Preliminary Breakdown Research Articles

Proposal of Simplified Method of Analysis of Charge Transfer Associated with Return Strokes

Charge transfer is one of the most important parameters when one discusses the damage to the equipments on a power line due to the energy of the lightning. The amount of charge transfer associated with a lightning flash or individual strokes can be estimated by using the electric field change measured with a slow antenna. In this letter, the authors propose a simplified method of analysis of charge transfer associated with cloud-to-ground strokes along with estimation of the height of a charge in the point charge model. The height is evaluated by the product of the average speed of the downward propagating stepped leader and the time difference between the beginning of the preliminary breakdown and the onset of a return stroke.

Electrostatic Field Simulation Study of Nanoparticles Suspended in Synthetic Insulating Oil

Electrostatic field simulations have been performed to investigate the effect of barium strontium titanate (BST) nanoparticle suspensions on electric fields within synthetic oil dielectrics. We predict that by physically integrating nanoparticles of high dielectric constants into the breakdown regime, the self-break jitter in rep-rate oil switches might be reduced. The simulations show that the nanoparticle suspensions generate nonlinear and random electric field enhancements within the oil dielectric and also on the electrode surfaces. The BST nanoparticles have been modeled as perfect spheres which have an approximate dielectric constant of 2000. The oil in the simulation was given a dielectric constant of 2.33 and the electrodes are modeled as perfect electrical conductors with no field enhancements. A comparison is made between simulated electric fields on the surface of the cathode with increasing nanoparticle concentration, radius, and distance from cathode. Effects on capacitance with increasing nanoparticle concentration and radii are also investigated. All electrostatic simulations were performed with CST EM Studio. Preliminary experimental electric field breakdown data are included to validate simulation results.

Using lightning locating system based on time-of-arrival technique to study three-dimensional lightning discharge processes

A time-of-arrival (TOA) system based on GPS technology for locating VHF radiation sources from lightning has been developed and used in observation sites in the northern Shandong Province, China. The 3D images of the lightning progression have been obtained successfully for the first time in China. The 3D-channel evolutions of typical negative CG, positive CG and IC lightning flashes have been discussed together with the data of fast electric field change. It was found that significant differences existed between the negative and positive CG lightning flashes in terms of the initiation and propagation of the radiation sources. The preliminary breakdown of a negative CG lightning flash propagated at a speed about 5.2×104 m/s. The stepped leader of negative CG lightning flashes was trigged by negative initial breakdown. Thereafter, it propagated downward at a speed of 1.3×105 m/s. The initial process of the positive CG lightning flashes was also a propagation process of negative streamer. These streamers propagated dominantly horizontally in the positive charge region and accumulated positive charges at the origin of the lightning, and as a consequence, initiated downward positive streamers. A new type of lightning discharge that was triggered by a narrow bipolar pulse (NBP) is discussed in this study. The NBP was originated at altitude of about 10.5 km in the upper positive charge region. As a distinct difference from normal IC flash, its channels extended horizontally all around and produced a lot of radiation sources. The source power of the NBP could approach 16.7 kW, which is much greater than that of normal lightning discharge ranging between 100 mW and 500 W. The 3D propagation of this new type of lightning discharge was observed and obtained for the first time in China. The possible initiation mechanism of this new type of lightning is discussed here.

Some inferences on the role of lower positive charge region in facilitating different types of lightning

It is generally thought that the lower positive charge region serves to enhance the electric field at the bottom of the main negative charge region and thereby facilitate the launching of a negatively‐charged leader toward ground. On the other hand, the presence of excessive lower positive charge region may prevent the occurrence of negative cloud‐to‐ground discharges by “blocking” the progression of descending negative leader from reaching ground and thus “converting” the potential cloud‐to‐ground flash to an intracloud (or cloud‐to‐air) one. Assuming that the preliminary breakdown pulse train is a manifestation of interaction of a downward‐extending negative leader channel with the lower positive charge region, we qualitatively examine the inferred dependence of lightning type on the magnitude of this charge region.

