Shaodong Chen

Performance Evaluation for a Lightning Location System Based on Observations of Artificially Triggered Lightning and Natural Lightning Flashes

AbstractPerformance evaluation for the lightning location system (LLS) of the power grid in Guangdong Province, China, was conducted based on observation data of the triggered lightning flashes obtained in Conghua, Guangzhou, during 2007–11 and natural lightning flashes to tall structures obtained in Guangzhou during 2009–11. The results show that the flash detection efficiency and stroke detection efficiency were about 94% (58/62) and 60% (97/162), respectively. The arithmetic mean and median values for location error were estimated to be about 710 and 489 m, respectively, when more than two reporting sensors were involved in the location retrieval (based on 87 samples). After eliminating one obviously abnormal sample, the absolute percentage errors of peak current estimation were within 0.4%–42%, with arithmetic mean and median values of about 16.3% and 19.1%, respectively (based on 21 samples).

Influence of the Ground Potential Rise on the Residual Voltage of Low-Voltage Surge Protective Devices due to Nearby Lightning Flashes

The characteristics of the residual voltage of a surge protective device (SPD) connected to an overhead distribution line due to nearby natural cloud-to-ground lightning and to rocket-triggered lightning are analyzed in this paper. The residual voltage of the SPD is found to be closely related to the ground potential rise at the grounding terminal of the SPD. For natural lightning occurring 1.8 km to 10.5 km away from the SPD, the ground potential rise (GPR) is too small to influence the residual voltage of SPD. For rocket-triggered lightning with a 40-m distance between the lightning channel and the SPD, the residual voltage of SPD is primarily determined by the voltage induced in the distribution line for return stroke and large M-components process, whereas the influence of the GPR becomes strong in the minor M-components stage. For a 5-m distance between the lightning channel and the SPD, the residual voltage of SPD originates primarily from the GPR during the entire flash, exhibiting the characteristics of reversed polarity. The duration of SPDs residual voltage may be up to the order of milliseconds due to the GPR in the case of the large M-components and a long continuing current process, which may cause damage to the SPD.

Optical and Electrical Observations of an Abnormal Triggered Lightning Event with two Upward Propagations

This study investigates an abnormal artificially triggered lightning event that produced two positive upward propagations: one during the initial stage (i.e., the upward leader (UL)) and the other after a negative downward aborted leader (DAL). The triggered lightning was induced in a weak thunderstorm over the experiment site and did not produce a return stroke. All of the intra-cloud lightning around the experiment site produced positive changes in the electric field. The initial stage was a weak discharge process. A downward dart leader propagated along the channel produced by the first UL, ending at a height of approximately 453 m and forming a DAL. Under the influence of the DAL, the electric field at a point located 78 m from the rod experienced a steady reduction of about 6.8 kV m−1 over 5.24 ms prior to the initiation of a new upward channel (i.e., the second upward propagation (UP)). The second UP, which started approximately 4.1 ms after the termination of the DAL and propagated along the original channel, was triggered by the DAL and sustained for approximately 2.95 ms. Two distinct current pulses were superimposed on the current of the second UP. The first pulse, which was related to the sudden initiation of the second UP, was characterized by a more rapid increase and decrease and a larger peak value than the second pulse, which was related to the development of the second UP into the area affected by the DAL. The second UP contained both a similar-to-leader process and a following neutralization process. This study introduces a new type of triggering leader, in which a new upward discharge is triggered in an established channel by an aborted leader propagating along the same channel with opposite polarity and propagation direction.

Characteristics of the initial stage and return stroke currents of rocket-triggered lightning flashes in southern China

This study investigates the initial stage (IS) and return stroke (RS) currents of 50 triggered lightning flashes (TLFs) that were conducted in southern China. The IS of the negative TLFs has a longer duration, and larger average current, charge transfer, and action integral than those reported elsewhere, with geometric means (GMs) of 347.9 ms, 132.5 A, 45.1 C, and 10.0 × 103 A2 s, respectively. Two positive TLFs containing no RS have much greater average currents, charge transfers, and action integrals in the IS when compared with the negative TLFs. The RS has a greater peak current (17.2 kA; GM, same to below), charge transfer within 1 ms (1.3 C), and action integral within 1 ms (5.8 × 103 A2 s), and shorter 10% to 90% rise time (0.4 μs) than elsewhere. The peak current is prominently correlated with the rate of rise, charge transfer within 1 ms, and action integral within 1 ms. Furthermore, when the total duration of the RS and any following continuing currents is longer than 40 ms, the peak current, charge transfer within 1 ms, and action integral within 1 ms of the RS are seldom greater than 25 kA, 2.6 C, and 15 × 103 A2 s, respectively. It is indicated that TLFs containing RSs tend to have a longer duration but a smaller charge transfer during the IS than those without RS. The peak current of the RS is weakly correlated with its preceding silence period when there was no channel base current.

Observation on induced voltages on overhead distribution lines caused by natural lightning

This paper carries out a summary and analysis on the observation result of induced voltage waveforms caused by nearby natural lightning on 220-V rated low-voltage overhead distribution lines in Guangzhou Field Experiment Site for Lightning Research and Testing (GFESLRT) during Summer 2008. It can be observed that when surge protective device (SPD) is not connected, the maximum peak value of induced voltages caused by seven lightning return strokes reaches 6.12 kV. When SPD is connected to the test line, the positive and negative peak values of lightning induced voltages on the live conductor and neutral conductor are less than 1.3 kV. Despite that induced voltages on two wires erected at the same height of an overhead line are almost the same, although some peak values of the induced voltages are not exactly the same. Lines with SPD connected can be protected effectively, while the waveforms are greatly different from the residual voltage waveforms of the SPD under impulse current obtained in laboratory. Measured peak values of induced voltages in this paper are much smaller than estimated values by the Rusck theory.

