For smaller transmission lines that operate at a higher frequency you would use a Time Domain Reflectometer. I don't know if it is practical for high voltage p

For smaller transmission lines that operate at a higher frequency you would use a Time Domain Reflectometer. I don't know if it is practical for high voltage power transmission lines. See https://en.wikipedia.org/wiki/Time-domain_reflectometer https://en.wikipedia.org/wiki/Time-domain_reflectometer