There is power line carrier signal used between substations and generators on a line but expensive high voltage wave traps are required and you get about 14bits

There is power line carrier signal used between substations and generators on a line but expensive high voltage wave traps are required and you get about 14bits of bandwidth. The applications I’ve done if your bit drops out and health is still good then you have to disconnect. Transmission lines often run fiber too, but used to still use a whole fiber to transmit 8 bits, or serial at 9600 baud