Electric Field Pulse Trains Occurring Prior to the First Stroke in Negative Cloud-to-Ground Lightning

In this study, we examine the characteristics of electric field pulse trains that are attributed to preliminary breakdown in negative cloud-to-ground lightning discharges and compare them to those of similar pulse trains associated with attempted cloud-to-ground leaders. The data were acquired in 2006 in Gainesville, Florida. The largest pulses in the train can exceed in magnitude the following first return-stroke pulse. The arithmetic mean pulse duration and interpulse interval for pulse trains in negative cloud-to-ground discharges are 4.8 and 65 mus, respectively. The arithmetic mean pulse duration and interpulse interval for pulse trains in attempted cloud-to-ground leaders are 17 and 73 mus, respectively. This implies that pulse trains in ground discharges contain a larger fraction of ldquonarrowrdquo pulses (apparently disregarded in previous studies), defined here as those with durations equal to or less than 4 mus, than the pulse trains in attempted cloud-to-ground leaders. Submicrosecond-scale pulses are observed as part of pulse trains associated with cloud-to-ground discharges, but not with attempted leaders. We also examine the occurrence of pulses of different duration and amplitude in different parts of the preliminary breakdown pulse train of ground discharges. Pulses with larger durations (>4 mus) tend to occur in the initial part of pulse train.

온도변화에 따른 SF6/N2혼합가스의 임펄스 절연파괴특성

본 논문은 온도변화에 따른 SF<SUB>6</SUB>/N<SUB>2</SUB> 혼합가스 중에서 높은 불평등전계의 임펄스절연파괴특성에 대한 실험적인 결과를 기술하였다. 온도범위는 -25~25[℃]로 정하여 실힘을 수행하였다. 임펄스 전구방전진전은 방전전류와 방전 광신호의 측정에 의해 분석되었다. 결과로써, 절연파괴전압은 정극성보다 부극성에서 온도변화에 대한 의존성이 강하게 나타났다. 온도가 상승함에 따라 부극성에서의 리더진전 스텝핑시간이 정극성보다 더 길게 나타났다. 본 연구 결과는 뇌서지에 대하여 우수한 성능을 가지는 가스절연선로의 섣계에 유용한 정보가 될 것이다.

Properties of preliminary breakdown processes in Scandinavian lightning

Lightning flashes are usually preceded by preliminary breakdown processes (PBPs) before a stepped leader is initiated. These breakdown processes are not well understood. An early model, the so-called BIL model, has been called into question in later studies. However, we have found that the BIL model is quite successful in describing initial processes at least in high-latitude Scandinavian lightning. We present results from one summer of measurements in Finland, during which the vertical electric field was measured with a standard broadband plate antenna system. Lightning flash locations were provided by a lightning detection network and magnetic fields were measured with an experimental narrowband detection system. The relationship between the preliminary breakdown and the first return stroke (RS) is studied for 193 flashes at distances of 5–70 km. We can identify a preliminary breakdown in at least 90% of the flashes. The peak electric field of the RS is on average four times as intensive as the highest peak of the PBP. However, in 25% of the cases the PBP peak is more intensive. On the other hand, we show that this method of comparing intensities is physically arbitrary, since the PBP is continuous and the RS is impulsive. The narrowband measurement allows a physically consistent definition for intensities as the root-mean-square (RMS) sum of the most intense parts of signals. The PBP and RS are shown to have almost equal intensities at small distances. At larger distances, the PBP weakens more rapidly. This is suggested to be due to different propagation regimes, with the PBP signal changing from space-wave to ground-wave propagation with increasing distance, while the RS is predominantly ground wave at all distances. The result may have practical applications in narrowband detection of lightning. The BIL model suggests a characteristic signal in the narrowband signal, which could be used to identify the start of a lightning flash. The change in the RS–PBP ratio as a function of distance is statistically significant, but is too weak to significantly improve ranging methods.

