Online Identification on Operational Risks of the Second and Third Defense Line of UHVDC Sending-End Power GridRui Yu, Zhen Xiang, Jun Xiong, Gu Jianhui, Fan Tang, Xiaoyu Wang and Xiongfei WangE3S Web Conf., 252 (2021) 01008DOI: https://doi.org/10.1051/e3sconf/202125201008