Observation of Residual Voltage in Low-Voltage Surge Protective Devices Due to Nearby M-Components

This paper presents experimental results obtained from the Guangdong comprehensive observation experiment on lightning discharge during summer 2014. Residual voltages and current flows in a surge protective device (SPD) connected to an overhead distribution line were observed due to nearby M-components of a triggered lightning flash. Residual voltages with varying characteristics caused by different M-components are analyzed at two terminals of the SPD, and corresponding formation mechanisms for the different characteristics are also discussed. Our results show that the residual voltages at two terminals of the SPD caused by three types of M-component are determined from both the line induction and the ground potential rise (GPR) in a nearby triggered lightning at 40 m distance. The M-component with a large peak current would produce large surge energies in the power line. Under a given peak current, the M-component has greater surge energy than the return stroke. The ground terminal of the SPD is still affected by the GPR, and our results also show that the continuing current superimposed with M-components is an important factor in determining the magnitude of line coupling in power distribution lines when a lightning flash occurs nearby.

Low-frequency E-field Detection Array (LFEDA)—Construction and preliminary results

In recent years, locating total lightning at the VLF/LF band has become one of the most important directions in lightning detection. The Low-frequency E-field Detection Array (LFEDA) consisting of nine fast antennas was developed by the Chinese Academy of Meteorological Sciences in Guangzhou between 2014 and 2015. This paper documents the composition of the LFEDA and a lightning-locating algorithm that applies to the low-frequency electric field radiated by lightning pulse discharge events (LPDEs). Theoretical simulation and objective assessment of the accuracy and detection efficiency of LFEDA have been done using Monte Carlo simulation and artificial triggered lightning experiment, respectively. The former results show that having a station in the network with a comparatively long baseline improves both the horizontal location accuracy in the direction perpendicular to the baseline and the vertical location accuracy along the baseline. The latter results show that detection efficiencies for triggered lightning flashes and return strokes are 100% and 95%, respectively. The average planar location error for return strokes of triggered lightning flashes is 102 m. By locating LPDEs in thunderstorms, we find that LPDEs are consistent with convective regions as indicated by strong reflectivity columns, and present a reasonable distribution in the vertical direction. In addition, the LFEDA can reveal an image of lightning development through mapping the channels of lightning. Based on three-dimensional locations, the vertical propagation speed of the preliminary breakdown and the changing trend of the leader’s speed in an intra-cloud and a cloud-to-ground flash are investigated. The research results show that the LFEDA has the capability for three-dimensional location of lightning, which provides a new technique for researching lightning development characteristics and thunderstorm electricity.

A Review of Advances in Lightning Observations during the Past Decade in Guangdong, China

This paper reviews recent advances in understanding the physical processes of artificially triggered lightning and natural lightning as well as the progress in testing lightning protection technologies, based on a series of lightning field campaigns jointly conducted by the Chinese Academy of Meteorological Sciences and Guangdong Meteorological Bureau since 2006. During the decade-long series of lightning field experiments, the technology of rocket-wire artificially triggered lightning has been improved, and has successfully triggered 94 lightning flashes. Through direct lightning current waveform measurements, an average return stroke peak current of 16 kA was obtained. The phenomenon that the downward leader connects to the lateral surface of the upward leader in the attachment process was discovered, and the speed of the upward leader during the connection process being significantly greater than that of the downward leader was revealed. The characteristics of several return strokes in cloud-to-ground lighting have also been unveiled, and the mechanism causing damage to lightning protection devices (i.e., ground potential rise within the rated current) was established. The performance of three lightning monitoring systems in Guangdong Province has also been quantitatively assessed.

Unconnected upward leaders observed in Guangzhou during 2009–2010

More than ten unconnected upward positive leaders initiated from high structures in response to natural downward-moving negative leaders are analyzed. These leaders are observed by using high-speed cameras with sampling rates at the order of 104 fps (frames per second). The propagation velocity, channel width of the unconnected upward leader and the distances between it and strike point are presented. The results can deepen our understanding of the lightning attachment process.

Analysis on the induced overvoltage generated by near triggered lightning in the AWS power distribution system

The artificially triggered lightning test was used and a 4-element AWS was simulated near the lightning channel to analyze and study the induced effects caused by the lightning and the key lightning protection techniques for AWS. This paper analyzes the induced overvoltage characteristics and SPD residue voltage characteristics caused by triggered lightning with multiple return strokes on the transmission line of an AWS, as well as the relationship with the triggered lightning. The results show that: (a) The return strokes of the near triggered lightning generate bipolar induced overvoltages on the overhead line, with peaks up to more than 10 kV. The overvoltages can be divided into the main peak phase and the subsequent overvoltage phase, which last about 100µs and 4ms respectively on average. The period of the subsequent overvoltages is related to the fluctuation of the current of the triggered lightning; (b) Overvoltages of 2kV or above can be induced at the initial continuous current phase. They last a long period of time and concentrate about 12ms, with the mean voltage being 332.5V. Its potential damage to the transmission line cannot be neglected.