Analysis of microsecond- and submicrosecond-scale electric field pulses produced by cloud and ground lightning discharges

We examined microsecond- and submicrosecond-scale pulses in electric field records of cloud and cloud-to-ground lightning discharges acquired in summer 2006, in Gainesville, Florida. A total of 12 cloud and 12 ground flashes were analyzed in detail, with the electric field record length being 96 or 200 ms and sampling interval being 4 or 10 ns. The majority of pulses in both cloud and ground discharges analyzed in this study were associated with the initial breakdown process and were relatively small in amplitude and duration. The typical durations were an order of magnitude smaller than tens of microseconds characteristic of “classical” preliminary breakdown pulses. We estimated that 26% of the pulses in the 12 cloud discharges and 22% of the pulses in the 12 cloud-to-ground discharges had total durations less that 1 µs.

Modeling of thundercloud VHF/UHF radiation on the lightning preliminary breakdown stage

It is well known that there are two basic parts of electromagnetic emissions from a thunderstorm cloud. The first one is due to a return stroke and the second is generated by microdischarges on the lightning preliminary stage and between successive return strokes. The purpose of this paper is to consider the second part of electromagnetic emissions from thunderstorm clouds in a frequency range from one to hundreds of MHz. A new approach is developed, which is based on a three-dimensional computer simulation of microdischarge activity in thunderstorm clouds. We suggest that microdischarges on the lightning preliminary stage are connected with the growth of internal electric cell structures in a thunderstorm cloud. The characteristic scale of cells ranges from ten to hundred meters. The source of these cells can be a beam-plasma-like instability in the thunderstorm cloud medium where microdischarges appear as a saturation mechanism for this instability. Interaction of neighboring cells leads to the formation of dynamic chains of microdischarges. Following step-by-step computer simulations, we calculate radio emissions from every microdischarge and sum up the wave amplitudes from all intracloud volume at the reception point. The standard model for a separate microdischarge current is adopted, and the electromagnetic radiation is estimated in the far zone. We obtain the waveforms of electromagnetic field, the temporal development of radiation and the number of electromagnetic pulses. We have found that signal statistics and calculated frequency spectra exhibit a universal power-law (fractal) behavior. The results of simulations are found to be in satisfactory agreement with the experimental data, because the model waveforms demonstrate a close similarity to the observed ones. Also the temporal development with the duration of pulse trains from ten to hundreds of microseconds and the microdischarge number rate up to hundreds of thousands per second are in agreement with the corresponding experimental data.

Horizontal lightning propagation, preliminary breakdown, and electric potential in New Mexico thunderstorms

Characteristics of lightning flashes in three storms are compared to simultaneous electric field (E) measurements at various altitudes to examine three hypotheses. The first is the idea that horizontal lightning branches propagate at altitudes near potential extrema (or wells). The analyses show that horizontal lightning activity and potential extrema are coincident in time and altitude, and so are consistent with the idea that lightning moves charges into potential wells as a means of using a storm's electrostatic energy to drive a lightning flash's dielectric breakdown processes. Second, these data are used to verify the usual interpretation of breakdown polarity of lightning radiation sources detected by the Lightning Mapping Array. The third hypothesis investigated is that normal cloud‐to‐ground flashes have a period of preliminary breakdown if and only if a potential well for negative charge exists between the altitudes of flash initiation and ground. The analyses show that in 14 flashes when a low‐level well was indicated, the period of preliminary breakdown before the first return stroke lasted an average of 117 ms, considerably longer than the average lifetime of a stepped leader. In 15 flashes in which no low‐level well was indicated, the time between initiation and first return stroke averaged 15 ms.

Observation and study on the whole process of cloud-to-ground lightning using narrowband radio interferometer

