I have seen these balls on power lines in Western Australia for decades, and literally only just found out what they were.

They are used (maybe among other things) to understand exactly where a fault has occurred in a mlln outage.

They give you sensor data between substations, and allow the grid operator to better isolate the fault and restore power to the largest possible area, without reenergising the fault.

They use parasitic power transfer to be totally disconnected from any dedicated power supply.

Very cool