Spatio-temporal Characteristics of the Cloud-to-ground Lightning Activity Along the Transmission Lines in the Tibet High-altitude Area

In order to carry out more scientific and targeted lightning protection for Tibet’s power grids, based on the data collected by the wide-area lightning location system operated by State Grid Corporation of China, the spatio-temporal distribution characteristics of the Cloud-to-ground (CG) lightning along the transmission lines with voltage level of 220 kV and above in Tibet, and specifically, over the 220 kV “Humo Line” corridor area, which is seriously affected by lightning damage, were analyzed. The results show that the distribution of lightning density along the transmission lines is “more in the east and west but less in the middle area”. There are three main areas along the lines with high lightning density, namely Lhasa, Changdu and Jiacha, while Linzhi area has the lowest lightning density. About 95% of the CG lightning along the transmission lines occur from April to September every year, and the peak value mainly occurs from June to July. The lightning activity generally develops from the east to the west and then retreats to the east. The lightning activity in Changdu area in the east is mainly concentrated in May to September, while that in Lhasa area in the west is concentrated in June to August. The peak value of CG lightning activity generally appears at 15:00—18:00 (local time). The positive CG lightning peak value in Lhasa and Shigatse in the west lags behind the CG lightning peak value, while that in Changdu in the east is ahead of the CG lightning peak value. The area near the transmission lines is dominated by single return stroke CG lightning. The negative CG lightning current is obviously high in the east and low in the west. The average current of negative CG lightning at the east and west ends near the transmission line is about –40 kA and –20 kA, respectively. After the 220 kV “Humo Line” is completed and put into operation, there is a significant increase in CG lightning activities in the western section, CG lightning density increases from Level B1 (0.8 flashes/(km2·a)≤NG<2 flashes/(km2·a)) to Level B2 (2.0 flashes/(km2·a)≤NG<2.8 flashes/(km2·a)). In addition, the positive CG lightning activity in the line corridor is significantly enhanced, with the density and proportion of positive CG lightning increasing by 2.7 time and 2.3 times, respectively, which may be related to the lightning attractive effect of the erected lines and towers. © 2023 Science Press. All rights reserved.