A narrowband radio interferometer has been developed and used to locate the entire sources of VHF radiations from a negative cloud-to-ground (CG) lightning discharge which contains 19 strokes. This system uses five antennas to form an array consisting of short-and long-baselines along two orthogonal directions. The system error which comes from frequency conversion is reduced by phase detection through direct high frequency amplifying. An interactive graphic analysis procedure is used to remove the fringe ambiguities which exist inherently in interferometry and to determine the direction of lightning radiation sources in two dimensions (azimuth and elevation) as a function of time at a time resolution of microsecond orders. With the developed system, the whole progression process in time and space of a lightning flash can be reconstructed. In this paper, combining the synchronous data of electric filed change and VHF radiation, the whole processes of an example negative CG flash have been studied in detail. It is found that the preliminary breakdown event of the CG flash started from negative charge region and exhibited firstly a downward pregression and then an upward propagation. There were very intense and continuous radiations during stepped leaders which became much stronger when the first return stroke began. In contrast, there were less and only discrete radiations during dart leaders. Stepped leader and dart leader may transform to each other depending on the state of the ionization of the path. The progression speed of initial stepped leaders was about 105 ms−1, while that was about 4.1×106 and 6.0×106 ms−1 for dart leaders and dart-stepped leaders, respectively. M events produced hook-shaped field changes accompanied by active burst of radiations at their beginnings. Followed these active radiation processes, M events appeared to contact finally into conducting main discharge channels. The mean progression speed of M events was about 7×107 ms−1, greater than that of the dart leaders and dart-step leaders. K events and attempted leaders were essentially the same as dart leaders except that they could not reach the ground and initiate return strokes.

Isolated breakdown activity in Swedish lightning

The initial breakdown processes or preliminary breakdown (PB) processes are generally associated with either cloud or cloud-ground lightning flashes, and hence have been studied mainly in connection with those subsequent activities. However, it has been observed in the summer thunderstorms of Sweden that there are breakdown processes that may not culminate into any subsequent activity. As these processes do not lead to any subsequent activity, they have been termed as isolated breakdown activities. Such isolated breakdown activities involve microsecond-scale pulses with both initial polarities. Based on their polarities, breakdown processes are divided into two groups; the negative breakdown pulses that are similar to the breakdown pulses leading to negative return strokes in ground flashes and the positive breakdown pulses similar to the breakdown pulses generally leading to the cloud flashes. The occurrence of the two types of breakdown processes is found to vary from a thunderstorm day to the other. In the present study, the signatures of isolated breakdown activities have been analyzed and are compared with those leading to the subsequent activities observed during the same measurement campaign. The average duration of the isolated breakdown activity associated with the negative initial polarity pulses is found to be 0.98 ms with average number of pulses 8.5. Similarly, the average duration and number of pulses in the isolated breakdown process with positive initial polarity pulses are 6.9 ms and 3.9, respectively.

Pulse trains that are characteristic of preliminary breakdown in cloud‐to‐ground lightning but are not followed by return stroke pulses

In this study, we identify and examine electric field pulse trains that are characteristic of preliminary breakdown in negative cloud‐to‐ground discharges but are not followed by return stroke waveforms. We assume that such trains are manifestations of the initiation of downward negative stepped leaders that fail to propagate all the way to the ground and refer to these events as “attempted first cloud‐to‐ground leaders,” although some of them were followed by full‐fledged cloud discharges. We examined a total of 2475 electric field records of lightning events acquired in Gainesville, Florida, in 2006, and waveforms in 33 of them were found to satisfy criteria set for attempted cloud‐to‐ground leaders. In addition to pronounced bipolar pulses with positive (atmospheric electricity sign convention) initial half cycle, negative unipolar and negative (initial half cycle) bipolar pulses were sometimes seen toward the end of the train. We also observed that at the beginning and at the end of the pulse train, there were narrower pulses, often having durations in the range of 1–2 μs, which are more than an order of magnitude shorter than for “classical” preliminary breakdown pulses. The arithmetic mean of total pulse train durations is 2.7 ms, and the weighted arithmetic means of individual pulse durations and interpulse intervals are 17 and 73 μs, respectively. Some of the attempted cloud‐to‐ground leaders, which should belong to the cloud discharge category, can be misclassified as negative cloud‐to‐ground discharges by lightning locating systems such as the U.S. National Lightning Detection Network.

