Shanqiang Gu

Waveforms recorded by lightning location networks mix source variability with propagation effects, making terrain-associated distortion difficult to isolate. We developed a path-incremental method in which the additional segment between two stations observing the same stroke carries the propagation signal. From 4466 records of 554 negative cloud-to-ground return strokes, 469 near-collinear pairs were stratified by additional path length and split at the within-stratum median of a digital-elevation-model terrain complexity index. Higher-complexity (rugged) paths showed the clearest near–far increases in rise time and half-peak width, whereas fall time and zero-crossing time showed no stable ordering, indicating that terrain acts mainly on the pulse front and main peak. In the frequency domain, these paths retained lower normalized band-energy fractions at 50–150 and 100–300 kHz, most systematically at 100–300 kHz for subsequent strokes, whereas the 200–500 kHz response was unstable. Separate mixed-effects models linked path elongation, occlusion, and diffraction geometry individually to a 39.7–42.5% lower 100–300 kHz ratio for subsequent strokes. Twelve representative-path axisymmetric finite-difference time-domain simulations under matched source currents reproduced the same ordering in these two bands across three ground conductivities. Rise time, half-peak width, and the normalized 100–300 kHz ratio are the most consistent terrain-associated indicators, supporting terrain-aware waveform interpretation.

The difference in ground flash density is studied under various terrains. It is found that a large error occurs when using a single ground flash density value to calculate the lightning trip-out rate of transmission lines in mountainous areas. This is because terrains have a greater effect on the ground flash density within a certain range. This range is larger than microscopic terrain ranging from tens to a few hundred meters, but smaller than macroscopic terrain ranging from tens to hundreds of kilometers or more. Therefore, the concepts of mesoscopic terrain and mesoscopic range are proposed in this paper. An approximation method for finding the probability model of the lightning distribution is proposed. It is found that the probability model of the lightning distribution changes from a uniform distribution to a non-uniform distribution during the transition from flatland to mountain. Furthermore, a method for determining the mesoscopic range is proposed using the maximum, minimum, and average values of ground flash density. The mesoscopic terrain concept proposed in this paper aids in further studies on the differences in lightning distribution and lightning performance between different areas, and offers theoretical support for improving the accuracy of lightning protection calculations in power systems.

Operation data show lightning faults account for >70% for the main ultra‐high voltage (UHV) DC transmission channels, very different from the design view. In order to accurately master the lightning characteristics and the lightning protection performance of the line so as to propose solutions to weak points, this study firstly obtains and analyses the density and strength distributions of lightning risk source. Then the study proposes a set of risk assessment process where the key model electrogeometric model is improved according to the polarity effect of DC line. Then the work realises the calculation of the lightning shielding failure risk of single tower and whole line. The example shows the assessment result is consistent to the line's actual operation. Next, to further evaluate and predict the lightning risk in real time, the study adopts the backpropagation neural network algorithm to integrate the lightning detection data, atmospheric electric fields, and radar echoes to develop the early warning model of lightning risk source, and proposed a method to realise the early warning of lightning damage risk for UHV DC channels. The results show that the effective warning ratio is 73% and the failure‐to‐warn ratio is 27% which indicates very good application effects.

A single-station-based lighting mapping system comprising a microphone array, which detects electromagnetic (EM) and thunder signals, has recently been developed and deployed for lightning observations. Using one microphone array consisting of 19 electret microphones installed on a 3-D steel frame, this system receives and processes the EM and thunder signals to determine the location of lightning thunder sources. We implement a new broadband direction-of-arrival estimation technique, namely, the maximum power beamforming algorithm and derive the 3-D location results based on the time difference between the acoustic signal and the EM signal. In this paper, four cloud-to-ground flashes with different branch channels recorded by the system are analyzed and presented in which the located thunder sources of two lightning flashes are compared with the photograph of the high-speed camera. The details of the system implementation along with the successful reconstruction of the lightning channel in 2-D and 3-D space are discussed. The results indicate that the location system could effectively map the lightning thunder sources, and the result is highly consistent with the high-speed video camera images. Moreover, the acoustic mapping system is capable of locating the main channel produced by the return stroke process; it also depicts the branching channels. It is shown that the system is capable of distinguish different branches of the same lightning; it also obtains different lightning channels occurring almost simultaneously.

In order to solve the frequently occurring lightning flashover problems on ±500 kV dc transmission lines in China, the authors have conducted the research on the dc line arrester since 2011. In this paper, the structure and installation, technical parameters, and protection performances, as well as their deterministic processes of the arrester are presented and analyzed in detail. In 2013, the authors successfully developed the arrester products, and the type tests show that they have excellent performance parameters and can act effectively against the lightning impulse and cutoff the dc follow current. By now more than 500 dc line arresters have been installed and used on seven ±500 kV dc transmission lines in eight provinces of China. About four years of operating experience shows that the arresters work safely and reliably over a long period of time, and have been effectively reducing the lightning flashover rate of the ±500 kV dc lines.

In order to optimize lightning protection design and operation to ensure safe and stable operation of Beijing-Shanghai high-speed railway, annual average ground flash density of the adjacent areas along Beijing-Shanghai High-Speed Railway is plotted base on cloud-to-ground flash data of Hebei, Beijing, Tianjin, Anhui, Jiangsu, Shanghai and Shandong during 2005~2011 detected by lightning location system. The ground flash density gradually increases from north to south, which achieve less than 4.7 times/(km ² ·a) in North China. According to the line corridor grid method, the Beijing-Shanghai High-Speed Railway is divided into 126 statistical sections with 10km×10km each grid and those sections are labeled as #1~126# respectively from north to south. Lightning prone sections are found out on the basis of the distribution of ground flash density for each statistical section. Three statistical sections are established including North China section, Shandong section, east China section. The lightning current amplitude probability distribution for each section comply with a lognormal distribution.