I have seen little gizmos that appear to be about the size of a toilet paper tube hanging under high voltage power transmission lines. They are typically about a foot away from the insulators. Sometimes they’re on both sides of every tower, sometimes only every other tower or on one side only. Anybody know what they are?
According to my Dad, who was a power company engineer until his retirement, they are vibration dampeners. Wind blowing across conductors can set up waves, and those little doohickeys are there to negate oscillations before they grow to the point of being damaging.
Here’s a picture of the common Stockbridge Vibration Damper.