Electrical bonding in high voltage line maintenance

[yoghurt]

Electrical "bonding" in high voltage line maintenance

Consider a high voltage line worker about to exit a helicopter on to a high voltage "live" line, as in this video :

As the helicopter approaches the HV line, the worker holds out a conducting rod. I am led to believe this is to neutralize the potential-difference between the helicopter and the HV line; the rod clearly providing a high resistance path for the current to prevent a potentially dangerous discharge. Indeed in this video there appears to be arcing between the line and the rod, indicating a large p.d.

What I don't get, is that the chopper is completely insulated from earth, yet there is clearly a current flowing from the chopper to the HV line (via the arc) for as long as the rod is held near the line. What gives rise to this potential-difference?

BTW hiya, I am new to the forum

 

[mgb_phys]

The helicopter builds up a static charge with respect to the air (and especially clouds)
It's a big danger with helicopters picking up people from ships - you have to be careful not to grab the basket until the earthing strap hanging below it has touched the deck.

 

[subtech]

The arcing you see is ionization of the air beween the chopper and the line thus creating a conductive path.
A small amount of current does flow through the arc path to helicopter thus bringing it to the same potential as the line.
This current is often referred to as "charging current".
It helps to remember that at the most basic level, differences of potential are just relative excesses and deficiencies in the amount of electrons in conductive materials.