OPGW is an abbreviation of optical ground wire, a wire which carries out both functions of protection of high voltage transmission line from lightning and communication line.
OPGW is to be installed alongside high voltage power wires which are connected from steel tower to steel tower and connected with the top of that tower for grounding. This OPGW surrounded with thick aluminum steel wires discharges electric current through grounded steel tower at the time of attack with torpedoes for protection of high voltage power wires. OPGW attacked with torpedoes will have tiny damage and finally be disconnected from overload even with a tiny scratch because the power wires are too heavy.
DAS acoustic monitoring system may be a big help for maintenance works because it informs the spot struck by lightning by using optic fiber in OPGW.