SF6/CO2혼합기체 중에서 뇌임펄스코로나방전의 특성

본 논문은 불평등 전계의 SF?/CO₂혼합기체 중에서 전구방전특성에 대한 실험결과를 제시한다. 임펄스 전구방전 진전을 코로나 전류와 방전광 이미지의 측정으로 조사하였다. 정ㆍ부극성의 전구방전 진전메커니즘은 기본적으로 같았으며, 초기스트리머코로나는 침전극의 끝단에서 발단되어 계단상으로 진전하는 리더에 의해 시험갭을 교락시킨다. 정극성에서 리더펄스의 휴지시간은 부극성에서보다 매우 짧았다. 또한 부극성에서 초기스트리머코로나와 절연파괴사이의 시간간격은 정극성에서보다 매우 길게 나타났다. 정극성에서 방전채널경로는 임의적으로 나타났으며, 부극성에서 리더 채널은 정극성에서 보다 굵고 밝게 나타났다.

Spectral Patterns of Lightning Radiations in Intervals of 25 to 100 MHz

Characteristic average power spectra in intervals from 25 to 100MHz are presented for electromagnetic radiation fields from some specific lightning events: preliminary breakdown processes, downward negative stepped- and dart- leaders, return strokes, K changes in cloud-to-ground lightning (CG) and in intra-cloud lightning (IC) flashes, and upward positive leaders in artificially triggered lightning flashes. The spectra are obtained by means of the Fourier transformation of wideband records of electric fields from lightning. Results show that the spectral patterns for these events are obviously dissimilar in the frequency band studied. The spectrum for the IC, the preliminary breakdown process and the K change usually peaks once around 60MHz, while that for the downward negative leader peaks initially around 60-70MHz then around 26MHz as the leader propagates down out the clouds. The spectrum for the upward positive leader in artificially triggered lightning, however, peaks at about 26MHz, whether the leader is propagating below or within the clouds. The dissimilarities in the spectral pattern in the range of 25-100MHz between different lightning events may imply that these events have dissimilar discharge mechanisms and provide a basis for identifying these different discharge events.

Radiation field pulses associated with the initiation of positive cloud to ground lightning flashes

Seventy one electric field pulse trains that occurred during millisecond-scale time intervals before positive cloud to ground lightning flashes were analysed. These pulses are bipolar in nature and somewhat similar in pulse characteristics to the breakdown pulses preceding negative cloud to ground lightning. However, in the case of these positive flashes, the pulse characteristics of the pulse trains are confined in a much wider range of values than those of the pulse trains associated with negative return strokes. The leading edge of the pulses of the most commonly observed pulse trains that precede positive return strokes are relatively smooth, thus, different from their counterparts associated with negative flashes, in which case a few narrow pulses are superimposed on the rising edge of the bipolar pulses. Considering the initial polarity of pulses, four types of bipolar pulse trains preceding positive return strokes were identified. For each type of pulse trains, statistics of pulse characteristics were given. In contrast, in the case of negative ground flashes, the bipolar pulse trains were almost always composed of pulses of the same polarity as that of the succeeding return stroke. The possible causes of the observation of several types of pulse trains and the significantly diversified pulse characteristics of the breakdown pulse trains of positive flashes were discussed. The frequency spectrum of the electric fields of the most common type of pulse trains was compared with the spectrum of the breakdown pulses of negative flashes and those of negative return strokes. This spectrum of the preliminary breakdown pulse trains of positive ground flashes is comparable with that of the preliminary breakdown pulse trains of negative ground flashes.

Observations on the leader-return stroke of cloud-to-ground lightning with the broadband interferometer

Radio frequency observations of cloud-to-ground lightning (CG) were made in 1999 in Guangdong Province with the broadband lightning interferometer. In this paper, radiation source locations and electric field waveforms are analyzed for different types of breakdown events, including the preliminary breakdown of in-cloud activities, the stepped leaders of initial strokes to ground and activities during and following return strokes. It is shown that the structure and development of lightning discharges and associated breakdown processes can be reconstructed by using this new type of lightning radiation source location system. The detectable radiation of lightning was primarily produced by the negative breakdown process. The channel was concentrated with few branches during the preliminary breakdown stage of CG lightning flashes. The radiation sources appeared generally at the tip of the channel. During the late period of the stepped leader, the radiation sources were dispersed with branches extended away from the main channel. The radiation sources were in a certain length segment of the channel and the altitude of the segment descended along with the propagation of the leader to the ground. During the preliminary breakdown and the stepped leader of initial strokes to the ground, a sequence of fast negative streamers were observed to start continually from or farther away the lightning-initiated region and propagate along the developed leader channel, which may supply negative charge that assisted the leader’s development. The progression speed of fast negative streamers was about ten times faster than the average speed of lightning channel.

