parameters on breakdown characteristics and the possible reasons were discussed. After comparing waveforms and corresponding results, the specific relationship between waveform parameters and U50 were expressed as a single equation. As a result, the breakdown voltage was 1.106 to 1.435 times higher than that under SLIW depending on frequency and damping rate. The steepness of the wave peak and the duration of high voltage around wave crests are considered to be two important factors affecting the breakdown voltage. An effective way was proposed to predict U50 of oil-impregnated paper as a reference for insulation specifications irrespective of wave shape. These results support the rationalization of insulation for actual lightning impulse waveforms in the power transformers.

Electric stresses on transformer winding insulation under standard and non-standard impulse voltages

This work presents an extension of our previous work on voltage stress analysis of a 3MVA, 33/11kV, 3-phase, 50Hz, Dyn 11 transformer against the application of standard and non-standard impulse voltages. A preliminary comparative study on the variation of maximum voltage to ground and voltage across the coils under different impulse voltages indicated that non-standard impulse voltage waveforms develop higher voltage stress in the windings. They pose high risk and are critical to transformer insulation system. The obtained test results provide the basis for further study of non-standard impulse voltage waveforms and make necessary correction in the existing impulse testing standards. However, to take care of the stringent effect of actual lightning and other impulse voltages occurring in practical field a more detailed study considering a wide variety of non-standard impulse voltage waveforms is aimed to be done in future.

Development of a Method of Calculating the Melting Characteristics of OPGW Strands Due to DC Arc Simulating Lightning Strike

Some strands of composite fiber-optic ground wire (OPGW) are sometimes melted and broken by high-energy lightning strikes. DC arc tests simulating lightning strikes have been performed to obtain the melting and breaking characteristics of OPGW strands. The tests have to be performed under many conditions concerning the arc (e.g., current, duration, polarity, gap length) and the OPGW (e.g., size, type, and number of strands) to clarify the melting and breaking characteristics of the strands. In this paper, the calculations regarding the melting characteristics of strands are performed considering the transferred heat and its area from the arc to the strands under the aforementioned conditions. The melting characteristics of strands are calculated with an arc current of 1-100 kA considering the measured current of actual lightning. The calculation results of the strand melting duration depending on arc current show good agreement with the experimental values obtained in dc arc tests.

Fractal Nature of Simulated Lightning Channels

Cloud-to-ground lightning discharges in 2D and 3D domains were simulated using a stochastic dielectric breakdown model. The dependency between fractal dimension of the discharge patterns and the power of the local electric field η was critically evaluated. An exponential decrease in fractal dimension was observed as η increases. Fractal dimension of simulated 3D discharge patterns and 2D images of lightning discharges were compared by taking projections of simulated patterns. Discharge patterns similar to actual lightning were obtained when η ≈ 5.2. Influence of ground objects on simulated lightning discharges was also studied by introducing additional boundary conditions to the ground plane. It was observed that pointed structures on the ground have a higher probability of attracting simulated lightning discharges. An extension was introduced to dielectric breakdown model to simulate the development of upward connecting positive leader discharges that occur during the decent of a downward moving negative leader. It was found that the height of the stepped leader tip above the ground (at the time when the upward connecting leader initiation occurs) is dependent on the initial breakdown voltage threshold. The height of the point of interception was found to decrease exponentially as the breakdown threshold is increased. DOI: http://dx.doi.org/10.4038/sljp.v13i2.5433 Sri Lankan Journal of Physics, Vol. 13 ( 2 ) ( 2012 ) 09 - 25

Research and Analyze on the Lightning Test of Aircraft Model

According to the China Aviation Industry Standard HB6129 “The requirements of aircraft lightning protection and test method” and standards of foreign countries. The high voltage generator was used to make the lightning attachment point test on a scale model of airplane. The lightning attachment zone was determined, and the result was agreed with the actual lightning experience of F-4 aircraft. The technical factors such as test method, the model scale, gap spacing, and polar discharge relative positions in respect to the model are related to the laboratory test; the lightning discharging theory will be discussed in detail. The test method has been proved feasible and the experience of test research work has accumulated for future use.

