“…Planning-based resilience enhancement methods have also been widely studied [3], [5], [6], [32], [33], [46], [51], [52], [59], [73], [83], [84], [86], [108]- [114], [118], [121]- [123]. These methods are classified as follows: (i) undergrounding distribution and transmission lines, building redundant transmission/distribution routes, and upgrading poles and other structure with stronger materials [43], [85], [90], [95], [96], [105], [124]; (ii) elevating substation and facilities, adding backup generators, and installing remote control switches [91], [92]; (iii) enhancing vegetation management [125], [126]; (iv) determining optimal locations and sizes of battery energy storage units and renewable energy sources (RES) [75], [103], optimal placement of separation relays, and optimal allocation of black start resources; and (v) developing protocols for encrypted communication of critical data [80]; and integrated electricity and natural gas transportation system planning [66], [127].…”