Characteristics of Cloud-to-Ground Lightning in Chinese Inland Plateau.

Characteristics of cloud-to-ground (CG) lightning flashes in the Chinese inland plateau have been analyzed by using the data obtained from a broadband slow antenna system, with a time resolution of 1 microsecond in 1996, and a CG lightning location network from 1997 to 1998. It has been found that lightning discharges in a plateau summer thunderstorm usually present some special characteristics compared with the typical summer thunderstorm. On the average, positive CG flashes comprised 16% of total CG flashes in the Chinese inland plateau. After comparison with radar echo, it is found that some weak thunderstorms are conducive to positive CG flashes. The first return strokes are usually preceded by a long duration preliminary breakdown process which is characterized by discrete bipolar pulses for both positive and negative CG flashes. The mean duration of electric field change prior to first return stroke is about 126.1 ms, in which 23% exceeds 200 ms for negative CG flashes, and the corresponding value is 165.1 ms for positive CG flashes. The mean interval between 152 successive analyzed pulses is 211.0±148.0 ms, and the total duration of the pulses is 32.0±20.0 ms for negative CG flashes, while the mean time interval between the 50 analyzed pulses is 165.0±120.0 ms and the total duration of pulses is 27.0±19.0 ms for positive CG flashes. Other discharge features, such as interstroke intervals, amplitude distribution of the subsequent return strokes and etc., are also analyzed in the paper.

Electromagnetic pulse environment of cloud-to-ground lightning for EMC studies

The characteristics of lightning electromagnetic pulse (LEMP) from individual processes in lightning such as return strokes, preliminary breakdown pulses, pulses associated with the leader process, K-changes and M-changes, the isolated narrow bipolar pulses, and the pulse bursts have been known. However, there is a need for a combined characterization of the total LEMP environment created during the entire duration of lightning. An attempt is made to provide such a description that gives the distribution of the LEMP characteristics, which is important in its ability to interfere with electronic systems, such as peak amplitude, peak time derivative, pulse duration, number of pulses, and time interval between pulses, during the entire duration of a cloud-to-ground lightning. Separate electromagnetic environment characterizations for negative cloud-to-ground lightning and positive cloud-to-ground lightning are proposed, including all the significant LEMP sources. Based on the LEMP characterization, models for negative and positive cloud-to-ground lightning flashes, that could be used in electromagnetic compatibility (EMC) studies are proposed. The electromagnetic environment models for cloud-to-ground lightning can be coupled to the locations of lightning given by the lightning location system to give comprehensive information about the electromagnetic environment at a desired geographical location.

What directs a lightning flash towards ground?

Birthday LSK Birthday 11.6568 Normal 0 false false false MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:Table Normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Times New Roman; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} In this paper we attempt to show that the necessary condition to create a lightning ground flash is the generation of a vertical conducting channel below the main negative charge centre. The probability of such an event increases if frequent breakdown takes place between the negative charge centre and the lower positive charge centre (LPCC). Analysis of electromagnetic field signatures produced by ground flashes in Sweden show pronounced radiation during the preliminary breakdown process. Such strong pulses are rarely found in tropical thunderstorms in Sri Lanka. We attribute these signatures to preliminary breakdown between the main negative charge centre and the LPCC and argue that meteorological conditions which favour the production of strong LPCC's are more likely to be found at mid and high latitudes than in the tropics, thus explaining why there is a greater probability of lightning flashes striking the ground in these regions. doi:10.4038/sljp.v1i0.165 Sri Lankan Journal of Physics, Vol. 1 (2000) 1-10