A Case Study on Lightning Protection, Building Resonances Considered

In a recent paper (G. Bargboer and A. P. J. van Deursen, IEEE Trans. Electromagn. Compat., vol. 52, no. 3, pp. 684-90, Aug. 2010) we dealt with current injection measurements to test the lightning protection system of a newly built pharmaceutical plant. In a tentative extrapolation, the measurements were extrapolated to actual lightning. Here, we extend the model and calculate the response of the installation on lightning currents and include resonances in the cable trays and test cables contained in it. It turned out that suspension rods between roof support and cable tray were indispensable to suppress the resonances. The time dependence of the present results and the earlier simplified model given in differ greatly, but the amplitudes of induced voltages appear to be of the same order of magnitude.

A Case Study on Lightning Protection, Current Injection Measurements, and Model

A newly built pharmaceutical plant has been investigated by measurements. Currents of 0.3 kA were injected in the lightning protection grid on the roof. Inside the building, test cables of 100 m length followed a path typical for cables belonging to the installation. We measured induced cable currents and voltages. A reduced model of the building incorporated most of the designed current paths. Measurements and model showed that the roof steel skeleton carried about 80% of the current and the intended lightning conductors 20%. The calculated current through a cable support was larger than measured. This is explained by also considering a nearby nonintended conductor. For three types of cables, we determined the transfer impedances. The measurements and model have been combined and extrapolated to actual lightning.

Mechanism of pole‐mounted transformer damage by backflow lightning and measures against the damage on low‐voltage distribution line

AbstractPole‐mounted transformers are especially vulnerable to lightning damage. The progress of the information society imposes increasingly stringent requirements for the reliability of electric power supply, and this in turn necessitates a reduction in lightning damage to pole‐mounted transformers. Lightning protective devices (surge arresters) are now being installed around the primary bushing of the transformers, which has decreased the number of disconnections around the primary bushing due to lightning. But surge arresters installed on the primary side of the transformer cannot protect it against backflow lightning entering the secondary side of the transformer. The characteristic of transformer damage by backflow lightning is that the electromagnetic force produced by the current flowing into the secondary side deforms the transformer windings. This paper elucidates the mechanism of transformer damage by lightning flowing into the secondary side by comparing actual lightning damage cases with the results of verification tests using a short‐circuit generator. Effective countermeasures against transformer damage by backflow lightning are examined by EMTP calculations, which indicate that neutral grounding on the low‐voltage distribution line is the most effective way of decreasing the current flowing into the transformer. The lower the grounding resistance, the less current flows into the transformer. In addition, decreasing the voltage on the secondary side is important in order to protect the secondary‐side bushing. The calculation results indicate that surge arresters installed around the secondary side of the transformer are effective in decreasing the voltage on the secondary side. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(2): 1–11, 2010; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20921

逆流雷による配電用柱上変圧器の被害メカニズムと低圧配電線で実施する対策

Pole-mounted transformer is one of the equipment that is easier to receive lightning damage. As our information society advances, the needs for supply reliability of electric power become higher, and the decreasing of lightning damages of pole-mounted transformers becomes necessary. In recent years, lightning protective devices (surge arresters) have been installed around the primary bushing of the transformers. Therefore, the number of disconnections around the primary bushing caused by lightning has been decreasing. However, the surge arrester that installed at the primary side of transformer cannot protect the transformer against backflow lightning that invades to the secondary side of transformer. The characteristic of the transformer damage by the backflow lightning is that electro-magnetic force occurring by the current flowing into the secondary side of transformer deforms the windings of the transformer. In this paper, the mechanism of transformer damage by the current flowing into the secondary side is clarified by the comparison between actual lightning damage case and the results of verification test using short-circuit generator. Effective counter measures against the damage of transformer by the backflow lightning are examined by EMTP calculations. From the calculation results, neutral grounding on low-voltage distribution line is the most effective measures in the point of decreasing of the amount of current flowing into the transformer. The less the grounding resistance, the less the amount of current flowing into the transformer. Moreover, decreasing the voltage of the secondary-side of the transformer is important to protect the bushing of the secondary-side. By the calculation result, it is clarified that the surge arresters installed around the secondary side of the transformer are effective for decreasing the voltage of the secondary side of the transformer.