Abstract: In order to obtain the multiple return-stroke characteristics of positive and negative cloud-to-ground lightening in the corridor of the ±800 kV Binjin line in Zhejiang province, the statistical parameters of the 3 032 cloud-to-ground lightening samples monitored from June to September 2017 are statistically analyzed, including return-stroke times, cloud-to-ground lightening duration, return-stroke time interval, and return-stroke intensity. The multiple return-stroke parameters show obvious systematic variations with the return-stroke number, and the difference between positive and negative return-stroke characteristics is obvious. The statistical results show that the number of positive and negative lightening samples accounted for 27.57% and 72.43%, respectively. Single return-stroke account for 52.60% of negative lightening samples. The maximum number of return-stroke reaches 13, and the average number of return-stroke is 2.47. Single return-stroke account for 77.04% of positive lightening samples, and the number of return-stroke is relatively small. The maximum number of return-stroke is 5 and the average number is only 1.26. The durations of multiple return-stroke for positive and negative lightening are both positively correlated with the number of return-stroke and the overall arithmetic mean values are 250.20 ms and 343.02 ms, respectively. The negative return-stroke time interval does not vary significantly with the return-stroke order, while the positive one decreases with the return-stroke order. Overall, subsequent return-stroke intensity ratios of positive and negative lightening decrease with the subsequent return-stroke order. The first return-stroke current intensity of negative lightening increases with the number of return-stroke, while the trend of positive lightening is not obvious.

Key words: UHVDC, multiple return-stroke, cloud-to-ground lightening characteristics, return-stroke times, return-stroke time interval, return stroke intensity