Insulators are one of the widely used important devices in power systems, and proposing an accurate and effective online monitoring method for insulator defects is an urgent need for intelligent and informative power systems. We propose a multiscale residual neural network for insulator surface breakage recognition. The proposed multiscale convolution filter uses three different size convolution kernels for convolution filtering, and performs feature maps fusion, which can enrich the spatial correlation and channel correlation of feature maps. We investigated the effects of different learning rates on the model performance, and confirmed that the model performs best with learning rate of 10-6. Compared with VGG16, Inception_v3 and Resnet50, the multiscale residual neural network model has significant advantages in detection capability and occupies less computational resources, and the detection speed can meet the industrial real-time detection requirements. Through dark-light and noise experiments, it is demonstrated that the proposed method is robust and can effectively deal with low-quality insulator images.

Far-field measurements of lightning-produced electromagnetic fields are of high importance for lightning location systems. Data from recorded lightning strokes can be, for example, used to assess the risk of lightning-induced damage in some geographical areas. Artificially triggered lightning, usually generated using rocket-wire technology, plays an important role in the study of lightning physics. Multiple-station observations of far (typically larger than 20 km) electric field waveforms produced by rocket-triggered lightning are quite rare. In 2014, electric field waveforms were measured for return strokes through the rocket-and-wire technique at Conghua. They were measured by electric field sensors at nine sites belonging to the lightning locating system in Foshan, Guangzhou, China. A total of 38 events were recorded and overall statistics of those waveforms are presented. The results were compared to previous experimental data related to natural and artificially triggered lightning to validate their similarity.

This paper presents the observation results of the induced voltage at the terminal of a 10 kV distribution line with 40 m distance from nearby triggered lightning pole at Guangzhou in the Summer of 2018. It is shown that the induced voltage waveforms exhibit three components including a slow increase preceding the initial negative peak, following a rapid polarity reversal and attenuated oscillations. The characteristic waveform parameters are defined in this paper. The observed negative peak value voltage ranges from -47.1 kV to -7.5 kV. The positive peak value voltage ranges from 5.3 kV to 20.9 kV, and the peak to peak value voltage ranges from 12.8 kV to 63.2 kV. The test results show that the negative peak value voltage of the induced voltage at the terminal of distribution generated by nearby negative triggered lightning generally exceeds the positive peak value, and in some cases the negative peak value even reaches twice the positive peak value. The negative 10%-90% peak rise time ranges from 2.3 's to 88.5 μs, and the average oscillation period is about 18 μs for oscillation component. Both negative and positive peaks of induced voltage show good linear relationship with the lightning current.

In the summer of 2013, a three-dimensional (3D)-based Foshan Total Lightning Location System (FTLLS), embedded with differential time of arrival (DTOA) techniques, was installed and started its operation in Foshan, Guangdong Province, China. In this paper, the geographical distribution and set-up information of FTLLS, the estimated locating errors and locating results, as well as its initial operation results are presented. FTLLS consists of nine sub-stations that receive electromagnetic waves associated with lightning discharges and locates VLF/LF (200 Hz–500 kHz) radiation sources in 3D. The remote sub-stations acquired triggered waveforms with a duration of 0.5 ms, a resolution of 12-bits, and a GPS-based sferic time tags of 24 h per day. Cloud-to-ground (CG) lightning events, intra-cloud (IC) lightning events and narrow bipolar events (NBEs) were located by FTLLS. Based on the Monte Carlo simulation, the two-dimensional horizontal location error is basically less than 100 m, and the vertical error (altitude) is less than 200 m when the lightning event occurs within the network. On the other hand, over 14 million lightning strikes were recorded successfully by FTLLS during the period of May to October in 2014, among which IC events, CG events and NBEs accounted for 65%, 34% and 1%, respectively. It is shown that FTLLS is capable of a fine three-dimensional (3D) location, in which the altitude parameters obtained are reasonable and well consistent with observed data in the previous studies. The location results of thunderstorms were additionally verified through simultaneously-observed radar data.

Appropriate shielding methods can reduce the lightning induced voltage and current of cables. In this article, different lightning surge currents (8/20 and 5/320 μ s) are coupled to the tested multi-core cable with single shielding layer and double shielding layers. The shielding effectiveness (SE) on the lightning surge current is compared for different cable shielding methods. The experimental results show that the cable induced current is effectively reduced when the shielding layer, the shielding spare core wire or the metal tube are grounded at two ends. A better shielding effect for the cable with double shielding layers is achieved by grounding both ends of the outer shielding layer and one end of the inner shielding layer, reducing the induced current to about 5% when the shielding layer is not grounded. Moreover, the SE of the spare core wire, used as the shielding wire in the multi-core cable, is better than that of the external shielding wire of the cable. The SE of the metal tube increases more and more slowly with the increase of the tube coverage percentage. Furthermore, the descending order of the SE of shielding methods involved here are grounding both ends of double shielding layers, grounding both ends of single shielding layer, spare core wire shielding and metal tube shielding. Finally, some engineering recommendations are proposed through the comparison between the shielding methods in this article and relevant works.

Simultaneous measurements of current and multiple‐station electric fields associated with a 5.4‐kA‐peak M‐component in rocket‐triggered lightning are presented in this study. A close‐range electric field measurement site was located northeast of the triggering site, 195° clockwise from South, at a distance of 78 m, while the distant multiple stations in this study were located southwest of the lightning triggering site (25–48°, clockwise from South) at a distance ranging from 69 to 126 km. Both the fast microsecond‐scale and slow millisecond‐scale pulses were observed at six distant stations. At the close station, the fast pulse was not noticeable. The magnitude and half‐peak width of the fast pulse were in the range of 0.91–1.93 V/m and 2.0–3.0 μs, respectively. The corresponding parameters for the slow pulse were, respectively, in the range of 0.59–1.29 V/m and 20.0–25.1 μs. The time lag between the onset of the channel‐base current and the far electric field of the M‐component was 18 μs. This time lag was used to deduce the ratio of the M‐component channel length and the wave speed. The classical guided wave M‐component model proposed by Rakov et al. (1995,https://doi.org/10.1029/95JD01924) to simulate the slow, millisecond‐scale field pulse assumes that neither the incident nor the reflected current wave undergoes attenuation even though the wave propagation occurs along a lossy channel. A modified guided wave M‐component model is proposed in this study in which the M‐component current wave attenuates with an exponential decay. Based on the best agreement achieved between the simulated fields using the modified two‐wave M‐component model and the observed near and far electric fields, the channel length, the M‐component wave speed, and the current attenuation constant were inferred, respectively, as 1.8 km, 1 × 10⁸ m/s, and 3 km. It is shown that the modified guided wave M‐component model is able to reproduce reasonably well the electric fields both at close and far distance ranges.